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Sample records for mukaiyama aldol reactions

  1. Mukaiyama Aldol Reactions in Aqueous Media

    PubMed Central

    Kitanosono, Taku; Kobayashi, Shū

    2013-01-01

    Mukaiyama aldol reactions in aqueous media have been surveyed. While the original Mukaiyama aldol reactions entailed stoichiometric use of Lewis acids in organic solvents under strictly anhydrous conditions, Mukaiyama aldol reactions in aqueous media are not only suitable for green sustainable chemistry but are found to produce singular phenomena. These findings led to the discovery of a series of water-compatible Lewis acids such as lanthanide triflates in 1991. Our understanding on these beneficial effects in the presence of water will be deepened through the brilliant examples collected in this review. 1 Introduction 2 Rate Enhancement by Water in the Mukaiyama Aldol Reaction 3 Lewis Acid Catalysis in Aqueous or Organic Solvents 3.1 Water-Compatible Lewis Acids 4 Lewis-Base Catalysis in Aqueous or Organic Solvents 5 The Mukaiyama Aldol Reactions in 100% Water 6 Asymmetric Catalysts in Aqueous Media and Water 7 Conclusions and Perspective PMID:24971045

  2. Mukaiyama Aldol Reactions in Aqueous Media.

    PubMed

    Kitanosono, Taku; Kobayashi, Sh?

    2013-11-11

    Mukaiyama aldol reactions in aqueous media have been surveyed. While the original Mukaiyama aldol reactions entailed stoichiometric use of Lewis acids in organic solvents under strictly anhydrous conditions, Mukaiyama aldol reactions in aqueous media are not only suitable for green sustainable chemistry but are found to produce singular phenomena. These findings led to the discovery of a series of water-compatible Lewis acids such as lanthanide triflates in 1991. Our understanding on these beneficial effects in the presence of water will be deepened through the brilliant examples collected in this review. 1 Introduction 2 Rate Enhancement by Water in the Mukaiyama Aldol Reaction 3 Lewis Acid Catalysis in Aqueous or Organic Solvents 3.1 Water-Compatible Lewis Acids 4 Lewis-Base Catalysis in Aqueous or Organic Solvents 5 The Mukaiyama Aldol Reactions in 100% Water 6 Asymmetric Catalysts in Aqueous Media and Water 7 Conclusions and Perspective. PMID:24971045

  3. Iron- and bismuth-catalyzed asymmetric Mukaiyama aldol reactions in aqueous media.

    PubMed

    Kitanosono, Taku; Ollevier, Thierry; Kobayashi, Sh?

    2013-12-01

    We have developed asymmetric Mukaiyama aldol reactions of silicon enolates with aldehydes catalyzed by chiral Fe(II) and Bi(III) complexes. Although previous reactions often required relatively harsh conditions, such as strictly anhydrous conditions, very low temperatures (-78 °C), etc., the reactions reported herein proceeded in the presence of water at 0 °C. To find appropriate chiral water-compatible Lewis acids for the Mukaiyama aldol reaction, many Lewis acids were screened in combination with chiral bipyridine L1, which had previously been found to be a suitable chiral ligand in aqueous media. Three types of chiral catalysts that consisted of a Fe(II) or Bi(III) metal salt, a chiral ligand (L1), and an additive have been discovered and a wide variety of substrates (silicon enolates and aldehydes) reacted to afford the desired aldol products in high yields with high diastereo- and enantioselectivities through an appropriate selection of one of the three catalytic systems. Mechanistic studies elucidated the coordination environments around the Fe(II) and Bi(III) centers and the effect of additives on the chiral catalysis. Notably, both Brønsted acids and bases worked as efficient additives in the Fe(II) -catalyzed reactions. The assumed catalytic cycle and transition states indicated important roles of water in these efficient asymmetric Mukaiyama aldol reactions in aqueous media with the broadly applicable and versatile catalytic systems. PMID:24101589

  4. C1-symmetric aminosulfoximines in copper-catalyzed asymmetric vinylogous Mukaiyama aldol reactions.

    PubMed

    Frings, Marcus; Atodiresei, Iuliana; Wang, Yutian; Runsink, Jan; Raabe, Gerhard; Bolm, Carsten

    2010-04-19

    Vinylogous Mukaiyama-type aldol reactions have been catalyzed by a combination of Cu(OTf)2 and readily available C1-symmetric aminosulfoximines. After a fine-tuning of the reaction conditions and an optimization of the modularly assembled ligand structure, high stereoselectivities and excellent yields have been achieved in catalyzed reactions involving various electrophile/nucleophile combinations. The relative and absolute configurations of two products were assigned by X-ray single crystal structure analysis and a comparison of calculated and experimental CD spectra. PMID:20229533

  5. Efficient Mukaiyama aldol reaction in water with TiO4 tetrahedra on a hydrophobic mesoporous silica surface.

    PubMed

    Shintaku, Hiroshi; Nakajima, Kiyotaka; Kitano, Masaaki; Hara, Michikazu

    2014-11-14

    A new heterogeneous catalyst, hydrophobic TiO4-deposited mesoporous silica, has been designed for the efficient Mukaiyama-aldol condensation, a water-participating Lewis acid-catalyzed reaction between a hydrophobic carbonyl compound and silyl enol ether. The prepared catalyst suspended in water exhibited high catalytic performance as a reusable catalyst for the reaction without a surfactant. PMID:25234202

  6. Sodium phenoxide-phosphine oxides as extremely active Lewis base catalysts for the Mukaiyama aldol reaction with ketones.

    PubMed

    Hatano, Manabu; Takagi, Eri; Ishihara, Kazuaki

    2007-10-25

    A highly efficient Mukaiyama aldol reaction between ketones and trimethylsilyl enolates catalyzed by sodium phenoxide-phosphine oxides as simple homogeneous Lewis base catalysts (0.5-10 mol %) was developed, which minimized competing retro-aldol reaction. For a variety of aromatic ketones and aldimines, aldol and Mannich-type products with an alpha-quaternary carbon center were obtained in good to excellent yields. Up to 100 mmol scale of benzophenone and trimethylsilyl enolate with 0.5 mol % of catalyst was established in 97% yield (34.8 g). PMID:17894505

  7. Iron(II) and zinc(II) complexes with designed pybox ligand for asymmetric aqueous Mukaiyama-aldol reactions.

    PubMed

    Jankowska, Joanna; Paradowska, Joanna; Rakiel, Bartosz; Mlynarski, Jacek

    2007-03-16

    An iron(II) complex with a hindered hydroxyethyl-pybox (he-pybox) ligand shows improved catalytic activity and enantioselectivity for asymmetric Mukaiyama-aldol reactions in aqueous media. This water-stable chiral Lewis acid promotes condensation of aromatic silyl enol ethers with a range of aldehydes with good yields, excellent syn-diastereoselectivity and up to 92% ee. The combination of the same ligand with ZnII salt is also demonstrated as a remarkably efficient and water-compatible chiral Lewis acid. PMID:17315931

  8. CALIX[6]ARENE DERIVATIVES BEARING SULFONATE AND ALKYL GROUPS AS SURFACTANTS IN SC(OTF)3-CATALYZED MUKAIYAMA ALDOL REACTIONS IN WATER. (R822668)

    EPA Science Inventory

    Abstract

    Amphiphilic calix[6]arene derivatives 1a¯b were found to be efficient surfactants for Sc(OTf)3-catalyzed Mukaiyama aldol reaction of silyl enol ethers with aldehydes in water. The results indicated t...

  9. The Mechanism of Iron(II)-Catalyzed Asymmetric Mukaiyama Aldol Reaction in Aqueous Media: Density Functional Theory and Artificial Force-Induced Reaction Study.

    PubMed

    Sameera, W M C; Hatanaka, Miho; Kitanosono, Taku; Kobayashi, Sh?; Morokuma, Keiji

    2015-09-01

    Density functional theory (DFT), combined with the artificial force-induced reaction (AFIR) method, is used to establish the mechanism of the aqueous Mukaiyama aldol reactions catalyzed by a chiral Fe(II) complex. On the bases of the calculations, we identified several thermodynamically stable six- or seven-coordinate complexes in the solution, where the high-spin quintet state is the ground state. Among them, the active intermediates for the selectivity-determining outer-sphere carbon-carbon bond formation are proposed. The multicomponent artificial force-induced reaction (MC-AFIR) method found key transition states for the carbon-carbon bond formation, and explained the enantioselectivity and diastereoselectivity. The overall mechanism consists of the coordination of the aldehyde, carbon-carbon bond formation, the rate-determining proton transfer from water to aldehyde, and dissociation of trimethylsilyl group. The calculated full catalytic cycle is consistent with the experiments. This study provides important mechanistic insights for the transition metal catalyzed Mukaiyama aldol reaction in aqueous media. PMID:26267294

  10. FeCl3·6H2O-catalyzed Mukaiyama-aldol type reactions of enolizable aldehydes and acetals.

    PubMed

    Rodríguez-Gimeno, Alejandra; Cuenca, Ana B; Gil-Tomás, Jesús; Medio-Simón, Mercedes; Olmos, Andrea; Asensio, Gregorio

    2014-09-01

    Mukaiyama-aldol type reactions of acetals derived from enolizable aldehydes with FeCl3·6H2O, an eco-friendly, low-cost, and stable catalyst, lead to ?-methoxycarbonyl compounds with nearly quantitative yields. The methodology is extended to the parent aldehydes as starting materials, leading to the corresponding aldols with lower yields, but efficiently. Different alkyl and aryl substituted acetals and aldehydes have been tested in the reaction with linear and cyclic silyl enol ethers. Reactions are carried out in an open air atmosphere, and additives are not required. Acetals can be considered activating groups of the carbonyl moiety rather than a protecting group in this type of FeCl3·6H2O-catalyzed condensation. PMID:25102027

  11. Highly diastereoselective synthesis of beta-carboxy-gamma-lactams and their ethyl esters via Sc(OTf)(3)-catalyzed imino Mukaiyama-aldol type reaction of 2,5-bis(trimethylsilyloxy)furan with imines.

    PubMed

    Pohmakotr, Manat; Yotapan, Nattawut; Tuchinda, Patoomratana; Kuhakarn, Chutima; Reutrakul, Vichai

    2007-06-22

    Functionalized gamma-lactams are found to be crucial intermediates in the synthesis of biologically important natural products. We herein described a highly diastereoselective synthesis of beta-carboxy-gamma-lactams and their ethyl ester derivatives, in high yields with high diastereomeric ratio, via the Mukaiyama-aldol type reaction of 2,5-bis(trimethysilyloxy)furan with imines, employing Sc(OTf)(3) as a catalyst. PMID:17506584

  12. Synthetic studies on furanosteroids: construction of the viridin core structure via Diels-Alder/retro-Diels-Alder and vinylogous Mukaiyama aldol-type reaction.

    PubMed

    Onyango, Evans O; Jacobi, Peter A

    2012-09-01

    The synthesis of the viridin class of furanosteroids core skeleton from the readily available 2,3-dihydro-4-hydroxyinden-1-one (6) is described. Our strategy was broken down into three parts: (1) Synthesis of functionalized alkyne oxazoles of type 5; (2) intramolecular Diels-Alder/retro-Diels-Alder reaction of 5 followed by tautomerization and elaboration of R to give silylated furanonaphthols 4 bearing an aldehyde side chain; and (3) annulation of ring A by intramolecular vinylogous Mukaiyama aldol-type cyclization. Two major challenges were faced in the last step: (i) furanonaphthol derivatives bearing a ?-hydroxyaldehyde functionality (R(1) = OH) suffered from dehydration to the E-enal, which is geometrically incapable of cyclization, and (ii) the functionality at C17 had a strong influence on the conversion of 4 to 3, as exemplified by the failure of the free ketone (X = O) or its derivatives (X = H, OH; X = H, OAc) to cyclize. In the end, success was realized with the analogous C17-norketone (X = H, H). PMID:22849426

  13. The Mukaiyama aldol reaction of in situ generated nitrosocarbonyl compounds: selective C-N bond formation and N-O bond cleavage in one-pot for ?-amination of ketones.

    PubMed

    Ramakrishna, Isai; Grandhi, Gowri Sankar; Sahoo, Harekrishna; Baidya, Mahiuddin

    2015-09-21

    A practical protocol for the ?-amination of ketones (up to 99% yield) has been developed via the Mukaiyama aldol reaction of in situ generated nitrosocarbonyl compounds. The reaction with silyl enol ethers having a disilane (-SiMe2TMS) backbone proceeded not only with perfect N-selectivity but concomitant N-O bond cleavage was also accomplished. Such a cascade of C-N bond formation and N-O bond cleavage in a single step was heretofore unknown in the field of nitrosocarbonyl chemistry. A very high diastereoselectivity (dr = 19?:?1) was accomplished using (-)-menthol derived chiral nitrosocarbonyl compounds. PMID:26245149

  14. 5-Hydroxyalkyl derivatives of tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate: diastereoselectivity of the Mukaiyama crossed-aldol-type reaction.

    PubMed

    Vallat, Olivier; Buciumas, Ana-Maria; Neier, Reinhard; Stoeckli-Evans, Helen

    2009-04-01

    The title compounds, rac-(1'R,2R)-tert-butyl 2-(1'-hydroxyethyl)-3-(2-nitrophenyl)-5-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate, C(17)H(20)N(2)O(6), (I), rac-(1'S,2R)-tert-butyl 2-[1'-hydroxy-3'-(methoxycarbonyl)propyl]-3-(2-nitrophenyl)-5-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate, C(20)H(24)N(2)O(8), (II), and rac-(1'S,2R)-tert-butyl 2-(4'-bromo-1'-hydroxybutyl)-5-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate, C(13)H(20)BrNO(4), (III), are 5-hydroxyalkyl derivatives of tert-butyl 2-oxo-2,5-dihydropyrrole-1-carboxylate. In all three compounds, the tert-butoxycarbonyl (Boc) unit is orientated in the same manner with respect to the mean plane through the 2-oxo-2,5-dihydro-1H-pyrrole ring. The hydroxyl substituent at one of the newly created chiral centres, which have relative R,R stereochemistry, is trans with respect to the oxo group of the pyrrole ring in (I), synthesized using acetaldehyde. When a larger aldehyde was used, as in compounds (II) and (III), the hydroxyl substituent was found to be cis with respect to the oxo group of the pyrrole ring. Here, the relative stereochemistry of the newly created chiral centres is R,S. In compound (I), O-H...O hydrogen bonding leads to an interesting hexagonal arrangement of symmetry-related molecules. In (II) and (III), the hydroxyl groups are involved in bifurcated O-H...O hydrogen bonds, and centrosymmetric hydrogen-bonded dimers are formed. The Mukaiyama crossed-aldol-type reaction was successful when using the 2-nitrophenyl-substituted hydroxypyrrole, or the unsubstituted hydroxypyrrole, and boron trifluoride diethyl ether as catalyst. The synthetic procedure leads to a syn configuration of the two newly created chiral centres in all three compounds. PMID:19346616

  15. THE EFFECTS OF AROMATIC AND ALIPHATIC ANIONIC SURFACTANTS ON SC(OTF)3-CATALYZED MUKAIYAMA ALDOL REACTION IN WATER. (R822668)

    EPA Science Inventory

    Abstract

    Aromatic (2c and 2d) and aliphatic (2a and 2b) anionic surfactants were employed in Sc(OTf)3-catalyzed aldol reactions of some labile silyl enol ethers (3a and

  16. Sequential Mukaiyama-Michael reaction induced by carbon acids.

    PubMed

    Yanai, Hikaru; Kobayashi, Osamu; Takada, Kenji; Isono, Takuya; Satoh, Toshifumi; Matsumoto, Takashi

    2016-02-16

    In the presence of a strong carbon acid, the sequential Mukaiyama-Michael reaction using two different Michael acceptors proceeded and the reaction of ketene silyl acetal derived from EtOAc with α-pyrones as primal acceptors yielded the corresponding cyclic ketene silyl acetals, which were reactive enough to undergo the following reaction with second acceptors. PMID:26734829

  17. Organolanthanide reagents and the Mukaiyama reaction

    SciTech Connect

    Gong, L.

    1989-01-01

    The bis(pentamethylcyclopentadienyl) lutetium halide complex ((C/sub 5/Me/sub 5/)/sub 2/LuCl/center dot/THF) was synthesized and characterized. The crystal structure of this complex shows that the Lu is at the center of a distorted tetrahedron consisting of the centroids of two cyclopentadienyl rings, the oxygen atom of a tetrahydrofuran molecule and a chlorine atom. /sup 1/H NMR studies of toluene-d/sub 8/ solutions of (C/sub 5/Me/sub 5/LuCl(THF) + THF, (TMS/sub 2/CP)/sub 2/LuCl(THF) + THF, and (MeCp)/sub 2/LuCl(THF) + THF at various temperatures showed exchange processes between co- ordinated THF and free THF with average values of ..delta..G/sup ne/ of 13.0 /+-/ 0.3 kcal/mol, 11.1 /+-/ 0.1 kcal/mol and <11 kcal/mol at 0/degree/C, respectively. It has been found that under the influence of a catalytic amount (1--5 mol %) of (TMS/sub 2/Cp)/sub 2/YbCl dimer, silyl enol ethers (R/sub 1/R/sub 2/C = C(OR/sub 3/)OSiMe/sub 3/)) react with benzaldehyde smoothly in dichloromethane at room temperature, giving >99% of the aldol silyl ether (isolated yield: 90%) within 3 h. At /minus/78/degrees/C, the reaction gives kinetically controlled diastereoselectivity, which was not observed in the TiCl/sub 4/-mediated aldol reaction. The use of organoytterbium enolates shows promise result with respect to increased stereoselectivity, and indicates the importance of the bulky ligands on the metal center. In addition, Yb(III) species can retard retroaldol reaction owing to its mild Lewis acidity. 118 refs., 14 figs., 30 tabs.

  18. Enantioselective aldol reactions with masked fluoroacetates

    NASA Astrophysics Data System (ADS)

    Saadi, Jakub; Wennemers, Helma

    2016-03-01

    Despite the growing importance of organofluorines as pharmaceuticals and agrochemicals, the stereoselective introduction of fluorine into many prominent classes of natural products and chemotherapeutic agents is difficult. One long-standing unsolved challenge is the enantioselective aldol reaction of fluoroacetate to enable access to fluorinated analogues of medicinally relevant acetate-derived compounds, such as polyketides and statins. Herein we present fluoromalonic acid halfthioesters as biomimetic surrogates of fluoroacetate and demonstrate their use in highly stereoselective aldol reactions that proceed under mild organocatalytic conditions. We also show that the methodology can be extended to formal aldol reactions with fluoroacetaldehyde and consecutive aldol reactions. The synthetic utility of the fluorinated aldol products is illustrated by the synthesis of a fluorinated derivative of the top-selling drug atorvastatin. The results show the prospects of the method for the enantioselective introduction of fluoroacetate to access a wide variety of highly functionalized fluorinated compounds.

  19. Enantioselective aldol reactions with masked fluoroacetates.

    PubMed

    Saadi, Jakub; Wennemers, Helma

    2016-03-01

    Despite the growing importance of organofluorines as pharmaceuticals and agrochemicals, the stereoselective introduction of fluorine into many prominent classes of natural products and chemotherapeutic agents is difficult. One long-standing unsolved challenge is the enantioselective aldol reaction of fluoroacetate to enable access to fluorinated analogues of medicinally relevant acetate-derived compounds, such as polyketides and statins. Herein we present fluoromalonic acid halfthioesters as biomimetic surrogates of fluoroacetate and demonstrate their use in highly stereoselective aldol reactions that proceed under mild organocatalytic conditions. We also show that the methodology can be extended to formal aldol reactions with fluoroacetaldehyde and consecutive aldol reactions. The synthetic utility of the fluorinated aldol products is illustrated by the synthesis of a fluorinated derivative of the top-selling drug atorvastatin. The results show the prospects of the method for the enantioselective introduction of fluoroacetate to access a wide variety of highly functionalized fluorinated compounds. PMID:26892561

  20. Stereodefined Acyclic Polysubstituted Silyl Ketene Aminals: Asymmetric Formation of Aldol Products with Quaternary Carbon Stereocenters.

    PubMed

    Nairoukh, Zackaria; Marek, Ilan

    2015-11-23

    The regio- and stereoselective formation of stereodefined polysubstituted silyl ketene aminals is easily achieved through selective combined carbometalation-oxidation-silylation reactions. These substrates are ideal candidates for Mukaiyama aldol reactions with aliphatic aldehydes as they give the aldol products with a quaternary carbon stereocenter ? to the carbonyl groups in outstanding diastereoselectivities. PMID:26448575

  1. Direct catalytic enantio- and diastereoselective aldol reaction of thioamides.

    PubMed

    Iwata, Mitsutaka; Yazaki, Ryo; Chen, I-Hon; Sureshkumar, Devarajulu; Kumagai, Naoya; Shibasaki, Masakatsu

    2011-04-13

    A direct catalytic asymmetric aldol reaction of thioamides using a soft Lewis acid/hard Brønsted base cooperative catalyst comprising (R,R)-Ph-BPE/[Cu(CH(3)CN)(4)]PF(6)/LiOAr is described. Exclusive enolate generation from thioacetamides through a soft-soft interaction with the soft Lewis acid allowed for a direct aldol reaction to ?-nonbranched aliphatic aldehydes, which are usually susceptible to self-condensation under conventional basic conditions. A hard Lewis basic phosphine oxide has emerged as an effective additive to constitute a highly active ternary soft Lewis acid/hard Brønsted base/hard Lewis base cooperative catalyst, enabling a direct enantio- and diastereoselective aldol reaction of thiopropionamides. Strict control of the amount of the hard Lewis base was essential to drive the catalytic cycle efficiently with a minimized retro-aldol pathway, affording syn-aldol products with high stereoselectivity. Divergent transformation of the thioamide functionality is an obvious merit of the present aldol methodology, allowing for a facile transformation of the aldol product into the corresponding aldehyde, ketone, amide, amine, and ketoester. An aldehyde derived from the direct aldol reaction was subjected to a second direct aldol reaction, which proceeded in a catalyst-controlled manner to provide 1,3-diols with high stereoselectivity. PMID:21417332

  2. A designed amide as an aldol donor in the direct catalytic asymmetric aldol reaction.

    PubMed

    Weidner, Karin; Kumagai, Naoya; Shibasaki, Masakatsu

    2014-06-10

    The direct catalytic asymmetric aldol reaction offers efficient access to ?-hydroxy carbonyl entities. Described is a robust direct catalytic asymmetric aldol reaction of ?-sulfanyl 7-azaindolinylamide, thus affording both aromatic and aliphatic ?-hydroxy amides with high ee?values. The design of this transformation features a cooperative interplay of a soft and a hard Lewis acid, which together facilitate the challenging chemoselective enolization by a hard Brønsted base. PMID:24789121

  3. One-pot enol silane formation-Mukaiyama aldol-type addition to dimethyl acetals mediated by TMSOTf.

    PubMed

    Downey, C Wade; Johnson, Miles W; Tracy, Kathryn J

    2008-04-18

    Various ketones, esters, amides, and thioesters add in high yield to dimethyl acetals in the presence of silyl trifluoromethanesulfonates and an amine base. Acetals derived from aryl, unsaturated, and aliphatic aldehydes are all effective substrates. The reaction proceeds in a single reaction flask, with no purification of the intermediate enol silane necessary. PMID:18335962

  4. Synthetic studies toward the brasilinolides: controlled assembly of a protected C1-C38 polyol based on fragment union by complex aldol reactions.

    PubMed

    Paterson, Ian; Housden, Michael P; Cordier, Christopher J; Burton, Paul M; Mühlthau, Friedrich A; Loiseleur, Olivier

    2015-05-28

    The brasilinolides are an architecturally complex family of 32-membered macrolides, characterised by potent immunosuppressant and antifungal properties, which represent challenging synthetic targets. By adopting a highly convergent strategy, a range of asymmetric aldol/reduction sequences and catalytic protocols were employed to assemble a series of increasingly elaborate fragments. The controlled preparation of suitable C1-C19 and C20-C38 acyclic fragments 5 and 6, containing seven and 12 stereocentres respectively, was first achieved. An adventurous C19-C20 fragment union was then explored to construct the entire carbon chain of the brasilinolides. This pivotal coupling step could be performed in a complex boron-mediated aldol reaction to install the required C19 hydroxyl stereocentre when alternative Mukaiyama-type aldol protocols proved unrewarding. A protected C1-C38 polyol 93 was subsequently prepared, setting the stage for future late-stage diversification toward the various brasilinolide congeners. Throughout this work, asymmetric boron-mediated aldol reactions of chiral ketones with aldehydes proved effective both for controlled fragment assembly and coupling with predictable stereoinduction from the enolate component. PMID:25900249

  5. Direct Catalytic Enantio- and Diastereoselective Ketone Aldol Reactions of Isocyanoacetates**

    PubMed Central

    delaCampa, Raquel; Ortín, Irene; Dixon, Darren J

    2015-01-01

    A catalytic asymmetric aldol addition/cyclization reaction of unactivated ketones with isocyanoacetate pronucleophiles has been developed. A quinine-derived aminophosphine precatalyst and silver oxide were found to be an effective binary catalyst system and promoted the reaction to afford chiral oxazolines possessing a fully substituted stereocenter with good diastereoselectivities and excellent enantioselectivities. PMID:25735645

  6. Switching diastereoselectivity in proline-catalyzed aldol reactions.

    PubMed

    Martínez-Castañeda, Ángel; Rodríguez-Solla, Humberto; Concellón, Carmen; del Amo, Vicente

    2012-11-16

    The choice of the anion of an achiral TBD-derived guanidinium salt, used as cocatalyst for proline, allows reacting cycloketones with aromatic aldehydes and preparing either anti- or syn-aldol adducts with very high enantioselectivity. As a proof of principle, we show how the judicious choice of an additive allows individual access to all possible products, thus controlling the stereochemical outcome of the asymmetric aldol reaction. The origin of the syn diastereoselectivity unfolds from an unusual equilibrium process coupled to the enamine-based catalytic cycle standard for proline. PMID:23101761

  7. Asymmetric direct aldol reactions of acetoacetals catalyzed by a simple chiral primary amine.

    PubMed

    Luo, Sanzhong; Qiao, Yupu; Zhang, Long; Li, Jiuyuan; Li, Xin; Cheng, Jin-Pei

    2009-12-18

    An asymmetric direct aldol reaction of acetoacetals is described. Under the catalysis of a simple chiral primary amine, the direct aldol reactions of acetoacetals occur exclusively on the gamma-position to give vinylogous-type aldol products with high diastereo- and enantioselectivity. PMID:19883088

  8. Development of a general, enantioselective organocatalytic Mukaiyama–Michael reaction with ?,?-unsaturated aldehydes

    PubMed Central

    Borths, Christopher J.; Carrera, Diane E.; MacMillan, David W.C.

    2014-01-01

    LUMO-lowering organocatalysis has been extended to promote the conjugate addition of S-alkyl and -pyrrolyl silylketene acetals to ?,?-unsaturated aldehydes, yielding both, syn and anti Mukaiyama–Michael products with high levels of enantioselectivity. This strategy allows for the generation of chemically useful 1,5-dicarbonyl systems and again highlights the utility of organocatalysis. PMID:25214677

  9. Stereoselectivity in aldol reactions of chiral N-acyl selones

    SciTech Connect

    Li, Z.; Wu, R.; Michalczyk, R.; Dunlap, R.B.; Odom, J.D.; Silks, L.A. III

    2000-01-19

    Aldol reactions have played a central role in many stereoselective constructions of carbon-carbon bonds. During the past several years the selenocarbonyl group has been used both as a chiral interrogation tool (using {sup 77} SeNMR spectroscopy) and as a platform for the development of new chemical methods associated with selone based chiral derivatizing agents. During the course of these studies the authors have uncovered a new type of aldol reaction using chiral selone reagents in which the selenocarbonyl plays a pivotal role in determining the stereoselectivity of these reactions. This report describes the results of the studies involving the use of titanium(IV) enolates of N-acyl-oxaxolidin-2-selones with a variety of aldehydes.

  10. Functionalized multi-walled carbon nanotubes in an aldol reaction

    NASA Astrophysics Data System (ADS)

    Chronopoulos, D. D.; Kokotos, C. G.; Karousis, N.; Kokotos, G.; Tagmatarchis, N.

    2015-01-01

    The covalent functionalization of multi-walled carbon nanotubes (MWCNTs) with a proline-based derivative is reported. Initially, MWCNTs were oxidized in order to introduce a large number of carboxylic units on their tips followed by N-tert-butoxycarbonyl-2,2'(ethylenedioxy)bis-(ethylamine) conjugation through an amide bond. Then, a proline derivative bearing a carboxylic terminal moiety at the 4-position was coupled furnishing proline-modified MWCNTs. This new hybrid material was fully characterized by spectroscopic and microscopy means and its catalytic activity in the asymmetric aldol reaction between acetone and 4-nitrobenzaldehyde was evaluated for the first time, showing to proceed almost quantitatively in aqueous media. Furthermore, several amino-modified MWCNTs were prepared and examined in the particular aldol reaction. These new hybrid materials exhibited an enhanced catalytic activity in water, contrasting with the pristine MWCNTs as well as the parent organic molecule, which failed to catalyze the reaction efficiently. Furthermore, the modified MWCNTs proved to catalyze the aldol reaction even after three repetitive cycles. Overall, a green approach for the aldol reaction is presented, where water can be employed as the solvent and modified MWCNTs can be used as catalysts, which can be successfully recovered and reused, while their catalytic activity is retained.The covalent functionalization of multi-walled carbon nanotubes (MWCNTs) with a proline-based derivative is reported. Initially, MWCNTs were oxidized in order to introduce a large number of carboxylic units on their tips followed by N-tert-butoxycarbonyl-2,2'(ethylenedioxy)bis-(ethylamine) conjugation through an amide bond. Then, a proline derivative bearing a carboxylic terminal moiety at the 4-position was coupled furnishing proline-modified MWCNTs. This new hybrid material was fully characterized by spectroscopic and microscopy means and its catalytic activity in the asymmetric aldol reaction between acetone and 4-nitrobenzaldehyde was evaluated for the first time, showing to proceed almost quantitatively in aqueous media. Furthermore, several amino-modified MWCNTs were prepared and examined in the particular aldol reaction. These new hybrid materials exhibited an enhanced catalytic activity in water, contrasting with the pristine MWCNTs as well as the parent organic molecule, which failed to catalyze the reaction efficiently. Furthermore, the modified MWCNTs proved to catalyze the aldol reaction even after three repetitive cycles. Overall, a green approach for the aldol reaction is presented, where water can be employed as the solvent and modified MWCNTs can be used as catalysts, which can be successfully recovered and reused, while their catalytic activity is retained. Electronic supplementary information (ESI) available: Experimental details for the synthesis of 5, 8 and 11; 1H & 13C NMR of compounds 8 and 11; ATR-IR spectra, thermographs and TEM imaging of hybrids 10 and 13. See DOI: 10.1039/c4nr06543c

  11. An unprecedented, tandem Aldol-Grob reaction sequence

    SciTech Connect

    Kabalka, G.W.; Tejedor, D.; Li, N.S.; Malladi, R.R.; Trotman, S.

    1998-09-18

    The authors report an unprecedented, tandem Aldol-Grob sequence involving the reaction of ketones with aromatic aldehydes in nonnucleophilic solvents in the presence of boron trifluoride. Although a detailed study of the reaction mechanism has not yet been completed, the consistent formation of (E)-alkene products, as well as the fact that aromatic aldehydes appear to be required, would point toward the intermediacy of a carbocation derivative. A reasonable mechanism would involve the formation of the mixed aldol followed by the formation and subsequent nonsynchronous ring opening of a lactol. The proposed fragmentation is reminiscent of two-step Grob fragmentations that have been reported for N-halo-{alpha}-amino acids and cyclobutane hemiacetals as well as the acid-catalyzed fragmentation of {beta}-hydroxy acetals. The authors examined the effect of various acids on the reaction sequence in order to ascertain which would be most efficient. They conclude that boron trifluoride is the most effective of the acids studied in achieving the new tandem condensation-cleavage sequence.

  12. Chiral picolylamines for Michael and aldol reactions: probing substrate boundaries.

    PubMed

    Nugent, Thomas C; Bibi, Ahtaram; Sadiq, Abdul; Shoaib, Mohammad; Umar, M Naveed; Tehrani, Foad N

    2012-12-14

    Here we report on inroads concerning increased substrate breadth via the picolylamine organocatalyst template, a vicinal chiral diamine based on a pyridine-primary amine motif. The addition of cyclohexanone to ?-nitrostyrene has many catalyst solutions, but cyclopentanone and isobutyraldehyde additions continue to be challenging. PicAm-3 (10 mol%) readily allows the Michael addition of cyclopentanone or isobutyraldehyde (5.0 equiv.) to ?-nitrostyrene derivatives. By contrast, PicAm-1 (7.0 mol%) is optimal for catalyzing the aldol reaction of cyclohexanone or cycloheptanone (3.3 equiv.) with aromatic aldehydes. Eighteen products are reported and for each reaction type new products are reported (4b-d, 9c). Very good yields and stereoselectivities are generally noted. The reactions, which require an acid additive, proceed via a transient chiral enamine and a mechanistic case is put forth for a bifunctional catalysis model. PMID:23104278

  13. Method of carbon chain extension using novel aldol reaction

    DOEpatents

    Silks, Louis A; Gordon, John C; Wu, Ruilan; Hangson, Susan Kloek

    2013-08-13

    Method of producing C.sub.8-C.sub.15 hydrocarbons comprising providing a ketone starting material; providing an aldol starting material comprising hydroxymethylfurfural; mixing the ketone starting material and the aldol starting material in a reaction in the presence of a proline-containing catalyst selected from the group consisting of Zn(Pro).sub.2, Yb(Pro).sub.2, and combinations thereof, or a catalyst having one of the structures (I), (II) or (III), and in the presence of a solvent, wherein the solvent comprises water and is substantially free of organic solvents, where (I), (II) and (III) respectively are: ##STR00001## where R.sub.1 is a C.sub.1-C.sub.6 alkyl moiety, X=(OH) and n=2. ##STR00002## In (III), X may be CH.sub.2, sulfur or selenium, M may be Zn, Mg, or a lanthanide, and R.sub.1 and R.sub.2 each independently may be a methyl, ethyl, phenyl moiety.

  14. Method of carbon chain extension using novel aldol reaction

    SciTech Connect

    Silks, Louis A; Gordon, John C; Wu, Ruilan; Hanson, Susan Kloek

    2013-07-30

    Method of producing C.sub.8-C.sub.15 hydrocarbons. comprising providing a ketone starting material; providing an aldol starting material comprising chloromethylfurfural; mixing the ketone starting material and the aldol starting material in a reaction in the presence of a proline-containing catalyst selected from the group consisting of Zn(Pro).sub.2, Yb(Pro).sub.3, and combinations thereof, or a catalyst having one of the structures (I), (II) or (III), and in the presence of a solvent, wherein the solvent comprises water and is substantially free of organic solvents, where (I), (II) and (III) respectively are: ##STR00001## where R.sub.1 is a C.sub.1-C.sub.6 alkyl moiety, X=(OH) and n=2. ##STR00002## In (III), X may be CH.sub.2, sulfur or selenium, M may be Zn, Mg, or a lanthanide, and R.sub.1 and R.sub.2 each independently may be a methyl, ethyl, phenyl moiety.

  15. Direct catalytic asymmetric aldol reactions of thioamides: toward a stereocontrolled synthesis of 1,3-polyols.

    PubMed

    Iwata, Mitsutaka; Yazaki, Ryo; Suzuki, Yuta; Kumagai, Naoya; Shibasaki, Masakatsu

    2009-12-30

    A direct catalytic asymmetric aldol reaction of thioamides with a soft Lewis acid/hard Brønsted base cooperative catalytic system comprising (R,R)-Ph-BPE/[Cu(CH(3)CN)(4)]PF(6)/LiOAr is described. Highly chemoselective deprotonative activation of thioamides allows for a direct aldol reaction of alpha-nonbranched aliphatic aldehydes, which are susceptible to self-condensation. Facile reduction of the thioamide functionality and a catalyst-controlled second aldol reaction provides 1,3-diols in a highly stereoselective manner. PMID:19994862

  16. Spontaneous Mirror Symmetry Breaking in the Aldol Reaction and its Potential Relevance in Prebiotic Chemistry

    NASA Astrophysics Data System (ADS)

    Mauksch, Michael; Wei, Shengwei; Freund, Matthias; Zamfir, Alexandru; Tsogoeva, Svetlana B.

    2010-02-01

    The origin of the single chirality of most biomolecules is still a great puzzle. Carbohydrates could form in the formose reaction, which is proposed to be autocatalytic and contains aldol reaction steps. Based on our earlier observation of organoautocatalysis and spontaneous enantioenrichment in absence of deliberate chiral influences in the aldol reaction of acetone and p-nitrobenzaldehyde we suggest that a similar effect might be present also in the aldol reactions involved in gluconeogenesis. Herein we show that reactant precipitation observed in our earlier reported experiments does not affect the asymmetric autocatalysis in the aldol reaction we studied. We explain the phenomenon of spontaneous mirror symmetry breaking in such organocatalytic homogenous systems qualitatively by non-linear reaction network kinetics and classical transition state theory.

  17. Synthesis of a potential intermediate for TMC-95A via an organocatalyzed aldol reaction.

    PubMed

    Pearson, Anthony J; Panda, Santanu; Bunge, Scott D

    2013-10-01

    N-Prolinylanthranilamide-based pseudopeptide organocatalyst 14 was shown to promote enantioselective direct aldol reaction of 7-iodoisatin and 2,2-dimethyl-1,3-dioxan-5-one with 90% conversion (75% isolated yield), 90% enantioselectivity, and 23:1 diastereoselectivity. To demonstrate the synthetic utility of this chemistry, the racemic aldol reaction product was converted in five steps to a potential intermediate for construction of the natural product TMC-95A. PMID:24024913

  18. Domino Michael-Michael and Aldol-Aldol Reactions: Diastereoselective Synthesis of Functionalized Cyclohexanone Derivatives Containing Quaternary Carbon Center.

    PubMed

    Ghorai, Manas K; Halder, Sandipan; Das, Subhomoy

    2015-10-01

    A simple strategy for the synthesis of highly functionalized cyclohexanone derivatives containing an all-carbon quaternary center from ?-(aryl/alkyl)methylidene-?-keto esters or ?-diketones via a K-enolate mediated domino Michael-Michael reaction sequence with moderate to good yield and excellent diastereoselectivity (de > 99%) is described. Interestingly, Li-base mediated reaction of ?-arylmethylidene-?-diketones affords functionalized 3,5-dihydroxy cyclohexane derivatives as the kinetically controlled products via a domino aldol-aldol reaction sequence with excellent diastereoselectivity. Li-enolates of the ?-keto esters or ?-diketones undergo facile domino Michael-Michael reaction with nitro-olefins to afford the corresponding nitrocyclohexane derivatives in good yields and excellent diastereoselectivity (de > 99%). The formation of the products and the observed stereoselectivity were explained by plausible mechanisms and supported by extensive computational study. An asymmetric version of the protocol was explored with (L)-menthol derived nonracemic substrates, and the corresponding nonracemic cyclohexanone derivatives containing an all-carbon quaternary center were obtained with excellent stereoselectivity (de, ee > 99%). PMID:26334184

  19. A closer look at spontaneous mirror symmetry breaking in aldol reactions.

    PubMed

    Valero, Guillem; Ribó, Josep M; Moyano, Albert

    2014-12-22

    The aldol reaction between acetone and 4-nitrobenzaldehyde run in the nominal absence of any enantioselective catalyst was monitored by chiral HPLC with the aid of an internal standard. The collected data show the presence of a detectable initial enantiomeric excess of the aldol product in the early stages of the reaction in about 50?% of the experiments. Only a small fraction of the reaction contained the non-racemic aldol product after 24?h. This temporary emergence of natural optical activity could be the signature of a coupled reaction network that leads to a spontaneous mirror-symmetry-breaking process, which originates at very low conversions (i.e., strongly depends on events taking place at the very first stages of the process). The reaction is not autocatalytic in the aldol product, which rules out a simple Frank-type reaction network as the source of the observed symmetry breaking. On the other hand, the isolation and characterisation of a double-aldol adduct suggested a reaction network that involved both indirect autocatalysis and indirect mutual inhibition between the enantiomers of the reaction product. PMID:25346447

  20. A Tandem Michael-Aldol Reaction Sequence: An Undergraduate Research Organic Experiment.

    ERIC Educational Resources Information Center

    Coutlangus, Marilyn L.; And Others

    1989-01-01

    Presents a short reaction sequence that allows the student to determine by spectroscopic methods the constitution and stereochemistry of the reaction products. Reports the interpretations needed to illustrate the usefulness of the spectroscopic method. Notes the products of the Michael-Aldol reaction have not been reported in the literature. (MVL)

  1. Rapid and Efficient Functionalized Ionic Liquid-Catalyzed Aldol Condensation Reactions Associated with Microwave Irradiation

    PubMed Central

    Wang, Chang; Liu, Jing; Leng, Wenguang; Gao, Yanan

    2014-01-01

    Five quaternary ammonium ionic liquid (IL) and two tetrabutylphosphonium ILs were prepared and characterized. An environmentally benign and convenient functionalized ionic liquid catalytic system was thus explored in the aldol condensation reactions of aromatic aldehydes with acetone. The aldol reactions proceeded more efficiently through microwave-assisted heating than through conventional thermal heating. The yield of products obtained under microwave heating for 30 min was approximately 90%, and the ILs can be recovered and reused at least five times without apparent loss of activity. In addition, this catalytic system can be successfully extended to the Henry reactions. PMID:24445262

  2. ?-Hydroxyallylsilanes as propionaldehyde enolate equivalents and their use toward iterative aldol reactions.

    PubMed

    Ruiz, Johal; Murthy, Akondi Srirama; Roisnel, Thierry; Chandrasekhar, Srivari; Grée, René

    2015-02-20

    Smooth and efficient reaction conditions have been found for the transformation of protected ?-hydroxyacylsilanes into the corresponding aldehydes. This opens a new route to iterative aldol reactions, and it has been used for the synthesis of fragments of several bioactive natural products. PMID:25636066

  3. A NOVEL CHIRAL GALLIUM LEWIS ACID CATALYST WITH SEMI-CROWN LIGAND IN AQUEOUS ASYMMETRIC MUKAIYAMA ALDOL REACTIONS. (R828129)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  4. Unexpected Retroaldol-Aldol Reaction during O-Alkylation of Hydroxylated Vince Lactam Derivatives.

    PubMed

    Bengtsson, Christoffer; Wetzel, Alexander; Bergman, Joakim; Brånalt, Jonas

    2016-01-15

    The unexpected retroaldol-aldol reaction during O-alkylation of a β-hydroxy lactam was found to be highly dependent on the temperature and shows a remarkable solvent effect. In DMF, O-alkylation is faster than retroaldol-aldol rearrangement giving exclusively products with retention of configuration. In THF, O-alkylation is slower than rearrangement, giving selectively products with inversion of stereochemistry. In DMSO, a retroaldol reaction followed by fast intramolecular proton transfer occurs to give the ring-opened aldehyde. PMID:26703240

  5. Bifunctional Brønsted Base Catalyzes Direct Asymmetric Aldol Reaction of ?-Keto Amides.

    PubMed

    Echave, Haizea; López, Rosa; Palomo, Claudio

    2016-03-01

    The first enantioselective direct cross-aldol reaction of ?-keto amides with aldehydes, mediated by a bifunctional ureidopeptide-based Brønsted base catalyst, is described. The appropriate combination of a tertiary amine base and an aminal, and urea hydrogen-bond donor groups in the catalyst structure promoted the exclusive generation of the ?-keto amide enolate which reacted with either non-enolizable or enolizable aldehydes to produce highly enantioenriched polyoxygenated aldol adducts without side-products resulting from dehydration, ?-keto amide self-condensation, aldehyde enolization, and isotetronic acid formation. PMID:26835655

  6. Stereoselective titanium-mediated aldol reactions of a chiral isopropyl ketone.

    PubMed

    Zambrana, Joana; Romea, Pedro; Urpí, Fèlix

    2013-05-18

    A novel substrate-controlled aldol reaction of a chiral isopropyl ketone is reported. The outstanding regioselective enolization by TiCl4-i-Pr2NEt provides a chelated enolate that can participate in highly diastereoselective additions to a wide array of aldehydes favouring the corresponding 2,5-syn adducts. PMID:23576096

  7. RUTHENIUM-CATALYZED TANDEM OLEFIN MIGRATION-ALDOL AND MANNICH-TYPE REACTIONS IN IONIC LIQUID.

    EPA Science Inventory

    In the presence of a catalytic amount of RuCl2(PPh3)3, a cross-coupling of 3-buten-2-ol with aldehydes and imines was developed via a tandem olefin migration--aldol--Mannich reaction in bmim[PF6]. With In(OAc)3 as a co-catalyst, a-vinylbenzyl alcohol and aldehydes underwent sim...

  8. ALDOL- AND MANNICH-TYPE REACTIONS VIA IN SITU OLEFIN MIGRATION IN IONIC LIQUID

    EPA Science Inventory


    An aldol-type and a Mannich-type reaction via the cross-coupling of aldehydes and imines with allylic alcohols catalyzed by RuCl2(PPh3)3 was developed with ionic liquid as the solvent. The solvent/catalyst system could be reused for at least five times with no loss of reactiv...

  9. A General Diastereoselective Catalytic Vinylogous Aldol Reaction Among Tetramic Acid-Derived Pyrroles

    PubMed Central

    2015-01-01

    A catalytic diastereoselective aldol reaction has been developed for N1-arylated/C2-O-silylated/C3-methylated and brominated/C4-O-methylated pyrroles in its reactions with various aldehydes. Syn adducts emerge with regard to the vicinal nitrogen and oxygen heteroatom substituents. The N1-aryl residue undergoes oxidative cleavage, and the C3-bromine atom undergoes palladium-mediated coupling reactions, both without disturbing the newly created stereocenters. PMID:25119431

  10. A general diastereoselective catalytic vinylogous aldol reaction among tetramic acid-derived pyrroles.

    PubMed

    David, Jonathan G; Bai, Wen-Ju; Weaver, Marisa G; Pettus, Thomas R R

    2014-09-01

    A catalytic diastereoselective aldol reaction has been developed for N1-arylated/C2-O-silylated/C3-methylated and brominated/C4-O-methylated pyrroles in its reactions with various aldehydes. Syn adducts emerge with regard to the vicinal nitrogen and oxygen heteroatom substituents. The N1-aryl residue undergoes oxidative cleavage, and the C3-bromine atom undergoes palladium-mediated coupling reactions, both without disturbing the newly created stereocenters. PMID:25119431

  11. Stereoselective titanium-mediated aldol reactions of a chiral lactate-derived ethyl ketone with ketones.

    PubMed

    Alcoberro, Sandra; Gómez-Palomino, Alejandro; Solà, Ricard; Romea, Pedro; Urpí, Fèlix; Font-Bardia, Mercè

    2014-01-17

    Aldol reactions of titanium enolates of lactate-derived ethyl ketone 1 with other ketones proceed in a very efficient and stereocontrolled manner provided that a further equivalent of TiCl4 is added to the reacting mixture. The scope of these reactions encompasses simple ketones such as acetone or cyclohexanone as well as other ketones that contain potential chelating groups such as pyruvate esters or ?- and ?-hydroxy ketones. PMID:24372372

  12. Theoretical mechanistic study of the TBD-catalyzed intramolecular aldol reaction of ketoaldehydes.

    PubMed

    Hammar, Peter; Ghobril, Cynthia; Antheaume, Cyril; Wagner, Alain; Baati, Rachid; Himo, Fahmi

    2010-07-16

    The intramolecular aldol reaction of acyclic ketoaldehydes catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) is investigated using density functional theory calculations. Compared to the proline-catalyzed aldol reaction, the use of TBD provides a unique and unusual complete switch of product selectivity. Three mechanistic pathways are proposed and evaluated. The calculations provide new insights into the activation mode of bifunctional guanidine catalysts. In the favored mechanism, TBD first catalyzes the enolization of the substrate and then the C-C bond formation through two concerted proton transfers. In addition, the computationally predicted stereochemical outcome of the reaction is in agreement with the experimental findings. PMID:20545376

  13. Diastereodivergent aldol reactions of beta-alkoxy ethyl ketones: modular access to (1,4)-syn and -anti polypropionates.

    PubMed

    Arikan, Fatih; Li, Jun; Menche, Dirk

    2008-08-21

    Asymmetric substrate-controlled aldol reactions of ethyl ketones of type 4 with aldehyde 3 are reported. Modular access to all possible syn- and anti-aldol products was obtained by careful choice of reaction conditions. To achieve good selectivities in this diastereodivergent approach, selection of the protective group on the beta-oxygen of the enolate (R (2)) was of critical importance. PMID:18630925

  14. Origins of stereoselectivity in intramolecular aldol reactions catalyzed by cinchona amines.

    PubMed

    Lam, Yu-Hong; Houk, K N

    2015-02-11

    The intramolecular aldol condensation of 4-substituted heptane-2,6-diones leads to chiral cyclohexenones. The origins of the enantioselectivities of this reaction, disclosed by List et al. using a cinchona alkaloid-derived primary amine (cinchona amine) organocatalyst, have been determined with dispersion-corrected density functional theory (DFT). The stereocontrol hinges on the chair preference of the substrate-enamine intermediate and the conformational preferences of a hydrogen-bonded nine-membered aldol transition state containing eight heavy atoms. The conformations of the hydrogen-bonded ring in the various stereoisomeric transition structures have been analyzed in detail and shown to closely resemble the conformers of cyclooctane. A model of stereoselectivity is proposed for the cinchona amine catalysis of this reaction. The inclusion of Grimme's dispersion corrections in the DFT calculations (B3LYP-D3(BJ)) substantially improves the agreement of the computed energetics and experiment, attesting to the importance of dispersion effects in stereoselectivity. PMID:25629689

  15. Acid-Base Pairs in Lewis Acidic Zeolites Promote Direct Aldol Reactions by Soft Enolization.

    PubMed

    Lewis, Jennifer D; Van de Vyver, Stijn; Román-Leshkov, Yuriy

    2015-08-17

    Hf-, Sn-, and Zr-Beta zeolites catalyze the cross-aldol condensation of aromatic aldehydes with acetone under mild reaction conditions with near quantitative yields. NMR studies with isotopically labeled molecules confirm that acid-base pairs in the Si-O-M framework ensemble promote soft enolization through ?-proton abstraction. The Lewis acidic zeolites maintain activity in the presence of water and, unlike traditional base catalysts, in acidic solutions. PMID:26138135

  16. Solvent-Induced Reversal of Activities between Two Closely Related Heterogeneous Catalysts in the Aldol Reaction

    SciTech Connect

    Kandel, Kapil; Althaus, Stacey M; Peeraphatdit, Chorthip; Kobayashi, Takeshi; Trewyn, Brian G; Pruski, Marek; Slowing, Igor I

    2013-01-11

    The relative rates of the aldol reaction catalyzed by supported primary and secondary amines can be inverted by 2 orders of magnitude, depending on the use of hexane or water as a solvent. Our analyses suggest that this dramatic shift in the catalytic behavior of the supported amines does not involve differences in reaction mechanism, but is caused by activation of imine to enamine equilibria and stabilization of iminium species. The effects of solvent polarity and acidity were found to be important to the performance of the catalytic reaction. This study highlights the critical role of solvent in multicomponent heterogeneous catalytic processes.

  17. Catalytic Asymmetric Iterative/Domino Aldehyde Cross-Aldol Reactions for the Rapid and Flexible Synthesis of 1,3-Polyols.

    PubMed

    Lin, Luqing; Yamamoto, Kumiko; Mitsunuma, Harunobu; Kanzaki, Yamato; Matsunaga, Shigeki; Kanai, Motomu

    2015-12-16

    We report here catalytic asymmetric iterative and domino cross-aldol reactions between aldehydes, endowed with a high level of robustness, flexibility, and generality. A Cu(I)-DTBM-SEGPHOS complex catalyzes an asymmetric cross-aldol reaction between acceptor aldehydes and boron enolates derived from donor aldehydes, which are generated through Ir-catalyzed isomerization of allyloxyboronates. The unit process can be repeated using the aldol products in turn as acceptor substrates for the subsequent asymmetric aldol reaction. The donor aldehydes and stereoselectivity can be flexibly switched in a stepwise manner for the double-aldol reaction. Furthermore, asymmetric triple- and quadruple-aldol reactions are possible in one-pot using the appropriate amounts of donors and amine additives, rapidly elongating the carbon skeleton with controlling up to eight stereocenters. The method should be useful for straightforward synthesis of enantiomerically and diastereomerically enriched 1,3-polyols. PMID:26632863

  18. Highly stereoselective titanium-mediated aldol reaction from (S)-4-benzyloxy-3-methyl-2-butanone.

    PubMed

    Zambrana, Joana; Romea, Pedro; Urpí, Fèlix; Luján, Cristina

    2011-11-01

    Substrate-controlled titanium-mediated aldol reactions from (S)-4-benzyloxy-3-methyl-2-butanone provide satisfactory levels of 2,5-syn asymmetric induction if they are carried out in the presence of a second equivalent of TiCl(4). Such reactions give high yields and excellent diastereoselectivity with a wide array of achiral and chiral aldehydes without needing other sources of chirality. This procedure is thus of interest for the synthesis of natural products. Furthermore, spectroscopic studies and analyses of the reacting species have revealed a possible mechanism to account for the experimental results. PMID:21739992

  19. Practical asymmetric synthesis of ?-hydroxy ?-amino acids via complimentary aldol reactions

    PubMed Central

    Pandya, Bhaumik A.; Dandapani, Sivaraman; Duvall, Jeremy R.; Rowley, Ann; Mulrooney, Carol A.; Ryba, Troy; Dombrowski, Michael; Harton, Marie; Young, Damian W.; Marcaurelle, Lisa A.

    2011-01-01

    Orthogonally protected chiral ?-hydroxy-?-amino acids can be accessed in >100 g quantities from readily available starting materials and reagents in 3–4 steps. These chiral synthons contain two adjacent stereocenters along with suitably protected functional groups (O-TBS, N-Boc) for downstream reactivity. Implementation of two existing aldol technologies allows rapid access to all possible stereoisomers of 1. The guiding principles during reaction optimization were reaction scalability and operational efficiency. Conversion of the amino acids to a variety of chiral building blocks in 1–2 steps demonstrates their synthetic utility. PMID:21822337

  20. Kinetics of acid-catalyzed aldol condensation reactions of aliphatic aldehydes

    NASA Astrophysics Data System (ADS)

    Casale, Mia T.; Richman, Aviva R.; Elrod, Matthew J.; Garland, Rebecca M.; Beaver, Melinda R.; Tolbert, Margaret A.

    Field observations of atmospheric aerosols have established that organic compounds compose a large fraction of the atmospheric aerosol mass. However, the physical/chemical pathway by which organic compounds are incorporated into atmospheric aerosols remains unclear. The potential role of acid-catalyzed reactions of organic compounds on acidic aerosols has been explored as a possible chemical pathway for the incorporation of organic material into aerosols. In the present study, ultraviolet-visible (UV-vis) spectroscopy was used to monitor the kinetics of formation of the products of the acid-catalyzed aldol condensation reaction of a range of aliphatic aldehydes (C 2-C 8). The experiments were carried out at various sulfuric acid concentrations and a range of temperatures in order to estimate the rate constants of such reactions on sulfuric acid aerosols under tropospheric conditions. The rate constants were generally found to decrease as the chain length of the aliphatic aldehyde increased (except for acetaldehyde, which had an unusually small rate constant), increase as a function of sulfuric acid concentration as predicted by excess acidity theory, and showed normal Arrhenius behavior as a function of temperature. While the kinetic data are generally consistent with previous laboratory reports of aldehyde reactivity in various sulfuric acid media, the aldol condensation reactions involving aliphatic aldehydes do not appear fast enough to be responsible for significant transfer of organic material into atmospheric aerosols.

  1. Anti-Selective Aldol Reactions of Pentafluorosulfanylacetic Acid Esters with Aldehydes Mediated by Dicyclohexylchloroborane.

    PubMed

    Friese, Florian W; Dreier, Anna-Lena; Matsnev, Andrej V; Daniliuc, Constantin G; Thrasher, Joseph S; Haufe, Günter

    2016-03-01

    Aldol reactions of pentafluorosulfanyl (SF5)-substituted acetic acid esters with both aromatic and aliphatic aldehydes proceeded with excellent anti-diastereoselectivity and good to high yields using dicyclohexylchloroborane/triethylamine. This methodology enabled the synthesis of hitherto unknown α-SF5-β-hydroxy esters. Using a norephedrine-based auxiliary, high asymmetric induction was observed. The stereochemistry of products was assigned by NMR spectroscopy and proved by X-ray diffraction analysis. The intermediate enolate was identified as a highly unstable species. PMID:26909525

  2. Synthesis of substituted chromanones: an organocatalytic aldol/oxa-Michael reaction.

    PubMed

    Butler, Jeffrey D; Conrad, Wayne E; Lodewyk, Michael W; Fettinger, James C; Tantillo, Dean J; Kurth, Mark J

    2010-08-01

    A diastereoselective organocatalytic aldol/oxa-Michael reaction has been developed to efficiently deliver medicinally relevant 2,3-ring-substituted chromanones. Development of this synthetic strategy revealed an unexpected kinetic anti-Saytzeff elimination; an origin for the observed selectivity is suggested on the basis of the results of quantum chemical calculations. This unusual kinetic selectivity necessitated an isomerization protocol that in turn led to the discovery of an intriguing Pd-mediated isomerization/intramolecular Friedel-Crafts-type alkylation. PMID:20617821

  3. Asymmetric synthesis of trisubstituted oxazolidinones by the thiourea-catalyzed aldol reaction of 2-isocyanatomalonate diester.

    PubMed

    Sakamoto, Shota; Kazumi, Naoya; Kobayashi, Yusuke; Tsukano, Chihiro; Takemoto, Yoshiji

    2014-09-19

    A new method has been developed for the synthesis of chiral 4-carboxyl oxazolidinones by the catalytic asymmetric aldol reaction of an isocyanatomalonate diester with an aldehyde in the presence of a thiourea catalyst. The resulting chiral 4-carboxyl oxazolidinones are the equivalent of ?-hydroxy-?-amino acids bearing a tri- or tetrasubstituted carbon center at their ? position. With this in mind, this procedure was successfully applied to the first total synthesis of mycestericin C, which was completed in 12 steps and represents one of the shortest reported sequences for the construction of natural products of this type. PMID:25203516

  4. The effect of the hydrophobic environment on the retro-aldol reaction: Comparison to a computationally-designed enzyme

    PubMed Central

    Schmidt, Joshua; Ehasz, Clayton; Epperson, Michael; Klas, Kimberly; Wyatt, Justin; Hennig, Mirko

    2014-01-01

    Recent work on a computationally-designed retroaldolase RA-61 suggested that most of the rate-acceleration brought about by this enzyme was due to non-specific interactions with the aromatic substrate. To provide a benchmark for the role of non-specific interactions in this system, we measured the second-order rate constant for the amine-catalysed retro-aldol reaction of methodol in the presence of non-specific hydrophobic pockets such as micelles. We found that a simple micellar system, that consists of a positively-charged surfactant and a long-chain amine, can accelerate the retro-aldol reaction of methodol by 9,500-fold. This effect rivals the 105-fold rate acceleration of RA-61. Similar results were obtained with BSA used as the catalyst, implying that the retro-aldol reaction of methodol can be greatly accelerated by non-specific hydrophobic pockets that contain an amino group. PMID:24189834

  5. A fluorogenic aldehyde bearing a 1,2,3-triazole moiety for monitoring the progress of aldol reactions.

    PubMed

    Guo, Hai-Ming; Tanaka, Fujie

    2009-03-20

    We have developed a new type of fluorogenic aldehyde bearing a 1,2,3-triazole moiety that is useful for monitoring the progress of aldol reactions through an increase in fluorescence. Whereas 6-methoxy-2-naphthaldehyde was highly fluorescent, the fluorogenic aldehyde, 4-formylbenzene connected to the 6-methoxy-2-naphthyl group through a 1,2,3-triazole moiety, was essentially nonfluorescent in aqueous solutions. We suggest that the 4-formylphenyl group acts as a quencher to suppress the fluorescence of the 6-methoxy-2-naphthyltriazole moiety. The product of the aldol reaction of this aldehyde does not have a quenching moiety and showed more than 800-fold higher fluorescence than the aldehyde. Assay systems using the fluorogenic aldehyde were validated by screening of aldol catalysts, ranking of the activities of the catalysts, and evaluation of reaction conditions. PMID:19222210

  6. A highly efficient Mukaiyama-Mannich reaction of N-Boc isatin ketimines and other active cyclic ketimines using difluoroenol silyl ethers catalyzed by Ph3PAuOTf.

    PubMed

    Yu, Jin-Sheng; Zhou, Jian

    2015-12-01

    Ph3PAuOTf is identified as a powerful catalyst for the addition of difluoroenol silyl ethers to N-Boc isatin ketimines and other two kinds of active cyclic ketimines. This represents the first Au(i)-catalyzed Mukaiyama-Mannich reaction, and the corresponding non-fluorinated enol silyl ether proves to be even much more reactive under the same conditions. This method paves the way to the total synthesis of difluoromethylated analogues of AG-041R, a gastrin/CCK-B receptor antagonist. PMID:26443467

  7. Total synthesis of (+)-geldanamycin and (-)-o-quinogeldanamycin: asymmetric glycolate aldol reactions and biological evaluation.

    PubMed

    Andrus, Merritt B; Meredith, Erik L; Hicken, Erik J; Simmons, Bryon L; Glancey, Russell R; Ma, Wei

    2003-10-17

    The total synthesis of (+)-geldanamycin (GA), following a linear route, has been completed using a demethylative quinone-forming reaction as the last step. Key steps include the use of two new asymmetric boron glycolate aldol reactions. To set the anti-C11,12 hydroxymethoxy functionality, (S,S)-5,6-bis-4-methoxyphenyldioxanone 8 was used. Methylglycolate derived from norephedrine 5 set the C6,7 methoxyurethane stereochemistry. The quinone formation step using nitric acid gave the non-natural o-quino-GA product 55 10:1 over geldanamycin. Other known oxidants gave an unusual azaquinone product 49. o-Quino-GA 55 binds Hsp90 with good affinity but is less cytotoxic compared to GA. PMID:14535799

  8. L-Proline/CoCl2-catalyzed highly diastereo- and enantioselective direct aldol reactions.

    PubMed

    Karmakar, Ananta; Maji, Tapan; Wittmann, Sebastian; Reiser, Oliver

    2011-09-19

    The CoCl(2)/L-proline (1:2) system was found to be an excellent catalyst for direct aldol reactions. Excellent yields (up to 93%) and a significant improvement in diastereoselectivity (anti/syn up to 45:1) as well as enantioselectivity (up to more than 99% ee) compared with using proline as the sole catalyst were observed. This catalyst system was successfully applied to both cyclic and acyclic ketones in combination with aromatic and aliphatic aldehydes. In situ chelation of CoCl(2) and proline (1:2) is proposed to promote the reaction through a six-membered Zimmermann-Traxler type transition state involving the positioning of proline-enamine and the aldehyde through chelation to Co(II). PMID:21932236

  9. Dynamic assembly of a zinc-templated bifunctional organocatalyst in the presence of water for the asymmetric aldol reaction.

    PubMed

    Serra-Pont, Anna; Alfonso, Ignacio; Jimeno, Ciril; Solà, Jordi

    2015-12-21

    A bifunctional organocatalytic system consisting of simple pyridine ligands containing separate catalytic functionalities was assembled using ZnCl2. This novel metal-templated catalyst furnished high yields and stereoselectivities towards the aldol reaction. The addition of controlled amounts of water turned out to be crucial to dissolve the system and achieve optimal results. PMID:26478115

  10. Tandem aldol-Michael reactions in aqueous diethylamine medium: a greener and efficient approach to bis-pyrimidine derivatives.

    PubMed

    Al-Majid, Abdullah M; Barakat, Assem; Al-Najjar, Hany J; Mabkhot, Yahia N; Ghabbour, Hazem A; Fun, Hoong-Kun

    2013-01-01

    A simple protocol, involving the green synthesis for the construction of novel bis-pyrimidine derivatives, 3a-i and 4a-e are accomplished by the aqueous diethylamine media promoted tandem Aldol-Michael reaction between two molecules of barbituric acid derivatives 1a,b with various aldehydes. This efficient synthetic protocol using an economic and environmentally friendly reaction media with versatility and shorter reaction time provides bis-pyrimidine derivatives with high yields (88%-99%). PMID:24317435

  11. Construction of contiguous tetrasubstituted chiral carbon stereocenters via direct catalytic asymmetric aldol and Mannich-type reactions.

    PubMed

    Matsunaga, Shigeki; Yoshino, Tatsuhiko

    2011-09-01

    Catalytic asymmetric synthesis of unnatural amino acids with vicinal tetrasubstituted chiral carbon stereocenters is described. In the first part, direct catalytic asymmetric aldol reaction of simple non-activated ketone electrophiles with ?-substituted ?-isothiocyanato ester donors was realized. A Mg/Schiff base catalyst promoted the aldol reaction, and ?-amino-?-hydroxy esters were obtained in up to 98% ee and 98:2 d.r. In the second part, the Mg/Schiff base catalyst and a Sr/Schiff base catalyst were utilized for stereodivergent direct asymmetric Mannich-type reaction of ketimines. The Mg/Schiff base catalyst gave syn-?,?-diamino esters, while the Sr/Schiff base catalyst produced anti-?,?-diamino esters in good to high enantioselectivity, up to 97% ee. PMID:21898777

  12. Kinetics of Acid-Catalyzed Aldol Condensation Reactions of Aliphatic Aldehydes

    NASA Astrophysics Data System (ADS)

    Elrod, M. J.; Casale, M. T.; Richman, A. R.; Beaver, M. R.; Garland, R. M.; Tolbert, M. A.

    2006-12-01

    While it is well established that organic compounds compose a large fraction of the atmospheric aerosol mass, the mechanisms through which organics are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds with carbonyl groups have recently been suggested as important pathways for transfer of volatile organics into acidic aerosols. In the present study, ultraviolet-visible (UV-Vis) spectroscopy was used to monitor the kinetics of formation of the products of the aldol condensation reaction of a range of aliphatic aldehydes (C2-C8) The experiments were carried out at various sulfuric acid concentrations and a range of temperatures in order to estimate the rate constants of such reactions on sulfuric acid aerosols under tropospheric conditions. The rate constants were generally found to decrease as the chain length of the aliphatic aldehyde increased (except for acetaldehyde, which had an unusually small rate constant), increase as a function of sulfuric acid concentration as predicted by excess acidity theory, and showed normal Arrhenius behavior as a function of temperature.

  13. Brønsted acid mediated N-O bond cleavage for ?-amination of ketones through the aromatic nitroso aldol reaction.

    PubMed

    Ramakrishna, Isai; Sahoo, Harekrishna; Baidya, Mahiuddin

    2016-02-11

    A Brønsted acid mediated N-O bond cleavage for ?-amination of ketones has been developed through the nitroso aldol reaction of less-reactive aromatic nitroso compounds and silyl enol ethers having a disilane (-SiMe2TMS) backbone. This transformation is operationally simple and scalable, offering structurally diverse ?-amino ketones in high yields (up to 98%) with complete regioselectivity. It represents a mechanistically unique and rare example of a metal-free N-O bond cleavage process. PMID:26810365

  14. Direct Access to 6/5/7/5- and 6/7/5/5-Fused Tetracyclic Triterpenoids via Divergent Transannular Aldol Reaction of Lanosterol-Derived Diketone

    PubMed Central

    Ignatenko, Vasily A.; Han, Yong

    2013-01-01

    In an effort to access biologically relevant chemical space, a complex natural product-derived non-symmetrical diketone was prepared as a substrate for divergent transannular aldol reactions. The use of common aldol conditions resulted in predominant syn-addition via pathway a, while the use of alumina provided access to the anti-adduct. Screening of a range of Lewis acids of varying strength unexpectedly resulted in the formation of aldol products with 6/7/5/5-fused molecular skeleton via pathway b. PMID:24161022

  15. Sequential aldol condensation-transition metal-catalyzed addition reactions of aldehydes, methyl ketones, and arylboronic acids.

    PubMed

    Liao, Yuan-Xi; Xing, Chun-Hui; Israel, Matthew; Hu, Qiao-Sheng

    2011-04-15

    Sequential aldol condensation of aldehydes with methyl ketones followed by transition metal-catalyzed addition reactions of arylboronic acids to form ?-substituted ketones is described. By using the 1,1'-spirobiindane-7,7'-diol (SPINOL)-based phosphite, an asymmetric version of this type of sequential reaction, with up to 92% ee, was also realized. Our study provided an efficient method to access ?-substituted ketones and might lead to the development of other sequential/tandem reactions with transition metal-catalyzed addition reactions as the key step. PMID:21417359

  16. Highly Stereoselective and Scalable anti-Aldol Reactions using N-(p-dodecylphenylsulfonyl)-2-Pyrrolidinecarboxamide: Scope and Origins of Stereoselectivities

    PubMed Central

    Yang, Hua; Mahapatra, Subham; Cheong, Paul Ha-Yeon; Carter, Rich G.

    2010-01-01

    A highly enantio- and diastereoselective anti-aldol process (up to >99% ee, >99:1 dr) catalyzed by a proline mimetic – N-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide – has been developed. Catalyst loading as low as 2 mol% can be employed. Use of industry-friendly solvents for this transformation as well as neat reaction conditions have been demonstrated. The scope of this transformation on a range of aldehydes and ketones is explored. Density Functional Theory computations reveal that the origins of enhanced diastereoselectivity is due to the presence of non-classical hydrogen bonds between the sulfonamide, the electrophile and the catalyst enamine that favor the major Anti-Re aldol TS in the Houk-List model. PMID:20932013

  17. Characterization and mechanism insight of accelerated catalytic promiscuity of Sulfolobus tokodaii (ST0779) peptidase for aldol addition reaction.

    PubMed

    Li, Rong; Perez, Bianca; Jian, Hui; Jensen, Mads Mørk; Gao, Renjun; Dong, Mingdong; Glasius, Marianne; Guo, Zheng

    2015-11-01

    A novel peptidase from thermophilic archaea Sulfolobus tokodaii (ST0779) is examined for its catalytic promiscuity of aldol addition, which shows comparable activity as porcine pancreatic lipase (PPL, one of the best enzymes identified for biocatalytic aldol addition) at 30 °C but much accelerated activity at elevated temperature. The molecular catalytic efficiency kcat/Km (M(-1) s(-1)) of this thermostable enzyme at 55 °C adds up to 140 times higher than that of PPL at its optimum temperature 37 °C. The fluorescence quenching analysis depicts that the binding constants of PPL are significantly higher than those of ST0779, and their numbers of binding sites show opposite temperature dependency. Thermodynamic parameters estimated by fluorescence quenching analysis unveil distinctly different substrate-binding modes between PPL and ST0779: the governing binding interaction between PPL and substrates is hydrophobic force, while the dominating substrate-binding forces for ST0779 are van der Waals and H-bonds interactions. A reasonable mechanism for ST0779-catalyzed aldol reaction is proposed based on kinetic study, spectroscopic analysis, and molecular stereostructure simulation. This work represents a successful example to identify a new enzyme for catalytic promiscuity, which demonstrates a huge potential to discover and exploit novel biocatalyst from thermophile microorganism sources. PMID:26169629

  18. The mimic of type II aldolases chemistry: asymmetric synthesis of beta-hydroxy ketones by direct aldol reaction.

    PubMed

    Lu, Zhijin; Mei, Haibo; Han, Jianlin; Pan, Yi

    2010-08-01

    An efficient direct aldol reaction has been developed for the synthesis of chiral beta-hydroxy ketone using a combination of C(1)-symmetric chiral prolinamides based on o-phenylenediamine and zinc triflate as catalyst. The reaction was convenient to carry out in aqueous media with up to 98% chemical yields and up to 94% ee values. The current strategy can be regarded as the analogue of aldolase type II, which suggests a new pathway for the designing of new organocatalysts. PMID:20572810

  19. One-Pot Synthesis of (S)-Baclofen via Aldol Condensation of Acetaldehyde with Diphenylprolinol Silyl Ether Mediated Asymmetric Michael Reaction as a Key Step.

    PubMed

    Hayashi, Yujiro; Sakamoto, Daisuke; Okamura, Daichi

    2016-01-01

    An efficient asymmetric total synthesis of (S)-baclofen was accomplished via a one-pot operation from commercially available materials using sequential reactions, such as aldol condensation of acetaldehyde, diphenylprolinol silyl ether mediated asymmetric Michael reaction of nitromethane, Kraus-Pinnick oxidation, and Raney Ni reduction. Highly enantioenriched baclofen was obtained in one pot with a good yield over four reactions. PMID:26636719

  20. A convenient enantioselective decarboxylative aldol reaction to access chiral ?-hydroxy esters using ?-keto acids

    PubMed Central

    Duan, Zhiqiang; Han, Jianlin; Qian, Ping; Zhang, Zirui; Pan, Yi

    2014-01-01

    Summary We show a convenient decarboxylative aldol process using a scandium catalyst and a PYBOX ligand to generate a series of highly functionalized chiral ?-hydroxy esters. The protocol tolerates a broad range of ?-keto acids with inactivated aromatic and aliphatic ?-keto esters. The possible mechanism is rationalized. PMID:24991246

  1. Catalytic anions embedded into avidin: importance of their chirality and the chiral environment on the stereocontrol of the aldol reaction.

    PubMed

    Gauchot, Vincent; Schmitzer, Andreea R

    2014-03-21

    Several catalytic anions bearing a pseudo-dipeptide scaffold, in combination with a biotinylated imidazolium cation, were prepared. The assembly of these salts with avidin resulted in the formation of stable biohybrid catalysts, active in ionic liquid/aqueous media for the aldol reaction. By using natural and non-natural amino alcohols as "side chains" for the proline derivative anion, we studied the cooperativity between the anion and its position in avidin. Taking advantage of the large freedom of movement of the anion inside avidin, we also investigated the substrate scope of this type of biohybrid catalyst. PMID:24559501

  2. Equilibrium between a vinylogous ylide and a phosphonium dienolate zwitterion: vinylogous Wittig olefination versus vinylogous aldol-type reaction

    PubMed Central

    Khong, San N.; Tran, Yang S.; Kwon, Ohyun

    2010-01-01

    This paper describes the equilibrium established between a phosphonium dienolate zwitterion and a vinylogous phosphorus ylide, and their reactions with aldehydes. The reactions between ethyl 2-methyl-2,3-butadienoate and various aldehydes occur through either a phosphonium dienolate or a vinylogous ylide intermediate, depending on the presence/absence of a Lewis acid and the nature of the phosphine. We observed a rare vinylogous Wittig olefination from the reaction between ethyl 2-methyl-2,3-butadienoate and an electron-deficient aromatic aldehyde in the presence of a stoichiometric amount of an electron-deficient triarylphosphine and a catalytic amount of a Lewis acid (e.g., BF3·Et2O). On the other hand, the use of triphenylphosphine, in the absence of a Lewis acid, facilitated vinylogous aldol addition, accompanied by a rare 1,2-aryl phosphorus-to-carbon migration. PMID:21359169

  3. Equilibrium between a vinylogous ylide and a phosphonium dienolate zwitterion: vinylogous Wittig olefination versus vinylogous aldol-type reaction.

    PubMed

    Khong, San N; Tran, Yang S; Kwon, Ohyun

    2010-06-01

    This paper describes the equilibrium established between a phosphonium dienolate zwitterion and a vinylogous phosphorus ylide, and their reactions with aldehydes. The reactions between ethyl 2-methyl-2,3-butadienoate and various aldehydes occur through either a phosphonium dienolate or a vinylogous ylide intermediate, depending on the presence/absence of a Lewis acid and the nature of the phosphine. We observed a rare vinylogous Wittig olefination from the reaction between ethyl 2-methyl-2,3-butadienoate and an electron-deficient aromatic aldehyde in the presence of a stoichiometric amount of an electron-deficient triarylphosphine and a catalytic amount of a Lewis acid (e.g., BF(3)·Et(2)O). On the other hand, the use of triphenylphosphine, in the absence of a Lewis acid, facilitated vinylogous aldol addition, accompanied by a rare 1,2-aryl phosphorus-to-carbon migration. PMID:21359169

  4. Highly enantioselective cross-aldol reactions of acetaldehyde mediated by a dual catalytic system operating under site isolation.

    PubMed

    Fan, Xinyuan; Rodríguez-Escrich, Carles; Wang, Shoulei; Sayalero, Sonia; Pericàs, Miquel A

    2014-10-01

    Polystyrene-supported (PS) diarylprolinol catalysts 1?a (Ar = phenyl) and 1?b (Ar = 3,5-bis(trifluoromethyl)phenyl) have been developed. Operating under site-isolation conditions, PS-1?a/1?b worked compatibly with PS-bound sulfonic acid catalyst 2 to promote deoligomerization of paraldehyde and subsequent cross-aldol reactions of the resulting acetaldehyde in one pot, affording aldol products in high yields with excellent enantioselectivities. The effect of water on the performance of the catalytic system has been studied and its optimal amount (0.5?equiv) has been determined. The dual catalytic system (1/2) allows repeated recycling and reuse (10 cycles). The potential of this methodology is demonstrated by a two-step synthesis of a phenoperidine analogue (68% overall yield; 98%?ee) and by the preparation of highly enantioenriched 1,3-diols 4 and 3-methylamino-1-arylpropanols 5, key intermediates in the synthesis of a variety of druglike structures. PMID:25168085

  5. Role of pseudoephedrine as chiral auxiliary in the "acetate-type" aldol reaction with chiral aldehydes; asymmetric synthesis of highly functionalized chiral building blocks.

    PubMed

    Ocejo, Marta; Carrillo, Luisa; Vicario, Jose L; Badía, Dolores; Reyes, Efraim

    2011-01-21

    We have studied in depth the aldol reaction between acetamide enolates and chiral ?-heterosubstituted aldehydes using pseudoephedrine as chiral auxiliary under double stereodifferentiation conditions, showing that high diastereoselectivities can only be achieved under the matched combination of reagents and provided that the ?-heteroatom-containing substituent of the chiral aldehyde is conveniently protected. Moreover, the obtained highly functionalized aldols have been employed as very useful starting materials for the stereocontrolled preparation of other interesting compounds and chiral building blocks such as pyrrolidines, indolizidines, and densely functionalized ?-hydroxy and ?-amino ketones using simple and high-yielding methodologies. PMID:21188970

  6. Brønsted acid/rhodium(II) cooperative catalytic asymmetric three-component aldol-type reaction for the synthesis of 3-amino oxindoles.

    PubMed

    Ren, Lei; Lian, Xiao-Lei; Gong, Liu-Zhu

    2013-03-01

    Cooperation is key! Chiral Brønsted acid/rhodium(II) cooperative catalysis enabled an enantioselective three-component aldol-type reaction of 3-diazo oxindoles and anilines with glyoxylates to give highly functionalized and structurally diverse 3-amino oxindoles in high stereoselectivity (>20:1 d.r., 99?% ee; see scheme). PMID:23401186

  7. Unexpected Synthesis of 5,6-Dihydropyridin-2(1H)-ones by a Domino Ugi/Aldol/Hydrolysis Reaction Starting from Baylis-Hillman Phosphonium Salts.

    PubMed

    Zeng, Xiao-Hua; Wang, Hong-Mei; Ding, Ming-Wu

    2015-05-01

    A one-pot synthetic approach to 5,6-dihydropyridin-2(1H)-ones has been developed using a domino process involving Ugi, aldol, and hydrolysis reactions, starting with Baylis-Hillman phosphonium salts, primary amines, isocyanides, and arylglyoxals. PMID:25875533

  8. TANDEM BIS-ALDOL REACTION OF KETONES: A FACILE ONE-POT SYNTHESIS OF 1,3-DIOXANES IN AQUEOUS MEDIUM

    EPA Science Inventory

    A novel tandem bis-aldol reaction of ketone with paraformaldehyde catalyzed by polystyrenesulfonic acid in aqueous medium delivers 1,3-dioxanes in high yield. This one pot, operationally simple microwave-assisted synthetic protocol proceeds efficiently in water in the absence of ...

  9. Organocatalyzed aldol reaction between pyridine-2-carbaldehydes and ?-ketoacids: a straightforward route towards indolizidines and isotetronic acids.

    PubMed

    Liautard, Virginie; Jardel, Damien; Davies, Clotilde; Berlande, Muriel; Buffeteau, Thierry; Cavagnat, Dominique; Robert, Frédéric; Vincent, Jean-Marc; Landais, Yannick

    2013-10-18

    Enantioselective aldol reactions between substituted pyridine carbaldehydes and ?-ketoacids were shown to provide isotetronic acids or their corresponding pyridinium salts, depending on the nature of the substituents on the pyridine ring. The pyridinium salts were generated through nucleophilic attack of the pyridine nitrogen atom onto the reactive keto functional group. Moderate-to-good yields of both compounds were typically obtained and high levels of enantioselectivity were observed by using benzimidazole pyrrolidine I as a catalyst. Hydrogenation of the resulting pyridinium salts led to new indolizidines with high ee values and diastereocontrol. X-ray diffraction studies allowed the determination of the relative configuration of the products. Finally, DFT calculations were performed to rationalize the divergent pathway as a function of the pyridine substituents. PMID:24038579

  10. Asymmetric assembly of aldose carbohydrates from formaldehyde and glycolaldehyde by tandem biocatalytic aldol reactions

    NASA Astrophysics Data System (ADS)

    Szekrenyi, Anna; Garrabou, Xavier; Parella, Teodor; Joglar, Jesús; Bujons, Jordi; Clapés, Pere

    2015-09-01

    The preparation of multifunctional chiral molecules can be greatly simplified by adopting a route via the sequential catalytic assembly of achiral building blocks. The catalytic aldol assembly of prebiotic compounds into stereodefined pentoses and hexoses is an as yet unmet challenge. Such a process would be of remarkable synthetic utility and highly significant with regard to the origin of life. Pursuing an expedient enzymatic approach, here we use engineered D-fructose-6-phosphate aldolase from Escherichia coli to prepare a series of three- to six-carbon aldoses by sequential one-pot additions of glycolaldehyde. Notably, the pertinent selection of the aldolase variant provides control of the sugar size. The stereochemical outcome of the addition was also altered to allow the synthesis of L-glucose and related derivatives. Such engineered biocatalysts may offer new routes for the straightforward synthesis of natural molecules and their analogues that circumvent the intricate enzymatic pathways forged by evolution.

  11. Asymmetric assembly of aldose carbohydrates from formaldehyde and glycolaldehyde by tandem biocatalytic aldol reactions.

    PubMed

    Szekrenyi, Anna; Garrabou, Xavier; Parella, Teodor; Joglar, Jesús; Bujons, Jordi; Clapés, Pere

    2015-09-01

    The preparation of multifunctional chiral molecules can be greatly simplified by adopting a route via the sequential catalytic assembly of achiral building blocks. The catalytic aldol assembly of prebiotic compounds into stereodefined pentoses and hexoses is an as yet unmet challenge. Such a process would be of remarkable synthetic utility and highly significant with regard to the origin of life. Pursuing an expedient enzymatic approach, here we use engineered D-fructose-6-phosphate aldolase from Escherichia coli to prepare a series of three- to six-carbon aldoses by sequential one-pot additions of glycolaldehyde. Notably, the pertinent selection of the aldolase variant provides control of the sugar size. The stereochemical outcome of the addition was also altered to allow the synthesis of L-glucose and related derivatives. Such engineered biocatalysts may offer new routes for the straightforward synthesis of natural molecules and their analogues that circumvent the intricate enzymatic pathways forged by evolution. PMID:26291944

  12. Concise Enantioselective Synthesis of Oxygenated Steroids via Sequential Copper(II)-Catalyzed Michael Addition/Intramolecular Aldol Cyclization Reactions

    PubMed Central

    Cichowicz, Nathan R.; Kaplan, Will; Khomutnyk, Yaroslav; Bhattarai, Bijay; Sun, Zhankui; Nagorny, Pavel

    2015-01-01

    A new scalable enantioselective approach to functionalized oxygenated steroids is described. This strategy is based on chiral bis(oxazoline) copper(II) complex-catalyzed enantioselective and diastereoselective Michael reactions of cyclic ketoesters and enones to install vicinal quaternary and tertiary stereocenters. In addition, the utility of copper(II) salts as highly active catalysts for the Michael reactions of traditionally unreactive ???-enones and substituted ???-ketoesters that results in unprecedented Michael adducts containing vicinal all-carbon quaternary centers is also demonstrated. The Michael adducts subsequently undergo base-promoted diastereoselective aldol cascade reactions resulting in the natural or unnatural steroid skeletons. The experimental and computational studies suggest that the torsional strain effects arising from the presence of the ?5-unsaturation are key controling elements for the formation of the natural cardenolide scaffold. The described method enables expedient generation of polycyclic molecules including modified steroidal scaffolds as well as challenging-to-synthesize Hajos-Parrish and Wieland-Miescher ketones. PMID:26491886

  13. The tandem chain extension aldol reaction used for synthesis of ketomethylene tripeptidomimetics targeting hPEPT1

    PubMed Central

    Thorn, Karina; Nielsen, Carsten Uhd; Jakobsen, Palle; Steffansen, Bente; Zercher, Charles K.; Begtrup, Mikael

    2011-01-01

    The rationale for targeting the human di-/tripeptide transporter hPEPT1 for oral drug delivery has been well established by several drug and prodrug cases. The aim of this study was to synthesize novel ketomethylene modified tripeptidomimetics and to investigate their binding affinity for hPEPT1. Three related tripeptidomimetics of the structure H-Phe-?[COCH2]-Ser(Bz)-Xaa-OH were synthesized applying the tandem chain extension aldol reaction, where amino acid derived ?-keto imides were stereoselectively converted to ?-substituted ?-keto imides. In addition, three corresponding tripeptides, composed of amide bonds, were synthesized for comparison of binding affinities. The six investigated compounds were all defined as high affinity ligands (Ki-values <0.5 mM) for hPEPT1 by measuring the concentration dependent inhibition of apical [14C]Gly-Sar uptake in Caco-2 cells. Consequently, the ketomethylene replacement for the natural amide bond and ?-side chain modifications appears to offer a promising strategy to modify tripeptidic structures while maintaining a high affinity for hPEPT1. PMID:21703856

  14. Formal homologous aldol reactions: interrupting the Nazarov cyclization via carboalkoxylation of alkynes.

    PubMed

    Wu, Yen-Ku; West, F G

    2014-05-01

    Reactions between 1,4-pentadien-3-ones and aryl acetylenes in the presence of BF3·OEt2 furnish ?-phenacyl cyclopentanones via a domino electrocyclization/carboalkoxylation reaction sequence. The overall process underscores a new mode of interrupted Nazarov trapping, where two new carbon-carbon bonds are installed with concomitant formation of carbonyl functionality. PMID:24735109

  15. The Aldol Addition and Condensation: The Effect of Conditions on Reaction Pathway

    ERIC Educational Resources Information Center

    Crouch, R. David; Richardson, Amie; Howard, Jessica L.; Harker, Rebecca L.; Barker, Kathryn H.

    2007-01-01

    The reaction of a ketone and an aldehyde in aqueous Na[subscript 2]CO[subscript 2] is described. This experiment is performed in the absence of strong bases or organic solvents and offers the opportunity for students to observe the critical role that reaction temperature and base strength have in determining the product of the base-mediated…

  16. Divergent Stereocontrol of Acid Catalyzed Intramolecular Aldol Reactions of 2,3,7-Triketoesters: Synthesis of Highly Functionalized Cyclopentanones

    PubMed Central

    Truong, Phong; Shanahan, Charles S.; Doyle, Michael P.

    2012-01-01

    The intramolecular acid catalyzed aldol cyclization of 2,3,7-triketoesters formed from ?-keto-?-diazo-?-ketoesters provides highly functionalized cyclopentanones with good diastereoselectivity in high overall yields via kinetically controlled and stereodivergent catalytic processes. Lewis acid catalysis gives high selectivity for the 1,3-anti tetrasubstituted cyclopentanones, whereas Brønsted acid catalysis produces the corresponding 1,3-syn diastereomer. PMID:22738671

  17. Towards organo-click chemistry: development of organocatalytic multicomponent reactions through combinations of aldol, Wittig, Knoevenagel, Michael, Diels-Alder and Huisgen cycloaddition reactions.

    PubMed

    Ramachary, Dhevalapally B; Barbas, Carlos F

    2004-10-25

    Here we report on our studies on combinations of amino acids and copper(I) for catalyzing multicomponent reactions (MCRs). We aimed to prepare both diene and dienophiles simultaneously, under very mild and environmentally friendly conditions, thus giving the constituents for a stereocontrolled Diels-Alder reaction, which in turn yields compounds 4 to 8. A diversity-oriented synthesis of polysubstituted spirotriones 4 to 6 were assembled from simple substrates like 1-(triphenylphosphanylidene)-propan-2-one, two aldehydes, and cyclic-1,3-diketones through Wittig/Knoevenagel/Diels-Alder and aldol/Knoevenagel/Diels-Alder reaction sequences in one pot under stereospecific organocatalysis. Chemical diversity libraries of polysubstituted spirotrione-1,2,3-traizoles 8 were assembled from simple substrates by means of Wittig/Knoevenagel/Diels-Alder/Huisgen cycloaddition reaction sequences in one pot under stereospecific organo/Cu(I) catalysis. Functionalized dispirolactones such as 6 are biologically active antioxidants and radical scavengers, and spirotrione-1,2,3-traizoles 8 have found wide applications in chemistry, biology, and materials science. Experimentally simple and environmentally friendly, organocatalytic, asymmetric four-component Diels-Alder (AFCDA) reactions of 1-(triphenylphosphanylidene)- propan-2-one, two different aldehydes, and cyclic-1,3-diketones produced diastereospecific and highly enantioselective substituted spirotriones 4 by means of a Wittig/Knoevenagel/Diels-Alder reaction sequence in one pot. Additionally we have developed an organocatalytic, asymmetric three-component Michael (ATCM) reaction of 1-(triphenylphosphanylidene)-propan-2-one, aldehyde, and cyclic-1,3-diketones that produced Michael adducts 15, 16 through a Wittig/Michael reaction sequence in a highly enantioselective one-pot process. PMID:15390208

  18. Intramolecular Diels-Alder (IMDA) Studies toward the Synthesis of Australifungin. Stereocontrol in the Acetate Aldol Reaction of β,β'-Branched Aldehydes.

    PubMed

    Williams, David R; Klein, J Cullen

    2016-02-01

    Studies of australifungin illustrate an enantiocontrolled synthesis of the trans-decalin core 28 via an intramolecular [4π + 2π] cycloaddition. This strategy utilizes the nitroalkene dienophile of 27 as a surrogate ketene equivalent. Stereocontrol at C-2 is critically important for an effective intramolecular Diels-Alder (IMDA) process. Our studies report high asymmetric induction using a nonracemic Duthaler titanium enolate in the acetate aldol reaction with β,β'-branched aldehyde 13 to introduce the required C-2 chirality. PMID:26782107

  19. Direct synthesis of C-glycosides from unprotected 2-N-acyl-aldohexoses via aldol condensation-oxa-Michael reactions with unactivated ketones.

    PubMed

    Johnson, Sherida; Tanaka, Fujie

    2016-01-01

    C-glycosides are important compounds as they are used as bioactive molecules and building blocks. We have developed methods to concisely synthesize C-glycosides from unprotected 2-N-acyl-aldohexoses and unactivated ketones; we designed aldol-condensation-oxa-Michael addition reactions catalyzed by amine-based catalysts using additives. Depending on the conditions used, C-glycosides were stereoselectively obtained. Our methods allowed the C-C bond formations at the anomeric centers of unprotected carbohydrates under mild conditions to lead the C-glycosides in atom- and step-economical ways. PMID:26565955

  20. Organocatalytic enantioselective Michael-Michael-Michael-aldol condensation reactions: control of five stereocenters in a quadruple-cascade asymmetric synthesis of highly functionalized hexahydrophenanthrenes.

    PubMed

    Raja, Arun; Hong, Bor-Cherng; Lee, Gene-Hsiang

    2014-11-01

    A cascade organocatalysis has been developed for the enantioselective synthesis of a highly functionalized hexahydrophenanthrene-2-carbaldehyde containing five contiguous stereogenic centers with high diastereoselectivity and high enantioselectivity (>99% ee). The one-pot method comprises a cascade of organocatalytic Michael-Michael-Michael-aldol reactions of 2-methyl-1,5-dinitro-3-((E)-2-nitrovinyl)benzene and ?,?-unsaturated aldehydes (e.g., cinnamaldehyde). The structure and absolute configuration of a product were confirmed by X-ray analysis of an appropriate derivative. PMID:25337635

  1. Evidence for the formation of an enamine species during aldol and Michael-type addition reactions promiscuously catalyzed by 4-oxalocrotonate tautomerase.

    PubMed

    Poddar, Harshwardhan; Rahimi, Mehran; Geertsema, Edzard M; Thunnissen, Andy-Mark W H; Poelarends, Gerrit J

    2015-03-23

    The enzyme 4-oxalocrotonate tautomerase (4-OT), which has a catalytic N-terminal proline residue (Pro1), can promiscuously catalyze various carbon-carbon bond-forming reactions, including aldol condensation of acetaldehyde with benzaldehyde to yield cinnamaldehyde, and Michael-type addition of acetaldehyde to a wide variety of nitroalkenes to yield valuable ?-nitroaldehydes. To gain insight into how 4-OT catalyzes these unnatural reactions, we carried out exchange studies in D2 O, and X-ray crystallography studies. The former established that H-D exchange within acetaldehyde is catalyzed by 4-OT and that the Pro1 residue is crucial for this activity. The latter showed that Pro1 of 4-OT had reacted with acetaldehyde to give an enamine species. These results provide evidence of the mechanism of the 4-OT-catalyzed aldol and Michael-type addition reactions in which acetaldehyde is activated for nucleophilic addition by Pro1-dependent formation of an enamine intermediate. PMID:25728471

  2. Catalytic asymmetric synthesis of 3-(alpha-hydroxy-beta-carbonyl) oxindoles by a Sc(III)-catalyzed direct aldol-type reaction.

    PubMed

    Shen, Ke; Liu, Xiaohua; Zheng, Ke; Li, Wei; Hu, Xiaolei; Lin, Lili; Feng, Xiaoming

    2010-03-22

    A direct catalytic asymmetric aldol-type reaction of 3-substituted-2-oxindoles with glyoxal derivatives and ethyl trifluoropyruvate, catalyzed by a chiral N,N'-dioxide-Sc(OTf)(3) (Tf = trifluoromethanesulfonyl) complex, has been developed that tolerates a wide range of substrates. The reaction proceeds in good yields and excellent enantioselectivities (up to 93% yield, 99:1 diastereomeric ratio (dr), and >99% enantiomeric excess (ee)) under mild conditions, to deliver 3-(alpha-hydroxy-beta-carbonyl) oxindoles with vicinal quaternary-tertiary or quaternary-quaternary stereocenters. Even with 1 mol % catalyst loading or on scaleup (10 mmol of starting material), maintenance of ee was observed, which showed the potential value of the catalyst system. In studies probing the reaction mechanism, a positive nonlinear effect was observed and Sc(III)-based enolate intermediates were detected by using ESIMS. On the basis of the experimental results and previous reports, a possible catalytic cycle was assumed. PMID:20175165

  3. Steady-state kinetics and inhibition studies of the aldol condensation reaction catalyzed by bovine liver and Escherichia coli 2-keto-4-hydroxyglutarate aldolase.

    PubMed

    Grady, S R; Wang, J K; Dekker, E E

    1981-04-28

    Two sensitive assays, one which fluorometrically measures only the L isomer of 2-keto-4-hydroxyglutarate after decarboxylation to L-malate and the other which spectrophotometrically determines both enantiomers by reductive amination with glutamate dehydrogenase, are described. By use of these assays, the steady-state kinetics of the aldol condensation of pyruvate with glyoxylate, as catalyzed by 2-keto-4-hydroxyglutarate aldolase from either bovine liver or Escherichia coli, were studied as was the inhibition of this reaction by glyoxylate and other anions. For the E. coli aldolase, double-reciprocal plots are linear except at high (above 5 mM) glyoxylate concentrations; apparent Km values increase with increasing concentrations of the fixed substrate. The data are consistent with an ordered reaction sequence. Inhibition by halides follows the lyotropic or Hofmeister series. Esters are not good inhibitors; mono-, di-, and tricarboxylic acids are increasingly inhibitory. Of the substrate analogues tested, hydroxypyruvate is the most potent inhibitor. Inhibition studies with citrate, acetaldehyde, and glyoxylate (all competitive inhibitors) suggest there are two domains at the active site-the Schiff base forming lysyl residue which interacts with carbonyl analogues (like acetaldehyde) and a center of positive charge which binds anions (like citrate). In contrast to the bacterial enzyme, liver 2-keto-4-hydroxyglutarate aldolase is inhibited in a competitive manner by much lower concentrations (0.1 mM or even lower) of glyoxylate. Many salts and some carboxylic acids activate the liver enzyme. Similarly, substrate analogues like 2-ketobutyrate and fluoropyruvate are mild activators; no effect is seen with acetaldehyde. Besides glyoxylate, only glyoxal, 2-ketoglutarate, and hydroxypyruvate inhibit the aldol condensation reaction. A uniform value of 1 is found for the number of inhibitor molecules bound per active site of either liver or E. coli 2-keto-4-hydroxyglutarate aldolase. PMID:7016177

  4. A Brønsted Acid-Amino Acid as a Synergistic Catalyst for Asymmetric List-Lerner-Barbas Aldol Reactions.

    PubMed

    Ramachary, Dhevalapally B; Shruthi, Kodambahalli S

    2016-03-18

    Herein, for the first time, a combination of l-amino acid, (R)-5,5-dimethyl thiazolidinium-4-carboxylate (l-DMTC) with simple Brønsted acid TFA is reported as the suitable synergistic catalyst for the List-Lerner-Barbas aldol (LLB-A) reaction of less reactive 2-azidobenzaldehydes with various ketones at ambient temperature to furnish the optically active functionalized (2-azidophenyl)alcohols with very good yields, dr's, and ee's. This method gives first time access to the novel azido-containing multifunctional compounds, which are applicable in material to medicinal chemistry. Chiral functionalized (2-azidophenyl)alcohols were transformed into different molecular scaffolds in good yields with high selectivity through Lewis acid mediated NaBH4 reduction, aza-Wittig and Staudinger reaction (azide reduction), followed by oxidative cyclizations, allenone synthesis, and click reaction, respectively. Chiral LLB-A products might become suitable starting materials for the total synthesis of natural products, ingredients, and inhibitors in medicinal chemistry. The mechanistic synergy of l-DMTC with TFA to increase the rate and selectivity of LLB-A reaction in DMSO-D6 is explained with the controlled and online NMR experiments. PMID:26907463

  5. One-pot organocatalytic tandem aldol/polycyclization reactions between 1,3-dicarbonyl compounds and ?,?,?,?-unsaturated aldehydes for the straightforward assembly of cyclopenta[b]furan-type derivatives: new insight into the Knoevenagel reaction.

    PubMed

    Riveira, Martín J; Mischne, Mirta P

    2012-02-20

    A new cascade pathway viable for Knoevenagel chemistry that involves the coupling between 1,3-dicarbonyl systems and ?,?,?,?-unsaturated aldehydes has been developed. The process comprises the combination of a classic aldol-type condensation and a rare spontaneous metal-free cycloisomerization, representing a convergent and innovative approach for the stereoselective synthesis of cyclopenta[b]furan-type derivatives. The scope and limitations with respect to both reaction partners and mechanistic features were investigated. Meaningfully, our study provides valuable guidance concerning the structural and electronic effects controlling the reactivity of conjugated polyene carbonyl systems. PMID:22249912

  6. Dynamic kinetic asymmetric transformations of ?-stereogenic ?-ketoesters by direct aldolization.

    PubMed

    Corbett, Michael T; Johnson, Jeffrey S

    2014-01-01

    Dynamic kinetic asymmetric transformations (DyKAT) of racemic ?-bromo-?-keto esters by direct aldolization of nitromethane and acetone provide access to fully substituted ?-glycolic acid derivatives bearing a ?-stereocenter. The aldol adducts are obtained in excellent yield with high relative and absolute stereocontrol under mild reaction conditions. Mechanistic studies determined that the reactions proceed through a facile catalyst-mediated racemization of the ?-bromo-?-keto esters under a DyKAT Type I manifold. PMID:24222195

  7. Tandem semipinacol-type 1,2-carbon migration/aldol reaction toward the construction of [5-6-7] all-carbon tricyclic core of Calyciphylline A-type alkaloids.

    PubMed

    Yang, Ming; Wang, Lin; He, Zheng-He; Wang, Shao-Hua; Zhang, Shu-Yu; Tu, Yong-Qiang; Zhang, Fu-Min

    2012-10-01

    A Lewis acid promoted tandem semipinacol-type 1,2-carbon migration/aldol reaction of trimethylsilane-protected vinylogous ?-ketols with aldehyde or dimethyl acetals is reported. This reaction provides a direct and rapid way for the construction of 6-substituted spiro[4.5]decanes which extensively exist in Daphniphyllum alkaloids. By the use of this method, further construction of a [5-6-7] all-carbon tricyclic core of Calyciphylline A-type alkaloids was also completed. PMID:22992007

  8. A Multistep Organocatalysis Experiment for the Undergraduate Organic Laboratory: An Enantioselective Aldol Reaction Catalyzed by Methyl Prolinamide

    ERIC Educational Resources Information Center

    Wade, Edmir O.; Walsh, Kenneth E.

    2011-01-01

    In recent years, there has been an explosion of research concerning the area of organocatalysis. A multistep capstone laboratory project that combines traditional reactions frequently found in organic laboratory curriculums with this new field of research is described. In this experiment, the students synthesize a prolinamide-based organocatalyst…

  9. A Multistep Organocatalysis Experiment for the Undergraduate Organic Laboratory: An Enantioselective Aldol Reaction Catalyzed by Methyl Prolinamide

    ERIC Educational Resources Information Center

    Wade, Edmir O.; Walsh, Kenneth E.

    2011-01-01

    In recent years, there has been an explosion of research concerning the area of organocatalysis. A multistep capstone laboratory project that combines traditional reactions frequently found in organic laboratory curriculums with this new field of research is described. In this experiment, the students synthesize a prolinamide-based organocatalyst…

  10. Total synthesis of (+)-geldanamycin and (-)-o-quinogeldanamycin with use of asymmetric anti- and syn-glycolate aldol reactions.

    PubMed

    Andrus, Merritt B; Meredith, Erik L; Simmons, Bryon L; Soma Sekhar, B B V; Hicken, Erik J

    2002-10-01

    Geldanamycin (GA), an antitumor Hsp90 inhibitor, was made for the first time by using an oxidative demethylation reaction as the final step. A biaryldioxanone auxiliary set the anti C11-12 hydroxy-methoxy functionality and a methylglycolate auxiliary based on norephedrine was used for the syn C6-7 methoxy-urethane. p-Quinone-forming oxidants, CAN and AgO, produced an unusual aza-quinone product. Nitric acid gave GA from a trimethoxy precursor in 55% yield as a 1:10 mixture with nonnatural o-quino-GA. [structure: see text] PMID:12323066

  11. Mechanism of the lanthanum bromide assisted electrochemical aldolization of. alpha. -bromo ketones

    SciTech Connect

    Fry, A.J.; Susla, M. )

    1989-04-26

    Linear sweep voltammetry, preparative electrolyses under a variety of experimental conditions, and trapping experiments have been used to explore the mechanism of the formation of the aldol 2-benzoyl-1-phenylpropanol by electrochemical reduction of {alpha}-bromopropiophenone in the presence of benzaldehyde and lanthanum bromide. The aldol condensation occurs by reaction of the free (lithio) enolate with a lanthanum bromide-benzaldehyde-tetrahydrofuran complex. Electrochemical reduction of the bromo ketone forms the Z enolate highly stereospecifically. The erythro aldol is formed stereoselectively initially, but the condensation is reversible, and the equilibrium mixture of aldols, containing mostly the threo isomer, is isolated from the electrolysis.

  12. Diastereo- and enantioselective synthesis of nitroso Diels-Alder-type bicycloketones using dienamine: mechanistic insight into sequential nitroso Aldol/Michael reaction and application for optically pure 1-amino-3,4-diol synthesis.

    PubMed

    Momiyama, Norie; Yamamoto, Yuhei; Yamamoto, Hisashi

    2007-02-01

    This article presents complete diastereo- and highly enantioselective synthesis of nitroso Diels-Alder-type bicycloketones using dienamine. With the hydrogen bonding of two hydroxyls in the bulky binaphthol 1c, high enantioselectivities and complete diastereoselectivity are realized in 2-oxa-3-aza-bicycloketone synthesis. On the other hand, alpha,beta-unsaturated ketone can be employed as diene precursor, utilizing readily available tetrazole catalyst 3b, to provide the 3-oxa-2-aza-bicycloketones in moderate yields with complete enantioselectivities. Investigation into the reaction utilizing 2-morpholino-4,4-diphenylcyclohexadiene 2d clearly indicated that cyclization with the bulky binaphthol 1c is involved in the sequential process, the N-nitroso aldol reaction, followed by Michael addition. In addition, optically pure 1-amino-3,4-diol is synthesized from 2-oxa-3-aza-bicycloketones. Use of p-phenoxynitrosobenzene allows access to protected amino diol via cleavage of the N-Ph bond. PMID:17263400

  13. Synthesis of novel chromeno-annulated cis-fused pyrano[3,4-c]benzopyran and naphtho pyran derivatives via domino aldol-type/hetero Diels-Alder reaction and their cytotoxicity evaluation.

    PubMed

    Madda, Jyothi; Venkatesham, Akkaladevi; Naveen Kumar, Bejjanki; Nagaiah, Kommu; Sujitha, Pombala; Ganesh Kumar, C; Rao, Tadikamalla Prabhakar; Jagadeesh Babu, Nanubolu

    2014-09-15

    New chromeno-annulated cis-fused pyrano[3,4-c]benzopyran and naphtho pyran derivatives have been synthesized by domino aldol-type reaction/hetero Diels-Alder reaction generated from o-quinone methide in situ from 7-O-prenyl derivatives of 8-formyl-2,3-disubstituted chromenones with resorcinols/naphthols in the presence of 20 mol% ethylenediamine diacetate (EDDA), triethylamine (2 mL) as co-catalyst in CH3CN under reflux conditions in good yields. The structures were established based on spectroscopic data, and further confirmed by X-ray diffraction analysis. The results showed that compounds 4h and 4j exhibited very potent cytotoxicity against human cervical cancer cell line (HeLa). Compound 4h displayed good inhibitory activity against both breast cancer cell lines, MDA-MB-231 and MCF-7. Further, the compound 4i exhibited good cytotoxicity against only MDA-MB-231, and compound 4j showed promising activity against human lung cancer cell line, A549 with IC50 value of 2.53±0.07 ?M, which was comparable to the standard doxorubicin (IC50=1.21±0.1 ?M). PMID:25172420

  14. Aldol derivatives of Thioxoimidazolidinones as potential anti-prostate cancer agents.

    PubMed

    Khatik, Gopal L; Kaur, Jasmine; Kumar, Varun; Tikoo, Kulbhushan; Venugopalan, P; Nair, Vipin A

    2011-08-01

    The paper discusses the synthesis and stereochemical aspects of the anti aldol products, 3-(substituted phenyl)-5-[(substituted phenyl) hydroxy methyl]-5-methyl-4-oxo-2-thioxoimidazolidines. The stereochemistry observed in the aldol reactions with benzaldehydes was explained by transition state model of the endocyclic (E)-enolate formed from the rigid 4-oxo-2-thioxoimidazolidine skeleton. Proton NMR and ROESY spectral analyses were carried out to identify the syn and anti conformations of the aldol diastereomers. Configurations of the enantiomers of the representative anti aldol product 3-(4-chlorophenyl)-5-[(4-chlorophenyl) hydroxy methyl]-5-methyl-4-oxo-2-thioxoimidazolidine was determined by single crystal XRD studies. The compounds were screened in vitro against prostate cancer cell lines, PC-3 and LNCaP and the most potent derivatives were identified. PMID:21600678

  15. Illustrating the Utility of X-Ray Crystallography for Structure Elucidation through a Tandem Aldol Condensation/Diels-Alder Reaction Sequence

    ERIC Educational Resources Information Center

    Hoang, Giang T.; Kubo, Tomohiro; Young, Victor G., Jr.; Kautzky, Jacob A.; Wissinger, Jane E.

    2015-01-01

    Two introductory organic chemistry laboratory experiments are described based on the Diels-Alder reaction of 2,3,4,5-tetraphenylcyclopentadienone, which is synthesized prior to or in a one-pot reaction, with styrene. Students are presented with three possible products, the "endo" and "exo" diastereomers and the decarbonylated…

  16. Illustrating the Utility of X-Ray Crystallography for Structure Elucidation through a Tandem Aldol Condensation/Diels-Alder Reaction Sequence

    ERIC Educational Resources Information Center

    Hoang, Giang T.; Kubo, Tomohiro; Young, Victor G., Jr.; Kautzky, Jacob A.; Wissinger, Jane E.

    2015-01-01

    Two introductory organic chemistry laboratory experiments are described based on the Diels-Alder reaction of 2,3,4,5-tetraphenylcyclopentadienone, which is synthesized prior to or in a one-pot reaction, with styrene. Students are presented with three possible products, the "endo" and "exo" diastereomers and the decarbonylated…

  17. Autoxidation/Aldol Tandem Reaction of 2-Oxindoles with Ketones: A Green Approach for the Synthesis of 3-Hydroxy-2-Oxindoles.

    PubMed

    Zhang, Qing-Bao; Jia, Wen-Liang; Ban, Yong-Liang; Zheng, Yong; Liu, Qiang; Wu, Li-Zhu

    2016-02-01

    In the presence of tetrabutylammonium fluoride and molecular sieves (MS) 4 Å in DMF, an efficient autoxidation reaction of 2-oxindoles with ketones under air at room temperature has been developed. This approach may provide a green, practical, and metal-free protocol for a wide range of biologically important 3-hydroxy-3-(2-oxo-alkyl)-2-oxindoles. PMID:26714924

  18. Discovery-Oriented Approach To Organic Synthesis: Tandem Aldol Condensation-Michael Addition Reactions. Identifying Diastereotopic Hydrogens in an Achiral Molecule by NMR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wachter-Jurcsak, Nanette; Reddin, Kendra

    2001-09-01

    We have found a beautiful example of anisochrony of diastereotopic acyclic methylene hydrogens in a symmetric diketone, synthesized by techniques traditionally performed in an introductory organic laboratory course. Synthesis of the diketone is high-yielding and easy to carry out, and the products can be directly isolated with a good degree of purity with no need of further manipulation. The reaction can be accomplished in a single laboratory session.

  19. Mechanism of the aldol condensation of aldehydes, catalyzed by the salts of metals and higher organic acids

    SciTech Connect

    Katsnel'son, M.G.; Kagna, S.Sh.; Nikitina, L.I.; Oranskaya, O.M.; Semenskaya, I.V.

    1987-01-10

    The salts of transition metals are the most active catalysts for the aldol condensation of aliphatic aldehydes. By IR spectroscopy it was found that an intermediate complex between the aldehyde and the catalyst is formed at the initial stage of the reaction. A chelate mechanism of catalysis is proposed for the aldol condensation and satisfactorily explains the order of formation of the intermediate and final products.

  20. Asymmetric total synthesis of smyrindiol employing an organocatalytic aldol key step

    PubMed Central

    Fronert, Jeanne; Bisschops, Tom; Boeck, Florian

    2012-01-01

    Summary The first organocatalytic asymmetric synthesis of smyrindiol, by using an (S)-proline catalyzed enantioselective intramolecular aldol reaction as the key step, is described. Smyrindiol was synthesized from commercially available 2,4-dihydroxybenzaldehyde in 15 steps, with excellent stereoselectivity (de = 99%, ee = 99%). In the course of this total synthesis a new and mild coumarin assembly was developed. PMID:23019438

  1. Domino hydroformylation/aldol condensation/hydrogenation catalysis: highly selective synthesis of ketones from olefins.

    PubMed

    Fang, Xianjie; Jackstell, Ralf; Börner, Armin; Beller, Matthias

    2014-11-24

    A general and highly chemo- and regioselective synthesis of ketones from olefins by domino hydroformylation/aldol condensation/hydrogenation reaction has been developed. A variety of olefins are efficiently converted into various ketones in good to excellent yields and regioselectivities in the presence of a specific rhodium phosphine/base-acid catalyst system. PMID:25331557

  2. Asymmetric total synthesis and structural elucidation of NFAT-68.

    PubMed

    Wang, Lin; Xi, Yumeng; Yang, Shouliang; Zhu, Rong; Liang, Yufan; Chen, Jiahua; Yang, Zhen

    2011-01-01

    Total synthesis of NFAT-68 (7) has been achieved and its relative stereochemistry has been determined. A key step thereof is the utilization of the chelation-controlled vinylogous Mukaiyama aldol reaction (VMAR) to stereoselectively synthesize the syn-aldol product 8. This developed chemistry is anticipated to have wider application in total syntheses of many other natural products. PMID:21121639

  3. Aldol Condensation of Volatile Carbonyl Compounds in Acidic Aerosols

    NASA Astrophysics Data System (ADS)

    Noziere, B.; Esteve, W.

    2003-12-01

    Reactions of volatile organic compounds in acidic aerosols have been shown recently to be potentially important for organic aerosol formation and growth. Aldol condensation, the acid-catalyzed polymerization of carbonyl compounds, is a likely candidate to enhance the flux of organic matter from the gas phase to the condensed phase in the atmosphere. Until now these reactions have only been characterized for conditions relevant to synthesis (high acidities and liquid phase systems) and remote from atmospheric ones. In this work, the uptake of gas-phase acetone and 2,4\\-pentanedione by sulfuric acid solutions has been measured at room temperature using a Rotated Wetted Wall Reactor coupled to a Mass Spectrometer. The aldol condensation rate constants for 2,4\\-pentanedione measured so far for sulfuric acid solutions between 96 and 70 % wt. display a variation with acidity in agreement with what predicted in the organic chemical literature. The values of these constants, however, are much lower than expected for this compound, and comparable to the ones of acetone. Experiments are underway to complete this study to lower acidities and understand the discrepancies with the predicted reactivity.

  4. NMR investigations on the proline-catalyzed aldehyde self-condensation: Mannich mechanism, dienamine detection, and erosion of the aldol addition selectivity.

    PubMed

    Schmid, Markus B; Zeitler, Kirsten; Gschwind, Ruth M

    2011-05-01

    The proline-catalyzed self-condensation of aliphatic aldehydes in DMSO with varying amounts of catalyst was studied by in situ NMR spectroscopy. The reaction profiles and intermediates observed as well as deuteration studies reveal that the proline-catalyzed aldol addition and condensation are competing, but not consecutive, reaction pathways. In addition, the rate-determining step of the condensation is suggested to be the C-C bond formation. Our findings indicate the involvement of two catalyst molecules in the C-C bond formation of the aldol condensation, presumably by the activation of both the aldol acceptor and donor in a Mannich-type pathway. This mechanism is shown to be operative also in the oligomerization of acetaldehyde with high proline amounts, for which the first in situ detection of a proline-derived dienamine was accomplished. In addition, the diastereoselectivity of the aldol addition is evidenced to be time-dependent since it is undermined by the retro-aldolization and the competing irreversible aldol condensation; here NMR reaction profiles can be used as a tool for reaction optimization. PMID:21446689

  5. A unique approach to aldol products for the creation of all-carbon quaternary stereocentres.

    PubMed

    Das, Jaya Prakash; Chechik, Helena; Marek, Ilan

    2009-05-01

    Among the challenges facing asymmetric synthesis the selective construction of quaternary stereogenic centres, particularly those bearing all-carbon substituents, stands out. The aldol reaction has the potential to create such stereocentres, but, despite the many advances in this field, a highly selective and efficient procedure has remained elusive. Here we show that, by choosing an alternative retrosynthetic approach, such products can be prepared in a highly selective fashion. Through the consecutive addition of several organometallic derivatives, an allylzinc reagent is prepared and, on addition to an aldehyde, an aldol-type product is created. The one-pot operation involves the construction of three new carbon-carbon bonds and the formation of an all-carbon quaternary stereocentre. The products of the reaction are amenable to downstream modification, and the procedure should find applications in the fields of natural product synthesis and drug discovery. PMID:21378825

  6. Synthesis of isocoumarins with different substituted patterns via Passerini-aldol sequence.

    PubMed

    Ma, Guan-Hua; Jiang, Bo; Tu, Xing-Jun; Ning, Yi; Tu, Shu-Jiang; Li, Guigen

    2014-09-01

    An efficient combination between the Passerini three-component reaction and aldol condensation has been developed for the synthesis of bicyclic isocoumarins with different substituted patterns via solvent-dependent domino pathways. These two operationally friendly methods simultaneously install C-O and C-C bonds in a one-pot manner, allowing the utilization of low-cost and readily accessible 2-formylbenzoic acid, isocyanides, and arylglyoxals. Mechanisms of formation of different substituted isocoumarin derivatives are also proposed. PMID:25140818

  7. Synthesis of Isocoumarins with Different Substituted Patterns via Passerini–Aldol Sequence

    PubMed Central

    2015-01-01

    An efficient combination between the Passerini three-component reaction and aldol condensation has been developed for the synthesis of bicyclic isocoumarins with different substituted patterns via solvent-dependent domino pathways. These two operationally friendly methods simultaneously install C–O and C–C bonds in a one-pot manner, allowing the utilization of low-cost and readily accessible 2-formylbenzoic acid, isocyanides, and arylglyoxals. Mechanisms of formation of different substituted isocoumarin derivatives are also proposed. PMID:25140818

  8. Direct asymmetric aldol addition-isomerization of ?,?-unsaturated ?-butyrolactam with aryl ?-ketoesters: synthesis of MBH-type products.

    PubMed

    Zhang, Jinlong; Liu, Xihong; Ma, Xiaojuan; Wang, Rui

    2013-04-25

    A highly efficient direct asymmetric aldol addition-isomerization reaction at the ?-position of ?,?-unsaturated ?-butyrolactam and aryl ?-ketoesters by using a bifunctional thiourea catalyst was achieved. Morita-Baylis-Hillman type adducts containing a quaternary stereocenter can be obtained in high yields and with excellent enantioselectivities (up to 99% ee). PMID:23503364

  9. Light-absorbing aldol condensation products in acidic aerosols: Spectra, kinetics, and contribution to the absorption index

    NASA Astrophysics Data System (ADS)

    Nozière, Barbara; Esteve, William

    The radiative properties of aerosols that are transparent to light in the near-UV and visible, such as sulfate aerosols, can be dramatically modified when mixed with absorbing material such as soot. In a previous work we had shown that the aldol condensation of carbonyl compounds produces light-absorbing compounds in sulfuric acid solutions. In this work we report the spectroscopic and kinetic parameters necessary to estimate the effects of these reactions on the absorption index of sulfuric acid aerosols in the atmosphere. The absorption spectra obtained from the reactions of six different carbonyl compounds (acetaldehyde, acetone, propanal, butanal, 2-butanone, and trifluoroacetone) and their mixtures were compared over 190-1100 nm. The results indicated that most carbonyl compounds should be able to undergo aldol condensation. The products are oligomers absorbing light in the 300-500 nm region where few other compounds absorb, making them important for the radiative properties of aerosols. Kinetic experiments in 96-75 wt% H 2SO 4 solutions and between 273 and 314 K gave an activation energy for the rate constant of formation of the aldol products of acetaldehyde of -(70±15) kJ mol -1 in 96 wt% solution and showed that the effect of acid concentration was exponential. A complete expression for this rate constant is proposed where the absolute value in 96 wt% H 2SO 4 and at 298 K is scaled to the Henry's law coefficient for acetaldehyde and the absorption cross-section for the aldol products assumed in this work. The absorption index of stratospheric sulfuric acid aerosols after a 2-year residence time was estimated to 2×10 -4, optically equivalent to a content of 0.5% of soot and potentially significant for the radiative forcing of these aerosols and for satellite observations in channels where the aldol products absorb.

  10. Cu/MgAl(2)O(4) as bifunctional catalyst for aldol condensation of 5-hydroxymethylfurfural and selective transfer hydrogenation.

    PubMed

    Pupovac, Kristina; Palkovits, Regina

    2013-11-01

    Copper supported on mesoporous magnesium aluminate has been prepared as noble-metal-free solid catalyst for aldol condensation of 5-hydroxymethylfurfural with acetone, followed by hydrogenation of the aldol condensation products. The investigated mesoporous spinels possess high activity as solid-base catalysts. Magnesium aluminate exhibits superior activity compared to zinc and cobalt-based aluminates, reaching full conversion and up to 81 % yield of the 1:1 aldol product. The high activity can be correlated to a higher concentration of basic surface sites on magnesium aluminate. Applying continuous regeneration, the catalysts can be recycled without loss of activity. Focusing on the subsequent hydrogenation of aldol condensation products, Cu/MgAl2 O4 allows a selective hydrogenation and CO bond cleavage, delivering 3-hydroxybutyl-5-methylfuran as the main product with up to 84 % selectivity avoiding ring saturation. Analysis of the hydrogenation activity reveals that the reaction proceeds in the following order: CC>CO>CO cleavage>ring hydrogenation. Comparable activity and selectivity can be also achieved utilizing 2-propanol as solvent in the transfer hydrogenation, providing the possibility for partial recycling of acetone and optimization of the hydrogen management. PMID:24038987

  11. Structure-Reactivity Relationships in Lithiated Evans Enolates: Influence of Aggregation and Solvation on the Stereochemistry and Mechanism of Aldol Additions.

    PubMed

    Tallmadge, Evan H; Jermaks, Janis; Collum, David B

    2016-01-13

    Aldol additions to isobutyraldehyde and cyclohexanone with lithium enolates derived from acylated oxazolidinones (Evans enolates) are described. Previously characterized trisolvated dimeric enolates undergo rapid addition to isobutyraldehyde to give a 12:1 syn:syn selectivity in high yield along with small amounts of one anti isomer. The efficacy of the addition depends critically on aging effects and the reaction quench. Unsolvated tetrameric enolates that form on warming the solutions are unreactive toward isobutyraldehyde and undergo retroaldol reaction under forcing conditions. Additions to cyclohexanone are relatively slow but form a single isomeric adduct in >80% yield. The ketone-derived aldolates are robust. All attempts to control stereoselectivity by controlling aggregation failed. Rate studies of addition to cyclohexanone trace the lack of aggregation-dependent selectivities to a monomer-based mechanism. The synthetic implications and possible utility of lithium enolates in Evans aldol additions are discussed. PMID:26639525

  12. Copolymer-supported heterogeneous organocatalyst for asymmetric aldol addition in aqueous medium.

    PubMed

    Zhou, Jinqing; Wan, Jinwei; Ma, Xuebing; Wang, Wei

    2012-06-01

    In the current study, a convenient and simple way is presented to synthesize a novel type of supported heterogeneous organocatalyst in 21-81% yield by the copolymerization of 9-amino-9-deoxy-epi-cinchonine organocatalyst with acrylonitrile using AIBN as radical initiator. The chemical compositions (x/y) and weight-average molecular weights of copolymers 1a-d were determined by (1)H NMR and GPC analysis respectively. Their porous and layered structure, and surface morphology were characterized by nitrogen adsorption-desorption, XRD and TEM. In the asymmetric aldol addition of p-nitrobenzaldehyde to cyclohexanone and 1-hydroxy-2-propanone in water, all the supported organocatalysts 1a-d afforded excellent isolated yields (90.2-94.7%) and stereoselectivities (96.8-97.8%ee anti, anti/syn = 91/9). The highest catalytic property (96% yield, anti/syn = 90/10 and 99%ee anti) in water as the sole solvent was achieved under the optimized conditions. Compared with cyclohexanone, cyclopentanone and acetone showed the less desired enantioselectivities in the same aldol reactions. At the end of the aldol reaction, the copolymer-supported organocatalyst 1a was readily recovered in 95-98% yield from reaction mixture by simple filtration using an organic membrane. Even in the fifth run, there was no significant loss in catalytic activity and stereocontrol (94.3% yield, 97.2%ee anti, anti/syn = 90/10). After continuous reuse five times, there was some drop in catalytic activity and stereoselectivity. PMID:22546863

  13. Domino-hydroformylation/aldol condensation catalysis: highly selective synthesis of ?,?-unsaturated aldehydes from olefins.

    PubMed

    Fang, Xianjie; Jackstell, Ralf; Franke, Robert; Beller, Matthias

    2014-10-01

    A general and highly chemo-, regio-, and stereoselective synthesis of ?,?-unsaturated aldehydes by a domino hydroformylation/aldol condensation reaction has been developed. A variety of olefins and aromatic aldehydes were efficiently converted into various substituted ?,?-unsaturated aldehydes in good to excellent yields in the presence of a rhodium phosphine/acid-base catalyst system. In view of the easy availability of the substrates, the high atom-efficiency, the excellent selectivity, and the mild conditions, this method is expected to complement current methodologies for the preparation of ?,?-unsaturated aldehydes. PMID:25179918

  14. Organocatalytic atroposelective aldol condensation: synthesis of axially chiral biaryls by arene formation.

    PubMed

    Link, Achim; Sparr, Christof

    2014-05-19

    Axially chiral compounds are of significant importance in modern synthetic chemistry and particularly valuable in drug discovery and development. Nonetheless, current approaches for the preparation of pure atropisomers often prove tedious. We demonstrate here a synthetic method that efficiently transfers the stereochemical information of a secondary amine organocatalyst into the axial chirality of tri-ortho-substituted biaryls. An aromatic ring is formed during the dehydration step of the described aldol condensation cascade, leading to highly enantioenriched binaphthyl derivatives. The fundamental course of the reaction is related to the biosynthesis of aromatic polyketides. PMID:24757165

  15. Synthesis of ring-fused oxazolo- and pyrazoloisoquinolinones by a one-pot Pd-catalyzed carboxamidation and aldol-type condensation cascade process.

    PubMed

    Chouhan, Gagan; Alper, Howard

    2009-08-21

    A three-component cascade process is described for the synthesis of ring-fused oxazolo- and pyrazoloisoquinolinones by a one-pot carboxamidation/aldol-type condensation reaction. The cascade process involves Pd-catalyzed carboxamidation of an aryl halide/active methylene compound with oxazolidinone or pyrazolidinone, and subsequent intramolecular base-catalyzed cyclization/dehydration through an aldol-type condensation process, to give ring-fused oxazolo- and pyrazoloisoquinolinones. This methodology provides an easy one-step approach to these important classes of nitrogen-containing heterocycles and can tolerate a wide array of functional groups, including ester, nitrile, methoxy, and halide. PMID:19606884

  16. Direct synthesis of 1-indanones via Pd-catalyzed olefination and ethylene glycol-promoted aldol-type annulation cascade.

    PubMed

    Ruan, Jiwu; Iggo, Jonathan A; Xiao, Jianliang

    2011-01-21

    A wide range of multisubstituted 1-indanones of potential pharmaceutical use were synthesized in a one-pot fashion in moderate to excellent yields via palladium catalysis in ethylene glycol. The Heck reaction first installs an enol functionality on the aromatic ring; this is followed by an ethylene glycol promoted aldol-type annulation with a neighboring carbonyl group, resulting in the formation of various 1-indanones. PMID:21162549

  17. An amino-modified Zr-terephthalate metal-organic framework as an acid-base catalyst for cross-aldol condensation.

    PubMed

    Vermoortele, Frederik; Ameloot, Rob; Vimont, Alexandre; Serre, Christian; De Vos, Dirk

    2011-02-01

    After controlled pretreatment, some Zr-terephthalate metal-organic frameworks are highly selective catalysts for the cross-aldol condensation between benzaldehyde and heptanal. The proximity of Lewis acid and base sites in the amino-functionalized UiO-66(NH(2)) material further raises the reaction yields. PMID:21103462

  18. Total synthesis of the proposed structure of astakolactin

    PubMed Central

    Mameda, Keisuke; Fujishiro, Moe; Yoshinaga, Yutaka

    2014-01-01

    Summary The first total synthesis of the proposed structure of astakolactin, a sesterterpene metabolite isolated from the marine sponge Cacospongia scalaris, has been achieved, mainly featuring Johnson–Claisen rearrangement, asymmetric Mukaiyama aldol reaction and MNBA-mediated lactonization. PMID:25383112

  19. Synthesis, characterization, and properties of a benzofuran-based cage-shaped borate: photo activation of Lewis acid catalysts.

    PubMed

    Konishi, Akihito; Yasunaga, Ryosuke; Chiba, Kouji; Yasuda, Makoto

    2016-02-16

    A cage-shaped borate with benzofuran moieties was synthesized. This borate showed a higher degree of catalytic activity for Mukaiyama-aldol type reactions than a simple benzene-based cage-shaped borate induced by self-aggregation. Moreover, the exposure of the complex to black-light irradiation enhanced the catalytic activity. PMID:26823084

  20. Sequential Norrish type?II photoelimination and intramolecular aldol cyclization of ?-diketones: synthesis of polyhydroxylated cyclopentitols by ring contraction of hexopyranose carbohydrate derivatives.

    PubMed

    Alvarez-Dorta, Dimitri; León, Elisa I; Kennedy, Alan R; Martín, Angeles; Pérez-Martín, Inés; Riesco-Fagundo, Concepción; Suárez, Ernesto

    2013-07-29

    The excitation of the innermost carbonyl of nono-2,3-diulose derivatives by irradiation with visible-light initiates a sequential Norrish type?II photoelimination and aldol cyclization process that finally gives polyfunctionalized cyclopentitols. The rearrangement has been confirmed by the isolation of stable acyclic photoenol intermediates that can be independently cyclized by a thermal 5-(enolexo)-exo-trig uncatalyzed aldol reaction with high diastereoselectivity. In this last step, the large deuterium kinetic isotope effect found for the 1,5-hydrogen atom transfer seems to indicate that the aldol reaction runs through a concerted pericyclic mechanism. Owing to the ready availability of pyranose sugars of various configurations, this protocol has been used to study the influence of pyranose ring-substituents on the diastereoselectivity of the aldol cyclization reaction. In contrast with other pyranose ring contraction methodologies no transition-metal reagents are needed and the sequential rearrangement occurs simply by using visible light and moderate heating (0 to 60?°C). PMID:23788424

  1. A Green Enantioselective Aldol Condensation for the Undergraduate Organic Laboratory

    ERIC Educational Resources Information Center

    Bennett, George D.

    2006-01-01

    A number of laboratory exercises for the organic chemistry curriculum that emphasize enantioselective synthesis of the aldol condensation which involves the proline-catalyzed condensation between acetone and isobutyraldehyde are explored. The experiment illustrates some of the trade-offs involved in green chemistry like the use of acetone in large…

  2. A Green Enantioselective Aldol Condensation for the Undergraduate Organic Laboratory

    ERIC Educational Resources Information Center

    Bennett, George D.

    2006-01-01

    A number of laboratory exercises for the organic chemistry curriculum that emphasize enantioselective synthesis of the aldol condensation which involves the proline-catalyzed condensation between acetone and isobutyraldehyde are explored. The experiment illustrates some of the trade-offs involved in green chemistry like the use of acetone in large…

  3. Catalytic Aldol-Cyclization Cascade of 3-Isothiocyanato Oxindoles with α-Ketophosphonates for the Enantioselective Synthesis of β-Amino-α-hydroxyphosphonates.

    PubMed

    Kayal, Satavisha; Mukherjee, Santanu

    2015-11-01

    A cascade aldol-cyclization reaction between 3-isothiocyanato oxindoles and α-ketophosphonates has been developed for the synthesis of β-amino-α-hydroxyphosphonate derivatives. Catalyzed by a quinine-based tertiary amino-thiourea derivative, this reaction delivers 2-thioxooxazolidinyl phosphonates based on a spirooxindole scaffold bearing two contiguous quaternary stereogenic centers in high yields with excellent diastereo- (up to >20:1 dr) and enantioselectivities (up to >99:1 er). PMID:26512732

  4. Convergent fabrication of a nanoporous two-dimensional carbon network from an aldol condensation on metal surfaces

    NASA Astrophysics Data System (ADS)

    Landers, John; Chérioux, Frédéric; De Santis, Maurizio; Bendiab, Nedjma; Lamare, Simon; Magaud, Laurence; Coraux, Johann

    2014-12-01

    We report a convergent surface polymerization reaction scheme on Au(111), based on a triple aldol condensation, yielding a carbon-rich, covalent nanoporous two-dimensional network. The reaction is not self-poisoning and proceeds up to a full surface coverage. The deposited precursor molecules 1, 3, 5-tri(4’-acetylphenyl) first form supramolecular assemblies that are converted to the porous covalent network upon heating. The formation and structure of the network and of the intermediate steps are studied with scanning tunneling microscopy, Raman spectroscopy and density functional theory.

  5. One-pot aldol condensation and hydrodeoxygenation of biomass-derived carbonyl compounds for biodiesel synthesis.

    PubMed

    Faba, Laura; Díaz, Eva; Ordóñez, Salvador

    2014-10-01

    Integrating reaction steps is of key interest in the development of processes for transforming lignocellulosic materials into drop-in fuels. We propose a procedure for performing the aldol condensation (reaction between furfural and acetone is taken as model reaction) and the total hydrodeoxygenation of the resulting condensation adducts in one step, yielding n-alkanes. Different combinations of catalysts (bifunctional catalysts or mechanical mixtures), reaction conditions, and solvents (aqueous and organic) have been tested for performing these reactions in an isothermal batch reactor. The results suggest that the use of bifunctional catalysts and aqueous phase lead to an effective integration of both reactions. Therefore, selectivities to n-alkanes higher than 50% were obtained using this catalyst at typical hydrogenation conditions (T=493 K, P=4.5 MPa, 24 h reaction time). The use of organic solvent, carbonaceous supports, or mechanical mixtures of monofunctional catalysts leads to poorer results owing to side effects; mainly, hydrogenation of reactants and adsorption processes. PMID:25088473

  6. Substrate inhibition in the heterogeneous catalyzed aldol condensation: A mechanistic study of supported organocatalysts

    SciTech Connect

    Kandel, Kapil; Althaus, Stacey M.; Peeraphatdit, Chorthip; Kobayashi, Takeshi; Trewyn, Brian G.; Pruski, Marek; Slowing, Igor I.

    2012-05-23

    In this study, we demonstrate how materials science can be combined with the established methods of organic chemistry to find mechanistic bottlenecks and redesign heterogeneous catalysts for improved performance. By using solid-state NMR, infrared spectroscopy, surface and kinetic analysis, we prove the existence of a substrate inhibition in the aldol condensation catalyzed by heterogeneous amines. We show that modifying the structure of the supported amines according to the proposed mechanism dramatically enhances the activity of the heterogeneous catalyst. We also provide evidence that the reaction benefits significantly from the surface chemistry of the silica support, which plays the role of a co-catalyst, giving activities up to two orders of magnitude larger than those of homogeneous amines. This study confirms that the optimization of a heterogeneous catalyst depends as much on obtaining organic mechanistic information as it does on controlling the structure of the support.

  7. An Aldol-based Build/Couple/Pair Strategy for the Synthesis of Medium- and Large-Sized Rings: Discovery of Macrocyclic Histone Deacetylase Inhibitors

    PubMed Central

    Marcaurelle, Lisa A.; Comer, Eamon; Dandapani, Sivaraman; Duvall, Jeremy R.; Gerard, Baudouin; Kesavan, Sarathy; Lee, Maurice D.; Liu, Haibo; Lowe, Jason T.; Marie, Jean-Charles; Mulrooney, Carol A.; Pandya, Bhaumik A.; Rowley, Ann; Ryba, Troy D.; Suh, Byung-Chul; Wei, Jingqiang; Young, Damian W.; Akella, Lakshmi B.; Ross, Nathan T.; Zhang, Yan-Ling; Fass, Daniel M.; Reis, Surya A.; Zhao, Wen-Ning; Haggarty, Stephen J.; Palmer, Michelle; Foley, Michael A.

    2010-01-01

    An aldol-based ‘build/couple/pair’ (B/C/P) strategy was applied to generate a collection of stereochemically and skeletally diverse small molecules. In the build phase, a series of asymmetric syn- and anti- aldol reactions were performed to produce four stereoisomers of a Boc protected ?-amino acid. In addition both stereoisomers of O-PMB-protected alaninol were generated to provide a chiral amine coupling partner. In the couple step, eight stereoisomeric amides were synthesized by coupling the chiral acid and amine building blocks. The amides were subsequently reduced to generate the corresponding secondary amines. In the pair phase, three different reactions were employed to enable intramolecular ring-forming processes, namely: nucleophilic aromatic substitution (SNAr), Huisgen [3+2] cycloaddition and ring-closing metathesis (RCM). Despite some stereochemical dependencies, the ring-forming reactions were optimized to proceed with good to excellent yields providing a variety of skeletons ranging in size from 8- to 14-membered rings. Scaffolds resulting from the RCM pairing reaction were diversified on solid-phase to yield a 14,400-membered library of macrolactams. Screening of this library led to the discovery of a novel class of histone deacetylase inhibitors, which display mixed enzyme inhibition and led to increased levels of acetylation in a primary mouse neuron culture. The development of stereo-structure/activity relationships (SSAR) was made possible by screening all 16 stereoisomers of the macrolactams produced through the aldol-based B/C/P strategy. PMID:21067169

  8. Synthesis of aza-fused isoquinolines through domino cross-aldol condensation and palladium-catalyzed intramolecular direct arylation.

    PubMed

    Dhiman, Shiv; Pericherla, Kasiviswanadharaju; Nandwana, Nitesh K; Kumar, Dalip; Kumar, Anil

    2014-08-15

    A straightforward method has been developed for the synthesis of aroyl-substituted imidazo-/benzimidazo-fused isoquinolines. The cascade reaction proceeds via a cross-aldol condensation of 2-(1H-imidazol-1-yl/benzimidazolyl-1-yl)-1-arylethanones and 2-bromobenzaldehyde followed by palladium-catalyzed intramolecular C-H functionalization. This approach offers a simple and efficient alternative one-pot protocol for the assembly of imidazo/benzimidazo[2,1-a]isoquinolines in moderate to good yields. PMID:25046002

  9. Aldol condensation versus conjugate addition: intramolecular cyclization using a combination of Lewis acid and 1,2-diol.

    PubMed

    Yamada, S; Suemune, H

    2000-08-01

    The reactivity of 3-substituted 4-methyl-4-(3-oxobutyl)-2-cyclohexen-1-ones (1) in the presence of a combination of a Lewis acid and a 1,2-diol was studied. The results suggest several factors that influence 6-membered ring formation, including two types of intramolecular aldol reaction and intramolecular 1,4-addition, due to the C3-substituent, Lewis acid, and the presence of diol. In this study, novel methodology to prepare two types of decalin skeleton could be developed. PMID:10959582

  10. Diastereoselective Synthesis of Biheterocyclic Tetrahydrothiophene Derivatives via Base-Catalyzed Cascade Michael-Aldol [3 + 2] Annulation of 1,4-Dithiane-2,5-diol with Maleimides.

    PubMed

    Zhong, Yuan; Ma, Shixiong; Li, Bai; Jiang, Xianxing; Wang, Rui

    2015-07-01

    A highly diastereoselective intermolecular [3 + 2] annulation of 1,4-dithiane-2,5-diol to maleimides has been developed by using DABCO as a catalyst, which provides a series of highly functionalized biheterocyclic tetrahydrothiophene derivatives containing tetrahydrothiophene and pyrolidine backbones in excellent yields and diastereoselectivities (up to 98% yield and >20:1 d.r.). The cascade Michael-aldol reaction is capable of tolerating organic solvents as well as water. PMID:26035462

  11. A domino N-amidoacylation/aldol-type condensation approach to the synthesis of the topo-I inhibitor Rosettacin and derivatives.

    PubMed

    Pin, Frédéric; Comesse, Sébastien; Sanselme, Morgane; Daïch, Adam

    2008-03-01

    The pot, atom, and step-economic synthesis of Rosettacin topo-I poison and its derivatives has been achieved using a novel domino N-amidoacylation/aldol-type condensation, followed by decarboxylation of the ester function. The key domino procedure simply involves mixing HOBt ester as new reagent with lactam and NaH together in THF or THF/ DMF. The reaction seems to be general and led to suitable N-heterocyclic products in moderate to good yields. PMID:18254644

  12. Strong Lewis acids of air-stable metallocene bis(perfluorooctanesulfonate)s as high-efficiency catalysts for carbonyl-group transformation reactions.

    PubMed

    Qiu, Renhua; Xu, Xinhua; Peng, Lifeng; Zhao, Yalei; Li, Ningbo; Yin, Shuangfeng

    2012-05-14

    Strong Lewis acids of air-stable metallocene bis(perfluorooctanesulfonate)s [M(Cp)(2)][OSO(2)C(8)F(17)](2)?nH(2)O?THF (M = Zr (2?a?3?H(2)O?THF), M = Ti (2?b?2?H(2)O?THF)) were synthesized by the reaction of [M(Cp)(2)]Cl(2) (M = Zr (1?a), M = Ti (1?b)) with nBuLi and C(8)F(17)SO(3)H (2?equiv) or with C(8)F(17)SO(3)Ag (2?equiv). The hydrate numbers (n) of these complexes were variable, changing from 0 to 4 depending on conditions. In contrast to well-known metallocene triflates, these complexes suffered no change in open air for a year. thermogravimetry-differential scanning calorimetry (TG-DSC) analysis showed that 2?a and 2?b were thermally stable at 300 and 180?°C, respectively. These complexes exhibited unusually high solubility in polar organic solvents. Conductivity measurement showed that the complexes (2?a and 2?b) were ionic dissociation in CH(3)CN solution. X-ray analysis result confirmed 2?a?3?H(2)O?THF was a cationic organometallic Lewis acid. UV/Vis spectra showed a significant red shift due to the strong complex formation between 10-methylacridone and 2?a. Fluorescence spectra showed that the Lewis acidity of 2?a fell between those of Sc(3+) (?(em)=474?nm) and Fe(3+) (?(em)=478?nm). ESR spectra showed the Lewis acidity of 2?a (0.91?eV) was at the same level as that of Sc(3+) (1.00?eV) and Y(3+) (0.85?eV), while the Lewis acidity of 2?b (1.06?eV) was larger than that of Sc(3+) (1.00?eV) and Y(3+) (0.85?eV). They showed high catalytic ability in carbonyl-compound transformation reactions, such as the Mannich reaction, the Mukaiyama aldol reaction, allylation of aldehydes, the Friedel-Crafts acylation of alkyl aromatic ethers, and cyclotrimerization of ketones. Moreover, the complexes possessed good reusability. On account of their excellent catalytic efficiency, stability, and reusability, the complexes will find broad catalytic applications in organic synthesis. PMID:22504964

  13. Peculiar behavior of MWW materials in aldol condensation of furfural and acetone.

    PubMed

    Kikhtyanin, Oleg; Chlubná, Pavla; Jindrová, Tereza; Kubi?ka, David

    2014-07-21

    MWW family of different structural types (MCM-22, MCM-49, MCM-56 and MCM-36) was used as catalysts for aldol condensation of furfural and acetone studied in a batch reactor at 100 °C, autogenous pressure and a reaction time of 0-4 h. To establish a relation between physico-chemical and catalytic properties of microporous materials, the samples were characterized by XRD, SEM, N2 adsorption, FTIR and TGA. It was found that the acidic solids possessed appreciable activity in the reaction and resulted in the formation of products of aldehyde-ketone interaction. Surprisingly, MCM-22 and MCM-49, i.e. three-dimensional materials containing internal supercages, exhibited higher activity than two MCM-36 catalysts with two-dimensional character having larger accessible external surface area due to expansion of the interlayer space by swelling and pillaring treatments. Moreover, all MWW family catalysts gave higher conversion than the large-pore zeolite BEA. Nevertheless, furfural conversion decreased rapidly for all the studied materials due to coke formation. Unexpectedly, the deactivation was found to be more severe for MCM-36 catalysts than for MCM-22 and MCM-49, which was attributed to the reaction taking place also in supercages that are protected by 10-ring channels from severe coking. In contrast the cups located on the external surface were coked rapidly. PMID:24842149

  14. The Intramolecular Aldol Condensation Route to Fused Bi- and Tricyclic beta-Lactams(1)(,)(2).

    PubMed

    Alcaide, Benito; Polanco, Concepción; Sáez, Elena; Sierra, Miguel A.

    1996-10-01

    Staüdinger cycloaddition of activated acid chlorides to 1,3-ketoaldimines, prepared in quantitative yields from 1,3-ketoaldehydes and amino esters, gave in excellent yields cis-2-azetidinones, 6-8, having the adequate functionality to obtain fused bi- and tricyclic beta-lactams. Reaction of compounds 6 with LHMDS at low temperature gave a single diastereomer of fused bicyclic compounds with a carbapenam or carbacefam skeleton. Treatment of diastereomeric cis-2-azetidinones, 7/8, in analogous conditions resulted either in the exclusive cyclization of one of the two diastereomers to form tricyclic [4.n.m] (n = 5, 6; m = 5, 6) compounds, or in the cyclization of both diastereomers to form tricyclic [4.n.7] (n = 5, 6) 2-azetidinones. In all cases the cyclization step was totally stereoselective. Alternatively, trans-carbapenams and one example of a tricyclic system having a trans-2-azetidinone ring have been obtained by using longer reaction times and higher temperatures. Epimerization at C3 of the 2-azetidinone nucleus occurs in these reaction conditions to obtain a single diastereomer of the final products. This approach to fused policyclic 2-azetidinones is one of the scarce syntheses of this kind of compound making use of the aldol condensation. PMID:11667615

  15. Mineral catalysis of a potentially prebiotic aldol condensation

    NASA Technical Reports Server (NTRS)

    De Graaf, R. M.; Visscher, J.; Xu, Y.; Arrhenius, G.; Schwartz, A. W.

    1998-01-01

    Minerals may have played a significant role in chemical evolution. In the course of investigating the chemistry of phosphonoacetaldehyde (PAL), an analogue of glycolaldehyde phosphate, we have observed a striking case of catalysis by the layered hydroxide mineral hydrotalcite ([Mg2Al(OH)6][Cl.nH2O]). In neutral or moderately basic aqueous solutions, PAL is unreactive even at a concentration of 0.1 M. In the presence of a large excess of NaOH (2 M), the compound undergoes aldol condensation to produce a dimer containing a C3-C4 double-bond. In dilute neutral solutions and in the presence of the mineral, however, condensation takes place rapidly, to produce a dimer which is almost exclusively the C2-C3 unsaturated product.

  16. Diastereo- and Enantioselective Reductive Aldol Addition of Vinyl Ketones via Catalytic Hydrogenation

    PubMed Central

    Han, Soo Bong; Hassan, Abbas; Krische, Michael J.

    2011-01-01

    An overview of studies on hydrogenative reductive aldol addition is presented. By simply hydrogenating enones in the presence of aldehydes at ambient temperature and pressure, aldol adducts are generated under neutral conditions in the absence of any stoichiometric byproducts. Using cationic rhodium complexes modified by tri(2-furyl)phosphine, highly syn-diastereoselective reductive aldol additions of vinyl ketones are achieved. Finally, using novel monodentate TADDOL-like phosphonite ligands, the first highly diastereo- and enantioselective reductive aldol couplings of vinyl ketones were devised. These studies, along with other works from our laboratory, demonstrate that organometallics arising transiently in the course of catalytic hydrogenation offer byproduct-free alternatives to preformed organometallic reagents employed in classical carbonyl addition processes. PMID:21866204

  17. Organolanthanide-induced C-C bond formation. Preparation and properties of monomeric lanthanide aldolates and enolates

    SciTech Connect

    Heeres, H.J.; Maters, M.; Teuben, J.H.

    1992-01-01

    The reactivity of early-lanthanide carbyls Cp* {sub 2}LnCH(SiMe{sub 3}){sub 2} (1, Ln = La; 2, Ln = Ce) toward ketones has been studied. No reaction was observed with the bulky di-tert-butyl ketone. The corresponding lanthanum hydride [Cp* {sub 2}LaH]{sub 2} (3) is more reactive and afforded the addition product Cp*{sub 2}LaOCH(t-Bu){sub 2}{sup center-dot}O=C(t-Bu){sub 2} (4). Hydrogen transfer and formation of lanthanide aldolates Cp* {sub 2}LnOCMe{sub 2}C(=O)Me (5, Ln = Ce; 6, Ln =La) together with the protonated carbyl CH{sub 2}(SiMe{sub 3}){sub 2} were observed when 1 or 2 was treated with acetone. The molecular structure of the cerium analogue 5 was determined by X-ray diffraction and was found to be a monomeric bent metallocene compound with a {eta}{sup 2}-coordinated aldol fragment. Addition of 3-pentanone to the carbyls 1 and 2 did not result in C-C coupling but provided enolate-ketone adducts Cp*{sub 2}LnOC(Et)=C(H)MeO=CEt{sub 2} (7, Ln = La; 8, Ln = Ce). Reactions of the carbyls 1 and 2 with 4-methyl-5-hydroxy-5ethyl-3-heptanone yielded the enolate-ketone adducts as well and suggest that the differences in reactivity between acetone and 3-pentanone are thermodynamic and not kinetic in origin. 32 refs., 2 figs., 5 tabs.

  18. Sc3+-catalyzed aldol-type additions of N-benzoylcyclopropanecarboxamides via iodide-mediated ring-opening: stereoselective synthesis of gamma-lactams.

    PubMed

    Wiedemann, Sean H; Noda, Hidetoshi; Harada, Shinji; Matsunaga, Shigeki; Shibasaki, Masakatsu

    2008-04-17

    A new catalytic aldol-type addition of cyclopropanecarboximides to aldehydes via iodide-mediated ring-opening is presented. The reaction was found to be catalyzed at 0 degrees C using either a Sc(OTf)3/NaI system or ScI3. Stereoselective formation of alpha,alpha-disubstituted enolates occurred in situ. gamma-Lactams bearing alpha-carbonyl quaternary stereocenters were obtained in 97-57% yield and dr = 90:10-80:20 after ring closure. PMID:18345682

  19. Enantioselective synthesis of (–)-chloramphenicol via silver-catalysed asymmetric isocyanoacetate aldol reaction† †Electronic supplementary information (ESI) available: Experimental procedures, characterisation data, copies of 1H and 13C NMR spectra, and HPLC traces. See DOI: 10.1039/c5ob02141c Click here for additional data file.

    PubMed Central

    Franchino, Allegra; Jakubec, Pavol

    2015-01-01

    The highly enantio- and diastereoselective aldol reaction of isocyanoacetates catalysed by Ag2O and cinchona-derived amino phosphines applied to the synthesis of (–)- and (+)-chloramphenicol is described. The concise synthesis showcases the utility of this catalytic asymmetric methodology for the preparation of bioactive compounds possessing α-amino-β-hydroxy motifs. PMID:26510469

  20. The effect of the distance between acidic site and basic site immobilized on mesoporous solid on the activity in catalyzing aldol condensation

    SciTech Connect

    Yu Xiaofang; Yu Xiaobo; Wu Shujie; Liu Bo; Liu Heng; Guan Jingqi; Kan Qiubin

    2011-02-15

    Acid-base bifunctional heterogeneous catalysts containing carboxylic and amine groups, which were immobilized at defined distance from one another on the mesoporous solid were synthesized by immobilizing lysine onto carboxyl-SBA-15. The obtained materials were characterized by X-ray diffraction (XRD), N{sub 2} adsorption, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron micrographs (SEM), transmission electron micrographs (TEM), elemental analysis, and back titration. Proximal-C-A-SBA-15 with a proximal acid-base distance was more active than maximum-C-A-SBA-15 with a maximum acid-base distance in aldol condensation reaction between acetone and various aldehydes. It appears that the distance between acidic site and basic site immobilized on mesoporous solid should be an essential factor for catalysis optimization. -- Graphical abstract: Proximal-C-A-SBA-15 with a proximal acid-base distance and maximum-C-A-SBA-15 with a maximum acid-base distance were synthesized by immobilizing lysine onto carboxyl-SBA-15. Display Omitted Research highlights: {yields} Proximal-C-A-SBA-15 with a proximal acid-base distance. {yields} Maximum-C-A-SBA-15 with a maximum acid-base distance. {yields} Compared to maximum-C-A-SBA-15, proximal-C-A-SBA-15 was more active toward aldol condensation reaction between acetone and various aldehydes.

  1. D-Aminoacylase-initiated cascade Aldol condensation/Robinson annulation for synthesis of substituted cyclohex-2-enones from simple aldehydes and acetone.

    PubMed

    Xiang, Ziwei; Liang, Yiru; Chen, Xiang; Wu, Qi; Lin, Xianfu

    2014-08-01

    As an important building block, developing efficient and green synthesis strategy of cyclohex-2-enones is of great importance. In this present work, a general approach to the mild synthesis of substituted cyclohex-2-enones derivatives starting fro m simple aldehydes and acetone have been achieved via D-aminoacylase-initiated Aldol condensation/Robinson annulation cascade reaction using imidazole as an additive in organic media. The influences of reaction conditions including solvents, enzyme concentration, additives type, molar ratio of enzyme to additive, and substrate scopes were systematically investigated. Furthermore, some experiments were designed to explore the catalytic roles of D-aminoacylase and imidazole in the multistep cascade process, and one possible mechanism was proposed. PMID:24770961

  2. Mathematical model for aldol addition catalyzed by two D-fructose-6-phosphate aldolases variants overexpressed in E. coli.

    PubMed

    Sudar, Martina; Findrik, Zvjezdana; Vasi?-Ra?ki, Dur?a; Clapés, Pere; Lozano, Carles

    2013-09-10

    Two D-fructose-6-phosphate aldolase variants namely, single variant FSA A129S and double variant FSA A129S/A165G, were used as catalysts in the aldol addition of dihydroxyacetone (DHA) to N-Cbz-3-aminopropanal. Mathematical model for reaction catalyzed by both enzymes, consisting of kinetic and mass balance equations, was developed. Kinetic parameters were estimated from the experimental data gathered by using the initial reaction rate method. The model was validated in the batch and continuously operated ultrafiltration membrane reactor (UFMR). The same type of kinetic model could be applied for both enzymes. The operational stability of the aldolases was assessed by measuring enzyme activity during the experiments. FSA A129S/A165G had better operational stability in the batch reactor (half-life time 26.7 h) in comparison to FSA A129S (half-life time 5.78 h). Both variants were unstable in the continuously operated UFMR in which half-life times were 1.99 and 3.64 h for FSA A129S and FSA A129S/A165G, respectively. PMID:23876482

  3. The effect of the distance between acidic site and basic site immobilized on mesoporous solid on the activity in catalyzing aldol condensation

    NASA Astrophysics Data System (ADS)

    Yu, Xiaofang; Yu, Xiaobo; Wu, Shujie; Liu, Bo; Liu, Heng; Guan, Jingqi; Kan, Qiubin

    2011-02-01

    Acid-base bifunctional heterogeneous catalysts containing carboxylic and amine groups, which were immobilized at defined distance from one another on the mesoporous solid were synthesized by immobilizing lysine onto carboxyl-SBA-15. The obtained materials were characterized by X-ray diffraction (XRD), N 2 adsorption, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron micrographs (SEM), transmission electron micrographs (TEM), elemental analysis, and back titration. Proximal-C-A-SBA-15 with a proximal acid-base distance was more active than maximum-C-A-SBA-15 with a maximum acid-base distance in aldol condensation reaction between acetone and various aldehydes. It appears that the distance between acidic site and basic site immobilized on mesoporous solid should be an essential factor for catalysis optimization.

  4. Synthesis of 2,6-disubstituted dihydropyrans via an efficient BiBr3-initiated three component, one-pot cascade

    PubMed Central

    Lian, Yajing; Speight, Lee C.; Stevenson, Heather E.; Sprachman, Melissa M.; Katkish, Lauren A.; Mattern, M. Christa

    2009-01-01

    The rapid synthesis of cis-2,6-disubstituted dihydropyrans is achieved in a three-component, one-pot cascade reaction. BiBr3-ediated addition of ketene silyl acetals or silyl enol ethers to ?,?-unsaturated cis-4-trimethylsilyl-3-butenal provides a Mukaiyama aldol adduct containing a vinylsilane moiety tethered to a silyl ether. Addition of a second aldehyde initiates a domino sequence involving intermolecular addition followed by an intramolecular silyl-modified Sakurai (ISMS) reaction. Isolated yields of this one-pot reaction vary from 44 to 80% and all compounds were isolated as the cis-diastereomers (10 examples). PMID:20161364

  5. Organic Reactions in Aqueous Media (by Chao-Jun Li and Tak-Hang Chan)

    NASA Astrophysics Data System (ADS)

    Rosan, Reviewed Alan M.

    2000-06-01

    This concise book joins the series of Wiley Interscience special topic publications. In seven chapters it selectively reviews the burgeoning literature on organic reactions conducted in water or in aqueous media as a reaction cosolvent, nicely complementing another recent book on the subject by Grieco. Following a short introduction there are six chapters that vary in length from 10 to 50 pages; they cover pericyclic reactions, nucleophilic additions and substitutions, metal-mediated reactions, transition metal-catalyzed reactions, oxidation and reduction reactions, and industrial applications. These chapters, each of which is prefaced with a short provocative quotation, also vary in depth, containing from 11 to more than 180 references. The literature is complete through 1996 and commendably includes citations of original papers by Barbier, Faraday, Frankland, Grignard, Kolbe, Lapworth, and Reformatsky as well as references to selected U.S. and foreign patents and the Russian literature. There is a subject index but no author index. This book is timely and effective. From the title, one might expect a broad discussion of the unique properties of water and water-soluble components (salts, surfactants, etc.) that would be thought to bear on organic reactivity. The first chapter opens by noting that water is the most abundant volatile material in comets and briefly describes those properties that suggest its utility as a solvent or cosolvent, summarizing the potential technical, economic, and environmental advantages. Also described are the remarkable changes in density, conductance, heat capacity, dielectric constant, and ionization constant that accompany the transition to the critical point, but the emphasis here is on the effect of water under non-critical conditions. Discussion of the structure of liquid water and the role of hydrogen bonding in mediating molecular recognition events is abbreviated. In fact, the term "hydrogen bond" is surprisingly absent from the index. The text does not explicitly include a discussion of what has come to be broadly termed biphasic reaction conditions. Understandably, enzymatic reactions are beyond the scope of the presentation. This book has a decidedly applied character with an understated environmental theme, and the authors succinctly present the extraordinary effects of water on the kinetics, efficiency, and stereoselectivity of a large number of diverse reactions. In addition to their emphasis on the historically significant aqueous Diels-Alder reaction, discovered in 1980, and the literature regarding reactions of various nucleophilic organometals, the authors are to be commended for gathering together a wide and diverse body of information: it is clear that many of the examples shown are gems buried among larger bodies of work. Thus the book does an excellent job of culling and surveying a vast amount of data. There is, however, less emphasis on organizing the mechanistic bases underlying these often dramatic effects. For example, the apparent lack of generality of the effect of water on rate and selectivity in pericyclic reactions calls for some theoretical foundation. The singularly effective use of aqueous TlOH in the Suzuki reaction is cited without comment. On the other hand, the authors' concept of a mechanistic triad that incorporates to various degrees anion, radical, or covalent character in the carbon-carbon bond-forming step between various organometals and carbonyl substrates is appealing and suggests the need for future sophisticated experimental design. The most interesting sections are those dealing with synthesis and industrial applications. Unfortunately the latter is also the shortest chapter. The synthetic examples are timely and well chosen and include water-promoted Heck, Stille, Suzuki, and aldol reactions. There is an extensive, highly informative listing and survey of the use of water-soluble phosphines (both achiral and chiral) and an excellent discussion of the diastereoselectivity that often accompanies carbonyl attack by indium, tin, and zinc organometals (Barbier-Grignard reaction). The liberal use, on nearly every page, of clear, detailed drawings enhances the text, and substantive errors are few. Inexplicably, water is described as serving as a presumptive weak Lewis acid (pages 54-55) in the aqueous Mukaiyama reaction. Occasional slips of grammar, spelling, and syntax, including confusion over the difference between media and medium, are relatively minor. Some expressions, such as "olefinated", are unfortunate and there are several mysterious changes in font. This is not a textbook and no problems are offered. Many technical advances, some occurring since this book was published, have impacted the economic and environmental advantages of water. However, these more recent findings, involving the use of triphase aqueous-fluorous-organic systems, the discovery of living homogeneous ROMP catalysis in water, the utilization of supercritical water oxidation for toxic cleanup, and the utility of biphasic supercritical carbon dioxide-water emulsions, can be appreciated within the broad scope of reactivity described here. With the emerging wide interest, technical feasibility, and rapid innovative advances and an increasingly vast literature in this area, this book is most useful as a selected compendium rather than a definitive treatise. It is certainly suitable as a reference in a special topics or an advanced course. Rich with well-explicated examples and reactions, it is an invitingly readable and valuable survey of this fascinating area.

  6. Copper-catalyzed cascade reactions of ?,?-unsaturated esters with keto esters

    PubMed Central

    Wang, Chongnian; Li, Zengchang

    2015-01-01

    Summary A copper-catalyzed cascade reaction of ?,?-unsaturated esters with keto esters is reported. It features a copper-catalyzed reductive aldolization followed by a lactonization. This method provides a facile approach to prepare ?-carboxymethyl-?-lactones and ?-carboxymethyl-?-lactones under mild reaction conditions. PMID:25815072

  7. Enantioselective Robinson-type annulation reaction catalyzed by chiral phosphoric acids.

    PubMed

    Akiyama, Takahiko; Katoh, Takuya; Mori, Keiji

    2009-01-01

    Let's resolve our differences: Implementation of an enantioselective Michael addition followed by an intramolecular aldol reaction catalyzed by two phosphoric acids has enabled the synthesis of cyclohexenone derivatives with excellent enantioselectivities. Prominent kinetic resolution was observed in the latter reaction. Ar = aromatic group, X = H, halogen, Y = H, Me, halogen. PMID:19405071

  8. An Exercise on Structure Elucidation Based on a Tricky Aldol Reaction

    ERIC Educational Resources Information Center

    Sierra, Manuel Gonzalez; Pellegrinet, Silvina C.; Colombo, Maria I.; Ruveda, Edmundo A.

    2008-01-01

    An exercise on structure elucidation for advanced undergraduate students is described. To determine the structure of an unknown product, students are required to use spectra together with an organic chemistry mechanism. This exercise exemplifies the procedure commonly used in research, thus helping students develop problem-solving skills. In…

  9. Catalytic insertion of aldehydes into dihalonitroacetophenones via sequential bond scission-aldol reaction-acyl transfer.

    PubMed

    Ding, Ransheng; Wolf, Christian

    2016-02-28

    A catalytic process that provides dihalogenated nitro alcohols in up to 99% yield and with 100% atom economy is described. In situ cleavage of dihalonitroacetophenones affords nitronates that undergo Lewis acid catalyzed addition to aldehydes. Final benzoylation renders the sequence irreversible and regenerates the bond scission and acyl transfer agent. PMID:26846436

  10. ALDOL- AND MANNICH-TYPE REACTIONS VIA IN SITU OLEFIN MIGRATION IN IONIC LIQUID. (R828129)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  11. Concise total synthesis of albaflavenone utilizing sequential intramolecular aldol condensation: determination of absolute configuration.

    PubMed

    Kobayashi, Toyoharu; Kon, Yutaro; Abe, Hideki; Ito, Hisanaka

    2014-12-19

    The first total synthesis of albaflavenone, a novel antibiotic sesquiterpene, has been accomplished via the concise construction of its zizaene skeleton utilizing sequential intramolecular aldol condensation followed by chemo- and diastereoselective reduction of the conjugated carbon-carbon double bond. This synthetic work was completed in nine steps from 2-cyclopenten-1-one as a starting material without the use of protecting groups and with high stereocontrol. In addition, the absolute configuration of naturally occurring albaflavenone was determined to be 1R,2S and 8S. PMID:25469861

  12. Asymmetric synthesis of anti-aldol segments via a nonaldol route: synthetic applications to statines and (-)-tetrahydrolipstatin.

    PubMed

    Ghosh, Arun K; Shurrush, Khriesto; Kulkarni, Sarang

    2009-06-19

    An asymmetric synthesis of anti-aldol segments via a nonaldol route is described. The strategy involves a highly diastereoselective synthesis of functionalized tetrahydrofuran derivatives from optically active 4-phenylbutyrolactone. Treatment of the tetrahydrofuran derivatives with a Lewis acid and acetic anhydride provided the corresponding ring-opened styrene derivatives. Oxidative cleavage of the styrene derivatives provided access to the anti-aldol segments. The utility of this methodology was demonstrated by the synthesis of statine derivatives and pancreatic lipase inhibitor, (-)-tetrahydrolipstatin. PMID:19438217

  13. Stereocontrolled synthesis of syn-β-Hydroxy-α-amino acids by direct aldolization of pseudoephenamine glycinamide.

    PubMed

    Seiple, Ian B; Mercer, Jaron A M; Sussman, Robin J; Zhang, Ziyang; Myers, Andrew G

    2014-04-25

    β-Hydroxy-α-amino acids figure prominently as chiral building blocks in chemical synthesis and serve as precursors to numerous important medicines. Reported herein is a method for the synthesis of β-hydroxy-α-amino acid derivatives by aldolization of pseudoephenamine glycinamide, which can be prepared from pseudoephenamine in a one-flask protocol. Enolization of (R,R)- or (S,S)-pseudoephenamine glycinamide with lithium hexamethyldisilazide in the presence of LiCl followed by addition of an aldehyde or ketone substrate affords aldol addition products that are stereochemically homologous with L- or D-threonine, respectively. These products, which are typically solids, can be obtained in stereoisomerically pure form in yields of 55-98 %, and are readily transformed into β-hydroxy-α-amino acids by mild hydrolysis or into 2-amino-1,3-diols by reduction with sodium borohydride. This new chemistry greatly facilitates the construction of novel antibiotics of several different classes. PMID:24692320

  14. A modular approach to the total synthesis of tunicamycins.

    PubMed

    Li, Jiakun; Yu, Biao

    2015-05-26

    The tunicamycins constitute a delicate mimic of the bisubstrate intermediates of N-acetyl-D-hexosamine-1-phosphate translocases and thus inhibit bacterial cell-wall synthesis and the N?glycosylation of eukaryotic proteins. An efficient approach to the synthesis of this unique type of nucleoside antibiotics is now reported and features the assembly of five modules in a highly stereoselective and robust manner. A Mukaiyama aldol reaction, intramolecular acetal formation, gold(I)-catalyzed O and N?glycosylation, and final N?acylation were used as the key steps. PMID:25873339

  15. Total Synthesis of (+)-Azaspiracid-1. An Exhibition of the Intricacies of Complex Molecule Synthesis

    PubMed Central

    Evans, David A.; Kværnø, Lisbet; Dunn, Travis B.; Beauchemin, André; Raymer, Brian; Mulder, Jason A.; Olhava, Edward J.; Juhl, Martin; Kagechika, Katsuji; Favor, David A.

    2012-01-01

    The synthesis of the marine neurotoxin azaspiracid-1 has been accomplished. The individual fragments were synthesized by catalytic enantioselective processes: A hetero-Diels-Alder reaction to afford the E- and HI-ring fragments, a carbonyl-ene reaction to furnish the CD-ring fragment, and a Mukaiyama aldol reaction to deliver the FG-ring fragment. The subsequent fragment couplings were accomplished by aldol and sulfone anion methodologies. All ketalization events to form the non-acyclic target were accomplished under equilibrating conditions utilizing the imbedded configurations of the molecule to adopt one favored conformation. A final fragment coupling of the anomeric EFGHI-sulfone anion to the ABCD-aldehyde completed the convergent synthesis of (+)-azaspiracid-1. PMID:19006391

  16. Development of asymmetric reactions catalyzed by chiral organotin-alkoxide reagents.

    PubMed

    Yanagisawa, Akira; Yoshida, Kazuhiro

    2013-02-01

    Asymmetric catalysis under almost-neutral reaction conditions is key for the efficient synthesis of optically active polar molecules. We have developed catalytic enantioselective reactions of acyclic or cyclic alkenyl esters by using an (S)-BINOL-derived chiral tin-dibromide reagent that possesses a bulky aryl group at the 3 or 3' position as the chiral pre-catalyst in the presence of a sodium alkoxide and an alcohol, in which a chiral tin alkoxide bromide is generated in situ and recycled with the assistance of an alcohol. In this Personal Account, we describe three types of asymmetric transformation that proceed through a chiral tin enolate: 1) The asymmetric aldol reaction of alkenyl esters or unsaturated lactones with aldehydes or isatins; 2) the asymmetric three-component Mannich-type reaction of alkenyl esters and related cycloaddition reactions; and 3) the asymmetric N-nitroso aldol reaction of unsaturated lactones with nitrosoarenes. PMID:23424074

  17. Radical addition-initiated domino reactions of conjugated oxime ethers.

    PubMed

    Ueda, Masafumi

    2014-01-01

    The application of conjugated oxime ethers to the synthesis of complex chemical scaffolds using domino radical reactions has been described in detail. The triethylborane-mediated hydroxysulfenylation reaction allows for the regioselective construction of a carbon-sulfur bond and a carbon-oxygen bond in a single operation for the formation of ?-hydroxy sulfides. This reaction proceeds via a radical pathway involving regioselective thiyl addition and the subsequent trapping of the resulting ?-imino radical with O?, where the imino group enhances the stability of the intermediate radical. Hydroxyalkylation reactions that occur via a carbon radical addition reaction followed by the hydroxylation of the resulting N-borylenamine with O? have also been developed. We investigated sequential radical addition aldol-type reactions in detail to explore the novel domino reactions that occur via the generation of N-borylenamine. The radical reaction of a conjugated oxime ether with triethylborane in the presence of an aldehyde affords ?-butyrolactone via sequential processes including ethyl radical addition, the generation of N-borylenamine, an aldol-type reaction with an aldehyde, and a lactonization reaction. A novel domino reaction has also been developed involving the [3,3]-sigmatropic rearrangement of N-boryl-N-phenoxyenamine. The triethylborane-mediated domino reactions of O-phenyl-conjugated oxime ethers afforded the corresponding benzofuro[2,3-b]pyrrol-2-ones via a radical addition/[3,3]-sigmatropic rearrangement/cyclization/lactamization cascade. PMID:25177013

  18. A Simple Organic Microscale Experiment Illustrating the Equilibrium Aspect of the Aldol Condensation

    NASA Astrophysics Data System (ADS)

    Harrison, Ernest A., Jr.

    1998-05-01

    A simple microscale experiment has been developed that illustrates the equilibrium aspect of the aldol condensation by using two versions of the standard preparation of tetraphenylcyclopentadienone (5) from benzil (1) and 1,3-diphenyl-2-propanone (2). In version (high base concentration) a mixture of 5 and the diastereomeric 4-hydroxy-2,3,4,5-tetraphenyl-2-cyclopenten-1-ones 3 and 4 are produced, while in the other (low base concentration) a mixture of 1, 2, 3, and 4 results. The experiment is typically carried out in conjunction with the previously reported preparation/dehydration of 3, thus the students provide themselves with authentic samples of 3 and 5. Using these, plus authentic samples of 1 and 2 which are made available, students are able to identify all of the components in the equilibrium mixtures, except 4, by TLC analysis. In the case of 4, students are expected to propose a reasonable structure for this compound based on the observed chemistry and the spectroscopic evidence which is provided (i.e., NMR, IR and mass spectra). The experiment lends itself nicely to either the traditional or problem-solving approach, and it also opens up opportunities for collaborative learning.

  19. Quantum mechanical investigations on the role of neutral and negatively charged enamine intermediates in organocatalyzed reactions

    NASA Astrophysics Data System (ADS)

    Hubin, Pierre O.; Jacquemin, Denis; Leherte, Laurence; Vercauteren, Daniel P.

    2014-04-01

    The proline-catalyzed aldol reaction is the seminal example of asymmetric organocatalysis. Previous theoretical and experimental studies aimed at identifying its mechanism in order to rationalize the outcome of this reaction. Here, we focus on key steps with modern first principle methods, i.e. the M06-2X hybrid exchange-correlation functional combined to the solvation density model to account for environmental effects. In particular, different pathways leading to the formation of neutral and negatively charged enamine intermediates are investigated, and their reactivity towards two electrophiles, i.e. an aldehyde and a benzhydrylium cation, are compared. Regarding the self-aldol reaction, our calculations confirm that the neutral enamine intermediate is more reactive than the negatively charged one. For the reaction with benzhydrylium cations however, the negatively charged enamine intermediate is more reactive.

  20. A four-component reaction involving in situ generated organometallic reagents: straightforward access to ?-amino esters.

    PubMed

    Le Gall, Erwan; Léonel, Eric

    2013-04-22

    Four in one: A straightforward synthesis of ?(2,3)-amino esters is described through a new zinc-mediated, cobalt-catalyzed four-component reaction between organic bromides, alkyl acrylates, amines, and aldehydes (see scheme). Synthesis involves a Mannich-related conjugate addition/aza-aldol domino sequence, allowing the formation of three single bonds in one step. A reaction mechanism, emphasizing the crucial role of zinc salts, is described. PMID:23463614

  1. Acid-catalyzed reactions of hexanal on sulfuric acid particles: Identification of reaction products

    NASA Astrophysics Data System (ADS)

    Garland, Rebecca M.; Elrod, Matthew J.; Kincaid, Kristi; Beaver, Melinda R.; Jimenez, Jose L.; Tolbert, Margaret A.

    While it is well established that organics compose a large fraction of the atmospheric aerosol mass, the mechanisms through which organics are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds with carbonyl groups have recently been suggested as important pathways for transfer of volatile organics into acidic aerosols. In the present study, we use the aerodyne aerosol mass spectrometer (AMS) to probe the uptake of gas-phase hexanal into ammonium sulfate and sulfuric acid aerosols. While both deliquesced and dry non-acidic ammonium sulfate aerosols showed no organic uptake, the acidic aerosols took up substantial amounts of organic material when exposed to hexanal vapor. Further, we used 1H-NMR, Fourier transform infrared (FTIR) spectroscopy and GC-MS to identify the products of the acid-catalyzed reaction of hexanal in acidic aerosols. Both aldol condensation and hemiacetal products were identified, with the dominant reaction products dependent upon the initial acid concentration of the aerosol. The aldol condensation product was formed only at initial concentrations of 75-96 wt% sulfuric acid in water. The hemiacetal was produced at all sulfuric acid concentrations studied, 30-96 wt% sulfuric acid in water. Aerosols up to 88.4 wt% organic/11.1 wt% H 2SO 4/0.5 wt% water were produced via these two dimerization reaction pathways. The UV-VIS spectrum of the isolated aldol condensation product, 2-butyl 2-octenal, extends into the visible region, suggesting these reactions may impact aerosol optical properties as well as aerosol composition. In contrast to previous suggestions, no polymerization of hexanal or its products was observed at any sulfuric acid concentration studied, from 30 to 96 wt% in water.

  2. Divergent Synthesis of Multisubstituted Tetrahydrofurans and Pyrrolidines via Intramolecular Aldol-type Trapping of Onium Ylide Intermediates.

    PubMed

    Jing, Changcheng; Xing, Dong; Gao, Lixin; Li, Jia; Hu, Wenhao

    2015-12-21

    This paper reports a divergent strategy for the synthesis of multisubstituted tetrahydrofurans and pyrrolidines, starting from easily accessible ?-hydroxyketones or ?-aminoketones to react with diazo compounds. Under Rh(II) catalysis, this transformation is proposed to proceed through a metal-carbene-induced oxonium ylide or ammonium ylide formation followed by an intramolecular aldol-type trapping of these active intermediates. A series of highly substituted tetrahydrofurans and pyrrolidines are synthesized in high yields with good to excellent diastereoselectivities. Preliminary biological evaluations revealed that both types of heterocycles show good PTP1B inhibitory activities. PMID:26592374

  3. Recent developments in enzyme promiscuity for carbon-carbon bond-forming reactions.

    PubMed

    Miao, Yufeng; Rahimi, Mehran; Geertsema, Edzard M; Poelarends, Gerrit J

    2015-04-01

    Numerous enzymes have been found to catalyze additional and completely different types of reactions relative to the natural activity they evolved for. This phenomenon, called catalytic promiscuity, has proven to be a fruitful guide for the development of novel biocatalysts for organic synthesis purposes. As such, enzymes have been identified with promiscuous catalytic activity for, one or more, eminent types of carbon-carbon bond-forming reactions like aldol couplings, Michael(-type) additions, Mannich reactions, Henry reactions, and Knoevenagel condensations. This review focuses on enzymes that promiscuously catalyze these reaction types and exhibit high enantioselectivities (in case chiral products are obtained). PMID:25598537

  4. Synthesis and Characterization of Aldol Condensation Products from Unknown Aldehydes and Ketones: An Inquiry-Based Experiment in the Undergraduate Laboratory

    ERIC Educational Resources Information Center

    Angelo, Nicholas G.; Henchey, Laura K.; Waxman, Adam J.; Canary, James W.; Arora, Paramjit S.; Wink, Donald

    2007-01-01

    An experiment for the undergraduate chemistry laboratory in which students perform the aldol condensation on an unknown aldehyde and an unknown ketone is described. The experiment involves the use of techniques such as TLC, column chromatography, and recrystallization, and compounds are characterized by [to the first power]H NMR, GC-MS, and FTIR.…

  5. Gallium(III)- and calcium(II)-catalyzed Meyer-Schuster rearrangements followed by intramolecular aldol condensation or endo-Michael addition.

    PubMed

    Presset, M; Michelet, B; Guillot, R; Bour, C; Bezzenine-Lafollée, S; Gandon, V

    2015-03-28

    The first gallium- and calcium-catalyzed Meyer-Schuster rearrangements are described. Under substrate control, the incipient conjugated ketones can be trapped intramolecularly by ?-keto esters or amides to yield cyclic products after aldol condensation or endo-Michael addition. An interesting additive effect that promotes the latter tandem process with calcium has been found. PMID:25503868

  6. Crystal Structure of Reaction Intermediates in Pyruvate Class II Aldolase

    PubMed Central

    Coincon, Mathieu; Wang, Weijun; Sygusch, Jurgen; Seah, Stephen Y. K.

    2012-01-01

    Crystal structures of divalent metal-dependent pyruvate aldolase, HpaI, in complex with substrate and cleavage products were determined to 1.8–2.0 Å resolution. The enzyme·substrate complex with 4-hydroxy-2-ketoheptane-1,7-dioate indicates that water molecule W2 bound to the divalent metal ion initiates C3–C4 bond cleavage. The binding mode of the aldehyde donor delineated a solvent-filled capacious binding locus lined with predominantly hydrophobic residues. The absence of direct interactions with the aldehyde aliphatic carbons accounts for the broad specificity and lack of stereospecific control by the enzyme. Enzymatic complex structures formed with keto acceptors, pyruvate, and 2-ketobutyrate revealed bidentate interaction with the divalent metal ion by C1-carboxyl and C2-carbonyl oxygens and water molecule W4 that is within close contact of the C3 carbon. Arg70 assumes a multivalent role through its guanidinium moiety interacting with all active site enzymatic species: C2 oxygen in substrate, pyruvate, and ketobutyrate; substrate C4 hydroxyl; aldehyde C1 oxygen; and W4. The multiple interactions made by Arg70 stabilize the negatively charged C4 oxygen following proton abstraction, the aldehyde alignment in aldol condensation, and the pyruvate enolate upon aldol cleavage as well as support proton exchange at C3. This role is corroborated by loss of aldol cleavage ability and pyruvate C3 proton exchange activity and by a 730-fold increase in the dissociation constant toward the pyruvate enolate analog oxalate in the R70A mutant. Based on the crystal structures, a mechanism is proposed involving the two enzyme-bound water molecules, W2 and W4, in acid/base catalysis that facilitates reversible aldol cleavage. The same reaction mechanism promotes decarboxylation of oxaloacetate. PMID:22908224

  7. RUTHENIUM-CATALYZED TANDEM OLEFIN MIGRATION-ALDOL AND MANNICH-TYPE REACTIONS IN WATER AND PROTIC SOLVENT. (R828129)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  8. Controlling reaction specificity in pyridoxal phosphate enzymes

    PubMed Central

    Toney, Michael D.

    2012-01-01

    Pyridoxal 5'-phosphate enzymes are ubiquitous in the nitrogen metabolism of all organisms. They catalyze a wide variety of reactions including racemization, transamination, decarboxylation, elimination, retro-aldol cleavage, Claisen condensation, and others on substrates containing an amino group, most commonly ?-amino acids. The wide variety of reactions catalyzed by PLP enzymes is enabled by the ability of the covalent aldimine intermediate formed between substrate and PLP to stabilize carbanionic intermediates at C? of the substrate. This review attempts to summarize the mechanisms by which reaction specificity can be achieved in PLP enzymes by focusing on three aspects of these reactions: stereoelectronic effects, protonation state of the external aldimine intermediate, and interaction of the carbanionic intermediate with the protein side chains present in the active site. PMID:21664990

  9. Molecular Mechanism by which One Enzyme Catalyzes Two Reactions

    NASA Astrophysics Data System (ADS)

    Nishimasu, Hiroshi; Fushinobu, Shinya; Wakagi, Takayoshi

    Unlike ordinary enzymes, fructose-1,6-bisphosphate (FBP) aldolase/phosphatase (FBPA/P) catalyzes two distinct reactions : (1) the aldol condensation of dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate to FBP, and (2) the dephosphorylation of FBP to fructose-6-phosphate. We solved the crystal structures of FBPA/P in complex with DHAP (its aldolase form) and FBP (its phosphatase form). The crystal structures revealed that FBPA/P exhibits the dual activities through a dramatic conformational change in the active-site architecture. Our findings expand the conventional concept that one enzyme catalyzes one reaction.

  10. Pd/NbOPO? multifunctional catalyst for the direct production of liquid alkanes from aldol adducts of furans.

    PubMed

    Xia, Qi-Neng; Cuan, Qian; Liu, Xiao-Hui; Gong, Xue-Qing; Lu, Guan-Zhong; Wang, Yan-Qin

    2014-09-01

    Great efforts have been made to convert renewable biomass into transportation fuels. Herein, we report the novel properties of NbO(x)-based catalysts in the hydrodeoxygenation of furan-derived adducts to liquid alkanes. Excellent activity and stability were observed with almost no decrease in octane yield (>90% throughout) in a 256?h time-on-stream test. Experimental and theoretical studies showed that NbO(x) species play the key role in C-O bond cleavage. As a multifunctional catalyst, Pd/NbOPO4 plays three roles in the conversion of aldol adducts into alkanes: 1)?The noble metal (in this case Pd) is the active center for hydrogenation; 2)?NbO(x) species help to cleave the C-O bond, especially of the tetrahydrofuran ring; and 3)?a niobium-based solid acid catalyzes the dehydration, thus enabling the quantitative conversion of furan-derived adducts into alkanes under mild conditions. PMID:25045056

  11. Synthesis of branched iminosugars through a hypervalent iodine(III)-mediated radical-polar crossover reaction.

    PubMed

    Santana, Andrés G; Paz, Nieves R; Francisco, Cosme G; Suárez, Ernesto; González, Concepción C

    2013-08-01

    The synthesis of a novel type of branched iminosugars is described. This synthetic strategy is based on two key reactions: first, an aldol reaction with formaldehyde in order to introduce selectively the hydroxymethyl branch, and second, a tandem ?-fragmentation-intramolecular cyclization reaction. The combination of both reactions afforded a battery of compounds exhibiting a great structural complexity, with the concomitant formation of a quaternary center, starting from readily available aldoses. With this approach we have demonstrated the usefulness of the fragmentation of anomeric alkoxyl radicals (ARF) promoted by the PhIO/I2 system for the preparation of new compounds with potential interest for both medicinal and synthetic chemists. PMID:23834195

  12. Evolution of aldolase antibodies in vitro: correlation of catalytic activity and reaction-based selection.

    PubMed

    Tanaka, Fujie; Fuller, Roberta; Shim, Hyunbo; Lerner, Richard A; Barbas, Carlos F

    2004-01-23

    Aldolase antibodies that operate via an enamine mechanism were developed by in vitro selection. Antibody Fab phage display libraries were created where the catalytic active site residues of aldolase antibodies 38C2 and 33F12 were combined with a naive human antibody V gene repertoire. Selection from these libraries with 1,3-diketones covalently trapped the amino groups of reactive lysine residues by formation of stable enaminones. The selected aldolase antibodies retained the essential catalytic lysine residue and its function in altered and humanized primary antibody structures. The substrate specificity of the aldolase antibodies was directly related to the structure of the diketone used for selection. The k(cat) values of the antibody-catalyzed retro-aldol reactions were correlated with the K(d) values, i.e. the reactivities of the selected aldolase antibodies for the corresponding diketones. Antibodies that bound to the diketone with a lower K(d) value displayed a higher k(cat) value in the retro-aldol reaction, and a linear relationship was observed in the plots of logk(cat) versus logK(d). These results indicate that selections with diketones directed the evolution of aldolase antibodies in vitro that operate via an enamine mechanism. This strategy provides a route to tailor-made aldol catalysts with different substrate specificities. PMID:14698295

  13. Synthesis of gamma-hydroxybutenolides applying crossed aldol condensation in the presence of a bulky lewis acid and their anti-tumor activity.

    PubMed

    Yamano, Yumiko; Fujita, Yumi; Mizuguchi, Yukari; Nakagawa, Kimie; Okano, Toshio; Ito, Masayoshi; Wada, Akimori

    2007-09-01

    An improved synthesis of gamma-hydroxybutenolides 1a-d was achieved via crossed aldol condensation between aldehydes 2a-d and the protected gamma-hydroxy-beta-methylbutenolides 3 or 4 using the bulky Lewis acid, aluminum tris(2,6-diphenylphenoxide) (ATPH). Using this same methodology, the gamma-hydroxybutenolides 17a-d having various heteroaromatic rings were synthesized and their anti-tumor activities were evaluated. PMID:17827763

  14. The Evans Aldol-Prins cyclization: a general and stereoselective method for the synthesis of 2,3,4,5,6-pentasubstituted tetrahydropyrans.

    PubMed

    Álvarez-Méndez, Sergio J; García, Celina; Martín, Víctor S

    2016-02-16

    A general and stereoselective method to synthesize 2,3,4,5,6-pentasubstituted tetrahydropyrans in three steps starting from three different aldehydes is described. Key substrates ?,?-unsaturated N-acyloxazolidin-2-ones were subjected to an "Evans Aldol-Prins" protocol to generate five ?-bonds and five stereocenters in only a one-pot process with yields up to 60% and excellent stereoselectivities. PMID:26878814

  15. Total synthesis of the protected aglycon of fidaxomicin (tiacumicin?B, lipiarmycin?A3).

    PubMed

    Miyatake-Ondozabal, Hideki; Kaufmann, Elias; Gademann, Karl

    2015-02-01

    Fidaxomicin, also known as tiacumicin?B or lipiarmycin?A3, is a novel macrocyclic antibiotic that is used in hospitals for the treatment of Clostridium difficile infections. This natural product has also been shown to have excellent bactericidal activity against multidrug-resistant Mycobacterium tuberculosis. In spite of its attractive biological activity, no total synthesis has been reported to date. The enantioselective synthesis of the central 18-membered macrolactone is reported herein. The key reactions include ring-closing metathesis between a terminal olefin and a dienoate moiety for macrocyclization, a vinylogous Mukaiyama aldol reaction, and a Stille coupling reaction of sterically demanding substrates. The retrosynthesis involves three medium-sized fragments, thus leading to a flexible yet convergent synthetic route. PMID:25431322

  16. A Shimizu non-aldol approach to the formal total synthesis of palmerolide A.

    PubMed

    Pujari, Sandip A; Gowrisankar, Parthasarathy; Kaliappan, Krishna P

    2011-11-01

    A formal total synthesis of palmerolide A has been accomplished by assembling three fragments by means of successive Julia-Kocienski olefination, Yamaguchi esterification, and ring-closing metathesis (RCM). Our initial efforts to combine the first two fragments through a Julia-Kocienski reaction between a secondary sulfone and a ketone were not successful; nevertheless, it was feasible between a primary sulfone and aldehyde. Yamaguchi esterification with the third fragment then set the stage for a RCM reaction. Initial failure of the RCM with a PMB-ether adjacent to the olefins and the difficulty in cleaving the PMB-ether prompted us to change the choice of protecting groups, which then paved the way to the macrocyclic core of palmerolide A. PMID:21913332

  17. 'Super Silyl' Group for Diastereoselective Sequential Reactions: Access to Complex Chiral Architecture in One Pot

    SciTech Connect

    Boxer, Matthew B.; Yamamoto, Hisashi

    2008-04-02

    We have shown that the tris(trimethylsilyl)silyl (TTMSS) silyl enol ether of acetaldehyde undergoes aldehyde cross-aldol reactions with high selectivity and the extremely low catalyst loading (0.05 mol % of HNTf{sub 2}) allows for one-pot sequential reactions where acidic or basic nucleophiles can be subsequently added. Various ketone-derived silyl enol ethers, Grignard reagents, and dienes succeeded, generating relatively complex molecular architectures in a single step. This represents the first case where, in a single pot, highly acidic conditions followed by very basic conditions were tolerated to give products with high diastereoselectivities and good yields.

  18. Design of chiral urea-quaternary ammonium salt hybrid catalysts for asymmetric reactions of glycine Schiff bases†

    PubMed Central

    Tiffner, Maximilian; Novacek, Johanna; Busillo, Alfonso; Gratzer, Katharina; Massa, Antonio; Waser, Mario

    2015-01-01

    Bifunctional chiral urea-containing quaternary ammonium salts can be straightforwardly synthesised in good yield and with high structural diversity via a scalable and operationally simple highly telescoped sequence starting from trans-1,2-cyclohexanediamine. These novel hybrid catalysts were systematically investigated for their potential to control glycine Schiff bases in asymmetric addition reactions. It was found that Michael addition reactions and the herein presented aldol-initiated cascade reaction can be carried out to provide enantiomeric ratios up to 95 : 5 and good yields under mild conditions at room temperature. PMID:26504516

  19. Total Synthesis and Structure Determination of JBIR-108-A 2-Hydroxy-2-(1-hydroxyethyl)-2,3-dihydro-3(2H)-furanone Isolated from Streptomyces gramineus IR087Pi-4.

    PubMed

    Fujiwara, Koichi; Tsukamoto, Hirokazu; Izumikawa, Miho; Hosoya, Takahiro; Kagaya, Noritaka; Takagi, Motoki; Yamamura, Hideki; Hayakawa, Masayuki; Shin-Ya, Kazuo; Doi, Takayuki

    2015-01-01

    The planar and stereostructures of JBIR-108 isolated from Streptomyces gramineus IR087Pi-4 were determined partly by spectral analysis, and these structural assignments were confirmed and completed by the total synthesis of both 1-epimers. The key stereocenters in JBIR-108 were constructed via a Corey-Bakshi-Shibata (CBS) reduction (C-1), vinylogous Mukaiyama aldol reaction (C-7), and Brown crotylation (C-14 and C-15). Although it was difficult to determine the stereochemistries at the C-1 and C-7 positions in the natural product using the modified Mosher's method, the synthesis of two possible C-1 diastereomers enabled the identification of the configurations at the hitherto unknown stereocenters. PMID:25437251

  20. An aromatic ion platform for enantioselective Brønsted acid catalysis.

    PubMed

    Gheewala, Chirag D; Collins, Bridget E; Lambert, Tristan H

    2016-02-26

    Chiral acid catalysts are useful for the synthesis of enantioenriched small molecules, but the standard catalysts require laborious and expensive preparations. Here, we describe a chiral Brønsted acid prepared in one step from naturally occurring (-)-menthol and readily available 1,2,3,4,5-pentacarbomethoxycyclopentadiene. Aromatic stabilization serves as a key contributing factor to the potent acidity of the resulting compound, which is shown to catalyze both Mukaiyama-Mannich and oxocarbenium aldol reactions with high efficiency and enantioselectivity. Catalyst loadings as low as 0.01 mole percent and preparative scalability (25 grams) are demonstrated. Alternative amide catalysts are also shown to be promising platforms. In addition to proton catalysis, a chiral anion pathway is demonstrated to be viable with this catalyst system. PMID:26917768

  1. Linked strategy for the production of fuels via formose reaction

    PubMed Central

    Deng, Jin; Pan, Tao; Xu, Qing; Chen, Meng-Yuan; Zhang, Ying; Guo, Qing-Xiang; Fu, Yao

    2013-01-01

    Formose reaction converts formaldehyde to carbohydrates. We found that formose reaction can be used linking the biomass gasification with the aqueous-phase processing (APP) to produce liquid transportation fuel in three steps. First, formaldehyde from syn-gas was converted to triose. This was followed by aldol condensation and dehydration to 4-hydroxymethylfurfural (4-HMF). Finally, 4-HMF was hydrogenated to produce 2,4-dimethylfuran (2,4-DMF) or C9-C15 branched-chain alkanes as liquid transportation fuels. In the linked strategy, high energy-consuming pretreatment as well as expensive and polluting hydrolysis of biomass were omitted, but the high energy recovery of APP was inherited. In addition, the hexoketoses via formose reaction could be converted to HMFs directly without isomerization. A potential platform molecule 4-HMF was formed simultaneously in APP. PMID:23393625

  2. Enantioselective, organocatalytic Morita-Baylis-Hillman and Aza-Morita-Baylis-Hillman reactions: stereochemical issues.

    PubMed

    Mansilla, Javier; Saá, José M

    2010-02-01

    Conscious of the importance that stereochemical issues may have on the design of efficient organocatalyts for both Morita-Baylis-Hillman and aza-Morita-Baylis-Hillman reaction we have analyzed them in this minireview. The so-called standard reactions involve "naked" enolates which therefore should lead to the syn adducts as the major products, irrespective of the E, Z stereochemistry of the enolate. Accordingly, provided the second step is rate determining step, the design of successful bifunctional or polyfunctional catalysts has to consider the geometrical requirements imposed by the transition structures of the second step of these reactions. On the other hand, MBH and aza-MBH reactions co-catalyzed by (S)-proline and a secondary or tertiary amine (co-catalyst) involve the aldol-type condensation of either a 3-amino-substituted enamine, dienamine, or both, depending on the cases. A Zimmerman-Traxler mechanism defines the stereochemical issues regarding these co-catalyzed condensations which parallel those of the well established (S)-proline catalyzed aldol-like reactions. PMID:20335941

  3. Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—Part 1: aldehydes and ketones

    NASA Astrophysics Data System (ADS)

    Barsanti, Kelley C.; Pankow, James F.

    The term "accretion reactions" is introduced here to refer to the large collection of reactions by which atmospheric organic molecules can add mass, especially as by combination with other organic molecules. A general thermodynamic approach is developed for evaluating the tendency of atmospheric constituents (e.g., C 10 aldehydes) to undergo accretion reactions (e.g., dimerization) and thereby form less volatile molecules (e.g., aldol condensation products) that may subsequently condense and so contribute to the levels of organic particulate matter (OPM) observed in the atmosphere. As an example, gaseous compounds A and B may contribute to OPM formation by the net overall reaction A g+B g=C liq. This reaction may occur according to any of three kinetic schemes. Scheme I: (1) A g+B g=C g (accretion in the gas phase): then (2) C g=C liq (condensation of the accretion product); Scheme II: (1) B g=B liq (condensation of B); then (2) A g+B liq=C liq (heterogeneous accretion reaction of gaseous A with condensed B); or Scheme III: (1) A g+B g=A liq+B liq (condensation of A and B); then (2) A liq+B liq=C liq (accretion of A with B within the PM phase). For all three schemes, the net overall reaction remains A g+B g=C liq. The overall thermodynamic tendency of the net reaction remains the same regardless of the actual predominating kinetic mechanism. If an accretion reaction between two atmospheric components is to produce significant new OPM, appreciable amounts of the product C must form, and the vapor pressure of C must be relatively low so that a significant proportion of C can condense into the multicomponent liquid OPM phase. This study considers the thermodynamics of accretion reactions of atmospheric aldehydes including: (a) hydration, polymerization (i.e., oligomer formation), hemiacetal/acetal formation; and (b) aldol condensation. It was concluded regarding OPM formation that: (1) the reactions in the first group are not thermodynamically favored, either in the atmosphere, or in the "acid-catalyzed" chamber experiments of Jang and Kamens (Environ. Sci. Technol. 35 (2001b) 4758) with n-butanal, n-hexanal, n-octanal, and n-decanal; (2) aldol condensation is not thermodynamically favored for the conditions of the Jang and Kamens (2001b) experiments with those four aldehydes; (3) the mechanism for any observed OPM formation from n-butanal, n-hexanal, and n-octanal in those experiments remains unknown, and may also have been involved in the "acid-catalyzed" experiments with n-decanal; (4) whether Jang and Kamens (2001b) observed the consequences of aldol condensation in their n-decanal experiments remains unclear due in part to uncertainties in the free energy of formation (? Gf0) values for the aldol products of n-decanal; (5) analogous refinement in the quality of needed ? Gf0 values is required to clarify the potential importance of aldol products of pinonaldehyde in the formation of ambient OPM; and (6) the possibility that photo-assisted mechanisms may compensate for unfavorable thermodyamics in the formation of accretion products in the atmosphere should be considered.

  4. Temperature-programmed reaction of C sub 4 oxygenates on unpromoted and K-promoted ZnCr oxide in relation to the mechanism of the higher alcohol synthesis

    SciTech Connect

    Lietti, L.; Forzatti, P.; Tronconi, E.; Pasquon, I. )

    1990-12-01

    The reaction mechanisms operating in the chain growth to C{sub 3+}primary alcohols and in the formation of ketones, secondary alcohols, methyl esters, ethers, and hydrocarbons during higher alcohol synthesis (HAS) over high-temperature modified methanol catalysts have been investigated by the temperature-programmed surface reaction (TPSR) technique. Experiments with linear and branched C{sub 4} alcohols, aldehydes, and acids over an unpromoted ZnCr oxide sample have indicated a series of major catalyst functions, namely aldol-like condensation (also with oxygen retention reversal), decarboxylation and decarboxylative condensations, hydrogenation-dehydrogenation, dehydration and hydrolysis, along with isomerization and cracking. TPSR experiments with linear C{sub 4} molecules over K-promoted ZnCr oxide have demonstrated the effects of alkali addition on the catalyst functions. The results are supportive of a mechanism of chain growth to C{sub 3+} primary alcohols based on a sequence of aldolic condensations of aldehydes, which do not operate over 2-methyl species. Formation of ketones under TPSR conditions is explained by decarboxylative condensation reactions of aldehydic and carboxylate species, as well as by aldol-like condensation reactions with oxygen retention reversal. Secondary alcohols detected in the products of the synthesis are formed by hydrogenation of ketones. Methyl esters and ethers are produced in the synthesis by alcoholysis of carboxylate and alkoxide species, respectively. Decarboxylation of carboxylate species, along with dehydration, may also play a role in the formation hydrocarbons during HAS.

  5. Effects of water on reactions for waste treatment, organic synthesis, and bio-refinery in sub- and supercritical water.

    PubMed

    Akizuki, Makoto; Fujii, Tatsuya; Hayashi, Rumiko; Oshima, Yoshito

    2014-01-01

    Current research analyzing the effects of water in the field of homogeneous and heterogeneous reactions of organics in sub- and supercritical water are reviewed in this article. Since the physical properties of water (e.g., density, ion product and dielectric constants) can affect the reaction rates and mechanisms of various reactions, understanding the effects that water can have is important in controlling reactions. For homogeneous reactions, the effects of water on oxidation, hydrolysis, aldol condensation, Beckman rearrangement and biomass refining were introduced including recent experimental results up to 100 MPa using special pressure-resistance equipment. For heterogeneous reactions, the effects of ion product on acid/base-catalyzed reactions, such as hydrothermal conversion of biomass-related compounds, organic synthesis in the context of bio-refinery, and hydration of olefins were described and how the reaction paths are controlled by the concentration of water and hydrogen ions was summarized. PMID:23867097

  6. Stereoselective Synthesis of Functionalized Pyrrolidines by the Diverted N-H Insertion Reaction of Metallocarbenes with ?-Aminoketone Derivatives.

    PubMed

    Nicolle, Simon M; Lewis, William; Hayes, Christopher J; Moody, Christopher J

    2016-03-01

    A highly stereoselective route to functionalized pyrrolidines by the metal-catalyzed diverted N-H insertion of a range of diazocarbonyl compounds with ?-aminoketone derivatives is described. A number of catalysts (rhodium(II) carboxylate dimers, copper(I) triflate, and an iron(III) porphyrin) are shown to promote the process under mild conditions to give a wide range of highly substituted proline derivatives. The reaction starts as a metallocarbene N-H insertion but is diverted by an intermolecular aldol reaction. PMID:26847664

  7. Reaction of propionaldehyde over Rh-Y zeolite

    SciTech Connect

    Takahashi, N.; Takizawa, M.; Sato, Y.

    1986-03-01

    During the desorption of propionaldehyde from the Rh-Y zeolite into a He-CO(10%) stream, the concentration of propionaldehyde decreased with desorption time. n-Propanol formation was enhanced in the desorption of propionaldehyde into a He-H/sub 2/(10%) stream, while no appreciable enhancement was observed in the desorption into a He-H/sub 2/(10%)-CO(10%) stream. A faster decrease in the concentration of propionaldehyde was observed during the desorption into a helium stream than the desorption into the He-CO stream. In the desorption into the helium stream, formation of pentene was observed. However, no formation of pentene was observed in the desorption into a He-C/sub 2/H/sub 4/(10%) stream. In the desorption into a He-C/sub 3/H/sub 6/(10%) stream, the rate of pentene formation was lower than that in the desorption into the helium stream. These results suggest that the pentene is not formed by ethylene-propylene codimerization. The reduced RhCl/sub 3//SiO/sub 2/ catalyst which was physically mixed with the Na-Y zeolite showed comparable activity for pentene formation to that of Rh-Y zeolite in the reaction of propionaldehyde. However, neither the RhCl/sub 3//SiO/sub 2/ catalyst nor the Na-Y zeolite was effective by itself for pentene formation. The reduced RhCl/sub 3//SiO/sub 2/ and Rh-Y zeolite catalysts also showed activity for pentene formation in the reaction of 2-methyl-2-pentenal which is the product of aldol condensation of propionaldehyde. On the basis of the results, two sequential reactions, aldol condensation of propionaldehyde by the zeolite support followed by decarbonylation of 2-methyl-2-pentenal by rhodium metal particles, are proposed as a reaction path for the formation of pentene over the Rh-Y zeolite.

  8. Hydroxyapatite catalyzed aldol condensation: synthesis, spectral linearity, antimicrobial and insect antifeedant activities of some 2,5-dimethyl-3-furyl chalcones.

    PubMed

    Subramanian, M; Vanangamudi, G; Thirunarayanan, G

    2013-06-01

    A series of 2,5-dimethyl-3-furyl chalcones [2E-1-(2,5-dimethyl-3-furyl)-3-(substituted phenyl)-2-propen-1-ones] have been synthesized by Hydrotalcite catalyzed aldol condensation between 3-acetyl-2,5-dimethylfuron and substituted benzaldehydes. Yields of chalcones are more than 80%. These chalcones were characterized by their physical constants and spectral data. The group frequencies of infrared ?(cm(-1)) of CO s-cis and s-trans, CH in-plane and out of plane, CH=CH out of plane, C=C out of plane modes, NMR chemical shifts ?(ppm) of H?, H?, CO, C? and C? of these chalcones were correlated with Hammett substituent constants, F and R parameters using single and multi-regression analyses. From the results of statistical analyses, the effects of substituents on the group frequencies are explained. Antibacterial, antifungal and insect antifeedant activities of these chalcones have been studied. PMID:23562741

  9. Hydroxyapatite catalyzed aldol condensation: Synthesis, spectral linearity, antimicrobial and insect antifeedant activities of some 2,5-dimethyl-3-furyl chalcones

    NASA Astrophysics Data System (ADS)

    Subramanian, M.; Vanangamudi, G.; Thirunarayanan, G.

    2013-06-01

    A series of 2,5-dimethyl-3-furyl chalcones [2E-1-(2,5-dimethyl-3-furyl)-3-(substituted phenyl)-2-propen-1-ones] have been synthesized by Hydrotalcite catalyzed aldol condensation between 3-acetyl-2,5-dimethylfuron and substituted benzaldehydes. Yields of chalcones are more than 80%. These chalcones were characterized by their physical constants and spectral data. The group frequencies of infrared ?(cm-1) of CO s-cis and s-trans, CH in-plane and out of plane, CHdbnd CH out of plane, lbond2 Cdbnd Crbond2 out of plane modes, NMR chemical shifts ?(ppm) of H?, H?, CO, C? and C? of these chalcones were correlated with Hammett substituent constants, F and R parameters using single and multi-regression analyses. From the results of statistical analyses, the effects of substituents on the group frequencies are explained. Antibacterial, antifungal and insect antifeedant activities of these chalcones have been studied.

  10. Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—2. Dialdehydes, methylglyoxal, and diketones

    NASA Astrophysics Data System (ADS)

    Barsanti, Kelley C.; Pankow, James F.

    Predicting the formation of organic particulate matter (OPM) in the atmosphere by absorptive gas/particle partitioning requires a knowledge of the identities, atmospheric levels, and physical properties of all condensable species. Data from field and chamber experiments have shown that a portion of atmospheric OPM samples are comprised of products generated during oxidation of volatile organic compounds. It has been suggested that some of these initially formed oxidation products also contribute to the formation of atmospheric OPM via molecular-weight (MW) building "accretion reactions". The role of such reactions as well as a general theoretical approach for evaluating their thermodynamic relevance in regard to atmospheric OPM formation, have been discussed in prior work. This work utilizes that approach in considerations of accretion reactions of glyoxal, two other dialdehydes, methylglyoxal, and two diketones. The methods used to predict free energy of formation ( ?G°) values (and hence equilibrium constant ( K) values) indicate that: (1) for 1,4-butanedial, 2,3-butanedione, and 2,5-hexanedione, the accretion reactions considered are not favorable; (2) for C 6 and higher dialdehydes, reaction by aldol condensation may contribute to atmospheric OPM formation under certain circumstances, if kinetically favorable; and (3) for glyoxal, diol and subsequent oligomer formation, and for methylglyoxal, aldol condensation, are thermodynamically favorable, and may contribute significantly to OPM in the atmosphere, if kinetically favorable.

  11. Tris(pentafluorophenyl)borane: a special boron Lewis acid for special reactions.

    PubMed

    Erker, Gerhard

    2005-06-01

    Tris(pentafluorophenyl)borane is best known for its role as an excellent activator component in homogeneous Ziegler-Natta chemistry. However, the special properties of B(C6F5)3 have made this strong boron Lewis acid an increasingly used catalyst or stoichiometric reagent in organic and organometallic chemistry. This includes catalytic hydrometallation reactions, alkylations and catalyzed aldol-type reactions. B(C6F5)3 catalyzes tautomerizations and can sometimes stabilize less favoured tautomeric forms by adduct formation. It induces some rather unusual reactions of early metal acetylide complexes and can help in stabilizing uncommon coordination geometries of carbon. The growing number of such examples indicates an increasing application potential of the useful Lewis acid B(C6F5)3 aside from its established role in olefin polymerization catalysis. PMID:15909033

  12. Hydrogenolysis of cellulose over Cu-based catalysts-analysis of the reaction network.

    PubMed

    Tajvidi, Kameh; Hausoul, Peter J C; Palkovits, Regina

    2014-05-01

    A series of polyols, carbohydrates, and cellulose were tested in the aqueous, CuO/ZnO/Al2O3-catalyzed hydrogenolysis reaction at 245 °C and 50 bar H2. The compositions of liquid-phase products were analyzed; based on these results a unified reaction mechanism is proposed that accounts for the observed product distribution. Elementary transformations such as dehydration, dehydrogenation/hydrogenation, Lobry de Bruyn-van Ekenstein isomerization and retro-aldol cleavage were identified as most important for controlling the selectivity of simple polyols and carbohydrates. For cellulose the product distribution is considerably different than for glucose or sorbitol, indicating a change in the reaction pathway. Therefore, next to the traditional hydrolysis of the glycosidic bond, an additional depolymerization mechanism involving only the reducing ends of cellulose oligomers is proposed to account for this observation. PMID:24596082

  13. Complex chemical composition of colored surface films formed from reactions of propanal in sulfuric acid at upper troposphere/lower stratosphere aerosol acidities

    NASA Astrophysics Data System (ADS)

    Van Wyngarden, A. L.; Pérez-Montaño, S.; Bui, J. V. H.; Li, E. S. W.; Nelson, T. E.; Ha, K. T.; Leong, L.; Iraci, L. T.

    2014-11-01

    Particles in the upper troposphere and lower stratosphere (UT/LS) consist mostly of concentrated sulfuric acid (40-80 wt %) in water. However, airborne measurements have shown that these particles also contain a significant fraction of organic compounds of unknown chemical composition. Acid-catalyzed reactions of carbonyl species are believed to be responsible for significant transfer of gas phase organic species into tropospheric aerosols and are potentially more important at the high acidities characteristic of UT/LS particles. In this study, experiments combining sulfuric acid (H2SO4) with propanal and with mixtures of propanal with glyoxal and/or methylglyoxal at acidities typical of UT/LS aerosols produced highly colored surface films (and solutions) that may have implications for aerosol properties. In order to identify the chemical processes responsible for the formation of the surface films, Attenuated Total Reflectance-Fourier Transform Infrared and 1H Nuclear Magnetic Resonance spectroscopies were used to analyze the chemical composition of the films. Films formed from propanal were a complex mixture of aldol condensation products, acetals and propanal itself. The major aldol condensation products were the dimer (2-methyl-2-pentenal) and 1,3,5-trimethylbenzene, which was formed by cyclization of the linear aldol condensation trimer. Additionally, the strong visible absorption of the films indicates that higher order aldol condensation products must also be present as minor species. The major acetal species were 2,4,6-triethyl-1,3,5-trioxane and longer-chain linear polyacetals which are likely to separate from the aqueous phase. Films formed on mixtures of propanal with glyoxal and/or methylglyoxal also showed evidence for products of cross-reactions. Since cross-reactions would be more likely than self-reactions under atmospheric conditions, similar reactions of aldehydes like propanal with common aerosol organic species like glyoxal and methylglyoxal have the potential to produce significant organic aerosol mass and therefore could potentially impact chemical, optical and/or cloud-forming properties of aerosols, especially if the products partition to the aerosol surface.

  14. Complex chemical composition of colored surface films formed from reactions of propanal in sulfuric acid at upper troposphere/lower stratosphere aerosol acidities

    NASA Astrophysics Data System (ADS)

    Van Wyngarden, A. L.; Pérez-Montaño, S.; Bui, J. V. H.; Li, E. S. W.; Nelson, T. E.; Ha, K. T.; Leong, L.; Iraci, L. T.

    2015-04-01

    Particles in the upper troposphere and lower stratosphere (UT/LS) consist mostly of concentrated sulfuric acid (40-80 wt%) in water. However, airborne measurements have shown that these particles also contain a significant fraction of organic compounds of unknown chemical composition. Acid-catalyzed reactions of carbonyl species are believed to be responsible for significant transfer of gas phase organic species into tropospheric aerosols and are potentially more important at the high acidities characteristic of UT/LS particles. In this study, experiments combining sulfuric acid (H2SO4) with propanal and with mixtures of propanal with glyoxal and/or methylglyoxal at acidities typical of UT/LS aerosols produced highly colored surface films (and solutions) that may have implications for aerosol properties. In order to identify the chemical processes responsible for the formation of the surface films, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and 1H nuclear magnetic resonance (NMR) spectroscopies were used to analyze the chemical composition of the films. Films formed from propanal were a complex mixture of aldol condensation products, acetals and propanal itself. The major aldol condensation products were the dimer (2-methyl-2-pentenal) and 1,3,5-trimethylbenzene that was formed by cyclization of the linear aldol condensation trimer. Additionally, the strong visible absorption of the films indicates that higher-order aldol condensation products must also be present as minor species. The major acetal species were 2,4,6-triethyl-1,3,5-trioxane and longer-chain linear polyacetals which are likely to separate from the aqueous phase. Films formed on mixtures of propanal with glyoxal and/or methylglyoxal also showed evidence of products of cross-reactions. Since cross-reactions would be more likely than self-reactions under atmospheric conditions, similar reactions of aldehydes like propanal with common aerosol organic species like glyoxal and methylglyoxal have the potential to produce significant organic aerosol mass and therefore could potentially impact chemical, optical and/or cloud-forming properties of aerosols, especially if the products partition to the aerosol surface.

  15. Synthesis of two subunits of the macrolide domain of the immunosuppressive agent sanglifehrin a and assembly of a macrolactone precursor. application of masamune anti-aldol condensation.

    PubMed

    Suttisintong, Khomson; White, James D

    2015-02-20

    Asymmetric anti-aldol coupling of a norephedrine-derived ester with an α-chiral aldehyde was used to synthesize a carboxylic acid representing the C13-C19 segment of the macrocyclic domain present in the immunosuppressive agent sanglifehrin A. Felkin addition set configuration at the C14-C17 stereotetrad in this unit in which hydroxyl functions at C15 and C17 were masked as an internal ketal. The carboxyl group of this segment was coupled to the N-terminus of the tripeptide portion (C1-N12) of sanglifehrin A macrolactone to assemble the C1-C19 domain. Synthesis of the C20-C25 subunit of sanglifehrin A containing a (23S) alcohol was completed via asymmetric allylation of (E)-3-iodo-2-methylprop-2-enal followed by oxidative cleavage of the terminal vinyl appendage and a Takai olefination with pinacol dichloromethylboronate. Esterification of this alcohol with a C1-C19 carboxylic acid furnished an open C1-C25 macrolactone precursor, but this substance failed to undergo macrocyclization via intramolecular Suzuki-Miyaura coupling. PMID:25584782

  16. Organic reactions increasing the absorption index of atmospheric sulfuric acid aerosols

    NASA Astrophysics Data System (ADS)

    Nozière, B.; Esteve, W.

    2005-02-01

    Unlike most environments present at Earth's surface atmospheric aerosols can be favorable to organic reactions. Among them, the acid-catalyzed aldol condensation of aldehydes and ketones produces light-absorbing compounds. In this work the increase of the absorption index of sulfuric acid solutions 50-96 wt. % resulting from the uptake of gas-phase acetaldehyde, acetone, and 2-butanone (methyl ethyl ketone), has been measured in the near UV and visible range. Our results indicate that the absorption index between 200 and 500 nm for stratospheric sulfuric aerosols exposed to 100 pptV of acetaldehyde (1 pptV = 10-12 v/v) would increase by four orders of magnitude over a two-year lifetime. Rough estimates based on previous radiative calculations suggest that this reaction could result in an increase of the radiative forcing of sulfate aerosols of the order of 0.01 W m-2, and that these processes are worth further investigation.

  17. Stereoselective synthesis of the C13-C22 fragment of callystatin A by a non-aldol approach.

    PubMed

    Raghavan, Sadagopan; Rajendar, Sheelamanthula

    2015-05-01

    An efficient synthetic route to the C13-C22 subunit of callystatin A is reported. The key features include diastereoselective alkylation, using Myers auxiliary, for the preparation of the three carbon synthon 7, stereo- and regioselective oxidative vicinal functionalization of an electron deficient trisubstituted (Z)-olefin using an intramolecular sulfinyl group as the nucleophile, diastereoselective radical debromination of a bromohydrin derivative using Guindon's protocol to prepare the C16-C18 anti-anti stereotriad, Lewis acid promoted crotylation following Keck's protocol to create C19, C20 stereocenters and the use of the Pummerer reaction to reveal an aldehyde for the extension of two carbons by Wittig olefination. PMID:25827465

  18. Aldol-type compounds from water-soluble indole-3,4-diones: synthesis, kinetics, and antiviral properties.

    PubMed

    Scala, Angela; Cordaro, Massimiliano; Mazzaglia, Antonino; Risitano, Francesco; Venuti, Assunta; Sciortino, Maria Teresa; Grassi, Giovanni

    2013-08-01

    A straightforward transformation of indole-3,4-diones is reported. The reaction feasibility is evidenced by kinetic studies on a model substrate, revealing a double phase process with a first faster pseudo-first-order step (i.e., deprotonation of the dione and self-nucleophilic attack of the anion) and a subsequent slower dehydration of the intermediate. The overall process is faster at pH higher than the pK value of the investigated substrate. The biological relevance of new compounds has been assessed in vitro against herpes simplex virus type-1 (HSV-1), showing a more promising biological profile with respect to their precursors. PMID:23640033

  19. Investigation of thermochemistry associated with the carbon-carbon coupling reactions of furan and furfural using ab initio methods.

    PubMed

    Liu, Cong; Assary, Rajeev S; Curtiss, Larry A

    2014-06-26

    Upgrading furan and small oxygenates obtained from the decomposition of cellulosic materials via formation of carbon-carbon bonds is critical to effective conversion of biomass to liquid transportation fuels. Simulation-driven molecular level understanding of carbon-carbon bond formation is required to design efficient catalysts and processes. Accurate quantum chemical methods are utilized here to predict the reaction energetics for conversion of furan (C4H4O) to C5-C8 ethers and the transformation of furfural (C5H6O2) to C13-C26 alkanes. Furan can be coupled with various C1 to C4 low molecular weight carbohydrates obtained from the pyrolysis via Diels-Alder type reactions in the gas phase to produce C5-C8 cyclic ethers. The computed reaction barriers for these reactions (?25 kcal/mol) are lower than the cellulose activation or decomposition reactions (?50 kcal/mol). Cycloaddition of C5-C8 cyclo ethers with furans can also occur in the gas phase, and the computed activation energy is similar to that of the first Diels-Alder reaction. Furfural, obtained from biomass, can be coupled with aldehydes or ketones with ?-hydrogen atoms to form longer chain aldol products, and these aldol products can undergo vapor phase hydrocycloaddition (activation barrier of ?20 kcal/mol) to form the precursors of C26 cyclic hydrocarbons. These thermochemical studies provide the basis for further vapor phase catalytic studies required for upgrading of furans/furfurals to longer chain hydrocarbons. PMID:24902118

  20. Enantio- and Diastereoselective Formal Hetero-Diels-Alder Reactions of Trifluoromethylated Enones Catalyzed by Chiral Primary Amines.

    PubMed

    Lin, Yong-Jun; Du, Li-Na; Kang, Tai-Ran; Liu, Quan-Zhong; Chen, Ze-Qin; He, Long

    2015-08-10

    Enantioselective formal hetero-Diels-Alder reactions of trifluoromethylated enones and 2-amino-1,3-butadienes generated in situ from aliphatic acyclic enones and chiral primary amines are reported. The corresponding tetrahydropyran-4-ones are formed in up to 94?% yield and with up to 94?%?ee. The reaction was carried out through a stepwise mechanism, including initial aminocatalytic aldol condensation of 2-amino-1,3-butadiene to the trifluoromethylated carbonyl group followed by an intramolecular oxa-Michael addition. Both NMR investigation and theoretical calculations on the transition state indicate that the protonated tertiary amine could effectively activate the carbonyl group of the trifluoromethyl ketone to promote the addition process through hydrogen-bonding interaction of N-H???F and N-H???O simultaneously, and thus provide a chiral environment for the approach of amino-1,3-butadienes to the activated trifluoromethyl ketone, resulting in high enantioselectivity. PMID:26179273

  1. Markers of heterogeneous reaction products in ?-pinene ozone secondary organic aerosol

    NASA Astrophysics Data System (ADS)

    Czoschke, Nadine M.; Jang, Myoseon

    A gas chromatograph iontrap mass spectrometer (GC-ITMS) was used to analyze the gas-and particle-phase products of ?-pinene ozone oxidation in the presence of three different inorganic seed aerosols: sodium chloride, ammonium sulfate only, and ammonium sulfate with sulfuric acid. Products of ?-pinene ozone oxidation common to the literature showed little difference in gas or particle-phase concentrations between seed types within the precision of the measurements even though significantly different aerosol yields were found between seed types. Small amounts of ring-opening products of four-membered cyclic oxygenates and markers of aldol condensation products were tentatively identified in the particle-phase for all seed types. These tentatively identified products are thought to be the result of acid-catalyzed heterogeneous reactions in the particle-phase or during sampling processes or analysis. The mechanisms for their formation are also proposed in this study.

  2. Reaction theory

    NASA Astrophysics Data System (ADS)

    Typel, Stefan

    2016-01-01

    Reactions with atomic nuclei play a pivotal role in the experimental study of nuclei. They are a tool in order to obtain crucial information on nuclear structure of nuclei, in particular for unstable nuclei far off the valley of stability. Besides the investigation of nuclear properties, nuclear reactions can be used as indirect methods to extract cross sections of astrophysical interest that cannot be measured directly in the laboratory. After an overview over the variety of nuclear reactions and their major characteristics, the basic formalism of reaction theory is introduced and essential concepts are presented in order to describe direct reactions. The main challenges in the future development of reaction theory are addressed.

  3. [Synthesis of carbohydrate related compounds by using aldolase catalyzed reaction].

    PubMed

    Kajimoto, T

    2000-01-01

    Enzymes proceed the reaction with high regio- and stereoselectivity under mild conditions, i.e. in an aqueous medium at room temperature. However, enzymatic reactions that catalyze carbon-carbon bond formation have not been utilized in organic synthesis until recently. We had an interest in an aldolase-catalyzed reaction which proceed carbon-carbon bond formation referred to aldol condensation, by which many bioactive compounds have been rationally synthesized. On the other hand, recent biological studies on cell recognition (cell adhesion) have disclosed the important roles of oligosaccharides on cell surfaces, especially which include glucuronic acid, 3-deoxy-D-manno-oct-2-ulosonic acid (KDO), and sialic acid in the structures e.g., sialyl Lewis X and endotoxins, in differentiation, induction, viral and bacterial infections, and immune response. As well as acidic oligosaccharides, basic ones have been utilized as practical medicines in the clinical level, like acarbose that acts as an amylase inhibitor. Based on these background, we embarked the synthesis of carbohydrate related compounds which can control the interaction between carbohydrates and carbohydrate recognition protein by the use of several aldolases. Azasugars, potent inhibitors toward glycosidases, were synthesized using fructose-1,6-diphosphate (FDP)-aldolase and other dihdroxyacetonephosphate (DHAP)-dependent aldolases in the key step. Sialyl Lewis X mimetic, peptidic mimetic of RNA having anti-Vero toxin activity, mycestericin D, and aza-idulonic acid were prepared by taking advantage of L-threonine aldolase catalyzed reaction, which afford beta-hydroxy-alpha-L-amino acids. A precursor of KDO, featured acidic sugar of endotoxins was provided by the reaction catalyzed with kynureninase, which generates beta-anion of L-alanine in its active site during the metabolic reaction from kynurenine to anthranilic acid. PMID:10655781

  4. On the mechanism of the Dakin-West reaction.

    PubMed

    Dalla-Vechia, Luciana; Santos, Vanessa G; Godoi, Marla N; Cantillo, David; Kappe, C Oliver; Eberlin, Marcos N; de Souza, Rodrigo O M A; Miranda, Leandro S M

    2012-12-01

    The mechanism of the Dakin-West reaction has been thoroughly investigated by monitoring the reaction using ESI-MS/MS techniques in combination with M06-2X/6-311++G(d,p) calculations. Several of the key intermediates in the previously proposed "azlactone" mechanism have been experimentally detected and characterized. In particular, interception of the mixed anhydrides involved in the early and late stages of the mechanistic scheme, as well as of the cyclic acyl-oxazolone intermediate, supports the original pathway suggested by Dakin and West. All intermediates and transition structures involved in several competing mechanisms have been calculated. The theoretical calculations support the experimental results and corroborate the proposed "azlactone" mechanism. The pathway involving the cyclic oxazolone ("azlactone") intermediate represents an energy barrier more than 3 kcal mol(-1) lower than for the competing aldol-type mechanism, thus ruling out this alternative mechanism. The DFT calculations explain the observed ESI-MS data and assess those intermediates which the experiments cannot fully elucidate. PMID:23070278

  5. Stereocontrolled total synthesis of polygalolide?A.

    PubMed

    Yamada, Hitomi; Adachi, Masaatsu; Isobe, Minoru; Nishikawa, Toshio

    2013-07-01

    The total synthesis of polygalolide?A, a secondary metabolite that was isolated from a Chinese medicinal plant, is reported. A key issue in this synthesis was construction of an oxabicyclo[3.2.1] skeleton, which was solved by the development of an intramolecular Ferrier-type C-glycosylation of a glucal with siloxyfuran as an internal nucleophile. The substrate was prepared from D-glucal by the introduction of trimethylsilylacetylene and siloxyfuran groups. Although C-glycosylation did not occur under the conditions found from model experiments, further examination revealed that the combination of trimethylsilyl trifluoromethanesulfonate (TMSOTf) and 2,4,6-collidine successfully afforded the desired product as a single diastereomer. The siloxy group at the C3 position played a crucial role in the stereocontrol of this reaction. The product was further transformed into a tetracyclic compound as follows: The vinyl ether and acetylenic moieties were reduced and the siloxy group was removed with a Barton-McCombie reaction. The construction of the six-membered ether and the ?-lactone provided the tetracyclic compound. Finally, a phenolic moiety was introduced by using a Mukaiyama aldol reaction to furnish polygalolide?A. PMID:23670825

  6. Exploring the synthetic versatility of the Lewis acid induced decomposition reaction of ?-diazo-?-hydroxy esters. The case of ethyl diazo(3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)acetate.

    PubMed

    Gioiello, Antimo; Venturoni, Francesco; Marinozzi, Maura; Natalini, Benedetto; Pellicciari, Roberto

    2011-09-16

    Ethyl diazo(3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)acetate was prepared by aldol-type condensation of ethyl diazoacetate with isatin. A systematic and mechanistic study on the Lewis acid induced decomposition reaction of this valuable diazo precursor was carried out with the aim to gain new insights into the mechanistic aspects of the reaction as well as to further understand the factors and experimental conditions which affect the relative product distribution. The reaction, which may proceed via cationic and noncationic mechanisms, was found to be significantly influenced by the reaction environment determined by the characteristics of the Lewis acid employed, by the ability of the Lewis acid to form a complex with the alcohol functionality of the ?-diazo-?-hydroxy ester, and by the polarity and nucleophilicity of the solvent used. PMID:21800851

  7. Adsorption and Reaction of Acetaldehyde on Stoichiometric and Defective SrTiO?(100) Surfaces

    SciTech Connect

    Wang, Li Q.; Ferris, Kim F.; Azad, Samina; Engelhard, Mark H.; Peden, Charles HF.

    2004-02-05

    The adsorption and reaction of acetaldehyde (CH{sub 3}CHO), on stoichiometric (TiO{sub 2}-terminated) and reduced SrTiO{sub 3}(100) surfaces, have been investigated using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Acetaldehyde adsorbs molecularly on the stoichiometric SrTiO{sub 3}(100) surface that contains predominantly Ti{sup 4+} cations. The Ti{sup 4+} sites on the stoichiometric SrTiO{sub 3}(100) surface are not sufficiently active for surface reactions such as aldol condensation, as opposed to the Ti{sup 4+} ions on the TiO{sub 2}(001) surface. However, decomposition and redox reactions of acetaldehyde occur in the presence of surface defects created by Ar{sup +} sputtering. The decomposition products following reactions of acetaldehyde on the defective surface include H{sub 2}, C{sub 2}H{sub 4}, CO, C{sub 4}H{sub 6}, and C{sub 4}H{sub 8}. Reductive coupling, to produce C{sub 2}H{sub 4} and C{sub 4}H{sub 8} is the main reaction pathway for decomposition of acetaldehyde on the sputter reduced SrTiO{sub 3}(100) surface.

  8. Isosynthesis reactions of CO/H/sub 2/ over zirconium dioxide

    SciTech Connect

    Tseng, S.C.

    1987-01-01

    The isosynthesis reactions of an equimolar mixture of carbon monoxide and hydrogen were studied over zirconium dioxide catalysts. The main objectives of this work were: (1) to investigate the reaction pathway, (2) identify the surface intermediates leading to the formation of i-butene, and (3) determine the mechanisms of carbon chain propagation. The reactions were conducted at 250-450/sup 0/C, 35 atm (500 psig) total pressure, and 100-200 cc/min total flow rate in a differential reactor. Oxygenated intermediates are proposed to exist on the zirconia surface. This is supported by the observations that oxygenated products were favored at lower reaction temperatures or at shorter residence times. Propylene, propionaldehyde, acetone, i-propanol, and n-propanol were used as probe molecules to examine the chain growth and branching mechanisms, leading to the formation of i-butene. Reaction schemes are proposed. Carbon-13 labeled acetone and methanol were utilized to examine quantitatively the above two schemes. The labeled acetone studies revealed that both the branched and linear olefins were formed from the acetone added. The presence of carbon-13 carbons in linear olefins indicated that methylation at the acetone methyl occurred. The labeled methanol studies revealed that aldol-type condensation did proceed over zirconia, leading to the formation of branching olefins.

  9. Total syntheses of (+)-polygalolide?a and (+)-polygalolide?b: elucidation of the absolute stereochemistry and biogenetic implications.

    PubMed

    Sugano, Yukihito; Kikuchi, Fumiaki; Toita, Akinori; Nakamura, Seiichi; Hashimoto, Shunichi

    2012-07-27

    The total syntheses of (+)-polygalolide?A and (+)-polygalolide?B have been completed by using a carbonyl ylide cycloaddition strategy. Three of the four stereocenters, including two consecutive tetrasubstituted carbon atoms at C2 and C8, were incorporated through internal asymmetric induction from the stereocenter at C7 by a [Rh(2) (OAc)(4)]-catalyzed carbonyl ylide formation/intramolecular 1,3-dipolar cycloaddition sequence. The arylmethylidene moiety of these natural products was successfully installed by a Mukaiyama aldol-type reaction of a silyl enol ether with a dimethyl acetal, followed by elimination under basic conditions. We have also developed an alternative approach to the carbonyl ylide precursor based on a hetero-Michael reaction. This approach requires 18 steps, and the natural products were obtained in 9.8 and 9.3?% overall yields. Comparison of specific rotations of the synthetic materials and natural products suggests that polygalolides are biosynthesized in nearly racemic forms through a [5+2] cycloaddition between a fructose-derived oxypyrylium zwitterion with an isoprene derivative. PMID:22760948

  10. Design and Synthesis of Chiral Zn2+ Complexes Mimicking Natural Aldolases for Catalytic C–C Bond Forming Reactions in Aqueous Solution

    PubMed Central

    Itoh, Susumu; Sonoike, Shotaro; Kitamura, Masanori; Aoki, Shin

    2014-01-01

    Extending carbon frameworks via a series of C–C bond forming reactions is essential for the synthesis of natural products, pharmaceutically active compounds, active agrochemical ingredients, and a variety of functional materials. The application of stereoselective C–C bond forming reactions to the one-pot synthesis of biorelevant compounds is now emerging as a challenging and powerful strategy for improving the efficiency of a chemical reaction, in which some of the reactants are subjected to successive chemical reactions in just one reactor. However, organic reactions are generally conducted in organic solvents, as many organic molecules, reagents, and intermediates are not stable or soluble in water. In contrast, enzymatic reactions in living systems proceed in aqueous solvents, as most of enzymes generally function only within a narrow range of temperature and pH and are not so stable in less polar organic environments, which makes it difficult to conduct chemoenzymatic reactions in organic solvents. In this review, we describe the design and synthesis of chiral metal complexes with Zn2+ ions as a catalytic factor that mimic aldolases in stereoselective C–C bond forming reactions, especially for enantioselective aldol reactions. Their application to chemoenzymatic reactions in aqueous solution is also presented. PMID:24481060

  11. Key reaction for formation of isobutene over ZrO{sub 2} and isoprene over CeO{sub 2} in CO hydrogenation

    SciTech Connect

    Maruya, K.; Hara, M.; Kondo, J.; Domen, K.; Onishi, T.

    1996-12-31

    CO hydrogenation over ZrO{sub 2} at 623 and 673 K selectively forms isobutene. {sup 13}C tracer experiment with {sup 13}CO showed that carbon of surface methoxide species is incorporated in central carbon of isobutene. CeO{sub 2} forms 2-methylpropanal and diisopropyl ketone at 523 K and isobutene and isoprene with high selectivities in C{sub 4} and C{sub 5} hydrocarbons, respectively, at 673 K. Addition of H{sub 2}O to a mixture of CO H{sub 2} at 583 and 653 K led to formation of ketones and secondary alcohol`s. These suggest that there is acyl species as a common intermediate, which converts to isobutene via aldol-condensation with formaldehyde and to isoprene via acetone formed from its reaction with H{sub 2}O or bulk oxygen followed by ketonization reaction.

  12. Drug Reactions

    MedlinePLUS

    Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions. One problem is ...

  13. Exclusive Reactions

    NASA Astrophysics Data System (ADS)

    Mueller, A. H.

    1997-02-01

    After some introductory remarks a brief review of the status of exclusive reactions and of color transparency is given. Special emphasis is given to the ?y transition form factor, which appears to be the first exclusive reaction where the hard scattering perturbative QCD picture seems to work well. Deeply virtual Compton scattering, which may become an exciting source of new information on partonic spin and angular momentum structure, is also briefly reviewed.

  14. The Reactions of Acetone with the Surfaces of Uranium Dioxide Single Crystal and Thin Film

    SciTech Connect

    King,R.; Senanayake, S.; Chong, S.; Idriss, H.

    2007-01-01

    The reaction of acetone, as an example of a carbonyl compound, is studied over UO2 (1 1 1) single crystal and thin film surfaces. Over the stoichiometric single crystal surface, acetone is molecularly and weakly adsorbed with a computed activation energy for desorption in the range of 95-65 kJ/mol with pre-exponential factors between 1011 and 1013 s-1. On the contrary, acetone reacts very strongly on the O-defected single crystal and thin film surfaces. In addition to total decomposition evidence of aldolization and cyclization reactions were seen. The thin film of UO2 was studied by synchrotron light, providing high resolution photoelectron spectroscopy in the core level, and high sensitivity in the both the core and valence band regions. The U5f line was considerably enhanced at grazing angle when compared to that obtained at normal angle for the O-defected surface, showing that the surface is more reduced than the next layers. The U 4f lines indicated the presence of U cations in lower oxidation states than +4 for the O-defected surface. These lines were considerably attenuated upon adsorption of acetone, due to surface oxidation by C{double_bond}O bond dissociation. The reaction pathway for acetone on the O-defected surface is presented, and compared to that of the previously studied acetaldehyde molecule.

  15. Glucose and fructose decomposition in subcritical and supercritical water: Detailed reaction pathway, mechanisms, and kinetics

    SciTech Connect

    Kabyemela, B.M.; Adschiri, T.; Malaluan, R.M.; Arai, K.

    1999-08-01

    The authors are developing a new catalyst-free process of cellulose decomposition in supercritical water. In their initial study on the cellulose decomposition in supercritical water, the main products of cellulose decomposition were found to be oligomers of glucose (cellobiose, cellotriose, etc.) and glucose at short residence times (400 C, 25 MPa, 0.05 s). The kinetics of glucose at these conditions can be useful in understanding the reaction pathways of cellulose. Experiments were performed on the products of glucose decomposition at short residence times to elucidate the reaction pathways and evaluate kinetics of glucose and fructose decomposition in sub- and supercritical water. The conditions were a temperature of 300--400 C and pressure of 25--40 MPa for extremely short residence times between 0.02 and 2 s. The products of glucose decomposition were fructose, a product of isomerization, 1,6-anhydroglucose, a product of dehydration, and erythrose and glyceraldehyde, products of C-C bond cleavage. Fructose underwent reactions similar to glucose except that it did not form 1,6-anhydroglucose and isomerization to glucose is negligible. The mechanism for the products formed from C-C bond cleavage could be explained by reverse aldol condensation and the double-bond rule of the respective enediols formed during the Lobry de Bruyn Alberda van Ekenstein transformation. The differential equations resulting from the proposed pathways were fit to experimental results to obtain the kinetic rate constants.

  16. Common inorganic ions are efficient catalysts for organic reactions in atmospheric aerosols and other natural environments

    NASA Astrophysics Data System (ADS)

    Nozière, B.; Dziedzic, P.; Córdova, A.

    2009-01-01

    In this work, inorganic ammonium ions, NH4+, and carbonate ions, CO32-, are reported for the first time as catalysts for organic reactions in atmospheric aerosols and other natural environments at the Earth's surface. These reactions include the formation of C-C and C-O bonds by aldol condensation and acetal formation, and reveal a new aspect of the interactions between organic and inorganic materials in natural environments. The catalytic properties of inorganic ammonium ions, in particular, were not previously known in chemistry. The reactions were found to be as fast in tropospheric ammonium sulfate composition as in concentrated sulfuric acid. The ubiquitous presence and large concentrations of ammonium ions in tropospheric aerosols would make of ammonium catalysis a main consumption pathway for organic compounds in these aerosols, while acid catalysis would have a minor contribution. In particular, ammonium catalysis would account quantitatively for the aging of carbonyl compounds into secondary ''fulvic'' compounds in tropospheric aerosols, a transformation affecting the optical properties of these aerosols. In general, ammonium catalysis is likely to be responsible for many observations previously attributed to acid catalysis in the troposphere.

  17. Adsorption and Reaction of Acetaldehyde on Stoichiometric and Defective SrTiO{sub 3}(100) Surfaces

    SciTech Connect

    Wang, Li Q.; Ferris, Kim F.; Azad, Samina; Engelhard, Mark H.; Peden, Charles HF.

    2004-02-05

    The adsorption and reaction of acetaldehyde (CH{sub 3}CHO), on stoichiometric (TiO{sub 2}-terminated) and reduced SrTiO{sub 3}(100) surfaces, have been investigated using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Acetaldehyde adsorbs molecularly on the stoichiometric SrTiO{sub 3}(100) surface that contains predominantly Ti{sup 4+} cations. The Ti{sup 4+} sites on the stoichiometric SrTiO{sub 3}(100) surface are not sufficiently active for surface reactions such as aldol condensation, as opposed to the Ti{sup 4+} ions on the TiO{sub 2}(001) surface. However, decomposition and redox reactions of acetaldehyde occur in the presence of surface defects created by Ar{sup +} sputtering. The decomposition products following reactions of acetaldehyde on the defective surface include H{sub 2}, C{sub 2}H{sub 4}, CO, C{sub 4}H{sub 6} and C{sub 4}H{sub 8}. Reductive coupling, to produce C{sub 2}H{sub 4} and C{sub 4}H{sub 8}, is the main reaction pathway for decomposition of acetaldehyde on the sputter reduced SrTiO{sub 3}(100) surface.

  18. Organocatalytically Generated Donor-Acceptor Cyclopropanes in Domino Reactions. One-Step Enantioselective Synthesis of Pyrrolo[1,2-a]quinolines.

    PubMed

    Sanchez-Diez, Eduardo; Vesga, Diana L; Reyes, Efraim; Uria, Uxue; Carrillo, Luisa; Vicario, Jose L

    2016-03-18

    An easy and straightforward procedure has been developed for the synthesis of highly enantioenriched pyrrolo[1,2-a]quinolines through a one-pot process that comprises a domino cyclopropane ring opening/aza-Michael/aldol reaction followed by acid-promoted lactamization. The key feature of the synthetic approach relies on the ability of conveniently functionalized cyclopropaneacetaldehydes to undergo organocatalytic activation by a chiral secondary amine that enables the catalytic generation of a donor-acceptor cyclopropane. This intermediate has the potential to undergo a ring opening that generates an electrophilic α,β-unsaturated iminium ion that subsequently reacts through the already mentioned domino sequence and in which stereochemical information is very efficiently transferred from the amine catalyst to the final products. Moreover, one of the alkoxycarbonyl moieties can be easily removed by standard hydrolysis/decarboxylation, providing access to the target adducts as single stereoisomers. PMID:26916408

  19. Formation of Lactic Acid from Cellulosic Biomass by Alkaline Hydrothermal Reaction

    NASA Astrophysics Data System (ADS)

    Yan, X.; Jini, F.; Kishita, A.; Enomoto, H.; Tohji, K.

    2008-02-01

    Glucose, as a model compound of cellulosic biomass, was used as a test material. Ca(OH)2 and NaOH were selected as alkali. Results showed that both NaOH and Ca(OH)2, can promote the formation of lactic acid in a hydrothermal reaction of glucose. In the case of the addition of NaOH, lactic acid was obtained with a good yield of 27% based on a carbon base at 300 °C for 60 s with a NaOH concentration of 2.5 M. In the case of the addition of Ca(OH)2, the highest yield of lactic acid is 20%, which occurred at 300 °C for 60 s with a Ca(OH)2 concentration of 0.32 M. The formation mechanisms of lactic acid from glucose were also discussed according to intermediate products identified. Lactic acid may be generated via formaldehyde, glycolaldehyde besides via the aldose having three carbon atoms in hydrothermal reaction which all formed by the reverse aldol condensation of hexoses.

  20. Early stage composition of SOA produced by ?-pinene/ozone reaction: ?-Acyloxyhydroperoxy aldehydes and acidic dimers

    NASA Astrophysics Data System (ADS)

    Witkowski, Bart?omiej; Gierczak, Tomasz

    2014-10-01

    Composition of the freshly formed secondary organic aerosol (SOA) generated by ozonolysis of cyclohexene, cyclohexene-d10 (model precursors) and ?-pinene was studied using liquid chromatography coupled to electrospray ionization tandem mass spectrometry (LC-ESI/MS2). SOA was generated in the flow-tube reactor under the following conditions: 22 ± 2 °C, 1 atm and reaction time was approx. 30 s. In an attempt to resolve the current ambiguities, regarding the structure of ?-pinene SOA nucleating agents, analytical methods for analysis of ?-acyloxyhydroperoxy aldehydes and oligomers containing carboxylic group were developed to study the potential nucleating agents. Negatively charged m/z 351, 341, 337, 357 and 367 ions corresponding to the acidic oligomers were detected in freshly formed ?-pinene SOA. For the first time, structures and formation mechanism for compounds detected as m/z 337 and 351 ions were proposed. Based on the model precursor analysis (cyclohexene and cyclohexene-d10) it was concluded that these compounds were most likely formed via aldol reaction of the lower molecular weight aerosol components. ?-Acyloxyhydroperoxy aldehydes were studied in the SOA samples using previously developed, novel method, based on the prediction of fragmentation spectrum for the compounds of interest. It was concluded that ?-acyloxyhydroperoxy aldehydes were not formed in significant quantities. Based on the obtained results, possible SOA formation and growth mechanism is discussed.

  1. The effects of interactions between proline and carbon nanostructures on organocatalysis in the Hajos-Parrish-Eder-Sauer-Wiechert reaction

    NASA Astrophysics Data System (ADS)

    Rance, G. A.; Khlobystov, A. N.

    2014-09-01

    The non-covalent interactions of S-(-)-proline with the surfaces of carbon nanostructures (fullerene, nanotubes and graphite) change the nucleophilic-electrophilic and acid-base properties of the amino acid, thus tuning its activity and selectivity in the organocatalytic Hajos-Parrish-Eder-Sauer-Wiechert (HPESW) reaction. Whilst our spectroscopy and microscopy measurements show no permanent covalent bonding between S-(-)-proline and carbon nanostructures, a systematic investigation of the catalytic activity and selectivity of the organocatalyst in the HPESW reaction demonstrates a clear correlation between the pyramidalisation angle of carbon nanostructures and the catalytic properties of S-(-)-proline. Carbon nanostructures with larger pyramidalisation angles have a stronger interaction with the nitrogen atom lone pair of electrons of the organocatalyst, thereby simultaneously decreasing the nucleophilicity and increasing the acidity of the organocatalyst. These translate into lower conversion rates but higher selectivities towards the dehydrated product of Aldol addition.The non-covalent interactions of S-(-)-proline with the surfaces of carbon nanostructures (fullerene, nanotubes and graphite) change the nucleophilic-electrophilic and acid-base properties of the amino acid, thus tuning its activity and selectivity in the organocatalytic Hajos-Parrish-Eder-Sauer-Wiechert (HPESW) reaction. Whilst our spectroscopy and microscopy measurements show no permanent covalent bonding between S-(-)-proline and carbon nanostructures, a systematic investigation of the catalytic activity and selectivity of the organocatalyst in the HPESW reaction demonstrates a clear correlation between the pyramidalisation angle of carbon nanostructures and the catalytic properties of S-(-)-proline. Carbon nanostructures with larger pyramidalisation angles have a stronger interaction with the nitrogen atom lone pair of electrons of the organocatalyst, thereby simultaneously decreasing the nucleophilicity and increasing the acidity of the organocatalyst. These translate into lower conversion rates but higher selectivities towards the dehydrated product of Aldol addition. Electronic supplementary information (ESI) available: Control experiments in the absence of carbon nanostructures and additional spectroscopic measurements and titrations are described in the ESI. See DOI: 10.1039/c4nr04009k

  2. Temperature- and pH-dependent aqueous-phase kinetics of the reactions of glyoxal and methylglyoxal with atmospheric amines and ammonium sulfate

    NASA Astrophysics Data System (ADS)

    Sedehi, Nahzaneen; Takano, Hiromi; Blasic, Vanessa A.; Sullivan, Kristin A.; De Haan, David O.

    2013-10-01

    Reactions of glyoxal (Glx) and methylglyoxal (MG) with primary amines and ammonium salts may produce brown carbon and N-containing oligomers in aqueous aerosol. 1H NMR monitoring of reactant losses and product appearance in bulk aqueous reactions were used to derive rate constants and quantify competing reaction pathways as a function of pH and temperature. Glx + ammonium sulfate (AS) and amine reactions generate products containing C-N bonds, with rates depending directly on pH: rate = (70 ± 60) M-1 s-1fAld [Glx]totfAm [Am]tot, where fAld is the fraction of aldehyde with a dehydrated aldehyde functional group, and fAm is the fraction of amine or ammonia that is deprotonated at a given pH. MG + amine reactions generate mostly aldol condensation products and exhibit less pH dependence: rate = 10[(0.36 ± 0.06) × pH - (3.6 ± 0.3)] M-1 s-1fAld [MG]tot [Am]tot. Aldehyde + AS reactions are less temperature-dependent (Ea = 18 ± 8 kJ mol-1) than corresponding amine reactions (Ea = 50 ± 11 kJ mol-1). Using aerosol concentrations of [OH] = 10-12 M, [amine]tot = [AS] = 0.1 M, fGlx = 0.046 and fMG = 0.09, we estimate that OH radical reactions are normally the major aerosol-phase sink for both dicarbonyl compounds. However, reactions with AS and amines together can account for up to 12 and 45% of daytime aerosol-phase glyoxal and methylglyoxal reactivity, respectively, in marine aerosol at pH 5.5. Reactions with AS and amines become less important in acidic or non-marine aerosol, but may still be significant atmospheric sources of brown carbon, imidazoles, and nitrogen-containing oligomers.

  3. Catalysis of Photochemical Reactions.

    ERIC Educational Resources Information Center

    Albini, A.

    1986-01-01

    Offers a classification system of catalytic effects in photochemical reactions, contrasting characteristic properties of photochemical and thermal reactions. Discusses catalysis and sensitization, examples of catalyzed reactions of excepted states, complexing ground state substrates, and catalysis of primary photoproducts. (JM)

  4. S(N)1-type substitution reactions of N-protected ?-hydroxytyrosine esters: stereoselective synthesis of ?-aryl and ?-alkyltyrosines.

    PubMed

    Wilcke, David; Herdtweck, Eberhardt; Bach, Thorsten

    2012-06-01

    The title compounds were prepared by aldol reaction of anisaldehyde and the respective N,N-dibenzyl glycinates. Deprotection of the nitrogen atom with Pearlman's catalyst delivered the unprotected ?-hydroxytyrosine esters, which were further N-protected as N,N-phthaloyl (Phth) and N-fluorenylmethylcarbonyloxy (Fmoc) derivatives. The Friedel-Crafts reaction with various arenes was studied employing these alcohols as electrophiles. It turned out that the facial diastereoselectivitiy depends on the nitrogen protecting group and on the ester group. The unprotected substrates (NH(2)) gave preferentially syn-products but the anti-selectivity increased when going from NHFmoc over NPhth to NBn(2). If the ester substituent was varied the syn-preference increased in the order Me < Et < iPr. The reactions were shown to be fully stereoconvergent and proceeded under kinetic product control. A model is suggested to explain the facial diastereoselectivity based on a conformationally locked benzylic cation intermediate. The reactions are preparatively useful for the N-unprotected isopropyl ester, which gave Friedel-Crafts alkylation products with good syn-selectivity (anti/syn=21:79 to 7:93), and for the N,N-dibenzyl-protected methyl ester, which led preferentially to anti-products (anti/syn=80:20 to >95:5). Upon acetylation of the latter compound to the respective acetate, Bi(OTf)(3) -catalyzed alkylation reactions became possible, in which silyl enol ethers served as nucleophiles. The respective alkylation products were obtained in high yield and with excellent anti-selectivitiy (anti/syn?95:5). PMID:22407877

  5. Leprosy type 1 reaction (formerly reversal reaction).

    PubMed

    Naafs, Bernard; van Hees, Colette L M

    2016-01-01

    Nerve damage leading to impairment and permanent disability is the major problem in the course of a leprosy infection. Most of the damage occurs during two types of leprosy reactions, type 1 reaction (T1R) and type 2 reaction (T2R). Timely and adequate treatment may prevent this damage. Particular T1R reactions, however, are often diagnosed too late and are even missed. Clinical symptoms and warning signs are therefore covered, as are the immunology and pathophysiology of nerve damage. The differences between upgrading and downgrading, old terms but still relevant, are explained. Methods to detect reactions and to monitor their treatment are given. Triggering factors, the mechanisms of the reactions, including autoimmunity, and the presence of physical compression are discussed. Treatment over the years is placed in its context, and based on this information a treatment schedule is recommended. PMID:26773622

  6. Synthesis of alcohols from carbon oxides and hydrogen. VIII. A temperature-programmed reaction study of n-butanal on a Zn-Cr-O catalyst

    SciTech Connect

    Lietti, L.; Botta, D.; Forzatti, P.; Mantica, E.; Tronconi, E.; Pasquon, I.

    1988-06-01

    The interaction of n-butanal with a Zn-Cr-O catalyst has been studied by temperature-programmed reaction. Using combined GC, GC-FTIR, and GC-MS techniques, a large number of desorption products have been identified, including 1-butanol, C/sub 8/ and C/sub 12/ aldehydes, C/sub 7/ and C/sub 8/ ketones, and C/sub 3/, C/sub 4/, and C/sub 7/ olefins, as well as CO/sub 2/, dienes, trienes, aromatics, and light hydrocarbons. The formation of most products is explained by assuming surface reactions of two classes of intermediate species originating from the adsorption of n-butanal and from the surface aldol-like condensation of two molecules of n-butanal. Results indicate that the Zn-Cr oxide catalyst is active in performing aldehyde condensation, hydrogenation, hydrolysis, dehydrogenation, decarboxylation, and dehydration, along with isomerization and cracking reactions. Different functionalities are associated with different temperature ranges. The detected chemical functionalities are discussed with respect to their relevance to the direct synthesis of methanol and higher alcohols from CO and H/sub 2/.

  7. The Glyoxal Clock Reaction

    ERIC Educational Resources Information Center

    Ealy, Julie B.; Negron, Alexandra Rodriguez; Stephens, Jessica; Stauffer, Rebecca; Furrow, Stanley D.

    2007-01-01

    Research on the glyoxal clock reaction has led to adaptation of the clock reaction to a general chemistry experiment. This particular reaction is just one of many that used formaldehyde in the past. The kinetics of the glyoxal clock makes the reaction suitable as a general chemistry lab using a Calculator Based Laboratory (CBL) or a LabPro. The…

  8. The Glyoxal Clock Reaction

    ERIC Educational Resources Information Center

    Ealy, Julie B.; Negron, Alexandra Rodriguez; Stephens, Jessica; Stauffer, Rebecca; Furrow, Stanley D.

    2007-01-01

    Research on the glyoxal clock reaction has led to adaptation of the clock reaction to a general chemistry experiment. This particular reaction is just one of many that used formaldehyde in the past. The kinetics of the glyoxal clock makes the reaction suitable as a general chemistry lab using a Calculator Based Laboratory (CBL) or a LabPro. The…

  9. Reaction mechanism of pyridoxal 5'-phosphate synthase. Detection of an enzyme-bound chromophoric intermediate.

    PubMed

    Raschle, Thomas; Arigoni, Duilio; Brunisholz, René; Rechsteiner, Helene; Amrhein, Nikolaus; Fitzpatrick, Teresa B

    2007-03-01

    Vitamin B6 is an essential metabolite in all organisms. De novo synthesis of the vitamin can occur through either of two mutually exclusive pathways referred to as deoxyxylulose 5-phosphate-dependent and deoxyxylulose 5-phosphate-independent. The latter pathway has only recently been discovered and is distinguished by the presence of two genes, Pdx1 and Pdx2, encoding the synthase and glutaminase subunit of PLP synthase, respectively. In the presence of ammonia, the synthase alone displays an exceptional polymorphic synthetic ability in carrying out a complex set of reactions, including pentose and triose isomerization, imine formation, ammonia addition, aldol-type condensation, cyclization, and aromatization, that convert C3 and C5 precursors into the cofactor B6 vitamer, pyridoxal 5'-phosphate. Here, employing the Bacillus subtilis proteins, we demonstrate key features along the catalytic path. We show that ribose 5-phosphate is the preferred C5 substrate and provide unequivocal evidence that the pent(ul)ose phosphate imine occurs at lysine 81 rather than lysine 149 as previously postulated. While this study was under review, corroborative crystallographic evidence has been provided for imine formation with the corresponding lysine group in the enzyme from Thermotoga maritima (Zein, F., Zhang, Y., Kang, Y.-N., Burns, K., Begley, T. P., and Ealick, S. E. (2006) Biochemistry 45, 14609-14620). We have detected an unanticipated covalent reaction intermediate that occurs subsequent to imine formation and is dependent on the presence of Pdx2 and glutamine. This step most likely primes the enzyme for acceptance of the triose sugar, ultimately leading to formation of the pyridine ring. Two alternative structures are proposed for the chromophoric intermediate, both of which require substantial modifications of the proposed mechanism. PMID:17189272

  10. Oxygen-dependent fragmentation reactions during the degradation of 1-deoxy-D-erythro-hexo-2,3-diulose.

    PubMed

    Voigt, Michael; Smuda, Mareen; Pfahler, Christoph; Glomb, Marcus A

    2010-05-12

    With this work, we report on further insights into the chemistry of 1-deoxy-D-erythro-hexo-2,3-diulose (1-deoxyglucosone, 1-DG). This alpha-dicarbonyl plays an important role as a highly reactive intermediate in the Maillard chemistry of hexoses. Degradation of 1-DG in the presence of the amino acid l-alanine led to the formation of several products. Lactic acid and glyceric acid were found to be major degradation products. Their formation was dependent on the presence of oxygen. Therefore, a mechanism is postulated based on oxidation leading to a tricarbonyl intermediate. Carbonyl cleavage of this structure should then give rise to carboxylic acids. This mechanism was supported by the isotope distribution observed during degradation of different (13)C-labeled D-glucose isotopomers. Furthermore, we identified 3,5-dihydroxy-6-methyl-2,3-dihydro-4H-pyran-4-one (gamma-pyranone) to be capable of rehydration forming 1-DG to a minor extent and therefore leading to the same degradation products. The formation of carboxylic acids from gamma-pyranone was also dependent on the presence of oxygen in agreement with the postulated oxidative fragmentation. Finally, we investigated the formation of aldehydes expected as retro-aldol products formed within the degradation of 1-DG. Results seemed to rule out this reaction as an important degradation pathway under the conditions investigated herein. PMID:20441226

  11. Microfluidic chemical reaction circuits

    SciTech Connect

    Lee, Chung-cheng; Sui, Guodong; Elizarov, Arkadij; Kolb, Hartmuth C.; Huang, Jiang; Heath, James R.; Phelps, Michael E.; Quake, Stephen R.; Tseng, Hsian-rong; Wyatt, Paul; Daridon, Antoine

    2012-06-26

    New microfluidic devices, useful for carrying out chemical reactions, are provided. The devices are adapted for on-chip solvent exchange, chemical processes requiring multiple chemical reactions, and rapid concentration of reagents.

  12. Microscale Thermite Reactions.

    ERIC Educational Resources Information Center

    Arnaiz, Francisco J.; Aguado, Rafael; Arnaiz, Susana

    1998-01-01

    Describes the adaptation of thermite (aluminum with metal oxides) reactions from whole-class demonstrations to student-run micro-reactions. Lists detailed directions and possible variations of the experiment. (WRM)

  13. Anaphylaxis-Like Reactions

    MedlinePLUS

    ... Clinical Immunology View full profile Anaphylaxis: Anaphylaxis-Like Reactions When exposed to a foreign substance, some people ... the same as for anaphylaxis. More Anaphylaxis-Like Reactions Information Back to Anaphylaxis Reviewed on 7/12 ...

  14. Allergic reactions (image)

    MedlinePLUS

    Allergic reaction is a sensitivity to a specific substance, called an allergen, that is contacted through the skin, inhaled into the lungs, swallowed or injected. The body's reaction to an allergen can be mild, such as ...

  15. Classification of clock reactions.

    PubMed

    Horváth, Attila K; Nagypál, István

    2015-02-23

    Autocatalytic systems are sometimes designated as clock reactions or reactions that exhibit clock behavior. To resolve the recent dispute over the term clock reaction, we describe a new approach to classify systems featuring clock behavior into three distinct groups: substrate-depletive clock reactions, autocatalysis-driven clock reactions, and systems that have pseudo clock behavior. Many of the well-known classical and recently discovered reactions can conveniently be put into these categories. We also provide a convincing argument for classifying some autocatalytic processes as clock reactions, but it does not necessarily mean that all autocatalytic processes should be classified as autocatalysis-driven clock reactions. This classification can be conveniently performed if the kinetic nature of the given system has been completely elucidated and understood. PMID:25425415

  16. Symmetry-Driven Strategy for the Assembly of the Core Tetracycle of (+)-Ryanodine: Synthetic Utility of a Cobalt-Catalyzed Olefin Oxidation and α-Alkoxy Bridgehead Radical Reaction.

    PubMed

    Nagatomo, Masanori; Hagiwara, Koji; Masuda, Kengo; Koshimizu, Masaki; Kawamata, Takahiro; Matsui, Yuki; Urabe, Daisuke; Inoue, Masayuki

    2016-01-01

    Ryanodine (1) is a potent modulator of intracellular calcium release channels, designated as ryanodine receptors. The exceptionally complex molecular architecture of 1 comprises a highly oxygenated pentacyclic system with eleven contiguous stereogenic centers, which makes it a formidable target for organic synthesis. We identified the embedded C2 -symmetric tricyclic substructure within 1. This specific recognition permitted us to design a concise synthetic route to enantiopure tricycle 9 by utilizing a series of pairwise functionalizations. The four tetrasubstituted carbon centers of 9 were effectively constructed by three key reactions, a dearomatizing Diels-Alder reaction, the kinetic resolution of the obtained racemic 14 through asymmetric methanolysis, and the transannular aldol reaction of the eight-membered diketone 10. A new combination of cobalt-catalyzed hydroperoxidation and NfF-promoted elimination enabled conversion of the hindered olefin of 9 into the corresponding ketone, thus realizing the desymmetrization. Finally, the tetrasubstituted carbon was stereospecifically installed by utilizing the α-alkoxy bridgehead radical to deliver the core tetracycle 7 with the six contiguous tetrasubstituted carbon centers. Consequently, the present work not only accomplishes efficient assembly of four out of the five fused rings of 1, but also develops two new powerful methodologies: two-step ketone formation and bridgehead radical reaction. PMID:26616151

  17. Synthesis and Applications of Silyl 2-Methylprop-2-ene-1-sulfinates in Preparative Silylation and GC-Derivatization Reactions of Polyols and Carbohydrates.

    PubMed

    Marković, Dean; Tchawou, Wandji Augustin; Novosjolova, Irina; Laclef, Sylvain; Stepanovs, Dmitrijs; Turks, Māris; Vogel, Pierre

    2016-03-14

    Trimethylsilyl, triethylsilyl, tert-butyldimethylsilyl, and triisopropylsilyl 2-methylprop-2-ene-1-sulfinates were prepared through (CuOTf)2 ⋅C6 H6 -catalyzed sila-ene reactions of the corresponding methallylsilanes with SO2 at 50 °C. Sterically hindered, epimerizable, and base-sensitive alcohols gave the corresponding silyl ethers in high yields and purities at room temperature and under neutral conditions. As the byproducts of the silylation reaction (SO2 +isobutylene) are volatile, the workup was simplified to solvent evaporation. The developed method can be employed for the chemo- and regioselective semiprotection of polyols and glycosides and for the silylation of unstable aldols. The high reactivity of the developed reagents is shown by the synthesis of sterically hindered per-O-tert-butyldimethylsilyl-α-d-glucopyranose, the X-ray crystallographic analysis of which is the first for a per-O-silylated hexopyranose. The per-O-silylation of polyols, hydroxy carboxylic acids, and carbohydrates with trimethylsilyl 2-methylprop-2-ene-1-sulfinate was coupled with the GC analysis of nonvolatile polyhydroxy compounds both qualitatively and quantitatively. PMID:26864218

  18. The polymorphic phototest reaction

    SciTech Connect

    Jansen, C.

    1982-09-01

    One hundred tem patients with polymorphic light eruption (PMLE) and 58 control subjects were tested with an overdose of erythemogenic radiation. A morphologically abnormal phototest reaction was demonstrable in 72% of the patients with PMLE and in 9% of the control subjects. On the average, a dose of 3.8 times the patient's minimal erythemal dose was needed to produce the reaction. The most common findings in positive phototest reaction sites were edema and itching. A medium-pressure mercury lamp was shown to be as effective as a xenon arc lamp in producing the phototest reaction. The time of the reaction varied considerably in different patients, and frequent inspections of test sites were necessary to detect positive phototest reactions. When properly performed and interpreted, phototesting is a valuable diagnostic procedure for PMLE.

  19. Radical reactions of borohydrides.

    PubMed

    Kawamoto, Takuji; Ryu, Ilhyong

    2014-12-28

    Borohydrides are an important class of reagents in both organic and inorganic chemistry. Though popular as hydride-transfer reagents for reduction, since earlier work from the 1970s, borohydride reagents have also been known to serve as hydrogen-transfer reagents. In pursuit of greener tin hydride substitutes, recent progress has been made to mediate radical C-C bond forming reactions, including Giese reactions, radical carbonylation and addition to HCHO reactions, with borohydride reagents. This review article focuses on state-of-the-art borohydride based radical reactions, also covering earlier work, kinetics and some DFT calculations with respect to the hydrogen transfer mechanism. PMID:25349957

  20. Sleeve reaction chamber system

    DOEpatents

    Northrup, M. Allen (Berkeley, CA); Beeman, Barton V. (San Mateo, CA); Benett, William J. (Livermore, CA); Hadley, Dean R. (Manteca, CA); Landre, Phoebe (Livermore, CA); Lehew, Stacy L. (Livermore, CA); Krulevitch, Peter A. (Pleasanton, CA)

    2009-08-25

    A chemical reaction chamber system that combines devices such as doped polysilicon for heating, bulk silicon for convective cooling, and thermoelectric (TE) coolers to augment the heating and cooling rates of the reaction chamber or chambers. In addition the system includes non-silicon-based reaction chambers such as any high thermal conductivity material used in combination with a thermoelectric cooling mechanism (i.e., Peltier device). The heat contained in the thermally conductive part of the system can be used/reused to heat the device, thereby conserving energy and expediting the heating/cooling rates. The system combines a micromachined silicon reaction chamber, for example, with an additional module/device for augmented heating/cooling using the Peltier effect. This additional module is particularly useful in extreme environments (very hot or extremely cold) where augmented heating/cooling would be useful to speed up the thermal cycling rates. The chemical reaction chamber system has various applications for synthesis or processing of organic, inorganic, or biochemical reactions, including the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction.

  1. Tissue Reaction and Biomechanics.

    PubMed

    Melsen, Birte

    2016-01-01

    Tissue reaction to orthodontic force has been a subject of research with the purpose of providing the orthodontists with information necessary for the application of a force system that can generate a maximum of tooth movement and modeling of the alveolar process with a minimum of damage. Traditionally, the studies of bone biological reactions have been distinguishable from those performed by bone biologists. This has led to a controversy regarding both the terminology and perception of the reaction to mechanical perturbation. The present chapter, with its basis in bone biology, surveys the attempts by orthodontists to optimize the tissue reaction and shorten treatment time. PMID:26599116

  2. Cu(II)-Gd(III) cryogenic magnetic refrigerants and Cu8Dy9 single-molecule magnet generated by in situ reactions of picolinaldehyde and acetylpyridine: experimental and theoretical study.

    PubMed

    Liu, Jun-Liang; Lin, Wei-Quan; Chen, Yan-Cong; Gómez-Coca, Silvia; Aravena, Daniel; Ruiz, Eliseo; Leng, Ji-Dong; Tong, Ming-Liang

    2013-12-16

    A series of heterometallic [Ln(III)(x)Cu(II)(y)] complexes, [Gd2Cu2]n (1), [Gd4Cu8] (2), [Ln9Cu8] (Ln=Gd, 3·Gd; Ln=Dy, 3·Dy), were successfully synthesized by a one-pot route at room temperature with three kinds of in situ carbonyl-related reactions: Cannizzaro reaction, aldol reaction, and oxidation. This strategy led to dysprosium analogues that behaved as single-molecule magnets (SMMs) and gadolinium analogues that showed significant magnetocaloric effect (MCE). In this study a numerical DFT approach is proposed by using pseudopotentials to calculate the exchange coupling constants in three polynuclear [Gd(x)Cu(y)] complexes; with these values exact diagonalization or quantum Monte Carlo simulations have been performed to calculate the variation of the magnetic entropy involved in the MCE. For the [Dy9Cu8] complexes, local magnetic properties of the Dy(III) centers have been determined by using the CASSCF+RASSI method. PMID:24265054

  3. Hydrogen evolution reaction catalyst

    DOEpatents

    Subbaraman, Ram; Stamenkovic, Vojislav; Markovic, Nenad; Tripkovic, Dusan

    2016-02-09

    Systems and methods for a hydrogen evolution reaction catalyst are provided. Electrode material includes a plurality of clusters. The electrode exhibits bifunctionality with respect to the hydrogen evolution reaction. The electrode with clusters exhibits improved performance with respect to the intrinsic material of the electrode absent the clusters.

  4. Applications of Reaction Rate

    ERIC Educational Resources Information Center

    Cunningham, Kevin

    2007-01-01

    This article presents an assignment in which students are to research and report on a chemical reaction whose increased or decreased rate is of practical importance. Specifically, students are asked to represent the reaction they have chosen with an acceptable chemical equation, identify a factor that influences its rate and explain how and why it…

  5. Chemical Reaction Problem Solving.

    ERIC Educational Resources Information Center

    Veal, William

    1999-01-01

    Discusses the role of chemical-equation problem solving in helping students predict reaction products. Methods for helping students learn this process must be taught to students and future teachers by using pedagogical skills within the content of chemistry. Emphasizes that solving chemical reactions should involve creative cognition where…

  6. Degradations and Rearrangement Reactions

    NASA Astrophysics Data System (ADS)

    Zhang, Jianbo

    This section deals with recent reports concerning degradation and rearrangement reactions of free sugars as well as some glycosides. The transformations are classified in chemical and enzymatic ways. In addition, the Maillard reaction will be discussed as an example of degradation and rearrangement transformation and its application in current research in the fields of chemistry and biology.

  7. THE CUTANEOUS TRICHOPHYTIN REACTION

    PubMed Central

    Amberg, Samuel

    1910-01-01

    There exists a far-reaching analogy between the cutaneous trichophytin reaction and the cutaneous tuberculin reaction. Both indicate that the organism is the seat of a definite infection or that it has passed through such an infection. Both may persist for a long time after the active disease has come to rest, indicating that the infection has left the organism in a state of altered reactivity—allergy. Under certain conditions both may be of diagnostic value, but since the reaction persists for a long time after the infection has passed, the negative reaction may be of greater value, excluding the existence of a specific infection. The analogy of the trichophytin reaction with the tuberculin reaction is not only limited to the obvious clinical manifestations, but, as in the tuberculin reaction, it can be shown that with uniform concentration of antibody, the intensity of the reaction is dependent on the concentration of the trichophytin. A tentative explanation of the halo formation is offered, based on a rapidly renewed formation of antibody stimulated probably by the entrance of a small amount of allergen into the general circulation. PMID:19867336

  8. Oscillating Reactions: Two Analogies

    ERIC Educational Resources Information Center

    Petruševski, Vladimir M.; Stojanovska, Marina I.; Šoptrajanov, Bojan T.

    2007-01-01

    Oscillating chemical reactions are truly spectacular phenomena, and demonstrations are always appreciated by the class. However, explaining such reactions to high school or first-year university students is problematic, because it may seem that no acceptable explanation is possible unless the students have profound knowledge of both physical…

  9. Clock Reaction: Outreach Attraction

    ERIC Educational Resources Information Center

    Carpenter, Yuen-ying; Phillips, Heather A.; Jakubinek, Michael B.

    2010-01-01

    Chemistry students are often introduced to the concept of reaction rates through demonstrations or laboratory activities involving the well-known iodine clock reaction. For example, a laboratory experiment involving thiosulfate as an iodine scavenger is part of the first-year general chemistry laboratory curriculum at Dalhousie University. With…

  10. Clock Reaction: Outreach Attraction

    ERIC Educational Resources Information Center

    Carpenter, Yuen-ying; Phillips, Heather A.; Jakubinek, Michael B.

    2010-01-01

    Chemistry students are often introduced to the concept of reaction rates through demonstrations or laboratory activities involving the well-known iodine clock reaction. For example, a laboratory experiment involving thiosulfate as an iodine scavenger is part of the first-year general chemistry laboratory curriculum at Dalhousie University. With…

  11. Precompound Reactions: Basic Concepts

    SciTech Connect

    Weidenmueller, H. A.

    2008-04-17

    Because of the non-zero nuclear equilibration time, the compound-nucleus scattering model fails when the incident energy exceeds 10 or 20 MeV, and precompound reactions become important. Basic ideas used in the quantum-statistical approaches to these reactions are described.

  12. Applications of Reaction Rate

    ERIC Educational Resources Information Center

    Cunningham, Kevin

    2007-01-01

    This article presents an assignment in which students are to research and report on a chemical reaction whose increased or decreased rate is of practical importance. Specifically, students are asked to represent the reaction they have chosen with an acceptable chemical equation, identify a factor that influences its rate and explain how and why it…

  13. Chemical Reaction Problem Solving.

    ERIC Educational Resources Information Center

    Veal, William

    1999-01-01

    Discusses the role of chemical-equation problem solving in helping students predict reaction products. Methods for helping students learn this process must be taught to students and future teachers by using pedagogical skills within the content of chemistry. Emphasizes that solving chemical reactions should involve creative cognition where…

  14. Nuclear Reaction Data Centers

    SciTech Connect

    McLane, V.; Nordborg, C.; Lemmel, H.D.; Manokhin, V.N.

    1988-01-01

    The cooperating Nuclear Reaction Data Centers are involved in the compilation and exchange of nuclear reaction data for incident neutrons, charged particles and photons. Individual centers may also have services in other areas, e.g., evaluated data, nuclear structure and decay data, reactor physics, nuclear safety; some of this information may also be exchanged between interested centers. 20 refs., 1 tab.

  15. High Resolution Reaction Intermediates of rabbit Muscle Fructose-1,6-bisphosphate Aldolase: Substrate Cleavage and Induced Fit

    SciTech Connect

    St-Jean,M.; Lafrance-Vanasse, J.; Liotard, B.; Sygusch, J.

    2005-01-01

    Crystal structures were determined to 1.8-Angstrom resolution of the glycolytic enzyme fructose-1, 6-bis(phosphate) aldolase trapped in complex with its substrate and a competitive inhibitor, mannitol-1, 6-bis(phosphate). The enzyme substrate complex corresponded to the postulated Schiff base intermediate and has reaction geometry consistent with incipient C3-C4 bond cleavage catalyzed by Glu-187, which is adjacent to the Schiff base forming Lys-229. Atom arrangement about the cleaved bond in the reaction intermediate mimics a pericyclic transition state occurring in non-enzymatic aldol condensations. Lys-146 hydrogen bonds the substrate C4 hydroxyl and assists substrate cleavage by stabilizing the developing negative charge on the C4 hydroxyl during proton abstraction. Mannitol-1, 6-bis(phosphate) forms a non-covalent complex in the active site whose binding geometry mimics the covalent carbinolamine precursor. Glu-187 hydrogen bonds the C2 hydroxyl of the inhibitor in the enzyme complex substantiating a proton transfer role by Glu-187 in catalyzing the conversion of the carbinolamine intermediate to Schiff base. Modeling of the acyclic substrate configuration into the active site shows Glu-187, in acid form, hydrogen bonding both substrate C2 carbonyl and C4 hydroxyl, thereby aligning the substrate ketose for nucleophilic attack by Lys-229. The multi-functional role by Glu-187 epitomizes a canonical mechanistic feature conserved in Schiff base forming aldolases catalyzing carbohydrate metabolism. Trapping of tagatose-1, 6-bis(phosphate), a diastereoisomer of fructose-1, 6-bis(phosphate), displayed stereospecific discrimination and reduced ketohexose binding specificity. Each ligand induces homologous conformational changes in two adjacent a-helical regions that promote phosphate binding in the active site.

  16. Hypersensitivity reactions to corticosteroids.

    PubMed

    Vatti, Rani R; Ali, Fatima; Teuber, Suzanne; Chang, Christopher; Gershwin, M Eric

    2014-08-01

    Hypersensitivity reactions to corticosteroids (CS) are rare in the general population, but they are not uncommon in high-risk groups such as patients who receive repeated doses of CS. Hypersensitivity reactions to steroids are broadly divided into two categories: immediate reactions, typically occurring within 1 h of drug administration, and non-immediate reactions, which manifest more than an hour after drug administration. The latter group is more common. We reviewed the literature using the search terms "hypersensitivity to steroids, adverse effects of steroids, steroid allergy, allergic contact dermatitis, corticosteroid side effects, and type I hypersensitivity" to identify studies or clinical reports of steroid hypersensitivity. We discuss the prevalence, mechanism, presentation, evaluation, and therapeutic options in corticosteroid hypersensitivity reactions. There is a paucity of literature on corticosteroid allergy, with most reports being case reports. Most reports involve non-systemic application of corticosteroids. Steroid hypersensitivity has been associated with type I IgE-mediated allergy including anaphylaxis. The overall prevalence of type I steroid hypersensitivity is estimated to be 0.3-0.5%. Allergic contact dermatitis (ACD) is the most commonly reported non-immediate hypersensitivity reaction and usually follows topical CS application. Atopic dermatitis and stasis dermatitis of the lower extremities are risk factors for the development of ACD from topical CS. Patients can also develop hypersensitivity reactions to nasal, inhaled, oral, and parenteral CS. A close and detailed evaluation is required for the clinician to confirm the presence of a true hypersensitivity reaction to the suspected drug and choose the safest alternative. Choosing an alternative CS is not only paramount to the patient's safety but also ameliorates the worry of developing an allergic, and potentially fatal, steroid hypersensitivity reaction. This evaluation becomes especially important in high-risk groups where steroids are a life-saving treatment. The assessment should be done when the patient's underlying condition is in a quiescent state. PMID:23567983

  17. Yb(OTf)3-Mediated Access to Furans from ?-Ketothioamides via Eschenmoser Sulfide Contraction Reaction.

    PubMed

    Li, Ming; Kong, Xiang-Jing; Wen, Li-Rong

    2015-12-18

    A mild and straightforward synthetic protocol for construction of a furan skeleton promoted by Yb(OTf)3 from ?-ketothioamides and arylglyoxals has been developed at room temperature. Importantly, this protocol involves a tandem sequence that includes aldol condensation, N-cyclization, ring opening, O-cyclization, S-cyclization, and Eschenmoser sulfide contraction. PMID:26551164

  18. gem-Difluoroolefination of diaryl ketones and enolizable aldehydes with difluoromethyl 2-pyridyl sulfone: new insights into the Julia-Kocienski reaction.

    PubMed

    Gao, Bing; Zhao, Yanchuan; Hu, Mingyou; Ni, Chuanfa; Hu, Jinbo

    2014-06-16

    The direct conversion of diaryl ketones and enolizable aliphatic aldehydes into gem-difluoroalkenes has been a long-standing challenge in organofluorine chemistry. Herein, we report efficient strategies to tackle this problem by using difluoromethyl 2-pyridyl sulfone as a general gem-difluoroolefination reagent. The gem-difluoroolefination of diaryl ketones proceeds by acid-promoted Smiles rearrangement of the carbinol intermediate; the gem-difluoroolefination is otherwise difficult to achieve through a conventional Julia-Kocienski olefination protocol under basic conditions due to the retro-aldol type decomposition of the key intermediate. Efficient gem-difluoroolefination of aliphatic aldehydes was achieved by the use of an amide base generated in situ (from CsF and tris(trimethylsilyl)amine), which diminishes the undesired enolization of aliphatic aldehydes and provides a powerful synthetic method for chemoselective gem-difluoroolefination of multi-carbonyl compounds. Our results provide new insights into the mechanistic understanding of the classical Julia-Kocienski reaction. PMID:24807811

  19. Adverse reactions to sulfites

    PubMed Central

    Yang, William H.; Purchase, Emerson C.R.

    1985-01-01

    Sulfites are widely used as preservatives in the food and pharmaceutical industries. In the United States more than 250 cases of sulfite-related adverse reactions, including anaphylactic shock, asthmatic attacks, urticaria and angioedema, nausea, abdominal pain and diarrhea, seizures and death, have been reported, including 6 deaths allegedly associated with restaurant food containing sulfites. In Canada 10 sulfite-related adverse reactions have been documented, and 1 death suspected to be sulfite-related has occurred. The exact mechanism of sulfite-induced reactions is unknown. Practising physicians should be aware of the clinical manifestations of sulfite-related adverse reactions as well as which foods and pharmaceuticals contain sulfites. Cases should be reported to health officials and proper advice given to the victims to prevent further exposure to sulfites. The food industry, including beer and wine manufacturers, and the pharmaceutical industry should consider using alternative preservatives. In the interim, they should list any sulfites in their products. PMID:4052897

  20. Chemisorption And Precipitation Reactions

    EPA Science Inventory

    The transport and bioavailability of chemical components within soils is, in part, controlled by partitioning between solids and solution. General terms used to describe these partitioning reactions include chemisorption and precipitation. Chemisorption is inclusive of the suit...

  1. Untoward penicillin reactions

    PubMed Central

    Guthe, T.; Idsöe, O.; Willcox, R. R.

    1958-01-01

    The literature on untoward reactions following the administration of penicillin is reviewed. These reactions, including a certain number of deaths which have been reported, are of particular interest to health administrations and to WHO in view of the large-scale programmes for controlling the treponematoses which are now under way—programmes affecting millions of people in many parts of the world. The most serious problems are anaphylactic sensitivity phenomena and superinfection or cross-infection with penicillin-resistant organisms, and the reactions involved range in intensity from the mildest to the fatal; the incidence of the latter is estimated at 0.1-0.3 per million injections. The authors point out that with increasing use of penicillin, more persons are likely to become sensitized and the number of reactions can therefore be expected to rise. The best prevention against such an increase is the restriction of the unnecessary use of penicillin. PMID:13596877

  2. Reactor for exothermic reactions

    DOEpatents

    Smith, Jr., Lawrence A. (Bellaire, TX); Hearn, Dennis (Houston, TX); Jones, Jr., Edward M. (Friendswood, TX)

    1993-01-01

    A liquid phase process for oligomerization of C.sub.4 and C.sub.5 isoolefins or the etherification thereof with C.sub.1 to C.sub.6 alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120.degree. to 300.degree. F. Wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

  3. Reactor for exothermic reactions

    DOEpatents

    Smith, L.A. Jr.; Hearn, D.; Jones, E.M. Jr.

    1993-03-02

    A liquid phase process is described for oligomerization of C[sub 4] and C[sub 5] isoolefins or the etherification thereof with C[sub 1] to C[sub 6] alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120 to 300 F. Wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

  4. An Illuminating Reaction.

    ERIC Educational Resources Information Center

    Matthews, Catherine E.

    1996-01-01

    Describes the use of carbide lights as an excellent mechanism for introducing or reviewing many basic chemistry concepts including elements and compounds, endothermic and exothermic reactions, physical and chemical changes, and balancing chemical equations. (JRH)

  5. Reaction wheel assembly

    NASA Technical Reports Server (NTRS)

    1976-01-01

    The fabrication and testing of three reaction wheels with associated drive and system monitoring electronics and brushless dc spin motors are discussed; the wheels are intended for use in a teleoperator simulator. Test results are included as graphs.

  6. Iodine Clock Reaction.

    ERIC Educational Resources Information Center

    Mitchell, Richard S.

    1996-01-01

    Describes a combination of solutions that can be used in the study of kinetics using the iodine clock reaction. The combination slows down degradation of the prepared solutions and can be used successfully for several weeks. (JRH)

  7. Jets in hadronic reactions

    SciTech Connect

    Paige, F.E.

    1983-01-01

    Recent experimental data on the properties of jets in hadronic reactions are reviewed and compared with theoretical expectations. Jets are clearly established as the dominant process for high E/sub T/ events in hadronic reactions. The cross section and the other properties of these events are in qualitative and even semiquantitative agreement with expectations based on perturbative QCD. However, we can not yet make precise tests of QCD, primarily because there are substantial uncertainties in the theoretical calculations. 45 references. (WHK)

  8. The black reaction.

    PubMed

    Pannese, E

    1996-01-01

    Camillo Golgi (1843-1926) invented the black reaction in 1873, when he was head physician at the hospice for old people in Abbiategrasso, near Milan. Unlike the procedures that were available before its invention, the black reaction was able to reveal neurons in their entirety, i.e., with all their processes. This weighty event at first passed unnoticed. The first stirring of interest in the black reaction outside Italy began in 1885. The reasons the Golgi technique took so long to receive wide international attention are here analyzed. After it became known, the black reaction was widely employed for almost 30 years, during which time it was responsible for bringing about major advances in our knowledge of the microscopic anatomy of the nervous system, as well as in other fields of study. A number of results obtained by other researchers with the black reaction were vitally important for establishing the neuron theory. In the period between the two World Wars, the Golgi technique was almost forgotten, but returned in vogue once more around the middle of the 20th century following the introduction of the electron microscope to neurocytological research. One-hundred and twenty years after its invention, the black reaction is still widely employed, not only in combination with electron microscopy, but also as an autonomous technique for light microscope studies on the organization of the nervous system in normal conditions and after experimental manipulations. PMID:8973838

  9. Hypersensitivity reactions from taxol.

    PubMed

    Weiss, R B; Donehower, R C; Wiernik, P H; Ohnuma, T; Gralla, R J; Trump, D L; Baker, J R; Van Echo, D A; Von Hoff, D D; Leyland-Jones, B

    1990-07-01

    Taxol is an antitumor agent in clinical trial that has been shown to have activity against advanced ovarian carcinoma and melanoma. Hypersensitivity reactions (HSRs) have been one of the toxicities observed with administration of this drug. Of 301 patients treated, 32 patients have had definite (27 patients) or possible (five patients) hypersensitivity reactions to taxol. All but one patient had the reaction from the first or second exposure to this agent. Reactions occurred at a variety of doses and were characterized most frequently by dyspnea, hypotension, bronchospasm, urticaria, and erythematous rashes. Thirteen (41%) patients had received premedication designed to prevent such toxicity; nevertheless, they sustained HSRs. Prolonging the drug infusion appears to have somewhat reduced, but not obviated, the risk of HSRs. The cause (taxol itself or its excipient Cremophor EL; Badische Anilin und Soda-Fabrik AG [BASF], Ludwigshafen, Federal Republic of Germany) and the mechanism of these reactions to taxol are unknown. We provide guidelines to prevent or minimize such toxicity and treat reactions if they still occur. PMID:1972736

  10. [Reactional status of leprosy].

    PubMed

    Alonso, A M

    1975-01-01

    Reactional leprosy is studied according to its clinical forms A) Lepromatous a) Acute lepromatization: encroaching and invasive nature; the patient becomes more and more lepromatous ; bad prognosis. b) Erythema nodosum: "contusiform dermatitis"; variable prognosis not so bad as it is in the preceding case; allergic nature and its evolution is usually detained and therapeutics efficient. c) Erythema multiform. d) Lucio's phenomenon: vascular lesions and consequently necrosis as a complication of the "erythema necrotisans" (beautiful leprosy). B) Tuberculoid Reactional tuberculoid is the only one in this benign type, the Mitsuda's test must always be positive and prognosis consequently good. C) Dimorphous or "Borderline" whose Mitsuda's test is mostly negative, sometimes positive, but not stable. The lesions may stimulate the tuberculoid leprids but they invade mucous membranes, are impregnated by pigmentation, may present the Unna's band, and other characteristics of the Lepromatous type. Are associated (fever, asthenia and emaciation). Prognosis not very good, because of the possibility of lepromatization, according to its tendency. Evolution slower and frequent relapses. Besides there are nodular lesions. Pathogeny 1) Perifocal allergic reaction (Jadassohn). Similar to epituberculosis and Herxheimer reaction. 2) Septicemia. Sensitized tissues inside or outside the lesions, are invaded by the bacilli and so the allergic reaction takes place. Even without culture resources, Mycobacterium leprae has been found in the blood by direct examination. 3) Autoimmunization (Waldenstrom, Matthews and Trantman, 1965). Based upon the similarity between both humoral syndromes, in leprosy reactions and collagenous, diseases, as to: hypergammaglobulins, hypercryoproteins, antigammaglobulins, serological reactions (Wassermann, Kahn, Kline, VDRL) positives, Antistreptolysin O, protein C reactive, antinuclear factors, latex and Wadler-Rose test positives (rheumatoid tests) lowering of complement. If leprosy reaction is like this, it should be the less agressive of the autoimmune diseases. a) Its eruptions are cyclic not of long standing duration, as a general rule. b) Its prognosis has been recognized as good, except lately, because of the use of corticoid therapy which has been fatal, in many cases. After some years the leprosy reaction cures spontaneously. Treatment (see article) PMID:1241072

  11. Bacterial metabolism of naphthalene: Construction and use of recombinant bacteria to study ring cleavage of 1,2-dihydroxynaphthalene and subsequent reactions

    SciTech Connect

    Eaton, R.W.; Chapman, P.J.

    1992-01-01

    The reactions involved in the bacterial metabolism of naphthalene to salicylate have been reinvestigated by using recombinant bacteria carrying genes cloned from plasmid NAH7. When intact cells of Pseudomonas aeruginosa PAO1 carrying DNA fragments encoding the first three enzymes of the pathway were incubated with naphthalene, they formed products of the dioxygenase-catalyzed ring cleavage of 1,2-dihydroxynaphthalene. These products were separated by chromatography on Sephadex G-25 and were identified by (1)H and (13)C nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry as 2-hydroxychromene-2-carboxylate (HCCA) and trans-o-hydroxybenzylidenepyruvate (tHBPA). HCCA was detected as the first reaction product in these incubation mixtures by its characteristic UV spectrum, which slowly changed to a spectrum indicative of an equilibrium mixture of HCCA and tHBPA. Isomerization of either purified product occurred slowly and spontaneously to give an equilibrium mixture of essentially the same composition. tHBPA is also formed from HCCA by the action of an isomerase enzyme encoded by plasmid NAH7. The gene encoding this enzyme, nahD, was cloned on a 1.95-kb KpnI-Bg/II fragment. Extracts of Escherichia coli JM109 carrying this fragment catalyzed the rapid equilibration of HCCA and tHBPA. Metabolism of tHBPA to salicylaldehyde by hydration and aldol cleavage is catalyzed by a single enzyme encoded by a 1-kb MluI-StuI restriction fragment. A mechanism for the hydratase-aldolase-catalyzed reaction is proposed. (Copyright (c) 1992 American Society for Microbiology.)

  12. Thermal decomposition of specifically phosphorylated D-glucoses and their role in the control of the Maillard reaction.

    PubMed

    Yaylayan, Varoujan A; Machiels, David; Istasse, Louis

    2003-05-21

    One of the main shortcomings of the information available on the Maillard reaction is the lack of knowledge to control the different pathways, especially when it is desired to direct the reaction away from the formation of carcinogenic and other toxic substances to more aroma and color generation. The use of specifically phosphorylated sugars may impart some elements of control over the aroma profile generated by the Maillard reaction. Thermal decomposition of 1- and 6-phosphorylated glucoses was studied in the presence and absence of ammonia and selected amino acids through pyrolysis/gas chromatography/mass spectrometry using nonpolar PLOT and medium polar DB-1 columns. The analysis of the data has indicated that glucose-1-phosphate relative to glucose undergoes more extensive phosphate-catalyzed ring opening followed by formation of sugar-derived reactive intermediates as was indicated by a 9-fold increase in the amount of trimethylpyrazine and a 5-fold increase in the amount of 2,3-dimethylpyrazine, when pyrolyzed in the presence of glycine. In addition, glucose-1-phosphate alone generated a 6-fold excess of acetol as compared to glucose. On the other hand, glucose-6-phosphate enhanced retro-aldol reactions initiated from a C-6 hydroxyl group and increased the subsequent formation of furfural and 4-cyclopentene-1,3-dione. Furthermore, it also stabilized 1- and 3-deoxyglucosone intermediates and enhanced the formation of six carbon atom-containing Maillard products derived directly from them through elimination reactions such as 1,6-dimethyl-2,4-dihydroxy-3-(2H)-furanone (acetylformoin), 2-acetylpyrrole, 5-methylfurfural, 5-hydroxymethylfurfural, and 4-hydroxy-2,5-dimethyl-3-(2H)-furanone (Furaneol), due to the enhanced leaving group ability of the phosphate moiety at the C-6 carbon. However, Maillard products generated through the nucleophilic action of the C-6 hydroxyl group such as 2-acetylfuran and 2,3-dihydro-3,5-dihydroxy-4H-pyran-4-one were retarded, due to the blocked nucleophilic atom at C-6. PMID:12744667

  13. Nanoparticle Reactions on Chip

    NASA Astrophysics Data System (ADS)

    Köhler, J. M.; Kirner, Th.; Wagner, J.; Csáki, A.; Möller, R.; Fritzsche, W.

    The handling of heterogenous systems in micro reactors is difficult due to their adhesion and transport behaviour. Therefore, the formation of precipitates and gas bubbles has to be avoided in micro reaction technology, in most cases. But, micro channels and other micro reactors offer interesting possibilities for the control of reaction conditions and transport by diffusion and convection due to the laminar flow caused by small Reynolds numbers. This can be used for the preparation and modification of objects, which are much smaller than the cross section of microchannels. The formation of colloidal solutions and the change of surface states of nano particles are two important tasks for the application of chip reactors in nanoparticle technology. Some concepts for the preparation and reaction of nanoparticles in modular chip reactor arrangements will be discussed.

  14. Reaction/Momentum Wheel

    NASA Technical Reports Server (NTRS)

    1997-01-01

    CTA Space Systems, Inc. has been licensed to sell commercially a reaction/momentum wheel originally developed for NASA's scientific satellites. NASA originally identified a need for the wheel in its Small Explorer program. The Submillimeter Wave Astronomy Satellite required extremely low jitter and a reaction/momentum wheel with a torque greater than any comparably sized commercially available wheel to keep the instrument pointed at celestial objects to a high degree of precision. After development, a market assessment by Research Triangle Institute was completed, showing commercial potential for the flywheel technology. A license was granted to CTA in the fall of 1996. The company currently uses the technology in its complete spacecraft fabrication services and has built over 10 reaction/momentum wheels for commercial, scientific, and military customers.

  15. Cutaneous reactions to vaccinations.

    PubMed

    Rosenblatt, Adena E; Stein, Sarah L

    2015-01-01

    Vaccinations are important for infectious disease prevention; however, there are adverse effects of vaccines, many of which are cutaneous. Some of these reactions are due to nonspecific inflammation and irritation at the injection site, whereas other reactions are directly related to the live attenuated virus. Rarely, vaccinations have been associated with generalized hypersensitivity reactions, such as erythema multiforme, Stevens-Johnson syndrome, urticaria, acute generalized exanthematous pustulosis, and drug hypersensitivity syndrome. The onset of certain inflammatory dermatologic conditions, such as lichen planus, granuloma annulare, and pemphigoid, were reported to occur shortly after vaccine administration. Allergic contact dermatitis can develop at the injection site, typically due to adjuvant ingredients in the vaccine, such as thimerosal and aluminum. Vaccinations are important to promote development of both individual and herd immunity. Although most vaccinations are considered relatively safe, there may be adverse effects associated with any vaccine. Cutaneous manifestations make up a large portion of the types of reactions associated with vaccines. There are many different reasons for the development of a cutaneous reaction to a vaccination. Some are directly related to the injection of a live attenuated virus, such as varicella or vaccinia (for immunity to smallpox), whereas others cause more nonspecific erythema and swelling at the injection site, as a result of local inflammation or irritation. Vaccinations have also been associated in rare reports with generalized hypersensitivity reactions, such as erythema multiforme, Stevens-Johnson syndrome, urticaria, acute generalized exanthematous pustulosis, and drug hypersensitivity syndrome. There have been case reports associating the administration of a vaccine with the new onset of a dermatologic condition, such as lichen planus, granuloma annulare, and Sweet syndrome. Finally, allergic contact dermatitis can develop at the injection site, typically due to adjuvant ingredients in the vaccine, such as thimerosal and aluminum. PMID:25889134

  16. Velocity pump reaction turbine

    DOEpatents

    House, P.A.

    An expanding hydraulic/two-phase velocity pump reaction turbine including a dual concentric rotor configuration with an inter-rotor annular flow channel in which the inner rotor is mechanically driven by the outer rotor. In another embodiment, the inner rotor is immobilized and provided with gas recovery ports on its outer surface by means of which gas in solution may be recovered. This velocity pump reaction turbine configuration is capable of potential energy conversion efficiencies of up to 70%, and is particularly suited for geothermal applications.

  17. Velocity pump reaction turbine

    DOEpatents

    House, Palmer A. (Walnut Creek, CA)

    1982-01-01

    An expanding hydraulic/two-phase velocity pump reaction turbine including a dual concentric rotor configuration with an inter-rotor annular flow channel in which the inner rotor is mechanically driven by the outer rotor. In another embodiment, the inner rotor is immobilized and provided with gas recovery ports on its outer surface by means of which gas in solution may be recovered. This velocity pump reaction turbine configuration is capable of potential energy conversion efficiencies of up to 70%, and is particularly suited for geothermal applications.

  18. Velocity pump reaction turbine

    DOEpatents

    House, Palmer A. (Walnut Creek, CA)

    1984-01-01

    An expanding hydraulic/two-phase velocity pump reaction turbine including a dual concentric rotor configuration with an inter-rotor annular flow channel in which the inner rotor is mechanically driven by the outer rotor. In another embodiment, the inner rotor is immobilized and provided with gas recovery ports on its outer surface by means of which gas in solution may be recovered. This velocity pump reaction turbine configuration is capable of potential energy conversion efficiencies of up to 70%, and is particularly suited for geothermal applications.

  19. Adverse reaction to pseudoephedrine.

    PubMed

    Rochina, A; Burchés, E; Morales, C; Brasó, J V; Pelaéz, A

    1995-01-01

    A patient developed a scarlatina-like rash on two separate occasions after receiving a dose of pseudoephedrine. Patch tests with this substance and other structurally related substances (i.e. ephedrine, phenylephrine, and epinephrine) were negative. The oral test with pseudoephedrine provoked a new episode. It is difficult to clarify the exact mechanism of the described reaction; the nature of this eruption probably resembles many other drug-induced adverse reactions in which there is no certainty if mechanisms of type I or III are involved. PMID:8705016

  20. A Principal's Reaction

    ERIC Educational Resources Information Center

    Zaretsky, Lindy

    2004-01-01

    This article presents a principal's reaction to Catherine Marshall and Michael Ward's article on research on social justice and training for leadership. The author applauds Marshall and Ward's efforts to address what is undoubtedly among the most fundamentally important issues facing principals today. Marshall and Ward illuminate the importance of…

  1. Introducing the Wittig Reaction.

    ERIC Educational Resources Information Center

    Armstead, D. E. F.

    1979-01-01

    An experiment is described which provides a simple example of the application of the Wittig reaction to the synthesis of unsaturated compounds. The experiment was designed with British HNC chemistry students in mind, but it is also suitable as a project-type exercise for final year GCE A-level students. (Author/BB)

  2. The aromatic ene reaction

    NASA Astrophysics Data System (ADS)

    Niu, Dawen; Hoye, Thomas R.

    2014-01-01

    The ene reaction is a pericyclic process in which an alkene with an allylic hydrogen atom (the ene donor) reacts with a second unsaturated species (the enophile) to form a new product with a transposed π-bond. The aromatic ene reaction, in which the alkene component is embedded in an aromatic ring, has only been reported in a few (four) instances and has proceeded in low yield (≤6%). Here, we show efficient aromatic ene reactions in which a thermally generated aryne intermediate engages a pendant m-alkylarene substituent to produce a dearomatized isotoluene, itself another versatile but rare reactive intermediate. Our experiments were guided by computational studies that revealed structural features conducive to the aromatic ene process. We proceeded to identify a cascade comprising three reactions: (1) hexadehydro-Diels-Alder (for aryne generation), (2) intramolecular aromatic ene and (3) bimolecular Alder ene. The power of this cascade is evident from the structural complexity of the final products, the considerable scope, and the overall efficiency of these multistage, reagent- and by-product-free, single-pot transformations.

  3. Reaction and Response.

    ERIC Educational Resources Information Center

    Armento, Beverly J.; And Others

    1993-01-01

    Provides a reaction by three economic educators to an article by Raymond C. Miller calling for the elimination of economics. Contends that traditional economics does not necessarily lead to the degradation of the environment. Argues that economics should not promote any set of social values. (CFR)

  4. Chemical Reactions at Surfaces

    SciTech Connect

    Michael Henderson and Nancy Ryan Gray

    2010-04-14

    Chemical reactions at surfaces underlie some of the most important processes of today, including catalysis, energy conversion, microelectronics, human health and the environment. Understanding surface chemical reactions at a fundamental level is at the core of the field of surface science. The Gordon Research Conference on Chemical Reactions at Surfaces is one of the premiere meetings in the field. The program this year will cover a broad range of topics, including heterogeneous catalysis and surface chemistry, surfaces in environmental chemistry and energy conversion, reactions at the liquid-solid and liquid-gas interface, electronic materials growth and surface modification, biological interfaces, and electrons and photons at surfaces. An exciting program is planned, with contributions from outstanding speakers and discussion leaders from the international scientific community. The conference provides a dynamic environment with ample time for discussion and interaction. Attendees are encouraged to present posters; the poster sessions are historically well attended and stimulate additional discussions. The conference provides an excellent opportunity for junior researchers (e.g. graduate students or postdocs) to present their work and interact with established leaders in the field.

  5. Three Reaction Papers.

    ERIC Educational Resources Information Center

    Smith, B. Othanel; And Others

    1983-01-01

    In reaction to presentations at the Airlie House Conference on the Implications of Research on Teaching for Practice, two papers (by O. Smith and N. L. Gage, respectively) discuss how far research on teaching has come as a field, while a third (by G. D. Fenstermacher) explains how implications of research on teaching can be used. (MP)

  6. Exocharmic Reactions up Close

    ERIC Educational Resources Information Center

    Ramette, R. W.

    2007-01-01

    The exocharmic reactions that can be observed microscopically are discussed. The students can discover the optimal concentration of an acidic lead nitrate solution, so that a crystal of potassium iodide, nudged to the edge of a drop, results in glinting golden hexagons of lead iodide.

  7. Chain Reaction Polymerization.

    ERIC Educational Resources Information Center

    McGrath, James E.

    1981-01-01

    The salient features and importance of chain-reaction polymerization are discussed, including such topics as the thermodynamics of polymerization, free-radical polymerization kinetics, radical polymerization processes, copolymers, and free-radical chain, anionic, cationic, coordination, and ring-opening polymerizations. (JN)

  8. Reaction Formulation: A Bibliography.

    ERIC Educational Resources Information Center

    Pedrini, D. T.; Pedrini, Bonnie C.

    Reaction formation was studied by Sigmund Freud. This defense mechanism may be related to repression, substitution, reversal, and compensation (or over-compensation). Alfred Adler considered compensation a basic process in his individual psychology. Anna Freud discussed some defense mechanisms, and Bibring, Dwyer, Huntington, and Valenstein…

  9. Bad Reaction to Cosmetics?

    MedlinePLUS

    ... Home For Consumers Consumer Updates Bad Reaction to Cosmetics? Tell FDA Share Tweet Linkedin Pin it More ... M.D., director of the agency’s Office of Cosmetics and Colors. “So, consumers are one of FDA’s ...

  10. Polymerase chain reaction system

    DOEpatents

    Benett, William J.; Richards, James B.; Stratton, Paul L.; Hadley, Dean R.; Milanovich, Fred P.; Belgrader, Phil; Meyer, Peter L.

    2004-03-02

    A portable polymerase chain reaction DNA amplification and detection system includes one or more chamber modules. Each module supports a duplex assay of a biological sample. Each module has two parallel interrogation ports with a linear optical system. The system is capable of being handheld.

  11. A Principal's Reaction

    ERIC Educational Resources Information Center

    Zaretsky, Lindy

    2004-01-01

    This article presents a principal's reaction to Catherine Marshall and Michael Ward's article on research on social justice and training for leadership. The author applauds Marshall and Ward's efforts to address what is undoubtedly among the most fundamentally important issues facing principals today. Marshall and Ward illuminate the importance of…

  12. Reaction product imaging

    SciTech Connect

    Chandler, D.W.

    1993-12-01

    Over the past few years the author has investigated the photochemistry of small molecules using the photofragment imaging technique. Bond energies, spectroscopy of radicals, dissociation dynamics and branching ratios are examples of information obtained by this technique. Along with extending the technique to the study of bimolecular reactions, efforts to make the technique as quantitative as possible have been the focus of the research effort. To this end, the author has measured the bond energy of the C-H bond in acetylene, branching ratios in the dissociation of HI, the energetics of CH{sub 3}Br, CD{sub 3}Br, C{sub 2}H{sub 5}Br and C{sub 2}H{sub 5}OBr dissociation, and the alignment of the CD{sub 3} fragment from CD{sub 3}I photolysis. In an effort to extend the technique to bimolecular reactions the author has studied the reaction of H with HI and the isotopic exchange reaction between H and D{sub 2}.

  13. Photoneutron reactions in astrophysics

    NASA Astrophysics Data System (ADS)

    Varlamov, V. V.; Ishkhanov, B. S.; Orlin, V. N.; Peskov, N. N.; Stopani, K. A.

    2014-12-01

    Among key problems in nuclear astrophysics, that of obtaining deeper insight into the mechanism of synthesis of chemical elements is of paramount importance. The majority of heavy elements existing in nature are produced in stars via radiative neutron capture in so-called s- and r processes, which are, respectively, slow and fast, in relation to competing ? --decay processes. At the same time, we know 35 neutron-deficient so-called bypassed p-nuclei that lie between 74Se and 196Hg and which cannot originate from the aforementioned s- and r-processes. Their production is possible in ( ?, n), ( ?, p), or ( ?, ?) photonuclear reactions. In view of this, data on photoneutron reactions play an important role in predicting and describing processes leading to the production of p-nuclei. Interest in determining cross sections for photoneutron reactions in the threshold energy region, which is of particular importance for astrophysics, has grown substantially in recent years. The use of modern sources of quasimonoenergetic photons obtained in processes of inverse Compton laser-radiation scattering on relativistic electronsmakes it possible to reveal rather interesting special features of respective cross sections, manifestations of pygmy E1 and M1 resonances, or the production of nuclei in isomeric states, on one hand, and to revisit the problem of systematic discrepancies between data on reaction cross sections from experiments of different types, on the other hand. Data obtained on the basis of our new experimental-theoretical approach to evaluating cross sections for partial photoneutron reactions are invoked in considering these problems.

  14. Photoneutron reactions in astrophysics

    SciTech Connect

    Varlamov, V. V. Ishkhanov, B. S.; Orlin, V. N.; Peskov, N. N.; Stopani, K. A.

    2014-12-15

    Among key problems in nuclear astrophysics, that of obtaining deeper insight into the mechanism of synthesis of chemical elements is of paramount importance. The majority of heavy elements existing in nature are produced in stars via radiative neutron capture in so-called s- and r processes, which are, respectively, slow and fast, in relation to competing ?{sup ?}-decay processes. At the same time, we know 35 neutron-deficient so-called bypassed p-nuclei that lie between {sup 74}Se and {sup 196}Hg and which cannot originate from the aforementioned s- and r-processes. Their production is possible in (?, n), (?, p), or (?, ?) photonuclear reactions. In view of this, data on photoneutron reactions play an important role in predicting and describing processes leading to the production of p-nuclei. Interest in determining cross sections for photoneutron reactions in the threshold energy region, which is of particular importance for astrophysics, has grown substantially in recent years. The use of modern sources of quasimonoenergetic photons obtained in processes of inverse Compton laser-radiation scattering on relativistic electronsmakes it possible to reveal rather interesting special features of respective cross sections, manifestations of pygmy E1 and M1 resonances, or the production of nuclei in isomeric states, on one hand, and to revisit the problem of systematic discrepancies between data on reaction cross sections from experiments of different types, on the other hand. Data obtained on the basis of our new experimental-theoretical approach to evaluating cross sections for partial photoneutron reactions are invoked in considering these problems.

  15. What Is a Reaction Rate?

    ERIC Educational Resources Information Center

    Schmitz, Guy

    2005-01-01

    The definition of reaction rate is derived and demonstrations are made for the care to be taken while using the term. Reaction rate can be in terms of a reaction property, the extent of reaction and thus it is possible to give a definition applicable in open and closed systems.

  16. Inorganic Reaction Mechanisms. Part I

    ERIC Educational Resources Information Center

    Cooke, D. O.

    1976-01-01

    Provides a collection of data on the mechanistic aspects of inorganic chemical reactions. Wherever possible includes procedures for classroom demonstration or student project work. The material covered includes gas phase reactions, reactions in solution, mechanisms of electron transfer, the reaction between iron III and iodine, and hydrolysis. (GS)

  17. Rhodium-catalyzed [5 + 2 + 1] cycloaddition of ene-vinylcyclopropanes and CO: reaction design, development, application in natural product synthesis, and inspiration for developing new reactions for synthesis of eight-membered carbocycles.

    PubMed

    Wang, Yi; Yu, Zhi-Xiang

    2015-08-18

    Practical syntheses of natural products and their analogues with eight-membered carbocyclic skeletons are important for medicinal and biological investigations. However, methods and strategies to construct the eight-membered carbocycles are limited. Therefore, developing new methods to synthesize the eight-membered carbocycles is highly desired. In this Account, we describe our development of three rhodium-catalyzed cycloadditions for the construction of the eight-membered carbocycles, which have great potential in addressing the challenges in the synthesis of medium-sized ring systems. The first reaction described in this Account is our computationally designed rhodium-catalyzed two-component [5 + 2 + 1] cycloaddition of ene-vinylcyclopropanes (ene-VCPs) and CO for the diastereoselective construction of bi- and tricyclic cyclooctenones. The design of this reaction is based on the hypothesis that the C(sp(3))-C(sp(3)) reductive elimination of the eight-membered rhodacycle intermediate generated from the rhodium-catalyzed cyclopropane cleavage and alkene insertion, giving Wender's [5 + 2] cycloadduct, is not easy. Under CO atmosphere, CO insertion may occur rapidly, converting the eight-membered rhodacycle into a nine-membered rhodacycle, which then undergoes an easy C(sp(2))-C(sp(3)) reductive elimination process and furnishes the [5 + 2 + 1] product. This hypothesis was supported by our preliminary DFT studies and also served as inspiration for the development of two [7 + 1] cycloadditions: the [7 + 1] cycloaddition of buta-1,3-dienylcyclopropanes (BDCPs) and CO for the construction of cyclooctadienones, and the benzo/[7 + 1] cycloaddition of cyclopropyl-benzocyclobutenes (CP-BCBs) and CO to synthesize the benzocyclooctenones. The efficiency of these rhodium-catalyzed cycloadditions can be revealed by the application in natural product synthesis. Two eight-membered ring-containing natural products, (±)-asterisca-3(15),6-diene and (+)-asteriscanolide, have been synthesized using the [5 + 2 + 1] cycloaddition as the key step. In the latter case, excellent asymmetric induction was obtained using a chiral substrate. The efficiency of the [5 + 2 + 1] reaction was further demonstrated by the synthesis of four sesquiterpene natural products, (±)-pentalenene, (+)-hirsutene, (±)-1-desoxyhypnophilin, and (±)-hirsutic acid C, containing linear or branched triquinane skeletons utilizing the tandem or stepwise [5 + 2 + 1] cycloaddition/aldol reaction strategy. With the success of [5 + 2 + 1] cycloaddition in natural product synthesis, application of the [7 + 1] and benzo/[7 + 1] cycloadditions in target- and function-oriented syntheses can be envisioned. PMID:26227886

  18. Water Nanodroplets as a Reaction Medium: FT-ICR Studies of the Stability, Structure and Reactivity of Hydrated Ions and Ionic Water Clusters

    NASA Astrophysics Data System (ADS)

    Bondybey, Vladimir E.

    2001-03-01

    With the help of a versatile ion source coupling laser vaporization with supersonic expansion, ionic clusters of the type X^±(H_2O)n are easily generated, and if desired, they can be mass selected in a Fourier Transform Ion Cyclotron (FT-ICR) mass spectrometer. The central ion, X^± can be for instance H^+ or OH^-, a free electron, or an ionized metal such as Na^+, Ag^+, Mg^+, or Al^+. Such "nanodroplets" solvated with up to 200 molecules of water or other ligands slowly fragment in the collision-free environment of the FT-ICR trap. They lose in a controlled way the solvent molecules, one by one on a millisecond timescale. The products of reactions which occur in the nanodroplet as a result of the loss of the stabilizing ligand can in the high-resolution mass spectrometer be unambiguously identified. In this way, a variety of solution processes such as ionic dissolution, fragmentation, neutralization, precipitation, reduction-oxidation reactions, or acid-base catalyzed reactions can be investigated in molecular, microscopic detail. Small droplets and particles are important for a variety of atmospheric processes and reactions occurring both in the troposphere and the stratosphere. This suggests the possibility of preparing such nano-droplets of suitable composition, and using them as a model system for investigating a large variety of reactions important for atmospheric chemistry. In the present talk, we will describe our apparatus and external source, and discuss a variety of results obtained recently with it in our laboratory. The aldol condensation of acetaldehyde as an example of an acid-base catalyzed reaction and the precipitation of AgCl show that a number of well-known reactions in solution have their counterpart on a single molecule level in the cluster. The competition between electron detachment and water loss of hydrated electrons e^-(H_2O)_n, n=13-36, provides interesting and unexpected insights into the coupling dynamics of the electron to its water environment.

  19. Uptake and Reactions of Formaldehyde, Acetaldehyde, Acetone, Propanal and Ethanol in Sulfuric Acid solutions at 200-240 K: Implications for upper tropospheric aerosol composition

    NASA Astrophysics Data System (ADS)

    Iraci, L. T.; Williams, M. B.; Axson, J.; Michelsen, R.

    2007-12-01

    The production of light absorbing, organic material in aerosol that is normally considered to be transparent in the UV and visible wavelength regions has significant implications for biogeochemical cycling and climate modelling. Production mechanisms likely involve carbonyl compounds such as formaldehyde, acetone, acetaldehyde and propanal that are present in significant quantities in the upper troposphere (UT). In this study, we have performed experiments focusing on a class of acid catalyzed carbonyl reactions, the formation of acetals. R2C=O + 2R'OH --> R2C(OR')2 + H2O Using a Knudsen cell apparatus, we have measured the rate of uptake of formaldehyde, acetaldehyde, acetone, propanal, and ethanol into sulfuric acid solutions ranging between 40-70 wt% of acid, containing 0-0.1 M of ethanol, acetone or formaldehyde at temperatures of 220-250 K. For all reactant pairs, the aldol condensation path, including self reaction, should be insignificant at the acidities studied. Evidence for reaction between organics was observed for all pairs, except those involving propanal which were likely limited by the very low solubility. We attribute enhanced uptake to the formation of acetals, such as 1,1-diethoxyethane and 2,2- diethoxypropane, among others. Enhanced uptake was observed to proceed on timescales > 1 hour and sometimes shows complex dependence on acidity that is likely related to speciation of the individual carbonyls in acidic solution. The acetal products do not absorb in the visible but are less volatile than parent molecules, allowing for accumulation in sulfuric acid particles, and enhanced uptake. Cross reactions of carbonyls with alcohols in sulfuric acid medium have not been previously measured, yet methanol and ethanol show high solubility and are present at significant concentrations in the UT. Thus even at slow reaction rates, the acetal reaction has ample starting material and proceeds under conditions common to the UT. We will present results for the enhanced uptake of carbonyls in the presence of alcohols, derive rate constants, and discuss the atmospheric impact of the acetal reaction path.

  20. Reaction chemistry of cerium

    SciTech Connect

    1997-01-01

    It is truly ironic that a synthetic organic chemist likely has far greater knowledge of the reaction chemistry of cerium(IV) than an inorganic colleague. Cerium(IV) reagents have long since been employed as oxidants in effecting a wide variety of organic transformations. Conversely, prior to the late 1980s, the number of well characterized cerium(IV) complexes did not extend past a handful of known species. Though in many other areas, interest in the molecular chemistry of the 4f-elements has undergone an explosive growth over the last twenty years, the chemistry of cerium(IV) has for the most part been overlooked. This report describes reactions of cerium complexes and structure.

  1. Implant site Nexplanon reaction?

    PubMed

    Pedroso, Célia; Martins, Isabel; Palma, Fátima; Machado, Ana Isabel

    2015-01-01

    Nexplanon (Schering-Plough Limited/Merck Sharp & Dohme Limited (MSD)) is a long active reversible contraceptive method that provides effective contraception for 3 years. It consists of a single, flexible, rod-shaped implant, containing 68 mg etonogestrel. It is 4 cm long, consists of an ethylene vinyl acetate copolymer, a non-absorbable material, and also contains 15 mg of barium sulfate, which makes it visible by X-ray. We describe a case of a 39-year-old woman who experienced a local reaction to the barium sulfate in Nexplanon. She was given medical treatment, but only the removal of the implant resolved the symptoms. After removal there was gradual improvement and 72 h later the patient was asymptomatic. Allergic reaction to barium sulfate is extremely rare: until now, there have only been two cases associated with Nexplanon described in the literature. PMID:25953577

  2. Concordant Chemical Reaction Networks

    PubMed Central

    Shinar, Guy; Feinberg, Martin

    2015-01-01

    We describe a large class of chemical reaction networks, those endowed with a subtle structural property called concordance. We show that the class of concordant networks coincides precisely with the class of networks which, when taken with any weakly monotonic kinetics, invariably give rise to kinetic systems that are injective — a quality that, among other things, precludes the possibility of switch-like transitions between distinct positive steady states. We also provide persistence characteristics of concordant networks, instability implications of discordance, and consequences of stronger variants of concordance. Some of our results are in the spirit of recent ones by Banaji and Craciun, but here we do not require that every species suffer a degradation reaction. This is especially important in studying biochemical networks, for which it is rare to have all species degrade. PMID:22659063

  3. Photochemical reaction dynamics

    SciTech Connect

    Moore, B.C.

    1993-12-01

    The purpose of the program is to develop a fundamental understanding of unimolecular and bimolecular reaction dynamics with application in combustion and energy systems. The energy dependence in ketene isomerization, ketene dissociation dynamics, and carbonyl substitution on organometallic rhodium complexes in liquid xenon have been studied. Future studies concerning unimolecular processes in ketene as well as energy transfer and kinetic studies of methylene radicals are discussed.

  4. Factors augmenting allergic reactions.

    PubMed

    Niggemann, B; Beyer, K

    2014-12-01

    Elicitors of anaphylactic reactions are any sources of protein with allergenic capacity. However, not all allergic reactions end up in the most severe form of anaphylaxis. Augmenting factors may explain why certain conditions lead to anaphylaxis. Augmenting factors may exhibit three effects: lowering the threshold, increasing the severity, and reversing acquired clinical tolerance. Common augmenting factors are physical exercise, menstruation, NSAIDs, alcohol, body temperature, acute infections, and antacids. Therapeutic options may address causative, preventive, pragmatic, or symptomatic considerations: avoid the eliciting food, take an antihistamine before any situation with a possible risk of augmentation, separate food and sport (at least for 2 h), and carry an adrenaline autoinjector at all times. Individual patterns include summation effects and specific patterns. In conclusion, in the case of a suggestive history but a negative oral challenge, one should consider the possible involvement of augmenting factors; after anaphylactic reactions, always ask for possible augmentation and other risk factors during the recent past; if augmentation is suspected, oral food challenges should be performed in combination with augmenting factors; and in the future, standardized challenge protocols including augmenting factors should be established. PMID:25306896

  5. Chemical Reactions in DSMC

    SciTech Connect

    Bird, G. A.

    2011-05-20

    DSMC simulations of chemically reacting gas flows have generally employed procedures that convert the macroscopic chemical rate equations to reaction cross-sections at the microscopic level. They therefore depend on the availability of experimental data that has been fitted to equations of the Arrhenius form. This paper presents a physical model for dissociation and recombination reactions and a phenomenological model for exchange and chain reactions. These are based on the vibrational states of the colliding molecules and do not require any experimentally-based data. The simplicity of the models allows the corresponding rate equations to be written down and, while these are not required for the implementation of the models, they facilitate their validation. The model is applied to a typical hypersonic atmospheric entry problem and the results are compared with the corresponding results from the traditional method. It is also used to investigate both spontaneous and forced ignition as well as the structure of a deflagration wave in an oxygen-hydrogen mixture.

  6. Total Synthesis of a Diacetonide Derivative of Thuggacin A.

    PubMed

    Yadav, Jhillu S; Dutta, Palash

    2016-03-01

    A highly stereoselective total synthesis of the diacetonide derivative of the antibiotic thuggacin A has been described. The synthesis features the stereoselective Stille cross-coupling reaction to set up the whole carbon framework, aldol condensation to construct the highly substituted conjugated diene, non-Evans syn aldol, CBS reduction, Hantzsch's thiazole synthesis, Horner-Wadsworth-Emmons reaction, and Shiina's macrolactonization. PMID:26856208

  7. Atomic force microscopy imaging of TiO{sub 2} surfaces active for C-C bond formation reactions in ultrahigh vacuum

    SciTech Connect

    Watson, B.A.; Barteau, M.A.

    1994-06-01

    TiO{sub 2}(001) single crystal surfaces active for a variety of different chemistries were examined using atomic force microscopy (AFM). C-C bond forming reactions previously identified on these surfaces include carboxylic acid ketonization, aldol condensation, reductive carbonyl coupling, and alkyne cyclotrimerization. The surfaces were prepared in ultrahigh vacuum (UHV) and examined by AFM in air. Surfaces examined included the (011)-faceted surface, (114)-faceted surface, and argon-ion-bombarded surfaces, as well as the mechanically polished single-crystal surface prior to treatment in UHV. The one unifying feature of all the images was their extreme flatness. Root-mean-square roughnesses were routinely less than 10 {Angstrom} in 500 x 500 nm scans. These same scans showed the surfaces to have surface areas exceeding that of an ideal flat surface by no more than 1.2%. Images of the polished surface revealed a variety of surface features, including polishing scratches and particle-like features. The argon-ion-bombarded surface and the faceted surfaces were composed of large flat plateaus ranging in size from 21 to 75 nm. The size of the plateaus was essentially the same for the ion bombarded surface and the (011)-faceted surface. The (114)-faceted surfaced exhibited slightly smaller plateau regions than the other surfaces. The images indicate that argon-ion bombardment, while disordering the surface and causing significant composition changes, does not lead to observable morphological changes on this scale. The relative uniformity of the surfaces examined is consistent with the selectivity of carbon-carbon bond-forming reactions that have been shown to take place on these surfaces. The images also reveal how the surface topography on the scale of the plateau structures observed is only slightly changed during the transformation of the surface unit cell structure from the (011)- to the (114)-faceted surface. 29 refs., 6 figs., 1 tab.

  8. Astrophysical Reaction Rates as a Challenge for Nuclear Reaction Theory

    SciTech Connect

    Rauscher, T.

    2010-08-12

    The relevant energy ranges for stellar nuclear reactions are introduced. Low-energy compound direct reactions are discussed. Stellar modifications of the cross sections are presented. Implications for experiments are outlined.

  9. Reaction Extrema: Extent of Reaction in General Chemistry

    ERIC Educational Resources Information Center

    Vandezande, Jonathon E.; Vander Griend, Douglas A.; DeKock, Roger L.

    2013-01-01

    Nearly 100 years ago de Donder introduced the term "extent of reaction", ?. We build on that work by defining the concept of reagent extrema for an arbitrary chemical reaction, aA + bB [reversible reaction] yY + zZ. The central equation is ?^[subscript i] = -n[subscript i,0]/?[subscript i]. The symbol ?^[subscript i] represents the…

  10. Procedures for Decomposing a Redox Reaction into Half-Reaction

    ERIC Educational Resources Information Center

    Fishtik, Ilie; Berka, Ladislav H.

    2005-01-01

    A simple algorithm for a complete enumeration of the possible ways a redox reaction (RR) might be uniquely decomposed into half-reactions (HRs) using the response reactions (RERs) formalism is presented. A complete enumeration of the possible ways a RR may be decomposed into HRs is equivalent to a complete enumeration of stoichiometrically…

  11. Procedures for Decomposing a Redox Reaction into Half-Reaction

    ERIC Educational Resources Information Center

    Fishtik, Ilie; Berka, Ladislav H.

    2005-01-01

    A simple algorithm for a complete enumeration of the possible ways a redox reaction (RR) might be uniquely decomposed into half-reactions (HRs) using the response reactions (RERs) formalism is presented. A complete enumeration of the possible ways a RR may be decomposed into HRs is equivalent to a complete enumeration of stoichiometrically…

  12. Reaction Extrema: Extent of Reaction in General Chemistry

    ERIC Educational Resources Information Center

    Vandezande, Jonathon E.; Vander Griend, Douglas A.; DeKock, Roger L.

    2013-01-01

    Nearly 100 years ago de Donder introduced the term "extent of reaction", ?. We build on that work by defining the concept of reagent extrema for an arbitrary chemical reaction, aA + bB [reversible reaction] yY + zZ. The central equation is ?^[subscript i] = -n[subscript i,0]/?[subscript i]. The symbol ?^[subscript i] represents the…

  13. Insect bite reactions.

    PubMed

    Singh, Sanjay; Mann, Baldeep Kaur

    2013-01-01

    Insects are a class of living creatures within the arthropods. Insect bite reactions are commonly seen in clinical practice. The present review touches upon the medically important insects and their places in the classification, the sparse literature on the epidemiology of insect bites in India, and different variables influencing the susceptibility of an individual to insect bites. Clinical features of mosquito bites, hypersensitivity to mosquito bites Epstein-Barr virus NK (HMB-EBV-NK) disease, eruptive pseudoangiomatosis, Skeeter syndrome, papular pruritic eruption of HIV/AIDS, and clinical features produced by bed bugs, Mexican chicken bugs, assassin bugs, kissing bugs, fleas, black flies, Blandford flies, louse flies, tsetse flies, midges, and thrips are discussed. Brief account is presented of the immunogenic components of mosquito and bed bug saliva. Papular urticaria is discussed including its epidemiology, the 5 stages of skin reaction, the SCRATCH principle as an aid in diagnosis, and the recent evidence supporting participation of types I, III, and IV hypersensitivity reactions in its causation is summarized. Recent developments in the treatment of pediculosis capitis including spinosad 0.9% suspension, benzyl alcohol 5% lotion, dimethicone 4% lotion, isopropyl myristate 50% rinse, and other suffocants are discussed within the context of evidence derived from randomized controlled trials and key findings of a recent systematic review. We also touch upon a non-chemical treatment of head lice and the ineffectiveness of egg-loosening products. Knockdown resistance (kdr) as the genetic mechanism making the lice nerves insensitive to permethrin is discussed along with the surprising contrary clinical evidence from Europe about efficacy of permethrin in children with head lice carrying kdr-like gene. The review also presents a brief account of insects as vectors of diseases and ends with discussion of prevention of insect bites and some serious adverse effects of mosquito coil smoke. PMID:23442453

  14. [Food allergies and intolerance reactions].

    PubMed

    Thiel, C

    1991-09-01

    Adverse reactions to food and food additives are defined by its different pathomechanisms. Clinically most important are allergic (immunologic) reactions (types I and III), which occur in 7-10% of the general population, and nonimmunologic (pseudoallergic) reactions (PAR), which occur in 1-2%, besides nonallergic reactions by vasoactive amines. Clinical features are equal. Sources of antigens for allergic reactions are proteins of cow's milk, fish, hen's egg, meat, and all kinds of cereals, fruits, vegetables, and spices, while pseudoallergic reactions are induced by chemicals (preservatives, colorants, antioxidants). The diagnostic procedures of allergic reactions include the proof of sensitization by case history, skin test, specific IgE (and IgG) in-vitro, elimination diet and provocation test; pseudoallergic reactions with no underlying sensitization are diagnosed only by elimination and provocation procedures. PMID:1763553

  15. Organic chemistry: Reactions triggered electrically

    NASA Astrophysics Data System (ADS)

    Xiang, Limin; Tao, N. J.

    2016-03-01

    Single-molecule experiments have revealed that chemical reactions can be controlled using electric fields -- and that the reaction rate is sensitive to both the direction and the strength of the applied field. See Letter p.88

  16. Positive reaction to allergen (image)

    MedlinePLUS

    Allergic reaction is a sensitivity to a specific substance, called an allergen, that is contacted through the skin, inhaled into the lungs, swallowed or injected. The body's reaction to an allergen can be mild, such as ...

  17. Hydrazine decomposition and other reactions

    NASA Technical Reports Server (NTRS)

    Armstrong, Warren E. (Inventor); La France, Donald S. (Inventor); Voge, Hervey H. (Inventor)

    1978-01-01

    This invention relates to the catalytic decomposition of hydrazine, catalysts useful for this decomposition and other reactions, and to reactions in hydrogen atmospheres generally using carbon-containing catalysts.

  18. Demonstration of the Fenton Reaction

    ERIC Educational Resources Information Center

    Luehrs, Dean C.; Roher, Alex E.

    2007-01-01

    The study demonstrates the Fenton reaction, which is carried out using the Fenton reagent that is used for groundwater and soil remediation. The Fenton reaction can be implicated in DNA damage, Alzheimer's disease, cardiovascular disease and ageing in general.

  19. Medications and Drug Allergic Reactions

    MedlinePLUS

    ... a-fi-LAK-sis). Symptoms of anaphylaxis include hives, facial or throat swelling, wheezing, light-headedness, vomiting ... growths). Other reactions to NSAIDs can result in hives or in rare instances, severe reactions can result ...

  20. The Vitamin C Clock Reaction

    NASA Astrophysics Data System (ADS)

    Wright, Stephen W.

    2002-01-01

    An iodine clock reaction that gives a colorless to black result similar to that of the familiar Landolt iodate-bisulfite clock reaction is described. The vitamin C clock reaction uses chemicals that are readily available on the retail market: vitamin C, tincture of iodine, 3% hydrogen peroxide, and laundry starch. Orange juice may be used as the vitamin C source to give an orange to black reaction.

  1. Reactions with molybdenum atoms

    SciTech Connect

    Wilburn, B.E.

    1982-01-01

    The formation and reactions of (eta/sup 6/-arene)/sub 2/Mo(0), (eta/sup 6/-arene(eta/sup 5/-cyclopentadianyl)molybdenum(I) and (eta/sup 6/-arene)(eta/sup 5/-cyclopentadienyl)molybdenum(II) hydrides were examined. The formation of sandwich compounds of molybdenum by metal atoms was studied by the use of relative rates. The relative rates of reactions of Mo atoms with arene mixtures at approximately -170/sup 0/C are spaced over the small overall range of 3.7 for the following arenes: toluene, t-butylbenzene, o-xylene, benzotrifluoride, N-N-dimethylaniline, fluorobenzene, methyl benzoate and anisole. The photochemical behavior of (eta/sup 6/-C/sub 6/H/sub 5/N(CH/sub 3/)/sub 2/)(eta/sup 5/-C/sub 5/H/sub 5/)MoH was examined. Photolysis of the hydride produced hydrogen and a 17 electron compound, (eta/sup 6/-C/sub 6/H/sub 5/N(CH/sub 2/)/sub 2/)(eta/sup 5/-C/sub 5/H/sub 5/)Mo. Experiments indicated that the hydrogen was produced by a bimolecular mechanism instead of intramolecular elimination of H atom abstraction from the solvent mechanisms.

  2. The Redox-Mannich Reaction

    PubMed Central

    2015-01-01

    A complement to the classic three-component Mannich reaction, the redox-Mannich reaction, utilizes the same starting materials but incorporates an isomerization step that enables the facile preparation of ring-substituted ?-amino ketones. Reactions occur under relatively mild conditions and are facilitated by benzoic acid. PMID:24857691

  3. Mass Transfer with Chemical Reaction.

    ERIC Educational Resources Information Center

    DeCoursey, W. J.

    1987-01-01

    Describes the organization of a graduate course dealing with mass transfer, particularly as it relates to chemical reactions. Discusses the course outline, including mathematics models of mass transfer, enhancement of mass transfer rates by homogeneous chemical reaction, and gas-liquid systems with chemical reaction. (TW)

  4. More on Chemical Reaction Balancing.

    ERIC Educational Resources Information Center

    Swinehart, D. F.

    1985-01-01

    A previous article stated that only the matrix method was powerful enough to balance a particular chemical equation. Shows how this equation can be balanced without using the matrix method. The approach taken involves writing partial mathematical reactions and redox half-reactions, and combining them to yield the final balanced reaction. (JN)

  5. Catalytic reactions of dialkyl disulfides

    NASA Astrophysics Data System (ADS)

    Mashkina, A. V.

    2014-08-01

    The results of studies into catalytic transformations of lower dialkyl disulfides (Alk = C1-C4) are summarized and described systematically. The decomposition, cyclization, hydrogenolysis, oxidation and thioalkylation reactions are considered. The results of reactions are compared depending on the catalyst nature and reaction conditions. The bibliography includes 181 references.

  6. The Vitamin C Clock Reaction.

    ERIC Educational Resources Information Center

    Wright, Stephen W.

    2002-01-01

    Describes an iodine clock reaction that produces an effect similar to the Landolt clock reaction. This reaction uses supermarket chemicals and avoids iodate, bisulfite, and mercury compounds. Ascorbic acid and tincture of iodine are the main reactants with alternate procedures provided for vitamin C tablets and orange juice. (DDR)

  7. OH + HBr reaction revisited

    SciTech Connect

    Ravishankara, A.R.; Wine, P.H.; Wells, J.R.

    1985-07-01

    Variable-temperature measurements of the rate coefficient /k(1)/ for the reaction OH + HBr yield Br + H2O are presented. The measurements are verified by two techniques: one involved a 266-nm pulsed-laser photolysis of O3/H2O/HBr/He mixtures in conjunction with time-resolved resonance fluorescence detection of OH, the second comprised pulsed laser-induced fluorescence detection of OH following 248-nm pulsed-laser photolysis of H2O2/HBr/Ar mixtures. It is reported that k(1) = (11.9 + or -1.4 x 10 to the -12th (cu cm)/(molecule)(s) independent of temperature. The measurements are compared with other available results. 6 references.

  8. Hypersensitivity reaction with deferasirox.

    PubMed

    Sharma, Atul; Arora, Ekta; Singh, Harmanjit

    2015-01-01

    Thalassemias comprise a group of hereditary blood disorders. Thalassemia major presents with anemia within the first 2 years of life requiring frequent blood transfusions for sustaining life. Regular blood transfusions lead to iron overload-related complications. Prognosis of thalassemia has improved because of the availability of iron-chelating agents. Oral iron chelators are the mainstay of chelation therapy. Deferasirox is a new-generation oral iron chelator for once daily usage. We herein describe a patient of beta thalassemia major who developed an allergic manifestation in the form of erythematous pruritic skin rashes to the oral iron chelator deferasirox. This is a rare adverse reaction reported with deferasirox that led to a therapeutic dilemma in this particular case. PMID:25969661

  9. Hydrocracking reactions and catalysis

    SciTech Connect

    Dolbear, G.E.

    1995-12-31

    Hydrocracking processes convert aromatic gas oils into high quality gasoline, diesel, and turbine stocks. In doing this, they saturate aromatic rings, crack naphthenes and paraffins, and saturate olefins formed during cracking. The organic chemistry of these steps is well known. Catalysts for hydrocracking contain components for both the hydrogenation and cracking reactions. Hydrogenation activity is provided by Pd or promoted molybdenum or tungsten sulfides. Cracking takes place on strong acid sites in zeolites or amorphous silica aluminas. Specialty catalysts including narrow pore zeolites are used in dewaxing tube oil stocks. Basic nitrogen compounds such as quinoline can poison the acid sites. They are usually removed in a pretreating step, typically with a nickel/molybdenum sulfide catalyst that also removes sulfur.

  10. Ketoprofen allergic reactions.

    PubMed

    Cantisani, Carmen; Grieco, Teresa; Faina, Valentina; Mattozzi, Carlo; Bohnenberger, Hanibal; Silvestri, Emidio; Calvieri, Stefano

    2010-01-01

    Topical ketoprofen (KP) is widely used because of its anti-inflammatory effect. Parallel with its popular usage, the number of reported cases of ketoprofen-induced photoallergic contact dermatitis has increased. A review of the literature was made to evaluate the spectrum of cross sensitization in patients with ketoprofen-induced photoallergic contact dermatitis using ketoprofen and other structurally similar chemicals and sunscreens, fragrance components, as well as the presence of prolonged photosensitivity related to it. Furthermore, the distinction between true cross-reactivity and concomitant sensitization may be difficult. Therefore, further investigations are needed to gain a more complete understanding of this important topic. This article also reviews some patents related to alternative treatment of musculoskeletal diseases and/or treatment of allergic reactions due to NSAIDs use. PMID:19832694

  11. Subdiffusion-reaction processes with A ?B reactions versus subdiffusion-reaction processes with A +B?B reactions

    NASA Astrophysics Data System (ADS)

    Koszto?owicz, Tadeusz; Lewandowska, Katarzyna D.

    2014-09-01

    We consider the subdiffusion-reaction process with reactions of a type A +B?B (in which particles A are assumed to be mobile, whereas B are assumed to be static) in comparison to the subdiffusion-reaction process with A ?B reactions which was studied by Sokolov, Schmidt, and Sagués [Phys. Rev. E 73, 031102 (2006), 10.1103/PhysRevE.73.031102]. In both processes a rule that reactions can only occur between particles which continue to exist is taken into account. Although in both processes a probability of the vanishing of particle A due to a reaction is independent of both time and space variables (assuming that in the system with the A +B?B reactions, particles B are distributed homogeneously), we show that subdiffusion-reaction equations describing these processes as well as their Green's functions are qualitatively different. The reason for this difference is as follows. In the case of the former reaction, particles A and B have to meet with some probability before the reaction occurs in contradiction with the case of the latter reaction. For the subdiffusion process with the A +B?B reactions we consider three models which differ in some details concerning a description of the reactions. We base the method considered in this paper on a random walk model in a system with both discrete time and discrete space variables. Then the system with discrete variables is transformed into a system with both continuous time and continuous space variables. Such a method seems to be convenient in analyzing subdiffusion-reaction processes with partially absorbing or partially reflecting walls. The reason is that within this method we can determine Green's functions without a necessity of solving a fractional differential subdiffusion-reaction equation with boundary conditions at the walls. As an example, we use the model to find the Green's functions for a subdiffusive reaction system (with the reactions mentioned above), which is bounded by a partially absorbing wall. This example shows how the model can be used to analyze the subdiffusion-reaction process in a system with partially absorbing or reflecting thin membranes. Employing a simple phenomenological model, we also derive equations related to the reaction parameters used in the considered models.

  12. Formation of aromatic compounds from carbohydrates. Reaction of xylose, glucose, and glucuronic acid in acidic solution at 300/sup 0/C

    SciTech Connect

    Theander, O.; Nelson, D.A.; Hallen, R.T.

    1987-04-01

    For several years respective groups have investigated the formation of aromatic compounds from carbohydrates in aqueous solution at various pH values under reflux or hydrothermolytic conditions. Previous hydrothermolytic studies of cellulose indicated that certain aromatic products could be obtained when the pH was maintained in the range of 4-11. This suggested that aldol condensation, a prime route for the production of aromatics from saccharides, could function under moderately acidic conditions. The current research was initiated to study the competition between the formation of phenolic compounds (aldol involvement) and that of furans (dehydration and cyclization).

  13. Sulfided heterogeneous, bimetallic RuMo catalysts derived from mixtures of Ru{sub 3}(CO){sub 12} (or RuCl{sub 3}) and a molybdenum heteropolyanion. The reactions of ethanol with tetrahydroquinoline

    SciTech Connect

    Koo, Sang-Man; Ryan, D.; Laine, R.M.

    1992-09-01

    Efforts have been made to develop Ru/Mo bimetallic catalyst systems for hydrodenitrogenation (HDN) of tetrahydroquinoline (THQ)- In the course of these studies, it was discovered that in ethanol, under H{sub 2} and in the presence Of CS2, Precatalyst solutions containing Ru [as Ru{sub 3} (CO){sub 12} or RuCl{sub 3}] and Mo [as the H{sub 3}PMO{sub 12}0{sub 40} heteropolyanion (HPA)] decompose to form bimetallic, sulfided particles. Particle diameters run from 0.1 to 5 {mu}m depending on the rate of stirring. Catalyst particles with sizes ranging from 0.1--1 {mu}m can be prepared reproducibly. BET measured surface areas for these size particles ranged from 2 to 20 m2/g. These sulfided particles were found to catalyze, at temperatures of 200--250{degrees}C and hydrogen pressures of 200--1000 psig H{sub 2}, the N-ethylation of THQ to form NEt-THQ; rather than the formation of propylcyclohexane or propylbenzene, reaction products expected for HDN of THQ. Monometallic heterogeneous catalysts prepared from the individual precatalyst complexes, under identical conditions, show minimal activity for N-ethylation by comparison with the bimetallic catalyst. In the absence of H{sub 2}, the reaction proceeds such that THQ is converted to Q, N-EtTHQ, N-C{sub 6}H{sub 9}-THQ, and N-C{sub 6}H{sub 13}-THQ. The latter products appear to arise via acetaldehyde, formed as an intermediate by dehydrogenation of ethanol. Acetaldehyde either condenses with THQ to form N-Et-THQ, or self condenses (aldol condensation) prior to reaction with THQ thereby giving higher homolog alkylation products.

  14. Sulfided heterogeneous, bimetallic RuMo catalysts derived from mixtures of Ru sub 3 (CO) sub 12 (or RuCl sub 3 ) and a molybdenum heteropolyanion. The reactions of ethanol with tetrahydroquinoline

    SciTech Connect

    Koo, Sang-Man; Ryan, D.; Laine, R.M.

    1992-01-01

    Efforts have been made to develop Ru/Mo bimetallic catalyst systems for hydrodenitrogenation (HDN) of tetrahydroquinoline (THQ)- In the course of these studies, it was discovered that in ethanol, under H{sub 2} and in the presence Of CS2, Precatalyst solutions containing Ru (as Ru{sub 3} (CO){sub 12} or RuCl{sub 3}) and Mo (as the H{sub 3}PMO{sub 12}0{sub 40} heteropolyanion (HPA)) decompose to form bimetallic, sulfided particles. Particle diameters run from 0.1 to 5 {mu}m depending on the rate of stirring. Catalyst particles with sizes ranging from 0.1--1 {mu}m can be prepared reproducibly. BET measured surface areas for these size particles ranged from 2 to 20 m2/g. These sulfided particles were found to catalyze, at temperatures of 200--250{degrees}C and hydrogen pressures of 200--1000 psig H{sub 2}, the N-ethylation of THQ to form NEt-THQ; rather than the formation of propylcyclohexane or propylbenzene, reaction products expected for HDN of THQ. Monometallic heterogeneous catalysts prepared from the individual precatalyst complexes, under identical conditions, show minimal activity for N-ethylation by comparison with the bimetallic catalyst. In the absence of H{sub 2}, the reaction proceeds such that THQ is converted to Q, N-EtTHQ, N-C{sub 6}H{sub 9}-THQ, and N-C{sub 6}H{sub 13}-THQ. The latter products appear to arise via acetaldehyde, formed as an intermediate by dehydrogenation of ethanol. Acetaldehyde either condenses with THQ to form N-Et-THQ, or self condenses (aldol condensation) prior to reaction with THQ thereby giving higher homolog alkylation products.

  15. Intermolecular reaction screening as a tool for reaction evaluation.

    PubMed

    Collins, Karl D; Glorius, Frank

    2015-03-17

    Synthetic organic chemistry underpins many scientific disciplines. The development of new synthetic methods proceeds with the ultimate intention of providing access to novel structural motifs or providing safer, increasingly efficient, or more economical chemical reactions. To facilitate the identification and application of new methods in solving real synthetic problems, this Account will highlight the benefits of providing a fuller picture of both the scope and limitations of new reactions, with a primary focus on the evaluation of functional group tolerance and stability of a reaction using intermolecular screens. This Account will begin with a discussion on reaction evaluation, specifically considering the suitability of a given reaction for application in target-oriented synthesis. A comparison of desirable and essential criteria when choosing a reaction is given, and a short discussion on the value of negative and qualitative data is provided. The concept of intermolecular reaction screening will be introduced, and a direct comparison with a traditional substrate scope highlights the benefits and limitations of each and thus the complementary nature of these approaches. In recent years, a number of ad hoc applications of intermolecular screens to evaluate the functional group tolerance of a reaction or the stability of functional groups to a given set of reaction conditions have been reported, and will be discussed. More recently, we have developed a formal high-throughput intermolecular screening protocol that can be utilized to rapidly evaluate new chemical reactions. This simple and rapid protocol enables a much broader evaluation of a reaction in terms of functional group tolerance and the stability of chemical motifs to the reaction conditions than is feasible with a typical reaction scope. The development, evaluation, and application of this method within our group will be discussed in detail, with both the potential benefits and limitations highlighted and discussed. In addition, we will discuss more recent applications of intermolecular screens from both industrial and academic groups. Modifications in protocols and applications will be highlighted, including problem based evaluations, assessment of biomolecule compatibility, establishment of relative rate data, and the identification of new reactivity. Such screens have been applied in diverse chemistries including C-H functionalization reactions, frustrated Lewis-pair-catalyzed hydrogenations, heterogeneous catalysis, photoredox catalysis, enantioselective organocatalysis, and polymer science. We feel that the application of intermolecular screens to such a diversity of reactions highlights the practical simplicity of such screens. A summary of the applications and potential utility of intermolecular reaction evaluation is provided. PMID:25699585

  16. Communication: Resonance reaction in diffusion-influenced bimolecular reactions.

    PubMed

    Kolb, Jakob J; Angioletti-Uberti, Stefano; Dzubiella, Joachim

    2016-02-28

    We investigate the influence of a stochastically fluctuating step-barrier potential on bimolecular reaction rates by exact analytical theory and stochastic simulations. We demonstrate that the system exhibits a new "resonant reaction" behavior with rate enhancement if an appropriately defined fluctuation decay length is of the order of the system size. Importantly, we find that in the proximity of resonance, the standard reciprocal additivity law for diffusion and surface reaction rates is violated due to the dynamical coupling of multiple kinetic processes. Together, these findings may have important repercussions on the correct interpretation of various kinetic reaction problems in complex systems, as, e.g., in biomolecular association or catalysis. PMID:26931674

  17. Characterising Complex Enzyme Reaction Data

    PubMed Central

    Rahman, Syed Asad; Thornton, Janet M.

    2016-01-01

    The relationship between enzyme-catalysed reactions and the Enzyme Commission (EC) number, the widely accepted classification scheme used to characterise enzyme activity, is complex and with the rapid increase in our knowledge of the reactions catalysed by enzymes needs revisiting. We present a manual and computational analysis to investigate this complexity and found that almost one-third of all known EC numbers are linked to more than one reaction in the secondary reaction databases (e.g., KEGG). Although this complexity is often resolved by defining generic, alternative and partial reactions, we have also found individual EC numbers with more than one reaction catalysing different types of bond changes. This analysis adds a new dimension to our understanding of enzyme function and might be useful for the accurate annotation of the function of enzymes and to study the changes in enzyme function during evolution. PMID:26840640

  18. Formaldehyde reactions in dark clouds

    NASA Technical Reports Server (NTRS)

    Sen, A. D.; Anicich, V. G.; Federman, S. R.

    1992-01-01

    The low-pressure reactions of formaldehyde (H2CO) with D(+), D2(+), D3(+), and He(+) are studied by the ion-cyclotron resonance technique. These reactions are potential loss processes for formaldehyde in cores of dark interstellar clouds. The deuterated reactants represent direct analogs for protons. Rate coefficients and branching ratios of product channels have been measured. Charge transfer is observed to be the dominant reaction of H2CO with D(+), D2(+), and He(+) ions. Only the D3(+) reaction exhibits a proton-transfer channel. All reactions proceed at rate coefficients near the collision limit. Proton-deuteron exchange reactions are found to be inefficient processes in the formaldehyde system.

  19. Characterising Complex Enzyme Reaction Data.

    PubMed

    Dönerta?, Handan Melike; Martínez Cuesta, Sergio; Rahman, Syed Asad; Thornton, Janet M

    2016-01-01

    The relationship between enzyme-catalysed reactions and the Enzyme Commission (EC) number, the widely accepted classification scheme used to characterise enzyme activity, is complex and with the rapid increase in our knowledge of the reactions catalysed by enzymes needs revisiting. We present a manual and computational analysis to investigate this complexity and found that almost one-third of all known EC numbers are linked to more than one reaction in the secondary reaction databases (e.g., KEGG). Although this complexity is often resolved by defining generic, alternative and partial reactions, we have also found individual EC numbers with more than one reaction catalysing different types of bond changes. This analysis adds a new dimension to our understanding of enzyme function and might be useful for the accurate annotation of the function of enzymes and to study the changes in enzyme function during evolution. PMID:26840640

  20. Reactions inside nanoscale protein cages.

    PubMed

    Bode, Saskia A; Minten, Inge J; Nolte, Roeland J M; Cornelissen, Jeroen J L M

    2011-06-01

    Chemical reactions are traditionally carried out in bulk solution, but in nature confined spaces, like cell organelles, are used to obtain control in time and space of conversion. One way of studying these reactions in confinement is the development and use of small reaction vessels dispersed in solution, such as vesicles and micelles. The utilization of protein cages as reaction vessels is a relatively new field and very promising as these capsules are inherently monodisperse, in that way providing uniform reaction conditions, and are readily accessible to both chemical and genetic modifications. In this review, we aim to give an overview of the different kinds of nanoscale protein cages that have been employed as confined reaction spaces. PMID:21461437

  1. Two chamber reaction furnace

    DOEpatents

    Blaugher, R.D.

    1998-05-05

    A vertical two chamber reaction furnace is described. The furnace comprises a lower chamber having an independently operable first heating means for heating the lower chamber and a gas inlet means for admitting a gas to create an ambient atmosphere, and an upper chamber disposed above the lower chamber and having an independently operable second heating means for heating the upper chamber. Disposed between the lower chamber and the upper chamber is a vapor permeable diffusion partition. The upper chamber has a conveyor means for conveying a reactant there through. Of particular importance is the thallinating of long-length thallium-barium-calcium-copper oxide (TBCCO) or barium-calcium-copper oxide (BCCO) precursor tapes or wires conveyed through the upper chamber to thereby effectuate the deposition of vaporized thallium (being so vaporized as the first reactant in the lower chamber at a temperature between about 700 C and 800 C) on TBCCO or BCCO tape or wire (the second reactant) at its simultaneous annealing temperature in the upper chamber of about 800 to 950 C to thereby replace thallium oxide lost from TBCCO tape or wire because of the high annealing temperature or to deposit thallium on BCCO tape or wire. Continuously moving the tape or wire provides a single-step process that effectuates production of long-length TBCCO superconducting product. 2 figs.

  2. Hemolytic Transfusion Reactions

    PubMed Central

    Strobel, Erwin

    2008-01-01

    Summary The risk of hemolytic transfusion reactions (HTRs) is approximately 1:70,000 per unit. Acute HTRs occurring during or within 24 h after administration of a blood product are usually caused by transfusion of incompatible red blood cells (RBCs), and, more rarely, of a large volume of incompatible plasma. Delayed HTRs are caused by a secondary immune response to an antigen on the donor's RBCs. In some patients with delayed HTRs, an additional bystander hemolysis of the patient's RBCs can be assumed. Different mechanisms lead to intra- and extra-vascular hemolysis, such as complete complement activation, phagocytosis of RBCs covered with C3b by macrophages after incomplete complement activation, or destruction of RBCs covered only with IgG by direct cell-cell contact with K cells. The clinical consequences of HTRs are triggered via several pathophysiological pathways like formation of anaphylatoxins, release of cytokines causing a systemic inflammatory response syndrome, activation of the kinin system, the intrinsic clotting cascade and fibrinolysis resulting in hypotension, disseminated intravascular coagulation, diffuse bleeding, and disruption of microcirculation leading to renal failure and shock. In the following, the symptoms of HTR are introduced, laboratory investigations and treatment are described, and some recommendations for prevention are given. PMID:21512623

  3. Two chamber reaction furnace

    DOEpatents

    Blaugher, Richard D. (Evergreen, CO)

    1998-05-05

    A vertical two chamber reaction furnace. The furnace comprises a lower chamber having an independently operable first heating means for heating the lower chamber and a gas inlet means for admitting a gas to create an ambient atmosphere, and an upper chamber disposed above the lower chamber and having an independently operable second heating means for heating the upper chamber. Disposed between the lower chamber and the upper chamber is a vapor permeable diffusion partition. The upper chamber has a conveyor means for conveying a reactant there through. Of particular importance is the thallinating of long-length thallium-barium-calcium-copper oxide (TBCCO) or barium-calcium-copper oxide (BCCO) precursor tapes or wires conveyed through the upper chamber to thereby effectuate the deposition of vaporized thallium (being so vaporized as the first reactant in the lower chamber at a temperature between about 700.degree. and 800.degree. C.) on TBCCO or BCCO tape or wire (the second reactant) at its simultaneous annealing temperature in the upper chamber of about 800.degree. to 950.degree. C. to thereby replace thallium oxide lost from TBCCO tape or wire because of the high annealing temperature or to deposit thallium on BCCO tape or wire. Continuously moving the tape or wire provides a single-step process that effectuates production of long-length TBCCO superconducting product.

  4. Charge Transfer Reactions

    NASA Astrophysics Data System (ADS)

    Dennerl, Konrad

    2010-12-01

    Charge transfer, or charge exchange, describes a process in which an ion takes one or more electrons from another atom. Investigations of this fundamental process have accompanied atomic physics from its very beginning, and have been extended to astrophysical scenarios already many decades ago. Yet one important aspect of this process, i.e. its high efficiency in generating X-rays, was only revealed in 1996, when comets were discovered as a new class of X-ray sources. This finding has opened up an entirely new field of X-ray studies, with great impact due to the richness of the underlying atomic physics, as the X-rays are not generated by hot electrons, but by ions picking up electrons from cold gas. While comets still represent the best astrophysical laboratory for investigating the physics of charge transfer, various studies have already spotted a variety of other astrophysical locations, within and beyond our solar system, where X-rays may be generated by this process. They range from planetary atmospheres, the heliosphere, the interstellar medium and stars to galaxies and clusters of galaxies, where charge transfer may even be observationally linked to dark matter. This review attempts to put the various aspects of the study of charge transfer reactions into a broader historical context, with special emphasis on X-ray astrophysics, where the discovery of cometary X-ray emission may have stimulated a novel look at our universe.

  5. Racemization in Prins Cyclization Reactions

    PubMed Central

    Jasti, Ramesh

    2008-01-01

    Isotopic labeling experiments were performed in order to elucidate a new mechanism for racemization in Prins cyclization reactions. The loss in optical activity for these reactions was shown to occur by 2-oxonia-Cope rearrangements by way of a (Z)-oxocarbenium ion intermediate. Reaction conditions such as solvent, temperature, and the nucleophile employed played a critical role in whether an erosion in enantiomeric excess was observed. Additionally, certain structural features of Prins cyclization precursors were also shown to be important for preserving optical purity in these reactions. PMID:17031979

  6. Microstructure Manifestations in Nuclear Reactions

    NASA Astrophysics Data System (ADS)

    Karamian, S. A.

    2015-06-01

    Photonuclear reaction yields were studies at the range of giant dipole resonance for medium-mass targets and the probabilities for population of different final states were deduced and analyzed. In addition to the expected statistical trends expressed in the influence of the reaction threshold and of the product spin, there are observed the microstructure manifestations due to the individual level schemes of the products. The internal status of nucleons and their single-particle orbital momentum also make influence onto the reaction yield. The effects are isolated on the scale from tens % to orders of magnitude for the probability and branching ratio in reactions at modest energy.

  7. Dynamic Reaction Figures: An Integrative Vehicle for Understanding Chemical Reactions

    ERIC Educational Resources Information Center

    Schultz, Emeric

    2008-01-01

    A highly flexible learning tool, referred to as a dynamic reaction figure, is described. Application of these figures can (i) yield the correct chemical equation by simply following a set of menu driven directions; (ii) present the underlying "mechanism" in chemical reactions; and (iii) help to solve quantitative problems in a number of different…

  8. Dynamic Reaction Figures: An Integrative Vehicle for Understanding Chemical Reactions

    ERIC Educational Resources Information Center

    Schultz, Emeric

    2008-01-01

    A highly flexible learning tool, referred to as a dynamic reaction figure, is described. Application of these figures can (i) yield the correct chemical equation by simply following a set of menu driven directions; (ii) present the underlying "mechanism" in chemical reactions; and (iii) help to solve quantitative problems in a number of different…

  9. Acute dystonic reaction with rivastigmine.

    PubMed

    Dhikav, Vikas; Anand, Kuljeet Singh

    2013-08-01

    Dystonic reactions are adverse extrapyramidal side effects and are common to antipsychotics, antiemetics, and a variety of other drugs. Rivastigmine, an anticholinesterase of carbamate variety, is well tolerated. A case of acute dystonic reaction with rivastigmine patch is being reported. PMID:23561545

  10. Chemistry of heavy ion reactions

    SciTech Connect

    Hoffman, D.C.

    1988-10-01

    The use of heavy ions to induce nuclear reactions was reported as early as 1950. Since that time it has been one of the most active areas of nuclear research. Intense beams of ions as heavy as uranium with energies high enough to overcome the Coulomb barriers of even the heaviest elements are available. The wide variety of possible reactions gives rise to a multitude of products which have been studied by many ingenious chemical and physical techniques. Chemical techniques have been of special value for the separation and unequivocal identification of low yield species from the plethora of other nuclides present. Heavy ion reactions have been essential for the production of the trans-Md elements and a host of new isotopes. The systematics of compound nucleus reactions, transfer reactions, and deeply inelastic reactions have been elucidated using chemical techniques. A review of the variety of chemical procedures and techniques which have been developed for the study of heavy ion reactions and their products is given. Determination of the chemical properties of the trans-Md elements, which are very short-lived and can only be produced an ''atom-at-a-time'' via heavy ion reactions, is discussed. 53 refs., 19 figs.

  11. Adverse Reactions to Hallucinogenic Drugs.

    ERIC Educational Resources Information Center

    Meyer, Roger E. , Ed.

    This reports a conference of psychologists, psychiatrists, geneticists and others concerned with the biological and psychological effects of lysergic acid diethylamide and other hallucinogenic drugs. Clinical data are presented on adverse drug reactions. The difficulty of determining the causes of adverse reactions is discussed, as are different…

  12. Isosinglet approximation for nonelastic reactions

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.

    1972-01-01

    Group theoretic relations are derived between different combinations of projectile and secondary particles which appear to have a broad range of application in spacecraft shielding or radiation damage studies. These relations are used to reduce the experimental effort required to obtain nuclear reaction data for transport calculations. Implications for theoretical modeling are also noted, especially for heavy-heavy reactions.

  13. "Greening up" the Suzuki Reaction

    ERIC Educational Resources Information Center

    Aktoudianakis, Evangelos; Chan, Elton; Edward, Amanda R.; Jarosz, Isabel; Lee, Vicki; Mui, Leo; Thatipamala, Sonya S.; Dicks, Andrew P.

    2008-01-01

    This article describes the rapid, green synthesis of a biaryl compound (4-phenylphenol) via a Pd(0)-catalyzed Suzuki cross-coupling reaction in water. Mild reaction conditions and operational simplicity makes this experiment especially amenable to both mid- and upper-level undergraduates. The methodology exposes students to purely aqueous…

  14. Free Radical Reactions in Food.

    ERIC Educational Resources Information Center

    Taub, Irwin A.

    1984-01-01

    Discusses reactions of free radicals that determine the chemistry of many fresh, processed, and stored foods. Focuses on reactions involving ascorbic acid, myoglobin, and palmitate radicals as representative radicals derived from a vitamin, metallo-protein, and saturated lipid. Basic concepts related to free radical structure, formation, and…

  15. [Intolerance reactions of the skin].

    PubMed

    Sacher, R

    1987-07-01

    Intolerance reactions of the skin in which a decision is made on allergic and toxic genesis have increased in significance in recent years. Whereas antibodies blocking bacterial or viral antigens are formed in the normergic immune reaction, nonblocking antibodies to animal, plant or chemical heterologous substances are formed in an allergy as a result of an misdirected immunological reaction. Sensitization is favored by a) large structure and protein affinity of the allergen, b) irritation of the affected part of the skin by fungi or chemicals and c) genetic predisposition. Depending on the clinical manifestation, a distinction is made between inhaled allergens (bronchial asthma, hay fever), allergens ingested with the food (food allergy) and allergens which have come in contact with the skin (immediate reaction - urticaria, late reaction - contact eczema). Intolerance reactions of the skin which can be ruled out as the cause of an allergy are designated as toxic. Acute toxic reactions are based on violent or intensively physical (heat, cold, radiation), chemical (acids, alkalis, heavy metal salts, oils, solvents) or microbial damage to the skin (infection by fungi, bacteria, viruses). The degenerative eczema as the most important form of chronic toxic intolerance reaction arises by weak but continuously acting longterm mechanical or chemical exposures. PMID:2957865

  16. Participants' Reactions to Computerized Testing.

    ERIC Educational Resources Information Center

    Moe, Kim C.; Johnson, Marilyn F.

    This study investigated participants' reactions to computerized testing and assessed the practicability of this testing method in the classroom. A sample of 315 secondary-level students took a computerized and a printed version of a standardized aptitude test battery and a survey assessing their reactions to the computerized testing. Overall…

  17. Allergic reactions to insect secretions.

    PubMed

    Pecquet, Catherine

    2013-01-01

    Some products derived from insects can induce allergic reactions. The main characteristics of some products from honeybees, cochineal and silkworms are summarised here. We review allergic reactions from honey-derived products (propolis, wax, royal jelly), from cochineal products (shellac and carmine) and from silk : clinical features, allergological investigations and allergens if they are known. PMID:24449611

  18. TALYS: Comprehensive Nuclear Reaction Modeling

    SciTech Connect

    Koning, A.J.; Duijvestijn, M.C.; Hilaire, S.

    2005-05-24

    TALYS is a nuclear-reaction program which simulates nuclear reactions that involve neutrons, gamma-rays, protons, deuterons, tritons, helions, and alpha-particles, in the 1 keV - 200 MeV energy range. A suite of nuclear-reaction models has been implemented into a single code system, enabling us to evaluate basically all nuclear reactions beyond the resonance range. An overview is given of the main nuclear models used, such as newly developed optical models, various compound nucleus, fission, gamma-ray strength, level density, and pre-equilibrium models, all driven by a comprehensive database of nuclear-structure parameters. The predictive power of the code is demonstrated by comparing calculated results with a very diverse set of experimental observables. Our aim is to show that TALYS represents a robust computational approach that covers the whole path from fundamental nuclear-reaction models to the creation of complete data libraries for nuclear applications.

  19. Effective reaction rates for diffusion-limited reaction cycles.

    PubMed

    Na??cz-Jawecki, Pawe?; Szyma?ska, Paulina; Kocha?czyk, Marek; Mi?kisz, Jacek; Lipniacki, Tomasz

    2015-12-01

    Biological signals in cells are transmitted with the use of reaction cycles, such as the phosphorylation-dephosphorylation cycle, in which substrate is modified by antagonistic enzymes. An appreciable share of such reactions takes place in crowded environments of two-dimensional structures, such as plasma membrane or intracellular membranes, and is expected to be diffusion-controlled. In this work, starting from the microscopic bimolecular reaction rate constants and using estimates of the mean first-passage time for an enzyme-substrate encounter, we derive diffusion-dependent effective macroscopic reaction rate coefficients (EMRRC) for a generic reaction cycle. Each EMRRC was found to be half of the harmonic average of the microscopic rate constant (phosphorylation c or dephosphorylation d), and the effective (crowding-dependent) motility divided by a slowly decreasing logarithmic function of the sum of the enzyme concentrations. This implies that when c and d differ, the two EMRRCs scale differently with the motility, rendering the steady-state fraction of phosphorylated substrate molecules diffusion-dependent. Analytical predictions are verified using kinetic Monte Carlo simulations on the two-dimensional triangular lattice at the single-molecule resolution. It is demonstrated that the proposed formulas estimate the steady-state concentrations and effective reaction rates for different sets of microscopic reaction rates and concentrations of reactants, including a non-trivial example where with increasing diffusivity the fraction of phosphorylated substrate molecules changes from 10% to 90%. PMID:26646890

  20. Do reaction conditions affect the stereoselectivity in the Staudinger reaction?

    PubMed

    Wang, Yikai; Liang, Yong; Jiao, Lei; Du, Da-Ming; Xu, Jiaxi

    2006-09-01

    The stereochemistry is one of the critical issues in the Staudinger reaction. We have proposed the origin of the stereoselectivity recently. The effects of solvents, additives, and pathways of ketene generation on the stereoselectivity were investigated by using a clean Staudinger reaction, which is a sensitive reaction system to the stereoselectivity. The results indicate that the additives, usually existed and generated in the Staudinger reaction, and the pathways of the ketene generation do not generally affect the stereoselectivity. The solvent affects the stereoselectivity. The polar solvent is favorable to the formation of trans-beta-lactams. The addition orders of the reagents affect the stereoselectivity in the Staudinger reaction between acyl chlorides and imines. The addition of a tertiary amine into a solution of the acyl chloride and the imine generally decreases the stereoselectivity, which is affected by the interval between additions of the acyl chloride and the tertiary amine, and the imine substituents. Our current results provide further understanding on the stereochemistry of the Staudinger reaction between acyl chlorides and imines and on the factors affecting the stereochemistry and also provide a method to prepare beta-lactams with the desired relative configuration via rationally tuning the stereoselectivity-controlling factors in the Staudinger reaction. PMID:16930052

  1. Effective reaction rates for diffusion-limited reaction cycles

    NASA Astrophysics Data System (ADS)

    Nałecz-Jawecki, Paweł; Szymańska, Paulina; Kochańczyk, Marek; Miekisz, Jacek; Lipniacki, Tomasz

    2015-12-01

    Biological signals in cells are transmitted with the use of reaction cycles, such as the phosphorylation-dephosphorylation cycle, in which substrate is modified by antagonistic enzymes. An appreciable share of such reactions takes place in crowded environments of two-dimensional structures, such as plasma membrane or intracellular membranes, and is expected to be diffusion-controlled. In this work, starting from the microscopic bimolecular reaction rate constants and using estimates of the mean first-passage time for an enzyme-substrate encounter, we derive diffusion-dependent effective macroscopic reaction rate coefficients (EMRRC) for a generic reaction cycle. Each EMRRC was found to be half of the harmonic average of the microscopic rate constant (phosphorylation c or dephosphorylation d), and the effective (crowding-dependent) motility divided by a slowly decreasing logarithmic function of the sum of the enzyme concentrations. This implies that when c and d differ, the two EMRRCs scale differently with the motility, rendering the steady-state fraction of phosphorylated substrate molecules diffusion-dependent. Analytical predictions are verified using kinetic Monte Carlo simulations on the two-dimensional triangular lattice at the single-molecule resolution. It is demonstrated that the proposed formulas estimate the steady-state concentrations and effective reaction rates for different sets of microscopic reaction rates and concentrations of reactants, including a non-trivial example where with increasing diffusivity the fraction of phosphorylated substrate molecules changes from 10% to 90%.

  2. Reactions of cold trapped anions

    NASA Astrophysics Data System (ADS)

    Wester, Roland

    2008-03-01

    Interactions of negative ions with small organic molecules represent model systems for the investigation of reaction dynamics in few-body systems. Their corrugated potential energy landscape, originating in long-range attractive and short-range repulsive forces, requires the coupling of different degrees of freedom for reactions to occur. We have adopted two complementary approaches to study anion-molecule reaction dynamics. Using velocity map imaging in combination with crossed beams at low energy we study the differential cross section of negative ion reactions. For nucleophilic substitution reactions we have observed several distinct reaction mechanisms when varying the collision energy [1]. Total reaction rate measurements, which we carry out in the box-shaped potential of a 22pole ion trap [2], have revealed unexpected temperature-dependences for proton transfer and for cluster stabilisation at low temperatures. In addition, laser-induced photodetachment is studied in the trap to obtain absolute destruction cross sections for negative ions in light fields [3]. These results are relevant for the understanding of the negative ion abundances in interstellar molecular clouds. [1] J. Mikosch et al., Science (in press) [2] J. Mikosch et al., Phys. Rev. Lett. 98, 223001 (2007) [3] S. Trippel et al., Phys. Rev. Lett. 97, 193003 (2006)

  3. Mycoplasma-Latex Agglutination Reaction

    PubMed Central

    Morton, Harry E.

    1966-01-01

    Morton, Harry E. (University of Pennsylvania, Philadelphia). Mycoplasma-latex agglutination reaction. J. Bacteriol. 92:1196–1205. 1966.—The building up of Mycoplasma cell mass through adsorption to carrier particles as a method for enhancing the agglutination reaction to identify Mycoplasma is described. Mycoplasma cells of human, avian, swine, goat, sewage, and tissue-culture origin were adsorbed to latex particles (0.81 μ) and then were agglutinated by immune sera. The adsorption was demonstrated by electron microscopy. Either the cells or their antibodies, depending on which came into contact with the latex particles first, were adsorbed. The test, completed in less than 2 hr, consisted of serially diluting immune sera with buffered saline, adding the antigen, incubating in a water bath, centrifuging, and reading the reaction under 50 × microscope magnification. The antigen in each reaction tube, representing the growth from about 1.6 ml of culture, was estimated to contain 23 μg of protein (approximately one-tenth the amount of Mycoplasma cells needed for a direct agglutination reaction). In the sera from rabbits undergoing immunization with Mycoplasma antigens, the presence of anti-Mycoplasma antibodies was detected much sooner in the Mycoplasma-latex agglutination reaction test than in the agar-gel diffusion reaction and the growth inhibition tests. Four different lots of latex particles showed excellent uniformity of behavior and stability during storage and testing. Images PMID:4959043

  4. Siloxy alkynes in annulation reactions.

    PubMed

    Qian, Hui; Zhao, Wanxiang; Sun, Jianwei

    2014-12-01

    Siloxy alkynes are a family of versatile species in organic synthesis. This account reviews the annulation reactions of siloxy alkynes for the synthesis of a variety of carbo- and heterocyclic products. With various dipolarophiles or dipolarophile-like reaction partners, siloxy alkynes are capable of forming small (three- to six-membered) rings. Recently, we have expanded the scope to the synthesis of medium- and large-ring lactones, enabled by the design of new amphoteric molecules as well as a new ring-expansion strategy. These annulation reactions provide not only practically useful syntheses of cyclic molecules, but also important understanding of the fundamental reactivity of siloxy alkynes. PMID:25171137

  5. Hypersensitivity reaction associated with phenytoin

    PubMed Central

    Indu, T. H.; Basutkar, Roopa Satyanarayan

    2015-01-01

    Hypersensitivity reactions with antiepileptic drugs (AEDs) are generally associated with aromatic AEDs. We present a case of hypersensitivity reactions followed by administration of phenytoin with diazepam and ranitidine in a patient with generalized tonic-clonic seizures. Antigen-antibody reactions or decreased levels of epoxide hydrolase are well known with phenytoin. Increased level of serum phenytoin causing toxicities due to competitive inhibition with diazepam on co-administration was also reported in the literature. Prevention of the adverse effects with AEDs is a multi-stage process, which requires implementation of preventive measures through careful monitoring and prompts interventions. PMID:26692739

  6. Magnetically suspended reaction wheel assembly

    NASA Technical Reports Server (NTRS)

    Stocking, G.

    1984-01-01

    The magnetically suspended reaction wheel assembly (MSRWA) is the product of a development effort funded by the Air Force Materials Laboratory (AFML) at Wright Patterson AFB. The specific objective of the project was to establish the manufacturing processes for samarium cobalt magnets and demonstrate their use in a space application. The development was successful on both counts. The application portion of the program, which involves the magnetically suspended reaction wheel assembly, is emphasized. The requirements for the reaction wheel were based on the bias wheel requirements of the DSP satellite. The tasks included the design, fabrication, and test of the unit to the DSP program qualification requirements.

  7. [Arthropod bite reactions and pyodermias].

    PubMed

    Hengge, U R

    2008-08-01

    Tourists in the tropics often develop reactions to bites or stings of mosquitoes, fleas, mites, ants, bedbugs, beetles, larva, millipedes, spiders and scorpions. In addition, they may have fresh or salt water exposure to sponges, corals, jellyfish and sea urchins with resultant injury and inflammation. Bacterial skin infections (pyodermias) can follow bites or stings as well as mechanical trauma. The most common bacteria involved in skin infections are staphylococci and streptococci. For tourists, bacterial infections are often complicating a pruritic bite reaction and scratching. It is important to know the cause of the bite reaction and pyoderma in order to take appropriate therapeutic measures. PMID:18626616

  8. Catalytic Organometallic Reactions of Ammonia

    PubMed Central

    Klinkenberg, Jessica L.

    2012-01-01

    Until recently, ammonia had rarely succumbed to catalytic transformations with homogeneous catalysts, and the development of such reactions that are selective for the formation of single products under mild conditions has encountered numerous challenges. However, recently developed catalysts have allowed several classes of reactions to create products with nitrogen-containing functional groups from ammonia. These reactions include hydroaminomethylation, reductive amination, alkylation, allylic substitution, hydroamination, and cross-coupling. This Minireview describes examples of these processes and the factors that control catalyst activity and selectivity. PMID:20857466

  9. Color Changes Mark Polymer Reactions.

    ERIC Educational Resources Information Center

    Krieger, James H.

    1980-01-01

    Describes how polydiacetylenes can be used as educational aids. These polymers have conjugated backbones, which cause changes in color when the polydiacetylenes undergo various chemical and physical processes. Diagrams summarize all chemical reactions and their associated color changes. (CS)

  10. Method for conducting exothermic reactions

    DOEpatents

    Smith, Jr., Lawrence (Bellaire, TX); Hearn, Dennis (Houston, TX); Jones, Jr., Edward M. (Friendswood, TX)

    1993-01-01

    A liquid phase process for oligomerization of C.sub.4 and C.sub.5 isoolefins or the etherification thereof with C.sub.1 to C.sub.6 alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120.degree. to 300.degree. F. wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

  11. Method for conducting exothermic reactions

    DOEpatents

    Smith, L. Jr.; Hearn, D.; Jones, E.M. Jr.

    1993-01-05

    A liquid phase process for oligomerization of C[sub 4] and C[sub 5] isoolefins or the etherification thereof with C[sub 1] to C[sub 6] alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120 to 300 F. wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

  12. Experimental Study of Serpentinization Reactions

    NASA Technical Reports Server (NTRS)

    Cohen, B. A.; Brearley, A. J.; Ganguly, J.; Liermann, H.-P.; Keil, K.

    2004-01-01

    Current carbonaceous chondrite parent-body thermal models [1-3] produce scenarios that are inconsistent with constraints on aqueous alteration conditions based on meteorite mineralogical evidence, such as phase stability relationships within the meteorite matrix minerals [4] and isotope equilibration arguments [5, 6]. This discrepancy arises principally because of the thermal runaway effect produced by silicate hydration reactions (here loosely called serpentinization, as the principal products are serpentine minerals), which are so exothermic as to produce more than enough heat to melt more ice and provide a self-sustaining chain reaction. One possible way to dissipate the heat of reaction is to use a very small parent body [e.g., 2] or possibly a rubble pile model. Another possibility is to release this heat more slowly, which depends on the alteration reaction path and kinetics.

  13. Solar-thermal reaction processing

    DOEpatents

    Weimer, Alan W; Dahl, Jaimee K; Lewandowski, Allan A; Bingham, Carl; Raska Buechler, Karen J; Grothe, Willy

    2014-03-18

    In an embodiment, a method of conducting a high temperature chemical reaction that produces hydrogen or synthesis gas is described. The high temperature chemical reaction is conducted in a reactor having at least two reactor shells, including an inner shell and an outer shell. Heat absorbing particles are included in a gas stream flowing in the inner shell. The reactor is heated at least in part by a source of concentrated sunlight. The inner shell is heated by the concentrated sunlight. The inner shell re-radiates from the inner wall and heats the heat absorbing particles in the gas stream flowing through the inner shell, and heat transfers from the heat absorbing particles to the first gas stream, thereby heating the reactants in the gas stream to a sufficiently high temperature so that the first gas stream undergoes the desired reaction(s), thereby producing hydrogen or synthesis gas in the gas stream.

  14. Thermodynamics of Random Reaction Networks

    PubMed Central

    Fischer, Jakob; Kleidon, Axel; Dittrich, Peter

    2015-01-01

    Reaction networks are useful for analyzing reaction systems occurring in chemistry, systems biology, or Earth system science. Despite the importance of thermodynamic disequilibrium for many of those systems, the general thermodynamic properties of reaction networks are poorly understood. To circumvent the problem of sparse thermodynamic data, we generate artificial reaction networks and investigate their non-equilibrium steady state for various boundary fluxes. We generate linear and nonlinear networks using four different complex network models (Erd?s-Rényi, Barabási-Albert, Watts-Strogatz, Pan-Sinha) and compare their topological properties with real reaction networks. For similar boundary conditions the steady state flow through the linear networks is about one order of magnitude higher than the flow through comparable nonlinear networks. In all networks, the flow decreases with the distance between the inflow and outflow boundary species, with Watts-Strogatz networks showing a significantly smaller slope compared to the three other network types. The distribution of entropy production of the individual reactions inside the network follows a power law in the intermediate region with an exponent of circa ?1.5 for linear and ?1.66 for nonlinear networks. An elevated entropy production rate is found in reactions associated with weakly connected species. This effect is stronger in nonlinear networks than in the linear ones. Increasing the flow through the nonlinear networks also increases the number of cycles and leads to a narrower distribution of chemical potentials. We conclude that the relation between distribution of dissipation, network topology and strength of disequilibrium is nontrivial and can be studied systematically by artificial reaction networks. PMID:25723751

  15. Thermodynamics of random reaction networks.

    PubMed

    Fischer, Jakob; Kleidon, Axel; Dittrich, Peter

    2015-01-01

    Reaction networks are useful for analyzing reaction systems occurring in chemistry, systems biology, or Earth system science. Despite the importance of thermodynamic disequilibrium for many of those systems, the general thermodynamic properties of reaction networks are poorly understood. To circumvent the problem of sparse thermodynamic data, we generate artificial reaction networks and investigate their non-equilibrium steady state for various boundary fluxes. We generate linear and nonlinear networks using four different complex network models (Erd?s-Rényi, Barabási-Albert, Watts-Strogatz, Pan-Sinha) and compare their topological properties with real reaction networks. For similar boundary conditions the steady state flow through the linear networks is about one order of magnitude higher than the flow through comparable nonlinear networks. In all networks, the flow decreases with the distance between the inflow and outflow boundary species, with Watts-Strogatz networks showing a significantly smaller slope compared to the three other network types. The distribution of entropy production of the individual reactions inside the network follows a power law in the intermediate region with an exponent of circa -1.5 for linear and -1.66 for nonlinear networks. An elevated entropy production rate is found in reactions associated with weakly connected species. This effect is stronger in nonlinear networks than in the linear ones. Increasing the flow through the nonlinear networks also increases the number of cycles and leads to a narrower distribution of chemical potentials. We conclude that the relation between distribution of dissipation, network topology and strength of disequilibrium is nontrivial and can be studied systematically by artificial reaction networks. PMID:25723751

  16. Reaction pathways and possible path bifurcation for the Schmidt reaction.

    PubMed

    Katori, Tetsuji; Itoh, Shuhei; Sato, Makoto; Yamataka, Hiroshi

    2010-03-17

    The N(2) liberation from iminodiazonium ion (2-X) is a key step of the Schmidt rearrangement of ketones. Molecular orbital calculations showed that two concurrent reaction channels, syn-benzyl fragmentation and anti-Me rearrangement, exist for syn-2, whereas anti-2-X proceeds via a single TS. Substituent effect analyses of the reactions of syn-2-X gave concave-upward plots, typical for a concurrent reaction mechanism. On the other hand, the reactions of anti-2-X gave linear Hammett plots, indicative of a single reaction mechanism for all anti-2-X. IRC calculations, however, revealed that the TS led to either an anti-benzyl rearrangement or an anti-benzyl fragmentation product depending on the substituent. Thus, the change of the mechanism (identity of the product) could not be detected by the Hammett plots. Ab initio dynamics simulations for anti-2-X were found to follow the IRC path for X = p-NO(2), giving the rearrangement product, and almost so for X = p-MeO, giving the fragmentation products. However, in borderline cases where X is less donating than p-MeO and less withdrawing than p-NO(2), the trajectories did not follow the minimum energy path on the potential energy surface but gave both rearrangement and fragmentation products directly from the single TS. This is a novel example of path bifurcation for a closed shell anionic reaction. It was concluded that a reactivity-selectivity argument based on the traditional TS theory might not always be applicable even to a well-known textbook organic reaction. PMID:20166731

  17. Reciprocity theory of homogeneous reactions

    NASA Astrophysics Data System (ADS)

    Agbormbai, Adolf A.

    1990-03-01

    The reciprocity formalism is applied to the homogeneous gaseous reactions in which the structure of the participating molecules changes upon collision with one another, resulting in a change in the composition of the gas. The approach is applied to various classes of dissociation, recombination, rearrangement, ionizing, and photochemical reactions. It is shown that for the principle of reciprocity to be satisfied it is necessary that all chemical reactions exist in complementary pairs which consist of the forward and backward reactions. The backward reaction may be described by either the reverse or inverse process. The forward and backward processes must satisfy the same reciprocity equation. Because the number of dynamical variables is usually unbalanced on both sides of a chemical equation, it is necessary that this balance be established by including as many of the dynamical variables as needed before the reciprocity equation can be formulated. Statistical transformation models of the reactions are formulated. The models are classified under the titles free exchange, restricted exchange and simplified restricted exchange. The special equations for the forward and backward processes are obtained. The models are consistent with the H theorem and Le Chatelier's principle. The models are also formulated in the context of the direct simulation Monte Carlo method.

  18. Organic synthesis by quench reactions.

    PubMed

    Park, W K; Hochstim, A R

    1975-01-01

    The effects of chemical quench reactions on the formation of organic compounds at a water surface under simulated primordial earth conditions were investigated for the study of chemical evolution. A mixture of gaseous methane and ammonia over a water surface was exposed to an arc discharge between an electrode and the water surface. This discharge served as a source of dissociated, ionized and excited atomic and molecular species. Various organic molecules were formed in the gaseous, aqueous, and solid states by a subsequent quenching of these reactive species on the water surface. The effects of these water-surface quench reactions were assessed by comparing the amounts of synthesized molecules to the amounts which formed during the discharge of an arc above the water level. The results showed that: (1) the water-surface quench reaction permitted faster rates of formation of an insoluble solid and (2) the quench discharge yielded twice as much amino acids and 17 times more insoluble solids by weight than the other discharge. The highest yield of amino acids with the quench reaction was 9 x 10-7 molecules per erg of input energy. These observations indicate that quench reactions on the oceans, rain, and clouds that would have followed excitation by lightning and shock waves may have played an important role in the prebiotic milieu. Furthermore, the possibility exists that quench reactions can be exploited for the synthesis of organic compounds on a larger scale from simple starting materials. PMID:1153193

  19. Kinetics of actinide complexation reactions

    SciTech Connect

    Nash, K.L.; Sullivan, J.C.

    1997-09-01

    Though the literature records extensive compilations of the thermodynamics of actinide complexation reactions, the kinetics of complex formation and dissociation reactions of actinide ions in aqueous solutions have not been extensively investigated. In light of the central role played by such reactions in actinide process and environmental chemistry, this situation is somewhat surprising. The authors report herein a summary of what is known about actinide complexation kinetics. The systems include actinide ions in the four principal oxidation states (III, IV, V, and VI) and complex formation and dissociation rates with both simple and complex ligands. Most of the work reported was conducted in acidic media, but a few address reactions in neutral and alkaline solutions. Complex formation reactions tend in general to be rapid, accessible only to rapid-scan and equilibrium perturbation techniques. Complex dissociation reactions exhibit a wider range of rates and are generally more accessible using standard analytical methods. Literature results are described and correlated with the known properties of the individual ions.

  20. Nuclear Reactions for Astrophysics and Other Applications

    SciTech Connect

    Escher, J E; Burke, J T; Dietrich, F S; Scielzo, N D; Ressler, J J

    2011-03-01

    Cross sections for compound-nuclear reactions are required for many applications. The surrogate nuclear reactions method provides an indirect approach for determining cross sections for reactions on unstable isotopes, which are difficult or impossible to measure otherwise. Current implementations of the method provide useful cross sections for (n,f) reactions, but need to be improved upon for applications to capture reactions.

  1. Reaction rates for mesoscopic reaction-diffusion kinetics

    NASA Astrophysics Data System (ADS)

    Hellander, Stefan; Hellander, Andreas; Petzold, Linda

    2015-02-01

    The mesoscopic reaction-diffusion master equation (RDME) is a popular modeling framework frequently applied to stochastic reaction-diffusion kinetics in systems biology. The RDME is derived from assumptions about the underlying physical properties of the system, and it may produce unphysical results for models where those assumptions fail. In that case, other more comprehensive models are better suited, such as hard-sphere Brownian dynamics (BD). Although the RDME is a model in its own right, and not inferred from any specific microscale model, it proves useful to attempt to approximate a microscale model by a specific choice of mesoscopic reaction rates. In this paper we derive mesoscopic scale-dependent reaction rates by matching certain statistics of the RDME solution to statistics of the solution of a widely used microscopic BD model: the Smoluchowski model with a Robin boundary condition at the reaction radius of two molecules. We also establish fundamental limits on the range of mesh resolutions for which this approach yields accurate results and show both theoretically and in numerical examples that as we approach the lower fundamental limit, the mesoscopic dynamics approach the microscopic dynamics. We show that for mesh sizes below the fundamental lower limit, results are less accurate. Thus, the lower limit determines the mesh size for which we obtain the most accurate results.

  2. Concordant Chemical Reaction Networks and the Species-Reaction Graph

    PubMed Central

    Shinar, Guy; Feinberg, Martin

    2015-01-01

    In a recent paper it was shown that, for chemical reaction networks possessing a subtle structural property called concordance, dynamical behavior of a very circumscribed (and largely stable) kind is enforced, so long as the kinetics lies within the very broad and natural weakly monotonic class. In particular, multiple equilibria are precluded, as are degenerate positive equilibria. Moreover, under certain circumstances, also related to concordance, all real eigenvalues associated with a positive equilibrium are negative. Although concordance of a reaction network can be decided by readily available computational means, we show here that, when a nondegenerate network’s Species-Reaction Graph satisfies certain mild conditions, concordance and its dynamical consequences are ensured. These conditions are weaker than earlier ones invoked to establish kinetic system injectivity, which, in turn, is just one ramification of network concordance. Because the Species-Reaction Graph resembles pathway depictions often drawn by biochemists, results here expand the possibility of inferring significant dynamical information directly from standard biochemical reaction diagrams. PMID:22940368

  3. Nonlocality in deuteron stripping reactions.

    PubMed

    Timofeyuk, N K; Johnson, R C

    2013-03-15

    We propose a new method for the analysis of deuteron stripping reactions, A(d,p)B, in which the nonlocality of nucleon-nucleus interactions and three-body degrees of freedom are accounted for in a consistent way. The model deals with equivalent local nucleon potentials taken at an energy shifted by ∼40  MeV from the "E(d)/2" value frequently used in the analysis of experimental data, where E(d) is the incident deuteron energy. The "E(d)/2" rule lies at the heart of all three-body analyses of (d, p) reactions performed so far with the aim of obtaining nuclear structure properties such as spectroscopic factors and asymptotic normalization coefficients that are crucial for our understanding of nuclear shell evolution in neutron- and proton-rich regions of the nuclear periodic table and for predicting the cross sections of stellar reactions. The large predicted shift arises from the large relative kinetic energy of the neutron and proton in the incident deuteron in those components of the n+p+A wave function that dominate the (d, p) reaction amplitude. The large shift reduces the effective d-A potentials and leads to a change in predicted (d, p) cross sections, thus affecting the interpretation of these reactions in terms of nuclear structure. PMID:25166525

  4. Directly Imaging Fast Reaction Fronts

    SciTech Connect

    Kim, J S; LaGrange, T B; Reed, B W; Campbell, G H; Browning, N D

    2007-02-21

    Direct observation of fast intermetallic phase formation in Reactive Multilayer Foils (RMLFs) has been achieved. Snap-shots of the reaction appear to show development of mass-thickness contrast of the unmixed Al and Ni layers and an intermetallic phase. Electron imaging of these RMLF reaction fronts have never been attained in the past. The reaction front travels at {approx}10 meters per second as the nanoscale layers mix in an exothermic chain reaction, thus making traditional in situ electron microscopy {approx}10{sup 5} times too slow to produce such an image. The DTEM capability to produce several million electrons within nanoseconds for single-pulse imaging made this experiment possible. Additionally, the sample drive laser ensures reliable experiment initiation and repeatability. In no other way could such a high velocity event be captured at this magnification. RMLF reaction fronts continue to be analyzed via diffraction for complete phase evolution with respect to time. High quality diffraction patterns enable quantitative phase information to be obtained for future comparison to simulation.

  5. Aluminium and injection site reactions.

    PubMed Central

    Culora, G A; Ramsay, A D; Theaker, J M

    1996-01-01

    AIMS: To alert pathologists to the spectrum of histological appearances that may be seen in injection site reactions related to aluminium. METHODS: Four cases of injection site reaction were examined microscopically using routine staining with haematoxylin and eosin, electron microscopy and by electron probe microanalysis. RESULTS: As in previous reports, all four cases included collections of histiocytes which contained faint granular brownish refractile material within their cytoplasm; ultrastructural examination showed this to be aluminium. Two cases showed a prominent inflammatory reaction with numerous lymphoid follicles and a notable eosinophilic infiltrate. Two cases showed unusual features not described previously. In one, there was a sclerosing lipogranuloma-like reaction with unlined cystic spaces containing crystalline material. The other case presented as a large symptomatic subcutaneous swelling which microscopically showed diffuse and wide-spread involvement of the subcutis by a lymphoid infiltrate with prominent lymphoid follicles. CONCLUSIONS: This report highlights the changes encountered in aluminium injection site reactions and emphasises that the lesions have a wider range of histological appearances than described previously. Images PMID:8943754

  6. Quantifying mixing using equilibrium reactions

    SciTech Connect

    Wheat, Philip M.; Posner, Jonathan D.

    2009-03-15

    A method of quantifying equilibrium reactions in a microchannel using a fluorometric reaction of Fluo-4 and Ca{sup 2+} ions is presented. Under the proper conditions, equilibrium reactions can be used to quantify fluid mixing without the challenges associated with constituent mixing measures such as limited imaging spatial resolution and viewing angle coupled with three-dimensional structure. Quantitative measurements of CaCl and calcium-indicating fluorescent dye Fluo-4 mixing are measured in Y-shaped microchannels. Reactant and product concentration distributions are modeled using Green's function solutions and a numerical solution to the advection-diffusion equation. Equilibrium reactions provide for an unambiguous, quantitative measure of mixing when the reactant concentrations are greater than 100 times their dissociation constant and the diffusivities are equal. At lower concentrations and for dissimilar diffusivities, the area averaged fluorescence signal reaches a maximum before the species have interdiffused, suggesting that reactant concentrations and diffusivities must be carefully selected to provide unambiguous, quantitative mixing measures. Fluorometric equilibrium reactions work over a wide range of pH and background concentrations such that they can be used for a wide variety of fluid mixing measures including industrial or microscale flows.

  7. Combustion kinetics and reaction pathways

    SciTech Connect

    Klemm, R.B.; Sutherland, J.W.

    1993-12-01

    This project is focused on the fundamental chemistry of combustion. The overall objectives are to determine rate constants for elementary reactions and to elucidate the pathways of multichannel reactions. A multitechnique approach that features three independent experiments provides unique capabilities in performing reliable kinetic measurements over an exceptionally wide range in temperature, 300 to 2500 K. Recent kinetic work has focused on experimental studies and theoretical calculations of the methane dissociation system (CH{sub 4} + Ar {yields} CH{sub 3} + H + Ar and H + CH{sub 4} {yields} CH{sub 3} + H{sub 2}). Additionally, a discharge flow-photoionization mass spectrometer (DF-PIMS) experiment is used to determine branching fractions for multichannel reactions and to measure ionization thresholds of free radicals. Thus, these photoionization experiments generate data that are relevant to both reaction pathways studies (reaction dynamics) and fundamental thermochemical research. Two distinct advantages of performing PIMS with high intensity, tunable vacuum ultraviolet light at the National Synchrotron Light Source are high detection sensitivity and exceptional selectivity in monitoring radical species.

  8. Inorganic Reaction Mechanisms Part II: Homogeneous Catalysis

    ERIC Educational Resources Information Center

    Cooke, D. O.

    1976-01-01

    Suggests several mechanisms for catalysis by metal ion complexes. Discusses the principal factors of importance in these catalysis reactions and suggests reactions suitable for laboratory study. (MLH)

  9. A unified diabatic description for electron transfer reactions, isomerization reactions, proton transfer reactions, and aromaticity.

    PubMed

    Reimers, Jeffrey R; McKemmish, Laura K; McKenzie, Ross H; Hush, Noel S

    2015-10-14

    While diabatic approaches are ubiquitous for the understanding of electron-transfer reactions and have been mooted as being of general relevance, alternate applications have not been able to unify the same wide range of observed spectroscopic and kinetic properties. The cause of this is identified as the fundamentally different orbital configurations involved: charge-transfer phenomena involve typically either 1 or 3 electrons in two orbitals whereas most reactions are typically closed shell. As a result, two vibrationally coupled electronic states depict charge-transfer scenarios whereas three coupled states arise for closed-shell reactions of non-degenerate molecules and seven states for the reactions implicated in the aromaticity of benzene. Previous diabatic treatments of closed-shell processes have considered only two arbitrarily chosen states as being critical, mapping these states to those for electron transfer. We show that such effective two-state diabatic models are feasible but involve renormalized electronic coupling and vibrational coupling parameters, with this renormalization being property dependent. With this caveat, diabatic models are shown to provide excellent descriptions of the spectroscopy and kinetics of the ammonia inversion reaction, proton transfer in N2H7(+), and aromaticity in benzene. This allows for the development of a single simple theory that can semi-quantitatively describe all of these chemical phenomena, as well as of course electron-transfer reactions. It forms a basis for understanding many technologically relevant aspects of chemical reactions, condensed-matter physics, chemical quantum entanglement, nanotechnology, and natural or artificial solar energy capture and conversion. PMID:26193994

  10. Surface reactions of natural glasses

    SciTech Connect

    White, A.F.

    1986-12-31

    Reactions at natural glass surfaces are important in studies involving nuclear waste transport due to chemical control on ground water in host rocks such as basalt and tuff, to potential diffusion into natural hydrated glass surfaces and as natural analogs for waste glass stability. Dissolution kinetics can be described by linear surface reaction coupled with cation interdiffusion with resulting rates similar to those of synthetic silicate glasses. Rates of Cs diffusion into hydrated obsidian surfaces between 25{sup 0} and 75{sup 0}C were determined by XPS depth profiles and loss rates from aqueous solutions. Calculated diffusion coefficients were ten others of magnitude more rapid than predicted from an Arrhenius extrapolation of high temperature tracer diffusion data due to surface hydration reactions.

  11. Reaction theory for exotic nuclei

    SciTech Connect

    Bonaccorso, Angela

    2014-05-09

    Exotic nuclei are usually defined as those with unusual N/Z ratios. They can be found in the crust of neutron stars enbedded in a sea of electrons or created in laboratory by fragmentation of a primary beam (in-flight method) or of the target (ISOL method). They are extremely important for nuclear astrophysics, see for example Ref.[1]. Furthermore by studying them we can check the limits of validity of nuclear reaction and structure models. This contribution will be devoted to the understanding of how by using reaction theory and comparing to the data we can extract structure information. We shall discuss the differences between the mechanisms of transfer and breakup reactions, an we will try to explain how nowadays it is possible to do accurate spectroscopy in extreme conditions.

  12. Radiation reaction in quantum vacuum

    NASA Astrophysics Data System (ADS)

    Seto, Keita

    2015-02-01

    Since the development of the radiating electron theory by P. A. M. Dirac in 1938 [P. A. M. Dirac, Proc. R. Soc. Lond. A 167, 148 (1938)], many authors have tried to reformulate this model, called the "radiation reaction". Recently, this equation has become important for ultra-intense laser-electron (plasma) interactions. In our recent research, we found a stabilized model of the radiation reaction in quantum vacuum [K. Seto et al., Prog. Theor. Exp. Phys. 2014, 043A01 (2014)]. It led us to an updated Fletcher-Millikan charge-to-mass ratio including radiation. In this paper, I will discuss the generalization of our previous model and the new equation of motion with the radiation reaction in quantum vacuum via photon-photon scatterings and also introduce the new tensor d{E}^{? ? ? ? }/dm, as the anisotropy of the charge-to-mass ratio.

  13. Postcolumn reaction detectors for HPLC

    SciTech Connect

    Frei, R.W.; Jansen, H.; Brinkman, U.A.T.

    1985-12-01

    Currently, the best and most reliable HPLC (high-performance liquid chromatography) detectors are UV-VIS absorbance, fluorescence, and electrochemical detectors. It is attractive to try to expand their range of application by using suitable chemical derivatization techniques to convert the analytes of interest with their originally poor detection properties into compounds that can be detected with high sensitivity with these detectors. Besides an improvement of the detection properties, the chemical reaction can also enhance the selectivity of the total analytical method. The derivatization can be carried out either prior to the HPLC separation or by doing the reaction in an on-line postcolumn mode. Comparative advantages and disadvantages of these two approaches have been discussed previously. This paper will discuss on-line postcolumn derivatization. A general scheme of an HPLC system equipped with an on-line postcolumn reaction detector is given. 40 references, 6 figures, 2 tables.

  14. Urticarial intolerance reaction to cetirizine.

    PubMed

    Schröter, S; Damveld, B; Marsch, W C

    2002-05-01

    The paradoxical acute exacerbation of pre-existing chronic idiopathic urticaria accompanied by intense generalized pruritus, facial oedema, and dyspnoea in a 36-year-old-woman 3-4 h after a single oral dose of 10 mg cetirizine (Zyrtec tablets), suggested the presence of an underlying intolerance reaction. However, a type I hypersensitivity reaction also had to be excluded. Detailed allergy testing supported the view that the patient had suffered an intolerance reaction to cetirizine. This is the third known case of most probably a nonallergic generalized urticaria following the administration of cetirizine, a drug with extensive usage worldwide. However a type I sensitization to cetirizine is indeed possible, as has been demonstrated in this research with the verification of cetirizine-specific IgE antibodies in one of the control sera. PMID:12072003

  15. Coupled Reactions "versus" Connected Reactions: Coupling Concepts with Terms

    ERIC Educational Resources Information Center

    Aledo, Juan Carlos

    2007-01-01

    A hallmark of living matter is its ability to extract and transform energy from the environment. Not surprisingly, biology students are required to take thermodynamics. The necessity of coupling exergonic reactions to endergonic processes is easily grasped by most undergraduate students. However, when addressing the thermodynamic concept of…

  16. Coupled Reactions "versus" Connected Reactions: Coupling Concepts with Terms

    ERIC Educational Resources Information Center

    Aledo, Juan Carlos

    2007-01-01

    A hallmark of living matter is its ability to extract and transform energy from the environment. Not surprisingly, biology students are required to take thermodynamics. The necessity of coupling exergonic reactions to endergonic processes is easily grasped by most undergraduate students. However, when addressing the thermodynamic concept of…

  17. Vision 2020. Reaction Engineering Roadmap

    SciTech Connect

    Klipstein, David H.; Robinson, Sharon

    2001-01-01

    The Reaction Engineering Roadmap is a part of an industry- wide effort to create a blueprint of the research and technology milestones that are necessary to achieve longterm industry goals. This report documents the results of a workshop focused on the research needs, technology barriers, and priorities of the chemical industry as they relate to reaction engineering viewed first by industrial use (basic chemicals; specialty chemicals; pharmaceuticals; and polymers) and then by technology segment (reactor system selection, design, and scale-up; chemical mechanism development and property estimation; dealing with catalysis; and new, nonstandard reactor types).

  18. Learning to predict chemical reactions.

    PubMed

    Kayala, Matthew A; Azencott, Chloé-Agathe; Chen, Jonathan H; Baldi, Pierre

    2011-09-26

    Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles, respectively, are not high throughput, are not generalizable or scalable, and lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry data set consisting of 1630 full multistep reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top-ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of nonproductive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system is generalizable, making reasonable predictions over reactants and conditions which the rule-based expert does not handle. A web interface to the machine learning based mechanistic reaction predictor is accessible through our chemoinformatics portal ( http://cdb.ics.uci.edu) under the Toolkits section. PMID:21819139

  19. Learning to Predict Chemical Reactions

    PubMed Central

    Kayala, Matthew A.; Azencott, Chloé-Agathe; Chen, Jonathan H.

    2011-01-01

    Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles respectively are not high-throughput, are not generalizable or scalable, or lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry dataset consisting of 1630 full multi-step reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval, problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of non-productive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system is generalizable, making reasonable predictions over reactants and conditions which the rule-based expert does not handle. A web interface to the machine learning based mechanistic reaction predictor is accessible through our chemoinformatics portal (http://cdb.ics.uci.edu) under the Toolkits section. PMID:21819139

  20. Molecular Reaction Dynamics and Solvation.

    NASA Astrophysics Data System (ADS)

    Kim, Seong Keun

    A potential energy surface was constructed for the triatomic molecule Li_2H using a semiempirical method akin to the diatomics-in-molecules theory. Valence bond configurations were chosen to include the major ionic contributions in the ground state potential energy. Quasiclassical trajectories were run on this potential energy surface. The results of these calculations are shown to be generally in accord with the experimental investigations of analogous reactions of H atoms with bigger alkali dimer molecules. Certain aspects of chemical reaction dynamics which have been largely overlooked were examined. These involve correlations of vector properties in chemical reactions. Specifically, the strong correlation between orbital and rotational angular momenta in the product channel of this reaction was shown to be the reason for a seemingly contradictory set of distributions of different angles. Gas phase solvation of nucleic acid base molecules was studied using clusters produced by supersonic expansion. Relative stabilities of the species with different numbers of solvent molecules were studied by varying the expansion conditions. The ionization potentials were measured as a function of the number of solvent molecules. Rather distinct effects of hydration were observed for the ionization potentials of adenine and thymine.

  1. Runaway Reaction: Solving for X.

    ERIC Educational Resources Information Center

    Bartz, Solveig A.

    2003-01-01

    This article examines the runaway reaction as it was displayed by Barry, a 14-year-old eighth-grade boy with learning disabilities. It identifies some of the common characteristics of this response and proposes school intervention methods. Functional behavioral assessments and strength-based assessments are encouraged, along with using strategy…

  2. Knoevenagel Reaction of Unprotected Sugars

    NASA Astrophysics Data System (ADS)

    Scherrmann, Marie-Christine

    The Knoevenagel reaction of unprotected sugars was investigated in the 1950s using zinc chloride as promoter. The so-called Garcia Gonzalez reaction had been almost forgotten for 50 years, until the emergence of new water tolerant catalysts having Lewis acid behavior. The reaction was thus reinvestigated and optimal conditions have been found to prepare trihydroxylated furan derivatives from pentose or ?-tetrahydrofuranylfuran from hexoses with non-cyclic ?-keto ester or ?-diketones. Other valuable compounds such as ?-linked tetrahydrobenzofuranyl glycosides or hydroxyalkyl-3,3,6,6,-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione can be obtained using cyclic ?-dicarbonylic derivatives. Apart from one report in the 1950s, the Knoevenagel reaction of unprotected carbohydrate in basic condition has been studied only in the mid-1980s to prepare C-glycosyl barbiturates from barbituric acids and, later on, from non-cyclic ?-diketones, ?-C-glycosidic ketones. The efficient method exploited to prepare such compounds has found an industrial development in cosmetics.

  3. The Pitfalls of Precipitation Reactions.

    ERIC Educational Resources Information Center

    Slade, Peter W.; Rayner-Canham, Geoffrey W.

    1990-01-01

    Described are some of the difficulties presented in these reactions by competing equilibria that are usually ignored. Situations involving acid-base equilibria, solubility product calculations, the use of ammonia as a complexing agent, and semiquantitative comparisons of solubility product values are discussed. (CW)

  4. Reactions to threatening health messages

    PubMed Central

    2012-01-01

    Background Threatening health messages that focus on severity are popular, but frequently have no effect or even a counterproductive effect on behavior change. This paradox (i.e. wide application despite low effectiveness) may be partly explained by the intuitive appeal of threatening communication: it may be hard to predict the defensive reactions occurring in response to fear appeals. We examine this hypothesis by using two studies by Brown and colleagues, which provide evidence that threatening health messages in the form of distressing imagery in anti-smoking and anti-alcohol campaigns cause defensive reactions. Methods We simulated both Brown et al. experiments, asking participants to estimate the reactions of the original study subjects to the threatening health information (n = 93). Afterwards, we presented the actual original study outcomes. One week later, we assessed whether this knowledge of the actual study outcomes helped participants to more successfully estimate the effectiveness of the threatening health information (n = 72). Results Results showed that participants were initially convinced of the effectiveness of threatening health messages and were unable to anticipate the defensive reactions that in fact occurred. Furthermore, these estimates did not improve after participants had been explained the dynamics of threatening communication as well as what the effects of the threatening communication had been in reality. Conclusions These findings are consistent with the hypothesis that the effectiveness of threatening health messages is intuitively appealing. What is more, providing empirical evidence against the use of threatening health messages has very little effect on this intuitive appeal. PMID:23171445

  5. Reaction modeling in geothermal systems

    NASA Astrophysics Data System (ADS)

    Stefansson, A.

    2012-12-01

    Natural volcanic geothermal systems are open systems in term of matter and energy. Such systems are complex to model in terms of fluid chemistry, fluid flow and energy budget. Reaction modeling may be used to gain insight and possibly quantify chemical processes occurring within a system, for example fluid-fluid and fluid-rock interaction. Methods have been developed within the WATCH (Bjarnason, 1994; Arnórsson et al., 2007) and PHREEQC (Parkhurst and Appelo, 1999) programs to simulate reactions of multicomponent and multiphase systems to 300°C. The models include boiling and phase segregation (open system boiling), fluid-fluid mixing and fluid-rock interaction (gas-water-rock interaction). The models have been applied to quantify processes within the Hellisheidi geothermal system, Iceland. Open system boiling and fluid-rock interaction were simulated as a function of temperature, initial fluid composition and extent of reaction (T-X-?). In addition the interactions of magmatic gases with geothermal fluids and rocks were modeled. In this way various component behavior has been traced within the geothermal system and compared with observations of fluid composition and mineralogy. In addition, the reaction models have been used to evaluate the geochemical feasibility and best conditions of gas (CO2 and H2S) and waste water injection into geothermal system.

  6. Complexation reactions in aquatic systems

    SciTech Connect

    Buffle, J.; Chalmers, R.A.

    1988-01-01

    This book discusses the properties, reactivities, and ecological implications of all chemically ill-defined natural complexants in aquatic systems. Analytical and theoretical aspects are presented simultaneously, covering speciation parameters, nature, and properties of organic and inorganic ligands in natural waters, their reactions with inorganic elements (particularly metals), and methods of measurement of speciation parameters.

  7. Readers' Reactions to Newspaper Design.

    ERIC Educational Resources Information Center

    Bain, Chic; Weaver, David H.

    1979-01-01

    Four experiments tested reader reaction to selected newspaper design techniques, including jumps, wraps, type style, and picture size. The results implied that a newspaper striving for the highest overall readership of its stories will get the best results by keeping jumps to a minimum and running larger pictures. (RL)

  8. Interfacial Reaction Studies Using ONIOM

    NASA Technical Reports Server (NTRS)

    Cardelino, Beatriz H.

    2003-01-01

    In this report, we focus on the calculations of the energetics and chemical kinetics of heterogeneous reactions for Organometallic vapor phase epitaxy (OMVPE). The work described in this report builds upon our own previous thermochemical and chemical kinetics studies. The first of these articles refers to the prediction of thermochemical properties, and the latter one deals with the prediction of rate constants for gaseous homolytic dissociation reactions. The calculations of this investigation are at the microscopic level. The systems chosen consisted of a gallium nitride (GaN) substrate, and molecular nitrogen (N2) and ammonia (NH3) as adsorbants. The energetics for the adsorption and the adsorbant dissociation processes were estimated, and reaction rate constants for the dissociation reactions of free and adsorbed molecules were predicted. The energetics for substrate decomposition was also computed. The ONIOM method, implemented in the Gaussian98 program, was used to perform the calculations. This approach has been selected since it allows dividing the system into two layers that can be treated at different levels of accuracy. The atoms of the substrate were modeled using molecular mechanics6 with universal force fields, whereas the adsorbed molecules were approximated using quantum mechanics, based on density functional theory methods with B3LYP functionals and 6-311G(d,p) basis sets. Calculations for the substrate were performed in slabs of several unit cells in each direction. The N2 and NH3 adsorbates were attached to a central location at the Ga-lined surface.

  9. Multifractality in intracellular enzymatic reactions.

    PubMed

    Aranda, Juan S; Salgado, Edgar; Muñoz-Diosdado, Alejandro

    2006-05-21

    Enzymatic kinetics adjust well to the Michaelis-Menten paradigm in homogeneous media with dilute, perfectly mixed reactants. These conditions are quite different from the highly structured cell plasm, so applications of the classic kinetics theory to this environment are rather limited. Cytoplasmic structure produces molecular crowding and anomalous diffusion of substances, modifying the mass action kinetic laws. The reaction coefficients are no longer constant but time-variant, as stated in the fractal kinetics theory. Fractal kinetics assumes that enzymatic reactions on such heterogeneous media occur within a non-Euclidian space characterized by a certain fractal dimension, this fractal dimension gives the dependence on time of the kinetic coefficients. In this work, stochastic simulations of enzymatic reactions under molecular crowding have been completed, and kinetic coefficients for the reactions, including the Michaelis-Menten parameter KM, were calculated. The simulations results led us to confirm the time dependence of michaelian kinetic parameter for the enzymatic catalysis. Besides, other chaos related phenomena were pointed out from the obtained KM time series, such as the emergence of strange attractors and multifractality. PMID:16256143

  10. Deformed Space-Time Reactions

    NASA Astrophysics Data System (ADS)

    Albertini, Gianni; Kostro, Ludwik; Cardone, Fabio

    Recent experimental results, which are not easy to explain at the light of the current commonly accepted theories, can find an explanation in the framework of a theory of locally deformed space-time. Small cavities inside pressed solids and bubbles inside cavitated liquids are assumed as micro-reactors where deformed space-time reactions can take place.

  11. Hypersensitivity reactions to HIV therapy

    PubMed Central

    Chaponda, Mas; Pirmohamed, Munir

    2011-01-01

    Many drugs used for the treatment of HIV disease (including the associated opportunistic infections) can cause drug hypersensitivity reactions, which vary in severity, clinical manifestations and frequency. These reactions are not only seen with the older compounds, but also with the newer more recently introduced drugs. The pathogenesis is unclear in most cases, but there is increasing evidence to support that many of these are mediated through a combination of immunologic and genetic factors through the major histocompatibility complex (MHC). Genetic predisposition to the occurrence of these allergic reactions has been shown for some of the drugs, notably abacavir hypersensitivity which is strongly associated with the class I MHC allele, HLA-B*5701. Testing before the prescription of abacavir has been shown to be of clinical utility, has resulted in a change in the drug label, is now recommended in clinical guidelines and is practiced in most Western countries. For most other drugs, however, there are no good methods of prevention, and clinical monitoring with appropriate (usually supportive and symptomatic) treatment is required. There is a need to undertake further research in this area to increase our understanding of the mechanisms, which may lead to better preventive strategies through the development of predictive genetic biomarkers or through guiding the design of drugs less likely to cause these types of adverse drug reactions. PMID:21480946

  12. Pulp reactions to resin cements.

    PubMed

    Pameijer, C H; Stanley, H R

    1992-04-01

    Several formulas of a resin-filled cement that successfully passed a series of laboratory tests were evaluated for their pulp reactions in primates. Their performance was compared to three controls: a positive control (silicate cement), a negative control (zinc oxide-eugenol) and a control group with the protection of calcium hydroxide. The chemical cure resin cement scored the lowest reactions for the 5-day evaluation. The intermediate and prolonged periods demonstrated no significant differences while average, acceptable responses were recorded. No resin cement formula scored as low as the negative control for the three time periods. Silicate cement, the positive control, scored the greatest inflammatory reaction of any material in the intermediate period, but this response was resolved after 60 days. When the resin cements were used with calcium hydroxide, the traditional reactions to calcium hydroxide were observed; an initial mild irritation that diminished with time and was completely resolved after 60 days. The resin cements, with or without the calcium hydroxide, compared favorably to the negative control IRM after 60 days. If the resin cements are appropriately applied, they are expected to be well tolerated by the human pulp. The microorganisms associated with microleakage (MLM) were minimal and there appeared to be no correlation between the MLM and pulp inflammation. PMID:1524752

  13. Teachers' Reactions to Children's Aggression

    ERIC Educational Resources Information Center

    Nesdale, Drew; Pickering, Kaye

    2006-01-01

    Drawing on social schema theory (Fiske & Taylor, 1991) and social identity theory (Tajfel & Turner, 1979), this study examined the impact on teachers' reactions to children's aggression of three variables, two of which were related to the aggressors and one was related to the teachers. Experienced female elementary school teachers (N=90) each read…

  14. Reduction of chemical reaction models

    NASA Technical Reports Server (NTRS)

    Frenklach, Michael

    1991-01-01

    An attempt is made to reconcile the different terminologies pertaining to reduction of chemical reaction models. The approaches considered include global modeling, response modeling, detailed reduction, chemical lumping, and statistical lumping. The advantages and drawbacks of each of these methods are pointed out.

  15. Reactions of arsine with hemoglobin

    SciTech Connect

    Hatlelid, K.M.; Brailsford, C.; Carter, D.E.

    1996-02-09

    The mechanism of arsine (AsH{sub 3}) induced hemolysis was studied in vitro using isolated red blood cells (RBCs) from the rat or dog. AsH{sub 3}-induced hemolysis of dog red blood cells was completely blocked by carbon monoxide (CO) preincubation and was reduced by pure oxygen (O{sub 2}) compared to incubations in air. Since CO and O{sub 2} bind to heme and also reduced hemolysis, these results suggested a reaction between AsH{sub 3} and hemoglobin in the hemeligand binding pocket or with the heme iron. Further, sodium nitrite induction of methemoglobin (metHb) to 85% and 34% of total Hb in otherwise intact RBCs resulted in 56% and 16% decreases in hemolysis, respectively, after incubation for 4 h. This provided additional evidence for the involvement of hemoglobin in the AsH{sub 3}-induced hemolysis mechanism. Reactions between AsH{sub 3} and hemoglobin were studied in solutions of purified dog hemoglobin. Spectrophotometric studies of the reaction of AsH{sub 3} with various purified hemoglobin species revealed that AsH{sub 3} reacted with HbO{sub 2} to produce metHb and, eventually, degraded Hb characterized by gross precipitation of the protein. AsH{sub 3} did not alter the spectrum of deoxyHb and did not cause degradation of metHb in oxygen, but bound to and reduced metHb in the absence of oxygen. These data indicate that a reaction of AsH{sub 3} with oxygenated hemoglobin, HbO{sub 2}, may lead to hemolysis, but there are reactions between AsH{sub 3} and metHb that may not be directly involved in the hemolytic process. 17 refs., 6 figs.

  16. Ruthenium nanocatalysis on redox reactions.

    PubMed

    Veerakumar, Pitchaimani; Ramdass, Arumugam; Rajagopal, Seenivasan

    2013-07-01

    Nanoparticles have generated intense interest over the past 20 years due to their high potential applications in different areas such as catalysis, sensors, nanoscale electronics, fuel and solar cells and optoelectronics. As the large fractions of metal atoms are exposed to the surface, the use of metal nanoparticles as nanocatalysts allows mild reaction conditions and high catalytic efficiency in a large number of chemical transformations. They have emerged as sustainable heterogeneous catalysts and catalyst supports alternative to conventional materials. This review focuses on the synthesis, characterization and catalytic role of ruthenium nanoparticles (RuNPs) on the redox reactions of heteroatom containing organic compounds with the green reagent H2O2, a field that has attracted immense interest among the chemical, materials and industrial communities. We intend to present a broad overview of Ru nanocatalysts for redox reactions with an emphasis on their performance, stability and reusability. The growth in the chemistry of organic sulfoxides and N-oxides during last decade was due to their importance as synthetic intermediates for the production of a wide range of chemically and biologically active molecules. Thus design of efficient methods for the synthesis of sulfoxides and N-oxides becomes important. This review concentrates on the catalysis of RuNPs on the H2O2 oxidation of organic sulfides to sulfoxides and amines to N-oxides. The deoxygenation reactions of sulfoxides to sulfides and reduction of nitro compounds to amines are fundamental reactions in both chemistry and biology. Here, we also highlight the catalysis of metal nanoparticles on the deoxygenation of sulfoxides and sulfones and reduction of nitro compounds with particular emphasis on the mechanistic aspects. PMID:23901501

  17. Reaction of alkylcobalamins with thiols

    SciTech Connect

    Hogenkamp, H.P.C.; Bratt, G.T.; Kotchevar, A.T.

    1987-07-28

    Carbon-13 NMR spectroscopy and phosphorus-31 NMR spectroscopy have been used to study the reaction of several alkylcobalamins with 2-mercaptoethanol. At alkaline pH, when the thiol is deprotonated, the alkyl-transfer reactions involve a nucleophilic attack of the thiolate anion on the Co-methylene carbon of the cobalamins, yielding alkyl thioethers and cob(II)alamin. In these nucleophilic displacement reactions cob(I)alamin is presumably formed as an intermediate. The higher alkylcobalamins react more slowly than methylcobalamin. The lower reactivity of ethyl- and propylcobalamin is probably the basis of the inhibition of the corrinoid-dependent methyl-transfer systems by propyl iodide. The transfer of the upper nucleoside ligand of adenosylcobalamin to 2-mercaptoethanol is a very slow process; S-adenosylmercaptoethanol and cob(II)alamin are the final products of the reaction. The dealkylation of (carboxymethyl)cobalamin is a much more facile reaction. At alkaline pH S-(carboxymethyl)mercaptoethanol and cob(II)alamin are produced, while at pH values below 8 the carbon-cobalt bond is cleaved reductively to acetate and cob(II)alamin. The reductive cleavage of the carbon-cobalt bond of (carboxymethyl)cobalamin by 2-mercaptoethanol is extremely fast when the cobalamin is in the base-off form. Because the authors have been unable to detect trans coordination of 2-mercaptoethanol, they favor a mechanism that involves a hydride attack on the Co-methylene carbon of (carboxymethyl) rather than a trans attack of the thiol on the cobalt atom.

  18. Annulation Reactions of Allenyl Esters: An Approach to Bicyclic Diones and Medium-Sized Rings

    PubMed Central

    2015-01-01

    A flexible approach to construct sterically congested bicyclo-alkenedione frameworks is reported. Under the action of potassium carbonate, ?-sulphonyl cycloalkanones are added to functionalized allenyl esters, leading to a lactone intermediate that is subsequently reduced to initiate an intramolecular aldol cyclization to [3.2.1], [3.3.1], and [4.3.1] bicycles. Oxidation then affords bicyclic diones in good three-step yields. Under exceptionally mild conditions, these bicycles are converted to highly functionalized medium-sized rings through a Grob-type fragmentation. PMID:25184784

  19. Experimental Demonstrations in Teaching Chemical Reactions.

    ERIC Educational Resources Information Center

    Hugerat, Muhamad; Basheer, Sobhi

    2001-01-01

    Presents demonstrations of chemical reactions by employing different features of various compounds that can be altered after a chemical change occurs. Experimental activities include para- and dia-magnetism in chemical reactions, aluminum reaction with base, reaction of acid with carbonates, use of electrochemical cells for demonstrating chemical…

  20. Adverse Drug Reactions in Dental Practice

    PubMed Central

    Becker, Daniel E.

    2014-01-01

    Adverse reactions may occur with any of the medications prescribed or administered in dental practice. Most of these reactions are somewhat predictable based on the pharmacodynamic properties of the drug. Others, such as allergic and pseudoallergic reactions, are less common and unrelated to normal drug action. This article will review the most common adverse reactions that are unrelated to drug allergy. PMID:24697823

  1. Experimental Demonstrations in Teaching Chemical Reactions.

    ERIC Educational Resources Information Center

    Hugerat, Muhamad; Basheer, Sobhi

    2001-01-01

    Presents demonstrations of chemical reactions by employing different features of various compounds that can be altered after a chemical change occurs. Experimental activities include para- and dia-magnetism in chemical reactions, aluminum reaction with base, reaction of acid with carbonates, use of electrochemical cells for demonstrating chemical…

  2. Thermodynamics of Enzyme-Catalyzed Reactions Database

    National Institute of Standards and Technology Data Gateway

    SRD 74 Thermodynamics of Enzyme-Catalyzed Reactions Database (Web, free access)   The Thermodynamics of Enzyme-Catalyzed Reactions Database contains thermodynamic data on enzyme-catalyzed reactions that have been recently published in the Journal of Physical and Chemical Reference Data (JPCRD). For each reaction the following information is provided: the reference for the data, the reaction studied, the name of the enzyme used and its Enzyme Commission number, the method of measurement, the data and an evaluation thereof.

  3. Formation of gamma-lactones through CAN-mediated oxidative cleavage of hemiketals.

    PubMed

    Jacobine, Alexander M; Lin, Weimin; Walls, Bethany; Zercher, Charles K

    2008-09-19

    The generation of substituted gamma-lactones can be accomplished through application of a tandem chain extension-aldol reaction, followed by CAN-mediated oxidative cleavage of the aldol product. The oxidative cleavage requires the intermediacy of a hemiketal and the presence of an alpha-heteroatom. Formation of the gamma-lactone through the oxidative cleavage is used to assign stereochemistry of the aldol reaction and as the final step in a short synthesis of members of the phaseolinic acid family of natural products. PMID:18693768

  4. Chemoenzymatic synthesis of vitamin B5-intermediate (R)-pantolactone via combined asymmetric organo- and biocatalysis.

    PubMed

    Heidlindemann, Marcel; Hammel, Matthias; Scheffler, Ulf; Mahrwald, Rainer; Hummel, Werner; Berkessel, Albrecht; Gröger, Harald

    2015-04-01

    The combination of an asymmetric organocatalytic aldol reaction with a subsequent biotransformation toward a "one-pot-like" process for the synthesis of (R)-pantolactone, which to date is industrially produced by a resolution process, is demonstrated. This process consists of an initial aldol reaction catalyzed by readily available l-histidine followed by biotransformation of the aldol adduct by an alcohol dehydrogenase without the need for intermediate isolation. Employing the industrially attractive starting material isobutanal, a chemoenzymatic three-step process without intermediate purification is established allowing the synthesis of (R)-pantolactone in an overall yield of 55% (three steps) and high enantiomeric excess of 95%. PMID:25710713

  5. Programmability of Chemical Reaction Networks

    NASA Astrophysics Data System (ADS)

    Cook, Matthew; Soloveichik, David; Winfree, Erik; Bruck, Jehoshua

    Motivated by the intriguing complexity of biochemical circuitry within individual cells we study Stochastic Chemical Reaction Networks (SCRNs), a formal model that considers a set of chemical reactions acting on a finite number of molecules in a well-stirred solution according to standard chemical kinetics equations. SCRNs have been widely used for describing naturally occurring (bio)chemical systems, and with the advent of synthetic biology they become a promising language for the design of artificial biochemical circuits. Our interest here is the computational power of SCRNs and how they relate to more conventional models of computation. We survey known connections and give new connections between SCRNs and Boolean Logic Circuits, Vector Addition Systems, Petri nets, Gate Implementability, Primitive Recursive Functions, Register Machines, Fractran, and Turing Machines. A theme to these investigations is the thin line between decidable and undecidable questions about SCRN behavior.

  6. Prebiotic condensation reactions using cyanamide

    NASA Technical Reports Server (NTRS)

    Sherwood, E.; Nooner, D. W.; Eichberg, J.; Epps, D. E.; Oro, J.

    1978-01-01

    Condensation reactions in cyanamide, 4-amino-5-imidazole-carboxamide and cyanamide, imidazole systems under dehydrating conditions at moderate temperatures (60 to 100 deg C) were investigated. The cyanamide, imidazole system was used for synthesis of palmitoylglycerols from ammonium palmitate and glycerol. With the addition of deoxythymidine to the former system, P1, P2-dideoxythymidine 5 prime-phosphate was obtained; the same cyanamide, 4-amino-5-imidazole-carboxamide system was used to synthesize deoxythymidine oligonucleotides using deoxythymidine 5 prime-phosphate and deoxythymidine 5 prime-triphosphate, and peptides using glycine, phenylalanine or isoleucine with adenosine 5 prime-triphosphate. The pH requirements for these reactions make their prebiotic significance questionable; however, it is conceivable that they could occur in stable pockets of low interlayer acidity in a clay such as montmorillonite.

  7. Propulsive Reaction Control System Model

    NASA Technical Reports Server (NTRS)

    Brugarolas, Paul; Phan, Linh H.; Serricchio, Frederick; San Martin, Alejandro M.

    2011-01-01

    This software models a propulsive reaction control system (RCS) for guidance, navigation, and control simulation purposes. The model includes the drive electronics, the electromechanical valve dynamics, the combustion dynamics, and thrust. This innovation follows the Mars Science Laboratory entry reaction control system design, and has been created to meet the Mars Science Laboratory (MSL) entry, descent, and landing simulation needs. It has been built to be plug-and-play on multiple MSL testbeds [analysis, Monte Carlo, flight software development, hardware-in-the-loop, and ATLO (assembly, test and launch operations) testbeds]. This RCS model is a C language program. It contains two main functions: the RCS electronics model function that models the RCS FPGA (field-programmable-gate-array) processing and commanding of the RCS valve, and the RCS dynamic model function that models the valve and combustion dynamics. In addition, this software provides support functions to initialize the model states, set parameters, access model telemetry, and access calculated thruster forces.

  8. Investigating Reaction-Driven Cracking

    NASA Astrophysics Data System (ADS)

    Kelemen, P. B.; Hirth, G.; Savage, H. M.

    2013-12-01

    Many metamorphic reactions lead to large volume changes, and potentially to reaction-driven cracking [1,2]. Large-scale hydration of mantle peridotite to produce serpentine or talc is invoked to explain the rheology of plate boundaries, the nature of earthquakes, and the seismic properties of slow-spread ocean crust and the 'mantle wedge' above subduction zones. Carbonation of peridotite may be an important sink in the global carbon cycle. Zones of 100% magnesite + quartz replacing peridotite, up to 200 m thick, formed where oceanic mantle was thrust over carbonate-bearing metasediments in Oman. Talc + carbonate is an important component of the matrix in subduction mélanges at Santa Catalina Island , California, and the Sanbagawa metamorphic belt, Japan. Engineered systems to emulate natural mineral carbonation could provide relatively inexpensive CO2 capture and storage [3]. More generally, engineered reaction-driven cracking could supplement or replace hydraulic fracture in geothermal systems, solution mining, and extraction of tight oil and gas. The controls on reaction-driven cracking are poorly understood. Hydration and carbonation reactions can be self-limiting, since they potentially reduce permeability and armor reactive surfaces [4]. Also, in some cases, hydration or carbonation may take place at constant volume. Small changes in volume due to precipitation of solid products increases stress, destabilizing solid reactants, until precipitation and dissolution rates become equal at a steady state stress [5]. In a third case, volume change due to precipitation of solid products causes brittle failure. This has been invoked on qualitative grounds to explain, e.g., complete serpentinization of mantle peridotite [6]. Below ~ 300°C, the available potential energy for hydration and carbonation of olivine could produce stresses of 100's of MPa [2], sufficient to fracture rocks to 10 km depth or more, causing brittle failure below the steady state stress required for constant volume replacement. Natural examples have fracture energy densities due to strain energy density of 100's of MPa [2]. Despite theory and observation, until now lab experiments on peridotite hydration and carbonation have not produced reaction-driven cracking. Slow kinetics and limited reactive surface area in low porosity samples may be the cause. Also, maximum stress may be limited by 'disjoining pressure', above which nano-films along grain boundaries collapse, and crystal growth essentially ceases [7]. To address these issues, we've begun experiments on analog materials with fast reaction rates, e.g., CaO + H2O = Ca(OH)2, to efficiently investigate the role of confining pressure and other factors on reaction-driven fracture events. Intriguingly, commercially available 'demolition mortar', largely CaO, produces stresses of 70 MPa or more around 1 inch bore holes at room T and P [8], even though there is a free surface at the top of the borehole, and hydration in a 'closed' system creates ~ 40% air-filled pore space. [1] Jamtveit et al EPSL 08 [2] Kelemen & Hirth EPSL 12 [3] Kelemen et al AREPS 11 [4] Aharonov et al JGR 98 [5] Fletcher & Merino GCA 01 [6] Macdonald & Fyfe T'phys 85 [7] Espinosa-Marzal & Scherer GSL Special Papers 10 [8] Laefer et al Mag Concrete Res 10

  9. Modelling reaction kinetics inside cells

    PubMed Central

    Grima, Ramon; Schnell, Santiago

    2009-01-01

    In the past decade, advances in molecular biology such as the development of non-invasive single molecule imaging techniques have given us a window into the intricate biochemical activities that occur inside cells. In this article we review four distinct theoretical and simulation frameworks: (1) non-spatial and deterministic, (2) spatial and deterministic, (3) non-spatial and stochastic and (4) spatial and stochastic. Each framework can be suited to modelling and interpreting intracellular reaction kinetics. By estimating the fundamental length scales, one can roughly determine which models are best suited for the particular reaction pathway under study. We discuss differences in prediction between the four modelling methodologies. In particular we show that taking into account noise and space does not simply add quantitative predictive accuracy but may also lead to qualitatively different physiological predictions, unaccounted for by classical deterministic models. PMID:18793122

  10. MEANS FOR TERMINATING NUCLEAR REACTIONS

    DOEpatents

    Cooper, C.M.

    1959-02-17

    An apparatus is presented for use in a reactor of the heterogeneous, fluid cooled type for the purpose of quickly terminating the reaction, the coolant being circulated through coolant tubes extending through the reactor core. Several of the tubes in the critical region are connected through valves to a tank containing a poisoning fluid having a high neutron capture crosssection and to a reservoir. When it is desired to quickly terminate the reaction, the valves are operated to permit the flow of the poisoning fluid through these particular tubes and into the reservoir while normal coolant is being circulated through the remaining tubes. The apparatus is designed to prevent contamination of the primary coolant by the poisoning fluid.

  11. Adverse drug reactions: part II.

    PubMed

    Wooten, James M

    2010-11-01

    Pharmacovigilance is the process of identifying, monitoring, and effectively reducing adverse drug reactions. Adverse drug reactions (ADRs) are an important consideration when assessing a patient's health. The proliferation of new pharmaceuticals means that the incidence of ADRs is increasing. The goal for all health care providers must be to minimize the risk of ADRs as much as possible. Steps to achieve this include understanding the pharmacology for all drugs prescribed and proactively assessing and monitoring those patients at greatest risk for developing an ADR. Groups at greatest risk for developing ADRs include the elderly, children, and pregnant patients, as well as others. Pharmacovigilance must be effectively practiced by all health care providers in order to avoid ADRs. PMID:20890249

  12. [Adverse drug reactions in children].

    PubMed

    Jaffan, Linda; Läer, Stephanie

    2011-01-01

    Adverse drug reactions (ADRs) are important safety issues in pediatric pharmacotherapy because they can lead to significant morbidity and mortality in this population. It is currently assumed that the incidence of ADRs in children is between 0.6 % and 19.9 % and that between 0.6 % und 6 % of all hospital admissions of children are triggered by ADRs. Underreporting and insufficient documentation of ADRs in children, however, may obstruct the view on the true numbers. Pharmacovigilance centres in some countries are under way to increase the awareness of the problem. Their programs may help to systematically improve reporting and documentation of ADRs. One important goal is to better assess causality between the patients clinical reaction and drug use, because this is the key knowledge to specifically target an effective and safe pharmacotherapy. PMID:21184392

  13. Cascade reactions in multicompartmentalized polymersomes.

    PubMed

    Peters, Ruud J R W; Marguet, Maïté; Marais, Sébastien; Fraaije, Marco W; van Hest, Jan C M; Lecommandoux, Sébastien

    2014-01-01

    Enzyme-filled polystyrene-b-poly(3-(isocyano-L-alanyl-aminoethyl)thiophene) (PS-b-PIAT) nanoreactors are encapsulated together with free enzymes and substrates in a larger polybutadiene-b-poly(ethylene oxide) (PB-b-PEO) polymersome, forming a multicompartmentalized structure, which shows structural resemblance to the cell and its organelles. An original cofactor-dependent three-enzyme cascade reaction is performed, using either compatible or incompatible enzymes, which takes place across multiple compartments. PMID:24254810

  14. Molecular screening in nuclear reactions

    NASA Astrophysics Data System (ADS)

    Cvetinovic, A.; Lipoglavsek, M.; Markelj, S.; Vesic, J.

    2015-12-01

    The dependence of electron screening in nuclear reactions on projectile or target atomic number has been studied by bombarding different hydrogen-containing targets with beams of 7Li , 11B , and 19F . The largest electron screening potentials were obtained in a graphite target containing hydrogen as an impurity. Some measured potentials are almost two orders of magnitude above the theoretical predictions. To explain the measurements, a new concept of electron screening is introduced.

  15. Strangeness exchange reactions and hypernuclei

    SciTech Connect

    Dover, C.B.

    1982-01-01

    Recent progress in the spectroscopy of ..lambda.. and ..sigma.. hypernuclei is reviewed. Prospects for the production of doubly strange hypernuclei at a future kaon factory are assessed. It is suggested that the (K/sup -/,K/sup +/) reaction on a nuclear target may afford an optimal way of producing the H dibaryon, a stable six quark object with J/sup ..pi../ = O/sup +/, S = -2.

  16. Milestoning without a Reaction Coordinate

    PubMed Central

    Májek, Peter; Elber, Ron

    2010-01-01

    Milestoning is a method for calculating kinetics and thermodynamics of long time processes typically not accessible for straightforward Molecular Dynamics (MD) simulation. In the Milestoning approach, the system of interest is partitioned into cells by dividing hypersurfaces (Milestones) and transitions are computed between nearby hypersurfaces. Kinetics and thermodynamics are derived from the statistics of these transitions. The original Milestoning work concentrated on systems in which a one-dimensional reaction coordinate or an order parameter could be identified. In many biomolecular processes the reaction proceeds via multiple channels or following more than a single order parameter. A description based on a one-dimensional reaction coordinate may be insufficient. In the present paper we introduce a variation that overcomes this limitation. Following the ideas of Vanden-Eijnden and Venturoli on Voronoi cells that avoid the use of an order parameter (J. Chem. Phys. 2009, 130, 194101), we describe another way to “Milestone” systems without a reaction coordinate. We examine the assumptions of the Milestoning calculations of mean first passage times (MFPT) and describe strategies to weaken these assumptions. The method described in this paper, Directional Milestoning, arranges hypersurfaces in higher dimensions that “tag” trajectories such that efficient calculations can be done and at the same time the assumptions required for exact calculations of MFPTs are satisfied approximately. In the original Milestoning papers trajectories are initiated from an equilibrium set of conformations. Here a more accurate distribution, that mimics the first hitting point distribution, is used. We demonstrate the usage of Directional Milestoning in conformational transitions of alanine dipeptide (in vacuum and in aqueous solution) and compare the correctness, efficiency, and statistical stability of the method with exact MD and with a related method. PMID:20596240

  17. Redox Reactions in Polymeric Systems

    NASA Astrophysics Data System (ADS)

    Black, James R., II

    2011-12-01

    Reduction-Oxidization (redox) reactions performed in polymeric environments resulted in the reversible formation of stable silver nanoparticle and two reductive radicals. The reversible formation of stable silver nanoparticles in polyvinyl alcohol (PVA) and polyacrylic acid (PAA) crosslinked polymer films containing silver ions was achieved by electrochemical methods for potential applications in electrochromic devices. Cyclic voltammetry and galvanostatic methods were used to reversibly generate silver particles while the particle formation and decay optical absorption spectra were used to evaluate reversibility, relative particle size and minimum cycle speeds. Mechanisms for the formation and decay of particles are discussed with electron microscopy data determining actual size of generated silver particles. Light activated polymeric radicals produced from sulfonated polyether ether ketone (SPEEK) with PVA or SPEEK with sodium formate solutions were generated using 350 nm photons. The mechanism of radical generation is discussed for potential application for dehalogenating a well known environmental hazard carbon tetrachloride (CCl4). The reaction of the generated radicals with CCl4 was followed by ion selective electrode specific for chlorine allowing for the attainment of kinetic data and reaction mechanisms. The degradation of CCl4 was observed in both SPEEK/PVA and SPEEK/formate solutions but the kinetic data revealed SPEEK/formate to be more efficient. The success of SPEEK radicals in dechlorinating CCl4 lead to the investigation of polymeric blends, films and solution of SPEEK and polyamines for the generation of SPEEK radicals with a higher redox potential. SPEEK/polyamine radicals were generated by exposing polymer blends to 350 nm photons. Optical and electron spin resonance (ESR) spectra confirmed the generation of the anionic radical with a higher reducing potential. Kinetic data was obtained for selected system by following the formation and decay of the optical and ESR signatures. The reactions leading to the generation of highly reductive radicals is discussed.

  18. Multicomponent reactions in nucleoside chemistry

    PubMed Central

    Buchowicz, W?odzimierz

    2014-01-01

    Summary This review covers sixty original publications dealing with the application of multicomponent reactions (MCRs) in the synthesis of novel nucleoside analogs. The reported approaches were employed for modifications of the parent nucleoside core or for de novo construction of a nucleoside scaffold from non-nucleoside substrates. The cited references are grouped according to the usually recognized types of the MCRs. Biochemical properties of the novel nucleoside analogs are also presented (if provided by the authors). PMID:25161730

  19. Fundamental reaction pathways during coprocessing

    SciTech Connect

    Stock, L.M.; Gatsis, J.G.

    1990-06-30

    Coal petroleum resid coprocessing is a novel application of direct coal liquefaction which has potential for technical and cost improvement. Coprocessing of petroleum resid with coal can be considered as a bridge between coal liquefaction and hydrocracking. Several earlier studies indicated that coprocessing involves the simultaneous upgrading of coal and heavy oils. Previous batch autoclave studies showed that coprocessing of Illinois No. 6 coal and Wyodak coal with Lloydminster resid and Hondo resid increased the liquefaction yields of these coals. Much effort has been spent to elucidate the mechanism of the hydrogen atom transfer reactions from the donor solvent to various coal structures, but similar studies for coprocessing, up to the present, are not adequate and the reaction pathways involved in coprocessing are still largely obscure. A better understanding of chemistry of the coprocessing reaction is essential for development and improvement of coprocessing technology. In order to gain insight into this problem, batch autoclave studies were carried out using Illinois No. 6 coal and Wyodak coal with LLoydminister resid and Hondo resid under a dideuterium atmosphere in order to study the mechanism of incorporation using quantitative NMR methods. 5 refs., 2 figs., 5 tabs.

  20. Transfer reactions with heavy elements

    SciTech Connect

    Hoffman, D.C.

    1986-04-01

    Transfer reactions for several transuranium elements are studied. (/sup 248/Cm, /sup 249/Bk, /sup 249/CF, /sup 254/Es), /sup 16,18/O, /sup 20,22/Ne, and /sup 40,48/Ca projectiles are used. The production of neutron-rich heavy actinides is enhanced by the use of neutron-rich projectiles /sup 18/O and /sup 22/Ne. The maxima of the isotopic distributions occur at only 2 to 3 mass numbers larger for /sup 48/Ca than for /sup 40/Ca reactions with /sup 248/Cm. The cross sections decrease rapidly with the number of nucleons transferred. The use of neutron-rich targets favors the production of neutron-rich isotopes. ''Cold'' heavy targets are produced. Comparisons with simple calculations of the product excitation energies assuming binary transfers indicate that the maxima of the isotopic distributions occur at the lightest product isotope for which the energy exceeds the reaction barrier. The cross sections for transfer of the same nucleon clusters appear to be comparable for a wide variety of systems. 23 refs., 4 figs., 4 tabs.

  1. Reaction Selectivity in Heterogeneous Catalysis

    SciTech Connect

    Somorjai, Gabor A.; Kliewer, Christopher J.

    2009-02-02

    The understanding of selectivity in heterogeneous catalysis is of paramount importance to our society today. In this review we outline the current state of the art in research on selectivity in heterogeneous catalysis. Current in-situ surface science techniques have revealed several important features of catalytic selectivity. Sum frequency generation vibrational spectroscopy has shown us the importance of understanding the reaction intermediates and mechanism of a heterogeneous reaction, and can readily yield information as to the effect of temperature, pressure, catalyst geometry, surface promoters, and catalyst composition on the reaction mechanism. DFT calculations are quickly approaching the ability to assist in the interpretation of observed surface spectra, thereby making surface spectroscopy an even more powerful tool. HP-STM has revealed three vitally important parameters in heterogeneous selectivity: adsorbate mobility, catalyst mobility, and selective site-blocking. The development of size controlled nanoparticles from 0.8 to 10 nm, of controlled shape, and of controlled bimetallic composition has revealed several important variables for catalytic selectivity. Lastly, DFT calculations may be paving the way to guiding the composition choice for multi-metallic heterogeneous catalysis for the intelligent design of catalysts incorporating the many factors of selectivity we have learned.

  2. Fullerene derivatization by pyrolytic reaction

    SciTech Connect

    Hoke, S.H. II; Molstad, J.; Yang, Sheng Sheng; Kahr, B.; Cooks, R.G.

    1994-12-31

    The first observation of C{sub 60} was made in a time-of-flight mass spectrometer and mass spectrometry continues to play a major role in the identification of fullerenes and fullerene derivatives. Since the discovery of a method of producing macroscopic quantities of fullerenes, many fullerene derivatives have been reported and an increasing number have been fully characterized. The identification of the molecular weight of fullerene derivatives in reaction mixtures has been invaluable. Mass spectrometry has provided evidence for a plethora of novel compounds including metallic, alkyl, aryl, benzyl, phenyl, hydroxy, amino, fluoro, epoxy, and hydro fullerenes. In this study, new aromatic derivatives of C{sub 60} are produced by reaction with aryne or aryl radicals which are pyrolytically generated. The products are characterized by desorption chemical ionization mass spectrometry in the negative ion mode. Because of the high electron affinity of C{sub 60} abundant radical anions of C{sub 60} and derivatives are produced under chemical ionization conditions and can be detected in crude reaction mixtures with no sample preparation.

  3. Hydrogen tunneling in enzyme reactions

    SciTech Connect

    Cha, Y.; Murray, C.J.; Klinman, J.P.

    1989-03-10

    Primary and secondary protium-to-tritium (H/T) and deuterium-to-tritium (D/T) kinetic isotope effects for the catalytic oxidation of benzyl alcohol to benzaldehyde by yeast alcohol dehydrogenase (YADH) at 25 degrees Celsius have been determined. Previous studies showed that this reaction is nearly or fully rate limited by the hydrogen-transfer step. Semiclassical mass considerations that do not include tunneling effects would predict that kH/kT = (kD/kT)3.26, where kH, kD, and kT are the rate constants for the reaction of protium, deuterium, and tritium derivatives, respectively. Significant deviations from this relation have now been observed for both primary and especially secondary effects, such that experimental H/T ratios are much greater than those calculated from the above expression. These deviations also hold in the temperature range from 0 to 40 degrees Celsius. Such deviations were previously predicted to result from a reaction coordinate containing a significant contribution from hydrogen tunneling.

  4. Force approach to radiation reaction

    NASA Astrophysics Data System (ADS)

    López, Gustavo V.

    2016-02-01

    The difficulty of the usual approach to deal with the radiation reaction is pointed out, and under the condition that the radiation force must be a function of the external force and is zero whenever the external force be zero, a new and straightforward approach to radiation reaction force and damping is proposed. Starting from the Larmor formula for the power radiated by an accelerated charged particle, written in terms of the applied force instead of the acceleration, an expression for the radiation force is established in general, and applied to the examples for the linear and circular motion of a charged particle. This expression is quadratic in the magnitude of the applied force, inversely proportional to the speed of the charged particle, and directed opposite to the velocity vector. This force approach may contribute to the solution of the very old problem of incorporating the radiation reaction to the motion of the charged particles, and future experiments may tell us whether or not this approach point is in the right direction.

  5. Microfabricated electrochemiluminescence cell for chemical reaction detection

    DOEpatents

    Northrup, M. Allen; Hsueh, Yun-Tai; Smith, Rosemary L.

    2003-01-01

    A detector cell for a silicon-based or non-silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The detector cell is an electrochemiluminescence cell constructed of layers of silicon with a cover layer of glass, with spaced electrodes located intermediate various layers forming the cell. The cell includes a cavity formed therein and fluid inlets for directing reaction fluid therein. The reaction chamber and detector cell may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The ECL cell may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

  6. Electromagnetic wave propagation characteristics in unimolecular reactions

    NASA Astrophysics Data System (ADS)

    Liu, Xingpeng; Huang, Kama

    2016-01-01

    Microwave-assisted chemical reactions have attracted interests because of their benefits for enhancement of reaction rates. However, the problems, such as hot spots and thermal runaway, limit the application of microwaves in the chemical industry. To study the characteristics of electromagnetic wave propagation in a chemical reaction is critical to solve the problems. The research on the characteristics of electromagnetic wave propagation in the unimolecular reaction that is a simple model reaction, can be generalized to the research in a chemical reaction. The approximate expressions of the attenuation and dispersion characteristics of electromagnetic wave propagation in the unimolecular reaction are derived by the nonlinear propagation theory. Specially, when the reaction rate is zero, the derived approximate expressions can be reduced to the formulas in low-loss dispersive media. Moreover, a 1D mold is used to validate the feasibility of the approximate expressions. The influences of the reaction rate and initial reactant concentration on the characteristics are obtained.

  7. Visualization of chemical reaction dynamics: Toward understanding complex polyatomic reactions

    PubMed Central

    SUZUKI, Toshinori

    2013-01-01

    Polyatomic molecules have several electronic states that have similar energies. Consequently, their chemical dynamics often involve nonadiabatic transitions between multiple potential energy surfaces. Elucidating the complex reactions of polyatomic molecules is one of the most important tasks of theoretical and experimental studies of chemical dynamics. This paper describes our recent experimental studies of the multidimensional multisurface dynamics of polyatomic molecules based on two-dimensional ion/electron imaging. It also discusses ultrafast photoelectron spectroscopy of liquids for elucidating nonadiabatic electronic dynamics in aqueous solutions. PMID:23318678

  8. Highly diastereoselective synthesis of spiropyrazolones.

    PubMed

    Ceban, Victor; Olomola, Temitope O; Meazza, Marta; Rios, Ramon

    2015-01-01

    We report a highly diastereoselective synthesis of spiropyrazolones catalyzed by secondary amines. The reported Michael-Aldol cascade reaction affords the desired spiropyrazolones bearing four chiral centers as a single diastereomer in excellent yields. PMID:25985358

  9. The molecular dynamics of atmospheric reaction

    NASA Technical Reports Server (NTRS)

    Polanyi, J. C.

    1971-01-01

    Detailed information about the chemistry of the upper atmosphere took the form of quantitative data concerning the rate of reaction into specified states of product vibration, rotation and translation for exothermic reaction, as well as concerning the rate of reaction from specified states of reagent vibration, rotation and translation for endothermic reaction. The techniques used were variants on the infrared chemiluminescence method. Emphasis was placed on reactions that formed, and that removed, vibrationally-excited hydroxyl radicals. Fundamental studies were also performed on exothermic reactions involving hydrogen halides.

  10. Microfabricated sleeve devices for chemical reactions

    DOEpatents

    Northrup, M. Allen (Berkeley, CA)

    2003-01-01

    A silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and non-silicon based materials to provide the thermal properties desired. For example, the chamber may combine a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

  11. The Biginelli Reaction Is a Urea-Catalyzed Organocatalytic Multicomponent Reaction.

    PubMed

    Puripat, Maneeporn; Ramozzi, Romain; Hatanaka, Miho; Parasuk, Waraporn; Parasuk, Vudhichai; Morokuma, Keiji

    2015-07-17

    The recently developed artificial force induced reaction (AFIR) method was applied to search systematically all possible multicomponent pathways for the Biginelli reaction mechanism. The most favorable pathway starts with the condensation of the urea and benzaldehyde, followed by the addition of ethyl acetoacetate. Remarkably, a second urea molecule catalyzes nearly every step of the reaction. Thus, the Biginelli reaction is a urea-catalyzed multicomponent reaction. The reaction mechanism was found to be identical in both protic and aprotic solvents. PMID:26066623

  12. Fundamental reaction pathways during coprocessing

    SciTech Connect

    Stock, L.M.; Gatsis, J.

    1991-06-30

    Coal petroleum resid coprocessing is a novel application of direct coal liquefaction which has potential for technical and cost improvement. A better understanding of the chemistry of the coprocessing reaction is essential for the development and improvement of coprocessing technology. In order to gain insight into this problem, batch autoclave studies were carried out using Illinois No. 6 coal and Wyodak coal with Lloydminster resid and Hondo resid under a dideuterium atmosphere to study the mechanism of incorporation. Quantitative deuterium nuclear magnetic resonance methods were used analyze the liquid products, and gas chromatography-mass spectrometry was used to analyze the gas products.

  13. Operationally efficient reaction controls system

    NASA Astrophysics Data System (ADS)

    Fanciullo, Thomas J.; Judd, D. C.

    1993-06-01

    The development of the first flight demonstration of a reaction controls system utilizing O2/H2 propellants is reported. The pressure fed system uses four 500 lbf thrusters and a regulated propellant supply; composite overwrapped propellant tanks and mechanical regulators are used in conjunction with thruster modules containing all the electronics. The discussion covers a general description of the O2/H2 system and its main components, including thrusters, heat exchangers, electronic regulators, gas generators, and turbopump; controls and health monitoring; and systems performance and operations.

  14. Chemical reactions at aqueous interfaces

    NASA Astrophysics Data System (ADS)

    Vecitis, Chad David

    2009-12-01

    Interfaces or phase boundaries are a unique chemical environment relative to individual gas, liquid, or solid phases. Interfacial reaction mechanisms and kinetics are often at variance with homogeneous chemistry due to mass transfer, molecular orientation, and catalytic effects. Aqueous interfaces are a common subject of environmental science and engineering research, and three environmentally relevant aqueous interfaces are investigated in this thesis: 1) fluorochemical sonochemistry (bubble-water), 2) aqueous aerosol ozonation (gas-water droplet), and 3) electrolytic hydrogen production and simultaneous organic oxidation (water-metal/semiconductor). Direct interfacial analysis under environmentally relevant conditions is difficult, since most surface-specific techniques require relatively `extreme' conditions. Thus, the experimental investigations here focus on the development of chemical reactors and analytical techniques for the completion of time/concentration-dependent measurements of reactants and their products. Kinetic modeling, estimations, and/or correlations were used to extract information on interfacially relevant processes. We found that interfacial chemistry was determined to be the rate-limiting step to a subsequent series of relatively fast homogeneous reactions, for example: 1) Pyrolytic cleavage of the ionic headgroup of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) adsorbed to cavitating bubble-water interfaces during sonolysis was the rate-determining step in transformation to their inorganic constituents carbon monoxide, carbon dioxide, and fluoride; 2) ozone oxidation of aqueous iodide to hypoiodous acid at the aerosol-gas interface is the rate-determining step in the oxidation of bromide and chloride to dihalogens; 3) Electrolytic oxidation of anodic titanol surface groups is rate-limiting for the overall oxidation of organics by the dichloride radical. We also found chemistry unique to the interface, for example: 1) Adsorption of dilute PFOS(aq) and PFOA(aq) to acoustically cavitating bubble interfaces was greater than equilibrium expectations due to high-velocity bubble radial oscillations; 2) Relative ozone oxidation kinetics of aqueous iodide, sulfite, and thiosulfate were at variance with previously reported bulk aqueous kinetics; 3) Organics that directly chelated with the anode surface were oxidized by direct electron transfer, resulting in immediate carbon dioxide production but slower overall oxidation kinetics. Chemical reactions at aqueous interfaces can be the rate-limiting step of a reaction network and often display novel mechanisms and kinetics as compared to homogeneous chemistry.

  15. Cutaneous Adverse Reactions of Amiodarone

    PubMed Central

    Jaworski, Krzysztof; Walecka, Irena; Rudnicka, Lidia; Gnatowski, Maciej; Kosior, Dariusz A.

    2014-01-01

    Dermatological complications of amiodarone are commonly encountered problems in therapy. The incidence in the population of patients with prolonged use of amiodarone reaches nearly 75% according to various sources. Nevertheless, they are often misdiagnosed or overlooked. The aim of this review is to present the current state of knowledge about skin changes induced by amiodarone, including phototoxic and photoallergic reactions, as well as hyperpigmentation. In most cases, the adverse effects are reversible and disappear after discontinuation of the drug. Although the dermatological complications usually do not influence the outcome of the therapy and rarely cause discontinuation of treatment, they have a great impact on patient quality of life. PMID:25413691

  16. Nanomotors Propelled by Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Kapral, Raymond

    2013-12-01

    Molecular motors, like their macroscopic counterparts, consume energy and convert it to work; however, unlike macroscopic motors, they are subject to strong fluctuations and do not rely on inertia for their operation. In this chapter, the dynamics of synthetic chemically-powered nanomotors and mechanisms by which they operate are described. The focus is on motors that propel themselves by utilizing fuel in the environment to generate their own concentration gradients through chemical reactions. Macroscopic diffusiophoretic mechanisms for such motions are discussed, as well as microscopic and mesoscopic descriptions of motor dynamics.

  17. Reaction of rhodanese with dithiothreitol.

    PubMed

    Pecci, L; Pensa, B; Costa, M; Cignini, P L; Cannella, C

    1976-08-12

    The reaction between bovine rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) and reduced dithiothreitol has been studied. This reagent, in the absence of thiosulfate, reduces the amount of sulfur carried by rhodanese with formation of sulfide and oxidized dithiothreitol: E-S-SH + reduced dithiothreitol replaced by E-SH + HS- + oxidized dithiothreitol, (E = enzyme). An inactivation was observed at high dithiothreitol/enzyme ratios or at very low enzyme concentrations. The inactivation was not observed in the presence of thiosulfate and can be reversed by cyanide or thiosulfate. A thiosulfate reduction activity of rhodanese was also found using dithiothreitol as reductant. PMID:986188

  18. Effective radii of deuteron-induced reactions

    SciTech Connect

    Hashimoto, Shintaro; Chiba, Satoshi; Yahiro, Masanobu; Ogata, Kazuyuki; Minomo, Kosho

    2011-05-15

    The continuum-discretized coupled-channels method (CDCC) for exclusive reactions and the eikonal reaction theory (ERT) as an extension of CDCC to inclusive reactions are applied to deuteron-induced reactions. The CDCC result reproduces experimental data on the reaction cross section for d+{sup 58}Ni scattering at 200 MeV/nucleon, and ERT provides data on the neutron-stripping cross section for inclusive {sup 7}Li(d,n) reaction at 40 MeV. For deuteron-induced reactions at 200 MeV/nucleon, target-dependence of the reaction, elastic-breakup, nucleon-stripping, nucleon-removal, and complete- and incomplete-fusion cross sections is clearly explained by simple formulas. Accuracy of the Glauber model is also investigated.

  19. Heavy atom isotope effects on enzymatic reactions

    NASA Astrophysics Data System (ADS)

    Paneth, Piotr

    1994-05-01

    The theory of isotope effects, which has proved to be extremely useful in providing geometrical details of transition states in a variety of chemical reactions, has recently found an application in studies of enzyme-catalyzed reactions. These reactions are multistep in nature with few steps being partially rate-limiting, thus interpretation of these isotope effects is more complex. The theoretical framework of heavy-atom isotope effects on enzymatic reactions is critically analyzed on the basis of recent results of: carbon kinetic isotope effects on carbonic anhydrase and catalytic antibodies; multiple carbon, deuterium isotope effects on reactions catalyzed by formate decarboxylase; oxygen isotope effects on binding processes in reactions catalyzed by pyruvate kinase; and equilibrium oxygen isotope effect on binding an inhibitor to lactate dehydrogenase. The advantages and disadvantages of reaction complexity in learning details of formal and molecular mechanisms are discussed in the examples of reactions catalyzed by phosphoenolpyruvate carboxylase, orotidine decarboxylase and glutamine synthetase.

  20. Laser-induced tissue reactions and dermatology.

    PubMed

    Weber, Rebecca J; Taylor, Brent R; Engelman, Dendy E

    2011-01-01

    Knowledge of laser tissue reactions and tissue properties allows the practitioner to tailor a treatment to an individual patient's need and goals. A laser's power, spot size and pulse duration may be manipulated to yield different tissue reactions. Five tissue reactions, each the result of varying laser pulse durations and energy densities, may be achieved. They are photochemical, photothermal, photoablation, plasma-induced ablation and photomechanical. Of these, photothermal reactions are most utilized in dermatology. When higher powered pulses are applied, tissue often undergoes multiple reactions simultaneously. An understanding of these reactions allows their effects to be predicted. In this chapter, the various reactions are reviewed, and the reactions caused by many of the most commonly used lasers in dermatology are discussed. PMID:21865795

  1. A New Look at Reaction Rates

    NASA Astrophysics Data System (ADS)

    Cvitas, Tomislav

    1999-11-01

    Both rates of radioactive decays and rates of chemical reactions can be thought of as numbers of transformations per time. The rate of reaction, as an intensive quantity characteristic of the process, is obtained by dividing the amount of chemical transformations per time by the volume of the reaction system. The practical definition of the reaction rate found in the literature can then be derived by defining the stoichiometric numbers as changes in the number of specific molecules taking part in the reaction per chemical transformation. The name concentration of chemical transformations is introduced for what was previously called reaction variable. It is suggested that the conceptual definition of the advancement of reaction and reaction rate be introduced in general chemistry courses.

  2. Precautions and Adverse Reactions during Blood Transfusion

    MedlinePLUS

    ... reaction such as itching or a rash. Usually, acetaminophen to reduce fever is the only treatment needed. ... fever and need another transfusion may be given acetaminophen before the next transfusion. Allergic reactions Symptoms of ...

  3. Competing reaction channels in IR-laser-induced unimolecular reactions

    SciTech Connect

    Berman, M.R.

    1981-01-01

    The competing reaction channels in the unimolecular decomposition of two molecules, formaldehyde and tetralin were studied. A TEA CO/sub 2/ laser was used as the excitation source in all experiments. The dissociation of D/sub 2/CO was studied by infrared multiphoton dissociation (MPD) and the small-molecule nature of formaldehyde with regard to MPD was explored. The effect of collisions in MPD were probed by the pressure dependence of the MPD yield and ir fluorescence from multiphoton excited D/sub 2/CO. MPD yield shows a near cubic dependence in pure D/sub 2/CO which is reduced to a 1.7 power dependence when 15 torr of NO is added. The peak amplitude of 5 ..mu..m ir fluorescence from D/sub 2/CO is proportional to the square of the D/sub 2/CO pressure in pure D/sub 2/CO or in the presence of 50 torr of Ar. Results are explained in terms of bottlenecks to excitation at the v = 1 level which are overcome by a combination of vibrational energy transfer and rotational relaxation. The radical/molecule branching ratio in D/sub 2/CO MPD was 0.10 +- 0.02 at a fluence of 125 J/cm/sup 2/ at 946.0 cm/sup -1/. The barrier height to molecular dissociation was calculated to be 3.6 +- 2.0 kcal/mole below the radical threshold or 85.0 +- 3.0 kcal/mole above the ground state of D/sub 2/CO. In H/sub 2/CO, this corresponds to 2.5 +- 2.0 kcal/mole below the radical threshold or 83.8 +- 3.0 kcal/mole above the ground state. Comparison with uv data indicate that RRKM theory is an acceptable description of formaldehyde dissociation in the 5 to 10 torr pressure range. The unimolecular decomposition of tetralin was studied by MPD and SiF/sub 4/ - sensitized pyrolysis. Both techniques induce decomposition without the interference of catalytic surfaces. Ethylene loss is identified as the lowest energy reaction channel. Dehydrogenation is found to result from step-wise H atom loss. Isomerization via disproportionation is also identified as a primary reaction channel.

  4. Modeling the complex bromate-iodine reaction.

    PubMed

    Machado, Priscilla B; Faria, Roberto B

    2009-05-01

    In this article, it is shown that the FLEK model (ref 5 ) is able to model the experimental results of the bromate-iodine clock reaction. Five different complex chemical systems, the bromate-iodide clock and oscillating reactions, the bromite-iodide clock and oscillating reactions, and now the bromate-iodine clock reaction are adequately accounted for by the FLEK model. PMID:19361181

  5. The chlorate-iodine clock reaction.

    PubMed

    Oliveira, André P; Faria, Roberto B

    2005-12-28

    A clock reaction produced by mixing chlorate and iodine solutions in perchloric acid media is reported. This is the first example of a clock reaction using chlorate as a reagent. Increasing chlorate and acid concentration reduces the induction period. Changing the initial iodine concentration does not affect the length of the induction period. The discovery of this clock reaction opens the possibility that a new family of oscillation reactions can be built using chlorate as reagent. PMID:16366551

  6. Redox reaction rates using potentiostatic coulometry

    SciTech Connect

    Ramette, R.W.; Harris, R.Z.; Bengali, A.A.; Noll, R.J.

    1987-01-01

    A new method based on potentiostatic coulometry was used to study the kinetics of the aqueous redox reactions between the ions chlorate/iodide, bromate/iodide, and bromate/bromide. The halogen product was continuously and rapidly reduced back to halide at a large platinum gauze cathode, the current being a direct measure of reaction rate and the accumulated charge serving to measure the extent of reaction. The reactions were studied at several temperatures, and activation entropies and enthalpies were calculated.

  7. Affective reactions to acoustic stimuli.

    PubMed

    Bradley, M M; Lang, P J

    2000-03-01

    Emotional reactions to naturally occurring sounds (e.g., screams, erotica, bombs, etc.) were investigated in two studies. In Experiment 1, subjects rated the pleasure and arousal elicited when listening to each of 60 sounds, followed by an incidental free recall task. The shape of the two-dimensional affective space defined by the mean ratings for each sound was similar to that previously obtained for pictures, and, like memory for pictures, free recall was highest for emotionally arousing stimuli. In Experiment 2, autonomic and facial electromyographic (EMG) activity were recorded while a new group of subjects listened to the same set of sounds; the startle reflex was measured using visual probes. Listening to unpleasant sounds resulted in larger startle reflexes, more corrugator EMG activity, and larger heart rate deceleration compared with listening to pleasant sounds. Electrodermal reactions were larger for emotionally arousing than for neutral materials. Taken together, the data suggest that acoustic cues activate the appetitive and defensive motivational circuits underlying emotional expression in ways similar to pictures. PMID:10731770

  8. Nuclear reactions from lattice QCD

    DOE PAGESBeta

    Briceño, Raúl A.; Davoudi, Zohreh; Luu, Thomas C.

    2015-01-13

    In this study, one of the overarching goals of nuclear physics is to rigorously compute properties of hadronic systems directly from the fundamental theory of strong interactions, Quantum Chromodynamics (QCD). In particular, the hope is to perform reliable calculations of nuclear reactions which will impact our understanding of environments that occur during big bang nucleosynthesis, the evolution of stars and supernovae, and within nuclear reactors and high energy/density facilities. Such calculations, being truly ab initio, would include all two-nucleon and three- nucleon (and higher) interactions in a consistent manner. Currently, lattice QCD provides the only reliable option for performing calculationsmore » of some of the low-energy hadronic observables. With the aim of bridging the gap between lattice QCD and nuclear many-body physics, the Institute for Nuclear Theory held a workshop on Nuclear Reactions from Lattice QCD on March 2013. In this review article, we report on the topics discussed in this workshop and the path planned to move forward in the upcoming years.« less

  9. Chemical reactions in turbulent mixing

    NASA Astrophysics Data System (ADS)

    Liepmann, H. W.; Brown, G. L.; Dimotakis, P. E.; Roshko, A.

    1980-06-01

    The combustion facility (H2-F2) is now nearing completion. As of this writing, a high speed mixing layer has been realized in the test section, using high pressure air. This certifies the flow facility down to and including the test section. Preliminary results on the effect of high heat release in a turbulent mixing zone were obtained in the NO-O3 experiment. These results are consistent with predictions based on previously measured p.d.f.'s in non-reacting mixing layers, but in conspicuous disagreements with a variety of accepted model calculations. These results demonstrate again the important influence of the large scale coherent structures on chemical reactions in turbulent flows. The Laser Induced Fluorescence technique has now been extended to allow direct space and time resolved measurements of the reaction products. The first four channels of the multi-channel laser Doppler velocimetry system are essentially completed. The first experiments using this new development are expected in the course of this summer. Digital image analysis of particle streak photography has also been explored as a direct means of two dimensional measurements of the velocity field in a plane. Finally, a prototype system using a 100 element acoustic detector array has been completed. Initial measurements with four of these channels using 300 kHz sound have been successfully made.

  10. Nuclear reactions from lattice QCD

    SciTech Connect

    Briceño, Raúl A.; Davoudi, Zohreh; Luu, Thomas C.

    2015-01-13

    In this study, one of the overarching goals of nuclear physics is to rigorously compute properties of hadronic systems directly from the fundamental theory of strong interactions, Quantum Chromodynamics (QCD). In particular, the hope is to perform reliable calculations of nuclear reactions which will impact our understanding of environments that occur during big bang nucleosynthesis, the evolution of stars and supernovae, and within nuclear reactors and high energy/density facilities. Such calculations, being truly ab initio, would include all two-nucleon and three- nucleon (and higher) interactions in a consistent manner. Currently, lattice QCD provides the only reliable option for performing calculations of some of the low-energy hadronic observables. With the aim of bridging the gap between lattice QCD and nuclear many-body physics, the Institute for Nuclear Theory held a workshop on Nuclear Reactions from Lattice QCD on March 2013. In this review article, we report on the topics discussed in this workshop and the path planned to move forward in the upcoming years.

  11. Radiation Reaction and Thomson Scattering

    SciTech Connect

    Koga, James

    2007-07-11

    In recent years high power high irradiance lasers of peta-watt order have been or are under construction. In addition, in the next 10 years lasers of unprecedented powers, exa-watt, could be built If lasers such as these are focused to very small spot sizes, extremely high laser irradiances will be achieved. When electrons interact with such a laser, they become highly relativistic over very short time and spatial scales. Usually the motion of an electron under the influence of electromagnetic fields is influenced to a small extent by radiation emission from acceleration. However, under such violent acceleration the amount of radiation emitted by electrons can become so large that significant damping of the electron motion by the emission of this radiation can occur. In this lecture note we will study this problem of radiation reaction by first showing how the equations of motion are obtained. Then, we will examine the problems with such equations and what approximations are made. We will specifically examine the effects of radiation reaction on the Thomson scattering of radiation from counter-streaming laser pulses and high energy electrons through the numerical integration of the equations of motion. We will briefly address the fundamental physics, which can be addressed by using such high irradiance lasers interacting with high energy electrons.

  12. Coolside desulfurization reactions and mechanisms

    SciTech Connect

    Yoon, H.; Stouffer, M.R.; Burke, F.P.

    1987-01-01

    Coolside desulfurization is an emerging SO/sub 2/ control technology, involving injection of a dry sorbent such as hydrated lime and flue gas humidification by water spraying, downstream of the air preheater in a coal-fired boiler unit. The sorbent entrained in the flue gas removes SO/sub 2/ in the humidification zone. It also removes SO/sub 2/ in the particulate layer collected by the ESP or baghouse. Based on pilot-scale data, the desulfurization mechanism in the humidifier is highly complex. Hydrated lime entrained in the flue gas rapidly reacts with SO/sub 2/ at high relative humidity conditions but, in the absence of liquid water, the reaction utilizes only a small fraction of the sorbent. The presence of water droplets in the humidifier significantly increases the sorbent efficiency and the SO/sub 2/ removal level by making the sorbent-SO/sub 2/ reaction more effective. Increasing the water droplet size also increases the SO/sub 2/ removal in the humidifier. This paper discusses the results of pilot tests which studied the mechanisms of SO/sub 2/ capture by hydrated lime in the presence and absence of water droplets in the flue gas.

  13. Nuclear reactions from lattice QCD

    NASA Astrophysics Data System (ADS)

    Briceño, Raúl A.; Davoudi, Zohreh; Luu, Thomas C.

    2015-02-01

    One of the overarching goals of nuclear physics is to rigorously compute properties of hadronic systems directly from the fundamental theory of strong interactions, quantum chromodynamics (QCD). In particular, the hope is to perform reliable calculations of nuclear reactions which will impact our understanding of environments that occur during big bang nucleosynthesis, the evolution of stars and supernovae, and within nuclear reactors and high energy/density facilities. Such calculations, being truly ab initio, would include all two-nucleon and three-nucleon (and higher) interactions in a consistent manner. Currently, lattice quantum chromodynamics (LQCD) provides the only reliable option for performing calculations of some of the low-energy hadronic observables. With the aim of bridging the gap between LQCD and nuclear many-body physics, the Institute for Nuclear Theory held a workshop on Nuclear Reactions from LQCD on March 2013. In this review article, we report on the topics discussed in this workshop and the path planned to move forward in the upcoming years.

  14. 'GREENER' CHEMICAL SYNTHESES USING ALTERNATE REACTION CONDITIONS

    EPA Science Inventory

    Microwave (MW) irradiation in conjunction with water as reaction media has proven to be a greener chemical approach for expeditious N-alkylation reactions of amines and hydrazines wherein the reactions under mildly basic conditions afford tertiary amines and double N-alkylation t...

  15. Modified triglyceride oil through reactions with phenyltriazolinedione

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The synthesis of a modified triglyceride oil was achieved through the reactions with 4-phenyl-1,2-4-triazoline-3,5-dione (PTAD). 1H NMR was used for structure determination and to monitor the reactions. Several reaction products were produced, and their relative yields depended on the stoichiometry ...

  16. Catalytic reactions in heavy-ion collisions

    NASA Astrophysics Data System (ADS)

    Kolomeitsev, E. E.; Tomášik, B.

    2012-06-01

    We discuss a new type of reactions of a ?-meson production on hyperons, ?Y ? ?Y and antikaons -KN ? ?Y. These reactions are not suppressed according to Okubo-Zweig-Iizuka rule and can be a new efficient source of ? mesons in a nucleus-nucleus collision. We discuss how these reactions can affect the centrality dependence and the rapidity distributions of the ? yield.

  17. Reaction Order Ambiguity in Integrated Rate Plots

    ERIC Educational Resources Information Center

    Lee, Joe

    2008-01-01

    Integrated rate plots are frequently used in reaction kinetics to determine orders of reactions. It is often emphasised, when using this methodology in practice, that it is necessary to monitor the reaction to a substantial fraction of completion for these plots to yield unambiguous orders. The present article gives a theoretical and statistical…

  18. The Rate Laws for Reversible Reactions.

    ERIC Educational Resources Information Center

    King, Edward L.

    1986-01-01

    Provides background information for teachers on the rate laws for reversible reactions. Indicates that although prediction of the form of the rate law for a reverse reaction given the rate law for the forward reaction is not certain, the number of possibilities is limited because of relationships described. (JN)

  19. Reactions to Disability: A Dimensional Approach.

    ERIC Educational Resources Information Center

    Livneh, Hanoch

    1982-01-01

    Explored interrelationships among a set of clients' reactions to disability. Used a Likert-type scale to rate clients' reactions arranged in six contrasting pairs. Smallest space analysis yielded a two-dimensional solution of reactions. Described the resulting configuration in terms of active-passive and external-internal dimensions. (Author)

  20. An Iodine Fluorescence Quenching Clock Reaction

    ERIC Educational Resources Information Center

    Weinberg, Richard B.; Muyskens, Mark

    2007-01-01

    Clock reactions based upon competing oxidation and reduction reactions of iodine and starch as the most popular type of chemistry example is presented to illustrate the redox phenomena, reaction kinetics, and principles of chemical titration. The examination of the photophysical principles underlying the iodine fluorescence quenching clock…