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1

Direct microwave-assisted amino acid synthesis by reaction of succinic acid and ammonia in the presence of magnetite  

NASA Astrophysics Data System (ADS)

Since the discovery of submarine hot vents in the late 1970s, it has been postulated that submarine hydrothermal environments would be suitable for emergence of life on Earth. To simulate warm spring conditions, we designed a series of microwave-assisted amino acid synthesis involving direct reactions between succinic acid and ammonia in the presence of the magnetite catalyst. These reactions which generated aspartic acid and glycine were carried out under mild temperatures and pressures (90-180 °C, 4-19 bar). We studied this specific reaction inasmuch as succinic acid and ammonia were traditionally identified as prebiotic compounds in primitive deep-sea hydrothermal systems on Earth. The experimental results were discussed in both biochemical and geochemical context to offer a possible route for abiotic amino acid synthesis. With extremely diluted starting materials (0.002 M carboxylic acid and 0.002 M ammonia) and catalyst loading, an obvious temperature dependency was observed in both cases [neither product was detected at 90 °C in comparison with 21.08 ?mol L-1 (aspartic acid) and 70.25 umol L-1 (glycine) in 180 °C]. However, an opposite trend presented for reaction time factor, namely a positive correlation for glycine, but a negative one for aspartic acid.

Jiang, Nan; Liu, Dandan; Shi, Weiguang; Hua, Yingjie; Wang, Chongtai; Liu, Xiaoyang

2013-10-01

2

Sugar-Driven Prebiotic Synthesis of Ammonia from Nitrite  

NASA Astrophysics Data System (ADS)

Reaction of 3-5 carbon sugars, glycolaldehyde, and ?-ketoaldehydes with nitrite under mild anaerobic aqueous conditions yielded ammonia, an essential substrate for the synthesis of nitrogen-containing molecules during abiogenesis. Under the same conditions, ammonia synthesis was not driven by formaldehyde, glyoxylate, 2-deoxyribose, and glucose, a result indicating that the reduction process requires an organic reductant containing either an accessible ?-hydroxycarbonyl group or an ?-dicarbonyl group. Small amounts of aqueous Fe+3 catalyzed the sugar-driven synthesis of ammonia. The glyceraldehyde concentration dependence of ammonia synthesis, and control studies of ammonia’s reaction with glyceraldehyde, indicated that ammonia formation is accompanied by incorporation of part of the synthesized ammonia into sugar-derived organic products. The ability of sugars to drive the synthesis of ammonia is considered important to abiogenesis because it provides a way to generate photochemically unstable ammonia at sites of sugar-based origin-of-life processes from nitrite, a plausible prebiotic nitrogen species.

Weber, Arthur L.

2010-03-01

3

Ammonia synthesis at low temperatures  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) calculations of reaction paths and energies for the industrial and the biological catalytic ammonia synthesis processes are compared. The industrial catalyst is modeled by a ruthenium surface, while the active part of the enzyme is modeled by a MoFe6S9 complex. In contrast to the biological process, the industrial process requires high temperatures and pressures to proceed, and an explanation of this important difference is discussed. The possibility of a metal surface catalyzed process running at low temperatures and pressures is addressed, and DFT calculations have been carried out to evaluate its feasibility. The calculations suggest that it might be possible to catalytically produce ammonia from molecular nitrogen at low temperatures and pressures, in particular if energy is fed into the process electrochemically.

Rod, T. H.; Logadottir, A.; Nørskov, J. K.

2000-03-01

4

Sugar-driven prebiotic synthesis of ammonia from nitrite.  

PubMed

Reaction of 3-5 carbon sugars, glycolaldehyde, and alpha-ketoaldehydes with nitrite under mild anaerobic aqueous conditions yielded ammonia, an essential substrate for the synthesis of nitrogen-containing molecules during abiogenesis. Under the same conditions, ammonia synthesis was not driven by formaldehyde, glyoxylate, 2-deoxyribose, and glucose, a result indicating that the reduction process requires an organic reductant containing either an accessible alpha-hydroxycarbonyl group or an alpha-dicarbonyl group. Small amounts of aqueous Fe(+3) catalyzed the sugar-driven synthesis of ammonia. The glyceraldehyde concentration dependence of ammonia synthesis, and control studies of ammonia's reaction with glyceraldehyde, indicated that ammonia formation is accompanied by incorporation of part of the synthesized ammonia into sugar-derived organic products. The ability of sugars to drive the synthesis of ammonia is considered important to abiogenesis because it provides a way to generate photochemically unstable ammonia at sites of sugar-based origin-of-life processes from nitrite, a plausible prebiotic nitrogen species. PMID:20213158

Weber, Arthur L

2010-06-01

5

The Sugar Model: Autocatalytic Activity of the Triose-Ammonia Reaction  

NASA Technical Reports Server (NTRS)

Reaction of triose sugars with ammonia under anaerobic conditions yielded autocatalytic products. The autocatalytic behavior of the products was examined by measuring the effect of the crude triose-ammonia reaction product on the kinetics of a second identical triose-ammonia reaction. The reaction product showed autocatalytic activity by increasing both the rate of disappearance of triose and the rate formation of pyruvaldehyde, the product of triose dehydration. This synthetic process is considered a reasonable model of origin-of-life chemistry because it uses plausible prebiotic substrates, and resembles modern biosynthesis by employing the energized carbon groups of sugars to drive the synthesis of autocatalytic molecules.

Weber, Arthur L.

2006-01-01

6

Wittig Reaction 33 Reaction: Synthesis of Alkenes  

E-print Network

elimination reactions (E1 or E2 reactions from alcohols or alkyl halides, for example), in eliminationWittig Reaction 33 The Wittig Reaction: Synthesis of Alkenes Intro The "Wittig Reaction" is one reactions the carbon skeleton is already pre-assembled. In the Wittig reaction, however, two smaller carbon

Jasperse, Craig P.

7

Process for synthesis of ammonia borane for bulk hydrogen storage  

DOEpatents

The present invention discloses new methods for synthesizing ammonia borane (NH.sub.3BH.sub.3, or AB). Ammonium borohydride (NH.sub.4BH.sub.4) is formed from the reaction of borohydride salts and ammonium salts in liquid ammonia. Ammonium borohydride is decomposed in an ether-based solvent that yields AB at a near quantitative yield. The AB product shows promise as a chemical hydrogen storage material for fuel cell powered applications.

Autrey, S Thomas [West Richland, WA; Heldebrant, David J [Richland, WA; Linehan, John C [Richland, WA; Karkamkar, Abhijeet J [Richland, WA; Zheng, Feng [Richland, WA

2011-03-01

8

Theoretical investigation of the reaction between carbonyl oxides and ammonia.  

PubMed

The gas-phase reaction between carbonyl oxides and ammonia is investigated by quantum mechanical calculations. The density functional method B3LYP with the basis set 6-311++G(2d,2p) was employed for the geometry and energy optimization of the stationary points along the reaction path. The energies have been refined by CCSD(T) with various basis sets and Gaussian-3 level of theory. The reaction mechanisms are studied for three different carbonyl oxides, H2COO (methyl carbonyl oxide), CH3HCOO (ethyl carbonyl oxide), and (CH3)2COO (acetone carbonyl oxide). First, a prereactive complex is formed, where a hydrogen bond is formed between ammonia and the terminal oxygen atom in the COO moiety. Next, a structural rearrangement occurs, leading to the formation of a chemical bond between the nitrogen atom and the carbon in the COO moiety as well as a transfer of the hydrogen atom from nitrogen atom to the terminal oxygen atom in the COO moiety. The newly formed molecule is a hydroperoxide amine. All the studied reactions are exothermic. The estimated reaction rates range from 1.8 x 10(-13) to 6.9 x 10(-14) and to 5.1 x 10(-18) cm3 molecule(-1) s(-1) for H2COO, CH3HCOO, and (CH3)2COO, respectively. This shows that the investigated process are important in locations with intensive farming. PMID:19711931

Jørgensen, Solvejg; Gross, Allan

2009-09-24

9

Theoretical analysis and experimental results of a 1 kW chem ammonia synthesis reactor for a solar thermochemical energy storage system  

Microsoft Academic Search

A closed-loop solar thermochemical energy storage and transport system using the dissociation and synthesis reactions of ammonia has been investigated at the Australian National University (ANU). Work relating to the optimisation of the heat recovery part of the system is reported. Experimental investigation has shown a 1-kWchem laboratory-scale ammonia synthesis reactor to operate in a stable and repeatable manner. A

H. Kreetz; K. Lovegrove

1999-01-01

10

AMMONIA  

EPA Science Inventory

This document summarizes the available information on ammonia as it relates to its effects on man and his environment. Ammonia is a ubiquitous substance and is known widely as a household cleaning agent and as a fertilizer. It plays an important role in the nitrogen cycle--in the...

11

Synthesis of ammonia directly from air and water at ambient temperature and pressure.  

PubMed

The N?N bond (225?kcal mol?¹) in dinitrogen is one of the strongest bonds in chemistry therefore artificial synthesis of ammonia under mild conditions is a significant challenge. Based on current knowledge, only bacteria and some plants can synthesise ammonia from air and water at ambient temperature and pressure. Here, for the first time, we report artificial ammonia synthesis bypassing N? separation and H? production stages. A maximum ammonia production rate of 1.14 × 10???mol m?² s?¹ has been achieved when a voltage of 1.6?V was applied. Potentially this can provide an alternative route for the mass production of the basic chemical ammonia under mild conditions. Considering climate change and the depletion of fossil fuels used for synthesis of ammonia by conventional methods, this is a renewable and sustainable chemical synthesis process for future. PMID:23362454

Lan, Rong; Irvine, John T S; Tao, Shanwen

2013-01-01

12

Ammonia synthesis using a stable electride as an electron donor and reversible hydrogen store.  

PubMed

Industrially, the artificial fixation of atmospheric nitrogen to ammonia is carried out using the Haber-Bosch process, but this process requires high temperatures and pressures, and consumes more than 1% of the world's power production. Therefore the search is on for a more environmentally benign process that occurs under milder conditions. Here, we report that a Ru-loaded electride [Ca(24)Al(28)O(64)](4+)(e(-))(4) (Ru/C12A7:e(-)), which has high electron-donating power and chemical stability, works as an efficient catalyst for ammonia synthesis. Highly efficient ammonia synthesis is achieved with a catalytic activity that is an order of magnitude greater than those of other previously reported Ru-loaded catalysts and with almost half the reaction activation energy. Kinetic analysis with infrared spectroscopy reveals that C12A7:e(-) markedly enhances N(2) dissociation on Ru by the back donation of electrons and that the poisoning of ruthenium surfaces by hydrogen adatoms can be suppressed effectively because of the ability of C12A7:e(-) to store hydrogen reversibly. PMID:23089869

Kitano, Masaaki; Inoue, Yasunori; Yamazaki, Youhei; Hayashi, Fumitaka; Kanbara, Shinji; Matsuishi, Satoru; Yokoyama, Toshiharu; Kim, Sung-Wng; Hara, Michikazu; Hosono, Hideo

2012-11-01

13

Ammonia synthesis using a stable electride as an electron donor and reversible hydrogen store  

NASA Astrophysics Data System (ADS)

Industrially, the artificial fixation of atmospheric nitrogen to ammonia is carried out using the Haber-Bosch process, but this process requires high temperatures and pressures, and consumes more than 1% of the world's power production. Therefore the search is on for a more environmentally benign process that occurs under milder conditions. Here, we report that a Ru-loaded electride [Ca24Al28O64]4+(e-)4 (Ru/C12A7:e-), which has high electron-donating power and chemical stability, works as an efficient catalyst for ammonia synthesis. Highly efficient ammonia synthesis is achieved with a catalytic activity that is an order of magnitude greater than those of other previously reported Ru-loaded catalysts and with almost half the reaction activation energy. Kinetic analysis with infrared spectroscopy reveals that C12A7:e- markedly enhances N2 dissociation on Ru by the back donation of electrons and that the poisoning of ruthenium surfaces by hydrogen adatoms can be suppressed effectively because of the ability of C12A7:e- to store hydrogen reversibly.

Kitano, Masaaki; Inoue, Yasunori; Yamazaki, Youhei; Hayashi, Fumitaka; Kanbara, Shinji; Matsuishi, Satoru; Yokoyama, Toshiharu; Kim, Sung-Wng; Hara, Michikazu; Hosono, Hideo

2012-11-01

14

Exergy analysis of an ammonia synthesis reactor in a solar thermochemical power system  

Microsoft Academic Search

An ammonia-based thermochemical energy storage system is under investigation at the Australian National University. In recent years, one line of research has been the analysis of ammonia synthesis reactors. A two-dimensional numerical reactor model was previously validated with experimental results and was used in this study to compare maximum thermal output with maximum exergy output of the reactor investigated. The

H Kreetz; K Lovegrove

2002-01-01

15

Understanding the novolak synthesis reaction  

Microsoft Academic Search

We describe new tools for the characterization of novolac resins, for the understanding of the novolac synthesis reaction, and for the prediction of resin structures. These tools have been used to optimize the performance of photoresists for microlithography. The current state-of- the-art describes novolac copolymer compositions as the ratio of monomers charged in the reaction, even though it is well

Leonard E. Bogan

1993-01-01

16

Reaction of coordinated dinitrogen. 12. Identification of intermediates in the conversion of molybdenum-bound dinitrogen into ammonia and hydrazine. Factors affecting the ammonia-forming reaction  

SciTech Connect

When bis(dinitrogen) complexes of molybdenum and tungsten are treated with an excess of strong acid, with few exceptions, a complex containing the hydrazido(2-) ligand has been identified either as a product in the reaction or as an intermediate on the way to the formation of ammonia and hydrazine. In the case of those molybdenum complexes that produce ammonia, the stoichiometry of the reaction can be represented by eq 1 and 2: (1) )Mo/sup 0/(N/sub 2/)/sub 2/) ..-->../sup H/sup +// )Mo(NNH/sub 2/)) + N/sub 2/, (2) )Mo(NNH/sub 2/)) ..-->../sup H/sup +// 1/2N/sub 2/ + HN/sub 4//sup +/ + )Mo(III)), with a molybdenum(III) complex as the final molybdenum-containing product. Here the identification of two isomeric hydrazido(2-) complexes are reported upon, that are formed as a mixture in the reaction of excess HBr in tetrahydrofuran (THF) solution with trans-(Mo(N/sub 2/)/sub 2/(triphos)(PPh/sub 3/)), where triphos = PhP(CH/sub 2/CH/sub 2/PPh/sub 2/)/sub 2/. From this mixture of hydrazido(2-) complexes ammonia and a trace of hydrazine are produced in THF solution, but in benzene or toluene solution more hydrazine than ammonia is produced. On the basis of data presented, reversible phosphine dissociation is the next recognizable step toward ammonia formation.

Bossard, G.E.; George, T.A.; Howell, D.B.; Koczon, L.M.; Lester, R.K.

1983-07-06

17

Photoinduced catalytic synthesis of biologically important metabolites from formaldehyde and ammonia under plausible "prebiotic" conditions  

NASA Astrophysics Data System (ADS)

The article analyzes new and previously reported data on several catalytic and photochemical processes yielding biologically important molecules. UV-irradiation of formaldehyde aqueous solution yields acetaldehyde, glyoxal, glycolaldehyde and glyceraldehyde, which can serve as precursors of more complex biochemically relevant compounds. Photolysis of aqueous solution of acetaldehyde and ammonium nitrate results in formation of alanine and pyruvic acid. Dehydration of glyceraldehyde catalyzed by zeolite HZSM-5-17 yields pyruvaldehyde. Monosaccharides are formed in the course of the phosphate-catalyzed aldol condensation reactions of glycolaldehyde, glyceraldehyde and formaldehyde. The possibility of the direct synthesis of tetroses, keto- and aldo-pentoses from pure formaldehyde due to the combination of the photochemical production of glycolahyde and phosphate-catalyzed carbohydrate chain growth is demonstrated. Erythrulose and 3-pentulose are the main products of such combined synthesis with selectivity up to 10%. Biologically relevant aldotetroses, aldo- and ketopentoses are more resistant to the photochemical destruction owing to the stabilization in hemiacetal cyclic forms. They are formed as products of isomerization of erythrulose and 3-pentulose. The conjugation of the concerned reactions results in a plausible route to the formation of sugars, amino and organic acids from formaldehyde and ammonia under presumed 'prebiotic' conditions.

Delidovich, I. V.; Taran, O. P.; Simonov, A. N.; Matvienko, L. G.; Parmon, V. N.

2011-08-01

18

Tandem Reactions for Streamlining Synthesis  

PubMed Central

CONSPECTUS In 1980 Sharpless and Katsuki introduced the asymmetric epoxidation of prochiral allylic alcohols (the Sharpless-Katsuki Asymmetric Epoxidation), which enabled the rapid synthesis of highly enantioenriched epoxy alcohols. This reaction was a milestone in the development of asymmetric catalysis because it was the first highly enantioselective oxidation reaction. Furthermore, it provided access to enantioenriched allylic alcohols that are now standard starting materials in natural product synthesis. In 1981 Sharpless and coworkers made another seminal contribution by describing the kinetic resolution (KR) of racemic allylic alcohols. This work demonstrated that small-molecule catalysts could compete with enzymatic catalysts in KRs. For these pioneering works, Sharpless was awarded the 2001 Nobel Prize with Knowles and Noyori. Despite these achievements, the Sharpless KR is not an efficient method to prepare epoxy alcohols with high enantiomeric excess (ee). First, the racemic allylic alcohol must be prepared and purified. KR of the racemic allylic alcohol must be stopped at low conversion, because the ee of the product epoxy alcohol decreases as the KR progresses. Thus, better methods to prepare epoxy alcohols containing stereogenic carbinol carbons are needed. This Account summarizes our efforts to develop one-pot methods for the synthesis of various epoxy alcohols and allylic epoxy alcohols with high enantio-, diastereo-, and chemoselectivity. Our laboratory developed titanium-based catalysts for use in the synthesis of epoxy alcohols with tertiary carbinols. The catalysts are involved in the first step, which is an asymmetric alkyl or allyl addition to enones. The resulting intermediates are then subjected to a titanium-directed diastereoselective epoxidation to provide tertiary epoxy alcohols. Similarly, the synthesis of acyclic epoxy alcohols begins with asymmetric additions to enals and subsequent epoxidation. The methods described here enable the synthesis of skeletally diverse epoxy alcohols. PMID:18710197

HUSSAIN, MAHMUD M.; WALSH, PATRICK J.

2009-01-01

19

Understanding the novolak synthesis reaction  

NASA Astrophysics Data System (ADS)

We describe new tools for the characterization of novolac resins, for the understanding of the novolac synthesis reaction, and for the prediction of resin structures. These tools have been used to optimize the performance of photoresists for microlithography. The current state-of- the-art describes novolac copolymer compositions as the ratio of monomers charged in the reaction, even though it is well known that the actual product composition is quite different. Quantitative 13C NMR spectroscopy provides a direct method for accurately determining copolymer composition by integrating methyl carbon resonances. By using this method to analyze the results of competition reactions, relative monomer and site reactivities for phenol and the cresols with formaldehyde have been determined. These observed reactivities have been used in a simple, kinetic model to accurately predict copolymer composition, branch density, and molecular weight.

Bogan, Leonard E., Jr.

1993-09-01

20

Ammonia Inhibits Long-term Potentiation via Neurosteroid Synthesis in Hippocampal Pyramidal Neurons  

PubMed Central

Neurosteroids are a class of endogenous steroids synthesized in the brain that are believed to be involved in the pathogenesis of neuropsychiatric disorders and memory impairment. Ammonia impairs long-term potentiation (LTP), a synaptic model of learning, in the hippocampus, a brain region involved in memory acquisition. Although mechanisms underlying ammonia-mediated LTP inhibition are not fully understood, we previously found that activation of N-methyl-D-aspartate receptors (NMDARs) is important. Based on this, we hypothesize that metabolic stressors, including hyperammonemia, promote untimely NMDAR activation and result in neural adaptations that include the synthesis of allopregnanolone (alloP) and other ?-aminobutyric acid (GABA)-potentiating neurosteroids that dampen neuronal activity and impair LTP and memory formation. Using an antibody against 5?-reduced neurosteroids, we found that 100 ?M ammonia acutely enhanced neurosteroid immunostaining in pyramidal neurons in the CA1 region of rat hippocampal slices. The enhanced staining was blocked by finasteride, a selective inhibitor of 5?-reductase, a key enzyme required for alloP synthesis. Finasteride also overcame LTP inhibition by 100 ?M ammonia, as did picrotoxin, an inhibitor of GABA-A receptors. These results indicate that GABA enhancing neurosteroids, synthesized locally within pyramidal neurons, contribute significantly to ammonia-mediated synaptic dysfunction. These results suggest that manipulation of neurosteroid synthesis could provide a strategy to improve cognitive function in individuals with hyperammonemia. PMID:23276672

Izumi, Yukitoshi; Svrakic, Neda; O'Dell, Kazuko; Zorumski, Charles F.

2013-01-01

21

Studies on the use of supercritical ammonia for ceramic nitride synthesis and fabrication  

NASA Technical Reports Server (NTRS)

The extractability of ammonia halides (including ammonium thiocyanate) formed as byproducts from the synthesis of Si(NH)2 via ammonolysis of the corresponding silicon tetrahalides using supercritical NH3 as the extraction medium was investigated. It was found that the NH4SCN byproduct of ammonolysis of Si(SCN)4 can be almost completely extracted from the insoluble Si(NH)2 forming a promising system for the synthesis of pure Si(NH)2, one of the best precursors for Si3N4. In addition it was found that Si3N4, AlN, BN, and Si(NH)2 are insoluble in SC ammonia. Also discussed are design considerations for a supercritical ammonia extraction unit.

Cornell, Linda; Lin, Y. C.; Philipp, Warren H.

1990-01-01

22

Photochemical reactions for commercial synthesis  

SciTech Connect

Photochemical reactions are conducted using floating polymer beads on the surface of a moving body of water. The polymer bead is impregnated with a reactant, floated on the water in direct sunlight so as to expose the reactant to solar radiation, collected at a downstream location, treated to remove product from the polymer, and then the bead can be recycled. The process can be used to collect and store solar energy in chemical form, or for conducting photochemical synthesis to produce useful chemical products.

Guillet, J. E.

1985-06-25

23

Reaction synthesis of heat-resistant materials  

SciTech Connect

Exothermicity associated with the synthesis of aluminides can be utilized to obtain aluminides of transition metals. Combustion synthesis, extrusion, and hot pressing were utilized to obtain dense intermetallics and their composites. Composites were analyzed by X- ray diffraction and microscopy techniques, and tensile properties were measured on button-head and sheet specimens of intermetallics and their composites. Mechanical properties of intermetallics obtained by reaction synthesis and densification compare well with conventionally processed materials. Reaction-synthesis principles were also extended to weld overlays. Possible approaches to obtaining dense products by reaction synthesis and densification are summarized in a schematic illustration. 19 refs., 14 figs., 3 tabs.

Deevi, S.C.; Sikka, V.K.

1995-12-31

24

AMINO ACID SYNTHESIS IN PHOTO-SYNTHESIZING SPINACH CELLS. EFFECTS OF AMMONIA ON POOL SIZES AND RATES OF LABELING FROM {sup 14}CO{sub 2}  

SciTech Connect

Isolated cells from leaves of Spinacea oleracea have been maintained in a state capable of high rates of photosynthetic CO{sub 2} fixation for more than 60 h. The incorporation of {sup 14}CO{sub 2} under saturating CO{sub 2} conditions into carbohydrates, carboxylic acids, and amino acids, and the effect of ammonia on this incorporation have been studied. Total incorporation, specific radioactivity and pool size have been determined as a function of time for most of the protein amino acids and for {gamma}-aminobutyric acid. the measurements of specific activities and of the approaches to {sup 14}C "saturation" of some amino acids indicate the presence and relative sizes of metabolically active and passive pools of these amino acids. Added ammonia decreased carbon fixation into carbohydrates and increased fixation into carboxylic acids and amino acids. Different amino acids were, however, affected in different and highly specific ways. Ammonia caused large stimulatory effects in incorporation of {sup 14}C into glutamine (a factor of 16), No effect or slight decreases were seen in glycine, serine, phenylalanine, and tyrosine labeling, In.the case of glutamate, {sup 14}C-labeling decreased, but specific activity increased. The production of labeled {gamma}-aminobutyric acid was virtually stopped by ammonia. The results indicate that added ammonia stimulates the reactions mediated by pyruvate kinase and phosphoenolpyruvate carboxylase, as seen with other plant systems. The data on the effects of added ammonia on total labeling, pool sizes, and specific activities of several amino acids provides a number of indications about the intracellular sites of principal synthesis from carbon skeletons of these amino acids and the selective nature of effects of increased intracellular ammonia concentration on such synthesis.

Larsen, Peder Olesen; Cornwell, Karen L.; Gee, Sherry L.; Bassham, James A.

1980-10-01

25

Ion-molecule reactions of ammonia clusters with C60 aggregates embedded in helium droplets.  

PubMed

Helium nanodroplets are co-doped with C(60) and ammonia. Mass spectra obtained by electron ionization reveal cations containing ammonia clusters complexed with up to four C(60) units. The high mass resolution of ?m/m? 1/6000 makes it possible to separate the contributions of protonated, unprotonated and dehydrogenated ammonia. C(60) aggregates suppress the proton-transfer reaction which usually favors the appearance of protonated ammonia cluster ions. Unprotonated C(x)(NH(3))(n)(+) ions (x = 60, 120, 180) exceed the abundance of the corresponding protonated ions if n < 5; for larger values of n the abundances of C(60)(NH(3))(n)(+) and C(60)(NH)(n-1)NH(4)(+) become about equal. Dehydrogenated C(60)NH(2)(+) ions are relatively abundant; their formation is attributed to a transient doubly charged C(60)-ammonia complex which forms either by an Auger process or by Penning ionization following charge transfer between the primary He(+) ion and C(60). The abundance of C(x)NH(3)(+) and C(x)NH(4)(+) ions (x = 120 or 180) is one to two orders of magnitude weaker than the abundance of ions containing one or two additional ammonia molecules. However, a model involving evaporation of NH(3) or NH(4) from the presumably weakly bound C(x)NH(3)(+) and C(x)NH(4)(+) ions is at odds with the lack of enhancement in the abundance of C(120)(+) and C(180)(+). Mass spectra of C(60) dimers complexed with water complement a previous study of C(60)(H(2)O)(n)(+) recorded at much lower mass resolution. PMID:21072422

Schöbel, Harald; Leidlmair, Christian; Bartl, Peter; Aleem, Abid; Hager, Michaela; Echt, Olof; Märk, Tilmann D; Scheier, Paul

2011-01-21

26

Synthesis and application of a new fluorous-tagged ammonia equivalent.  

PubMed

A novel fluorous-tagged ammonia equivalent has been developed. It is based on a nitrogen-oxygen bond, which can be cleaved in a traceless manner by a molybdenum complex or samarium diiodide. The application in the synthesis of ureas, amides, sulfonamides, and carbamates is described. The scope of the fluorous N-O linker is exemplified by the synthesis of itopride, a drug used for the treatment of functional dyspepsia. Itopride was synthesized with the aid of fluorous purification methods and the product was isolated in good overall yield, with high purity. PMID:20333716

Nielsen, Simon D; Smith, Garrick; Begtrup, Mikael; Kristensen, Jesper L

2010-04-19

27

Reactions of sulfur dioxide with ammonia: Dependence on oxygen and nitric oxide  

SciTech Connect

The influence of oxygen and nitric oxide on the reactions of sulfur dioxide with ammonia were studied in a simulated flue gas in the range of 0--20% oxygen and 0--300 ppm nitric oxide at temperatures in the range of 40--60 C. A Fourier transform infrared spectrometer (FT-IR) analyzed the reaction products deposited on the reactor surface and revealed that ammonium sulfate was the main product of the reactions, with sulfamic acid and ammonium sulfamate as the minor products. The results showed that oxygen and nitric oxide enhanced the oxidation reactions of sulfur dioxide to form ammonium sulfate. The yield of the minor products markedly increased in the presence of nitrogen dioxide. The size and number concentration of product aerosols increased at lower temperature. The fraction of sulfur dioxide which formed aerosols increased with sulfur dioxide removal.

Hirota, Koichi; Maekelae, J.; Tokunaga, Okihiro [Japan Atomic Energy Research Inst., Takasaki, Gunma (Japan)] [Japan Atomic Energy Research Inst., Takasaki, Gunma (Japan)

1996-10-01

28

Process for the liquefaction of solid carbonaceous materials wherein nitrogen is separated from hydrogen via ammonia synthesis  

DOEpatents

In a process for the liquefaction of solid carbonaceous materials wherein bottoms residues are upgraded with a process wherein air is employed, the improvement wherein nitrogen buildup in the system is avoided by ammonia synthesis. In a preferred embodiment hydrogen from other portions of the liquefaction process will be combined with hydrogen produced as a result of the bottoms upgrading to increase the H.sub.2 :N.sub.2 ratio in the ammonia reactor.

Stetka, Steven S. (Fleetwood, PA); Nazario, Francisco N. (Parsippany, NJ)

1982-01-01

29

The Quest for the Neutral Sulfur-Selenium-Nitrogen Compounds. The Reaction of Dichlorodiselane-Dichlorodisulfane Mixtures With Ammonia  

Microsoft Academic Search

The reactions of dichlorodiselane and dichlorodisulfane mixtures with ammonia produce heterocyclic selenium sulfides as well as sulfur nitrides and imides. The reaction products have been identified with Se and N NMR spectroscopy. No evidence on the formation of sulfur-selenium nitrides and imides was observed.

Jarl Siivari; Risto S. Laitinen; Yrjo Hiltunen

1992-01-01

30

THE CHANGES IN CHOICE REACTION TIME RELATED TO TYPE OF MUSCULAR CONTRACTION AND THE CONCENTRATION OF AMMONIA  

Microsoft Academic Search

The objective of this research project was the determination of changes in choice reaction time during graded exercise efforts with different types of muscular contraction i.e. mixed, concentric and eccentric. The shortest reaction time was also compared with a level of ammonia threshold. Ten, healthy male students of the Academy of Physical Education in Katowice took part in the study

ADAM STASZKIEWICZ; JAN CHMURA

2002-01-01

31

Ammonia from Iron(II) Reduction of Nitrite and the Strecker Synthesis: Do Iron(II) and Cyanide Interfere with Each Other?  

NASA Technical Reports Server (NTRS)

The question of whether the production of ammonia, from the reduction of nitrite by iron(II), is compatible with its use in the Strecker synthesis of amino acids, or whether the iron and the cyanide needed for the Strecker synthesis interfere with each other, is addressed. Results show that the presence of iron(II) appears to have little, or no, affect on the Strecker synthesis. The presence of cyanide does interfere with reduction of nitrite, but the reduction proceeds at cyanide/iron ratios of less than 4:1. At ratios of about 2:1 and less there is only a small effect. The two reactions can be combined to proceed in each other's presence, forming glycine from nitrite, Fe(+2), formaldehyde, and cyanide.

Summers, David P.; Lerner, Narcinda; Chang, Sherwood (Technical Monitor)

1996-01-01

32

Synthesis of nanosilver on polyamide fabric using silver/ammonia complex.  

PubMed

In this paper, a novel synthesis method for nanosilver has been introduced on or within the polymeric chains of polyamide 6 fabric by using silver/ammonia complex [Ag(NH3)2](+). The silver complex was reduced directly by functional groups of polyamide chains without using any additional chemical reducing agents. The polyamide fabric was also stabilized with formation of new linkages between the polymeric chains of the nylon fabric through silver nanoparticle synthesis. The presence of nanosilver on the fabric was confirmed by UV-vis spectra, EDX patterns and XRD patterns. In addition, X-ray photoelectron spectroscopy (XPS) was utilized to identify the chemical state of silver in a range of silver oxide and silver metal. The SEM images confirmed the presence of nanosilver on the polyamide within the size of 20 and 150 nm. Excellent antibacterial properties were achieved with the treated fabrics against Staphylococcus aureus and Escherichia coli. Further, the antibacterial properties of the polyamide fabric treated with 35 mg/L silver/ammonia were durable against washing as they only decreased to 98.6% after 20 washes. In addition, some other properties of the treated fabrics including color changes, dimensional stability, water droplet adsorption, and reflectance spectrum are reported and thoroughly discussed. PMID:24656365

Montazer, Majid; Shamei, Ali; Alimohammadi, Farbod

2014-05-01

33

Surfactant-assisted synthesis, characterizations, and room temperature ammonia sensing mechanism of nanocrystalline CuO  

NASA Astrophysics Data System (ADS)

CuO nanocrystalline powder has been synthesized by a sol?gel auto combustion route with cetyltrimethylammonium bromide (CTAB) as cationic surfactant, and sodium dodecyl sulphate (SDS) as anionic surfactant. The powder samples are characterized by TGA/DTA, XRD, FESEM, and TEM techniques. Thermal analysis of the dried gel samples shows that addition of surfactant in the precursor increases the heat of reaction, which is evolved in the decomposition of metal citrate complex. The CTAB and SDS addition in the reaction mixture lowers the average crystallite size to few tens of nanometer. Surfactant doping in precursor causes a variation in lattice strain and changes to its type to compressive. CuO nanoparticles are bound together into facets-like weakly aggregated clusters, as indicated by FESEM images. TEM micrographs indicate the porous, nearly spherical particles having crystallite size around 7 and 18 nm for CTAB and SDS surfactant assisted CuO samples respectively. CuO nanoparticles assembled as thick film have been tested for their response to 100 ppm ammonia gas at room temperature. Cationic surfactant assisted sample shows maximum response to ammonia as compared to anionic surfactant. The CTAB assisted sensor shows almost completes recovery in 500 s whereas SDS assisted sample shows 75% recovery in the same time. The ammonia response of the films obeys the Elovich equation. The response rate of sensor is found to be maximum for CTAB assisted CuO films as compared to other samples. The kinetics of the response reaction shows that the ionic surfactants assisted CuO follows second order reaction kinetics.

Singh, Iqbal; Bedi, R. K.

2011-11-01

34

Synthesis of mono(dinitrogen) complexes of molybdenum. Formation of ammonia and hydrazine  

SciTech Connect

The synthesis and reactivity of a series of mono-N/sub 2/ complexes of molybdenum are reported. Reduction of MoCl/sub 3/(triphos), where triphos = PhP(CH/sub 2/CH/sub 2/PPh/sub 2/)/sub 2/, with sodium amalgam in the presence of 2L or L/sub 2/ and with a regulated amount of N/sub 2/ led to the formation of Mo(N/sub 2/)(triphos)(L/sub 2/) (1-5): 1, L = PMe/sub 2/Ph; 2, L/sub 2/ = Me/sub 2/PCH/sub 2/PMe/sub 2/, dmpm; 3, L/sub 2/ = 1,2-(Me/sub 2/As)/sub 2/C/sub 6/H/sub 4/, diars; 4, L/sub 2/ = Ph/sub 2/PCH/sub 2/PPh/sub 2/, dppm; 5, L/sub 2/ = Ph/sub 2/PCH/sub 2/CH/sub 2/PPh/sub 2/, dppe. Complexes 3 and 5 were each a mixture of two isomeric mono-N/sub 2/ complexes. Complexes 1-5 reacted with excess HX (X = Br, Cl) to afford varying yields of ammonia, hydrazine, and N/sub 2/ (and some H/sub 2/). Loss of N/sub 2/ occurred readily from 1 when it was evacuate in the solid state to give 7. Five-coordinate 7 reacted with H/sub 2/, CO, and C/sub 2/H/sub 4/ in the solid state to form MoH/sub 2/(triphos)(PMe/sub 2/Ph)/sub 2/ (8), Mo(CO)(triphos)(PMe/sub 2/Ph)/sub 2/ (9), and Mo(C/sub 2/H/sub 4/)(triphos)(PMe/sub 2/Ph)/sub 2/ (10), respectively. Reaction of solids 7, 8, and 10 with N/sub 2/ regenerated 1. Structural assignments of the new complexes are based upon /sup 31/P and /sup 1/H NMR spectral data. Triphos is shown to adopt both fac and mer configurations. 33 references, 1 table.

George, T.A.; Tisdale, R.C.

1988-08-24

35

Pericyclic reactions in organic synthesis  

E-print Network

Part I of this thesis describes a formal, metal-free, [2 + 2 + 2] cycloaddition strategy based on a cascade of two pericyclic processes. An intramolecular propargylic ene reaction of a 1,6-diyne is used to generate a ...

Robinson-Surry, Julia M. (Julia Mae)

2011-01-01

36

Formation of brown carbon via reactions of ammonia with secondary organic aerosols from biogenic and anthropogenic precursors  

E-print Network

in color (limonene SOA). The aqueous phase reactions with dissolved ammonium (NH4 þ ) salts t color from white to brown in pres- ence of ammonia. sources. Known examples of primary brown carbon sources are smoldering forest fires and residential coal

Nizkorodov, Sergey

37

Reprint of: The role of potassium in the catalytic synthesis of ammonia  

NASA Astrophysics Data System (ADS)

A model study on the promotor action of K in the synthesis of ammonia on iron catalysts was performed by studying the influence of preadsorbed potassium on the rate of dissociative nitrogen chemisorption (which is the rate-limiting step) on a Fe(100) single crystal surface. It was found that a concentration of 1.5 × 1014 K atoms/cm2 increases this rate by a factor of about 300 at 430 K and removes also the activation energy for this process. This effect is attributed to the increased adsorption energy of molecular N2 (11.5 kcal/mole) which is related with the pronounced transfer of electronic charge from K to the Fe surface.

Ertl, G.; Weiss, M.; Lee, S. B.

2013-12-01

38

Fundamental study of ammonia-sulfur dioxide reactions to form solid particles. Final report  

SciTech Connect

The effects of reaction residence time, presence of inert particles and moisture content on the SO{sub 2} removal and the product particle size distributions have been determined. Results indicated that both gas phase and particle phase reach equilibria in a very short time. The presence of inert particles increases the SO{sub 2} removal efficiency slightly, with a greater increase in removal efficiency at higher surface areas. Moisture content is the most important parameter affecting SO{sub 2} removal. Increasing the moisture content from 1.6% to 6.4% by volume results in a 30% increase of the SO{sub 2} removal at a reaction temperature of 51{degree}C. The products at near anhydrous conditions were concluded to be NH{sub 3}SO{sub 2}, (NH{sub 3}){sub 2}SO{sub 2} and (NH{sub 4}){sub 2}S{sub 2}O{sub 5}. While the products at humid conditions could be either the 1:1 sulfites, NH{sub 4}HSO{sub 3} and (NH{sub 4}){sub 2}S{sub 2}O{sub 5}, or the 2:1 sulfites, (NH{sub 4}){sub 2}SO{sub 3} and (NH{sub 4}){sub 2}SO{sub 3} {minus}H{sub 2}O, or a mixture of the 1:1 and 2:1 sulfite. Those sulfite particles could subsequently oxidize to form the more stable sulfate particles. A gas-to-particle formation model has been developed to simulate the NH{sub 3}-SO{sub 2} system in the presence and absence of seed aerosols at trace water conditions. This model accounts for simultaneous nucleation, coagulation, condensation and chemical reaction. The applicability of utilizing ammonia injection to a flue gas system has been discussed in terms of two possible removal schemes. One utilizes ammonia injection alone and the other is in conjunction with the injection of Ca(OH){sub 2} slurry in a spray dryer system. Both schemes have the potential of achieving over 90% SO{sub 2} removal from power plants burning high-sulfur coals.

Biswas, P.; Bai, H. [Cincinnati Univ., OH (United States). Dept. of Civil and Environmental Engineering

1994-01-18

39

Construction of the reaction networks for heterogeneous catalytic reactions: Fischer—Tropsch synthesis and related reactions  

Microsoft Academic Search

The key approaches to the generation of reaction networks for the synthesis of products from CO and H2 are considered. The selection rules for the elementary steps on the surface of heterogeneous catalysts are formulated. Data on the surface compounds and steps related to reactions of CO and H2 are analyzed and a set of transforms (models of elementary steps)

O. N. Temkin; A. V. Zeigarnik; A. E. Kuz\\; L. G. Bruk; E. V. Slivinskii

2002-01-01

40

Synthesis and photocatalytic performances of BiVO{sub 4} by ammonia co-precipitation process  

SciTech Connect

This paper reports the preparation and photocatalytic performance of Bismuth vanadate (BiVO{sub 4}) by a facile and inexpensive approach. An amorphous BiVO{sub 4} was first prepared by a co-precipitation process from aqueous solutions of Bi(NO{sub 3}){sub 3} and NH{sub 4}VO{sub 3} using ammonia. Followed by heating treatment at various temperatures, the amorphous phase converted to crystalline BiVO{sub 4} with a structure between monoclinic and tetragonal scheelite. The crystallization of BiVO{sub 4} occurred at about 523 K, while the nanocrystalline BiVO{sub 4} were formed with a heat-treatment of lower than 673 K. However, when the heat-treatment was carried out at 773 K, the accumulation of nanocrystals to bulk particles was observed. The photocatalytic performances of the materials were investigated by O{sub 2} evolution under visible-light, and MB decomposition under solar simulator. The results demonstrated that the crystalline structure is still the vital factor for the activities of both reactions. However, the crystallinity of BiVO{sub 4} gives a major influence on the activity of O{sub 2} evolution, whereas the surface area, plays an important role for photocatalytic MB decomposition. - Abstract: BiVO{sub 4} was prepared by a co-precipitation process using aqueous ammonia solution, followed by heating treatment at various temperatures. The crystalline structure and crystallization process, and their influences on photocatalytic O{sub 2} evolution and organic pollutants degradation were investigated. It demonstrated that the crystalline structure is still the vital factor for the activities of both reactions. However, the crystallinity of BiVO{sub 4} gives a major influence on the activity of O{sub 2} evolution, whereas the surface area, plays an important role for photocatalytic MB decomposition. Display Omitted.

Yu Jianqiang [Laboratory of Fiber Materials and Modern Textile, Institute of Multifunctional Materials, Qingdao University, No. 308 Ningxia Road, Qingdao 266071 (China); School of Chemistry, Chemical Engineering and Environment, Qingdao University, No. 308 Ningxia Road, Qingdao 266071 (China)], E-mail: jianqyu@qdu.edu.cn; Zhang Yan [School of Chemistry, Chemical Engineering and Environment, Qingdao University, No. 308 Ningxia Road, Qingdao 266071 (China); Kudo, Akihiko [Department of Applied Chemistry, Faculty of Science, Tokyo University of Sciences, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601 (Japan); Core Research for Evolutional Science and Technology, Japan Science and Technology Agency (CREST, JST), 4-1-8 Honcho, Kawaguchi-shi, Saitama 332-0012 (Japan)], E-mail: a-kudo@rs.kagu.tus.ac.jp

2009-02-15

41

Vibrational and Translational Energy Effects in the Reaction of Ammonia Ions with Water Michael A. Everest, John C. Poutsma, and Richard N. Zare*  

E-print Network

Vibrational and Translational Energy Effects in the Reaction of Ammonia Ions with Water Molecules, and 22 amu. The cross section for proton transfer decreases with increasing collisional energy of vibrationally state-selected ammonia ions with deuterated water is investigated with a quadrupole

Zare, Richard N.

42

Eddy covariance flux measurements of ammonia by electron transfer reaction-mass spectrometry  

NASA Astrophysics Data System (ADS)

A system for fast ammonia (NH3) measurements based on a commercial Proton Transfer Reaction-Mass Spectrometer is presented. It uses electron transfer reaction (eTR) as ionisation pathway and features a drift tube of polyetheretherketone (PEEK) and silica-coated steel. Heating the instrumental inlet and the drift tube to 180° C enabled an effective time resolution of ~1 s and made it possible to apply the eTR-MS for eddy covariance (EC) measurements. EC fluxes of NH3 were measured over two agricultural fields in Oensingen, Switzerland, following fertilisations with cattle slurry. Air was aspirated close to a sonic anemometer at a flow of 100 STP L min-1 and was directed through a 23 m long 1/2" PFA tube heated to 150°C to an air-conditioned trailer where the eTR-MS sub-sampled from the large bypass stream. This setup minimised damping of fast NH3 concentration changes between the sampling point and the actual measurement. High-frequency attenuation loss of the NH3 fluxes of 20 to 40% was quantified and corrected for using an empirical ogive method. The instrumental NH3 background signal showed a minor interference with H2O which was characterised in the laboratory. The resulting correction of the NH3 flux after slurry spreading was less than 1‰. The flux detection limit of the EC system was about 5 ng m-2 s-1 while the accuracy of individual flux measurements was estimated 16% for the high-flux regime during these experiments. The NH3 emissions after broad spreading of the slurry showed an initial maximum of 150 ?g m2 s-1 with a fast decline in the following hours.

Sintermann, J.; Spirig, C.; Jordan, A.; Kuhn, U.; Ammann, C.; Neftel, A.

2010-11-01

43

Optimization of green synthesis of ammonia by magnetic induction method using response surface methodology  

NASA Astrophysics Data System (ADS)

The current method for ammonia (NH3) production is a high energy consumption process and not environmentally friendly because it requires high operating temperature and pressure. A novel green method using nanotechnology and the magnetic induction method (MIM) to synthesize NH3 provides a new route to address this issue. In this preliminary study, ?-Fe2O3 nanocatalyst was chosen because iron is a very good catalyst for NH3 synthesis for a wide temperature range. The optimal mixture of nitrogen (N2) and hydrogen (H2) was found to be 1:2 molar ratio (N2: H2). The results from a trial-run experiment utilizing appropriate design of experiment (DOE) methods are also reported. From the simulation, 99.4% theoretical NH3 yield can be achieved by using the ?-Fe2O3 nanocatalyst and the following parameters: 3 pairs of Helmholtz coils, 710 MHz oscillating magnetic field, N2 flow rate of 50 mL/min, H2 flow rate of 100 mL/min and a 3 T static magnetic field. In conclusion it was found that the quantity of Helmholtz coils, frequency of Helmholtz coils, N2 flow rate and magnetic induction strength influence the amount of NH3 being produced. Utilization of 710 MHz of oscillating magnetic field and 3 T of magnetic induction strength together with the nanocatalyst are sufficient to dissociate the N2 and H2 bonds to form NH3 in our novel system.

Tshai, Kim Hoe; Yahya, Noorhana; Chong, Fai Kait; Yap, Vooi Voon

2014-10-01

44

A theoretical study on the mechanisms of the reactions between 1,3-dialkynes and ammonia derivatives for the formation of five-membered N-heterocycles.  

PubMed

The reactions between 1,3-dialkynes and ammonia derivatives (such as hydrazine and hydroxylamine) for the formation of five-membered N-heterocycles (i.e. 3,5-disubstituted pyrazole and 3,5-disubstituted isoxazole) have been investigated using the density functional theory (DFT) method. The calculated results indicate that the favorable mechanism of this kind of reaction generally contains four processes: (1) the Cope-type hydroamination reaction between the reactants coupled with the hydrazine/hydroxylamine-assisted proton transfer process or the trimolecular hydroamination reaction via a six-membered transition state, (2) the bimolecular proton transfer process for the formation of an allenyl oxime intermediate, (3) the cyclization process, and (4) another bimolecular or hydrazine/hydroxylamine-assisted proton transfer process to afford the final products (3,5-disubstituted pyrazole and 3,5-disubstituted isoxazole). The computational results demonstrate that the novel bimolecular proton transfer process occurs in a stepwise manner and the first step of the novel bimolecular proton transfer process is calculated to be the rate-determining step in both the reactions, and their energy barriers are 28.45 kcal mol(-1) associated with the formation of 3,5-disubstituted pyrazole and 31.07 kcal mol(-1) associated with the formation of 3,5-disubstituted isoxazole. In particular, the novel bimolecular proton transfer process has reasonably explained in detail on how and why this kind of reaction occurs, and this would provide valuable clues for the rational design of Brønsted acid/base catalysts to promote the synthesis of the five-membered N-heterocyclic compounds. PMID:24999759

Wang, Yang; Wei, Donghui; Zhang, Wenjing; Wang, Yanyan; Zhu, Yanyan; Jia, Yu; Tang, Mingsheng

2014-10-14

45

Effect of Ammonia Concentration on Activity of Enzymes of Ammonia Assimilation and on Synthesis of Amino Acids by Mixed Rumen Bacteria in Continuous Culture1  

Microsoft Academic Search

Rumen microorganisms from a cow fed a synthetic diet containing nonpro- tein nitrogen were maintained in an artifi- cial rumen on a similar diet. Ammonia concentration in the artificial rumen was varied by infusion of different concentra- tions of ammonium chloride, and activi- ties of enzymes associated with ammonia metabolism and concentration of free amino acids were assayed. Low ammonia

J. D. Erfle; F. D. Sauer; S. Mahadevan

1977-01-01

46

SOURCE ASSESSMENT: SYNTHETIC AMMONIA PRODUCTION  

EPA Science Inventory

The report describes a study of air emissions from the production of synthetic ammonia. In 1976, 90 synthetic ammonia plants in 30 states produced 15.2 million metric tons of anhydrous ammonia. Ammonia is synthesized by the reaction of nitrogen and hydrogen. Most plants produce h...

47

Experimental investigation of aminoacetonitrile formation through the Strecker synthesis in astrophysical-like conditions: reactivity of methanimine (CH2NH), ammonia (NH3), and hydrogen cyanide (HCN)  

NASA Astrophysics Data System (ADS)

Context. Studing chemical reactivity in astrophysical environments is an important means for improving our understanding of the origin of the organic matter in molecular clouds, in protoplanetary disks, and possibly, as a final destination, in our solar system. Laboratory simulations of the reactivity of ice analogs provide important insight into the reactivity in these environments. Here, we use these experimental simulations to investigate the Strecker synthesis leading to the formation of aminoacetonitrile in astrophysical-like conditions. The aminoacetonitrile is an interesting compound because it was detected in SgrB2, hence could be a precursor of the smallest amino acid molecule, glycine, in astrophysical environments. Aims: We present the first experimental investigation of the formation of aminoacetonitrile NH2CH2CN from the thermal processing of ices including methanimine (CH2NH), ammonia (NH3), and hydrogen cyanide (HCN) in interstellar-like conditions without VUV photons or particules. Methods: We use Fourier Transform InfraRed (FTIR) spectroscopy to monitor the ice evolution during its warming. Infrared spectroscopy and mass spectroscopy are then used to identify the aminoacetonitrile formation. Results: We demonstrate that methanimine can react with -CN during the warming of ice analogs containing at 20 K methanimine, ammonia, and [NH4+ -CN] salt. During the ice warming, this reaction leads to the formation of poly(methylene-imine) polymers. The polymer length depend on the initial ratio of mass contained in methanimine to that in the [NH4+ -CN] salt. In a methanimine excess, long polymers are formed. As the methanimine is progressively diluted in the [NH4+ -CN] salt, the polymer length decreases until the aminoacetonitrile formation at 135 K. Therefore, these results demonstrate that aminoacetonitrile can be formed through the second step of the Strecker synthesis in astrophysical-like conditions.

Danger, G.; Borget, F.; Chomat, M.; Duvernay, F.; Theulé, P.; Guillemin, J.-C.; Le Sergeant D'Hendecourt, L.; Chiavassa, T.

2011-11-01

48

The Role of Glutamine Synthetase and Glutamate Dehydrogenase in Cerebral Ammonia Homeostasis  

PubMed Central

In the brain, glutamine synthetase (GS), which is located predominantly in astrocytes, is largely responsible for the removal of both blood-derived and metabolically generated ammonia. Thus, studies with [13N]ammonia have shown that about 25% of blood-derived ammonia is removed in a single pass through the rat brain and that this ammonia is incorporated primarily into glutamine (amide) in astrocytes. Major pathways for cerebral ammonia generation include the glutaminase reaction and the glutamate dehydrogenase (GDH) reaction. The equilibrium position of the GDH-catalyzed reaction in vitro favors reductive amination of ?-ketoglutarate at pH 7.4. Nevertheless, only a small amount of label derived from [13N]ammonia in rat brain is incorporated into glutamate and the ?-amine of glutamine in vivo. Most likely the cerebral GDH reaction is drawn normally in the direction of glutamate oxidation (ammonia production) by rapid removal of ammonia as glutamine. Linkage of glutamate/?-ketoglutarate-utilizing aminotransferases with the GDH reaction channels excess amino acid nitrogen toward ammonia for glutamine synthesis. At high ammonia levels and/or when GS is inhibited the GDH reaction coupled with glutamate/?-ketoglutarate-linked aminotransferases may, however, promote the flow of ammonia nitrogen toward synthesis of amino acids. Preliminary evidence suggests an important role for the purine nucleotide cycle (PNC) as an additional source of ammonia in neurons (Net reaction: L-Aspartate + GTP + H2O ? Fumarate + GDP + Pi + NH3) and in the beat cycle of ependyma cilia. The link of the PNC to aminotransferases and GDH/GS and its role in cerebral nitrogen metabolism under both normal and pathological (e.g. hyperammonemic encephalopathy) conditions should be a productive area for future research. PMID:22618691

Cooper, Arthur J. L.

2012-01-01

49

The Art of Total Synthesis Through Cascade Reactions  

PubMed Central

The growing importance of cascade reactions reflects and imparts advances in the state of the art of organic synthesis and underscores the desire of synthetic chemists to achieve higher levels of elegance and efficiency. Besides their aesthetic appeal, cascade processes offer economical and environmentally friendly means for generating molecular complexity. Because of their many advantages, these reactions have found numerous applications in the synthesis of complex molecules, both natural and designed. In this Tutorial Review, we highlight the design and execution of cascade reactions within the context of total synthesis as demonstrated with selected examples from these laboratories. PMID:19847336

Chen, Jason S.

2009-01-01

50

Detection of nerve agents using proton transfer reaction mass spectrometry with ammonia as reagent gas.  

PubMed

The chemical warfare agents (CWA) Sarin, Soman, Cyclosarin and Tabun were characterised by proton transfer mass spectrometry (PTRMS). It was found that PTRMS is a suitable technique to detect nerve agents highly sensitively, highly selectively and in near real-time. Methods were found to suppress molecule fragmentation which is significant under PTRMS hollow cathode ionisation conditions. In this context, the drift voltage (as one of the most important system parameters) was varied and ammonia was introduced as an additional chemical reagent gas. Auxiliary chemicals such as ammonia affect ionisation processes and are quite common in context with detectors for CWAs based on ion mobility spectrometry (IMS). With both, variation of drift voltage and ammonia as the reagent gas, fragmentation can be suppressed effectively. Suppression of fragmentation is crucial particularly concerning the implementation of an algorithm for automated agent identification in field applications. On the other hand, appearance of particular fragments might deliver additional information. Degradation and rearrangement products of nerve agents are not distinctive for the particular agent but for the chemical class they belong to. It was found that switching between ammonia doped and ordinary water ionisation chemistry can easily be performed within a few seconds. Making use of this effect it is possible to switch between fragment and molecular ion peak spectra. Thus, targeted fragmentation can be used to confirm identification based only on single peak detection. PTRMS turned out to be a promising technique for future CWA detectors. In terms of sensitivity, response time and selectivity (or confidence of identification, respectively) PTRMS performs as a bridging technique between IMS and GC-MS. PMID:24308198

Ringer, Joachim M

2013-01-01

51

Development of transitional metal-catalyzed reactions for organic synthesis  

E-print Network

Chapter 1. A general catalyst system for the synthesis of tetra-ortho-substituted biaryls via the Suzuki-Miyaura cross-coupling reaction is described. It was found that the most efficient catalyst system is based on a ...

Rainka, Matthew P. (Matthew Paul)

2005-01-01

52

An efficient synthesis of chalcones based on the Suzuki reaction  

Microsoft Academic Search

A general method for the synthesis of chalcones based on the Suzuki reaction either between cinnamoyl chlorides and phenylboronic acids or between benzoyl chlorides and phenylvinylboronic acids is described.

Said Eddarir; Nicole Cotelle; Youssef Bakkour; Christian Rolando

2003-01-01

53

Model Catalysis of Ammonia Synthesis ad Iron-Water Interfaces - ASum Frequency Generation Vibrational Spectroscopic Study of Solid-GasInterfaces and Anion Photoelectron Spectroscopic Study of Selected Anionclusters  

SciTech Connect

The ammonia synthesis reaction has been studied using single crystal model catalysis combined with sum frequency generation (SFG) vibrational spectroscopy. The adsorption of gases N{sub 2}, H{sub 2}, O{sub 2} and NH{sub 3} that play a role in ammonia synthesis have been studied on the Fe(111) crystal surface by sum frequency generation vibrational spectroscopy using an integrated Ultra-High Vacuum (UHV)/high-pressure system. SFG spectra are presented for the dissociation intermediates, NH{sub 2} ({approx}3325 cm{sup -1}) and NH ({approx}3235 cm{sup -1}) under high pressure of ammonia or equilibrium concentrations of reactants and products on Fe(111) surfaces. Special attention was paid to understand how potassium promotion of the iron catalyst affects the intermediates of ammonia synthesis. An Fe(111) surface promoted with 0.2 monolayers of potassium red shifts the vibrational frequencies of the reactive surface intermediates, NH and NH{sub 2}, providing evidence for weakened the nitrogen-hydrogen bonds relative to clean Fe(111). Spectral features of these surface intermediates persisted to higher temperatures for promoted iron surfaces than for clean Fe(111) surfaces implying that nitrogen-iron bonds are stronger for the promoted surface. The ratio of the NH to NH{sub 2} signal changed for promoted surfaces in the presence of equilibrium concentrations of reactants and products. The order of adding oxygen and potassium to promoted surfaces does not alter the spectra indicating that ammonia induces surface reconstruction of the catalyst to produce the same surface morphology. When oxygen is co-adsorbed with nitrogen, hydrogen, ammonia or potassium on Fe(111), a relative phase shift of the spectra occurs as compared to the presence of adsorbates on clean iron surfaces. Water adsorption on iron was also probed using SFG vibrational spectroscopy. For both H{sub 2}O and D{sub 2}O, the only spectral feature was in the range of the free OH or free OD. From the absence of SFG spectra of ice-like structure we conclude that surface hydroxides are formed and no liquid water is present on the surface. Other than model catalysis, gas phase anion photoelectron spectroscopy of the Cl + H{sub 2} van der Waals well, silicon clusters, germanium clusters, aluminum oxide clusters and indium phosphide clusters were studied. The spectra help to map out the neutral potential energy surfaces of the clusters. For aluminum oxide, the structures of the anions and neutrals were explored and for silicon, germanium and indium phosphide the electronic structure of larger clusters was mapped out.

Ferguson, Michael James

2005-12-15

54

Synthesis of dendritic iridium nanostructures based on the oriented attachment mechanism and their enhanced CO and ammonia catalytic activities.  

PubMed

Branched iridium nanodendrites (Ir NDs) have been synthesized by a simple method based on the oriented attachment mechanism. Transmission electron microscopy images reveal the temporal growth process from small particles to NDs. Precursor concentrations and reaction temperatures have a limited effect on the morphology of Ir NDs. Metal oxide and hydroxide-supported Ir NDs exhibit enhanced activity for catalytic CO oxidation. Particularly, the Fe(OH)x-supported Ir NDs catalyst with a 4 wt% Ir loading show superior CO oxidation catalytic activity with a full conversion of CO at 120 °C. Furthermore, compared with Ir NPs and commercial Ir black, Ir NDs exhibit higher activity and stability for ammonia oxidation. The specific activity and mass activity of Ir NDs for ammonia oxidation are 1.7 and 7 times higher than that of Ir NPs. The improved catalytic activities of Ir NDs are attributed not only to their large specific surface area, but also to their considerably high index facets and rich edge and corner atoms. Hence, the obtained Ir NDs provide a promising alternative for direct ammonia fuel cells and proton-exchange membrane fuel cells. PMID:25366566

Wang, Chao; Xiao, Guanjun; Sui, Yongming; Yang, Xinyi; Liu, Gang; Jia, Mingjun; Han, Wei; Liu, Bingbing; Zou, Bo

2014-12-21

55

High yield shock synthesis of ammonia from iron, water and nitrogen available on the early Earth  

NASA Astrophysics Data System (ADS)

Ammonia is a necessary precursor of amino acids in terms of the origin of life on the early Earth. However, the formation of ammonia is problematic in the non-reducing atmosphere that presently believed on the early Earth. The abiotic reduction of nitrogen is, therefore, debated currently in the oceanic and hydrothermal conditions [[J.A. Brandes, N.Z. Boctor, G.D. Cody, B.A. Cooper, R.M. Hazen, H.S. Yoder Jr., Abiotic nitrogen reduction on the early Earth, Nature 395 (1998), 365-367; D.P. Summers, S. Chang, Prebiotic ammonia from reduction of nitrite by iron (II) on the early Earth, Nature 365 (1993), 630-633; M. Dörr, J. Kaessbohrer, R. Grunert, G. Kreisel, W.A. Brand, R.A. Werner, H. Geilmann, C. Apfel, C. Robl, W. Weigand, A possible prebiotic formation of ammonia from dinitrogen on iron sulfide surfaces, Angew. Chem. Int. Ed. 42 ( 2003), 1540-1543 [1-3

Nakazawa, Hiromoto; Sekine, Toshimori; Kakegawa, Takeshi; Nakazawa, Satoru

2005-06-01

56

A photochemical study of the kinetics of the reactions of NH2 with phosphine, ethylene, and acetylene using flash photolysis-laser induced fluorescence. Ph.D. Thesis Catholic Univ. of America; [ammonia in the atmosphere of Jupiter  

NASA Technical Reports Server (NTRS)

The photochemistry of the reactions of NH2 was investigated in an attempt to explain the existence of an abundance of ammonia in the Jovian atmosphere. The production of ammonia reservoirs from the coupling of ammonia with other atmospheric constituents was considered. The rate constants for the reactions of NH2 radicals with phosphine, acetylene, and ethylene were measured. Flash photolysis was used for the production of NH2 radicals and laser induced fluorescence was employed for radical detection. It was determined that the rates of the reactions were too slow to be significant as a source of ammonia reservoirs in the Jovian atmosphere.

Bosco, S. R.

1982-01-01

57

Organocatalytic cascade reactions as a new tool in total synthesis  

NASA Astrophysics Data System (ADS)

The total synthesis of natural products and biologically active compounds, such as pharmaceuticals and agrochemicals, has reached an extraordinary level of sophistication. We are, however, still far away from the 'ideal synthesis' and the state of the art is still frequently hampered by lengthy protecting-group strategies and costly purification procedures derived from the step-by-step protocols. In recent years several new criteria have been brought forward to solve these problems and to improve total synthesis: atom, step and redox economy or protecting-group-free synthesis. Over the past decade the research area of organocatalysis has rapidly grown to become a third pillar of asymmetric catalysis standing next to metal and biocatalysis, thus paving the way for a new and powerful strategy that can help to address these issues - organocatalytic cascade reactions. In this Review we present the first applications of such asymmetric organocascade reactions to the total synthesis of natural products.

Grondal, Christoph; Jeanty, Matthieu; Enders, Dieter

2010-03-01

58

Synthesis of epothilones via a silicon-tethered RCM reaction.  

PubMed

[reaction: see text] A short synthesis of epothilone B and D is reported. The key step for generating the C12-13-trisubstituted Z-double bond uses a ring-closing metathesis reaction of a disiloxane to form a nine-membered silicon-tethered ring. PMID:15787494

Gaich, Tanja; Mulzer, Johann

2005-03-31

59

Kinetics of reactions occurring during polyurethane synthesis  

NASA Astrophysics Data System (ADS)

We have used Fourier transform IR spectroscopy to study the kinetics of reaction between phenylisocyanate and oligomeric polyols at room temperature. We have determined the degree of conversion and the reaction rate constants for urethane formation.

Volkova, E. R.; Tereshatov, V. V.; Karmanov, V. I.

2010-11-01

60

D-Glucosamine as a green ligand for copper catalyzed synthesis of primary aryl amines from aryl halides and ammonia.  

PubMed

Replacing conventional reagents with environment friendly reagents is one of the primary goals of modern synthetic methodology and in this very primitive study about utilizing green, naturally available carbohydrate molecules as ligands in transition metal catalyzed reactions, we report Cu/D-glucosamine as an efficient catalyst for aniline synthesis. PMID:21437300

Thakur, Krishna Gopal; Ganapathy, Dhandapani; Sekar, Govindasamy

2011-05-01

61

Formaldehyde Reactions with Amines and Ammonia: Particle Formation and Product Identification  

NASA Astrophysics Data System (ADS)

Aqueous phase reactions between carbonyls and amines or ammonium salts have recently been implicated in secondary organic aerosol and brown carbon formation processes. Formaldehyde is ubiquitous in the atmosphere, and is present in both the gas and aqueous phases. However, the reactions of formaldehyde in the aqueous phase have not been completely characterized. This study aims to determine the interactions between formaldehyde and amines or ammonium salts present in atmospheric droplets. Bulk phase reactions of formaldehyde with these reactive nitrogen-containing compounds were monitored with ESI-MS and NMR to determine reaction kinetics and for product characterization, while UV-Vis spectroscopy was used to monitor changes in light absorption over time. Hexamethylenetetramine was found to be a major product of the formaldehyde/ammonium sulfate reaction, appearing within minutes of mixing. No products were formed that absorbed light beyond 225 nm. Mono-disperse particles containing mixtures of formaldehyde and ammonium sulfate or an amine were dried and analyzed via SMPS to determine the non-volatile fraction of the reaction products. Similarly, aqueous droplets were dried in a humid atmosphere to determine residual aerosol sizes over time as a function of formaldehyde concentration. This work indicates that formaldehyde plays a key role in aqueous-phase organic processing, as it has been observed to contribute to both an increase and reduction in the diameter and volume of residual aerosol particles.

Galloway, M. M.; Millage, K. D.; Rodriguez, A.; Sedehi, N.; Powelson, M. H.; De Haan, D. O.

2012-12-01

62

The synthesis of higher oxygenates from CO related reactions  

SciTech Connect

Higher oxygenate synthesis over Rh/SiO{sub 2} catalyst from CO hydrogenation, ethylene addition, and methylene chloride addition to syngas has been studied. The insertion of linear CO into the adsorbed alkyl intermediates is the key step in the formation of higher oxygenates from CO related reaction. A good understanding of the reactivity of alkyl group towards hydrogenation and CO insertion reaction steps is required for the design of a selective catalyst for C{sub 2+} oxygenate synthesis. This paper reports the use of in situ IR and dynamic approach to study the nature of active sites and elementary steps involved in the higher oxygenate synthesis from CO/H{sub 2} and CO/H{sub 2}/CH{sub 2}Cl{sub 2} reactions.

Chuang, S.S.C.; Krishnamurthy, R.; Lee, S. [Univ. of Akron, OH (United States). Dept. of Chemical Engineering

1994-12-31

63

Aqueous solution synthesis of Pt-M (M = Fe, Co, Ni) bimetallic nanoparticles and their catalysis for the hydrolytic dehydrogenation of ammonia borane.  

PubMed

Platinum-based bimetallic nanocatalysts have attracted much attention due to their high-efficiency catalytic performance in energy-related applications such as fuel cell and hydrogen storage, for example, the hydrolytic dehydrogenation of ammonia borane (AB). In this work, a simple and green method has been demonstrated to successfully prepare Pt-M (M = Fe, Co, Ni) NPs with tunable composition (nominal Pt/M atomic ratios of 4:1, 1:1, and 1:4) in aqueous solution under mild conditions. All Pt-M NPs with a small size of 3-5 nm show a Pt fcc structure, suggesting the bimetallic formation (alloy and/or partial core-shell), examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS) analysis. The catalytic activities of Pt-M NPs in the hydrolytic dehydrogenation of AB reveal that Pt-Ni NPs with a ratio of 4:1 show the best catalytic activity and even better than that of pure Pt NPs when normalized to Pt molar amount. The Ni oxidation state in Pt-Ni NPs has been suggested to be responsible for the corresponding catalytic activity for hydrolytic dehydrogenation of AB by XAFS study. This strategy for the synthesis of Pt-M NPs is simple and environmentally benign in aqueous solution with the potential for scale-up preparation and the in situ catalytic reaction. PMID:25058566

Wang, Shuai; Zhang, Duo; Ma, Yanyun; Zhang, Hui; Gao, Jing; Nie, Yuting; Sun, Xuhui

2014-08-13

64

Formation of brown carbon via reactions of ammonia with secondary organic aerosols from biogenic and anthropogenic precursors  

NASA Astrophysics Data System (ADS)

Filter samples of secondary organic aerosols (SOA) generated from the ozone (O3)- and hydroxyl radical (OH)-initiated oxidation of various biogenic (isoprene, ?-pinene, limonene, ?-cedrene, ?-humulene, farnesene, pine leaf essential oils, cedar leaf essential oils) and anthropogenic (tetradecane, 1,3,5-trimethylbenzene, naphthalene) precursors were exposed to humid air containing approximately 100 ppb of gaseous ammonia (NH3). Reactions of SOA compounds with NH3 resulted in production of light-absorbing "brown carbon" compounds, with the extent of browning ranging from no observable change (isoprene SOA) to visible change in color (limonene SOA). The aqueous phase reactions with dissolved ammonium (NH4+) salts, such as ammonium sulfate, were equally efficient in producing brown carbon. Wavelength-dependent mass absorption coefficients (MAC) of the aged SOA were quantified by extracting known amounts of SOA material in methanol and recording its UV/Vis absorption spectra. For a given precursor, the OH-generated SOA had systematically lower MAC compared to the O3-generated SOA. The highest MAC values, for brown carbon from SOA resulting from O3 oxidation of limonene and sesquiterpenes, were comparable to MAC values for biomass burning particles but considerably smaller than MAC values for black carbon aerosols. The NH3/NH4+ + SOA brown carbon aerosol may contribute to aerosol optical density in regions with elevated concentrations of NH3 or ammonium sulfate and high photochemical activity.

Updyke, Katelyn M.; Nguyen, Tran B.; Nizkorodov, Sergey A.

2012-12-01

65

Silicon nitride fiber synthesis from polycarbosilane fiber by radiation curing and pyrolysis under ammonia  

SciTech Connect

Silicon nitride(Si-N) fiber was synthesized by pyrolysis of radiation cured polycarbosilane(PCS) fiber in ammonia(NH{sub 3}) gas flow. The properties of Si-N fiber were very dependent on oxygen content included in the fiber during and after pyrolysis. The tensile strength of Si-N fiber was 2.5 GPa for a small content of 3wt% oxygen, and the electric resistivity was very high. The heat resistance in tensile strength and in electric resistivity was estimated to be 1300{degrees}C by ageing test in air for 1 hour.

Kamimura, S.; Watanabe, K. [Hitachi Cable Ltd. (Japan); Kasai, N. [JAERI Takasaki, Gunma (Japan)] [and others

1995-12-01

66

Shock-induced reaction synthesis (SRS) of nickel aluminides  

SciTech Connect

Shock-induced chemical reactions between nickel and aluminum powders (mixed in Ni{sub 3}Al stoichiometry) are used for the synthesis of nickel aluminides. It is shown that the extent of shock-induced chemical reactions and the nature of the shock-synthesized products are influenced by the morphology of the starting powders. Irregular (flaky type) and fine morphologies of the powders undergo complete reactions in contrast to partial reactions occurring in coarse and uniform morphology powders under identical shock loading conditions. Furthermore, irregular morphology powders result in the formation of the equiatomic (B2 phase) NiAl compound while the Ni{sub 3}Al (L1{sub 2} phase) compound is the reaction product with coarse and regular morphology powders. Shock-induced reaction synthesis can be characterized as a bulk reaction process involving an intense mechanochemical'' mechanism. It is a process in which shock compression induces fluid-like plastic flow and mixing, and enhances the reactivity due to the introduction of defects and cleansing of particle surfaces, which strongly influence the synthesis process.

Thadhani, N.N.; Work, S. (Center for Explosives Technology Research (CETR), New Mexico Tech, Socorro, New Mexico 87801 (United States)); Graham, R.A.; Hammetter, W.F. (Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States))

1992-05-01

67

Facile Synthesis and Characterizations of MOF-5 Coordination Polymer with Various Metal Linker Ratios for Ammonia Gas Storage  

NASA Astrophysics Data System (ADS)

Metal-organic framework coordination polymer materials of MOF-5 with Fm3m cubic structure and tetrahedral structure were successfully synthesized at room temperature and pressure using liquid-crystal (i.e. surfactant) templating method and direct mixing method. The crystallinity increased as metal (Zn)/linker (benzenedicarboxylic acid, BDC) ratios were varied from 0.3 to 0.5. However, the cubic structure of evacuated framework was relatively disrupted at metal/linker ratio of 0.7. Direct-mixing synthesis approach resulted in MOF-5 with layered tetragonal structure due to the increased mobility of the organic-linker as the metal/linker ratios were increased. On the other hand, liquid-crystal templating method resulted in MOF-5 with cubic structure with sizes of ca. 3-5 micron. Changing the solvent from dimethylformamide to chloroform during the synthesis affected the size of the single cubic to decrease from 5 micron to 3 micron, respectively. Furthermore, MOF-5 prepared with metal/linker ratio 0.5 and aged in solvents with higher crystallinity exhibited higher ammonia adsorption uptake at ca. 7.2%.

Misran, Halina; Aminuddin, A. M.; Zini, F. A. M.; Ghazali, M. J.; Ramesh, S.

2011-01-01

68

Synthesis of size tuneable cadmium sulphide nanoparticles from a single source precursor using ammonia as the solvent  

SciTech Connect

Graphical abstract: UV-vis absorption spectra for CdS prepared by decomposing cadmium xanthates (Cd(ROCS{sub 2}){sub 2}) exhibit a marked blue-shift with increasing the alkyl chain length (where R denotes: (a) -C{sub 2}H{sub 5}, (b) -C{sub 4}H{sub 9}, (c) -C{sub 8}H{sub 17}, and (d) -C{sub 12}H{sub 25}, respectively), indicating the progressive size reduction of formed CdS nanoparticles. Highlights: Black-Right-Pointing-Pointer Synthesis of CdS nanoparticles using a single source precursor. Black-Right-Pointing-Pointer Tailoring the nanocrystal sizes using cadmium alkyl xanthate with different carbonyl length. Black-Right-Pointing-Pointer Preparation in an environment-friendly solvent. -- Abstract: Size tuneable cadmium sulphide nanoparticles of a few nanometres in size were prepared by thermolysis of a single source precursor of cadmium xanthates with variable carbon chain length (Cd(ROCS{sub 2}){sub 2}, where R denotes -C{sub 2}H{sub 5}, -C{sub 4}H{sub 9}, -C{sub 8}H{sub 17} and -C{sub 12}H{sub 25}, respectively) in an ammonia solution. The particle size, morphology and crystallinity of these nanoparticles were characterized using X-ray powder diffractometry, transmission electron microscopy, and nitrogen adsorption/desorption techniques. The results show that hexagonal CdS nanoparticles can be produced by thermolysis of cadmium alkyl xanthate in an ammonia solution at a temperature as low as 100 Degree-Sign C. The size of CdS particles (between 5.60 nm and 3.71 nm) decreases with increasing length of carbon chain in the precursor, as further confirmed by UV-visible and fluorescence spectrophotometric measurements. The size tuning mechanism of CdS from cadmium alkyl xanthate is also discussed.

Zhang, Wei-Min [School of Chemistry and Chemical Engineering, University of Jinan, 250022 Jinan, Shandong (China)] [School of Chemistry and Chemical Engineering, University of Jinan, 250022 Jinan, Shandong (China); Sun, Zhong-Xi, E-mail: sunzx@ujn.edu.cn [School of Chemistry and Chemical Engineering, University of Jinan, 250022 Jinan, Shandong (China)] [School of Chemistry and Chemical Engineering, University of Jinan, 250022 Jinan, Shandong (China); Hao, Wei; Su, Da-Wei [School of Chemistry and Chemical Engineering, University of Jinan, 250022 Jinan, Shandong (China)] [School of Chemistry and Chemical Engineering, University of Jinan, 250022 Jinan, Shandong (China); Vaughan, David J. [Williamson Research Centre for Molecular Environmental Science, and School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Manchester M13 9PL (United Kingdom)] [Williamson Research Centre for Molecular Environmental Science, and School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Manchester M13 9PL (United Kingdom)

2011-12-15

69

McMurry reaction in the synthesis of photochromic dihetarylethenes  

NASA Astrophysics Data System (ADS)

Application of the McMurry reaction in the synthesis of thermally stable photochromic dihetarylethenes is described. Hetaryl rings in the target molecules are connected to the double bond of the cycloalkenes or heterocycles formed upon the McMurry cyclization.

Krayushkin, Mikhail M.; Kalik, Marina A.; Migulin, Vasilii A.

2009-04-01

70

A molybdenum complex bearing PNP-type pincer ligands leads to the catalytic reduction of dinitrogen into ammonia  

NASA Astrophysics Data System (ADS)

The synthesis of transition metal-dinitrogen complexes and the stoichiometric transformation of their coordinated dinitrogen into ammonia and hydrazine have been the subject of considerable research, with a view to achieving nitrogen fixation under ambient conditions. Since a single example in 2003, no examples have been reported of the catalytic conversion of dinitrogen into ammonia under ambient conditions. The dimolybdenum-dinitrogen complex bearing PNP pincer ligands was found to work as an effective catalyst for the formation of ammonia from dinitrogen, with 23 equiv. of ammonia being produced with the catalyst (12 equiv. of ammonia are produced based on the molybdenum atom of the catalyst). This is another successful example of the catalytic and direct conversion of dinitrogen into ammonia under ambient reaction conditions. We believe that the results described in this Article provide valuable information with which to develop a more effective nitrogen-fixation system under mild reaction conditions.

Arashiba, Kazuya; Miyake, Yoshihiro; Nishibayashi, Yoshiaki

2011-02-01

71

Synthesis of polyfluorene derivatives through polymer reaction  

NASA Astrophysics Data System (ADS)

A polyfluorene derivative with ester functional groups was synthesized with a high molecular weight and good solubility in common organic solvents through the Suzuki reaction. Efficient blue light emission and good electrochemical properties were demonstrated for this polymer with a decomposition temperature of 331 °C and a glass transition temperature of 111 °C. Due to the ester functional groups, the polymer could be further modified through polymer reactions. Hydrolysis of the polymer afforded a water-soluble carbonate functional polyfluorene derivative. While it underwent a reduction, a new polyfluorene derivative with hydroxy functional groups was obtained. Thermal and optical properties of the derivatives were also studied.

Liu, Bin; Yu, Wang-Lin; Lai, Yee-Hing; Huang, Wei

2003-01-01

72

Copper-catalyzed aerobic oxidative synthesis of aryl nitriles from benzylic alcohols and aqueous ammonia.  

PubMed

Copper-catalyzed direct conversion of benzylic alcohols to aryl nitriles was realized using NH3(aq.) as the nitrogen source, O2 as the oxidant and TEMPO as the co-catalyst. Furthermore, copper-catalyzed one-pot synthesis of primary aryl amides from alcohols was also achieved. PMID:23563148

Tao, Chuanzhou; Liu, Feng; Zhu, Youmin; Liu, Weiwei; Cao, Zhiling

2013-05-28

73

Reaction of Dimethylethylamine Alane and Ammonia on Si(100) during the Atomic Layer Growth of AIN: Static SIMS, TPSIMS, and TPD  

SciTech Connect

Dimethylethylamine alane (DMEAA; AIH3: N(CH3)2(CH2CH3)) has been used as an Al source in the chemical vapor deposition of AIN. In the Atomic Layer Growth (ALG) mode, ammonia and DMEAA interact selectively by nucleophilic displacement. In the first part of this study, the surface adsorption and reaction processes are characterized with static secondary-ion mass spectrometry (SIMS) and temperature-programmed secondary-ion mass spectrometry (TPSIMS). The secondary ion emission from DMEAA-covered Si surface shares similar general characteristics with the gas phase cracking pattern. The secondary ion emission spectrum is interpreted according to a unimolecular ion decomposition mechanism and is used as the fingerprint for the presence of molecular DMEAA. During the surface reaction between DMEAA and ammonia, the intensity of the fingerprint peaks diminishes, representing the departure of the amine ligand. The thermal stability of DMEAA and its decomposition behavior on Si are also examined.

Rogers, JW Bill W. (BATTELLE (PACIFIC NW LAB))

2000-01-01

74

Reduced phenylalanine ammonia-lyase and tyrosine ammonia-lyase activities and lignin synthesis in wheat grown under low pressure sodium lamps  

NASA Technical Reports Server (NTRS)

Wheat (Triticum aestivum L. cv Fremont) grown in hydroponic culture under 24-hour continuous irradiation at 560 to 580 micromoles per square meter per second from either metalhalide (MH), high pressure sodium (HPS), or low pressure sodium (LPS) lamps reached maturity in 70 days. Grain yields were similar under all three lamps, although LPS-grown plants lodged at maturity. Phenylalanine ammonia-lyase (PAL) and a tyrosine ammonia lyase (TAL) with lesser activity were detected in all extracts of leaf, inflorescence, and stem. Ammonia-lyase activities increased with age of the plant, and plants grown under the LPS lamp displayed PAL and TAL activities lower than wheat cultured under MH and HPS radiation. Greenhouse solar-grown wheat had the highest PAL and TAL activities. Lignin content of LPS-grown wheat was also significantly reduced from that of plants grown under MH or HPS lamps or in the greenhouse, showing a correlation with the reduced PAL and TAL activities. Ratios of far red-absorbing phytochrome to total phytochrome were similar for all three lamps, but the data do not yet warrant a conclusion about specific wavelengths missing from the LPS lamps that might have induced PAL and TAL activities in plants under the other lamps.

Guerra, D.; Anderson, A. J.; Salisbury, F. B.

1985-01-01

75

The vinylogous Mukaiyama aldol reaction (VMAR) in natural product synthesis.  

PubMed

The vinylogous Mukaiyama aldol reaction (VMAR) allows efficient access to larger segments for complex natural product synthesis, primarily polyketides, through the construction of vicinal hydroxyl and methyl groups as well as di and tri-substituted double bonds in one single operation. In this review, we will highlight stereoselective protocols that have been used in natural product synthesis and cluster them into the four groups that can be obtained from different silyl ketene acetals or enol ethers. At the beginning, an overview on different stereoselective VMARs is presented; disregarding their applications in total syntheses. PMID:24595879

Kalesse, Markus; Cordes, Martin; Symkenberg, Gerrit; Lu, Hai-Hua

2014-04-01

76

Regioselective Reactions for Programmable Resveratrol Oligomer Synthesis  

PubMed Central

Although much attention has been devoted to resveratrol, a unique polyphenol produced by plants throughout the world and credited as potentially being responsible for the so-called “French paradox” given its broad spectrum activity, the hundreds of oligomeric materials derived from it have been largely ignored despite their similarly high biochemical potential. Challenges in achieving their isolation in quantity from natural sources, coupled with an inability to rationally prepare them in the laboratory, are the main culprits. Here we show that a programmable, controlled, and potentially scaleable synthesis of the resveratrol family is possible through a unique three-stage design. These efforts required novel tactics coupled with strategy- and reagent-guided functionalizations to differentiate two distinct cores possessing multiple sites with the same and/or similar reactivity, ultimately leading to five higher-order natural products. We anticipate that this work 1) demonstrates that challenging, positionally-selective functionalizations of complex materials are possible where biosynthetic studies have indicated otherwise, 2) provides materials and tools to finally unlock the full biochemical potential of the family, particularly from the standpoint of activity and drug-property optimization, and 3) affords an intellectual framework to potentially access other oligomeric families controllably. PMID:21697944

Snyder, Scott A.; Gollner, Andreas; Chiriac, Maria I.

2011-01-01

77

Regioselective reactions for programmable resveratrol oligomer synthesis.  

PubMed

Although much attention has been devoted to resveratrol, a unique polyphenol produced by plants and credited as potentially being responsible for the 'French paradox'--the observation that French people have a relatively low incidence of coronary heart disease, even though their diet is high in saturated fats--the oligomers of resveratrol have been largely ignored despite their high biological activity. Challenges in achieving their isolation in sufficient quantity from natural sources, coupled with an inability to prepare them easily synthetically, are seen as the main obstacles. Here we report a programmable, controlled and potentially scalable synthesis of the resveratrol family via a three-stage design. The synthetic approach requires strategy- and reagent-guided chemical functionalizations to differentiate two distinct cores possessing multiple sites with the same or similar reactivity, ultimately leading to five higher-order natural products. This work demonstrates that challenging, positionally selective functionalizations of complex materials are possible where biosynthetic studies have indicated otherwise, it provides materials and tools with which to unlock the full biochemical potential of this family of natural products, and it affords an intellectual framework within which other oligomeric families could potentially be accessed. PMID:21697944

Snyder, Scott A; Gollner, Andreas; Chiriac, Maria I

2011-06-23

78

Synthesis of DiamidoPyrrolyl Molybdenum Complexes Relevant to Reduction of Dinitrogen to Ammonia  

PubMed Central

A potentially useful trianionic ligand for the reduction of dinitrogen catalytically by molybdenum complexes is one in which one of the arms in a [(RNCH2CH2)3N]3? ligand is replaced by a 2-mesitylpyrrolyl-?-methyl arm, i.e., [(RNCH2CH2)2NCH2(2-MesitylPyrrolyl)]3? (R = C6F5, 3,5-Me2C6H3, or 3,5-t-Bu2C6H3). Compounds have been prepared that contain the ligand in which R = C6F5 ([C6F5N)2Pyr]3?); they include [(C6F5N)2Pyr]Mo(NMe2), [(C6F5N)2Pyr]MoCl, [(C6F5N)2Pyr]MoOTf, and [(C6F5N)2Pyr]MoN. Compounds that contain the ligand in which R = 3,5-t-Bu2C6H3 ([Art-BuN)2Pyr]3?) include {[(Art-BuN)2Pyr]Mo(N2)}Na(15-crown-5), {[(Art-Bu N)2Pyr]Mo(N2)}[NBu4], [(Art-Bu N)2Pyr]Mo(N2) (?NN = 2012 cm?1 in C6D6), {[(Art-Bu N)2Pyr]Mo(NH3)}BPh4, and [(Art-Bu N)2Pyr]Mo(CO). X-ray studies are reported for [(C6F5N)2Pyr]Mo(NMe2), [(C6F5N)2Pyr]MoCl, and [(Art-BuN)2Pyr]MoN. The [(Art-BuN)2Pyr]Mo(N2)0/? reversible couple is found at ?1.96 V (in PhF versus Cp2Fe+/0), but the [(Art-BuN)2Pyr]Mo(N2)+/0 couple is irreversible. Reduction of {[(Art-BuN)2Pyr]Mo(NH3)}BPh4 under Ar at approximately ?1.68 V at a scan rate of 900 mV/sec is not reversible. Ammonia in [(Art-BuN)2Pyr]Mo(NH3) can be substituted for dinitrogen in about 2 hours if 10 equivalents of BPh3 are present to trap the ammonia that is released. [(Art-BuN)2Pyr]Mo-N=NH is a key intermediate in the proposed catalytic reduction of dinitrogen that could not be prepared. Dinitrogen exchange studies in [(Art-BuN)2Pyr]Mo(N2) suggest that steric hindrance by the ligand may be insufficient to protect decomposition of [(Art-BuN)2Pyr]Mo-N=NH through a variety of pathways. Three attempts to reduce dinitrogen catalytically with [(Art-BuN)2Pyr]Mo(N) as a “catalyst” yielded an average of 1.02 ± 0.12 equivalents of NH3. PMID:20799738

Chin, J. M.; Muller, P.

2010-01-01

79

Nuclear reactions and synthesis of new transuranium species  

SciTech Connect

In this short review, I shall describe the special aspects of heavy ion nuclear reaction mechanisms operative in the transuranium region, the role of new techniques, possible nuclear reactions for the production of additional transuranium elements and nuclear species and the importance of work in this region for the development of nuclear models and theoretical concepts. This discussion should make it clear that a continuing supply of leements and isotopes, some fo them relatively short-lived, produced by the HFIR-TRU facilities, will be a requirement for future synthesis of new elements and isotopes.

Seaborg, G.T.

1983-01-01

80

Flexible synthesis of anthracycline aglycone mimics via domino carbopalladation reactions  

PubMed Central

Summary A synthesis of anthracycline aglycone derivatives is described. The key step utilizes a powerful domino carbopalladation approach and subsequent ring closure. During this process two of the four rings of the anthracycline scaffold are formed. Differently substituted carbohydrates and dialkyne chains serve as versatile and simple starting materials for the reaction sequence. Diverse building blocks lead to a variety of different products and a broad range of structural diversity. PMID:24204433

Leibeling, Markus

2013-01-01

81

Synthesis of (+)-Sch 642305 by a Biomimetic Transannular Michael Reaction  

PubMed Central

The synthesis of (+)-Sch 642305 (1) has been completed in 17 steps in 1.6% overall yield. Transannular Michael reaction of 2b with NaH in THF provided cyclohexenone 23 stereospecifically. Heating 23 in TFA/CDCl3 provided a 3:1 equilibrium mixture of 23 and 25, which were hydrolyzed to give (+)-6-epi-Sch 642305 (24) and (+)-Sch 642305 (1), respectively. PMID:16562872

Snider, Barry B.; Zhou, Jingye

2008-01-01

82

Synthesis of superheavy nuclei: A search for new production reactions  

SciTech Connect

Nuclear reactions leading to the formation of new superheavy (SH) elements and isotopes are discussed in the paper. 'Cold' and 'hot' synthesis, fusion of fission fragments, transfer reactions, and reactions with radioactive ion beams are analyzed along with their abilities and limitations. If the possibility of increasing the beam intensity and the detection efficiency (by a total of one order of magnitude) is found, then several isotopes of new elements with Z=120-124 could be synthesized in fusion reactions of titanium, chromium, and iron beams with actinide targets. The use of light- and medium-mass neutron-rich radioactive beams may help us fill the gap between the SH nuclei produced in the hot fusion reactions and the mainland. In these reactions, we may really approach the 'island of stability.' Such a possibility is also provided by the multinucleon transfer processes in low-energy damped collisions of heavy actinide nuclei. The production of SH elements in fusion reactions with accelerated fission fragments looks less encouraging.

Zagrebaev, Valery [Flerov Laboratory of Nuclear Reactions, JINR, Dubna, Moscow Region (Russian Federation); Greiner, Walter [Frankfurt Institute for Advanced Studies, J. W. Goethe-Universitaet, Frankfurt (Germany)

2008-09-15

83

Differential methods of inoculation of plant growth-promoting rhizobacteria induce synthesis of phenylalanine ammonia-lyase and phenolic compounds differentially in chickpea.  

PubMed

Foliar spray and micro-injection of plant growth-promoting rhizobacterial species, viz. Pseudomonas fluorescens and P. aeruginosa on chickpea induced synthesis of phenylalanine ammonia-lyase (PAL) when tested against Sclerotinia sclerotiorum. Induction of PAL was also associated with increased synthesis of phenolic compounds such as tannic, gallic, caffeic, chlorogenic and cinnamic acids. Treatment with P. fluorescens was found to be more effective in inducing phenolic compounds as compared to P. aeruginosa. However, persistence of PAL activity was observed more with P. aeruginosa. Although both the inoculation methods were effective, foliar application was found to be superior to micro-injection in terms of rapid PAL activity leading to the synthesis of phenolic compounds. PMID:17176768

Basha, S A; Sarma, B K; Singh, D P; Annapurna, K; Singh, U P

2006-01-01

84

Synthesis and evaluation of novel biochar-based and metal oxide-based catalysts for removal of model tar (toluene), ammonia, and hydrogen sulfide from simulated producer gas  

NASA Astrophysics Data System (ADS)

Gasification is a thermochemical conversion process in which carbonaceous feedstock is gasified in a controlled atmosphere to generate producer gas. The producer gas is used for production of heat, power, fuels and chemicals. Various contaminants such as tars, NH3, and H2S in producer gas possess many problems due to their corrosive nature and their ability to clog and deactivate catalysts. In this study, several catalysts were synthesized, characterized, and tested for removal of three contaminants (toluene (model tar), NH3, and H2S) from the biomass-generated producer gas. Biochar, a catalyst, was generated from gasification of switchgrass. Activated carbon and acidic surface activated carbon were synthesized using ultrasonication method from biochar. Acidic surface was synthesized by coating activated carbon with dilute acid. Mixed metal oxide catalysts were synthesized from hydrotalcite precursors using novel synthesis technique using microwave and ultrasonication. Surface area of activated carbon (˜900 m2/g) was significantly higher than that of its precursor biochar (˜60 m2/g). Surface area of metal oxide catalyst was approximately 180 m2/g after calcination. Biochar, activated carbon, and acidic surface activated carbon showed toluene removal efficiencies of approximately 78, 88, and 88 %, respectively, when the catalysts were tested individually with toluene in the presence of producer gas at 800 °C. The toluene removal efficiencies increased to 86, 91, and 97 % using biochar, activated carbon and acidic surface activated carbon, respectively in the presence of NH3 and H2S in the producer gas. Increase in toluene removal efficiencies in presence of NH3 and H2S indicates that NH3 and H 2S play a role in toluene reforming reactions during simultaneous removal of contaminants. Toluene removal efficiency for mixed metal oxide was approximately 83%. Ammonia adsorption capacities were 0.008 g NH3/g catalyst for biochar and 0.03g NH3/g catalyst for activated carbon, acidic surface activated carbon, and mixed metal oxide catalyst. H2S adsorption capacities were 0.008 g H2S/g catalyst for all biochar-based catalysts and 0.01g H2S/g catalyst for mixed metal oxide. Thus, ultrasonication and microwave technology offer improved benefits for synthesis of high-performance catalysts intended for use in biomass-generated producer gas upgrading. High surface area biochar-based and metal-oxide based catalysts have high efficiencies for simultaneous removal of toluene, NH3, and H2S.

Bhandari, Pushpak

85

Reactions of coordinated dinitrogen. 8. Formation of ammonia by protonation of a molybdenum-dinitrogen complex and isolation and characterization of the molybdenum-containing product  

SciTech Connect

This is the first reported conversion of metal-coordinated dinitrogen into ammonia in which the fate of the metal has been determined. This reaction is shown in the following equation, where triphos = PhP(CH/sub 2/CH/sub 2/PPh/sub 2/)/sub 2/ and L = PPh/sub 3/:2Mo(N/sub 2/)/sub 2/(triphos)(L) + 8HBr ..-->.. 2NH/sub 4/Br + 2MoBr/sub 3/(triphos) + 3N/sub 2/ + 2L. The metal complex which is a new subclass of bis(dinitrogen) complexes of molybdenum, reacted in tetrahydrofuran (THF) solution with anhydrous hydrogen bromide to produce ammonium bromide. No hydrazine or hydrazinium bromide was detected among the reaction products. Ammonium bromide was detected by infrared spectroscopy among the reaction products after solvent and excess HBr had been removed in vacuo. The yield of ammonia was determined quantitatively by the indophenol method after either aqueous, nonaqueous (ethanol), or two-phase (dichloromethane-water) extraction of ammonium bromide from the residue. The molybdenum-containing product slowly decomposed during the dichloromethane-water extraction step. Isolation of pure MoBr/sub 3/(triphos) was carried out in a separate experiment in which only N/sub 2/ evolution was measured. All volatiles were removed from the reaction vessel and the resulting yellow solid was washed with ethanol and dried. Its identity was confirmed by elemental analysis.

Baumann, J.A.; George, T.A.

1980-09-10

86

Fischer-Tropsch synthesis in supercritical reaction media  

SciTech Connect

The goal of the proposed research is to develop novel reactor operating strategies for the catalytic conversion of syngas to transportation grade fuels and oxygenates using near-critical (nc) fluids as reaction media. This will be achieved through systematic investigations aimed at a better fundamental understanding of the physical and chemical rate processes underlying catalytic syngas conversion in nc reaction media. Syngas conversion to fuels and fuel additives on Fe catalysts (Fischer-Tropsch synthesis) was investigated. Specific objectives are to investigate the effects of various nc media, their flow rates and operating pressure on syngas conversion, reactor temperature profiles, product selectivity and catalyst activity in trickle-bed reactors. Solvents that exhibit gas to liquid-like densities with relatively moderate pressure changes (from 25 to 60 bars) at typical syngas conversion temperatures (in the 220-280{degree}C range) will be chosen as reaction media.

Subramaniam, B.

1995-05-01

87

An effective method to prepare imines from aldehyde, bromide/epoxide, and aqueous ammonia.  

PubMed

A three-component reaction of aldehydes, alkyl bromides, and ammonia to form imines was studied. Aqueous ammonia was applied as the nitrogen source and solvent in the reaction. For the aromatic aldehyde, the product yields are good to excellent and the reaction conditions are mild to be compatible with a range of functional groups. The reaction of aldehydes and aqueous ammonia with epoxides was also studied and imines bearing a vicinal hydroxyl group can be obtained efficiently and regioselectively. And studies showed that this method allows the synthesis of primary amines and especially 1,2-amino alcohol selectively in high yield. It is proposed that the reaction pathway might involve a key intermediate of hydrobenzamide. PMID:21428424

Huang, Jing-Mei; Zhang, Jue-Fei; Dong, Yi; Gong, Wen

2011-05-01

88

Pressure-reaction synthesis of titanium composite materials  

DOEpatents

A pressure-reaction synthesis process for producing increased stiffness and improved strength-to-weight ratio titanium metal matrix composite materials comprising exothermically reacting a titanium powder or titanium powder alloys with non-metal powders or gas selected from the group consisting of C, B, N, BN, B.sub.4 C, SiC and Si.sub.3 N.sub.4 at temperatures from about 900.degree. to about 1300.degree. C., for about 5 to about 30 minutes in a forming die under pressures of from about 1000 to 5000 psi.

Oden, Laurance L. (Albany, OR); Ochs, Thomas L. (Albany, OR); Turner, Paul C. (Albany, OR)

1993-01-01

89

Efficient indoles and anilines syntheses employing tert-butyl sulfinamide as ammonia surrogate  

Microsoft Academic Search

tert-Butyl sulfinamide is an ammonia equivalent for the palladium-catalyzed amination of aryl bromides and aryl chlorides. Using these amine derivatives, it has been observed that indoles and anilines with sensitive functional groups can be readily prepared. This surrogate has also been used for the synthesis of indoles from 2-halophenols using palladium catalyzed cross coupling reaction as the key step.

Anjanappa Prakash; Mullick Dibakar; Kumaravel Selvakumar; Kandasamy Ruckmani; Manickam Sivakumar

2011-01-01

90

Electron driven processes in ices: Surface functionalization and synthesis reactions  

NASA Astrophysics Data System (ADS)

The ability to control and orientate chemical reactivity in the condensed phase is a major challenge of modern research. Upon interaction with condensed molecules electrons drive bond cleavage thus generating a population of very reactive species in the condensed medium. These reactive species may interact either within the volume leading to the synthesis of new molecules or with the substrate surface by forming strong chemical bonds. The former reaction is known as electron induced synthesis and the latter one as electron induced surface functionalization. High-energy electrons achieve only a low chemical specificity due to the large number of dissociating open channels. In contrast, electrons with energies below ionization threshold of the irradiated matter are capable of high selectivity because of the dissociative electron attachment mechanism. In this review recent studies of electron interaction with condensed molecules on hydrogenated diamond substrates will be described. In particular electron induced functionalization of diamond surfaces by CH 2CN groups, decarboxylation reactions in condensed films of pure organic acids RCOOH (R = H, CH 3, C 2H 5, CF 3), carbamic acid formation in CO 2:NH 3, HCOOH:NH 3 and CF 3COOH:NH 3 binary ice mixtures, and glycine formation in a CH 3COOD:NH 3 mixture are presented and discussed.

Lafosse, A.; Bertin, M.; Azria, R.

2009-05-01

91

Double decarboxylative Claisen rearrangement reactions: microwave-assisted de novo synthesis of pyridines.  

PubMed

Microwave-assisted double decarboxylative Claisen rearrangement of bis(allyl) 2-tosylmalonates provides substituted 1,6-heptadienes, which may be alkylated, and then converted into pyridines by ozonolysis followed by reaction with ammonia generated in situ under microwave conditions. PMID:18633505

Craig, Donald; Paina, Federica; Smith, Stephen C

2008-08-01

92

A combined intramolecular Diels-Alder/intramolecular Schmidt reaction: Formal synthesis of (+/-)-stenine  

E-print Network

A Combined Intramolecular Diels-Alder/Intramolecular Schmidt Reaction Process: A Formal Synthesis of (?)-Stenine ** Jennifer E. Golden and Jeffrey Aub?* [*] Prof. Dr. J. Aub? University of Kansas Department of Medicinal Chemistry Malott... of the intramolecular Schmidt reaction of azides and ketones in total synthesis. [2] Herein, we describe the combination of an intramolecular Schmidt reaction with an intramolecular Diels-Alder process ? two efficient reactions that benefit from Lewis acid promotion...

Golden, Jennifer E.; Aubé , Jeffrey

2002-01-01

93

Polybromocyclopentadienes in the diene synthesis reaction. III. Reaction of hexabromo-1,3-cyclopentadiene with dienophiles of the acrylic series  

SciTech Connect

The diene synthesis reaction was realized between hexabromo-1,3-cyclopentadiene and dienophiles of the acrylic series, and it was shown that the reaction takes place strictly stereospecifically with the formation of the endo adducts. The kinetics of the reaction were studied, and the activation parameters were determined. In the investigated reaction series the hexabromo-1,3-cyclopentadiene is the diene-acceptor.

Mustafaev, A.M.; Alekperov, N.A.; Guseinov, M.M.; Imamaliev, A.B.; Mekhtiev, S.I.

1986-01-10

94

Templated Synthesis of Peptide Nucleic Acids via Sequence-Selective Base-Filling Reactions  

E-print Network

Templated Synthesis of Peptide Nucleic Acids via Sequence-Selective Base-Filling Reactions Jennifer describe the templated synthesis of both native and modified peptide nucleic acids (PNAs) through base, 2009; E-mail: drliu@fas.harvard.edu Template-directed nucleic acid synthesis is an essential compo

Liu, David R.

95

Enantioselective and regioselective pyrone Diels-Alder reactions of vinyl sulfones: total synthesis of (+)-cavicularin.  

PubMed

The total synthesis of (+)-cavicularin is described. The synthesis features an enantio- and regioselective pyrone Diels-Alder reaction of a vinyl sulfone to construct the cyclophane architecture of the natural product. The Diels-Alder substrate was prepared by a regioselective one-pot three-component Suzuki reaction of a non-symmetric dibromoarene. PMID:25082270

Zhao, Peng; Beaudry, Christopher M

2014-09-22

96

Transcriptional response of the archaeal ammonia oxidizer Nitrosopumilus maritimus to low and environmentally relevant ammonia concentrations.  

PubMed

The ability of chemoautotrophic ammonia-oxidizing archaea to compete for ammonia among marine microorganisms at low ambient concentrations has been in part attributed to their extremely high affinity for ammonia, but as yet there is no mechanistic understanding of supporting metabolism. We examined transcription of selected genes for anabolic functions (CO2 fixation, ammonia transport, and cell wall synthesis) and a central catabolic function (ammonia oxidation) in the thaumarchaeon Nitrosopumilus maritimus SCM1 growing at two ammonia concentrations, as measured by combined ammonia and ammonium, one well above the Km for ammonia oxidation (?500 ?M) and the other well below the Km (<10 nM). Transcript levels were generally immediately and differentially repressed when cells transitioned from ammonia-replete to ammonia-limiting conditions. Transcript levels for ammonia oxidation, CO2 fixation, and one of the ammonia transport genes were approximately the same at high and low ammonia availability. Transcripts for all analyzed genes decreased with time in the complete absence of ammonia, but with various rates of decay. The new steady-state mRNA levels established are presumably more reflective of the natural physiological state of ammonia-oxidizing archaea and offer a reference for interpreting message abundance patterns in the natural environment. PMID:23995944

Nakagawa, Tatsunori; Stahl, David A

2013-11-01

97

Transcriptional Response of the Archaeal Ammonia Oxidizer Nitrosopumilus maritimus to Low and Environmentally Relevant Ammonia Concentrations  

PubMed Central

The ability of chemoautotrophic ammonia-oxidizing archaea to compete for ammonia among marine microorganisms at low ambient concentrations has been in part attributed to their extremely high affinity for ammonia, but as yet there is no mechanistic understanding of supporting metabolism. We examined transcription of selected genes for anabolic functions (CO2 fixation, ammonia transport, and cell wall synthesis) and a central catabolic function (ammonia oxidation) in the thaumarchaeon Nitrosopumilus maritimus SCM1 growing at two ammonia concentrations, as measured by combined ammonia and ammonium, one well above the Km for ammonia oxidation (?500 ?M) and the other well below the Km (<10 nM). Transcript levels were generally immediately and differentially repressed when cells transitioned from ammonia-replete to ammonia-limiting conditions. Transcript levels for ammonia oxidation, CO2 fixation, and one of the ammonia transport genes were approximately the same at high and low ammonia availability. Transcripts for all analyzed genes decreased with time in the complete absence of ammonia, but with various rates of decay. The new steady-state mRNA levels established are presumably more reflective of the natural physiological state of ammonia-oxidizing archaea and offer a reference for interpreting message abundance patterns in the natural environment. PMID:23995944

Stahl, David A.

2013-01-01

98

Effect of dietary carbohydrate composition and availability on utilization of ruminal ammonia nitrogen for milk protein synthesis in dairy cows.  

PubMed

A trial with four ruminally and duodenally cannulated, late-lactation dairy cows was conducted to investigate the effect of dietary carbohydrate (CHO) composition and availability on ruminal ammonia N utilization and transfer into milk protein. Two diets were fed at 8-h intervals in a crossover design. The diets differed in CHO composition: the ruminally fermentable non-structural carbohydrates (RFSS) diet (barley and molasses) contained a larger proportion of ruminally available CHO in the nonstructural carbohydrate fractions and the ruminally fermentable fiber (RFNDF) diet (corn, beet pulp, and brewer's grains) contained a larger proportion of CHO in ruminally available fiber. Nitrogen-15 was used to label ruminal ammonia N and consequently microbial and milk N. Fermentation acids, enzyme activities, and microbial protein production in the rumen were not affected by diet. Ruminal ammonia concentration was lowered by RFNDF. Ruminal and total tract digestibility of nutrients did not differ between diets except that apparent ruminal degradability of crude protein was lower for RFNDF compared with RFSS. Partitioning of N losses between urine and feces was also not affected by diet. Milk yield and fat and protein content were not affected by treatment. Average concentration of milk urea N was lower for RFNDF than for RFSS. Proportion of milk protein N originating from ruminal microbial N (based on the areas under the 15N-enrichment curves) was higher for RFNDF than for RFSS. Cumulative recovery of 15N in milk protein was 13% higher for RFNDF than for RFSS indicating enhanced transfer of 15N-ammonia into milk protein with the former diet. The results suggested that, compared to diets containing higher levels of ruminally fermentable starch, diets providing higher concentration of ruminally fermentable fiber may enhance transfer of ruminal ammonia and microbial N into milk protein. PMID:12906060

Hristov, A N; Ropp, J K

2003-07-01

99

Solid-state reaction synthesis of boron carbonitride nanotubes  

NASA Astrophysics Data System (ADS)

In this study, a simple route for synthesis of ternary boron carbonitride (B-C-N) nanotubes was demonstrated, by heating ball-milled mixture powders of amorphous boron and activated charcoal with a small amount of iron oxide (Fe2O3) at 1000-1200°C under a mixture gas flow of nitrogen (N2) and hydrogen (H2). The reduction of Fe2O3 by H2 at 650°C produced Fe nanoparticles, playing the role of a catalyst during the nanotube growth. The nanotubes synthesized at 1100°C exhibit two morphologies. One is a bamboo-like structure with thick compartments. The other is a quasi-cylindrical structure with thin or disappearing compartments. The average diameter of the nanotubes is about 80 nm. It is found that the reaction temperature has a great influence on the morphology, diameter and yield of the B-C-N nanotubes. Higher temperature (1200°C) is favorable for the formation of quasi-cylindrical nanotubes with larger diameters, while lower temperature (1000°C) enhances the formation of bamboo-like nanotubes with smaller diameters; the yield of nanotubes decreases with the rise of reaction temperature. The nanotubes grow via a combination mechanism of solid-liquid-solid (SLS) and vapor-liquid-solid (VLS) models.

Mo, Libin; Chen, Yongjun; Luo, Lijie

2010-07-01

100

Method for polymer synthesis in a reaction well  

DOEpatents

A method of synthesis is described for building a polymer chain, oligonucleotides in particular, by sequentially adding monomer units to at least one solid support for growing and immobilizing a polymer chain thereon in a liquid reagent solution. The method includes the step of: (A) depositing a liquid reagent in a reaction well in contact with at least one solid support and at least one monomer unit of the polymer chain affixed to the solid support. The well includes at least one orifice extending into the well, and is of a size and dimension to form a capillary liquid seal to retain the reagent solution in the well to enable polymer chain growth on the solid support. The method further includes the step of (B) expelling the reagent solution from the well, while retaining the polymer chain therein. This is accomplished by applying a first gas pressure to the reaction well such that a pressure differential between the first gas pressure and a second gas pressure exerted on an exit of the orifice exceeds a predetermined amount sufficient to overcome the capillary liquid seal and expel the reagent solution from the well through the orifice exit. 9 figs.

Brennan, T.M.

1998-09-29

101

Method for polymer synthesis in a reaction well  

DOEpatents

A method of synthesis for building a polymer chain, oligonucleotides in particular, by sequentially adding monomer units to at least one solid support for growing and immobilizing a polymer chain thereon in a liquid reagent solution. The method includes the step of: A) depositing a liquid reagent in a reaction well (26) in contact with at least one solid support and at least one monomer unit of the polymer chain affixed to the solid support. The well (26) includes at least one orifice (74) extending into the well (26), and is of a size and dimension to form a capillary liquid seal to retain the reagent solution in the well (26) to enable polymer chain growth on the solid support. The method further includes the step of B) expelling the reagent solution from the well (26), while retaining the polymer chain therein. This is accomplished by applying a first gas pressure to the reaction well such that a pressure differential between the first gas pressure and a second gas pressure exerted on an exit (80) of the orifice (74) exceeds a predetermined amount sufficient to overcome the capillary liquid seal and expel the reagent solution from the well (26) through the orifice exit (80).

Brennan, Thomas M. (San Francisco, CA)

1998-01-01

102

Synthesis and selected micro-mechanical properties of titanium nitride thin films by the pyrolysis of tetrakis titanium in ammonia  

Microsoft Academic Search

Thin films of titanium nitride were chemical vapor deposited on (100)-oriented single-crystal silicon substrates from tetrakis (dimethylamino) titanium, Ti((CHâ)âN)â, and ammonia gas mixtures in a cold-wall reactor at 623 K and 655 Pa. The films were characterized by Auger electron spectroscopy, X-ray diffraction, and transmission electron spectroscopy. The nano-scale hardness of the film, measured by nanoindentation, was 12.7 ± 0.6

Y. W. Bae; W. Y. Lee; T. M. Besmann; P. J. Blau; L. Riester

1994-01-01

103

Synthesis and Hydride Transfer Reactions of Cobalt and Nickel Hydride Complexes to BX3 Compounds  

SciTech Connect

Hydrides of numerous transition metal complexes can be generated by the heterolytic cleavage of H{sub 2} gas such that they offer alternatives to using main group hydrides in the regeneration of ammonia borane, a compound that has been intensely studied for hydrogen storage applications. Previously, we reported that HRh(dmpe){sub 2}, dmpe = 1,2-bis(dimethylphosphinoethane) was capable of reducing a variety of BX{sub 3} compounds having hydride affinity (HA) greater than or equal to HA of BEt{sub 3}. This study examines the reactivity of less expensive cobalt and nickel hydride complexes, (HCo(dmpe){sub 2} and [HNi(dmpe){sub 2}]{sup +}), to form B-H bonds. The hydride donor abilities ({Delta}G{sub H{sup -}}{sup o}) of HCo(dmpe){sub 2} and [HNi(dmpe){sub 2}]{sup +} were positioned on a previously established scale in acetonitrile that is cross-referenced with calculated HAs of BX{sub 3} compounds. The collective data guided our selection of BX{sub 3} compounds to investigate and aided our analysis of factors that determine favorability of hydride transfer. HCo(dmpe){sub 2} was observed to transfer H{sup -} to BX{sub 3} compounds with X = H, OC{sub 6}F{sub 5} and SPh. The reaction with B(SPh){sub 3} is accompanied by formation of (BH{sub 3}){sub 2}-dmpe and (BH{sub 2}SPh){sub 2}-dmpe products that follow from reduction of multiple BSPh bonds and loss of a dmpe ligand from Co. Reactions between HCo(dmpe){sub 2} and B(SPh){sub 3} in the presence of triethylamine result in formation of Et{sub 3}N-BH{sub 2}SPh and Et{sub 3}N-BH{sub 3} with no loss of dmpe ligand. Reactions of the cationic complex [HNi(dmpe){sub 2}]{sup +} with B(SPh){sub 3} under analogous conditions give Et{sub 3}N-BH{sub 2}SPh as the final product along with the nickel-thiolate complex [Ni(dmpe){sub 2}(SPh)]{sup +}. The synthesis and characterization of HCo(dedpe){sub 2} (dedpe = diethyldiphenyl(phosphino)ethane) from H{sub 2} and a base is also discussed; including the formation of an uncommon trans dihydride species, trans-[(H{sub 2})Co(dedpe){sub 2}][BF{sub 4}].

Mock, Michael T.; Potter, Robert G.; O'Hagan, Molly J.; Camaioni, Donald M.; Dougherty, William G.; Kassel, W. S.; DuBois, Daniel L.

2011-12-05

104

Enantioselective Organocatalytic Intramolecular Diels-Alder Reactions. The Asymmetric Synthesis of Solanapyrone D  

E-print Network

Enantioselective Organocatalytic Intramolecular Diels-Alder Reactions. The Asymmetric Synthesis the development of enantioselective catalytic variants of the Diels-Alder reaction.1 During this time, remarkable levels of enantiocontrol in the intramolecular Diels-Alder (IMDA) reaction,2,3 a notable deficiency

MacMillan, David W. C.

105

Synthesis and selected micro-mechanical properties of titanium nitride thin films by the pyrolysis of tetrakis titanium in ammonia  

SciTech Connect

Thin films of titanium nitride were chemical vapor deposited on (100)-oriented single-crystal silicon substrates from tetrakis (dimethylamino) titanium, Ti((CH{sub 3}){sub 2}N){sub 4}, and ammonia gas mixtures in a cold-wall reactor at 623 K and 655 Pa. The films were characterized by Auger electron spectroscopy, X-ray diffraction, and transmission electron spectroscopy. The nano-scale hardness of the film, measured by nanoindentation, was 12.7 {plus_minus} 0.6 GPa. The average kinetic friction coefficient against unlubricated, type 440C stainless steel was determined using a computer-controlled friction microprobe to be {approximately}0.43.

Bae, Y.W.; Lee, W.Y.; Besmann, T.M.; Blau, P.J.; Riester, L.

1994-12-31

106

Sulfated zirconia as an efficient catalyst for organic synthesis and transformation reactions  

Microsoft Academic Search

The efficacy of sulfated zirconia catalyst was investigated towards various acid-catalyzed organic syntheses and transformation reactions in the liquid phase. The SO42?\\/ZrO2 efficiently catalyzes synthesis of 1,5-benzodiazepine derivatives, electrophilic substitution of indoles with aldehydes to afford the corresponding bis(indolyl)methanes, synthesis of 3,4-dihydropyrimidinones, synthesis of diaryl sulfoxides, and tetrahydropyranylation of alcohols and phenols. Various advantages associated with these protocols include, simple

Benjaram M. Reddy; Pavani M. Sreekanth; Pandian Lakshmanan

2005-01-01

107

Benzannulation via the Reaction of Ynamides and Vinylketenes. Application to the Synthesis of Highly Substituted Indoles  

E-print Network

A two-stage “tandem strategy” for the synthesis of indoles with a high level of substitution on the six-membered ring is described. Benzannulation based on the reaction of cyclobutenones with ynamides proceeds via a cascade ...

Lam, Tin Yiu

108

Advances in Understanding the Mechanism and Improved Stability of the Synthesis of Ammonia from Air and Water in Hydroxide Suspensions of Nanoscale Fe2O3.  

PubMed

We report a mechanism of electrochemical ammonia (NH3) production via an iron intermediate in which H2 and NH3 are cogenerated by different electron-transfer pathways. Solar thermal can contribute to the energy to drive this synthesis, resulting in a STEP, solar thermal electrochemical process, for NH3. Enhancements are presented to this carbon dioxide (CO2)-free synthesis, which uses suspensions of nano-Fe2O3 in high-temperature hydroxide electrolytes at nickel and Monel electrodes. In a 200 °C molten eutectic Na0.5K0.5OH electrolyte, the 3 Faraday efficiency per mole of synthesized NH3, ?NH3, increases with decreasing current density, and at jelectrolysis = 200, 25, 2, and 0.7 mA cm(-2), ?NH3 = 1%, 7%, 37%, and 71%, respectively. At 200 mA cm(-2), over 90% of applied current drives H2, rather than NH3, formation. Lower temperature supports greater electrolyte hydration. At 105 °C in the hydrated Na0.5K0.5OH electrolyte, ?NH3 increases and then is observed to be highly stable at ?NH3 = 24(+2)%. PMID:25247873

Li, Fang-Fang; Licht, Stuart

2014-10-01

109

Asymmetric synthesis of ?-alkylidene-?-hydroxy-?-butyrolactones via enantioselective tandem Michael-aldol reaction.  

PubMed

A simple and efficient method for the asymmetric synthesis of ?-alkylidene-?-hydroxy-?-butyrolactones and related natural products was developed on the basis of the catalytic asymmetric tandem Michael-aldol reaction and simple transformations. The synthetic utility of this method was illustrated by the facile synthesis of trisubstituted ?-butyrolactone natural products. PMID:23252990

Lee, Sung Il; Jang, Jin Hee; Hwang, Geum-Sook; Ryu, Do Hyun

2013-01-18

110

A formal synthesis of castanospermine using an olefin metathesis cyclisation reaction as a key step  

Microsoft Academic Search

The formal synthesis of castanospermine (1) starting from tetrabenzylgluconolactam (3) is described. Olefin metathesis cyclisation reaction of dialkene 9, derived from 3, leads to indolizidinone 10, which can be used as a key intermediate for the synthesis of castanospermine (1) and its analogues.

Herman S. Overkleeft; Upendra K. Pandit

1996-01-01

111

Vinylogous Mukaiyama aldol reactions with 4-oxy-2-trimethylsilyloxypyrroles: relevance to castanospermine synthesis  

Microsoft Academic Search

BACKGROUND: The diastereoselectivity of a vinylogous Mukaiyama aldol reaction of a series of N-substituted 4-oxy-2-trimethylsilyloxypyrroles with a tartrate-based aldehyde has been explored as a model reaction for castanospermine synthesis. RESULTS: The study has revealed that the reaction is sensitive to the nature of the combination of N- and 4-oxy substituents. With a N-PMB or N-Bn and 4-methoxy combination, the reaction

Roger Hunter; Sophie CM Rees-Jones; Hong Su

2007-01-01

112

Synthesis of Pyridazinones through the Copper(I)-Catalyzed Multicomponent Reaction of Aldehydes, Hydrazines, and Alkynylesters.  

PubMed

The copper-catalyzed multicomponent cyclization reaction, which combined aldehydes, hydrazines, and alkynylesters, was applied in the synthesis of pyridazinones. The reaction was regioselective and gave only six-membered pyridazinones in the complete absence of five-membered pyrazoles or a regioisomeric mixture. During this investigation, the use of 2-halobenzaldehyde as the starting material, under identical reaction conditions, gave 6-(2-ethoxyphenyl)pyridazinones after sequential Michael addition/1,2-addition/Ullmann cross-coupling reactions. PMID:25124722

Mantovani, Anderson C; Goulart, Tales A C; Back, Davi F; Zeni, Gilson

2014-09-22

113

Kinetics of the ammonia synthesis over Fe/TiO sub 2 , hydrazine-pretreated Fe/TiO sub 2 , and hydrazine-pretreated alkali-promoted Fe/TiO sub 2 catalysts  

SciTech Connect

The kinetics of the synthesis of ammonia from its elements over Fe/TiO{sub 2}, and hydrazine-pretreated alkali-promoted Fe/TiO{sub 2} catalysts was studied in a flow microreactor at 101 kPa pressure. The kinetic model was modified to account for deactivation of supported catalyst particles by Ostwald ripening. Pretreatment of Fe/TiO{sub 2} with hydrazine increased the ammonia synthesis turnover frequency by more than an order of magnitude over unpretreated Fe/TiO{sub 2}. The ammonia partial pressure dependence and apparent activation energy over hydrazine-pretreated Fe/TiO{sub 2} were more representative of iron uninfluenced by the strong metal-support interaction (SMSI) which occurs in Metal-titania systems. In situ CO chemisorption measurements following the ammonia synthesis kinetics measurements showed higher CO uptake with hydrazine-pretreated Fe/TiO{sub 2} then with unpretreated Fe/TiO{sub 2}. The increased turnover frequency, altered kinetic parameters, and higher CO uptake suggest that hydrazine pretreatment inhibited the onset of SMSI, which is attributed to titanium nitride formation on the support surface. Addition of the alkali promoters K and Cs to the catalysts not only increased the turnover frequency and decreased the apparent activation energy and ammonia partial pressure dependence, but acted to stabilize supported iron particles against growth by Ostwald ripening. The data suggest that physical covering of the surface by alkali inhibits Ostwald ripening of iron particles by blocking dissociation of iron atoms from supported particles thus suppressing their migration over the support surface to form larger particles.

Nobile, A. Jr.; Brunt, V.V.; Davis, M.W. Jr. (Univ. of South Carolina, Columbia (USA))

1991-01-01

114

Dynamics of ammonia exchange with cut grassland: synthesis of results and conclusions of the GRAMINAE Integrated Experiment  

NASA Astrophysics Data System (ADS)

Improved data on biosphere-atmosphere exchange are fundamental to understanding the production and fate of ammonia (NH3) in the atmosphere. The GRAMINAE Integrated Experiment combined novel measurement and modelling approaches to provide the most comprehensive analysis of the interactions to date. Major inter-comparisons of micrometeorological parameters and NH3 flux measurements using the aerodynamic gradient method and relaxed eddy accumulation (REA) were conducted. These showed close agreement, though the REA systems proved insufficiently precise to investigate vertical flux divergence. Grassland management had a large effect on fluxes: emissions increased after grass cutting (-50 to 700 ng m-2 s-1 NH3) and after N-fertilization (0 to 3800 ng m-2 s-1) compared with before the cut (-60 to 40 ng m-2 s-1). Effects of advection and air chemistry were investigated using horizontal NH3 profiles, acid gas and particle flux measurements. Inverse modelling of NH3 emission from an experimental farm agreed closely with inventory estimates, while advection errors were used to correct measured grassland fluxes. Advection effects were caused both by the farm and by emissions from the field, with an inverse dispersion-deposition model providing a reliable new approach to estimate net NH3 fluxes. Effects of aerosol chemistry on net NH3 fluxes were small, while the measurements allowed NH3-induced particle growth rates to be calculated and aerosol fluxes to be corrected. Bioassays estimated the emission potential ? = [NH4+]/[H+] for different plant pools, with the apoplast having the smallest values (30-1000). The main within-canopy sources of NH3 emission appeared to be leaf litter and the soil surface, with ? up to 3 million and 300 000, respectively. Cuvette and within-canopy analyses confirmed the role of leaf litter NH3 emission, which, prior to cutting, was mostly recaptured within the canopy. Measured ammonia fluxes were compared with three models: an ecosystem model (PaSim), a soil vegetation atmosphere transfer model (SURFATM-NH3) and a dynamic leaf chemistry model (DCC model). The different models each reproduced the main temporal dynamics in the flux, highlighting the importance of canopy temperature dynamics (Surfatm-NH3), interactions with ecosystem nitrogen cycling (PaSim) and the role of leaf surface chemistry (DCC model). Overall, net above-canopy fluxes were mostly determined by stomatal and cuticular uptake (before the cut), leaf litter emissions (after the cut) and fertilizer and litter emissions (after fertilization). The dynamics of ammonia emission from leaf litter are identified as a priority for future research.

Sutton, M. A.; Nemitz, E.; Milford, C.; Campbell, C.; Erisman, J. W.; Hensen, A.; Cellier, P.; David, M.; Loubet, B.; Personne, E.; Schjoerring, J. K.; Mattsson, M.; Dorsey, J. R.; Gallagher, M. W.; Horvath, L.; Weidinger, T.; Meszaros, R.; Dämmgen, U.; Neftel, A.; Herrmann, B.; Lehman, B. E.; Flechard, C.; Burkhardt, J.

2009-12-01

115

Absence of Pfr Destruction in the Modulation of Phenylalanine Ammonia-Lyase Synthesis of Mustard Cotyledons 1  

PubMed Central

The relationship between the amount of active phytochrome (Pfr) produced by 5-minute light pulses and the rate of subsequent enzyme accumulation (phenylalanine ammonia-lyase, EC 4.3.1.5) of mustard (Sinapis alba L.) cotyledons was investigated. The response rapidly adjusts to changes of the Pfr level produced by light pulses of different wavelengths. Regardless of total phytochrome levels in the cotyledons, response adjustments to new photostationary states (??) are correlated with ?? values. On the other hand, the kinetics of enzyme accumulation shows no influence of Pfr destruction as determined spectrophotometrically (?½ = 45 min) in the same organ (see Schäfer et al. 1973 Photochem Photobiol 18: 331-334). It is concluded that the phytochrome molecules involved in the regulation of this response by light pulses comprise a small fraction of the total phytochrome of the cotyledons. In contrast to bulk phytochrome this fraction appears to be not subject to Pfr destruction. PMID:16660237

Tong, Wu-Fu; Schopfer, Peter

1978-01-01

116

Novel formation of ?-amino acid from ?-oxo acids and ammonia in an aqueous medium  

NASA Astrophysics Data System (ADS)

In the course of a study of possible mechanisms for chemical evolution in the primeval sea, we found the novel formation of ?-amino acids and N-acylamino acids from ?-oxo acids and ammonia in an aqueous medium. Glyoxylic acid reacted with ammonia to form N-oxalylglycine, which gave glycine in a 5 39% yield after hydrolysis with 6N HCl. Pyruvic acid and ammonia reacted to give N-acetylalanine, which formed alanine in a 3 7% overall yield upon hydrolysis. The pH optima in these reactions were between pH 3 and 4. These reactions were further extended to the formation of other amino acids. Glutamic acid, phenylalanine and alanine were formed from ?-ketoglutaric acid, phenylpyruvic acid and oxaloacetic acid, respectively, under similar conditions. N-Succinylglutamic acid was obtained as an intermediate in glutamic acid synthesis. Phenylacetylphenyl-alanineamide was also isolated as an intermediate in phenylalanine synthesis. Alanine, rather than aspartic acid, was produced from oxaloacetic acid. These reactions provide a novel route for the prebiotic synthesis of amino acids. A mechanism for the reactions will be proposed.

Yanagawa, Hiroshi; Makino, Yumiko; Sato, Kazuki; Nishizawa, Masato; Egami, Fujio

1984-12-01

117

Facile Synthesis of ?-Ketophosphonates by an Intermolecular Stetter Reaction onto Vinylphosphonates.  

PubMed

The atom-economic and practical N-heterocyclic carbene (NHC) catalyzed Stetter reaction for the synthesis of ?-ketophosphonates by the reaction of aromatic aldehydes with vinylphosphonates is reported. The NHC derived from N-mesitylimidazolium salt (IMes) was an effective catalyst for this transformation, and the products were formed in moderate to good yields. PMID:25192401

Patra, Atanu; Bhunia, Anup; Biju, Akkattu T

2014-09-19

118

Synthesis of Chiral Cyanohydrins by Recombinant Escherichia coli Cells in a Micro-Aqueous Reaction System  

PubMed Central

Synthesis of chiral cyanohydrins is performed in a monophasic micro-aqueous reaction system using whole recombinant Escherichia coli cells expressing the Arabidopsis thaliana hydroxynitrile lyase (AtHNL). Microscopy studies employing a fusion of AtHNL with a flavin-based fluorescent protein (FbFP) reveal that the cells remain intact in the reaction system. PMID:22544258

Scholz, Kathrin Emmi; Okrob, Daniel; Kopka, Benita; Grunberger, Alexander; Pohl, Martina; Jaeger, Karl-Erich

2012-01-01

119

Synthesis of chiral cyanohydrins by recombinant Escherichia coli cells in a micro-aqueous reaction system.  

PubMed

Synthesis of chiral cyanohydrins is performed in a monophasic micro-aqueous reaction system using whole recombinant Escherichia coli cells expressing the Arabidopsis thaliana hydroxynitrile lyase (AtHNL). Microscopy studies employing a fusion of AtHNL with a flavin-based fluorescent protein (FbFP) reveal that the cells remain intact in the reaction system. PMID:22544258

Scholz, Kathrin Emmi; Okrob, Daniel; Kopka, Benita; Grünberger, Alexander; Pohl, Martina; Jaeger, Karl-Erich; Krauss, Ulrich

2012-07-01

120

Iodine-Catalyzed Synthesis of 3-Arylbenzoquinoline Derivatives by Three-Component Reactions  

Microsoft Academic Search

A mild, efficient, and general method for the synthesis of benzo[f]quinoline derivatives via three-component reaction of arylaldehyde, naphthalen-2-amine, and acetone or acetophenone is described using iodine as catalyst. The features of this procedure are mild reaction conditions, high yields, and operational simplicity.

Xiang-Shan Wang; Qing Li; Jian-Rong Wu; Yu-Ling Li

2009-01-01

121

Total Synthesis of Leucascandrolide A: A New Application of the Mukaiyama Aldol-Prins Reaction  

PubMed Central

A total synthesis of the marine natural product leucascandrolide A has been completed. The titanium tetrabromide-mediated Mukaiyama aldol-Prins (MAP) reaction with aldehydes developed in our group provided a highly convergent and stereoselective method for assembling the core of the molecule. A new class of MAP reactions with acetals is introduced and mechanistic considerations for both MAP methods are described. The total synthesis was completed by coupling of the side chain through two avenues: A known Still–Gennari olefination and a new Z-selective aldol/dehydroselenation reaction. Both procedures were highly selective and provided the natural product. PMID:17595145

Van Orden, Lori J.; Patterson, Brian D.; Rychnovsky, Scott D.

2008-01-01

122

Microwave assisted tandem reactions for the synthesis of 2-hydrazolyl-4-thiazolidinones.  

PubMed

A tandem method for the synthesis of 2-hydrazolyl-4-thiazolidinones (5) from commercially available materials in a 3 component reaction has been developed. The reaction connects aldehydes, thiosemicarbazides and maleic anhydride, effectively assisted by microwave irradiation. The synthesis of a new type of compound, 2-hydrazolyl-5,5-diphenyl-4-thiazolidinone (7), obtained by treatment of thiosemicarbazone with benzil in basic media is also reported. HOMO/LUMO energies, orbital coefficients and charge distribution were used to explain the proposed reaction mechanism. PMID:19756224

Saiz, Cecilia; Pizzo, Chiara; Manta, Eduardo; Wipf, Peter; Mahler, S Graciela

2009-02-25

123

Microwave assisted tandem reactions for the synthesis of 2-hydrazolyl-4-thiazolidinones  

PubMed Central

A tandem method for the synthesis of 2-hydrazolyl-4-thiazolidinones (5) from commercially available materials in a 3 component reaction has been developed. The reaction connects aldehydes, thiosemicarbazides and maleic anhydride, effectively assisted by microwave irradiation. The synthesis of a new type of compound, 2-hydrazolyl-5,5-diphenyl-4-thiazolidinone (7), obtained by treatment of thiosemicarbazone with benzil in basic media is also reported. HOMO/LUMO energies, orbital coefficients and charge distribution were used to explain the proposed reaction mechanism. PMID:19756224

Saiz, Cecilia; Pizzo, Chiara; Manta, Eduardo; Wipf, Peter; Mahler, S. Graciela

2009-01-01

124

Asymmetric Disulfonimide-Catalyzed Synthesis of ?-Amino-?-Ketoester Derivatives by Vinylogous Mukaiyama-Mannich Reactions.  

PubMed

An organocatalytic asymmetric synthesis of ?-amino-?-ketoester derivatives has been developed. A chiral disulfonimide (DSI) serves as a highly efficient precatalyst for a vinylogous Mukaiyama-Mannich reaction of readily available dioxinone-derived silyloxydienes with N-Boc-protected imines, delivering products in excellent yields and enantioselectivities. The synthetic utility of this reaction is illustrated in various transformations, including a new C?C bond-forming reaction, which provide useful enantioenriched building blocks. The methodology is applied in a formal synthesis of (-)-lasubin. PMID:25348924

Wang, Qinggang; van Gemmeren, Manuel; List, Benjamin

2014-12-01

125

Organic reactivity in liquid ammonia.  

PubMed

Liquid ammonia is a useful solvent for many organic reactions including aliphatic and aromatic nucleophilic substitution and metal-ion catalysed reactions. The acidity of acids is modified in liquid ammonia giving rise to differences from conventional solvents. The ionisation constants of phenols and carbon acids are the product of those for ion-pair formation and dissociation to the free ions. There is a linear relationship between the pK(a) of phenols and carbon acids in liquid ammonia and those in water of slope 1.68 and 0.7, respectively. Aminium ions exist in their unprotonated free base form in liquid ammonia. The rates of solvolysis and aminolysis by neutral amines of substituted benzyl chlorides in liquid ammonia show little or no dependence upon ring substituents, in stark contrast with the hydrolysis rates of substituted benzyl halides in water which vary 10(7) fold. However, the rates of the reaction of phenoxide ions and amine anions with 4-substituted benzyl chlorides gives a Hammett ? = 1.1 and 0.93, respectively. The second order rate constants for the substitution of benzyl chlorides by neutral and anionic amines show a single Brønsted ?(nuc) = 0.21 whereas those for substituted phenoxide ions generate a Brønsted ?(nuc) = 0.40. The rates of aromatic nucleophilic substitution reactions in liquid ammonia are much faster than those in protic solvents indicating that liquid ammonia behaves like a typical dipolar aprotic solvent in its solvent effects on organic reactions. Nitrofluorobenzenes (NFB) readily undergo solvolysis in liquid ammonia but oxygen nucleophiles, such as alkoxide and phenoxide ions, displace the fluorine of 4-NFB in liquid ammonia to give the corresponding substitution product with little or no competing solvolysis product. The Brønsted ?(nuc) for the reaction of 4-NFB with para-substituted phenoxides is 0.91, indicative that the decomposition of the Meisenheimer ?-intermediate is rate limiting. The aminolysis of 4-NFB occurs without general base catalysis by the amine and the second order rate constants generate a Brønsted ?(nuc) of 0.36, which is also interpreted in terms of rate limiting breakdown of the Meisenheimer ?-intermediate. PMID:22538452

Ji, Pengju; Atherton, John; Page, Michael I

2012-08-14

126

Intrinsic reaction coordinate calculations of the inversion/bending potentials in the X˜ and à states of ammonia  

NASA Astrophysics Data System (ADS)

Mass-weighted intrinsic reaction coordinate calculations were carried out for the inversion/bending motion in the ground and lowest excited singlet states of NH 3 and ND 3. Vibrational eigenstates were obtained from these IRC potentials directly, obviating the need to make assumptions about the coordinate dependence of the reduced mass. The 0 ± inversion splittings for the X˜ state of NH 3 and ND 3 are found to be 1.17 and 0.89 cm-1, respectively, at the MP4(SDQ)/aug-cc-pVTZ level of theory. CASPT2-refined IRC scans of both the relaxed and vertical Östate surfaces were carried out. The Ö X˜ absorption spectra of NH 3 and ND 3 were modeled using the respective Boltzmann-weighted vibrational electronic transition matrix elements.

Halpern, Arthur M.; Glendening, Eric D.

2001-01-01

127

The synthesis and benzannulation reactions of (trialkylsilyl)vinylketenes  

E-print Network

(Trialkylsilyl)vinylketenes ("TAS-vinylketenes") are versatile four-carbon building blocks in a variety of methods for the synthesis of carbocyclic and heterocyclic compounds. This thesis discusses the development of a new ...

Austin, Wesley F

2008-01-01

128

Synthesis of transactinide nuclei in cold fusion reactions using radioactive beams  

SciTech Connect

Chances of synthesis of transactinide nuclei in cold fusion reactions (one-neutron-out reactions) using radioactive beams are evaluated. Because in most of the cases intensities of radioactive beams are significantly less than those of the stable beams, reactions with the greatest radioactive-beam intensities for the particular elements are considered. The results are compared with the recent ones obtained by Loveland [Phys. Rev. C 76, 014612 (2007)], who investigated the same nuclei.

Smolanczuk, Robert [Theoretical Physics Department, Soltan Institute for Nuclear Studies, Hoza 69, PL-00-681 Warszawa (Poland)

2010-06-15

129

Catalytic Alkene Cyclization Reactions for the Stereoselective Synthesis of Complex "Terpenoid-like" Heterocycles  

PubMed Central

A new catalytic synthesis of densely-substituted tetrahydroquinolines is described. This reaction forms up to two rings, three bonds, and three stereogenic centers with excellent stereo- and regiocontrol in a single step. Although control experiments demonstrate that the active catalyst is protic acid, Sc(OTf)3 serves as an effective and practical pre-catalyst. The scope of this reaction is demonstrated with 21 monocyclizations and 14 bicyclization reactions. PMID:23565327

Moore, Jared T.; Soldi, Cristian; Fettinger, James C.

2012-01-01

130

Probing reaction pathways on model catalyst surfaces: Vinyl acetate synthesis and olefin metathesis  

Microsoft Academic Search

The reaction pathway for the palladium-catalyzed synthesis of vinyl acetate from acetic acid, ethylene and oxygen is investigated using reflection–absorption infrared spectroscopy by monitoring the rate of acetate titration by gas-phase ethylene. This reveals that acetate species are removed by reaction with gas-phase ethylene resulting in vinyl acetate formation. Reaction with C2D4 reveals a large (?6) isotope effect indicating that

Feng Gao; Yilin Wang; Florencia Calaza; Dario Stacchiola; Wilfred T. Tysoe

2008-01-01

131

Regeneration of ammonia borane from polyborazylene  

DOEpatents

Method of producing ammonia borane, comprising providing a reagent comprising a dehydrogenated material in a suitable solvent; and combining the reagent with a reducing agent comprising hydrazine, a hydrazine derivative, or combinations thereof, in a reaction which produces a mixture comprising ammonia borane.

Sutton, Andrew; Gordon, John C; Ott, Kevin C; Burrell, Anthony K

2013-02-05

132

Developing novel organocatalyzed aldol reactions for the enantioselective synthesis of biologically active molecules.  

PubMed

Aldol reaction is one of the most important methods for the formation of carbon-carbon bonds. Because of its significance and usefulness, asymmetric versions of this reaction have been realized with different approaches in the past. Over the last decade, the area of organocatalysis has made significant progresses. As one of most studied reactions in organocatalyses, organocatalyzed aldol reaction has emerged as a powerful tool for the synthesis of a large number of useful products in optically enriched forms. In this review, we summarize our efforts on the development of novel organocatalyzed aldol reactions for the enantioselective synthesis of biological active molecules. Literatures closely related to our studies are also covered. PMID:21918584

Bhanushali, Mayur; Zhao, Cong-Gui

2011-06-01

133

Gaseous species as reaction tracers in the solvothermal synthesis of the zinc oxide terephthalate MOF-5.  

PubMed

Gaseous species emitted during the zinc oxide/zinc hydroxide 1,4-benzenedicarboxylate metal organic framework synthesis (MOF-5, MOF-69c) have been used to investigate the reaction scheme that leads to the framework creation. Changes of the gas-phase composition over time indicate that the decomposition of the solvent diethylformamide occurs at least via two competing reaction pathways that can be linked to the reaction's overall water and pH management. From isotope exchange experiments, we deduce that one of the decomposition pathways leads to the removal of water from the reaction mixture, which sets the conditions when the synthesis of an oxide-based (MOF-5) instead of an hydroxide-based MOF (MOF-69c) occurs. A quantitative account of most reactants and byproducts before and after the MOF-5/MOF-69c synthesis is presented. From the investigation of the reaction intermediates and byproducts, we derive a proposal of a basic reaction scheme for the standard synthesis zinc oxide carboxylate MOFs. PMID:17455926

Hausdorf, Steffen; Baitalow, Felix; Seidel, Jürgen; Mertens, Florian O R L

2007-05-24

134

Is there in vivo evidence for amino acid shuttles carrying ammonia from neurons to astrocytes?  

PubMed Central

The high in vivo flux of the glutamate/glutamine cycle puts a strong demand on the return of ammonia released by phosphate activated glutaminase from the neurons to the astrocytes in order to maintain nitrogen balance. In this paper we review several amino acid shuttles that have been proposed for balancing the nitrogen flows between neurons and astrocytes in the glutamate/glutamine cycle. All of these cycles depend on the directionality of glutamate dehydrogenase, catalyzing reductive glutamate synthesis (forward reaction) in the neuron in order to capture the ammonia released by phosphate activated glutaminase, while catalyzing oxidative deamination of glutamate (reverse reaction) in the astrocytes to release ammonia for glutamine synthesis. Reanalysis of results from in vivo experiments using 13N and 15N labeled ammonia and leucine in rats suggests that the maximum flux of the alanine/lactate or branched chain amino acid/branched chain amino acid transaminase shuttles between neurons and astrocytes are approximately 3-5 times lower than would be required to account for the ammonia transfer from neurons to astrocytes needed for glutamine synthesis (amide nitrogen) to sustain the glutamate/glutamine cycle. However, in the rat brain both the total ammonia fixation rate by glutamate dehydrogenase and the total branched chain amino acid transaminase activity are sufficient to support a branched chain amino acid/branched chain keto acid shuttle, as proposed by Hutson and coworkers, which would support the de novo synthesis of glutamine in the astrocyte to replace the ? 20% of neurotransmitter glutamate that is oxidized. A higher fraction of the nitrogen needs of total glutamate neurotransmitter cycling could be supported by hybrid cycles in which glutamate and tricarboxylic acid cycle intermediates act as a nitrogen shuttle. A limitation of all in vivo studies in animals conducted to date is that none have shown transfer of nitrogen for glutamine amide synthesis, either as free ammonia or via an amino acid from the neurons to the astrocytes. Future work will be needed, perhaps using methods for selectively labeling nitrogen in neurons, to conclusively establish the rate of amino acid nitrogen shuttles in vivo and their coupling to the glutamate/glutamine cycle. PMID:23104556

Rothman, Douglas L.; De Feyter, Henk M.; Maciejewski, Paul K.; Behar, Kevin L.

2013-01-01

135

Electron driven processes in ices: Surface functionalization and synthesis reactions  

Microsoft Academic Search

The ability to control and orientate chemical reactivity in the condensed phase is a major challenge of modern research. Upon interaction with condensed molecules electrons drive bond cleavage thus generating a population of very reactive species in the condensed medium. These reactive species may interact either within the volume leading to the synthesis of new molecules or with the substrate

A. Lafosse; M. Bertin; R. Azria

2009-01-01

136

Formate ester synthesis via reaction of 2-bromoethylamines with dimethylformamide  

Microsoft Academic Search

2-Bromoethylamines are converted to the corresponding formate esters in the presence of DMF. Both primary and secondary bromides are smoothly transformed to the esters in satisfactory yields. The reaction mechanism involves the formation of an aziridinium ion, which upon reaction with DMF forms a Vilsmeier-type intermediate that is further hydrolyzed to the corresponding formates. Participation of the ?-amino group appears

Marianna Dakanali; George K. Tsikalas; Harald Krautscheid; Haralambos E. Katerinopoulos

2008-01-01

137

Synthesis and minisci reactions of organotrifluoroborato building blocks.  

PubMed

Copper-catalyzed borylation of a variety of organic halides with bis(pinacolato)diboron allows the preparation of diverse potassium organotrifluoroborates. The reactions are mild and general, providing access to a variety of interesting, boron-containing building blocks, including those containing piperidine, pyrrole, azetidine, tetrahydropyran, and oxetane substructures. Representative Minisci reactions are reported for select examples. PMID:23594305

Presset, Marc; Fleury-Brégeot, Nicolas; Oehlrich, Daniel; Rombouts, Frederik; Molander, Gary A

2013-05-01

138

Synthesis of some †-lactams via enolate-imine reactions  

E-print Network

Formation of cis- and trans-u-lactams. Reaction of Schiff base with u-bromo acid ester and zinc . Reaction of u-(bromozinc) ester enolate with imines. 10 12 13 14 15 16 17 18 Cycloaddition of diphenylketene and diisopropyl carbodiimide... of the imine nitrogen on the carbonyl group of the acyl chloride. 11 Another useful synthetic route to g-lactams which is similar to that described above is the reaction of an acid chloride with an imine in the presence of base. The stereochemistry...

McElveen, Margaret Lynn

2012-06-07

139

Synthesis of heterocycles through transition-metal-catalyzed isomerization reactions.  

PubMed

Metal-catalyzed isomerization of N- and O-allylic systems is emerging as an effective method to form synthetically useful iminium and oxocarbenium intermediates. In the presence of tethered nucleophiles, several recent examples illuminate this approach as a powerful strategy for the synthesis of structurally complex and diverse heterocycles. In this Concept article, we attempt to cover this area of research through a selection of recent versatile examples. PMID:24924616

Ishoey, Mette; Nielsen, Thomas E

2014-07-14

140

Synthesis of amides through the Cannizzaro-type reaction catalyzed by lanthanide chlorides  

Microsoft Academic Search

Amidation of aldehydes with lithium amides through the LnCl3-catalyzed Cannizzaro-type reactions afforded a variety of amides in high yields. The electronic and steric effects on the reaction were investigated. The features of the economical catalysts, high yields, tolerance of a wide range of lithium amides and aromatic aldehydes make this methodology an easy and valid contribution to the direct synthesis

Lijun Zhang; Shunpeng Su; Hongping Wu; Shaowu Wang

2009-01-01

141

Parallel, solution phase synthesis of dihydropyridine miticides via a versatile multicomponent reaction.  

PubMed

A novel class of highly active dihydropyridine miticides was prepared using a multicomponent reaction process. The initial lead was rapidly optimized using solution phase parallel synthesis techniques and a positional scanning approach. Detailed structure-activity relationships were developed for the amino and carbonyl components of the molecule and used to select the best candidates for broad field testing. The chemistry, biology and toxicology of these compounds will be presented along with numerous structural variants of the reaction products. PMID:16305359

Cottrell, K; Holyoke, C W; Kline, M; Lee, K C; Nassirpour, M R; Pasteris, R J; Shah, S

2005-11-01

142

Synthesis of optically active bisdifluorocyclopropanes through a chemo-enzymatic reaction strategy  

Microsoft Academic Search

The first synthesis of bisdifluorocyclopropane derivatives has been accomplished via a chemo-enzymatic reaction strategy; (E)- or (Z)-3-tributylstannyl-2-propenols were prepared and their conversion led to the (trans,trans)- and (cis,cis)-bisdifluorocyclopropanes. The subsequent lipase-catalyzed reaction efficiently afforded optically active (trans,trans)-2,2,5,5-tetrafluoro-1,6-bis(hydroxymethyl)bicyclopropane.

Koichi Mitsukura; Satoshi Korekiyo; Toshiyuki Itoh

1999-01-01

143

Carbon Nanotube Synthesis via the Catalytic CVD Method: A Review on the Effect of Reaction Parameters  

Microsoft Academic Search

This review covers the results obtained in carbon nanotube synthesis by chemical vapor deposition. Parameters such as catalysts, supports, carbon precursors, reaction time, temperature and gas flow rates that are used in the production of carbon nanotubes are discussed throughout the text. Purification of the synthesized carbon nanotubes and methods utilized for cost reduction were also explored.

Ç?nar Öncel; Yuda Yürüm

2006-01-01

144

Concise enantioselective synthesis of duloxetine via direct catalytic asymmetric aldol reaction of thioamide.  

PubMed

Direct catalytic asymmetric aldol reaction of thioamide offers a new entry to the concise enantioselective synthesis of duloxetine. The direct aldol protocol was scalable (>20 g) to afford the aldol product in 92% ee after LiAlH(4) reduction, and 84% of the chiral ligand was recovered after recrystallization. The following four steps of transformation delivered duloxetine. PMID:22494391

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

2012-05-01

145

Synthesis of antihypertensive agents via coupling reaction of Benzothiazepinone and 1,4-dihydropyridine derivatives  

Microsoft Academic Search

The synthesis of3a, 3b, 7a and7b from Benzothiazepinone and 1,4-dihyropyridine derivatives is described. Benzothiazepinone and 1,4-dihydropyridine derivatives\\u000a were prepared according to literature procedure. The key reactions involve esterification and amidation of benzothiazepinone\\u000a and 1,4-dihydropyridine derivatives.

Won-Hun Ham; Jae-Gwon Yang; Tae-Gyun Lim; Yun-Ho Jung; Yun-Sung Chung

1994-01-01

146

Reaction synthesis of dynamically densified titanium-based intermetallic and ceramic-forming powders  

NASA Astrophysics Data System (ADS)

The mechanism(s) and kinetics of the reaction synthesis of dynamically-densified Ti-based intermetallic and ceramic forming powder mixtures were investigated in this study. Dynamic densification employing shock-compression produces a dense-packed and highly-activated state of powder mixture constituents resulting in significantly increased mass transport rates and enhanced chemical reactivity. Green density compacts (˜85--95% TMD) of Ti-Si, Ti-B, and Ti-Al powder mixtures, obtained using shock-densification under different loading conditions, were heat treated in an inert atmosphere, at their respective eutectic temperatures. Microstructural observation showed evidence of reaction initiating in the solid state, but eventually being taken over by a self sustained combustion type reaction mechanism. Activation energies determined using differential thermal analysis were used to correlate the reaction behavior in Ti-Si (as the model system), based on Carter's kinetic model for solid-state reactions and the Johnson-Mehl-Avrami kinetics for the combustion-type reaction, with experimental measurements of fraction of Ti5Si3 formed as a function of time and temperature. It was confirmed that in Ti-Si dynamically-densified powder compacts the reaction occurs in the solid-state up to temperatures <1000°C, but with further increase in temperature the reaction is taken over by a combustion-type reaction. The Ti-Si compacts thus produced are 92--95% dense and show a fully reacted Ti5Si3 microstructure, with ~6 mum grain size and ˜800 kg/mm2 microhardness. A predictive model was developed, incorporating a balance between rate of heat generation (due to reaction) and heat dissipation, to determine optimum synthesis conditions under which the reaction occurs in the solid state without being taken over by the combustion mode. The model considered synthesis temperature, compact porosity, and activation energy as the variables, to determine the fraction reacted as a function of time under various conditions, based on which the dominant reaction mechanism can be inferred in any given shock-densified powder mixture (including Ti-Si, Ti-Al, and Ti-B). Functionally graded Ti5Si3-TiAl and TiB2-TiAl3 composite systems were also synthesized, showing the potential of the combined dynamic-densification and reaction synthesis technique for the fabrication of such materials.

Namjoshi, Shantanu Ashok

147

Synthesis of rhenabenzenes from the reactions of rhenacyclobutadienes with ethoxyethyne.  

PubMed

Treatment of Na[Re(CO)5 ] with RC?CCO2 Et (R=phenyl, naphthalen-1-yl, phenanthren-9-yl and pyren-1-yl) followed by reaction with acetyl chloride and ethanol afforded the rhenacyclobutadienes Re{-C(R)?C(CO2 Et)C(OEt)?}(CO)4 . Reactions of these rhenacyclobutadienes with HC?COEt produced rhenabenzenes Re{-C(R)?C(CO2 Et)C(OEt)?CHC(OEt)?}(CO)4 . Except for R=Ph, new rhenacyclobutadienes with pendant alkenyl substituents Re{-C(R)?C(C(OEt)?CH(CO2 Et))C(OEt)?}(CO)4 were also isolated from these reactions. The NMR spectroscopic and X-ray structural data, as well as the aromatic stabilization energy (ASE) values suggest that the rhenabenzenes are aromatic, with extensive delocalized ? character. PMID:25220667

Lin, Ran; Lee, Ka-Ho; Poon, Ka Chun; Sung, Herman H Y; Williams, Ian D; Lin, Zhenyang; Jia, Guochen

2014-11-01

148

STM CONTROL OF CHEMICAL REACTIONS: Single-Molecule Synthesis  

NASA Astrophysics Data System (ADS)

The fascinating advances in single atom/molecule manipulation with a scanning tunneling microscope (STM) tip allow scientists to fabricate atomic-scale structures or to probe chemical and physical properties of matters at an atomic level. Owing to these advances, it has become possible for the basic chemical reaction steps, such as dissociation, diffusion, adsorption, readsorption, and bond-formation processes, to be performed by using the STM tip. Complete sequences of chemical reactions are able to induce at a single-molecule level. New molecules can be constructed from the basic molecular building blocks on a one-molecule-at-a-time basis by using a variety of STM manipulation schemes in a systematic step-by-step manner. These achievements open up entirely new opportunities in nanochemistry and nanochemical technology. In this review, various STM manipulation techniques useful in the single-molecule reaction process are reviewed, and their impact on the future of nanoscience and technology are discussed.

Hla, Saw-Wai; Rieder, Karl-Heinz

2003-10-01

149

Prebiotic synthesis and reactions of nucleosides and nucleotides  

NASA Technical Reports Server (NTRS)

The potential of diiminosuccinonitrile (DISN) as a prebiotic phosphorylating agent is studied. This compound is formed readily by the oxidation of diaminomaleonitrile, a tetramer of HCN. DISN is shown to produce the cyclization of 3'-adenosine monophosphate to adenosine 2',3'-cyclic phosphate in up to 40 percent yield. The DISN-mediated phosphorylation of uridine to uridine monophosphate is determined not to proceed efficiently in aqueous solution. The reaction of DISN and BrCN with uridine-5'-phosphate and uridine is found to result in the formation of 2,2'-anhydronucleotides and 2,2'-anhydronucleosides, respectively, and other reaction products resulting from an initial reaction at the 2' and 3'-hydroxyl groups. Homoionic montmorillonites were employed to study the clay mineral catalysis of the cyclization of adenosine-3'-phosphate.

Ferris, J. P.; Yanagawa, H.; Hagan, W. J., Jr.

1983-01-01

150

Synthesis of novel photochromic pyrans via palladium-mediated reactions.  

PubMed

Photochromic pyrans for applications in material and life sciences were synthesized via palladium-mediated cyanation, carbonylation and Sonogashira cross-coupling starting from bromo-substituted naphthopyran 1 and benzopyrans 2a/b. A novel photoswitchable benzopyran-based omega-amino acid 6 for Fmoc-based solid-phase peptide synthesis is presented. The photochromic behaviour of the 3-cyano-substituted benzopyran 5a was investigated by time-resolved absorption spectroscopy in the picosecond time domain. PMID:19590750

Böttcher, Christoph; Zeyat, Gehad; Ahmed, Saleh A; Irran, Elisabeth; Cordes, Thorben; Elsner, Cord; Zinth, Wolfgang; Rueck-Braun, Karola

2009-01-01

151

Synthesis of nanosized silicon particles by a rapid metathesis reaction  

Microsoft Academic Search

A solid-state rapid metathesis reaction was performed in a bed of sodium silicofluoride (Na2SiF6) and sodium azide (NaN3) powders diluted with sodium fluoride (NaF), to produce silicon nanoparticles. After a local ignition of Na2SiF6+4NaN3+kNaF mixture (here k is mole number of NaF), the reaction proceeded in a self-sustaining combustion mode developing high temperatures (950–1000°C) on very short time scales (a

C. W. Won; H. H. Nersisyan; H. I. Won; H. H. Lee

2009-01-01

152

Synthesis of triple-layered Ag@Co@Ni core-shell nanoparticles for the catalytic dehydrogenation of ammonia borane.  

PubMed

Triple-layered Ag@Co@Ni core-shell nanoparticles (NPs) containing a silver core, a cobalt inner shell, and a nickel outer shell were formed by an in situ chemical reduction method. The thickness of the double shells varied with different cobalt and nickel contents. Ag0.04 @Co0.48 @Ni0.48 showed the most distinct core-shell structure. Compared with its bimetallic core-shell counterparts, this catalyst showed higher catalytic activity for the hydrolysis of NH3 BH3 (AB). The synergetic interaction between Co and Ni in Ag0.04 @Co0.48 @Ni0.48 NPs may play a critical role in the enhanced catalytic activity. Furthermore, cobalt-nickel double shells surrounding the silver core in the special triple-layered core-shell structure provided increasing amounts of active sites on the surface to facilitate the catalytic reaction. These promising catalysts may lead to applications for AB in the field of fuel cells. PMID:24302541

Qiu, Fangyuan; Liu, Guang; Li, Li; Wang, Ying; Xu, Changchang; An, Cuihua; Chen, Chengcheng; Xu, Yanan; Huang, Yanan; Wang, Yijing; Jiao, Lifang; Yuan, Huatang

2014-01-01

153

Synergistic rhodium(II) carboxylate and brønsted acid catalyzed multicomponent reactions of enalcarbenoids: direct synthesis of ?-pyrrolylbenzylamines.  

PubMed

The design of a synergistic rhodium(II) carboxylate and BINOL phosphoric acid catalyzed efficient multicomponent reaction of enaldiazo compounds, arylamines, and aryl aldehydes leading to the first transition-metal-catalyzed direct synthesis of valuable ?-pyrrolylbenzylamines is disclosed. The reaction is proposed to involve a transient ammonium ylide of a new class of electrophilic rhodium enalcarbenoid, its regioselective Mannich reaction, and a cyclocondensation cascade. The methodology was used in a highly diastereoselective synthesis of a binaphthyl based chiral pyrrole. PMID:24988365

Dawande, Sudam Ganpat; Kanchupalli, Vinaykumar; Lad, Bapurao Sudam; Rai, Jyoti; Katukojvala, Sreenivas

2014-07-18

154

Evaluating the impact of ammonia fiber expansion (AFEX) pretreatment conditions on the cost of ethanol production  

Microsoft Academic Search

Ammonia fiber expansion (AFEX) pretreatment is an ammonia-based process for improving the susceptibility of lignocellulosic biomass to enzymatic attack. Four parameters – ammonia loading, water loading, reaction temperature, and residence time – can be varied in order to optimize AFEX pretreatment. The effect of these parameters on process economics of ethanol production was studied using a leading biorefinery model. Ammonia

Bryan Bals; Chris Wedding; Venkatesh Balan; Elizabeth Sendich; Bruce Dale

2011-01-01

155

Membrane separation in green chemical processing: solvent nanofiltration in liquid phase organic synthesis reactions.  

PubMed

This paper describes ideas together with preliminary experimental results for applying solvent nanofiltration to liquid phase organic synthesis reactions. Membranes for organic solvent nanofiltration have only recently (during the 1990s) become available and, to date, have been applied primarily to food processing (vegetable oil processing, in particular) and refinery processes. Applications to organic synthesis, even at a laboratory feasibility level, are few. However, these membranes have great potential to improve the environmental performance of many liquid phase synthesis reactions by reducing the need for complex solvent handling operations. Examples that are shown to be feasible are solvent exchanges, where it is desired to swap a high molecular weight molecule from one solvent to another between separate stages in a complex synthesis, and recycle and reuse of homogeneous catalysts. In solvent exchanges, nanofiltration is shown to provide a fast and effective means of swapping from a high boiling point solvent to a solvent with a lower boiling point-this is a difficult operation by means of distillation. Solvent nanofiltration is shown to be able to separate two distinct types of homogeneous catalysts, phase transfer catalysts and organometallic catalysts, from their respective reaction products. In both cases the application of organic solvent nanofiltration allows several reuses of the same catalyst. Catalyst stability is shown to be an essential requirement for this technique to be effective. Finally, we present a discussion of scale-up aspects including membrane flux and process economics. PMID:12783814

Livingston, Andrew; Peeva, Ludmila; Han, Shejiao; Nair, Dinesh; Luthra, Satinder Singh; White, Lloyd S; Freitas Dos Santos, Luisa M

2003-03-01

156

Accessing an Azaborine Building Block: Synthesis and Substitution Reactions of 2-Chloromethyl-2,1-borazaronaphthalene.  

PubMed

One major synthetic route to the synthesis of benzyl amines, ethers, and esters is the nucleophilic substitution of a benzylic halide. To develop a method for the facile synthesis and functionalization of the isosteric azaborines, 2-chloromethyl-2,1-borazaronaphthalene has been synthesized in one step to afford a similar common precursor to a benzylic halide. This B-N isostere has been shown to be an effective building block by serving as an electrophile in substitution reactions with a large variety of nucleophiles. PMID:25317850

Molander, Gary A; Wisniewski, Steven R; Amani, Javad

2014-11-01

157

A formal synthesis of ezetimibe via cycloaddition/rearrangement cascade reaction.  

PubMed

A formal synthesis of a powerful cholesterol inhibitor, ezetymibe 1, is described. The crucial step of the synthesis is based on Cu(I)-mediated Kinugasa cycloaddition/rearrangement cascade reaction between terminal acetylene derived from acetonide of L-glyceraldehyde and suitable C,N-diarylnitrone. The adduct with (3R,4S) configuration at the azetidinone ring, obtained with high stereoselectivity, was subsequently subjected to deprotection of the diol side chain followed by glycolic cleavage and base-induced isomerization at the C3 carbon atom to afford the (3S,4S) aldehyde, which has been already transformed into ezetimibe by the Schering-Plough group. PMID:21744801

Michalak, Micha?; Stodulski, Maciej; Stecko, Sebastian; Mames, Adam; Panfil, Irma; Soluch, Magdalena; Furman, Bart?omiej; Chmielewski, Marek

2011-08-19

158

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

PubMed

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

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

2014-09-19

159

Chiral iminoesters derived from D-glyceraldehyde in [3 + 2] cycloaddition reactions. Asymmetric synthesis of a key intermediate in the synthesis of neuramidinase inhibitors.  

PubMed

Silver-catalyzed endo-selective and copper-catalyzed exo-selective asymmetric [3 + 2] cycloadditions of acrylates to chiral iminoesters derived from D-glyceraldehyde have been investigated. The reaction diastereoselectively provides highly functionalized pyrrolidines. This approach was used to develop the first asymmetric synthesis of a key intermediate in the synthesis of pyrrolidine influenza neuramidinase inhibitors. PMID:24143968

Gálvez, José A; Díaz-de-Villegas, María D; Alías, Miriam; Badorrey, Ramón

2013-11-15

160

Reaction synthesis and processing of nickel and iron aluminides  

SciTech Connect

Composites of Ni and Fe aluminides were obtained by hot pressing and hot extrusion of a blended mixture of Ni and Al or Fe and Al with ceramic phases such as TiC, ZrO{sub 2}, and Al{sub 2}O{sub 3}. Aluminides were analyzed by XRD to determine the phase structures, and optical and scanning electron microscopies were used to determine the grain sizes of the aluminides and dispersion of ceramics. Tensile properties (0.2% YS, UTS, total elong., RIA) were measured on buttonhead and sheet specimens of Ni and Fe aluminides and their composites at room and high temperatures in air at a strain rate of 1. 2x10{sup -3}/s. Tensile properties of Fe-8 wt% Al from partial mechanical alloying and then combustion synthesis compare very well with oxide-dispersed alloys of Fe. Fe aluminides of FeAl and their composites, based on Fe-24 wt% Al from hot pressing of Fe and Al powders with or without ceramic phases, exhibited full densities and uniform grain sizes. Tensile properties of FeAl and composites (hot pressing of elemental powders) were excellent compared to those of FeAl alloys from hot extrusion of water-atomized powders. Fe aluminides were also obtained by hot extrusion of Fe and Al powders at 950, 1000, and 1100 C.

Deevi, S.C. [Philip Morris U.S.A., Richmond, VA (United States). Research Center; Sikka, V.K. [Oak Ridge National Lab., TN (United States)

1996-12-31

161

Basic distinctions between cold- and hot-fusion reactions in the synthesis of superheavy elements  

NASA Astrophysics Data System (ADS)

Superheavy elements (SHE) of charge number in the range of Z = 106-112 were synthesized in so-called cold-fusion reactions. The smallness of the excitation energy of compound nuclei is the main advantage of cold-fusion reactions. However, the synthesis of SHEs of charge number in the region of Z ? 112 is strongly complicated in cold-fusion reactions by a sharp decrease in the cross section of a compound nucleus formation in the entrance channel because of superiority of quasifission in the competition with complete fusion. Two favorable circumstances contributed to the success of the experiments aimed at the synthesis of the Z = 113-118 elements and performed at the Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research: large cross sections for the production of a compound nucleus, which are characteristic of hot-fusion reactions, and an increase in the fission barrier for nuclei toward the stability island. The factor that complicates the formation of a compound nucleus in cold-fusion reactions is discussed.

Nasirov, A. K.; Muminov, A. I.; Giardina, G.; Mandaglio, G.

2014-07-01

162

Synthesis, characterization, and reaction chemistry of tert-butyl hypofluorite  

SciTech Connect

tert-Butyl hypofluorite ((CH[sub 3])[sub 3]COF) can be synthesized by the low-temperature reaction of elemental fluorine with tert-butyl alcohol dissolved in propionitrile or acetonitrile. The isolated compound, which melts around -94[degrees]C and has an extrapolated boiling point of about +40[degrees]C, has been characterized by mass, NMR, and IR spectrometry. The [sup 19]F NMR shift of +67 ppm lies between the corresponding shifts of HOF and CH[sub 3]OF and implies a rather high O-F bond energy. Although sterically crowded, tert-butyl hypofluorite adds to olefins to form [beta]-fluoro-tert-butoxy compounds. Addition is mainly in an anti mode, and the regioselectivity corresponds to the action of a hitherto unknown tert-butoxylium electrophile. Also formed are adducts containing F and CH[sub 2]CN, the latter deriving from the acetonitrile solvent. 19 refs., 1 tab.

Appelman, E.H.; French, D. (Argonne National Lab., IL (United States)); Mishani, E.; Rozen, S. (Tel-Aviv Univ. (Israel))

1993-02-24

163

Template-Based Synthesis: Polymerase Chain Reaction (PCR)  

NSDL National Science Digital Library

In this activity, by the Concord Consortium's Molecular Literacy project, students learn that "it is difficult, if not practically impossible, for organisms to create a polymer without some guiding template molecule. DNA is then discussed as an example and the basics of DNA replication are explored." Upon completion of this activity students should be able to demonstrate how using a template is an efficient way to create a molecule of specific sequence; discuss the basic mechanism of how DNA replicates; and apply their knowledge of DNA replication to the Polymerase Chain Reaction procedure. The activity itself is a java-based interactive resource built upon the free, open source Molecular Workbench software. In the activity, students are allowed to explore at their own pace in a digital environment full of demonstrations, illustrations, and models they can manipulate. In addition to the activity, visitors will find an overview of the activity, a test and rubric, central concepts, and their correlation to AAAS standards.

2008-10-17

164

In situ X-ray diffraction study of reduction processes of Fe{sub 3}O{sub 4}- and Fe{sub 1-x}O-based ammonia-synthesis catalysts  

SciTech Connect

The temperature-programmed reduction process of two types of industrial ammonia-synthesis catalysts, A110 and ZA-5, which are, respectively, based on Fe{sub 3}O{sub 4} and Fe{sub 1-x}O precursors, were studied by in situ X-ray power diffraction (XRD). It has been found that the ZA-5 has lower reduction temperature and faster reduction rate, and its active phase alpha-Fe possesses a higher value of lattice microstrain than A110. The simulation based on Rietveld refinement has also shown that the shape of alpha-Fe grain of ZA-5 has a mixed shape of cube and sphere with more exposing (111) and (211) planes, while that of A110 looks like a concave cube with more exposing (110) planes. Based on the results obtained, a growth model of alpha-Fe during the reduction of Fe{sub 3}O{sub 4}- and Fe{sub 1-x}O-based ammonia-synthesis catalysts is proposed, and the origins for the activity difference has been also discussed. - Graphical Abstract: A proposed growth model of active phase alpha-Fe during reduction. Due to H{sub 2} diffusing easily into the pores, reduction starts on outside and inside surface simultaneously to form 'microcrystalline film', and the particles shrink during reduction which results in breaking of the aggregated oxide particle.

Zheng Yifan, E-mail: zhengyifan@zjut.edu.c [College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014 (China); Catalysis Institute, Zhejiang University of Technology, Hangzhou 310014 (China); Liu Huazhang; Liu Zongjian; Li Xiaonian [College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014 (China); Catalysis Institute, Zhejiang University of Technology, Hangzhou 310014 (China)

2009-09-15

165

Pyrrolo-dC oligonucleotides bearing alkynyl side chains with terminal triple bonds: synthesis, base pairing and fluorescent dye conjugates prepared by the azide-alkyne "click" reaction.  

PubMed

5-(Octa-1,7-diynyl)-2'-deoxyuridine was converted into the furano-dU derivative 7 by copper-catalyzed cyclization; the pyrolodC-derivative 3 was formed upon ammonolysis. The bicyclic nucleosides 3 and 7 as well as the corresponding non-cyclic precursors 4 and 6 all containing terminal C[triple bond]C bonds were conjugated with the non-fluorescent 3-azido-7-hydroxycoumarin 5 employing the copper(I)-catalyzed Huisgen-Sharpless-Meldal cycloaddition "click reaction". Strongly fluorescent 1H-1,2,3-triazole conjugates (30-33) are formed incorporating two fluorescent reporters-the pyrdC nucleoside and the coumarin moiety. Oligonucleotides incorporating 6-alkynyl and 6-alkyl 7H-pyrrolo[2,3-d]pyrimidin-2(3H)-one nucleosides (3 and 2f) have been prepared by solid-phase synthesis using the phosphoramidite building blocks 10 and 13 ; the pyrrolo-dC oligonucleotides are formed during ammonia treatment. The duplex stability of oligonucleotides containing 3 and related derivatives was studied. Oligonucleotides with terminal triple bonded nucleosides such as 3 are more stabilizing than those lacking a side chain with terminal unsaturation; open-chain derivatives (4) are even more efficient. The click reaction was also performed on oligonucleotides containing the pyrdC-derivative and the fluorescence properties of nucleosides, oligonucleotides and their coumarin conjugates were studied. PMID:18421402

Seela, Frank; Sirivolu, Venkata Ramana

2008-05-01

166

Low-cost anodes for ammonia electrooxidation  

NASA Astrophysics Data System (ADS)

This research focused on the development of low-cost electrodes for the electrochemical oxidation of ammonia to nitrogen, a reaction that has possible applications in hydrogen generation, direct ammonia fuel cells, water treatment, and sensors. Statistical design of experiments was used to help develop an efficient and scalable process for electrodeposition of platinum with a specific electrochemical surface area of over 25 m2 /g. Catalyst surface area and activity were evaluated using cyclic voltammetry, and the material microstructure and morphology were investigated using x-ray diffraction and scanning electron microscopy. The synthesized electrodes were found to be active toward the ammonia electrooxidation reaction, particularly when supporting electrolyte was added. However, supporting electrolyte was not required in order to oxidize the ammonia. As proof of concept, a homemade direct ammonia fuel cell employing a commercial anion exchange membrane was tested at room temperature with gravity-fed fuel and without supporting electrolyte. At room temperature, with passive reactant supply and using dissolved oxygen at the cathode, the cell produced about one quarter the power of a direct methanol fuel cell that used active transport of humidified oxygen and preheated (50 °C) methanol. With continued development of the membrane, cathode and membrane electrode assembly, the passive direct ammonia fuel cell using anion exchange membrane could have performance similar to the equivalent direct methanol fuel cell, and it could benefit from many advantages of ammonia over methanol such as lower cost, higher energy density, and reduced greenhouse gas emissions.

Selverston, Steven M.

167

Unified synthesis of quinone sesquiterpenes based on a radical decarboxylation and quinone addition reaction.  

PubMed

A unified synthesis of several quinone sesquiterpenes is described herein. Essential to this strategy is a novel radical addition reaction that permits the attachment of a fully substituted bicyclic core 16 to a variably substituted quinone 10. The addition product 15 can be further functionalized, giving access to natural products with a high degree of oxygenation at the quinone unit. The quinone addition reaction is characterized by excellent chemoselectivity, taking place only at conjugated and unsubstituted double bonds, and regioselectivity, being strongly influenced by the resonance effect of heteroatoms located on the quinone ring. These features were successfully applied to the synthesis of avarol (1), avarone (2), methoxyavarones (4, 5), ilimaquinone (6), and smenospongidine (7), thereby demonstating the synthetic value of this new method. PMID:12371868

Ling, Taotao; Poupon, Erwan; Rueden, Erik J; Kim, Sun H; Theodorakis, Emmanuel A

2002-10-16

168

Concise Synthesis of Guanidine-Containing Heterocycles Using the Biginelli Reaction  

PubMed Central

Two general methods for the synthesis of 2-imino-5-carboxy-3,4-dihydropyrimidines were developed using the 3-component Biginelli reaction. The first method utilizes pyrazole carboxamidine, a ?-ketoester, and an aldehyde in an initial Biginelli reaction. After Boc protection, these products undergo aminolysis and acidic deprotection to generate 2-imino-5-carboxy-3,4-dihydropyrimidines in a 4-step sequence. The second method utilizes a triazone-protected guanidine, a ?-ketoester, and an aldehyde in a Biginelli reaction. Acidic cleavage of the triazone yields 2-imino-5-carboxy-3,4-dihydropyrimidines in a 2-step sequence. We also describe the further elaboration of several of these products using a tethered Biginelli reaction to give triazaacenaphthalene structures similar to those found in crambescidin and batzelladine alkaloids. PMID:16995677

Nilsson, Bradley L.; Overman, Larry E.

2008-01-01

169

Gold catalysis: one-pot alkylideneoxazoline synthesis/Alder-ene reaction.  

PubMed

Based on the gold-catalyzed synthesis of methyleneoxazolines, a one-pot combination with an Alder-ene reaction was developed. For azodicarboxylates, good to very good yields (51-99%) of the oxazolemethylhydrazinedicarboxylates were achieved with 3 mol% of the Gagosz catalyst, [Ph(3)PAuNTf(3)]. In a less-selective reaction, 4-phenyl-3H-1,2,4-triazol-3,5(4H)-dione gave lower yields (41-49%) of the corresponding oxazolemethylphenyltriazolidinediones. Overall, five new bonds were formed. Tetracyanoethylene afforded a cyclobutane derivative through a [2+2] cycloaddition reaction at -40 °C, but only 45% of the spiro compound was obtained. The less-readily available KITPHOS ligands on gold gave even higher yields at lower catalyst loadings (2 mol%), but longer reaction times were required. PMID:22434782

Hashmi, A Stephen K; Littmann, Anna

2012-06-01

170

Benzannulation via the Reaction of Ynamides and Vinylketenes. Application to the Synthesis of Highly Substituted Indoles  

PubMed Central

A two-stage “tandem strategy” for the synthesis of indoles with a high level of substitution on the six-membered ring is described. Benzannulation based on the reaction of cyclobutenones with ynamides proceeds via a cascade of four pericyclic reactions to produce multiply substituted aniline derivatives in which the position ortho to the nitrogen can bear a wide range of functionalized substituents. In the second stage of the tandem strategy, highly substituted indoles are generated via acid-, base-, and palladium-catalyzed cyclization and annulation processes. PMID:23952525

Lam, Tin Yiu; Wang, Yu-Pu

2013-01-01

171

Oxazoline-based organocatalyst for enantioselective strecker reactions: a protocol for the synthesis of levamisole.  

PubMed

A chiral oxazoline-based organocatalyst has been found to efficiently catalyze asymmetric Strecker reactions of various aromatic and aliphatic N-benzhydrylimines with trimethylsilyl cyanide (TMSCN) as a cyanide source at -20?°C to give ?-aminonitriles in high yield (96?%) with excellent chiral induction (up to 98?%?ee). DFT calculations have been performed to rationalize the enantioselective formation of the product with the organocatalyst in these reactions. The organocatalyst has been characterized by single-crystal X-ray diffraction analysis, as well as by other analytical methods. This protocol has been extended to the synthesis of the pharmaceutically important drug molecule levamisole in high yield and with high enantioselectivity. PMID:24009109

Sadhukhan, Arghya; Sahu, Debashis; Ganguly, Bishwajit; Khan, Noor-ul H; Kureshy, Rukhsana I; Abdi, Sayed H R; Suresh, E; Bajaj, Hari C

2013-10-11

172

Synthesis, reactions and antimicrobial activities of 8-ethoxycoumarin derivatives.  

PubMed

Condensation of 3-acetyl-8-ethoxycoumarin (3) with thiosemicarbazide gave ethylidenehydrazinecarbothioamide 5, which was transformed into the thiazolidin-4-one derivatives 6,7. Interaction of 3 with DMF/POCl(3) gave b-chloroacroline derivative 8. Treatment of 3 with malononitrile gave benzo[c]chromone and 2-aminobenzonitrile derivatives 9 and 10, respectively with respect to the reaction conditions. Condensation of 3-(2-bromoacetyl)-8-ethoxycoumarin (4) with o-phenylenediamine gave 3-(quioxaline-2-yl)-8-ethoxycoumarin hydrobromide (11), while 4 reacted with 2-aminopyridine to give chromenopyridopyrimidine derivative 12. Condensation of 4 with potassium thio-cyanate/methanol gave an unexpected derivative, 2H-chromeno-3-carboxy(methyl-carbonimidic)thioanhydride 16, which upon treatment with (NH(2))(2)·H(2)O gave 3-ethoxy-2-hydroxybenzaldehyde azine 19. Interaction of 4 with thiourea derivatives gave thiazole derivatives 20a-c. The structures of the newly synthesized compounds were confirmed by their spectra data. The newly synthesized compounds were also screened for their antimicrobial activity. PMID:22258342

Mohamed, Hany M; Abd El-Wahab, Ashraf H F; Ahmed, Kamal A; El-Agrody, Ahmed M; Bedair, Ahmed H; Eid, Fathy A; Khafagy, Mostafa M

2012-01-01

173

Stereoselective synthesis of caffeic acid amides via enzyme-catalyzed asymmetric aminolysis reaction.  

PubMed

In this study, a new method was developed to prepare enantiopure caffeic acid amides by enzyme-catalyzed asymmetric aminolysis reaction. Methoxymethyl chloride (MOMCl) was first introduced as a protective and esterified reagent to obtain the MOM-protected caffeic acid MOM ester 1d. Aminolysis reaction occurred between 1d and (R, S)-?-phenylethylamine in the presence of an immobilized lipase (Novozym 435) from Candida antarctica. Compared with the methyl-protected caffeic acid methyl ester 1c, 1d as substrate improved the lipase-catalyzed reaction rate by 5.5-fold. After Novozym 435-catalyzed aminolysis reaction was established, we evaluated the effects of synthesis parameters on the catalytic activity and enantioselectivity of Novozym 435. A reaction conversion rate of 25.5% and an E value of >100 were achieved under the following optimum conditions: reaction solvent, anhydrous isooctane; reaction temperature, 70°C; reaction time, 24h; ester-to-amine substrate molar ratio, 1:40; and enzyme additive amount, 40 mg. Kinetic and thermodynamic analyses were conducted to determine the main factors affecting enantiomeric discrimination. Novozym 435 still showed 80% of its initial activity after recycling five times. Highly optically pure caffeic acid amides with an enantiomeric excess of 98.5% were finally obtained by HCl deprotection. The established enzyme-catalyzed asymmetric aminolysis method in this study might be used to prepare other caffeic acid amides. PMID:24056082

Xiao, Peiliang; Zhang, Suoqin; Ma, Huayu; Zhang, Aijun; Lv, Xiaoli; Zheng, Liangyu

2013-12-01

174

Enzymatic synthesis of ?-xylanase substrates: transglycosylation reactions of the ?-xylosidase from Aspergillus sp  

Microsoft Academic Search

A ?-d-xylosidase with molecular mass of 250±5 kDa consisting of two identical subunits was purified to homogeneity from a cultural filtrate of Aspergillus sp. The enzyme manifested high transglycosylation activity in transxylosylation with p-nitrophenyl ?-d-xylopyranoside (PNP-X) as substrate, resulting in regio- and stereoselective synthesis of p-nitrophenyl (PNP) ?-(1?4)-d-xylooligosaccharides with dp 2–7. All transfer products were isolated from the reaction mixtures

Elena V Eneyskaya; Harry Brumer; Leon V Backinowsky; Dina R Ivanen; Anna A Kulminskaya; Konstantin A Shabalin; Kirill N Neustroev

2003-01-01

175

Mechanism of zeolite synthesis from coal fly ash by alkali hydrothermal reaction  

Microsoft Academic Search

To clarify the mechanism of zeolite synthesis from coal fly ash, the hydrothermal reaction was carried out in various alkali solutions. Zeolite was synthesized in an 800-cm3 autoclave under the condition of 393 K and 100 g\\/400 cm3 of solid–liquid ratio. The changes in various physical and chemical properties, such as crystal structure, surface structure and cation exchange capacity, of

Norihiro Murayama; Hideki Yamamoto; Junji Shibata

2002-01-01

176

Asymmetric synthesis of congested spiro-cyclopentaneoxindoles via an organocatalytic cascade reaction.  

PubMed

Starting from simple alkylidene oxindoles and nitroketones, a highly stereoselective methodology was developed for the synthesis of spiro-cyclopentaneoxindoles with four consecutive stereogenic centers. Using an organocatalytic cascade of Michael and aldol reactions in the presence of a chiral thiourea catalyst products were obtained in moderate to high yields and excellent enantioselectivities. Nitro, ester, and hydroxyl groups were introduced to the spiro ring, which could be used to facilitate further functionalization of the products. PMID:23879690

Noole, Artur; Ilmarinen, Kaja; Järving, Ivar; Lopp, Margus; Kanger, Tõnis

2013-08-16

177

Hydrothermal synthesis of vanadium nitride and modulation of its catalytic performance for oxygen reduction reaction.  

PubMed

A creative hydrothermal synthesis method followed by calcination for vanadium nitride (VN) is reported. The oxygen reduction reaction (ORR) study of the catalyst shows that VN possesses a comparable catalytic performance to commercial Pt/C catalyst. The ORR catalytic activity study of vanadium nitride, vanadium carbonitride, and vanadium carbide reveals that tuning anions offers a promising route for the activity enhancement of the non-precious metal catalysts. PMID:25029261

Huang, Taizhong; Mao, Shun; Zhou, Guihua; Wen, Zhenhai; Huang, Xingkang; Ci, Suqin; Chen, Junhong

2014-08-21

178

A Review of Study on Thermal Energy Transport System by Synthesis and Decomposition Reactions of Methanol  

NASA Astrophysics Data System (ADS)

The study on thermal energy transport system by synthesis and decomposition reactions of methanol was reviewed. To promote energy conservation and global environment protection, a two-step liquid-phase methanol synthesis process, which starts with carbonylation of methanol to methyl formate, then followed by the hydrogenolysis of the formate, was studied to recover wasted or unused discharged heat from industrial sources for the thermal energy demands of residential and commercial areas by chemical reactions. The research and development of the system were focused on the following three points. (1) Development of low-temperature decomposition and synthetic catalysts, (2) Development of liquid phase reactor (heat exchanger accompanying chemical reaction), (3) Simulation of the energy transport efficiency of entire system which contains heat recovery and supply sections. As the result of the development of catalyst, promising catalysts which agree with the development purposes for the methyl formate decomposition reaction and the synthetic reaction are being developed though some studies remain for the methanol decomposition and synthetic reactions. In the fundamental development of liquid phase reactor, the solubilities of CO and H2 gases in methanol and methyl formate were measured by the method of total pressure decrease due to absorption under pressures up to 1500kPa and temperatures up to 140°C. The diffusivity of CO gas in methanol was determined by measuring the diameter and solution time of single CO bubbles in methanol. The chemical reaction rate of methanol synthesis by hydrogenolysis of methyl formate was measured using a plate-type of Raney copper catalyst in a reactor with rectangular channel and in an autoclave reactor. The reaction characteristics were investigated by carrying out the experiments at various temperatures, flow rates and at various catalyst development conditions. We focused on the effect of Raney copper catalyst thickness on the liquid-phase chemical reaction by varying the development time of the catalyst. Investigation results of the catalyst such as surface area, pore radius, lattice size, and photographs of scanning electron microscope (SEM) were also given. In the simulation of energy transport efficiency of this system, by simulating the energy transfer system using two-step liquid phase methanol decomposition and synthetic reactions, and comparing with the technology so far, it can be expected that an innovative energy transfer system is possible to realize.

Liu, Qiusheng; Yabe, Akira; Kajiyama, Shiro; Fukuda, Katsuya

179

"Fragments of Fullerenes and Carbon Nanotubes: Designed Synthesis, Unusual Reactions, and Coordination Chemistry", John Wiley & Sons, 2011  

E-print Network

"Fragments of Fullerenes and Carbon Nanotubes: Designed Synthesis, Unusual Reactions the surfaces of fullerenes (and therefore often referred to as "fullerene fragments" or buckybowls covers all aspects related to the fullerene and nanotube fragment chemistry: current synthetic techniques

Linsley, Braddock K.

180

1,3-Dipolar cycloaddition reactions of nitrile oxides in the synthesis of natural compounds and their analogues  

NASA Astrophysics Data System (ADS)

The published data on the use of 1,3-dipolar cycloaddition reactions of nitrile oxides in the synthesis of natural compounds and their analogues are systematised and reviewed. The bibliography includes 145 references.

Kotyatkina, Anna I.; Zhabinsky, Vladimir N.; Khripach, Vladimir A.

2001-08-01

181

Formal synthesis of kingianin A based upon a novel electrochemically-induced radical cation Diels-Alder reaction.  

PubMed

The application of electrochemical reactions in natural product synthesis has burgeoned in recent years. We herein report a formal synthesis of the complex and dimeric natural product kingianin A, which employs an electrochemically-mediated radical cation Diels-Alder cycloaddition as the key step. PMID:25196219

Moore, Jonathan C; Davies, E Stephen; Walsh, Darren A; Sharma, Pallavi; Moses, John E

2014-10-25

182

Applied reaction dynamics: Efficient synthesis gas production via single collision partial oxidation of methane to CO on Rh,,111...  

E-print Network

to syn- thesis gas syngas , CO and H2, ideally in a 1:2 ratio. This is also a desirable feedstockApplied reaction dynamics: Efficient synthesis gas production via single collision partial dissociation. These results demonstrate the efficient conversion of methane to synthesis gas, CO+2H2

Sibener, Steven

183

Polybromocyclopentadienes in the diene synthesis reaction. VI. The reactivity of hexabromo- and 5,5-dimethoxytetrabromo-1,3-cyclopentadienes in the diene synthesis reaction with bismaleimides  

SciTech Connect

The adducts from the diene condensation of hexabromo- and 5,5-dimethoxytetrabromo-1,3-cyclopentadienes with bismaleimides were obtained and characterized. The reactivity of hexabromo- and 5,5-dimethoxytetrabromo-1,3-cyclopentadienes in the diene synthesis reactions with bismaleimides and with the monoadducts 1,4,5,6,7,7-hexabromo- and 1,4,5,6-tetrabromo-7,7-dimethoxybicyclo-(2.2.1)-hept-5-ene-2,3-dicarboximides was studied. In these reactions hexabromo-1,3-cyclopentadiene acts as diene-acceptor, while 5,5-dimethoxytetrabromo-1,3-cyclopentadiene acts as diene-donor. It is suggested that the reactivity of the addends in the investigated reaction series depends not only on their donor-acceptor characteristics but also on the localization energy. The IR spectra of the adducts were recorded in Vaseline oil on a UR-20 spectrophotometer. The PMR spectra were measured on a Tesla BS-487B instrument at 80 MHz with DMFA-d/sub 7/ as solvent and TMS as internal standard.

Mustafaev, A.M.; Guseinov, M.M.; Gasanova, K.M.; Gadzhieva, S.T.

1987-10-10

184

Highly enantioselective organocatalytic trifluoromethyl carbinol synthesis--a caveat on reaction times and product isolation.  

PubMed

Aldol reactions with trifluoroacetophenones as acceptors yield chiral ?-aryl, ?-trifluoromethyl tertiary alcohols, valuable intermediates in organic synthesis. Of the various organocatalysts examined, Singh's catalyst [(2S)-N-[(1S)-1-hydroxydiphenylmethyl-3-methylbutyl]-2-pyrrolidinecarboxamide] was found to efficiently promote this organocatalytic transformation in a highly enantioselective manner. Detailed reaction monitoring ((19)F-NMR, HPLC) showed that, up to full conversion, the catalytic transformation proceeds under kinetic control and affords up to 95% ee in a time-independent manner. At longer reaction times, the catalyst effects racemization. For the product aldols, even weak acids (such as ammonium chloride) or protic solvents, can induce racemization, too. Thus, acid-free workup, at carefully chosen reaction time, is crucial for the isolation of the aldols in high (and stable) enantiomeric purity. As evidenced by (19)F-NMR, X-ray structural analysis, and independent synthesis of a stable intramolecular variant, Singh's catalyst reversibly forms a catalytically inactive ("parasitic") intermediate, namely a N,O-hemiacetal with trifluoroacetophenones. X-ray crystallography also allowed the determination of the product aldols' absolute configuration (S). PMID:22631871

Duangdee, Nongnaphat; Harnying, Wacharee; Rulli, Giuseppe; Neudörfl, Jörg-M; Gröger, Harald; Berkessel, Albrecht

2012-07-11

185

Enzymatic synthesis of aroma compound xylosides using transfer reaction by Trichoderma longibrachiatum xylanase.  

PubMed

Enzymatic synthesis of aroma compound xylosides was performed by Trichoderma longibrachiatum xylanase. Information concerning the nature of xylosides present in the reaction medium was obtained by GC-EI-MS, by GC-NCI-MS of TFA derivatives, and by positive FAB-MS of the reaction mixtures. Moreover, the structures of isolated benzyl beta-D-xylopyranoside and 4-O-beta-xylopyranosyl-beta-D-xylopyranoside were established by (1)H and (13)C NMR and heteronuclear two-dimensional ((1)H-(13)C) chemical shift correlation. The results obtained for hexyl and benzyl alcohol xylosides indicated that a reaction implying a transfer of one to two or three xylose units from xylan was involved. The enzyme was able to recognize xylobiose, xylotriose, and xylan as xylose donors. Benzyl xyloside, produced independently of xylobioside and xylotrioside, was found as the major kinetic product of the reaction. Benzyl xyloside was produced in higher quantities and at a higher rate than that obtained for the di- and trixyloside derivatives. The maximum production for benzyl xyloside, 1.29 g/L, was obtained in the presence of hexane (50%) used as cosolvent. Xylosides and xylobiosides of several aroma compounds, (Z)-hex-3-en-1-ol, heptan-2-ol, geraniol, nerol, and citronellol, were synthesized in different amounts, from 850 mg/L for (Z)-hex-3-en-1-yl xylosides to 1.5 mg/L for citronellyl xylosides. No synthesis occurred when menthol, linalool, and eugenol were used as acceptors. PMID:12236678

Kadi, Nadia; Belloy, Laurence; Chalier, Pascale; Crouzet, Jean Claude

2002-09-25

186

Reaction calorimetry study of the liquid-phase synthesis of tert-butyl methyl ether  

SciTech Connect

The liquid-phase addition of methanol to isobutene to give tert-butyl methyl ether (MTBE) on the ion-exchange resin Lewatit K2631 has been studied in a calorimetric reactor. Heat capacity of MTBE and enthalpy of the MTBE synthesis reaction in the temperature range 312--333 K have been determined. MTBE heat capacity in the liquid phase has been found to obey the equation c[sub P] (J/mol[center dot]K) = 472.34 [minus] 2.468(T/K) + 0.005071(T/K)[sup 2]. At 298 K the standard molar reaction enthalpy is [Delta]H[degree] = [minus]33.8 kJ/mol. A method to estimate apparent activation energies from heat flow rate in a given reaction has been developed and proved to be valid for the MTBE synthesis. Using this method, an apparent activation energy of 91.1--95.2 kJ/mol is calculated. A [minus]3.8 kJ/mol value has been found for the adsorption enthalpy of methanol on the ion-exchange resin Lewatit K2631 by a combination of reaction calorimetry and thermogravimetry. This allows the calculation of an activation energy on the gel phase of the resin of 91 kJ/mol.

Sola, L.; Pericas, M.A.; Cunill, F.; Iborra, M. (Univ. de Barcelona (Spain). Dept. d'Enginyeria Quimica)

1994-11-01

187

Formation of ammonia and hydrazine from the reactions of acids with bis(dinitrogen) complexes of molybdenum. Identification and isolation of intermediates. Possible analogy with the hydrazine-forming property of nitrogenase  

SciTech Connect

The reactions of anhydrous HBr and HCl with trans-(Mo(N/sub 2/)/sub 2/(triphos)(PR/sub 3/)), where triphos = PhP(CH/sub 2/CH/sub 2/PPh/sub 2/)/sub 2/(PR/sub 3/ = PPh/sub 3/(1), PMePh/sub 2/ (2)), in tetrahydrofuran (THF) solution to produce ammonia and in benzene solution to produce hydrazine and ammonia have been examined. Complex 1 reacted with HBr in THF to produce 1.5 mol of N/sub 2//mol of 1 and routinely ca. 0.72 mol of NH/sub 3//mol of 1, respectively, and MoBr/sub 3/(triphos) (greater than or equal to94% yield). No more than a trace of hydrazine was detected. Total nitrogen balance was increased to 100% when amounts of HBr were added periodically during the reaction. The reaction of 1 or 2 with HBr or HCl led to the rapid loss of 1 mol of N/sub 2/ and the formation of a pair of isomeric hydrazido(2-) complexes, (MoX(NNH/sub 2/)(triphos)(PR/sub 3/))X (PR/sub 3/ = PPh/sub 3/ for 1 A(X) and 1 B(X), PPh/sub 2/Me for 2A(X) and 2B(X); X = Br, Cl). The same mixtures were formed in the absence of solvent. The presence of two isomers was the result of the position of the phenyl group on the central phosphorus atom of the triphos ligand relative to the hydrazido(2-) ligand. 48 references, 3 figures, 3 tables.

Baumann, J.A.; Bossard, G.E.; George, T.A.; Howell, D.B.; Koczon, L.M.; Lester, R.K.; Noddings, C.M.

1985-10-23

188

Methanol synthesis on ZnO(0001¯). IV. Reaction mechanisms and electronic structure.  

PubMed

Methanol synthesis from CO and H2 over ZnO, which requires high temperatures and high pressures giving rise to a complex interplay of physical and chemical processes over this heterogeneous catalyst surface, is investigated using ab initio simulations. The redox properties of the surrounding gas phase are known to directly impact on the catalyst properties and thus, set the overall catalytic reactivity of this easily reducible oxide material. In Paper III of our series [J. Kiss, J. Frenzel, N. N. Nair, B. Meyer, and D. Marx, J. Chem. Phys. 134, 064710 (2011)] we have qualitatively shown that for the partially hydroxylated and defective ZnO(0001¯) surface there exists an intricate network of surface chemical reactions. In the present study, we employ advanced molecular dynamics techniques to resolve in detail this reaction network in terms of elementary steps on the defective surface, which is in stepwise equilibrium with the gas phase. The two individual reduction steps were investigated by ab initio metadynamics sampling of free energy landscapes in three-dimensional reaction subspaces. By also sampling adsorption and desorption processes and thus molecular species that are in the gas phase but close to the surface, our approach successfully generated several alternative pathways of methanol synthesis. The obtained results suggest an Eley-Rideal mechanism for both reduction steps, thus involving "near-surface" molecules from the gas phase, to give methanol preferentially over a strongly reduced catalyst surface, while important side reactions are of Langmuir-Hinshelwood type. Catalyst re-reduction by H2 stemming from the gas phase is a crucial process after each reduction step in order to maintain the catalyst's activity toward methanol formation and to close the catalytic cycle in some reaction channels. Furthermore, the role of oxygen vacancies, side reactions, and spectator species is investigated and mechanistic details are discussed based on extensive electronic structure analysis. PMID:25273464

Frenzel, Johannes; Marx, Dominik

2014-09-28

189

Methanol synthesis on ZnO(000overline{1}). IV. Reaction mechanisms and electronic structure  

NASA Astrophysics Data System (ADS)

Methanol synthesis from CO and H2 over ZnO, which requires high temperatures and high pressures giving rise to a complex interplay of physical and chemical processes over this heterogeneous catalyst surface, is investigated using ab initio simulations. The redox properties of the surrounding gas phase are known to directly impact on the catalyst properties and thus, set the overall catalytic reactivity of this easily reducible oxide material. In Paper III of our series [J. Kiss, J. Frenzel, N. N. Nair, B. Meyer, and D. Marx, J. Chem. Phys. 134, 064710 (2011)] we have qualitatively shown that for the partially hydroxylated and defective ZnO(000overline{1}) surface there exists an intricate network of surface chemical reactions. In the present study, we employ advanced molecular dynamics techniques to resolve in detail this reaction network in terms of elementary steps on the defective surface, which is in stepwise equilibrium with the gas phase. The two individual reduction steps were investigated by ab initio metadynamics sampling of free energy landscapes in three-dimensional reaction subspaces. By also sampling adsorption and desorption processes and thus molecular species that are in the gas phase but close to the surface, our approach successfully generated several alternative pathways of methanol synthesis. The obtained results suggest an Eley-Rideal mechanism for both reduction steps, thus involving "near-surface" molecules from the gas phase, to give methanol preferentially over a strongly reduced catalyst surface, while important side reactions are of Langmuir-Hinshelwood type. Catalyst re-reduction by H2 stemming from the gas phase is a crucial process after each reduction step in order to maintain the catalyst's activity toward methanol formation and to close the catalytic cycle in some reaction channels. Furthermore, the role of oxygen vacancies, side reactions, and spectator species is investigated and mechanistic details are discussed based on extensive electronic structure analysis.

Frenzel, Johannes; Marx, Dominik

2014-09-01

190

E1 reaction-induced synthesis of hydrophilic oxide nanoparticles in a non-hydrophilic solvent  

NASA Astrophysics Data System (ADS)

In this paper, tert-amyl alcohol was employed to directly react with metal chlorides for the preparation of oxide nanoparticles. Some typical metal oxide or hydroxides with different morphologies, such as TiO2 nanoparticles, TiO2 nanorods, FeOOH nanowires, Fe2O3 nanoparticles, and SnO2 nanoparticles, can be easily fabricated through such simple chemical reactions. E1 reaction was found to play the leading role in the synthesis of metal oxides attributed to better stability of tertiary carbocations in tert-amyl alcohol and the strong interaction of metal chlorides with hydroxyl groups that results in the easy dissociation of carbon-oxygen bonds in tert-amyl alcohol. SN1 reaction can also occur in certain reactions due to nucleophilic substitution of chloride ions for hydroxyl groups. As-prepared metal oxides show good compatibility with an aqueous system while they were synthesized in a non-hydrophilic solvent probably attributed to the specific E1 reaction mechanism involving the generation of water, and can be directly incorporated into an aqueous soluble polymer, such as PVA, to exhibit many promising applications.In this paper, tert-amyl alcohol was employed to directly react with metal chlorides for the preparation of oxide nanoparticles. Some typical metal oxide or hydroxides with different morphologies, such as TiO2 nanoparticles, TiO2 nanorods, FeOOH nanowires, Fe2O3 nanoparticles, and SnO2 nanoparticles, can be easily fabricated through such simple chemical reactions. E1 reaction was found to play the leading role in the synthesis of metal oxides attributed to better stability of tertiary carbocations in tert-amyl alcohol and the strong interaction of metal chlorides with hydroxyl groups that results in the easy dissociation of carbon-oxygen bonds in tert-amyl alcohol. SN1 reaction can also occur in certain reactions due to nucleophilic substitution of chloride ions for hydroxyl groups. As-prepared metal oxides show good compatibility with an aqueous system while they were synthesized in a non-hydrophilic solvent probably attributed to the specific E1 reaction mechanism involving the generation of water, and can be directly incorporated into an aqueous soluble polymer, such as PVA, to exhibit many promising applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr32255b

Hu, Ming-Jun; Gao, Jiefeng; Yang, Shiliu; Dong, Yucheng; Ping Wong, Julia Shuk; Xu, Jiaju; Shan, Guangcun; Li, Robert K. Y.

2012-09-01

191

Tandem reactions initiated by copper-catalyzed cross-coupling: a new strategy towards heterocycle synthesis.  

PubMed

Copper-catalyzed cross-coupling reactions which lead to the formation of C-N, C-O, C-S and C-C bonds have been recognized as one of the most useful strategies in synthetic organic chemistry. During past decades, important breakthroughs in the study of Cu-catalyzed coupling processes demonstrated that Cu-catalyzed reactions are broadly applicable to a variety of research fields related to organic synthesis. Representatively, employing these coupling transformations as key steps, a large number of tandem reactions have been developed for the construction of various heterocyclic compounds. These tactics share the advantages of high atom economics of tandem reactions as well as the broad tolerance of Cu-catalyst systems. Therefore, Cu-catalyzed C-X (X = N, O, S, C) coupling transformation-initiated tandem reactions were quickly recognized as a strategy with great potential for synthesizing heterocyclic compounds and gained worldwide attention. In this review, recent research progress in heterocycle syntheses using tandem reactions initiated by copper-catalyzed coupling transformations, including C-N, C-O, C-S as well as C-C coupling processes are summarized. PMID:21879127

Liu, Yunyun; Wan, Jie-Ping

2011-10-21

192

Synthesis of functionalized chromans by PnBu3-catalyzed reactions of salicylaldimines and salicylaldehydes with allenic ester.  

PubMed

P(n)Bu(3)-catalyzed cyclization reactions of salicylaldimines and salicylaldehydes with ethyl 2,3-butadienoate gave the corresponding functionalized chromans in moderate to good yields in THF under mild conditions. The new reaction provides a new method for the synthesis of biologically active chroman products. PMID:21070027

Sun, Yin-Wei; Guan, Xiao-Yang; Shi, Min

2010-12-17

193

Organocatalytic Asymmetric Synthesis of Functionalized 1,3,5-Triarylpyrrolidin-2-ones via an Aza-Michael/Aldol Domino Reaction  

PubMed Central

The organocatalytic asymmetric synthesis of functionalized 1,3,5-triarylpyrrolidin-2-ones bearing three contiguous stereocenters through an aza-Michael/aldol domino reaction of ?-ketoamides with ?,?-unsaturated aldehydes is described. The domino products were further derivatized by aldehyde olefination under one-pot conditions. The reaction proceeds with excellent diastereoselectivities (>20:1) and good to excellent enantioselectivities (60–96% ee).

Joie, Celine; Deckers, Kristina; Enders, Dieter

2014-01-01

194

Palladium- and copper-mediated N-aryl bond formation reactions for the synthesis of biological active compounds.  

PubMed

N-Arylated aliphatic and aromatic amines are important substituents in many biologically active compounds. In the last few years, transition-metal-mediated N-aryl bond formation has become a standard procedure for the introduction of amines into aromatic systems. While N-arylation of simple aromatic halides by simple amines works with many of the described methods in high yield, the reactions may require detailed optimization if applied to the synthesis of complex molecules with additional functional groups, such as natural products or drugs. We discuss and compare in this review the three main N-arylation methods in their application to the synthesis of biologically active compounds: Palladium-catalysed Buchwald-Hartwig-type reactions, copper-mediated Ullmann-type and Chan-Lam-type N-arylation reactions. The discussed examples show that palladium-catalysed reactions are favoured for large-scale applications and tolerate sterically demanding substituents on the coupling partners better than Chan-Lam reactions. Chan-Lam N-arylations are particularly mild and do not require additional ligands, which facilitates the work-up. However, reaction times can be very long. Ullmann- and Buchwald-Hartwig-type methods have been used in intramolecular reactions, giving access to complex ring structures. All three N-arylation methods have specific advantages and disadvantages that should be considered when selecting the reaction conditions for a desired C-N bond formation in the course of a total synthesis or drug synthesis. PMID:21286396

Fischer, Carolin; Koenig, Burkhard

2011-01-01

195

Total synthesis of Elisabethin A: intramolecular Diels-Alder reaction under biomimetic conditions.  

PubMed

We describe the first total synthesis of the marine diterpenoid elisabethin A. The synthesis uses (S)-hydroxy-2-methyl-propionate as the chiral starting material, which is elaborated into a dienyl-iodide and added to an aryl acetic acid ester via enolate alkylation. The hydroquinoid system is oxidized to the quinone which serves as the dienophile in a highly stereocontrolled intramolecular Diels-Alder addition. This IMDA reaction, which to our knowledge is the first one to employ a terminal (Z)-diene, proceeds under biomimetic conditions (water, ferrichloride as the oxidant, room temperature) with high yield and stereoselectivity. The Diels-Alder adduct is transformed into the natural product via a three-step sequence including selective hydrogenation, base-catalyzed epimerization of the cis- into the trans-decalin system and O-demethylation. PMID:12696865

Heckrodt, Thilo J; Mulzer, Johann

2003-04-23

196

Comparison of solid-state reaction and modified citrate process for Bi-2212 ceramics synthesis  

NASA Astrophysics Data System (ADS)

Bi 2Sr 2CaCu 2O 8+ d (Bi-2212) superconductive ceramics powders were prepared using a modified citrate process which consists in forming powders from a gel. The obtained powders were characterised by X-ray diffraction and scanning electronic microscopy in order to determine their phase purity and their microstructure. Dilatometric tests have been carried out to study the sintering behaviour. The magnetic and resistivity curves of the investigated compositions will be also discussed. The obtained results were systematically confronted with the ones obtained from powders synthesized by the conventional solid-state reaction in the same conditions of temperature and calcination time. It has been found that the densification of Bi-2212 is very weak during sintering whatever the synthesis process. In both cases the critical temperature was determined approximately at 80 K but the comparison shows that the modified citrate process is an interesting way of elaboration in terms of purity, homogeneity and synthesis time.

Pignon, B.; Veron, E.; Noudem, J.; Ruyter, A.; Ammor, L.; Monot-Laffez, I.

2006-02-01

197

Sources of atmospheric ammonia  

NASA Technical Reports Server (NTRS)

The information available on factors that influence emissions from the principal societal sources of ammonia to the atmosphere, namely combustion processes, volatilization of farm animal wastes, and volatilization of fertilizers, is reviewed. Emission factors are established for each major source of atmospheric ammonia. The factors are then multiplied by appropriate source characterization descriptors to obtain calculated fluxes of ammonia to the atmosphere on a state-by-state basis for the United States.

Harriss, R. C.; Michaels, J. T.

1982-01-01

198

Catalytic Reaction Synthesis for the Partial Oxidation of Methane to Formaldehyde.  

NASA Astrophysics Data System (ADS)

Catalytic reaction synthesis for the partial oxidation of methane to formaldehyde has been studied by combining microkinetic analysis with molecular orbital calculations. This strategy is used to establish microscopic correlations between the structure and composition of the active site and the kinetic parameters of the reaction mechanism. Using atom clusters to represent the active site of transition metal oxide catalysts, the relationship was probed between coordination number, oxidation state, and ionization potential of the active cation and the reaction steps of methane activation and surface reactions leading to formaldehyde formation. The analysis suggests that in transition metal oxide catalysts, the d-band orbitals of the metal cation should be empty, since otherwise CO_2 formation from CO oxidation will be excessive. Furthermore, the transition metal oxide d-band must be located at sufficiently low energy that it may accept electrons during methane activation. Oxygen O- species, representing vacancies in the 2p cluster band, will favor methane activation. However, clusters with fully occupied 2p bands (O^ {2-}^ecies) will favor formaldehyde production. Such inferences illustrate how experimental and theoretical information already incorporated into an existing microkinetic model for the reaction over V _2O_5 and MoO _3 catalysts can be extended to describe the reaction over new materials in the search for more active and selective catalysts. Using parameters estimated from the molecular orbital calculations, microkinetic reaction simulations were also shown to be useful to identify reactor operating conditions that may favor the production of formaldehyde. The simulation can be used to identify key experiments necessary to test the performance of postulated catalytic materials. The economic evaluation of the process design sets important target goals for methane conversion and formaldehyde selectivity that a catalytic material must satisfy to create a new process that is industrially competitive with the established technologies for the production of formaldehyde. Elements of a clean manufacturing process with the new technology include two reactor stages and the use of unconverted methane as a fuel. The process economics demands certain reaction kinetic performance characteristics in new technologies, and cannot be ignored in the early stages of catalytic reaction synthesis.

Cardenas-Galindo, Maria-Guadalupe

199

Possibilities for synthesis of new isotopes of superheavy elements in fusion reactions  

NASA Astrophysics Data System (ADS)

Background. In the “cold” fusion reactions based on the use of lead and bismuth targets, the proton-rich isotopes of superheavy (SH) elements up to Z=113 have been produced. More neutron-rich isotopes of SH elements (up to Z=118) have been synthesized in “hotter” fusion reactions of 48Ca with actinide targets. ?-decay half-lives of different isotopes of the same SH elements (for example, 112) were found to vary by several orders of magnitude. This indicates strong shell effects in this area of the nuclear map. The understanding of these effects and other properties of SH nuclei is strongly impeded by the absence of experimental data on decay properties of the not-yet-synthesized isotopes of SH elements located between those produced in the “cold” fusion reactions and those produced in the “hot” fusion reactions and also by the yet missing neutron-enriched isotopes of these elements.Purpose. In this paper we search for the optimal fusion reactions which may be used to fill this gap of the nuclear map and significantly extend the area of known SH nuclei.Method. For the calculation of the cross sections we use the same approach which was employed earlier for successful predictions of all 48Ca induced fusion reactions.Results. Several fusion reactions of the stable projectiles 40Ar, 44Ca, and 48Ca with different isotopes of actinides (lighter and heavier than those that have been already utilized in the Dubna experiments) could be used for synthesis of new SH nuclei. Predicted cross sections for the production of new isotopes of SH nuclei were found to be quite large, and the corresponding experiments can be easily performed at existing facilities. For the first time a “narrow pathway” to the middle of the island of stability was found owing to possible ?+ decay of SH nuclei 291115 and 291114 which could be formed in ordinary fusion reactions.

Zagrebaev, V. I.; Karpov, A. V.; Greiner, Walter

2012-01-01

200

Biochemistry of Ammonia Monoxygenase from Nitrosomonas  

SciTech Connect

Major results. 1. CytochromecM552, a protein in the electron transfer chain to ammonia monooxygenase. Purification, modeling of protein structure based on primary structure, characterization of 4 hemes by magnetic spectroscopy, potentiometry, ligand binding and turnover. Kim, H. J., ,Zatsman, et al. 2008). 2. Characterization of proteins which thought to be involved in the AMO reaction or to protect AMO from toxic nitrogenous intermediates such as NO. Nitrosocyanin is a protein present only in bacteria which catalyze the ammonia monoxygenase reaction (1). Cytochrome c P460 beta and cytochrome c’ beta.

Alan Hooper

2009-07-15

201

Effect of Shock-Activation on Post-shock Reaction Synthesis of Ternary Ceramics  

NASA Astrophysics Data System (ADS)

The effects of shock-compression of powder precursors on subsequent reaction synthesis and formation of Ti3SiC2 and Ti2AlN ternary ceramics were investigated in this study. Mixtures of the powder precursors were shock-densified at different pressures using an 80-mm diameter gas gun and the double tube cylindrical implosion technique. Characterization of the shock-densified compacts showed an intimately mixed state of powders with high retained strain in unreacted compacts and little or no reaction at low pressures. The high pressure compact showed formation of non-stoichiometric TiC. The subsequent reaction behavior of the shock-densified compacts resulting in the formation of Ti3SiC2 was studied via heat treatments and differential thermal analysis (DTA). A non-stoichiometric TiCx phase was observed as an intermediate phase prior to the formation of Ti3SiC2. This paper will present the results of the effects of shock compression on the the reaction mechanisms and kinetics of reactions leading to the formation of the ternary ceramics in the shock-densified precursor powders.

Jordan, Jennifer L.; Thadhani, Naresh N.

2002-07-01

202

E1 reaction-induced synthesis of hydrophilic oxide nanoparticles in a non-hydrophilic solvent.  

PubMed

In this paper, tert-amyl alcohol was employed to directly react with metal chlorides for the preparation of oxide nanoparticles. Some typical metal oxide or hydroxides with different morphologies, such as TiO(2) nanoparticles, TiO(2) nanorods, FeOOH nanowires, Fe(2)O(3) nanoparticles, and SnO(2) nanoparticles, can be easily fabricated through such simple chemical reactions. E1 reaction was found to play the leading role in the synthesis of metal oxides attributed to better stability of tertiary carbocations in tert-amyl alcohol and the strong interaction of metal chlorides with hydroxyl groups that results in the easy dissociation of carbon-oxygen bonds in tert-amyl alcohol. S(N)1 reaction can also occur in certain reactions due to nucleophilic substitution of chloride ions for hydroxyl groups. As-prepared metal oxides show good compatibility with an aqueous system while they were synthesized in a non-hydrophilic solvent probably attributed to the specific E1 reaction mechanism involving the generation of water, and can be directly incorporated into an aqueous soluble polymer, such as PVA, to exhibit many promising applications. PMID:22990362

Hu, Ming-Jun; Gao, Jiefeng; Yang, Shiliu; Dong, Yucheng; Wong, Julia Shuk Ping; Xu, Jiaju; Shan, Guangcun; Li, Robert K Y

2012-10-21

203

Optimization of reaction conditions for enzymatic synthesis of palm fatty hydrazides using response surface methodology.  

PubMed

Optimization of the enzymatic synthesis of palm fatty hydrazide by the response surface methodology (RSM) was conducted using the Design-Expert 6 software. The palm fatty hydrazide was synthesized from refined, bleached and deodorized palm olein (RBDPOo) and neutralized hydrazine monohydrate in the presence of Rhizomucor miehei lipase, Lipozyme RMIM, an immobilized lipase in n-hexane. The reaction conditions such as the percentage of enzyme, reaction temperature, stirring speed and reaction time were selected as independent variables or studied factors, while the amount of crude palm fatty hydrazide obtained was selected as a dependent variable or response. The study was conducted using a central composite design (CCD) at five coded levels and the experimental data were analyzed using a quadratic model. The analysis of variance (ANOVA) indicates that the model was significant at 95% confidence level with Prob>F of 0.0033, where the regression coefficient value, R² was 0.8415 and lack-of-fit of 0.0984. A percentage of enzyme of 6%, a reaction temperature of 40°C, a stirring speed of 350 rpm and a reaction time of 18 h were found to be the optimum conditions for the conversion of RBDPOo into palm fatty hydrazide. PMID:22531058

Tuan Noor Maznee, T I; Hazimah, A H; Wan Zin, W Y

2012-01-01

204

Synthesis of 2,5-asymmetrically substituted 3,4-diaminothieno[2,3-b]thiophenes by domino reaction.  

PubMed

A convenient one pot synthesis of 2,5-asymmetrically substituted thieno[2,3-b]thiophenes is developed. The method is based on consecutive domino reactions (SN2 reaction ? Thorpe-Ziegler reaction) using malononitrile and carbon disulfide as starting materials with the generation of potassium 2,2-dicyanoethene-1,1-bis(thiolate) in a solution. The high yield of the target thienothiophenes was achieved using the Ziegler dilution effect. PMID:24028177

Zubarev, Andrey A; Larionova, Natalia A; Rodinovskaya, Lyudmila A; Mortikov, Valery Yu; Shestopalov, Anatoliy M

2013-10-14

205

One-Pot Protection-Glycosylation Reactions for Synthesis of Lipid II Analogues  

PubMed Central

(2,6-Dichloro-4-methoxyphenyl)(2,4-dichlorophenyl) methyl trichloroacetimidate (3) and its polymer-supported reagent 4 can be successfully applied to a one-pot protection-glycosylation reaction to form the disaccharide derivative 7d for the synthesis of lipid II analogues. The temporary protecting group or linker at the C-6 position and N-Troc protecting group of 7d can be cleaved simoultaneousely via a reductive condition. Overall yield of syntheses of lipid II, 1 and neryl-lipid II-N?-dansylthiourea are significantly improved via the described methods. PMID:24623584

Mitachi, Katsuhiko; Mohan, Priya; Siricilla, Shajila

2014-01-01

206

Vulcanism, mercury-sensitized photo-reactions and abiogenetic synthesis: a theoretical treatment.  

PubMed

Attention is called to the photodynamic and thermodynamic properties of Periodic Group IIb elements, most notably Hg, as they relate to ultra-violet sensitization in organic chemical reactions. The energy levels of 6(1) P1 and 6(3) P1 resonance states and the high vapor pressure ((greater than 10(-3) mm) of the metal at temperatures as low as 293 K bring Hg with the range of bond dissociation energies in most organic molecules and many inorganics. These capabilities considered together with recent evidence for Hg emission as a regular part of volcanic and geothermal processes provide the basis for our proposal that Hg-sensitized ultraviolet photo-reactions may have played a significant part in abiogenetic organic synthesis on the primative earth. PMID:1012707

Siegel, S M; Siegel, B Z

1976-08-01

207

Low-temperature synthesis of actinide tetraborides by solid-state metathesis reactions  

DOEpatents

The synthesis of actinide tetraborides including uranium tetraboride (UB.sub.4), plutonium tetraboride (PuB.sub.4) and thorium tetraboride (ThB.sub.4) by a solid-state metathesis reaction are demonstrated. The present method significantly lowers the temperature required to .ltoreq.850.degree. C. As an example, when UCl.sub.4 is reacted with an excess of MgB.sub.2, at 850.degree. C., crystalline UB.sub.4 is formed. Powder X-ray diffraction and ICP-AES data support the reduction of UCl.sub.3 as the initial step in the reaction. The UB.sub.4 product is purified by washing water and drying.

Lupinetti, Anthony J. (Los Alamos, NM); Garcia, Eduardo (Los Alamos, NM); Abney, Kent D. (Los Alamos, NM)

2004-12-14

208

Synthesis of Shape-Anisotropic Nanomaterials using Spontaneous Galvanic Displacement Reactions  

SciTech Connect

The direct synthesis of nanostructures using wet chemical reduction methods has had a major impact on catalysis and materials design. However, no mechanism has yet been reported that explicitly provides growth parameters for shapes and sizes as a function of desired metals, making it difficult to directly synthesize shaped particles from specific metals. There have been reports in the literature using this method to obtain core-shell, porous cage-like and irregular structures, however only one report proposing a mechanism of the displacement process exists, which does not explain surface and bulk morphology changes as a function of reaction condition. Here, we demonstrate the use of small angle x-ray scattering (SAXS), and microscopy to study the Ag-to-Pt displacement process of nanoparticles, nanowires and nanoplates at known intervals throughout the reaction. Obtaining a fundamental understanding of the displacement process will allow us to tune composition, morphology, and thus electronic properties of novel materials.

Leong, G. J.; Strand, M.; Schulze, M.; Maloney, D.; Larson, D.; Alia, S.; Perry, K.; Neyerlin, K. C.; Pivovar, B.; Wise, A. M.; Toney, M.; Richards, R. M.

2013-01-01

209

Origin of fatty acid synthesis - Thermodynamics and kinetics of reaction pathways  

NASA Technical Reports Server (NTRS)

The primitiveness of contemporary fatty acid biosynthesis was evaluated by using the thermodynamics and kinetics of its component reactions to estimate the extent of its dependence on powerful and selective catalysis by enzymes. Since this analysis indicated that the modern pathway is not primitive because it requires sophisticated enzymatic catalysis, an alternative pathway of primitive fatty acid synthesis is proposed that uses glycolaldehyde as a substrate. In contrast to the modern pathway, this primitive pathway is not dependent on an exogenous source of phosphoanhydride energy. Furthermore, the chemical spontaneity of its reactions suggests that it could have been readily catalyzed by the rudimentary biocatalysts available at an early stage in the origin of life.

Weber, Arthur L.

1991-01-01

210

The densities and reaction heat of methanol synthesis System from cornstalk syngas  

NASA Astrophysics Data System (ADS)

Methanol can be used as possibole replacement for conventional gasoline and Diesel fuel. In order to produce methanol, it is necessary to decompose biomass, including cornstalks, which is a raw material from agricultural residues. A promising route for processing cornstals is made cornstalks gasficated with thermochemical method to prepare the syngas, which has been conducted under a down-flow fixed bed gasifier. While the low-heat-value cornstalk gas produced in the down-flow fixed bed gasifier needs purified and a variety of technical procedures such as deoxygenation, desulfurization, catalytic cracking of tar and hydrogenation. In this paper, the catalytic experiments of methanol synthesis with cornstalk syngas were carried out in a tubular-flow integral and isothermal reactor. The effect of reaction temperature, pressure, catalyst types, catalyst particle size, syngas flow at entering end and composition of syngas was determind. The experimental results indicated that the proper catalyst of the synthetic reaction was C301 and the optimum catalyst size (?) was 0.833 mm×0.351 mm. The optimal operating temperature and pressure were found to be 235° C and 5 MPa, respectively. The suitable syngas flow 0.9-1.10 mol/h at entering end was selected and the suitable composition of syngas were CO 10.49%, CO28.8%, N237.32%, CnHm0.95% and H240.49%. The methanol yield is 0.418 g/g cornstalk. Moreover, the densities, state equation parameters and the total reaction heat ?HT,P, of methanol reacting system was calculated by SHBWR state equation under givern reaction pressure. The calculation results provided basic data for the design of the industrial equipments in which catalyzed synthesis of methanol from cornstalk gases is operated.

Zhu, Ling-feng; Zhao, Qing-ling; Chen, Jing; Zhang, Le; Zhang, Run-tao; Liu, Li-li; Zhang, Zhao-yue

2010-11-01

211

Assessing Ammonia Treatment Options  

EPA Science Inventory

This is the second of three articles to help water system operators understand ammonia and how to monitor and control its effects at the plant and in the distribution system. The first article (Opflow, April 2012) provided an overview of ammonia's chemistry, origins, and water sy...

212

Proline catalyzed ?-aminoxylation reaction in the synthesis of biologically active compounds.  

PubMed

The search for new and efficient ways to synthesize optically pure compounds is an active area of research in organic synthesis. Asymmetric catalysis provides a practical, cost-effective, and efficient method to create a variety of complex natural products containing multiple stereocenters. In recent years, chemists have become more interested in using small organic molecules to catalyze organic reactions. As a result, organocatalysis has emerged both as a promising strategy and as an alternative to catalysis with expensive proteins or toxic metals. One of the most successful and widely studied secondary amine-based organocatalysts is proline. This small molecule can catalyze numerous reactions such as the aldol, Mannich, Michael addition, Robinson annulation, Diels-Alder, ?-functionalization, ?-amination, and ?-aminoxylation reactions. Catalytic and enantioselective ?-oxygenation of carbonyl compounds is an important reaction to access a variety of useful building blocks for bioactive molecules. Proline catalyzed ?-aminoxylation using nitrosobenzene as oxygen source, followed by in situ reduction, gives enantiomerically pure 1,2-diol. This molecule can then undergo a variety of organic reactions. In addition, proline organocatalysis provides access to an assortment of biologically active natural products including mevinoline (a cholesterol lowering drug), tetrahydrolipstatin (an antiobesity drug), R(+)-?-lipoic acid, and bovidic acid. In this Account, we present an iterative organocatalytic approach to synthesize both syn- and anti-1,3-polyols, both enantio- and stereoselectively. This method is primarily based on proline-catalyzed sequential ?-aminoxylation and Horner-Wadsworth-Emmons (HWE) olefination of aldehyde to give a ?-hydroxy ester. In addition, we briefly illustrate the broad application of our recently developed strategy for 1,3-polyols, which serve as valuable, enantiopure building blocks for polyketides and other structurally diverse and complex natural products. Other research groups have also applied similar strategies to prepare such bioactive molecules as littoralisone, brasoside and (+)-cytotrienin A. Among the various synthetic approaches reported for 1,3-polyols, our organocatalytic iterative approach appears to be very promising and robust. This method combines the merit of organocatalytic reaction with an easy access to both enantiomerically pure forms of proline, mild reaction conditions, and tolerance to both air and moisture. In this Account, we present the latest applications of organocatalysis and how organic chemists can use this new tool for the total synthesis of complex natural products. PMID:23148510

Kumar, Pradeep; Dwivedi, Namrata

2013-02-19

213

Catalytic formation of monosaccharides: from the formose reaction towards selective synthesis.  

PubMed

The formose reaction (FR) has been long the focus of intensive investigations as a simple method for synthesis of complex biologically important monosaccharides and other sugar-like molecules from the simplest organic substrate-formaldehyde. The fundamental importance of the FR is predominantly connected with the ascertainment of plausible scenarios of chemical evolution which could have occurred on the prebiotic Earth to produce the very first molecules of carbohydrates, amino- and nucleic acids, as well as other vitally important substances. The practical importance of studies on the FR is the elaboration of catalytic methods for the synthesis of rare and non-natural monosaccharides and polyols. This Minireview considers the FR from the point of view of chemists working in the field of catalysis with emphasis on the mechanisms of numerous parallel and consequent catalytic transformations that take place during the FR. Based on its kinetics, the FR may be considered as a non-radical chain process with degenerate branching. The Minireview also considers different approaches to the control of selectivity of carbohydrate synthesis from formaldehyde and lower monosaccharides. PMID:24930572

Delidovich, Irina V; Simonov, Alexandr N; Taran, Oxana P; Parmon, Valentin N

2014-07-01

214

Ammonia - Did it have a role in chemical evolution. [abiogenesis  

NASA Technical Reports Server (NTRS)

The significance of ammonia in the chemical evolution related to the origin of life is evaluated. A computer program was employed to calculate the time needed for the decomposition of ammonia by means of a photochemical reaction. Various possible protection mechanisms for ammonia are discussed, giving attention to hydrogen sulfide, hydrogen, ozone, and CO. It is concluded that in the absence of a sufficiently high pressure of hydrogen, any ammonia present in the primitive atmosphere would have been decomposed by photolysis in a million years.

Ferris, J. P.; Nicodem, D. E.

1974-01-01

215

Excretory nitrogen metabolism and defence against ammonia toxicity in air-breathing fishes.  

PubMed

With the development of air-breathing capabilities, some fishes can emerge from water, make excursions onto land or even burrow into mud during droughts. Air-breathing fishes have modified gill morphology and morphometry and accessory breathing organs, which would tend to reduce branchial ammonia excretion. As ammonia is toxic, air-breathing fishes, especially amphibious ones, are equipped with various strategies to ameliorate ammonia toxicity during emersion or ammonia exposure. These strategies can be categorized into (1) enhancement of ammonia excretion and reduction of ammonia entry, (2) conversion of ammonia to a less toxic product for accumulation and subsequent excretion, (3) reduction of ammonia production and avoidance of ammonia accumulation and (4) tolerance of ammonia at cellular and tissue levels. Active ammonia excretion, operating in conjunction with lowering of ambient pH and reduction in branchial and cutaneous NH? permeability, is theoretically the most effective strategy to maintain low internal ammonia concentrations. NH? volatilization involves the alkalization of certain epithelial surfaces and requires mechanisms to prevent NH? back flux. Urea synthesis is an energy-intensive process and hence uncommon among air-breathing teleosts. Aestivating African lungfishes detoxify ammonia to urea and the accumulated urea is excreted following arousal. Reduction in ammonia production is achieved in some air-breathing fishes through suppression of amino acid catabolism and proteolysis, or through partial amino acid catabolism leading to alanine formation. Others can slow down ammonia accumulation through increased glutamine synthesis in the liver and muscle. Yet, some others develop high tolerance of ammonia at cellular and tissue levels, including tissues in the brain. In summary, the responses of air-breathing fishes to ameliorate ammonia toxicity are many and varied, determined by the behaviour of the species and the nature of the environment in which it lives. PMID:24438022

Chew, S F; Ip, Y K

2014-03-01

216

Synthesis and Biological Activities of 4-Aminoantipyrine Derivatives Derived from Betti-Type Reaction  

PubMed Central

The present work deals with the synthesis and evaluation of biological activities of 4-aminoantipyrine derivatives derived from a three-component Betti reaction. The synthesis was initiated by the condensation of aromatic aldehyde, 4-aminoantipyrine, and 8-hydroxyquinoline in presence of fluorite as catalyst in a simple one-step protocol. The reactions were stirred at room temperature for 10–15?min achieving 92–95% yield. The structures of synthesized derivatives were established on the basis of spectroscopic and elemental analysis. All derivatives 4(a–h) were screened in vivo and in vitro for anti-inflammatory and anthelmintic activity against a reference drug, Diclofenac and Albendazole, respectively. The screening results show that compounds 4c, 4d, 4f, and 4h were found to possess potential anti-inflammatory activity while compounds 4a, 4b, 4e, and 4g are potent anthelmintic agents when compared with reference drugs, respectively. The bioactivity of these derivatives has also been evaluated with respect to Lipinski's rule of five using molinspiration cheminformatics software. PMID:24955256

Meshram, Jyotsna

2014-01-01

217

Synthesis of nanocrystalline magnesium diboride (MgB 2) metallic superconductor by mechano-chemical reaction and post-annealing  

Microsoft Academic Search

MgB2 is recently discovered superconducting compound with a record-breaking transition temperature (Tc=39K) for a conventional metallic superconductor. Nanocrystallinity can improve its electrical properties by strong pinning. In the present work we report the results of the synthesis of nanocrystalline MgB2 superconducting compound by mechano-chemical reaction followed by post-annealing. The first stage of synthesis was carried out from elemental crystalline Mg

R. A. Varin; Ch. Chiu

2006-01-01

218

Regiocontrol by remote substituents. An enantioselective total synthesis of frenolicin B via a highly regioselective Diels-Alder reaction  

SciTech Connect

The quinone subunit is contained in a broad range of biologically important natural products such as frenolicin B, which is a member of the pyranonaphthoquinone family. The diverse biological activity of quinones has led to the development of several new synthetic methods for quinones. Among the pathways featuring a cycloaddition reaction, one of the most general methods for the regiospecific synthesis of substituted quinones was pioneered by H.J. Rapoport and others. This method involves the Diels-Alder reaction of a substituted quinone. As part of a program to evaluate the directing effects of functional groups not directly attached to the atoms undergoing Diels-Alder cycloaddition, we now report that remote substituents on a dienophile can confer excellent regioselectivity in Diels-Alder reactions. This work has led to an extremely direct synthesis of the pyranonaphthoquinone framework and to the first synthesis of frenolicin B (1). 19 refs., 1 fig.

Kraus, G.A.; Li, J. (Iowa State Univ., Ames (United States)); Gordon, M.S.; Jensen, J.H. (Ames Lab. US-DOE, IA (United States))

1993-06-30

219

Journey on greener pathways: from the use of alternate energy inputs and benign reaction media to sustainable applications of nano-catalysts in synthesis and environmental remediation  

EPA Science Inventory

Sustainable synthetic processes developed during the past two decades involving the use of alternate energy inputs and greener reaction media are summarized. These processes include examples of coupling reactions, the synthesis of heterocyclic compounds, and a variety of reactio...

220

An efficient synthesis of anhydrides of 2-monosubstituted succinic acid monoesters and their application to the Dakin–West reaction: Isolation of some 5-succinyloxyoxazole intermediates  

Microsoft Academic Search

A rapid and versatile synthesis of 2-monosubstituted monosuccinates and their bimolecular anhydrides is described. The reaction of these anhydrides with N-Fmoc-protected dipeptides under the modified Dakin–West reaction affords mainly the corresponding 5-succinyloxyoxazoles.

Joseph Richard Casimir; Laurent Ettouati; Joëlle Paris

1998-01-01

221

The Synthesis of "N"-Benzyl-2-Azanorbornene via Aqueous Hetero Diels-Alder Reaction: An Undergraduate Project in Organic Synthesis and Structural Analysis  

ERIC Educational Resources Information Center

The synthesis of "N"-benzyl-2-azanorbornene via aqueous hetero Diels-Alder reaction of cyclopentadiene and benzyliminium chloride formed in situ from benzylamine hydrochloride and formaldehyde is described. Characterization of the product was achieved by IR and NMR spectroscopies. The spectral data acquired are thoroughly discussed. Numerous…

Sauvage, Xavier; Delaude, Lionel

2008-01-01

222

Dynamic kinetic asymmetric synthesis of five contiguous stereogenic centers by sequential organocatalytic stetter and Michael-aldol reaction: enantioselective synthesis of fully substituted cyclopentanols bearing a quaternary stereocenter.  

PubMed

A synthesis of fully substituted cyclopentanes bearing a quaternary carbon center and five contiguous stereogenic centers has been achieved by sequential organocatalyzed Stetter and Michael-Aldol reactions of heteroaromatic aldehydes, nitroalkenes, and ?,?-unsaturated aldehydes via the [1 + 2 + 2] annulation strategy with dynamic kinetic asymmetric transformation and excellent enantioselectivities (up to >99% ee). PMID:21348455

Hong, Bor-Cherng; Dange, Nitin S; Hsu, Che-Sheng; Liao, Ju-Hsiou; Lee, Gene-Hsiang

2011-03-18

223

Molecular Structure of Ammonia  

NSDL National Science Digital Library

Ammonia is a non-ionic colorless gas at ambient temperatures and a hydrogen bonding liquid at 240 Kelvin that has the remarkable ability to dissolve alkali metals. Ammonia is a Lewis base and is readily absorbed by water to form small amounts of ammonium hydroxide (pKb = 4.74). Naturally, ammonia has its sources in the biosphere (the nitrogen cycle) and is a trace gas in air and a source of ammonium ions in rain and atmospheric aerosols. Ammonia is prepared industrially by the Haber-Bosch process in quantities exceeding 120 million metric tons per year. In this process, ammonia gas is formed when hydrogen and nitrogen (3:1) are compressed to pressures of 200 atm and passed over an iron catalyst at 380-450 degrees C. Much of the ammonia produced this way (85%) is used as fertilizers on crops, a significant portion of which leaches from croplands into streams causing nitrate pollution and eutrophication of waterways (e.g., dead-zone in the Gulf of Mexico). Other sources of ammonia include combustion (coal and biomass burning) and from bacterial decomposition of animal excreta.

2006-05-02

224

Ammonia Leak Locator Study  

NASA Technical Reports Server (NTRS)

The thermal control system of International Space Station Alpha will use liquid ammonia as the heat exchange fluid. It is expected that small leaks (of the order perhaps of one pound of ammonia per day) may develop in the lines transporting the ammonia to the various facilities as well as in the heat exchange equipment. Such leaks must be detected and located before the supply of ammonia becomes critically low. For that reason, NASA-JSC has a program underway to evaluate instruments that can detect and locate ultra-small concentrations of ammonia in a high vacuum environment. To be useful, the instrument must be portable and small enough that an astronaut can easily handle it during extravehicular activity. An additional complication in the design of the instrument is that the environment immediately surrounding ISSA will contain small concentrations of many other gases from venting of onboard experiments as well as from other kinds of leaks. These other vapors include water, cabin air, CO2, CO, argon, N2, and ethylene glycol. Altogether, this local environment might have a pressure of the order of 10(exp -7) to 10(exp -6) torr. Southwest Research Institute (SwRI) was contracted by NASA-JSC to provide support to NASA-JSC and its prime contractors in evaluating ammonia-location instruments and to make a preliminary trade study of the advantages and limitations of potential instruments. The present effort builds upon an earlier SwRI study to evaluate ammonia leak detection instruments [Jolly and Deffenbaugh]. The objectives of the present effort include: (1) Estimate the characteristics of representative ammonia leaks; (2) Evaluate the baseline instrument in the light of the estimated ammonia leak characteristics; (3) Propose alternative instrument concepts; and (4) Conduct a trade study of the proposed alternative concepts and recommend promising instruments. The baseline leak-location instrument selected by NASA-JSC was an ion gauge.

Dodge, Franklin T.; Wuest, Martin P.; Deffenbaugh, Danny M.

1995-01-01

225

Biotransformations Utilizing ?-Oxidation Cycle Reactions in the Synthesis of Natural Compounds and Medicines.  

PubMed

?-Oxidation cycle reactions, which are key stages in the metabolism of fatty acids in eucaryotic cells and in processes with a significant role in the degradation of acids used by microbes as a carbon source, have also found application in biotransformations. One of the major advantages of biotransformations based on the ?-oxidation cycle is the possibility to transform a substrate in a series of reactions catalyzed by a number of enzymes. It allows the use of sterols as a substrate base in the production of natural steroid compounds and their analogues. This route also leads to biologically active compounds of therapeutic significance. Transformations of natural substrates via ?-oxidation are the core part of the synthetic routes of natural flavors used as food additives. Stereoselectivity of the enzymes catalyzing the stages of dehydrogenation and addition of a water molecule to the double bond also finds application in the synthesis of chiral biologically active compounds, including medicines. Recent advances in genetic, metabolic engineering, methods for the enhancement of bioprocess productivity and the selectivity of target reactions are also described. PMID:23443116

Swizdor, Alina; Panek, Anna; Milecka-Tronina, Natalia; Ko?ek, Teresa

2012-01-01

226

Biotransformations Utilizing ?-Oxidation Cycle Reactions in the Synthesis of Natural Compounds and Medicines  

PubMed Central

?-Oxidation cycle reactions, which are key stages in the metabolism of fatty acids in eucaryotic cells and in processes with a significant role in the degradation of acids used by microbes as a carbon source, have also found application in biotransformations. One of the major advantages of biotransformations based on the ?-oxidation cycle is the possibility to transform a substrate in a series of reactions catalyzed by a number of enzymes. It allows the use of sterols as a substrate base in the production of natural steroid compounds and their analogues. This route also leads to biologically active compounds of therapeutic significance. Transformations of natural substrates via ?-oxidation are the core part of the synthetic routes of natural flavors used as food additives. Stereoselectivity of the enzymes catalyzing the stages of dehydrogenation and addition of a water molecule to the double bond also finds application in the synthesis of chiral biologically active compounds, including medicines. Recent advances in genetic, metabolic engineering, methods for the enhancement of bioprocess productivity and the selectivity of target reactions are also described. PMID:23443116

OEwizdor, Alina; Panek, Anna; Milecka-Tronina, Natalia; Kolek, Teresa

2012-01-01

227

Metal-ammonia reduction of triphenylene  

SciTech Connect

In the reaction of polynuclear aromatic hydrocarbons with alkali metals in liquid ammonia to produce hydroaromatics, it has been found that in certain instances protonation does not occur at the calculated position of highest electron density but rather at a position to produce the most stable monoanion. The isolation of a number of new and interesting hydrocarbons produced by this reaction are reported herein. UV- and NMR-spectral studies were used to determine the structures of the product compounds.

Marcinow, Z.; Sygula, A.; Rabideau, P.W.

1988-07-22

228

Synthesis of 1,2-disubstituted-3-alkylidenylpyrrolidines via a one-pot three-component reaction  

Microsoft Academic Search

Olsson’s three-component reaction of cyclopropylketones, aldehydes, and primary amines was investigated for application to parallel synthesis. Using an excess of Et2AlI at elevated temperatures, pyrrolidines 4, the initial products reported by Olsson and co-workers, could be completely converted to pyrrolium salts 5, by a reaction sequence involving a retro-aza-Michael addition followed by iminium salt formation. The pyrrolium salts 5 were

Wenwei Huang; Mary-Margaret O’Donnell; Grace Bi; Jifeng Liu; Libing Yu; Carmen M. Baldino; Andrew S. Bell; Toby J. Underwood

2004-01-01

229

The allenic Alder-ene reaction: constitutional group selectivity and its application to the synthesis of ovalicin  

Microsoft Academic Search

The scope of the novel allenic Alder-ene reaction using Rh(I) and Ir(I) catalysts has been extended to differentially substituted 1,1,3-trisubstituted allenes. This allenyl substitution pattern can give three possible cross-conjugated triene products. The selectivity of this transformation can be controlled by varying reaction temperature, solvent, and catalyst. Progress toward the synthesis of ovalicin using this triene forming protocol is described.

Kay M. Brummond; Jamie M. McCabe

2006-01-01

230

Nitrogenase switch-off by ammonia in Rhodopseudomonas palustris : Loss under nitrogen deficiency and independence from the adenylylation state of glutamine synthetase  

Microsoft Academic Search

Nitrogenase activity in Rhodopseudomonas palustris is subject to a rapid switch-off in response to exogenous ammonia. When cells were grown on limiting nitrogen and eventually became nitrogen deficient, nitrogenase synthesis was fully derepressed but the enzyme was insensitive to ammonia. The transformation of ammonia-sensitive to ammonia-insensitive cells was a slow, but fully reversible process. The switch-off effect in ammonia-sensitive cells

Kassem Alef; Daniel J. Arp; Walter G. Zumft

1981-01-01

231

Alternative E ammonia feedstock  

SciTech Connect

Power plants are using more Ammonia for increasing precipitator and baghouse efficiency, for SCR and SNCR processes, and for controlling acid stack plumes and dewpoint corrosion. These simple systems inject ammonia and air into the furnace or the precipitator or baghouse inlet ductwork. The common feedstocks in use today are Anhydrous ammonia [NH{sub 3}] and Aqueous ammonia [NH{sub 4}OH], both defined as poison gases by US authorities and most Western nations. Storage and handling procedures for these products are strictly regulated. Wilhelm Environmental Technologies Inc. is developing use of solid, formed or prilled Urea [CO(NH{sub 2}){sub 2}] as the feedstock. When heated in moist air, Urea sublimes to ammonia [NH{sub 3}] and carbon dioxide [CO{sub 2}]. Urea is stored and handled without restrictions or environmental concerns. Urea is a more expensive feedstock than NH{sub 3}, but much less expensive than [NH{sub 4}OH]. The design, and operating results, of a pilot system at Jacksonville Electric St. John's River Plant [Unit 2] are described. The pilot plant successfully sublimed Urea up to 100 pounds/hour. Further testing is planned. Very large ammonia use may favor NH{sub 3}, but smaller quantities can be produced at attractive prices with Urea based ammonia systems. Storage costs are far less. Many fluidized-bed boilers can use pastille or solid urea metered directly into the existing cyclones for NO{sub x} control. This is more economical than aqueous ammonia or aqueous urea based technology.

Lentz, M.J.; Wright, R.A. [Wilhelm Environmental Technologies, Indianapolis, IN (US)

1999-07-01

232

A concise synthesis of benzimidazoles via the microwave-assisted one-pot batch reaction of amino acids up to a 10-g scale.  

PubMed

An efficient method for the synthesis of aminomethyl benzimidazoles is developed by using a one-pot batch reaction between amino acids and o-phenylenediamines. This reaction proceeds smoothly in an unmodified household microwave oven, even though scale-up is to 10 g. A desirable method for the quick synthesis of benzimidazoles, which are used as a kind of important intermediates in drug synthesis, is provided by the scale-up utilization of amino acid resource. PMID:25030664

Peng, Pai; Xiong, Jin-Feng; Mo, Guang-Zhen; Zheng, Jia-Li; Chen, Ren-Hong; Chen, Xiao-Yun; Wang, Zhao-Yang

2014-10-01

233

Simultaneous Light-Directed Synthesis of Mirror-Image Microarrays in a Photochemical Reaction Cell with Flare Suppression  

PubMed Central

The use of photolabile protecting groups is a versatile and well-established means of synthesizing high complexity microarrays of biopolymers, such as nucleic acids and peptides, for high-throughput analysis. The synthesis takes place in a photochemical reaction cell which positions the microarray substrate at the focus of the optical system delivering the light and which can be connected to a fluidics system which delivers appropriate reagents to the surface in synchrony with the light exposure. Here we describe a novel photochemical reaction cell which allows for the simultaneous synthesis of microarrays on two substrates. The reaction cell positions both substrates within the limited depth-of-focus of the optical system while maintaining the necessary reagent flow conditions. The resulting microarrays are mirror images of each other but otherwise essentially identical. The new reaction cell doubles the throughput of microarray synthesis without increasing the consumption of reagents. In addition, a secondary flow chamber behind the reaction cell can be filled with an absorbent and index-matching fluid to eliminate reflections from light exiting the reaction cell assembly, greatly reducing unintended light exposure that reduces the sequence fidelity of the microarray probes. PMID:23968455

2013-01-01

234

Toward synthesis of third-generation spin-labeled podophyllotoxin derivatives using isocyanide multicomponent reactions.  

PubMed

Spin-labeled podophyllotoxins have elicited widespread interest due to their far superior antitumor activity compared to podophyllotoxin. To extend our prior studies in this research area, we synthesized a new generation of spin-labeled podophyllotoxin analogs via isocyanide multicomponent reactions and evaluated their cytotoxicity against four human cancer cell lines (A-549, DU-145, KB and KBvin). Most of the compounds exhibited potent cytotoxic activity against all four cell lines, notably against the drug resistant KBvin cancer cell line. Among the new analogs, compounds 12e (IC50: 0.60-0.75 ?M) and 12h (IC50: 1.12-2.03 ?M) showed superior potency to etoposide (IC50: 2.03 to >20 ?M), a clinically available anticancer drug. With a concise efficient synthesis and potent cytotoxic profiles, compounds 12e and 12h merit further development as a new generation of epipodophyllotoxin-derived antitumor clinical trial candidates. PMID:24553146

Kou, Liang; Wang, Mei-Juan; Wang, Li-Ting; Zhao, Xiao-Bo; Nan, Xiang; Yang, Liu; Liu, Ying-Qian; Morris-Natschke, Susan L; Lee, Kuo-Hsiung

2014-03-21

235

Three-component coupling reactions of arynes for the synthesis of benzofurans and coumarins.  

PubMed

The domino three-component coupling reaction of arynes with DMF and active methylenes or methines was studied as a highly efficient method for preparing heterocycles. Coumarin derivative 5 was formed when diethyl malonate (2) or ?-bromomalonate (3) were used as a C2-unit. In contrast, dihydrobenzofurans 7a and 7b were obtained by using ?-chloroenolates generated from ?-chloromalonates 4a and 4b and Et2Zn. The benzofuran 15a could be obtained by using ethyl iodoacetate (14) as a C1-unit. The one-pot conversion of dihydrobenzofurans 7a, 7b and 8a into benzofurans 15a and 15b was also studied. The direct synthesis of benzofuran 15b was achieved by using the active methine 18 having ketone and ester groups. PMID:24419139

Yoshioka, Eito; Kohtani, Shigeru; Miyabe, Hideto

2014-01-01

236

Palladium-catalyzed reactions in the synthesis of 3- and 4-substituted indoles. 4  

SciTech Connect

4-Bromo-1-tosylindole (1) was converted to tricyclic indole enone 11, a potential intermediate in the synthesis of tetracyclic ergot alkaloids, by a series of palladium-catalyzed processes. Attempts to construct the ergot D ring by the hetero-Diels-Alder reaction of enone 11 and 1-azabutadiene 12 produced not the expected (4 + 2) adduct 13 but the benz(cd)indoline derivative 14 resulting from attack of the aza diene at the indole 2-position. The thermodynamic stability of the naphthol nucleus makes enone 11 generally susceptible to attack at the indole 2-position, as evidenced by the attack of hydride and methyl cuprate nucleophiles at this portion forming indolines 16 and 17, respectively.

Hegedus, L.S.; Sestrick, M.R.; Michaelson, E.T.; Harrington, P.J. (Colorado State Univ., Fort Collins (USA))

1989-08-18

237

Synthesis of Diverse Heterocyclic Scaffolds via Tandem Additions to Imine Derivatives and Ring-Forming Reactions  

PubMed Central

A novel strategy has been developed for the efficient syntheses of diverse arrays of heterocyclic compounds. The key elements of the approach comprise a Mannich-type, multicomponent coupling reaction in which functionalized amines, aromatic aldehydes, acylating agents, and ?- and organometallic nucleophiles are combined to generate intermediates that are then further transformed into diverse heterocyclic scaffolds via a variety of cyclization manifolds. Significantly, many of these scaffolds bear functionality that may be exploited by further manipulation to create diverse collections of compounds having substructures found in biologically active natural products and clinically useful drugs. The practical utility of this strategy was exemplified by its application to the first, and extraordinarily concise synthesis of the isopavine alkaloid roelactamine. PMID:20625454

Sunderhaus, James D.; Dockendorff, Chris; Martin, Stephen F.

2009-01-01

238

Studies of stereocontrolled allylation reactions for the total synthesis of phorboxazole A  

PubMed Central

A highly convergent total synthesis of the potent anticancer agent (+)-phorboxazole A (1) is accomplished. Four components (3–6) are assembled with considerations for control of absolute and relative stereochemistry. Iterative asymmetric allylation methodology addresses key stereochemical features in the preparation of the 2,6-cis- and 2,6-trans-tetrahydropyranyl rings of the C3–C19 component (3). The stereocontrolled asymmetric allylation process is also used for development of the C28–C41 fragment (4). Novel Barbier coupling reactions of ?-iodomethyl oxazoles and related thiazoles are described with samarium iodide. The convergent assembly of components 4 and 5 features formation of the fully substituted C22–C26 pyran by intramolecular capture of an allyl cation intermediate with high facial selectivity, and further efforts lead to E-C19/C20 olefination. The synthesis culminates with use of a modified Julia olefination for attachment of the C42–C46 segment and subsequent late-stage macrocyclization by installation of the (Z)-C2/C3 ?,?-unsaturated lactone. PMID:15277662

Williams, David R.; Kiryanov, Andre A.; Emde, Ulrich; Clark, Michael P.; Berliner, Martin A.; Reeves, Jonathan T.

2004-01-01

239

Applications of Click Chemistry Reactions to the Synthesis of Functional Materials  

NASA Astrophysics Data System (ADS)

This body of work focuses on the production of functional materials using the most reliable carbon-hetoratom bond-forming processes available, which are widely termed "click chemistry" reactions in the literature. This focus on function is enabled by a basis in synthetic chemistry, and where appropriate, brings in techniques from the related fields of materials science and biology to address current needs in those areas. Chapter 1 concerns the in situ production of azide and alkyne-based click chemistry adhesive polymers. Screening of a library of multivalent azides and alkynes was accomplished on a custom-built highthroughput instrument and followed up on a lap-shear testing apparatus. The conductivity of composites made of the adhesive was also explored according to standard methods. The second and third chapters explore the synthesis and function of a family of related [3.3.1]-bicyclononane dichlorides, which we have termed "WCL" electrophiles, and their potential applications for surface functionalization, the synthesis of polycations, and candidate membrane disruptive compounds. The rates of consumption of dichlorides and hydrolysis of model compounds were also explored using NMR, GC-MS, and HPLC-based methods.

Accurso, Adrian A.

240

The synthesis and characterization of aluminum loaded SBA-type materials as catalyst for polypropylene degradation reaction  

Microsoft Academic Search

The performance of pure and aluminum containing SBA-type catalysts prepared using different aluminum sources and different Al\\/Si ratios were investigated in the polypropylene degradation reaction using a thermogravimetric analyzer. For the synthesis of catalysts, aluminum isopropoxide and aluminum sulphate were used as the aluminum sources. Synthesized materials had high surface areas and exhibited nitrogen adsorption isotherms of type IV. EDS

Zeynep Obal?; Naime Asl? Sezgi; Timur Do?u

241

Dual template synthesis of a highly mesoporous SSZ-13 zeolite with improved stability in the methanol-to-olefins reaction.  

PubMed

The dual template synthesis of zeolite SSZ-13 by use of trimethyl-adamantanammonium hydroxide and a diquaternary-ammonium mesoporogen induces considerable mesoporosity without impeding zeolite microporosity. The strongly improved accessibility of Brønsted sites in mesoporous SSZ-13 increases its stability during application as an acid catalyst in the methanol-to-olefins reaction. PMID:22896837

Wu, Leilei; Degirmenci, Volkan; Magusin, Pieter C M M; Szyja, Bart?omiej M; Hensen, Emiel J M

2012-10-01

242

Synthesis of biodiesel from a model waste oil feedstock using a carbon-based solid acid catalyst: Reaction and separation  

Microsoft Academic Search

A solid acid catalyst that can keep high activity and stability is necessary when low cost feedstocks are utilized for biodiesel synthesis because the reaction medium contains a large amount of water. Three solid acid catalysts were prepared by the sulfonation of carbonized vegetable oil asphalt and petroleum asphalt. The structure of these catalysts was characterized by a variety of

Qing Shu; Zeeshan Nawaz; Jixian Gao; Yuhui Liao; Qiang Zhang; Dezheng Wang; Jinfu Wang

2010-01-01

243

Ternary PtSnRhSnO2 nanoclusters: synthesis and electroactivity for ethanol oxidation fuel cell reaction  

E-print Network

Ternary PtSnRh­SnO2 nanoclusters: synthesis and electroactivity for ethanol oxidation fuel cell. Ethanol becomes an attractive fuel in the fuel cell reactions compared with methanol and hydrogen, because­4 A major impediment to the commercialization of ethanol fuel cell stacks is the difficulty in designing

Frenkel, Anatoly

244

Synthesis of BaZrO3 by a solid-state reaction technique using nitrate precursors  

E-print Network

Synthesis of BaZrO3 by a solid-state reaction technique using nitrate precursors Abdul-Majeed Azada of barium nitrate and zirconyl nitrate at 8008C up to 8 h. Simultaneous thermal analysis (TG-DTA) assisted

Azad, Abdul-Majeed

245

Selectivity engineered phase transfer catalysis in the synthesis of fine chemicals: reactions of p-chloronitrobenzene with sodium sulphide  

Microsoft Academic Search

Synthesis of chemicals from the same starting material wherein more than one step involving complex reactions are involved can be engineered to produce selectively the desired product by minimising both the by-product formation and separation stages. Several products of industrial importance can be produced from the same starting material by choosing proper conditions and nature and number of phases. The

Ganapati D Yadav; Yogeeta B Jadhav; Sonali Sengupta

2003-01-01

246

Nafion®-catalyzed microwave-assisted Ritter reaction: An atom-economic solvent-free synthesis of amides  

EPA Science Inventory

An atom-economic solvent-free synthesis of amides by the Ritter reaction of alcohols and nitriles under microwave irradiation is reported. This green protocol is catalyzed by solid supported Nafion®NR50 with improved efficiency and reduced waste production....

247

Photochemical Synthesis and Ligand Exchange Reactions of Ru(CO)[subscript 4] (Eta[superscript 2]-Alkene) Compounds  

ERIC Educational Resources Information Center

The photochemical synthesis and subsequent ligand exchange reactions of Ru(CO)[subscript 4] (eta[superscript2]-alkene) compounds has provided a novel experiment for upper-level inorganic chemistry laboratory courses. The experiment is designed to provide a system in which the changing electronic properties of the alkene ligands could be easily…

Cooke, Jason; Berry, David E.; Fawkes, Kelli L.

2007-01-01

248

A computational study of detoxification of lewisite warfare agents by British anti-lewisite: catalytic effects of water and ammonia on reaction mechanism and kinetics.  

PubMed

trans-2-Chlorovinyldichloroarsine (lewisite, L agent, Lew-I) acts as a blistering agents. British anti-lewisite (BAL, 2,3-dimercaptopropanol) has long been used as an L-agent antidote. The main reaction channels for the detoxification proceed via breaking of As-Cl bonds and formation of As-S bonds, producing stable, nontoxic ring product [(2-methyl-1,3,2-dithiarsolan-4-yl)methanol]. M06-2X/GENECP calculations have been carried out to establish the enhanced rate of detoxification mechanism in the presence of NH3 and H2O catalysts in both gas and solvent phases, which has been modeled by use of the polarized continuum model (PCM). In addition, natural bond orbital (NBO) and atoms in molecules (AIM) analysis have been performed to characterize the intermolecular hydrogen bonding in the transition states. Transition-state theory (TST) calculation establishes that the rates of NH3-catalyzed (2.88 × 10(-11) s(-1)) and H2O-catalyzed (2.42 × 10(-11) s(-1)) reactions are reasonably faster than the uncatalyzed detoxification (5.44 × 10(-13) s(-1)). The results obtained by these techniques give new insight into the mechanism of the detoxification process, identification and thermodynamic characterization of the relevant stationary species, the proposal of alternative paths on modeled potential energy surfaces for uncatalyzed reaction, and the rationalization of the mechanistic role played by catalysts and solvents. PMID:23540856

Sahu, Chandan; Pakhira, Srimanta; Sen, Kaushik; Das, Abhijit K

2013-04-25

249

Sodium dodecyl benzene sulfonate-assisted synthesis through a hydrothermal reaction  

SciTech Connect

Graphical abstract: Reaction of a SeCl{sub 4} aqueous solution with a NiCl{sub 2}·6H{sub 2}O aqueous solution in presence of sodium dodecyl benzene sulfonate (SDBS) as capping agent and hydrazine (N{sub 2}H{sub 4}·H{sub 2}O) as reductant, produces nanosized nickel selenide through a hydrothermal method. The effect of temperature, reaction time and amounts of reductant on the morphology, particle sizes of NiSe nanostructures has been investigated. Highlights: ? NiSe nanostructures were synthesized by hydrothermal method. ? A novel Se source was used to synthesize NiSe. ? SDBS as capping agent plays a crucial role on the morphology of products. ? A mixture of Ni{sub 3}Se{sub 2} and NiSe was prepared in the presence of 2 ml hydrazine. ? A pure phase of NiSe was prepared in the presence of 4 or 6 ml hydrazine. -- Abstract: The effects of the anionic surfactant on the morphology, size and crystallization of NiSe precipitated from NiCl{sub 2}·6H{sub 2}O and SeCl{sub 4} in presence of hydrazine (N{sub 2}H{sub 4}·H{sub 2}O) as reductant were investigated. The products have been successfully synthesized in presence of sodium dodecyl benzene sulfonate (SDBS) as surfactant via an improved hydrothermal route. A variety of synthesis parameters, such as reaction time and temperature, capping agent and amount of reducing agent have a significant effect on the particle size, phase purity and morphology of the obtained products. The sample size became bigger with decreasing reaction temperature and increasing reaction time. In the presence of 2 ml hydrazine, the samples were found to be the mixture of Ni{sub 3}Se{sub 2} and NiSe. With increasing the reaction time and amount of hydrazine a pure phase of hexagonal NiSe was obtained. X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) images indicate phase, particle size and morphology of the products. Chemical composition and purity of the products were characterized by X-ray energy dispersive spectroscopy (EDS). Photoluminescence (PL) was used to study the optical properties of NiSe samples.

Sobhani, Azam [Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P.O. Box 87317–51167, Islamic Republic of Iran (Iran, Islamic Republic of)] [Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P.O. Box 87317–51167, Islamic Republic of Iran (Iran, Islamic Republic of); Salavati-Niasari, Masoud, E-mail: salavati@kashanu.ac.ir [Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P.O. Box 87317–51167, Islamic Republic of Iran (Iran, Islamic Republic of) [Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P.O. Box 87317–51167, Islamic Republic of Iran (Iran, Islamic Republic of); Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box 87317–51167, Islamic Republic of Iran (Iran, Islamic Republic of)

2012-08-15

250

High-temperature slurry reactors for synthesis gas reactions. 1: Liquid thermal stability  

SciTech Connect

The use of slurry reactors has been limited to reactions that take place at temperatures below about 573 K because many of the liquids that have been used to suspend the solid catalyst are not stable above this temperature. The thermal stability of a number of organic liquids was evaluated at temperatures between 648 and 698 K and at H{sub 2} partial pressures of about 7 MPa. Certain saturated and partially-saturated, fused-ring compounds with no alkyl groups or bridges are quite stable at these conditions. Of the compounds tested, tetrahydronaphthalene, tetrahydroquinoline, and decahydronaphthalene were the most stable. Analysis of the liquids at the end of the thermal stability evaluation supports some speculation concerning possible degradation reactions. The motivation for this research was the desire to synthesize higher (C{sub 2}{minus}C{sub 6}) alcohols in a slurry reactor from a mixture of carbon monoxide (CO) and hydrogen (H{sub 2}), so-called synthesis gas. Alcohols such as isobutanol and isoamyl alcohol could be a source of the branched olefins that are needed to produce octane enhancers such as methyl tert-butyl ether (MTBE) and tert-amyl methyl ether (TAME).

Roberts, G.W.; Marquez, M.A.; McCutchen, M.S.; Haney, C.A. [North Carolina State Univ., Raleigh, NC (United States). Dept. of Chemical Engineering] [North Carolina State Univ., Raleigh, NC (United States). Dept. of Chemical Engineering; Shin, I.D. [Shaw Univ., Raleigh, NC (United States). Dept. of Chemistry] [Shaw Univ., Raleigh, NC (United States). Dept. of Chemistry

1997-10-01

251

Synthesis of heterogeneous catalysts with well shaped platinum particles to control reaction selectivity  

PubMed Central

Colloidal and sol-gel procedures have been used to prepare heterogeneous catalysts consisting of platinum metal particles with narrow size distributions and well defined shapes dispersed on high-surface-area silica supports. The overall procedure was developed in three stages. First, tetrahedral and cubic colloidal metal particles were prepared in solution by using a procedure derived from that reported by El-Sayed and coworkers [Ahmadi TS, Wang ZL, Green TC, Henglein A, El-Sayed MA (1996) Science 272:1924–1926]. This method allowed size and shape to be controlled independently. Next, the colloidal particles were dispersed onto high-surface-area solids. Three approaches were attempted: (i) in situ reduction of the colloidal mixture in the presence of the support, (ii) in situ sol-gel synthesis of the support in the presence of the colloidal particles, and (iii) direct impregnation of the particles onto the support. Finally, the resulting catalysts were activated and tested for the promotion of carbon–carbon double-bond cis-trans isomerization reactions in olefins. Our results indicate that the selectivity of the reaction may be controlled by using supported catalysts with appropriate metal particle shapes. PMID:18832170

Lee, Ilkeun; Morales, Ricardo; Albiter, Manuel A.; Zaera, Francisco

2008-01-01

252

Synthesis and Characterization of Isomaltulose-Derived Oligosaccharides Produced by Transglucosylation Reaction of Leuconostoc mesenteroides Dextransucrase.  

PubMed

This paper reports the efficient enzymatic synthesis of a homologous series of isomaltulose-derived oligosaccharides with degrees of polymerization ranging from 3 to 9 through the transglucosylation reaction using a dextransucrase from Leuconostoc mesenteroides B-512F. The total oligosaccharide yield obtained under optimal conditions was 41-42% (in weight with respect to the initial amount of isomaltulose) after 24-48 h of reaction. Nuclear magnetic resonance (NMR) structural characterization indicated that dextransucrase specifically transferred glucose moieties of sucrose to the C-6 of the nonreducing glucose residue of isomaltulose. Likewise, monitoring the progression of the content of each individual oligosaccharide indicated that oligosaccharide acceptor products of low molecular weight acted in turn as acceptors for further transglucosylation to yield oligosaccharides of a higher degree of polymerization. The produced isomaltulose-derived oligosaccharides can be considered as isomalto-oligosaccharides (IMOs) because they are linked by only ?-(1?6) bonds. In addition, having isomaltulose as the core structure, these IMO-like structures could possess appealing bioactive properties that could find potential applications as functional food ingredients. PMID:25175804

Barea-Alvarez, Montserrat; Benito, Maria Teresa; Olano, Agustín; Jimeno, Maria Luisa; Moreno, F Javier

2014-09-17

253

Memory of chirality (MOC) concept in imino-aldol reaction: enantioselective synthesis of ?,?-diamino esters and aziridines.  

PubMed

A simple strategy for the synthesis of chiral ?,?-diamino- and ?-amino,?-hydroxy ester derivatives in high yields with moderate to high ee has been developed via asymmetric imino-aldol and aldol reactions, respectively, starting from protected aminoesters employing memory of chirality concept for chiral induction. This strategy has been extended for the enantioselective synthesis of aziridines (ee up to 92%). The absolute configuration of the imino-aldol adducts has been determined. The stereochemical outcome of the products has been explained by a suitable mechanism and supported by computational studies. PMID:23320819

Ghorai, Manas K; Ghosh, Koena; Yadav, A K; Nanaji, Y; Halder, Sandipan; Sayyad, Masthanvali

2013-03-15

254

Application of the sila-Friedel-Crafts reaction to the synthesis of ?-extended silole derivatives and their properties.  

PubMed

The intramolecular sila-Friedel-Crafts reaction was developed as a new method for the construction of a dibenzosilole skeleton. This reaction proceeds under mild conditions to afford the target in relatively good yield, indicating its availability as a versatile synthetic method. This reaction can be applied to the synthesis of ?-extended silole derivatives such as ladder-type silafluorene 8 and spiro-type silabifluorene 9. Furthermore, the synthesis of two-dimensionally extended silole derivatives utilizing the sila-Friedel-Crafts reaction as the multiple intramolecular cyclization was achieved, including the first synthesis of trisilasumanene 18. The X-ray crystallographic analysis of trisilasumanene 18 demonstrated the planarity in the main ?-framework, in contrast to sumanene and its sulfur analogue, trithiasumanene, bearing the bowl-shaped structures. In the UV-vis absorption spectra, the absorption bands of triphenylenosiloles 18 and 19 were slightly red-shifted compared to that of hexabutoxytriphenylene 22. The weak absorption bands were also observed in the longer-wavelength region in 18 and 19, which is derived from ?*-?* conjugation of the silole skeletons. In addition, 18 and 19 showed the blue fluorescence in dichloromethane and in the solid state. PMID:20830392

Furukawa, Shunsuke; Kobayashi, Junji; Kawashima, Takayuki

2010-10-21

255

Sugar-Driven Prebiotic Synthesis of 3,5(6)-Dimethylpyrazin-2-one: A Possible Nucleobase of a Primitive Replication Process  

Microsoft Academic Search

Reaction of glyceraldehyde with alanine amide (or ammonia) under anaerobic aqueous conditions yielded 3,5(6)-dimethylpyrazin-2-one\\u000a that is considered a possible complementary residue of a primitive replicating molecule that preceded RNA. Synthesis of the\\u000a dimethylpyrazin-2-one isomers under mild aqueous conditions (65°C, pH 5.5) from 100 mM glyceraldehyde and alanine amide (or\\u000a ammonia) was complete in about 5 days. This synthesis using 25 mM glyceraldehyde and alanine

Arthur L. Weber

2008-01-01

256

Facile synthesis of dispirooxindole-fused heterocycles via domino 1,4-dipolar addition and Diels-Alder reaction of in situ generated Huisgen 1,4-dipoles.  

PubMed

A facile synthetic protocol was developed for the efficient synthesis of complex dispirooxindole-fused heterocycles via a three-component reaction. The key strategies involve a domino 1,4-dipolar addition and Diels-Alder reaction of the in situ generated Huisgen 1,4-dipoles from the addition reaction of 4-dimethylaminopyridine with acetylenedicarboxylate to 3-phenacylideneoxindole. PMID:23050691

Sun, Jing; Sun, Yan; Gong, Hui; Xie, Ya-Jing; Yan, Chao-Guo

2012-10-19

257

Preventing Theft of Anhydrous Ammonia  

E-print Network

Anhydrous ammonia is widely used as a fertilizer. The theft of anhydrous ammonia for use in producing illegal drugs is a growing problem. This publication describes how thieves operate and how farmers and agricultural dealers can protect themselves...

Smith, David

2004-09-16

258

Synthesis of Unsymmetrical Diarylureas via Pd-Catalyzed C–N Cross-Coupling Reactions  

E-print Network

A facile synthesis of unsymmetrical N,N?-diarylureas is described. The utilization of the Pd-catalyzed arylation of ureas enables the synthesis of an array of diarylureas in good to excellent yields from benzylurea via a ...

Breitler, Simon

259

Endothermic reactors for an ammonia based thermochemical solar energy storage and transport system  

Microsoft Academic Search

The ammonia dissociation reaction is one of a number of reactions which has been investigated for use in closed loop solar thermochemical energy storage systems, over a period of nearly two decades. A recent series of experiments with an electrically heated high pressure ammonia dissociation reactor has validated a two dimensional pseudo-homogenous theoretical reactor model, established rate parameters for the

K. Lovegrove; A. Luzzi

1996-01-01

260

Synthesis and crossover reaction of TEMPO containing block copolymer via ROMP.  

PubMed

We report on the block copolymerization of two structurally different norbornene monomers (±)-endo,exo-bicyclo[2.2.1]-hept-5-ene-2,3-dicarboxylic acid dimethylester (7), and (±)-endo,exo-bicyclo[2.2.1]-hept-5-ene-2,3-dicarboxylic acid bis(1-oxyl-2,2,6,6-tetramethyl-piperidin-4-yl) ester (9) using ruthenium based Grubbs' type initiators [(PCy?)?Cl?Ru(benzylidene)] G1 (PCy? = tricyclohexylphosphine), [(H?IMes)(PCy?)Cl?Ru(benzylidene)] G2 (H?IMes = 1,3-bis(mesityl)-2-imidazolidinylidene), [(H?IMes)(py)?Cl?Ru(benzylidene)] G3 (py = pyridine or 3-bromopyridine) and Umicore type initiators [(PCy?)?Cl?Ru(3-phenylinden-1-ylidene)] U1 (PCy?= tricyclohexylphosphine), [(H?IMes)(PCy?)Cl?Ru(3-phenylinden-1-ylidene)] U2 (H?IMes = 1,3-bis(mesityl)-2-imidazolidinylidene), [(H?IMes)(py)Cl?Ru(3-phenylinden-1-ylidene)] U3 (py = pyridine or 3-bromopyridine) via ring opening polymerization (ROMP). The crossover reaction and the polymerization kinetics were investigated using matrix assisted laser desorption ionization mass spectroscopy (MALDI-TOF) and nuclear magnetic resonance (NMR), respectively. MALDI showed that there was a complete crossover reaction after the addition of 25 equivalents of the second monomer. NMR investigation showed that U3 gave a faster rate of polymerization in comparison to U1. The synthesis of block copolymers with molecular weights up to M(n) = 31 000 g/mol with low polydispersities (M(w)/M(n) = 1.2) is reported. PMID:20625541

Adekunle, Olubummo; Tanner, Susanne; Binder, Wolfgang H

2010-01-01

261

Synthesis of primary amides via copper-catalyzed aerobic decarboxylative ammoxidation of phenylacetic acids and ?-hydroxyphenylacetic acids with ammonia in water.  

PubMed

A Cu2O-catalyzed aerobic oxidative decarboxylative ammoxidation to primary benzamides from phenylacetic acids and ?-hydroxyphenylacetic acids is developed. A variety of primary benzamides could be prepared smoothly, in good to excellent yields, by means of a one-pot domino protocol combining decarboxylation, dioxygen activation, oxidative C-H bond functionalization, and amidation reactions. PMID:24397736

Song, Qiuling; Feng, Qiang; Yang, Kai

2014-01-17

262

Ammonia Can Crush  

Microsoft Academic Search

When a 12-oz aluminum soft drink can filled with ammonia or hydrogen chloride gas is inverted and dipped into water, the rapidly dissolving gas evacuates the can and the can is crushed before water can be drawn into it. This demonstrates, among other things, the remarkable strength of hydrogen bonds.

Ed Vitz; Daniel T. Haworth

1999-01-01

263

Ammonia Can Crush  

NASA Astrophysics Data System (ADS)

When a 12-oz aluminum soft drink can filled with ammonia or hydrogen chloride gas is inverted and dipped into water, the rapidly dissolving gas evacuates the can and the can is crushed before water can be drawn into it. This demonstrates, among other things, the remarkable strength of hydrogen bonds.

Vitz, Ed

1999-07-01

264

Tandem multicomponent reactions toward the design and synthesis of novel antibacterial and cytotoxic motifs.  

PubMed

The synthesis of polysubstituted imidazopyridines and imidazopyrazines through the orthogonal union of Groebke-Blackburn and Ugi reactions is described. These motifs were produced efficiently in a tandem operation without intermediate isolation. The synthesized scaffolds were biologically evaluated and found to possess potent anticancer and anti bacterial activities. Importantly, some of these motifs (e.g. compound 5) were found to possess specific anti-breast cancer activity against MCF7 cell line and others (e.g. compound 15) possess specific effects against melanoma cancer cell line (M8). Interestingly, the introduction of imidazobenzothiazole framework produced compounds with potent anti cancer activities (e.g. compounds 29 and 33) in vitro. Interestingly, many of synthesized compounds displayed potent and broad spectrum antibacterial activity against hospital-resistant clinical isolates namely, Escherichia coli, Klebsiellapneuomoniae, Staph. epidermidis, Ps. aeruginosa and Proteus vulgaris. Furthermore, many of the synthesized motifs were found to effective against Gram positive methicillin-sensitive Staphylococcus aureus (MMSA; ATCC 25923), andmethicillin-resistant Staphylococcus aureus (MRSA; ATCC 35591). These findings, however, form the foundation for further investigation in our continuing efforts to develop selective anticancer and antibacterial agents. PMID:23409711

Semreen, Mohammad H; El-Awady, Raafat; Abu-Odeh, Raed; Saber-Ayad, Maha; Al-Qawasmeh, Raed A; Chouaib, Salem; Voelter, Wolfgang; Al-Tel, Taleb H

2013-01-01

265

Prediction of Reaction Kinetic in Mechanically Activated Self-Propagating High-Temperature Synthesis Process  

NASA Astrophysics Data System (ADS)

In this paper we have tried to develop a semi-empirical formula for estimation of starting time of reactions during mechanical alloying process according to self-propagating high temperature synthesis (SHS) mechanism. For this purpose, three SHS systems containing Ti-C, Mo-Si and Si-C were selected and their behaviors were observed. Aforementioned systems were milled in a planetary ball mill equipped with temperature sensor detector of cups. Samplings were done at different times of discontinuously milling. To change mills' energy, stainless steel and tungsten carbide balls were used. In order to detect the phases and characterizations of milled powder, XRD instrument was utilized. Results showed that all productions were synthesized after sudden increase in temperature. Maximum measured temperature and critical time had up and downtrends for production of TiC, MoSi2 and SiC, respectively. Crystalline size of milled powder had nano-meter scale. By using experimental data along with theoretical equations, a semi-empirical formula between critical time for transformation of raw materials to productions, type of milled system and ball mill parameter can be presented with high accuracy. According to calculated formula, critical time was related to ball mill energy and Gibbs free energy of milled system with direct and inverse proportionality, respectively.

Razavi, Mansour

2012-12-01

266

Synthesis of Al4SiC4 powders from kaolin grog, aluminum and carbon black by carbothermal reaction  

NASA Astrophysics Data System (ADS)

In this paper, the synthesis of Al4SiC4 used as natural oxide materials by carbothermal reduction was investigated in order to explore the synthesis route with low costs. The samples were calcined by using kaolin grog, aluminum and carbon black as raw materials with the selected proportion at the temperature from 1500 to 1800 ° C for 2 hours under flow argon atmosphere. The phase composition of reaction products were determined by X-ray diffraction. The microstructure and elemental composition of different phases were observed and identified by scanning electron microscopy and energy dispersive spectroscopy. The mechanism of reaction processing was discussed. The results show that Al4SiC4 powders composed of hexagonal plate-like particulates with various sizes and the thickness of less than 20 ?m are obtained when the temperature reaches 1800 °C.

Yuan, Wenjie; Yu, Chao; Deng, Chengji; Zhu, Hongxi

2013-12-01

267

Nonsymmetrical 3,4-dithienylmaleimides by cross-coupling reactions with indium organometallics: synthesis and photochemical studies.  

PubMed

The synthesis and photochemical study of novel nonsymmetrical 1,2-dithienylethenes (DTEs) with a maleimide bridge have been carried out. The synthetic approach to the DTEs was based on successive selective palladium-catalyzed cross-coupling reactions of 5-susbtituted-2-methyl-3-thiophenyl indium reagents with 3,4-dichloromaleimides. The required organoindium reagents were prepared from 2-methyl-3,5-dibromothiophene by a selective (C-5) coupling reaction with triorganoindium compounds (R3 In) and subsequent metal-halogen exchange. The coupling reactions usually gave good yields and have a high atom economy with substoichiometric amounts of R3 In. The results of photochemical studies show that these novel dithienylmaleimides undergo a photocyclization reaction upon irradiation in the UV region and a photocycloreversion after excitation in the visible region, thus they can be used as photochemical switches. ON-OFF operations can be repeated in successive cycles without appreciable loss of effectiveness in the process. PMID:25220815

Mosquera, Angeles; Férnandez, M Isabel; Canle Lopez, Moisés; Pérez Sestelo, José; Sarandeses, Luis A

2014-10-27

268

Cobalt- versus ruthenium-catalyzed Alder-ene reaction for the synthesis of credneramide A and B.  

PubMed

The first synthesis of the natural products credneramide A and B was accomplished by utilizing Alder-ene reactions between a terminal alkene and an internal alkyne to generate the rather uncommon 1,4-diene substructure of these compounds. Moreover, two different short linear sequences toward these targets are evaluated using either a cobalt-catalyzed Alder-ene reaction of 1-chloropent-1-yne or a ruthenium-catalyzed Alder-ene reaction of 1-trimethylsilyl-1-pentyne with 5-hexenoic acid derivatives in the key step transformation. In addition, saponification of the primary Alder-ene product derived from the cobalt-catalyzed Alder-ene reaction led to credneric acid, the biological precursor of both natural products. PMID:22568728

Erver, Florian; Hilt, Gerhard

2012-06-01

269

Synthesis of 1,5-Benzodiazepine and Its Derivatives by Condensation Reaction Using H-MCM-22 as Catalyst  

PubMed Central

A simple and versatile method for the synthesis of 1,5-benzodiazepines is via condensation of o-phenylenediamines (OPDA) and ketones in the presence of catalytic amount of H-MCM-22 using acetonitrile as solvent at room temperature. In all the cases, the reactions are highly selective and are completed within 1–3?h. The method is applicable to both cyclic and acyclic ketones without significant differences. The reaction proceeds efficiently under ambient conditions with good-to-excellent yields. PMID:22570531

Majid, Sheikh Abdul; Khanday, Waheed Ahmad; Tomar, Radha

2012-01-01

270

Metal-Catalyzed Carbon-Carbon Bond Forming Reactions for the Synthesis of Significant Chiral Building Blocks  

E-print Network

the process through getting this degree. I?m very proud of her. vii NOMENCLATURE COD Cyclooctadiene EtOAc Ethyl Acetate DABCO 1,4-diazabicyclic[2.2.2]octane DBU 1,8-diazabicyclic[5.4.0]undec-7-ene DMAP 4-N,N-dimethylaminopyridine DMF N... such as aldol, Michael, and Diels-Alder reactions, or 1,2- additions, among others. This in turn can lead to the synthesis of complex molecules including natural products and other biologically important materials. The mechanism of the MBH reaction is believed...

Bugarin Cervantes, Alejandro

2011-08-08

271

California's ammonia emissions have been drastically underestimated  

NASA Astrophysics Data System (ADS)

In California, Los Angeles and the Central Valley often have atmospheric concentrations of particulate matter that exceed the U.S. Environmental Protection Agency's health guidelines. In the air, chemical reactions between ammonia, nitrogen oxides, and sulfur oxides can create inorganic aerosols like ammonium nitrate and ammonium sulfate. With their small particle sizes, these compounds can be dangerous to breathe, particularly for those with respiratory problems.

Schultz, Colin

2014-08-01

272

Reaction of the Co(II)-substrate radical pair catalytic intermediate in coenzyme B12-dependent ethanolamine ammonia-lyase in frozen aqueous solution from 190 to 217 K.  

PubMed

The decay kinetics of the aminoethanol-generated Co(II)-substrate radical pair catalytic intermediate in ethanolamine ammonia-lyase from Salmonella typhimurium have been measured on timescales of <10(5) s in frozen aqueous solution from 190 to 217 K. X-band continuous-wave electron paramagnetic resonance (EPR) spectroscopy of the disordered samples has been used to continuously monitor the full radical pair EPR spectrum during progress of the decay after temperature step reaction initiation. The decay to a diamagnetic state is complete and no paramagnetic intermediate states are detected. The decay exhibits three kinetic regimes in the measured temperature range, as follows. i), Low temperature range, 190 < or = T < or = 207 K: the decay is biexponential with constant fast (0.57 +/- 0.04) and slow (0.43 +/- 0.04) phase amplitudes. ii), Transition temperature range, 207 < T < 214 K: the amplitude of the slow phase decreases to zero with a compensatory rise in the fast phase amplitude, with increasing temperature. iii), High temperature range, T > or = 214 K: the decay is monoexponential. The observed first-order rate constants for the monoexponential (k(obs,m)) and the fast phase of the biexponential decay (k(obs,f)) adhere to the same linear relation on an lnk versus T(-1) (Arrhenius) plot. Thus, k(obs,m) and k(obs,f) correspond to the same apparent Arrhenius prefactor and activation energy (logA(app,f) (s(-1)) = 13.0, E(a,app,f) = 15.0 kcal/mol), and therefore, a common decay mechanism. We propose that k(obs,m) and k(obs,f) represent the native, forward reaction of the substrate through the radical rearrangement step. The slow phase rate constant (k(obs,s)) for 190 < or = T < or = 207 K obeys a different linear Arrhenius relation (logA(app,s) (s(-1)) = 13.9, E(a,app,s) = 16.6 kcal/mol). In the transition temperature range, k(obs,s) displays a super-Arrhenius increase with increasing temperature. The change in E(a,app,s) with temperature and the narrow range over which it occurs suggest an origin in a liquid/glass or dynamical transition. A discontinuity in the activation barrier for the chemical reaction is not expected in the transition temperature range. Therefore, the transition arises from a change in the properties of the protein. We propose that a protein dynamical contribution to the reaction, which is present above the transition temperature, is lost below the transition temperature, owing to an increase in the activation energy barrier for protein motions that are coupled to the reaction. For both the fast and slow phases of the low temperature decay, the dynamical transition in protein motions that are obligatorily coupled to the reaction of the Co(II)-substrate radical pair lies below 190 K. PMID:18805934

Zhu, Chen; Warncke, Kurt

2008-12-15

273

Shock-activated reaction synthesis and high pressure response of titanium-based ternary carbide and nitride ceramics  

Microsoft Academic Search

The objectives of this study were to (a) investigate the effect of shock activation of precursor powders for solid-state reaction synthesis of Ti-based ternary ceramics and (b) to determine the high pressure phase stability and Hugoniot properties of Ti3SiC2. Dynamically densified compacts of Ti, SiC, and graphite precursor powders and Ti and AlN precursor powders were used to study the

Jennifer Lynn Jordan

2003-01-01

274

Effects of Reaction Gel Dehydration on the Synthesis of Cu(NC5H5)4VOF4 and  

E-print Network

Effects of Reaction Gel Dehydration on the Synthesis of Cu(NC5H5)4VOF4 and [Cu(NC5H5)4VOF4][Cu(NC5H5)4(H2O)VOF4],H2O Margaret E. Welk, Charlotte L. Stern, Kenneth R. Poeppelmeier, and Alexander JVed December 11, 2006 ABSTRACT: The acentric anion, [VOF4]2-, has been incorporated into two new compounds, [Cu

Poeppelmeier, Kenneth R.

275

Synthesis of quinolactacide via an acyl migration reaction and dehydrogenation with manganese dioxide, and its insecticidal activities.  

PubMed

Quinolactacide isolated from Penicillium citrinum F 1539 was synthesized and evaluated for its insecticidal activities. The key steps of the total synthesis were an acyl migration reaction of the enol ester intermediate and dehydrogenation of tetrahydroquinolactacide with manganese dioxide. The synthesized quinolactacide showed 100% and 42% mortality against the green peach aphid (Myzus persicae) and diamondback moth (Plutella xylostella) at 500 ppm, respectively. PMID:16428857

Abe, Masaki; Imai, Tetsuya; Ishii, Naoki; Usui, Makio

2006-01-01

276

(Diisopinocampheyl)borane-Mediated Reductive Aldol Reactions: Highly Enantio and Diastereoselective Synthesis of Syn-Aldols from N-Acryloylmorpholine**  

PubMed Central

An efficient and highly enantio- and diastereoselective synthesis of syn propionamide aldols is described. Formation of the Z-enolborinate via the hydroboration of 4-acryloylmorpholine with (diisopinocampheyl)borane followed by aldol reactions with representative achiral and chiral aldehydes provided syn-?-methyl-?-hydroxy morpholine carboxamides with excellent enantio- and diastereoselectivity (96–98% ee and d.r. >20:1). PMID:23818095

Nuhant, Philippe; Allais, Christophe

2013-01-01

277

Rare earth perfluorooctanoate [RE(PFO) 3] catalyzed one-pot Mannich reaction: three component synthesis of ?-amino carbonyl compounds  

Microsoft Academic Search

Mannich reaction of acetophenone, aldehydes and aromatic amines catalyzed efficiently by RE(PFO)3 was described firstly, which carried out smoothly in high yields with three component one-pot method. Furthermore, it was found these catalysts were completely recovered and reused without loss of their catalytic activities and are thus environmentally conscious, and this procedure is a new choice to synthesis ?-aminocarbonyl compounds.

Limin Wang; Jianwei Han; Jia Sheng; He Tian; Zhaoyu Fan

2005-01-01

278

Site regeneration in the Fischer-Tropsch synthesis reaction: a synchronized CO dissociation and C-C coupling pathway.  

PubMed

A critical issue in the Fischer-Tropsch synthesis reaction is the blocking of the active sites for low barrier CO dissociation by the C(1) adsorbed species generated from CO dissociation, which can hinder the further steps in the FT process. Here, we propose a synchronized pathway for low barrier CO dissociation and C-C coupling on a corrugated Ru surface. PMID:21818499

Shetty, Sharan G; Ciobîc?, Ionel M; Hensen, Emiel J M; van Santen, Rutger A

2011-09-21

279

Synthesis of Diels–Alder adducts of N -arylmaleimides by a multicomponent reaction between maleic anhydride, dienes, and anilines  

Microsoft Academic Search

\\u000a Abstract  We have carried out the synthesis and characterization of some hexahydroisoindolyl benzoic acids and their corresponding ethyl\\u000a esters by a multicomponent reaction (MCR) between aminobenzoic acids or aminobenzoates, maleic anhydride, and isoprene in\\u000a the absence of catalysts. According to additional experiments, the MCR takes place by sequential formation of N-arylmaleamic acids from the aminobenzoic acids or aminobenzoates and maleic anhydride,

J. Alberto Guevara-Salazar; Delia Quintana-Zavala; Hugo A. Jiménez-Vázquez; José Trujillo-Ferrara

2011-01-01

280

One-pot stereoselective synthesis of ?,?-differentiated diamino esters via the sequence of aminochlorination, aziridination and intermolecular SN2 reaction.  

PubMed

We report here an efficient one-pot method for the synthesis of ?,?-differentiated diamino esters directly from cinnamate esters using N,N-dichloro-p-toluenesulfonamide and benzylamine as nitrogen sources. The key transformations include a Cu-catalyzed aminohalogenation and aziridination, followed by an intermolecular SN2 nucleophilic ring opening by benzylamine. The reactions feature a wide scope of substrates and proceed with excellent stereo- and regioselectivity (anti:syn >99:1) . PMID:25161740

Xiong, Yiwen; Qian, Ping; Cao, Chenhui; Mei, Haibo; Han, Jianlin; Li, Guigen; Pan, Yi

2014-01-01

281

Trapping in water - an important prerequisite for complex reactivity in astrophysical ices: the case of acetone (CH3)2C = O and ammonia NH3  

NASA Astrophysics Data System (ADS)

Water is the most abundant compound in interstellar and cometary ices. Laboratory experiments on ice analogues have shown that water has a great influence on the chemical activity of these ices. In this study, we investigated the reactivity of acetone-ammonia ices, showing that water is an essential component in chemical reactions with high activation energies. In a water-free binary ice, acetone and ammonia do not react due to high activation energy, as the reactants desorb before reacting (at 120 and 140 K, respectively). By contrast, our study shows that under experimental conditions of ˜150 K, this reaction does occur in the presence of water. Here, water traps reactants in the solid phase above their desorption temperatures, allowing them to gather thermal energy as the reaction proceeds. Using infrared spectroscopy and mass spectrometry associated with isotopic labelling, as well as quantum chemical calculations, 2-aminopropan-2-ol (2HN-C(CH3)2-OH) was identified as the acetone-ammonia reaction product. The formation of this product may represent the first step towards formation of 2-aminoisobutyric acid (AIB) in the Strecker synthesis. The activation energy for the formation of 2-aminopropan-2-ol was measured to be 42 ± 3 kJ mol-1, while its desorption energy equalled 61.3 ± 0.1 kJ mol-1. Our work demonstrates that astrophysical water, rather than being a non-thermally reactive species, is crucial for the evolution of complex chemistry occurring in the Universe.

Fresneau, Aurélien; Danger, Grégoire; Rimola, Albert; Theule, Patrice; Duvernay, Fabrice; Chiavassa, Thierry

2014-10-01

282

Development of the Domino Pericyclic Oxy-Cope/Ene /Claisen /Diels-Alder Reaction and the Synthesis of Complex Bicyclo[3.3.1]alkenones .  

E-print Network

??This thesis is a dissertation to support the development of new domino pericyclic oxy-Cope/ene/Claisen/Diels-Alder reaction, diversity oriented synthesis of PPAPs scaffold via sequential one pot… (more)

Sow, Boubacar

2013-01-01

283

Enantioselective nickel-catalyzed reductive coupling reactions of alkynes and aldehydes. Synthesis of amphidinolides T1 and T4 via catalytic, stereoselective macrocyclizations  

E-print Network

I. Enantioselective Nickel-Catalyzed Reductive Couplings of Alkynes and Aldehydes Allylic alcohol synthesis via a nickel-catalyzed reductive coupling reaction of alkylsubstituted alkynes and aldehydes was studied for ligand ...

Colby Davie, Elizabeth A. (Elizabeth Anne)

2005-01-01

284

Investigations relating to ?-amino acids synthesis and reactions of ?-aminobutyric acid  

Microsoft Academic Search

Summary 1.In the condensation of malonic acid with acetaldehyde-ammonia, it was found possible to increase the yield of ß-aminobutyric acid, which was isolated in the form of its benzoyl derivative, up to the value of 36%, if a catalyst (trimethylphenylammonium hydroxide) was used.2.The benzoyl group does not split off from ß-benzamidobutyric acid when the latter is boiled for 6 hr

V. M. Rodionov; N. G. Yartseva

1952-01-01

285

Ammonia-dimethylchloramine system: kinetic approach in an aqueous medium and comparison with the mechanism involving in liquid ammonia  

E-print Network

-351" #12;2 The dimethylchloramine/ammonia interaction corresponds to a SN2 bimolecular mechanism (k4 = 0- methylmethanimine, 1,3,5-trimethylhexahydrotriazine, formaldehyde and methylamine. The kinetics of this reaction and chlorinated derivative. The reaction is of the second order and obeys an E2 mechanism (k1 = 4.2 Ã? 10-5 M-1 s-1

Paris-Sud XI, Université de

286

Ammonia in tritium systems  

Microsoft Academic Search

A recent tritium inventory imbalance at Mound required an investigation into its causes. Much tritium was found as HTO in unsuspected zeolite traps of a T-purification system. Isotopic exchange from ammonia was postulated as a mechanism for entry of T into the zeolitic water. Gases from a T-processing system which had experienced air in-leakage were shown, by trapping of condensibles,

J. T. Gill; R. E. Ellefson; R. P. Paulick; C. M. Colvin; R. L. Yauger; E. E. Johns; R. L. Anderson; E. L. Lewis; P. H. Lamberger; R. E. Vallee

1988-01-01

287

Ammonia in tritium systems  

Microsoft Academic Search

A recent tritium inventory imbalance at Mound required an investigation into its causes. Much tritium was found as HTO in unsuspected zeolite traps of a T-purification system. Isotropic exchange from ammonia was postulated as a mechanism for entry of T into the zeolitic water. Gases from a T-processing system which had experienced air in-leakage were shown, by trapping of condensibles,

J. T. Gill; R. E. Ellefson; R. P. Paulick; C. M. Colvin; R. L. Yauger; E. E. Johns; R. L. Anderson; E. L. Lewis; P. H. Lamberger; R. E. Vallee

1988-01-01

288

AMMONIA CONCENTRATION IN SALTSTONE HEADSPACE SUMMARY REPORT  

SciTech Connect

The Saltstone Facility Documented Safety Analysis (DSA) is under revision to accommodate changes in the Composite Lower Flammability Limit (CLFL) from the introduction of Isopar into Tank 50. Saltstone samples were prepared with an 'MCU' type salt solution spiked with ammonia. The ammonia released from the saltstone was captured and analyzed. The ammonia concentration found in the headspace of samples maintained at 95 C and 1 atm was, to 95% confidence, less than or equal to 3.9 mg/L. Tank 50 is fed by several influent streams. The salt solution from Tank 50 is pumped to the salt feed tank (SFT) in the Saltstone Production Facility (SPF). The premix materials cement, slag and fly ash are blended together prior to transfer to the grout mixer. The premix is fed to the grout mixer in the SPF and the salt solution is incorporated into the premix in the grout mixer, yielding saltstone slurry. The saltstone slurry drops into a hopper and then is pumped to the vault. The Saltstone Facility Documented Safety Analysis (DSA) is under revision to accommodate changes in the Composite Lower Flammability Limit (CLFL) from the introduction of Isopar{reg_sign} L into Tank 50. Waste Solidification-Engineering requested that the Savannah River National Laboratory (SRNL) perform testing to characterize the release of ammonia in curing saltstone at 95 C. The test temperature represents the maximum allowable temperature in the Saltstone Disposal Facility (SDF). Ammonia may be present in the salt solution and premix materials, or may be produced by chemical reactions when the premix and salt solution are combined. A final report (SRNS-STI-2008-00120, Rev. 0) will be issued that will cover in more depth the information presented in this report.

Zamecnik, J; Alex Cozzi, A

2008-09-26

289

TfOH-catalyzed synthesis of 3-aryl isoindolinones via a tandem reaction.  

PubMed

A convenient metal-free method for the synthesis of 3-aryl isoindolinones via TfOH catalyzed aromatic C-H functionalization of electron-rich arenes with 2-formylbenzonitriles is developed. This process provided a new efficient strategy for the synthesis of isoindolinone derivatives in good to high yields and regioselectivities by forming two bonds. PMID:25370938

Hu, Jiaxing; Qin, Hua-Li; Xu, Wengang; Li, Junli; Zhang, Fanglin; Zheng, Hua

2014-12-25

290

Rationalized design, synthesis and pharmacological screening of amino acid linked spiro pyrrolidino oxyindole analogs through environment friendly reaction  

PubMed Central

Introduction: The development of newer synthetic approaches toward the synthesis of polynuclear heteroaromatics and their application in the synthesis of some biologically active compounds has been discussed in this study. Materials and Methods: The synthesis of novel spiro pyrrolidino oxindoles was performed for the construction of amino acid linked polynuclear heteroaromatics by cycloaddition reaction. This reaction method is one of the most important methods for the construction of spiro pyrrolidino oxindole from the commercially available starting material isatin. Then the synthesized compounds were subjected for evaluation of nitric oxide scavenging and cytotoxic effects against tumor cell lines. Results: All the six synthesized compounds demonstrated promising antioxidant and cytotoxic effects in vitro. Conclusion: Form the present study, it can be concluded that the synthesized compounds are fruitful in terms of their chemical purity, structural novelty, marked biological activities (antioxidant and cytotoxic) in vitro and last of all the lucid and picturesque synthetic methodology to synthesize the molecules in a in a non-hazardous and environmental friendly way. PMID:24350050

Das, Sanjit Kumar; Bhattacharya, Sanjib; Kundu, Amit

2013-01-01

291

Effect of Shock-Activation on Post-Shock Reaction Synthesis of Ti3SiC2 Ternary Carbide  

NASA Astrophysics Data System (ADS)

The effect of shock-compression of titanium, silicon carbide, and graphite powders on subsequent reaction synthesis and formation of Ti3SiC2 was investigated in this study. Ti3SiC2 is a novel ceramic with metal-like properties, namely, high electrical conductivity and plastic-like deformation. The powder precursors were mixed by ball-milling and shock-densified at different pressures using 80-mm diameter gas gun and double implosion cylinder techniques. Characterization of the shock-densified compacts showed an intimately mixed state of powders with little or no reaction. The subsequent reaction behavior of the shock-densified compacts was studied via heat treatments and differential thermal analysis (DTA) at varying heating rates. Activation energies were obtained from these DTA studies and correlated with measurements of fraction reacted as a function of time and temperature to determine the reaction mechanism(s) and degree of activation caused by shock compression. This paper will present the results of the reaction mechanisms and the effects of shock compression on the kinetics of reactions leading to the formation of the ternary carbide in the shock-densified precursor powders.

Jordan, Jennifer; Thadhani, Naresh

2001-06-01

292

Scale-up synthesis of zinc borate from the reaction of zinc oxide and boric acid in aqueous medium  

NASA Astrophysics Data System (ADS)

Synthesis of zinc borate was conducted in a laboratory and a pilot scale batch reactor to see the influence of process variables on the reaction parameters and the final product, 2ZnO·3B 2O 3·3.5H 2O. Effects of stirring speed, presence of baffles, amount of seed, particle size and purity of zinc oxide, and mole ratio of H 3BO 3:ZnO on the zinc borate formation reaction were examined at a constant temperature of 85 °C in a laboratory (4 L) and a pilot scale (85 L) reactor. Products obtained from the reaction in both reactors were characterized by chemical analysis, X-ray diffraction, particle size distribution analysis, thermal gravimetric analysis and scanning electron microscopy. The kinetic data for the zinc borate production reaction was fit by using the logistic model. The results revealed that the specific reaction rate, a model parameter, decreases with increase in particle size of zinc oxide and the presence of baffles, but increases with increase in stirring speed and purity of zinc oxide; however, it is unaffected with the changes in the amount of seed and reactants ratio. The reaction completion time is unaffected by scaling-up.

K?l?nç, Mert; Çakal, Gaye Ö.; Ye?il, Sertan; Bayram, Göknur; Ero?lu, ?nci; Özkar, Saim

2010-11-01

293

Synthesis of polycyclic isoindoline derivatives via tandem Pd-catalyzed coupling, propargyl-allenyl isomerization, [4 + 2] cycloaddition and aromatization reaction.  

PubMed

We report in this paper an interesting sequential reaction involving sequential Sonogashira coupling, propargyl-allenyl isomerization, [4 + 2] cycloaddition and aromatization reaction, which provides a facile method for the synthesis of a variety of polycyclic isoindoline derivatives from easily accessible starting materials. PMID:23051023

Zhu, Shugao; Cao, Jian; Wu, Luling; Huang, Xian

2012-11-16

294

Multicatalytic synthesis of alpha-pyrrolidinyl ketones via a tandem palladium(II)/indium(III)-catalyzed aminochlorocarbonylation/Friedel-Crafts acylation reaction.  

PubMed

An oxidative carbonylation reaction that generates acid chloride functionality has been developed. Furthermore, this aminochlorocarbonylation reaction has been merged with a catalytic Friedel-Crafts acylation to produce a highly efficient tandem multicatalytic synthesis of pyrrolidinyl ketones. Significant variation of the aromatic nucleophile and substrate are shown. Two examples of incorporation of this method in triple-catalytic sequences are also demonstrated. PMID:19209934

Cernak, Tim A; Lambert, Tristan H

2009-03-11

295

Green chemistry: a facile synthesis of polyfunctionally substituted thieno[3,4-c]pyridinones and thieno[3,4-d]pyridazinones under neat reaction conditions.  

PubMed

A facile, solvent free, ecofriendly approach for the synthesis of pyridine-2,6-diones 4a-d, pyridazinone derivatives 8a-c and thienoazines 6 and 9 is herein described employing neat reaction conditions under both microwave and ultrasound irradiations. This solventless methodology is environmentally benign as it completely eliminates the use of solvent from the reaction procedure. PMID:20064736

Al-Zaydi, Khadijah M; Borik, Rita M; Mekheimer, Ramadan A; Elnagdi, Mohamed H

2010-06-01

296

An efficient synthesis of anhydrides of 2-monosubstituted succinic acid monoesters and their application to the Dakin-West reaction: Isolation of some 5-succinyloxyoxazole intermediates  

Microsoft Academic Search

Summary  A rapid and versatile synthesis of 2-monosubstituted monosuccinates and their bimolecular anhydrides is described. The reaction\\u000a of these anhydrides withN-Fmoc-protected dipeptides under the modified Dakin-West reaction affords mainly the corresponding 5-succinyloxyoxazoles.

Joseph Richard Casimir; Laurent Ettouati; Joëlle Paris

1998-01-01

297

A facile one-pot synthesis of functionalized 1,3-oxathiolan-2-yliden derivatives: multicomponent reaction of oxiranes in water.  

PubMed

An efficient synthesis of 1,3-oxathiolan-2-yliden derivatives is described via a simple reactions between CHacids, CS2 and oxiranes in the presence of triethylamine at 70° C in water as the solvent. The mild reaction conditions and high yields of the products exhibit the good synthetic advantage of this method. PMID:23755720

Rostami-Charati, Faramarz; Hosseini-Tabatabaei, Mohammad R; Shahraki, Mehdi

2014-01-01

298

Facile Method for the Synthesis of Vicinal Azidoiodides by the Reaction of the NaN3–I2 System with Unsaturated Compounds  

Microsoft Academic Search

A facile and efficient method was developed for the synthesis of vicinal azidoiodides in 62–77% yields by the reaction of sodium azide and iodine with unsaturated compounds in methanol, aqueous methanol, or the water–methanol–tetrahydrofuran solvent system. The reaction in Et2O or CHCl3 produced only vicinal diiodides.

Alexander O. Terentev; Igor B. Krylov; Vladimir A. Kokorekin; Gennady I. Nikishin

2008-01-01

299

The synthesis of methanol and the reverse water-gas shift reaction over Zn-deposited Cu(100) and Cu(110) surfaces: comparison with Zn/Cu(111)  

NASA Astrophysics Data System (ADS)

The catalytic activity of Zn vapor-deposited Cu(100) and Cu(110) surfaces for methanol synthesis by the hydrogenation of CO 2 and the reverse water-gas shift reaction were studied using an XPS apparatus combined with a high-pressure flow reactor (18 atm). At a reaction temperature of 523 K, no promotional effect of Zn was observed for the methanol synthesis on both Zn/Cu(100) and Zn/Cu(110). The results were quite different from those for Zn/Cu(111), on which a significant promotion of methanol synthesis activity appeared to be due to the deposition of Zn, indicating that the promotional effect of Zn was sensitive to the surface structure of Cu. However, hysteresis was observed in the catalytic activity for methanol synthesis over the Zn/Cu(110) surface upon heating above 543 K in the reaction mixture. The activity became twice that measured before heating, which was close to the methanol synthesis activity of Zn/Cu(111) at the same Zn coverage. On the other hand, no such hysteresis was observed for the reverse water-gas shift reaction on Zn/Cu(110), indicating that the active site for methanol synthesis was not identical to that for the reverse water-gas shift reaction. In the post-reaction surface analysis, formate species was detected on both Zn/Cu(100) and Zn/Cu(110), whose coverage increased with increasing Zn coverage at 0< ?Zn<0.2. No correlation between the formate coverage and the methanol synthesis activity was obtained, which was in contrast to the results for Zn/Cu(111). Thus, the structure sensitivity observed in the catalytic activity of methanol synthesis over Zn-deposited Cu surfaces is ascribed to the significant difference in the reactivity of the formate intermediate.

Nakamura, I.; Fujitani, T.; Uchijima, T.; Nakamura, J.

1998-03-01

300

Synthesis of complex benzenoids via the intermediate generation of o-benzynes through the hexadehydro-Diels-Alder reaction.  

PubMed

The hexadehydro-Diels-Alder (HDDA) cascade enables the synthesis of complex benzenoid products with various substitution patterns through aryne intermediates. The first stage of this cascade involves the generation of a highly reactive ortho-benzyne intermediate by a net [4+2] cycloisomerization of a triyne substrate. The benzyne can be rapidly 'trapped' either intramolecularly or intermolecularly with myriad nucleophilic or ?-bond-donating reactants. As a representative example of a general procedure for synthesizing highly substituted benzenoids, this protocol describes the synthesis of a typical triyne substrate and its use as the reactant in an HDDA cascade to form a phthalide. The synthetic procedure detailed herein (four chemical reactions) takes 16-20 h of active effort over a period of several days for the preparation of the triyne precursor and ?2 h of active effort over a 3-d period for the generation and trapping of the benzyne and isolation of the phthalide product. PMID:23411632

Baire, Beeraiah; Niu, Dawen; Willoughby, Patrick H; Woods, Brian P; Hoye, Thomas R

2013-03-01

301

Synthesis of complex benzenoids via the intermediate generation of o-benzynes through the hexadehydro-Diels-Alder reaction  

PubMed Central

The hexadehydro-Diels–Alder (HDDA) cascade enables the synthesis of complex benzenoid products with various substitution patterns via aryne intermediates. The first stage of this cascade involves generation of a highly reactive ortho-benzyne intermediate by a net [4+2] cycloisomerization of a triyne substrate. The benzyne can be rapidly ‘trapped’ either intra- or intermolecularly with a myriad of nucleophilic or ?-bond-donating reactants. As a representative example of a general procedure to synthesize highly substituted benzenoids, this protocol describes the synthesis of a typical triyne substrate and its use as the reactant in an HDDA cascade to form a phthalide. The synthetic procedure detailed herein (four chemical reactions) takes 16–20 h of active effort over a several day period for preparation of the triyne precursor and ~2 h of active effort over a 3-day period for generation and trapping of the benzyne and isolation of the phthalide product. PMID:23411632

Baire, Beeraiah; Niu, Dawen; Willoughby, Patrick H.; Woods, Brian P.; Hoye, Thomas R.

2014-01-01

302

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

PubMed Central

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

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

2014-01-01

303

Design and synthesis of chiral Zn2+ complexes mimicking natural aldolases for catalytic C-C bond forming reactions in aqueous solution.  

PubMed

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

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

2014-01-01

304

Practical experiences with the synthesis of [11C]CH3I through gas phase iodination reaction using a TRACERlabFXC synthesis module.  

PubMed

The results of [(11)C]CH(3)I synthesis through hydrogen gas reduction of [(11)C]CO(2) on different nickel catalysts (HARSHAW-nickel, SHIMALITE-nickel, nickel on silica/alumina, nickel nanosize 99.99%) followed by gas phase iodination using a TRACERlab FX(C) synthesis unit are reported. Further reaction parameters such as furnace temperatures, flow rate of hydrogen gas and reduction time were optimized. It was found that reduction of [(11)C]CO(2) proceeded in 28-83% yield depending on the nickel catalyst and temperature. The gas phase iodination (methane conversion) gave 31-62% of [(11)C]CH(3)I depending on temperature and amount of iodine in the iodine furnace. [(11)C]CH(3)I was used for heteroatom methylation reactions exemplified by a piperazine and a phenol (1 and 3). The specific activity of the (11)C-labelled products 2 and 4 was determined after HPLC purification and solid-phase extraction. Compounds 2 and 4 were obtained in 8-14% radiochemical yield (decay-corrected, based upon trapped [(11)C]CH(4)) within 30 min. The specific activity was determined to be in the range of 20-30 GBq/mumol at the end-of-synthesis. Nickel catalyst nanosize was found to be superior compared with other Ni catalysts tested. The relatively low specific activity may be mainly due to carbon contaminations originating from the long copper tubing (500 m) between the cyclotron and the radiochemistry facility. PMID:17683943

Kniess, Torsten; Rode, Katrin; Wuest, Frank

2008-04-01

305

Cell-free protein synthesis in a microchamber revealed the presence of an optimum compartment volume for high-order reactions.  

PubMed

The application of microelectromechanical systems (MEMS) to chemistry and biochemistry allows various reactions to be performed in microscale compartments. Here, we aimed to use the glass microchamber to study the compartment size dependency of the protein synthesis, one of the most important reactions in the cell. By encapsulating the cell-free protein synthesis system with different reaction orders in femtoliter microchambers, chamber size dependency of the reaction initiated with a constant copy number of DNA was investigated. We were able to observe the properties specific to the high order reactions in microcompartments with high precision and found the presence of an optimum compartment volume for a high-order reaction using real biological molecules. PMID:23991849

Okano, Taiji; Matsuura, Tomoaki; Suzuki, Hiroaki; Yomo, Tetsuya

2014-06-20

306

Synthesis, reactions and biological activity of some new bis-heterocyclic ring compounds containing sulphur atom  

PubMed Central

Background The derivatives of thieno[2,3-b]thiophene belong to a significant category of heterocyclic compounds, which have shown a wide spectrum of medical and industrial application. Results A new building block with two electrophilic center of thieno[2,3-b]thiophene derivatives 2 has been reported by one-pot reaction of diketone derivative 1 with Br2/AcOH in excellent yield. A variety of heteroaromatics having bis(1H-imidazo[1,2a] benzimidazole), bis(1H-imidazo[1,2-b][1,2,4]triazole)-3-methyl-4-phenylthieno[2,3-b]thiophene derivatives, dioxazolo-, dithiazolo-, and 1H-imidazolo-3-methyl-4-phenylthieno[2,3-b]thiophene derivatives as well pyrrolo, thiazolo -3-methyl-4-phenylthieno[2,3-b]thiophene derivatives have been designed, synthesized, characterized, and evaluated for their biological activity. Compounds 3–9 showed good bioassay result. These new derivatives were evaluated for anti-cancer activity against PC-3 cell lines, in vitro antioxidant potential and ?-glucuronidase and ?-glucosidase inhibitory activities. Compound 3 (IC50?=?56.26?±?3.18??M) showed a potent DPPH radical scavenging antioxidant activity and found to be more active than standard N-acetylcystein (IC50?=?105.9?±?1.1??M). Compounds 8a (IC50?=?13.2?±?0.34??M) and 8b (IC50?=?14.1?±?0.28??M) found as potent inhibitor of ?-glucusidase several fold more active than the standard acarbose (IC50?=?841?±?1.73??M). Most promising results were obtained in ?-glucuronidase enzyme inhibition assay. Compounds 5 (IC50?=?0.13?±?0.019??M), 6 (IC50?=?19.9?±?0.285??M), 8a (IC50?=?1.2?±?0.0785??M) and 9 (IC50?=?0.003?±?0.09??M) showed a potent inhibition of ?-glucuronidase. Compound 9 was found to be several hundred fold more active than standard D-Saccharic acid 1,4-lactone (IC50?=?45.75?±?2.16??M). Conclusions Synthesis, characterization, and in vitro biological activity of a series of thieno[2,3-b]thiophene have been investigated. PMID:23829861

2013-01-01

307

Hydrothermal reactions: From the synthesis of ligand to new lanthanide 3D-coordination polymers  

SciTech Connect

The organic ligand 2,5-piperazinedione-1,4-diacetic acid (H{sub 2}PDA) was synthesized under hydrothermal conditions starting from the iminodiacetic acid and catalyzed by oxalic acid. The X-ray powder diffraction data indicates that the compound crystallizes in the P2{sub 1}/c monoclinic system as reported in the literature. The ligand was also characterized by elemental analysis, magnetic nuclear resonance, infrared spectroscopy and thermogravimetric analysis. Two new coordination networks based on lanthanide ions were obtained with this ligand using hydrothermal reaction. In addition to single-crystal X-ray diffraction, the compounds were characterized by infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and elemental analysis. Single-crystal XRD showed that the compounds are isostructural, crystallizing in P2{sub 1}/n monoclinic system with chemical formula [Ln(PDA){sub 1.5}(H{sub 2}O)](H{sub 2}O){sub 3} (Ln=Gd{sup 3+}(1) and Eu{sup 3+}(2)).The luminescence properties of both compounds were studied. In the compound (1), a broad emission band was observed at 479 nm, redshifted by 70 nm in comparison of the free ligand. In (2), the typical f–f transition was observed with a maximum peak at 618 nm, related with the red emission of the europium ions. Computational methods were performed to simulate the crystal structure of (2). The theoretical calculations of the intensity parameters are in good agreement with the experimental values. - Graphical abstract: Scheme of obtaining the ligand 2,5-piperazinedione-1,4-diacetic acid (H{sub 2}PDA) and two new isostructural 3D-coordination polymers [Ln(PDA){sub 1.5}(H{sub 2}O)](H{sub 2}O){sub 3} (Ln=Gd{sup 3+} and Eu{sup 3+}) by hydrothermal synthesis. Display Omitted - Highlights: • The ligand 2,5-piperazinedione-1,4-diacetic acid was synthetized using the hydrothermic method and characterized. • Two new 3D-coordination polymers with this ligand containing Gd{sup 3+} and Eu{sup 3+} ions were also obtained. • The compounds are isostructural and the typical luminescent properties were observed in both structures.

Silva, Fausthon Fred da; Fernandes de Oliveira, Carlos Alberto; Lago Falcão, Eduardo Henrique [Laboratório de Terras Raras, Departamento de Química Fundamental, Universidade Federal de Pernambuco (DQF-UFPE), 50590-470 Recife, PE (Brazil); Gatto, Claudia Cristina [Laboratório de Síntese Inorgânica e Cristalografia, Instituto de Química, Universidade de Brasília (IQ-UnB), 70904-970 Brasilia, DF (Brazil); Bezerra da Costa, Nivan; Oliveira Freire, Ricardo [Pople Computational Chemistry Laboratory, Departamento de Química, Universidade Federal de Sergipe, São Cristóvão-SE 49100-000 (Brazil); Chojnacki, Jaros?aw [Department of Inorganic Chemistry, Gdansk University of Technology, 80-233 Gdansk (Poland); Alves Júnior, Severino, E-mail: salvesjr@ufpe.br [Laboratório de Terras Raras, Departamento de Química Fundamental, Universidade Federal de Pernambuco (DQF-UFPE), 50590-470 Recife, PE (Brazil)

2013-11-15

308

Novel reactions of a neutral organic reductant : reductive coupling and nanoparticle synthesis  

E-print Network

A recently developed bis-pyridinylidene neutral organic electron donor captured our interest as a potential source of new chemistries for reductive coupling and the synthesis of group IV nanoparticles. This super electron ...

Mork, Anna Jolene

2012-01-01

309

[4 + 1] annulation reactions of (trialkylsilyl)ketenes : synthesis of substituted indanones and cyclopentenones  

E-print Network

(Trialkylsilyl)vinylketenes ("(TAS)vinylketenes") and (trialkylsilyl)arylketenes ("(TAS)- arylketenes") function as versatile four-carbon building blocks for the synthesis of carbocyclic and heterocyclic compounds. A new ...

Davie, Christopher P

2005-01-01

310

A green synthesis of a layered titanate, potassium lithium titanate; lower temperature solid-state reaction and improved materials performance  

SciTech Connect

A layered titanate, potassium lithium titanate, with the size range from 0.1 to 30 µm was prepared to show the effects of the particle size on the materials performance. The potassium lithium titanate was prepared by solid-state reaction as reported previously, where the reaction temperature was varied. The reported temperature for the titanate preparation was higher than 800 °C, though 600 °C is good enough to obtain single-phase potassium lithium titanate. The lower temperature synthesis is cost effective and the product exhibit better performance as photocatalysts due to surface reactivity. - Graphical abstract: Finite particle of a layered titanate, potassium lithium titanate, was prepared by solid-state reaction at lower temperature to show modified materials performance. Display Omitted - Highlights: • Potassium lithium titanate was prepared by solid-state reaction. • Lower temperature reaction resulted in smaller sized particles of titanate. • 600 °C was good enough to obtain single phased potassium lithium titanate. • The product exhibited better performance as photocatalyst.

Ogawa, Makoto, E-mail: waseda.ogawa@gmail.com [Graduate School of Creative Science and Engineering, Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo 169-8050 (Japan); Department of Earth Sciences, Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo 169-8050 (Japan); Morita, Masashi, E-mail: m-masashi@y.akane.waseda.jp [Graduate School of Creative Science and Engineering, Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo 169-8050 (Japan); Igarashi, Shota, E-mail: uxei_yoshi_yoshi@yahoo.co.jp [Graduate School of Creative Science and Engineering, Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo 169-8050 (Japan); Sato, Soh, E-mail: rookie_so_sleepy@yahoo.co.jp [Graduate School of Creative Science and Engineering, Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo 169-8050 (Japan)

2013-10-15

311

Synthesis of PbS nanorods and other ionic nanocrystals of complex morphology by sequential cation exchange reactions.  

PubMed

We show that nanocrystals (NCs) with well-established synthetic protocols for high shape and size monodispersity can be used as templates to independently control the NC composition through successive cation exchange reactions. Chemical transformations like cation exchange reactions overcome a limitation in traditional colloidal synthesis, where the NC shape often reflects the inherent symmetry of the underlying lattice. Specifically we show that full or partial interconversion between wurtzite CdS, chalcocite Cu(2)S, and rock salt PbS NCs can occur while preserving anisotropic shapes unique to the as-synthesized materials. The exchange reactions are driven by disparate solubilites between the two cations by using ligands that preferentially coordinate to either monovalent or divalent transition metals. Starting with CdS, highly anisotropic PbS nanorods are created, which serve as an important material for studying strong two-dimensional quantum confinement, as well as for optoelectronic applications. In NC heterostructures containing segments of different materials, the exchange reaction can be made highly selective for just one of the components of the heterostructure. Thus, through precise control over ion insertion and removal, we can obtain interesting CdS|PbS heterostructure nanorods, where the spatial arrangement of materials is controlled through an intermediate exchange reaction. PMID:19863102

Luther, Joseph M; Zheng, Haimei; Sadtler, Bryce; Alivisatos, A Paul

2009-11-25

312

Truncated phenylalanine ammonia-lyase expression in tomato (Lycopersicon esculentum).  

PubMed

Southern blot analyses of genomic DNA fragments suggest there are five different classes of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) genomic sequence in tomato (Lycopersicon esculentum). Isolation and subsequent sequence analysis of three examples from genomic libraries reveal highly homologous coding sequences but also a surprisingly high frequency of single point mutations which would truncate protein synthesis. The nucleotide sequence for one of the genes (PAL5) encodes a normal polypeptide of 721 amino acids, interrupted by a 710-base pair intron in the codon for amino acid 139. In contrast, premature stop codons, 363 triplets from the end in PAL1 and 304 triplets from the end in PAL3 would result in substantially (51-43%) shorter polypeptides that are consistent with the protein polymorphism, recently reported in alfalfa (Jorrin, J., and Dixon, R. A. (1990) Plant Physiol. 92, 447-445) but ascribed to protein degradation. S1 mapping of the mRNA termini and polymerase chain reaction analysis of cDNA transcripts indicate that at least one of these truncated coding sequences is expressed, strongly suggesting that at least some of the shorter polypeptides constitute original gene products with a potentially important function. PMID:1601854

Lee, S W; Robb, J; Nazar, R N

1992-06-15

313

Povarov-type reaction using methyl as new input: direct synthesis of substituted quinolines by i2-mediated formal [3 + 2 + 1] cycloaddition.  

PubMed

A highly efficient molecular iodine mediated formal [3 + 2 + 1] cycloaddition reaction for the direct synthesis of substituted quinolines from methyl ketones, arylamines, and styrenes is developed. The methyl group of the methyl ketone represents uniquely reactive input in the Povarov reaction. A self-sequenced iodination/Kornblum oxidation/Povarov/aromatization mechanism has been proposed as a possible reaction sequence to account for the results observed in this study. PMID:25119142

Gao, Qinghe; Liu, Shan; Wu, Xia; Wu, Anxin

2014-09-01

314

Synthesis and in vivo antidiabetic activity of novel dispiropyrrolidines through [3+2] cycloaddition reactions with thiazolidinedione and rhodanine derivatives.  

PubMed

The synthesis of a series of novel dispiropyrrolidines has been accomplished by 1,3-dipolar cycloaddition reaction with 5-arylidene-1,3-thiazolidine-2,4-dione and 5-arylidene-4-thioxo-1,3-thiazolidine-2-one derivatives as dipolarophiles. The structure and stereochemistry of the cycloadduct have been established by single crystal X-ray structure and spectroscopic techniques. Molecular docking studies were performed on 1FM9 protein. The synthesized compounds were screened for their antidiabetic activity on male Wistar rats. PMID:19395129

Murugan, Ramalingam; Anbazhagan, S; Lingeshwaran; Sriman Narayanan, S

2009-08-01

315

An annulation reaction for the synthesis of cross-conjugated triene-containing hydroindanes from acyclic precursors.  

PubMed

In efforts directed toward the synthesis of seco-prezizaane sesquiterpenoids, a stereoselective annulation reaction has been developed between 4-hydroxy-1,6-enynes and TMS-alkynes that delivers cross-conjugated triene-containing hydroindanes. Contrary to previous reports, enyne substrates bearing two propargylic ethers enable the presumed organometallic intermediate to be trapped by double elimination. The tendency of products from this annulation to undergo Diels-Alder-based dimerization was harnessed to accomplish a two-step complexity-generating sequence en route to densely functionalized carbo- and heteorocyclic systems. PMID:25216381

Cheng, Xiayun; Micalizio, Glenn C

2014-10-01

316

Total synthesis of resveratrol-based natural products using a palladium-catalyzed decarboxylative arylation and an oxidative Heck reaction.  

PubMed

Controlled access to resveratrol-based natural products is offered by a novel, modular concept. A common building block readily available on a large scale serves as the starting material for the introduction of structurally important aryl groups by a Pd-catalyzed decarboxylative arylation and an oxidative Heck reaction with good yields and high stereoselectivity. The modular approach is convincingly documented by the successful synthesis of three racemic resveratrol-based natural products (quadrangularin?A, ampelopsin?D, and pallidol). PMID:24500870

Klotter, Felix; Studer, Armido

2014-02-24

317

Synthesis of 2-alkenyl- and 2-alkynyl-benzo[b]phospholes by using palladium-catalyzed cross-coupling reactions.  

PubMed

Heck, Stille, and Sonogashira reactions of 2-bromobenzo[b]phosphole P-oxide afforded a series of 2-alkenyl- and 2-alkynyl-benzo[b]phosphole P-oxides. The charge-transfer character of the new benzo[b]phosphole ?-systems in the excited state is enhanced by the terminal electron-donating substituents. Furthermore, the C-Sn cross-coupling of the bromide was applied to the facile synthesis of a new Stille-coupling precursor, 2-stannylbenzo[b]phosphole. PMID:23952285

Matano, Yoshihiro; Hayashi, Yukiko; Suda, Kayo; Kimura, Yoshifumi; Imahori, Hiroshi

2013-09-01

318

Nucleophilic Aromatic Substitution Reactions of meso-Bromosubporphyrin: Synthesis of a Thiopyrane-Fused Subporphyrin.  

PubMed

meso-Bromosubporphyrin undergoes nucleophilic aromatic substitution (SN Ar) reactions with arylamines, diarylamines, phenols, ethanol, thiophenols, and n-butanethiol in the presence of suitable bases to provide the corresponding substitution products. The SN Ar reactions also proceed well with pyrrole, indole, and carbazole to provide substitution products in moderate to good yields. Finally, the SN Ar reaction with 2-bromothiophenol and subsequent intramolecular peripheral arylation reaction affords a thiopyrane-fused subporphyrin. PMID:25336122

Shimizu, Daiki; Mori, Hirotaka; Kitano, Masaaki; Cha, Won-Young; Oh, Juwon; Tanaka, Takayuki; Kim, Dongho; Osuka, Atsuhiro

2014-12-01

319

Toward the Total Synthesis of Norzoanthamine: The Development of a Transannular Michael Reaction Cascade  

E-print Network

facile transannular reactions to give cis-syn-cis and trans-anti-trans ring systems, respectively. However, Z,E- and Z,Z- macrocycles did not cyclize under similar reactions. The similarities and differences between transannular Diels-Alder reactions...

Xue, Haoran

2013-03-06

320

A novel oxy-oxonia(azonia)-cope reaction: serendipitous discovery and its application to the synthesis of macrocyclic musks.  

PubMed

This brief review, including new experimental results, is the summary of a talk at the GDCh conference 'flavors & fragrances 2013' in Leipzig, Germany, 11th-13th September, 2013. Musk odorants are indispensable in perfumery to lend sensuality to fine fragrances, a nourishing effect to cosmetics, and a comforting feeling to laundry. We have recently found serendipitously a new oxy-oxonia-Cope rearrangement. In this account, we review the background of oxonia-sigmatropic rearrangements and the discovery of this novel reaction. Special attention is focused on the versatile lactone and lactam formation reactions via [n+4] ring enlargement and the macrocyclization in the synthesis of new macrocyclic musks. The synthesized structures provide new insights into the structure?odor relationships of musks. PMID:25329787

Zou, Yue; Zhou, Lijun; Ding, Changming; Wang, Quanrui; Kraft, Philip; Goeke, Andreas

2014-10-01

321

Synthesis of biodiesel from a model waste oil feedstock using a carbon-based solid acid catalyst: reaction and separation.  

PubMed

A solid acid catalyst that can keep high activity and stability is necessary when low cost feedstocks are utilized for biodiesel synthesis because the reaction medium contains a large amount of water. Three solid acid catalysts were prepared by the sulfonation of carbonized vegetable oil asphalt and petroleum asphalt. The structure of these catalysts was characterized by a variety of techniques. A new process that used the coupling of the reaction and separation was employed, which greatly improved the conversion of cottonseed oil (triglyceride) and free fatty acids (FFA) when a model waste oil feedstock was used. The vegetable oil asphalt-based catalyst showed the highest catalytic activity. This was due to the high density and stability of its acid sites, its loose irregular network, its hydrophobicity that prevented the hydration of -OH species, and large pores that provided more acid sites for the reactants. PMID:20219353

Shu, Qing; Nawaz, Zeeshan; Gao, Jixian; Liao, Yuhui; Zhang, Qiang; Wang, Dezheng; Wang, Jinfu

2010-07-01

322

Optimization of reaction parameters in hydrothermal synthesis: a strategy towards the formation of CuS hexagonal plates  

PubMed Central

Background For decades, copper sulphide has been renowned as the superior optical and semiconductor materials. Its potential applications can be ranged from solar cells, lithium-ion batteries, sensors, and catalyst systems. The synthesis methodologies of copper sulphide with different controlled morphology have been widely explored in the literature. Nevertheless, the understanding on the formation chemistry of CuS is still limited. The ultimate approach undertaking in this article is to investigate the formation of CuS hexagonal plates via the optimization of reaction parameters in hydrothermal reaction between copper (II) nitrate and sodium thiosulphate without appending any assistant agent. Results Covellite (CuS) hexagonal plates were formed at copper ion: thiosulphate ion (Cu2+:S2O32?) mole ratio of 1:2 under hydrothermal treatment of 155°C for 12 hours. For synthesis conducted at reaction temperature lower than 155°C, copper sulphate (CuSO4), krohnite (NaCu2(SO4)(H2O)2] and cyclooctasulphur (S8) were present as main impurities with covellite (CuS). When Cu2+:S2O32? mole ratio was varied to 1: 1 and 1: 1.5, phase pure plate-like natrochalcite [NaCu2(SO4)(H2O)] and digenite (Cu9S5) were produced respectively. Meanwhile, mixed phases of covellite (CuS) and cyclooctasulphur (S8) were both identified when Cu2+:S2O32? mole ratio was varied to 1: 2.5, 1: 3 and 1: 5 as well as when reaction time was shortened to 1 hour. Conclusions CuS hexagonal plates with a mean edge length of 1 ?m, thickness of 100 nm and average crystallite size of approximately (45?±?2) nm (Scherrer estimation) were successfully synthesized via assisting agent- free hydrothermal method. Under a suitable Cu2+:S2O32? mole ratio, we evidenced that the formation of covellite (CuS) is feasible regardless of the reaction temperature applied. However, a series of impurities were attested with CuS if reaction temperature was not elevated high enough for the additional crystallite phase decomposition. It was also identified that Cu2+:S2O32? mole ratio plays a vital role in controlling the amount of cyclooctasulphur (S8) in the final powder obtained. Finally, reaction time was recognized as an important parameter in impurity decomposition as well as increasing the crystallite size and crystallinity of the CuS hexagonal plates formed. PMID:23575312

2013-01-01

323

Polyol synthesis of silver nanocubes via moderate control of the reaction atmosphere.  

PubMed

Silver nanocubes were successfully synthesized at high yield in variously controlled reaction atmospheres by balancing etching of O2/Cl(-) and reduction of glycolaldehyde. There have been efforts to control the O2 content in reaction atmospheres by purging of O2 or Ar gas for the balancing, but we found that moderate control of reaction atmosphere, just by careful timing of the opening and the capping of the reaction vial, greatly enhanced reproducibility. Enhanced reproducibility is attributed to alleviation of evaporation and condensation of glycolaldehyde (b.p.=131°C) by using capping at reaction temperatures higher than the b.p. of glycolaldehyde rather than purging with gas. The most important finding is that seeding is initiated by HNO3 induced deoxygenation reaction in the gas phase. O2 is consumed by oxidation of NO generated from the silver etching reaction by HNO3, which effectively controls the reaction atmosphere without introduction of gas. Our simple method to control reaction atmosphere reduces the overall reaction time to one fifth of the previous result and provides excellent size and distribution selectivity of the Ag nanocube product. PMID:25233223

Jeon, Seog-Jin; Lee, Jae-Hwang; Thomas, Edwin L

2014-12-01

324

On-surface synthesis of single-layered two-dimensional covalent organic frameworks via solid-vapor interface reactions.  

PubMed

Surface covalent organic frameworks (SCOFs), featured by atomic thick sheet with covalently bonded organic building units, are promised to possess unique properties associated with reduced dimensionality, well-defined in-plane structure, and tunable functionality. Although a great deal of effort has been made to obtain SCOFs with different linkages and building blocks via both "top-down" exfoliation and "bottom-up" surface synthesis approaches, the obtained SCOFs generally suffer a low crystallinity, which impedes the understanding of intrinsic properties of the materials. Herein, we demonstrate a self-limiting solid-vapor interface reaction strategy to fabricate highly ordered SCOFs. The coupling reaction is tailored to take place at the solid-vapor interface by introducing one precursor via vaporization to the surface preloaded with the other precursor. Following this strategy, highly ordered honeycomb SCOFs with imine linkage are obtained. The controlled formation of SCOFs in our study shows the possibility of a rational design and synthesis of SCOFs with desired functionality. PMID:23786481

Liu, Xuan-He; Guan, Cui-Zhong; Ding, San-Yuan; Wang, Wei; Yan, Hui-Juan; Wang, Dong; Wan, Li-Jun

2013-07-17

325

Interactive oxidation-reduction reaction for the in situ synthesis of graphene-phenol formaldehyde composites with enhanced properties.  

PubMed

We report a facile in situ synthesis of reduced graphene oxide (RGO)-phenol formaldehyde (PF) composites with an interactive oxidation-reduction reaction. In this interactive chemical reaction, graphene oxide (GO) was reduced to RGO by phenol, and simultaneously phenol was oxidized to benzoquinone. The noncovalently adsorbed phenol on the RGO surface can not only serve as an effective reductant but also participate in the in situ polymerization and guide the formation of PF on the RGO surface. RGO-PF composites with different RGO contents were prepared successfully and further characterized with fluorescent spectroscopy, scanning electron microscopy, and transmission electron microscopy. The mechanical strength, electrical conductivity, thermal conductivity, and thermal resistance of the created RGO-PF were investigated. The results indicated that the dispersity of RGO in the PF matrix and the interfacial interaction between RGO and PF were improved greatly because of formation of the RGO-PF hybrid in the in situ synthesis. The homogeneous dispersion and in situ polymerization of RGO sheets help to enhance the thermal conductivity of RGO-PF composites from 0.1477 to 0.3769 W m(-1) K(-1) and endow the composites with a good electrical conductivity. In addition, the well-dispersed RGO-PF composites are much more effective in improving their mechanical property and heat resistance. PMID:24588055

Zhao, Xiaojia; Li, Yang; Wang, Jinhui; Ouyang, Zhaofei; Li, Jingfeng; Wei, Gang; Su, Zhiqiang

2014-03-26

326

Enantioselective Synthesis of anti- and syn-homopropargyl alcohols via Chiral Br?nsted Acid Catalyzed asymmetric Allenylboration reactions  

PubMed Central

Chiral Brønsted acid catalyzed asymmetric allenylboration reactions are described. Under optimized conditions, anti-homopropargyl alcohols 2 are obtained in high yields with excellent diastereo- and enantioselectivities from stereochemically matched aldehyde allenylboration reactions with (M)-1 catalyzed by the chiral phosphoric acid (S)-4. The syn-isomers 3 can also be obtained in good diastereoselectivities and excellent enantioselectivities from the mismatched allenylboration reactions of aromatic aldehydes using (M)-1 in the presence of the enantiomeric phosphoric acid (R)-4. The stereochemistry of the methyl group introduced into 2 and 3 is controlled by the chirality of the allenylboronate (M)-1, whereas the configuration of the new hydroxyl stereocenter is controlled by the enantioselectivity of the chiral phosphoric acid catalyst used in these reactions. The synthetic utility of this methodology was further demonstrated in triple asymmetric syntheses of a variety of anti,anti-stereotriads, the direct synthesis of which has constituted a significant challenge using previous generations of aldol and crotylmetal reagents. PMID:22731887

Chen, Ming; Roush, William R.

2012-01-01

327

Cooling-water chlorination: the kinetics of chlorine, bromine, and ammonia in sea water  

Microsoft Academic Search

The major inorganic reaction pathways for the chlorination of saline waters were measured by a variety of techniques including: (1) amperometric titration, (2) amperometric membrane covered electrode, (3) uv spectrophotometry, (4) conventional kinetics methods for slow reactions, and (5) stopped-flow kinetics measurements with a microcomputer data acquisition system. The major reactions studied were: (1) the competitive reactions of ammonia and

J. D. Johnson; G. W. Jr. Inman; T. W. Trofe

1982-01-01

328

Optimization of dicarboxylic acid cellulose synthesis: Reaction stoichiometry and role of hypochlorite scavengers.  

PubMed

The reaction conditions in terms of reaction time, sodium chlorite stoichiometry, and the effect of hypochlorite scavengers on the chlorite oxidation of dialdehyde cellulose (DAC) was studied. The impact of storage on the reactivity of DAC fibers was also investigated. It was found that chlorite oxidation of DAC is a rapid reaction, resulting in oxidation of 71% of the aldehyde after only 8min when 2.5 times excess of sodium chlorite compared to aldehyde groups was used. Reactivity of DAC was observed to decrease quickly during the storage and only 68% of the aldehyde groups reacted after two weeks storage compared to the reaction performed with freshly prepared DAC. Hydrogen peroxide and sulfamic acid were observed to increase the reaction efficiency of chlorite oxidation by reducing the amount of side-reactions between chlorite and hypochlorite. A minor amount of sulfamic acid can be used to replace acetic acid as a catalyst. PMID:25263866

Sirviö, Juho Antti; Liimatainen, Henrikki; Visanko, Miikka; Niinimäki, Jouko

2014-12-19

329

Cobalt Molybdenum Oxynitrides: Synthesis, Structural, Characterization, and Catalytic Activity for the Oxygen Reduction Reaction  

SciTech Connect

Here, we report the synthesis and characterization of CoxMo1 xOyNz compounds supported on carbon black as potential cathode catalysts for ORR. They were prepared by a conventional impregnation method. Their ORR activities in both acid and alkaline electrolytes were evaluated via half-cell measurements. The synthesis temperature and sample composition both strongly impacted their physical and chemical properties. Factors influencing their crystal structures, morphologies and ORR activities will be discussed based on the results of structural and spectroscopic studies.

Cao, Bingfei [ORNL; Veith, Gabriel M [ORNL; Diaz, Rosa [Brookhaven National Laboratory (BNL); Liu, Jue [State University of New York, Stony Brook; Stach, Eric [Brookhaven National Laboratory (BNL); Adzic, Radoslav R. [Brookhaven National Laboratory (BNL); Khalifah, P. [Stony Brook University (SUNY)

2013-01-01

330

Reactions of uranium atoms with ammonia: infrared spectra and quasi-relativistic calculations of the U:NH3, H2N--UH, and HN==UH2 complexes.  

PubMed

Ammonia molecules interact with U atoms, and the resulting U:NH3 complex rearranges upon visible irradiation to form the H2N--UH and HN==UH2 molecules in excess argon. These products are identified by functional group frequencies, 15NH3 and ND3 isotopic shifts, and comparison to frequencies calculated by using density functional theory. The N==U pi bond in HN==UH2 is enhanced by partial triple-bond character through N(2p) to U(5f) conjugation, which is comparable to that found in the analogous HN==ThH2 molecule. These products also form complexes with additional ammonia molecules in the matrix. The interesting higher-energy N[triple chemical bond]UH3 complex is not formed. PMID:18767108

Wang, Xuefeng; Andrews, Lester; Marsden, Colin J

2008-01-01

331

Mild conditions for the synthesis of functionalized pyrrolidines via Pd-catalyzed carboamination reactions.  

PubMed

[reaction: see text] The palladium-catalyzed carboamination of N-protected gamma-aminoalkenes with aryl bromides and triflates has been achieved under new, mild reaction conditions using the weak base Cs(2)CO(3) in dioxane solvent. These reactions tolerate a wide variety of functional groups, including enolizable ketones, nitro groups, methyl esters, and acetates, which are not compatible with previously described conditions. PMID:17249786

Bertrand, Myra Beaudoin; Leathen, Matthew L; Wolfe, John P

2007-02-01

332

Diverse microbial species survive high ammonia concentrations  

NASA Astrophysics Data System (ADS)

Planetary protection regulations are in place to control the contamination of planets and moons with terrestrial micro-organisms in order to avoid jeopardizing future scientific investigations relating to the search for life. One environmental chemical factor of relevance in extraterrestrial environments, specifically in the moons of the outer solar system, is ammonia (NH3). Ammonia is known to be highly toxic to micro-organisms and may disrupt proton motive force, interfere with cellular redox reactions or cause an increase of cell pH. To test the survival potential of terrestrial micro-organisms exposed to such cold, ammonia-rich environments, and to judge whether current planetary protection regulations are sufficient, soil samples were exposed to concentrations of NH3 from 5 to 35% (v/v) at -80°C and room temperature for periods up to 11 months. Following exposure to 35% NH3, diverse spore-forming taxa survived, including representatives of the Firmicutes (Bacillus, Sporosarcina, Viridibacillus, Paenibacillus, Staphylococcus and Brevibacillus) and Actinobacteria (Streptomyces). Non-spore forming organisms also survived, including Proteobacteria (Pseudomonas) and Actinobacteria (Arthrobacter) that are known to have environmentally resistant resting states. Clostridium spp. were isolated from the exposed soil under anaerobic culture. High NH3 was shown to cause a reduction in viability of spores over time, but spore morphology was not visibly altered. In addition to its implications for planetary protection, these data show that a large number of bacteria, potentially including spore-forming pathogens, but also environmentally resistant non-spore-formers, can survive high ammonia concentrations.

Kelly, Laura C.; Cockell, Charles S.; Summers, Stephen

2012-04-01

333

Optical reaction cell and light source for ›18F! fluoride radiotracer synthesis  

DOEpatents

Apparatus for performing organic synthetic reactions, particularly no-carrier-added nucleophilic radiofluorination reactions for PET radiotracer production. The apparatus includes an optical reaction cell and a source of broadband infrared radiant energy, which permits direct coupling of the emitted radiant energy with the reaction medium to heat the reaction medium. Preferably, the apparatus includes means for focusing the emitted radiant energy into the reaction cell, and the reaction cell itself is preferably configured to reflect transmitted radiant energy back into the reaction medium to further improve the efficiency of the apparatus. The apparatus is well suited to the production of high-yield syntheses of 2-›.sup.18 F!fluoro-2-deoxy-D-glucose. Also provided is a method for performing organic synthetic reactions, including the manufacture of ›.sup.18 F!-labeled compounds useful as PET radiotracers, and particularly for the preparation of 2-›.sup.18 F!fluoro-2-deoxy-D-glucose in higher yields than previously possible.

Ferrieri, Richard A. (Patchogue, NY); Schlyer, David (Bellport, NY); Becker, Richard J. (Islip, NY)

1998-09-15

334

Enantioselective synthesis of Janus kinase inhibitor INCB018424 via an organocatalytic aza-Michael reaction.  

PubMed

An enantioselective synthesis of INCB018424 via organocatalytic asymmetric aza-Michael addition of pyrazoles (16 or 20) to (E)-3-cyclopentylacrylaldehyde (23) using diarylprolinol silyl ether as the catalyst was developed. Michael adducts (R)-24 and (R)-27 were isolated in good yield and high ee and were readily converted to INCB018424. PMID:19385672

Lin, Qiyan; Meloni, David; Pan, Yongchun; Xia, Michael; Rodgers, James; Shepard, Stacey; Li, Mei; Galya, Laurine; Metcalf, Brian; Yue, Tai-Yuen; Liu, Pingli; Zhou, Jiacheng

2009-05-01

335

In-situ time resolved synchrotron powder diffraction studies of synthesis and chemical reactions  

Microsoft Academic Search

Equipment for time and temperature dependent powder diffraction has been developed, especially in order to be able to study hydrothermal syntheses of zeolites. The system is very versatile and has so far been used to study e.g. hydrothermal syntheses of zeolites and aluminophosphates, syntheses of layered phosphates, formation of Sorel cements, dehydration and phase transformations of zeolites, solid state synthesis

Norby

1995-01-01

336

The Synthesis and Reactions of Nickel(III) Stabilized by a Nitrogen-Donor Macrocycle  

NASA Astrophysics Data System (ADS)

This experiment describes the synthesis of 1,4,8,11-tetraazacyclotetradecane and its nickel(II & III) complexes avoiding the use of percholrate anion. The paramagnetic effects in solution and solid state are described for the nickel(III) dihalo derivatives along with a spectrophotometric study.

Berry, David E.; Girard, Suzanne; McAuley, Alexander

1996-06-01

337

Intramolecular redox reaction for the synthesis of N-aryl pyrroles catalyzed by Lewis acids.  

PubMed

An efficient approach to synthesize N-aryl pyrroles via Lewis acid-mediated 1,5-hydride shift and isomerization of 2-(3-pyrroline-1-yl)arylaldehydes has been achieved in up to 89% yield. This methodology is applicable to the synthesis of fluorazene derivatives as electron donor (D)/acceptor (A) molecules. PMID:25351145

Du, Hong-Jin; Zhen, Le; Wen, Xiaoan; Xu, Qing-Long; Sun, Hongbin

2014-12-21

338

Synthesis of novel functional polyolefin containing carboxylic acid via Friedel–Crafts acylation reaction  

Microsoft Academic Search

The strong polar group, carboxylic acid, has triumphantly been introduced into ethylene and allylbenzene copolymers without obvious degradation or crosslinking via Friedel–Crafts (F–C) acylation reaction with glutaric anhydride (GA), succinic anhydride (SA) and phthalic anhydride (PA) in the presence of anhydrous aluminum chloride in carbon disulfide. Some important reaction parameters were examined in order to optimize the acylation process. In

Yi Zheng; Yanguo Li; Li Pan; Yuesheng Li

2007-01-01

339

Dearomative Indole [5+2] Cycloaddition Reactions: Stereoselective Synthesis of Highly Functionalized Cyclohepta[b]indoles.  

PubMed

The first dearomative indole [5+2] cycloaddition reaction with an oxidopyrylium ylide resulted in efficient and diastereoselective construction of some highly functionalized and synthetically challenging oxacyclohepta[b]indoles. The protocol proceeds under very mild reaction conditions, thus enabling high functional-group tolerance and unique endo?selectivity. PMID:25146238

Mei, Guangjian; Yuan, Hao; Gu, Yueqing; Chen, Wei; Chung, Lung Wa; Li, Chuang-Chuang

2014-10-01

340

ROADSIDE AMMONIA MEASUREMENTS USING OPTICAL REMOTE SENSING INSTRUMENTS  

EPA Science Inventory

Fine particles less than 2.5 microns in diameter have been identified as a causal agent of excess mortality and other undesirable health impacts. A large part of these airborne particles, generally more than one-half, are formed in the atmosphere by reactions of ammonia with acid...

341

Laboratory measurements of ion-molecule reactions pertaining to interstellar hydrocarbon synthesis  

NASA Astrophysics Data System (ADS)

Measurements on a variety of three-body association reactions between hydrocarbon ions and molecular hydrogen in the presence of helium have been undertaken. The rate coefficients of most of the systems studied are vanishingly small (less than 1 x 10 to the -30th cm exp 6/s) even at 80 K. The results cast severe doubt on a recent gas-phase model of complex hydrocarbon formation in dense interstellar clouds in which radiative association reactions between hydrocarbon ions and molecular hydrogen play a key role. In addition to the three-body reactions, some two-body reactions between hydrocarbon ions and molecular hydrogen and some reactions between carbon ions (C/+/) and hydrocarbon neutrals have been studied.

Herbst, E.; Adams, N. G.; Smith, D.

1983-06-01

342

Raman spectroscopy as a tool for monitoring mesoscale continuous-flow organic synthesis: Equipment interface and assessment in four medicinally-relevant reactions  

PubMed Central

Summary An apparatus is reported for real-time Raman monitoring of reactions performed using continuous-flow processing. Its capability is assessed by studying four reactions, all involving formation of products bearing ?,?-unsaturated carbonyl moieties; synthesis of 3-acetylcoumarin, Knoevenagel and Claisen–Schmidt condensations, and a Biginelli reaction. In each case it is possible to monitor the reactions and also in one case, by means of a calibration curve, determine product conversion from Raman spectral data as corroborated by data obtained using NMR spectroscopy. PMID:24062851

Hamlin, Trevor A

2013-01-01

343

AQUEOUS AMMONIA EQUILIBRIUM - TABULATION OF PERCENT UN-IONIZED AMMONIA  

EPA Science Inventory

The percent of un-ionized ammonia as a function of pH and temperature in aqueous ammonia solutions of zero salinity is presented in tabular form over the following ranges: temperature 0.0 to 40.0 C in increments of 0.2 degree, and pH 5.00 to 12.00 in increments of 0.01 pH unit....

344

Synthesis of fused multicyclic compounds containing macrocycles by dienyne ring-closing metathesis and Diels-Alder reactions.  

PubMed

Fused bicyclic compounds comprising small and large rings were synthesised by dienyne ring-closing metathesis (RCM) using Grubbs' catalyst. By taking advantage of faster small ring cyclisation compared with macrocyclisation, single isomers were obtained rather than mixtures of two isomers with different ring sizes. Using this process, various fused bicyclic compounds comprising small rings (5-7- membered) and large rings (14-17- membered) were obtained. By increasing reaction temperature and catalyst loading, the product conversion was improved in a predicted manner. This method produced E-olefins on the macrocycles with high selectivity. Also, the selectivity issues of tandem RCM for the synthesis of fused bicyclic compounds comprising small and medium rings were investigated. Lastly, the prepared bicyclic compounds with small and large rings contained 1, 3-dienes that underwent a further modification reaction, such as Diels-Alder, to produce more complex compounds. These Diels-Alder reactions produced tri- and tetracyclic compounds containing a macrocycle with single diastereomers, suggesting that the methodology demonstrated here could be a powerful tool for rapid preparation of highly complex molecules. PMID:21738948

Park, Hyeon; Choi, Tae-Lim

2011-08-21

345

ENGINEERING DESIGN CONFIGURATIONS FOR BIOLOGICAL AMMONIA REMOVAL  

EPA Science Inventory

Many regions in the United States have excessive levels of nutrients including ammonia in their source waters. For example, farming and agricultural sources of ammonia in the Midwest contribute to relatively high levels of ammonia in many ground waters. Although ammonia in water ...

346

Breath Ammonia Analysis: Clinical Application and Measurement  

Microsoft Academic Search

This review covers in detail the complexity of human breath, how the body metabolizes ammonia, clinical conditions which are directly related to the regulation of ammonia concentration, and analysis of current techniques that are capable of detecting breath ammonia. Focusing on these areas provides the information needed to develop a breath ammonia sensor for monitoring dysfunction of the human body.

Troy Hibbard; Anthony J. Killard

2011-01-01

347

Stereoselective synthesis, NMR conformational study and Diels-Alder reaction of ?-functionalized 1-acetylvinyl arenecarboxylates  

Microsoft Academic Search

A stereoselective synthesis of novel ?-substituted 1-acetylvinyl arenecarboxylates 2a–2h, via the bromo derivative 4a, is described. Isomer Z was the only product formed. Low temperature NMR experiments showed an s-cis\\/s-trans (20:80) conformeric equilibrium, and also a restricted rotational C-N barrier in 2a. X-ray diffraction of the latter revealed a planar s-trans conformation. Alkene 4a proved to be more reactive than

Javier Peralta; Joseph P. Bullock; Roderick W. Bates; Simon Bott; Gerardo Zepeda; Joaquín Tamariz

1995-01-01

348

A New Synthesis of N-tert-Butylvinylketenimines and Their Cycloaddition Reactions  

Microsoft Academic Search

The [4+2] cycloadditions of vinylheterocumulenes such as vinylketenes and N-substituted vinylketenimines with olefins have presented a preparative method for the direct synthesis of cyclohexenone derivatives. Vinylketenes can readily react with electron-rich olefins to afford cyclohexenone derivatives. On the other hand, vinylketenimines can react with electronpoor olefins to afford N-substituted cyclohexenonimines, which are hydrolyzed to the corresponding cyclohexenone derivatives. Consequently, vinylketenes

Yoshihiko Ito; Toshikazu Hirao; Nobuhiro Ohta; Takeo Saegusa

1980-01-01

349

Asymmetric Synthesis of Functionalized Dihydro- and Tetrahydropyrans via an Organocatalytic Domino Michael-Hemiacetalization Reaction  

PubMed Central

Starting from ?-hydroxymethyl nitroalkenes and various 1,3-dicarbonyl compounds, a one-pot organocatalyzed diastereo- and enantioselective synthesis of polyfunctionalized dihydro- and tetrahydropyran derivatives via a domino Michael-hemiacetalization sequence is reported. The title compounds bearing a variety of functional groups can be synthesized in this way in good yields (59–91%) and with moderate to excellent diastereoselectivities (26–98% de) and enantioselectivities (71–99% ee).

Urbanietz, Gregor; Atodiresei, Iuliana; Enders, Dieter

2014-01-01

350

Conceptual Design of Biorefineries Through the Synthesis of Optimal Chemical-reaction Pathways  

E-print Network

on developing new pathways while optimizing existing ones. Here, potential chemicals are added to create a superstructure, then an algorithm is run to enumerate every feasible reaction stoichiometry through a mixed integer linear program (MILP). An optimal...

Pennaz, Eric James

2011-10-21

351

Development of odd-Z-projectile reactions for transactinide element synthesis  

SciTech Connect

The development of new odd-Z-projectile reactions leading to the production of transactinide elements is described. The cross section of the even-Z-projectile 208Pb(64Ni, n)271Ds reaction was measured at two new energies using the Berkeley Gas-filled Separator at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. In total, seven decay chains attributable to 271Ds were observed. These data, combined with previous results, establish an excitation function for the production of 271Ds. The maximum cross section was 20 +15 -11 pb at a center-of-target energy of 311.5 MeV in the laboratory frame.The data from the 271Ds experiments were used to estimate the optimum beam energy for the new odd-Z-projectile 208Pb(65Cu, n)272-111 reaction using the Fusion by Diffusion theory proposed by Swiatecki, Siwek-Wilczynska, and Wilczynski. A cross section for this reaction was measured for the first time, at a center-of-target energy of 321.1 MeV in the laboratory frame. The excitation energy f or compound nuclei formed at the target center was 13.2 MeV. One decay chain was observed, resulting in a measured cross section of 1.7 +3.9 -1.4 pb. This decay chain is in good agreement with previously published data on the decay of 272-111.The new odd-Z-projectile 208Pb(55Mn, n)262Bh reaction was studied at three different projectile energies, and 33 decay chains of 262Bh were observed. The existence of a previously reported alpha-decaying isomeric state in this nuclide was confirmed. Production of the ground state was preferred at all three beam energies. The maximum cross section was 540 +180 -150 pb at a projectile center-of-target energy of 264.0 MeV. This cross section is much larger than that previously reported for the even-Z-projectile 209Bi(54Cr, n)262Bh reaction, which may be because the 54Cr projectile energies in the latter reaction were too high for optimum production of the 1n product. At the highest projectile energy of 268.0 MeV in the target center, two decay chains from 261Bh were observed as a result of the 208Pb(55Mn, 2n) reaction. In summary, this work shows that odd-Z-projectile reactions can have cross sections comparable to analogous even-Z-projectile reactions, and that the energy of the maximum cross section for 1n reactions can be estimated simply.

Folden III, Charles Marvin

2004-11-04

352

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

PubMed

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

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

2013-10-01

353

Aza-Diels–Alder reactions in ionic liquids: a facile synthesis of pyrano- and furanoquinolines  

Microsoft Academic Search

Room temperature ionic liquids are found to catalyze efficiently the three component-coupling reactions of aldehydes, amines and cyclic enol ethers such as 3,4-dihydro-2H-pyran and 2,3-dihydrofuran under mild and convenient conditions to afford the corresponding pyrano- and furanoquinolines in excellent yields with high endo-selectivity. Interestingly, 2,3-dihydrofuran afforded selectively endo-products under the similar reaction conditions.

J. S Yadav; B. V. S Reddy; J. S. S Reddy; R. Srinivasa Rao

2003-01-01

354

Synthesis of Sultams and Related Sulfur Heterocycles Using the Ring-Closing Metathesis Reaction  

E-print Network

8 1.2.2.1 Heck Reaction 9 1.2.2.2 Diels-Alder Cyclization 13 1.2.2.3 Copper-Catalyzed Cyclization 17... been utilized to synthesize sultams, all of them based on intramolecular processess. The most common methods reported to date include the Heck reaction, Diels-Alder cycloaddition, 1,3-dipolar cycloaddition, base and acid-promoted cyclizations...

Jimenez, Maria del Sol

2007-09-19

355

The catalytic reduction of nitric oxide with ammonia over tetraamminecopper (II) complexes  

E-print Network

that the ennanced catalytic activity of the NO-NH system in the presence of oxygen is directly 3 proportional to the amount of surface oxygen. The unusual activity profile of the reaction of nitric oxide with 23 ammonia over Cuy zeolites was first reported... of nitric oxide with ammonia over tetraamminecopper(II) complexes in aqueous solutions to compare this reaction environment with the parallel reac- tion over Cu(II) NaY zeolites. Zeolites are crystalline aluminosilicates which contain exchangeable...

Oates, Margaret Deron

2012-06-07

356

Convenient synthesis of pyrano[3,2- c]quinolines and indeno[2,1- c] quinolines by imino Diels-Alder reactions  

Microsoft Academic Search

Anhydrous indium trichloride (InCl3) is found to catalyze the imino Diels-Alder reaction of 3,4-dihydro-2H-pyran and indene with Schiff's bases to afford pyrano[3,2-c]quinolines and indeno[2,1-c] quinolines. Imino Diels-Alder reactions of N-benzylidene 1-naphthylamine with 3,4-dihydro-2H-pyran and indene results in efficient synthesis of phenanthridine derivatives.

Govindarajulu Babu; Paramasivan T. Perumal

1998-01-01

357

Synthesis of an Inorganic–Organic Hybrid Material Based on Polyhedral Oligomeric Silsesquioxane and Polystyrene via Nitroxide-Mediated Polymerization and Click Reactions  

Microsoft Academic Search

Synthesis of an inorganic–organic hybrid polymeric material composed of polystyrene and polyhedral oligomeric silsesquioxane (POSS) was carried out via nitroxide-mediated polymerization (NMP) and Click reaction. First, 4-chloromethyl styrene was polymerized in bulk at 125°C using AIBN and 4hydroxy-TEMPO as the initiator and stable free radical, respectively. Reaction of poly(4-chloromethyl styrene) (PCMS) with NaN3 in DMF yielded azide side-functional polystyrene. In

Deniz Sinirlioglu; Ali Ekrem Muftuoglu

2011-01-01

358

Reaction temperature optimization procedure for the synthesis of ( R)-mandelonitrile by Prunus amygdalus hydroxynitrile lyase using a process model approach  

Microsoft Academic Search

The reaction temperature was optimized for the enzymatic synthesis of (R)-mandelonitrile in a biphasic system of aqueous buffer and methyl tert-butyl ether by including temperature effects in an existing process model. (R)-Mandelonitrile was synthesized by addition of hydrogen cyanide to benzaldehyde using Prunus amygdalus hydroxynitrile lyase as the catalyst. The reaction was investigated within a temperature range of 5 to

W. F Willeman; A. J. J Straathof; J. J Heijnen

2002-01-01

359

One-pot sequential synthesis of isocyanates and urea derivatives via a microwave-assisted Staudinger-aza-Wittig reaction  

PubMed Central

Summary A fast and efficient protocol for the synthesis of N,N'-disubstituted urea derivatives from alkyl halides and primary or secondary amines has been developed. The synthetic pathway combines nucleophilic substitutions and a Staudinger–aza-Wittig reaction in the presence of polymer-bound diphenylphosphine under 14 bar of CO2 pressure and has been performed in a one-pot two-step process. The protocol has been optimized under microwave irradiation and the scale-up experiment has been conducted under conventional conditions in a Parr reactor. The final compounds were isolated after simple filtration in almost quantitative overall yields which makes this procedure facile and rapid to execute. PMID:24367403

Carnaroglio, Diego; Martina, Katia; Palmisano, Giovanni; Penoni, Andrea; Domini, Claudia

2013-01-01

360

The synthesis of ZnP4 based on liquid-solid reaction under high pressure and temperature  

NASA Astrophysics Data System (ADS)

In this article we reported the successful high pressure and temperature synthesis of micron-sized zinc tetraphosphide (ZnP4) crystals based on the liquid-solid reaction between Zn and P at a large-volume cubic press. Techniques of X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDXA) were employed to investigate the phase structure, grain size, morphology and stoichiometric ratio of crystals. The results indicate that the synthesized ZnP4 has a tetragonal structure with the space group of P41212, and the grains with size of about 50 ?m can be prepared at 4.0 GPa and 1000 °C. We also obtained the pressure-temperature (P-T) formation region of ZnP4 and discussed the formative mechanism of ZnP4 crystals.

Li, Xin; Peng, Fang; Zhou, Xiaoling; Wang, Pei

2013-07-01

361

Synthesis of high specific activity (+)- and (-)-6-( sup 18 F)fluoronorepinephrine via the nucleophilic aromatic substitution reaction  

SciTech Connect

The first example of a no-carrier-added {sup 18}F-labeled catecholamine, 6-({sup 18}F)fluoronorepinephrine (6-({sup 18}F)FNE), has been synthesized via nucleophilic aromatic substitution. The racemic mixture was resolved on a chiral HPLC column to obtain pure samples of (-)-6-({sup 18}F)FNE and (+)6-({sup 18}F)FNE. Radiochemical yields of 20% at the end of bombardment (EOB) for the racemic mixture (synthesis time 93 min), 6% for each enantiomer (synthesis time 128 min) with a specific activity of 2-5 Ci/mumol at EOB were obtained. Chiral HPLC peak assignment for the resolved enantiomers was achieved by using two independent methods: polarimetric determination and reaction with dopamine beta-hydroxylase. Positron emission tomography (PET) studies with racemic 6-({sup 18}F)FNE show high uptake and retention in the baboon heart. This work demonstrates that nucleophilic aromatic substitution by ({sup 18}F)fluoride ion is applicable to systems having electron-rich aromatic rings, leading to high specific activity radiopharmaceuticals. Furthermore, the suitably protected dihydroxynitrobenzaldehyde 1 may serve as a useful synthetic precursor for the radiosynthesis of other complex {sup 18}F-labeled radiotracers.

Ding, Y.S.; Fowler, J.S.; Gatley, S.J.; Dewey, S.L.; Wolf, A.P. (Brookhaven National Laboratory, Upton, NY (USA))

1991-02-01

362

Rapid synthesis of hollow ag-au nanodendrites in 15 seconds by combining galvanic replacement and precursor reduction reactions.  

PubMed

Metallic nanomaterials displaying hollow interiors as well as sharp tips/branches at their surface (such as hollow nanodendrites) are attractive, because these features enable higher surface-to-volume ratios than their solid and/or rounded counterparts. This paper describes a simple strategy for the synthesis of Ag-Au nanodendrites in 15?s using Ag nanospheres prepared in a previous synthetic step as seeds. Our approach was based on the utilization of Ag nanospheres as seeds for Au deposition by a combination of galvanic replacement reaction between Ag and AuCl4 (-) (aq) and AuCl4 (-) (aq) reduction using hydroquinone in the presence of polyvinylpyrrolidone (PVP) as a stabilizer and water as the solvent. The produced Ag-Au nanodendrites presented monodisperse sizes, and their surface morphologies could be tuned as a function of growth time. Owing to their hollow interiors and sharp tips, the Ag-Au nanodendrites performed as effective substrates for surface-enhanced Raman scattering (SERS) detection of 4-MPy (4-mercaptopyridine) and R6G (rhodamine 6G) as probe molecules. We believe that the approach described herein can serve as a protocol for the fast and one-step synthesis of Ag-Au hollow nanondendrites with a wide range of sizes, compositions, and surface morphologies for applications in SERS and catalysis. PMID:25284169

da Silva, Anderson G M; de Souza, Michele L; Rodrigues, Thenner S; Alves, Rafael S; Temperini, Marcia L A; Camargo, Pedro H C

2014-11-10

363

Hydrothermal synthesis of BaTiO 3 nanoparticles using a supercritical continuous flow reaction system  

NASA Astrophysics Data System (ADS)

Highly crystalline BaTiO 3 nanoparticle was synthesized rapidly by hydrothermal reaction in supercritical water using a continuous flow reactor. The reactants of TiO 2 sol (or TiCl 4)/Ba(NO 3) 2 mixed solution and KOH solution were used as starting materials and that was heated quickly up to 400 °C under the pressure of 30 MPa for 8 ms as reaction time. The XRD results revealed that the crystal phase of the obtained particles was cubic BaTiO 3, indicating that the hydrothermal reaction in supercritical water was successfully proceeded under present reaction conditions. Primarily particle size of the BaTiO 3 nanoparticle was determined by means of BET surface area, as small as less than 10 nm with decreasing the reaction pH. In contrast, dispersed particle size in solution measured by DLS (dynamic light scattering) technique decreased from 260 to 90 nm with increasing the reactants concentration. Aggregation of BaTiO 3 nanoparticles might be depressed in the presence of coexisting nitrate anions.

Hayashi, Hiromichi; Noguchi, Takio; Islam, Nazrul M.; Hakuta, Yukiya; Imai, Yusuke; Ueno, Nobuhiko

2010-06-01

364

Na-K-Cl Cotransporter-1 in the Mechanism of Ammonia-induced Astrocyte Swelling*  

PubMed Central

Brain edema and the consequent increase in intracranial pressure and brain herniation are major complications of acute liver failure (fulminant hepatic failure) and a major cause of death in this condition. Ammonia has been strongly implicated as an important factor, and astrocyte swelling appears to be primarily responsible for the edema. Ammonia is known to cause cell swelling in cultured astrocytes, although the means by which this occurs has not been fully elucidated. A disturbance in one or more of these systems may result in loss of ion homeostasis and cell swelling. In particular, activation of the Na-K-Cl cotransporter (NKCC1) has been shown to be involved in cell swelling in several neurological disorders. We therefore examined the effect of ammonia on NKCC activity and its potential role in the swelling of astrocytes. Cultured astrocytes were exposed to ammonia (NH4Cl; 5 mm), and NKCC activity was measured. Ammonia increased NKCC activity at 24 h. Inhibition of this activity by bumetanide diminished ammonia-induced astrocyte swelling. Ammonia also increased total as well as phosphorylated NKCC1. Treatment with cyclohexamide, a potent inhibitor of protein synthesis, diminished NKCC1 protein expression and NKCC activity. Since ammonia is known to induce oxidative/nitrosative stress, and antioxidants and nitric-oxide synthase inhibition diminish astrocyte swelling, we also examined whether ammonia caused oxidation and/or nitration of NKCC1. Cultures exposed to ammonia increased the state of oxidation and nitration of NKCC1, whereas the antioxidants N-nitro-l-arginine methyl ester and uric acid all significantly diminished NKCC activity. These agents also reduced phosphorylated NKCC1 expression. These results suggest that activation of NKCC1 is an important factor in the mediation of astrocyte swelling by ammonia and that such activation appears to be mediated by NKCC1 abundance as well as by its oxidation/nitration and phosphorylation. PMID:18849345

Jayakumar, Arumugam R.; Liu, Mingli; Moriyama, Mitsuaki; Ramakrishnan, Ramugounder; Forbush, Bliss; Reddy, Pichili V. B.; Norenberg, Michael D.

2008-01-01

365

Branched-chain amino acids and muscle ammonia detoxification in cirrhosis.  

PubMed

Branched-chain amino acids (BCAA) are used as a therapeutic nutritional supplement in patients with cirrhosis and hepatic encephalopathy (HE). During liver disease, the decreased capacity for urea synthesis and porto-systemic shunting reduce the hepatic clearance of ammonia and skeletal muscle may become the main alternative organ for ammonia detoxification. We here summarize current knowledge of muscle BCAA and ammonia metabolism with a focus on liver cirrhosis and HE. Plasma levels of BCAA are lower and muscle uptake of BCAA seems to be higher in patients with cirrhosis and hyperammonemia. BCAA metabolism may improve muscle net ammonia removal by supplying carbon skeletons for formation of alfa-ketoglutarate that combines with two ammonia molecules to become glutamine. An oral dose of BCAA enhances muscle ammonia metabolism but also transiently increases the arterial ammonia concentration, likely due to extramuscular metabolism of glutamine. We, therefore, speculate that the beneficial effect of long term intake of BCAA on HE demonstrated in clinical studies may be related to an improved muscle mass and nutritional status rather than to an ammonia lowering effect of BCAA themselves. PMID:23315357

Dam, Gitte; Ott, Peter; Aagaard, Niels Kristian; Vilstrup, Hendrik

2013-06-01

366

Highly efficient and versatile synthesis of lactams and N-heterocycles via Al(OTf)3-catalyzed cascade cyclization and ionic hydrogenation reactions.  

PubMed

The discovery and development of an efficient and versatile method for the synthesis of N-substituted lactams is described. Pyrrolindinones, piperidones, and structurally related heterocycles were formed by Al(OTf)3-catalyzed cascade cyclization and ionic hydrogenation reactions of corresponding nitrogen substituted ketoamides in good yields. PMID:24313882

Qi, Jianguo; Sun, Chenbin; Tian, Yulin; Wang, Xiaojian; Li, Gang; Xiao, Qiong; Yin, Dali

2014-01-01

367

Synthesis of a Self-Healing Polymer Based on Reversible Diels-Alder Reaction: An Advanced Undergraduate Laboratory at the Interface of Organic Chemistry and Materials Science  

ERIC Educational Resources Information Center

This laboratory experiment exposes students to the chemistry of self-healing polymers based on a Diels-Alder reaction. Students accomplish a multistep synthesis of a monomer building block and then polymerize it to form a cross-linked polymer. The healing capability of the polymer is verified by differential scanning calorimetry (DSC) experiments.…

Weizman, Haim; Nielsen, Christian; Weizman, Or S.; Nemat-Nasser, Sia

2011-01-01

368

Synthesis of 3-heteryl substituted pyrrolidine-2,5-diones via catalytic Michael reaction and evaluation of their inhibitory activity against InhA and Mycobacterium tuberculosis.  

PubMed

In the present paper, we report the synthesis via catalytic Michael reaction and biological results of a series of 3-heteryl substituted pyrrolidine-2,5-dione derivatives as moderate inhibitors against Mycobacterium tuberculosis H37Rv growth. Some of them present also inhibition activities against InhA. PMID:24269516

Matviiuk, Tetiana; Mori, Giorgia; Lherbet, Christian; Rodriguez, Frédéric; Pasca, Maria Rosalia; Gorichko, Marian; Guidetti, Brigitte; Voitenko, Zoia; Baltas, Michel

2014-01-01

369

SOLID-LIQUID PHASE TRANSFER CATALYZED SYNTHESIS OF CINNAMYL ACETATE-KINETICS AND ANALYSIS OF FACTORS AFFECTING THE REACTION IN A BATCH REACTOR  

EPA Science Inventory

The use of solid-liquid phase transfer catalysis has an advantage of carrying out reaction between two immiscible substrates, one in solid phase and the other in liquid phase, with high selectivity and at relatively low temperatures. In this study we investigated the synthesis ci...

370

An efficient green protocol for the synthesis of chalcones by a Claisen–Schmidt reaction using bismuth(III)chloride as a catalyst under solvent-free condition  

Microsoft Academic Search

An environmentally benign protocol for the synthesis of chalcones by the Claisen–Schmidt condensation of aldehydes with ketones using eco-friendly non-toxic bismuth(III)chloride catalyst under solvent-free condition is reported. In this protocol, the reaction time is very short, yields are high, and there are no other pollutants formed.

Dhruva Kumar; Jagir S. Sandhu

2010-01-01

371

CATALYST-FREE REACTIONS UNDER SOLVENT-FEE CONDITIONS: MICROWAVE-ASSISTED SYNTHESIS OF HETEROCYCLIC HYDRAZONES BELOW THE MELTING POINT OF NEAT REACTANTS: JOURNAL ARTICLE  

EPA Science Inventory

NRMRL-CIN-1437 Jeselnik, M., Varma*, R.S., Polanc, S., and Kocevar, M. Catalyst-free Reactions under Solvent-fee Conditions: Microwave-assisted Synthesis of Heterocyclic Hydrazones below the Melting Point of Neat Reactants. Published in: Chemical Communications 18:1716-1717 (200...

372

Synthesis of unnatural amino acids via microwave-assisted regio-selective one-pot multi-component reactions of sulfamidates  

EPA Science Inventory

Synthesis of triazole-based unnatural amino acids, triazole bisaminoacids and ß-amino triazole has been described via stereo and regioselective one-pot multi-component reaction of sulfamidates, sodium azide, and alkynes under MW irradiation conditions. The developed method is app...

373

ZnO nanoparticles: An efficient nanocatalyst for the synthesis of ?-acetamido ketones\\/esters via a multi-component reaction  

Microsoft Academic Search

A convenient one-pot multi-component reaction of aromatic aldehydes, enolizable ketones or ?-keto esters and acetonitrile in the presence of acetyl chloride and 10mol% ZnO nanoparticles for the synthesis of ?-acetamido ketones\\/esters at room temperature is described.

Zohreh Mirjafary; Hamdollah Saeidian; Azam Sadeghi; Firouz Matloubi Moghaddam

2008-01-01

374

A New Reaction Manifold for the Barton Radical Intermediates: Synthesis of N-Heterocyclic Furanosides and Pyranosides via the Formation of the C1-C2  

E-print Network

A New Reaction Manifold for the Barton Radical Intermediates: Synthesis of N in the deoxygenation process is the collapse of the intermediate 1. Under carefully controlled conditions to deoxygenation.10 These expecta- tions have been borne out, and in this communication we report our initial

RajanBabu, T. V. "Babu"

375

Just 40 years ago, computational methods for simulating chemical reactions used in synthesis did not exist. Since then, the discovery of  

E-print Network

Just 40 years ago, computational methods for simulating chemical reactions used in synthesis did not exist. Since then, the discovery of several computational principles and algorithms -- together with the development of fast computers -- has resulted in enormous leaps in the accuracy and speed of computational

Cai, Long

376

A Fully Biobased Epoxy Resin from Vegetable Oils: From the Synthesis of the Precursors by Thiol-ene Reaction to the Study of the Final Material  

E-print Network

resins coming from biomass with hardeners derived from petroleum is not satisfactory in term of conceptsA Fully Biobased Epoxy Resin from Vegetable Oils: From the Synthesis of the Precursors by Thiol agent for bio-based epoxy resin. The thermal crosslinking reaction between AGSO and epoxi- dized linseed

Boyer, Edmond

377

One-pot, three-component, sequential Michael-Michael-ring-closure reactions. Annulation of meta-dicarboxylated aromatic rings. Total synthesis of juncunol  

Microsoft Academic Search

The preparative value of one-pot, multicomponent, sequential Michael-Michael-ring-closure reactions followed by aromatization\\u000a is illustrated in two ways: (1) by a multi-gram example, and (2) by a total synthesis of juncunol, an unusual vinyldihydrophenanthrene.

Gary H. Posner; Karen A. Canella; Ernest F. Silversmith

1988-01-01

378

Unexpected Pd-catalyzed coupling, propargyl-allenyl isomerization and alder-ene reaction: facile synthesis of some not readily available 2,3-dihydrofuran derivatives.  

PubMed

An interesting sequential reaction involving Pd-catalyzed coupling, propargyl-allenyl isomerization, and Alder-ene cycloaddition is reported, providing a facile synthesis of some not readily available 2,3-dihydrofurans from electron-deficient vinyl or aromatic halides and 1-aryl-prop-2-ynyl 3'-methylbut-2'-enyl ethers. PMID:19413278

Shen, Ruwei; Zhu, Shugao; Huang, Xian

2009-06-01

379

Carbon-bridged biphenolate lanthanide complexes: synthesis and their catalytic activity for the Diels Alder reaction  

NASA Astrophysics Data System (ADS)

Reaction of anhydrous ErCl 3 with sodium salt of carbon-bridged biphenolate, MBMPNa 2 (MBMP 2-=2,2'-methylene-bis (6- tert-butyl-4-methyl-phenoxo)), in 1:2 molar ratio in THF at room temperature gave the lanthanide 'ate' complexes (THF)Er(MBMP) 2Na(THF) 2 ( 1) in high isolated yield. Similarly reaction of anhydrous SmCl 3 with 2 equiv. of MBMPNa 2 in THF, then crystallization from toluene in the presence of TMEDA, afforded the final product (THF)Sm(MBMP) 2Na(TMEDA) ( 2). Both complexes 1 and 2 were well characterized by elemental analysis, IR spectra, and X-ray diffraction analysis. Preliminary results revealed that these complexes are able to act as Lewis acid to catalyze the Diels-Alder reaction of cyclopentadiene with methyl acrylate in good activity and stereoselectivity.

Xu, Xiaoping; Ma, Mengtao; Yao, Yingming; Zhang, Yong; Shen, Qi

2005-05-01

380

Suzuki Cross-Coupling Reactions: Synthesis of Unsymmetrical Biaryls in the Organic Laboratory  

NASA Astrophysics Data System (ADS)

An organic chemistry laboratory experiment in which unsymmetrical biaryl alcohols are synthesized in a two-step process is described. In the first step, an aryl boronic acid is coupled with p-bromoacetaldehyde or p-bromoacetophenone. The carbonyl group of the product is reduced with sodium borohydride in the second step. The products of both reactions are solids that can be easily purified by recrystallization. The primary purpose in implementing this experiment was to give students additional exposure to transition-metal-catalyzed reactions. The experiment provides an opportunity to discuss a number of topics, including the palladium-catalyzed cross-coupling mechanism, reactions that permit the formation of C-C bonds in an aqueous environment, the reduction of carbonyl groups with metal hydrides, and atropisomerism. The students can use IR and 1H NMR spectroscopy to determine the structure of their products, and so this laboratory also allows them to improve their spectral interpretation skills.

Callam, Christopher S.; Lowary, Todd L.

2001-07-01

381

Evaluation of a commercial packed bed flow hydrogenator for reaction screening, optimization, and synthesis  

PubMed Central

Summary The performance of the ThalesNano H-Cube®, a commercial packed bed flow hydrogenator, was evaluated in the context of small scale reaction screening and optimization. A model reaction, the reduction of styrene to ethylbenzene through a 10% Pd/C catalyst bed, was used to examine performance at various pressure settings, over sequential runs, and with commercial catalyst cartridges. In addition, the consistency of the hydrogen flow was indirectly measured by in-line UV spectroscopy. Finally, system contamination due to catalyst leaching, and the resolution of this issue, is described. The impact of these factors on the run-to-run reproducibility of the H-Cube® reactor for screening and reaction optimization is discussed. PMID:21915219

Bryan, Marian C; Wernick, David; Hein, Christopher D; Petersen, James V; Eschelbach, John W

2011-01-01

382

Synthesis of Polycyclic Nitrogen Heterocycles via Alkene Aminopalladation/Carbopalladation Cascade Reactions  

PubMed Central

A new method for the synthesis of tricyclic nitrogen heterocycles from N,2-diallylaniline derivatives is described. These transformations proceed via sequential alkene aminopalladation of an intermediate LnPd(Ar)(NRR’) species followed by alkene carbopalladation of the resulting LnPd(Ar)(R) complex. Both alkene insertion steps occur in preference to C–N or C–C bond-forming reductive elimination. An unusual 1,3-palladium shift occurs when 2-Allyl-N-(2-vinylphenyl)aniline is employed as substrate, which yields a tetracyclic molecule with three contiguous stereocenters. PMID:20141119

Schultz, Danielle M.; Wolfe, John P.

2010-01-01

383

(Diisopinocampheyl)borane-Mediated Reductive Aldol Reactions of Acrylate Esters: Enantioselective Synthesis of Anti-Aldols  

PubMed Central

The (diisopinocampheyl)borane promoted reductive aldol reaction of acrylate esters 4 is described. Isomerization of the kinetically formed Z(O)-enolborinate 5Z to the thermodynamic E(O)-enolborinate 5E via 1,3-boratropic shifts, followed by treatment with representative achiral aldehydes, leads to anti-?-methyl-?-hydroxy esters 9 or 10 with excellent diastereo- (up to ?20:1 dr) and enantioselectivity (up to 87% ee). Results of double asymmetric reactions of 5E with several chiral aldehydes are also presented. PMID:23885946

Allais, Christophe; Nuhant, Philippe; Roush, William R.

2013-01-01

384

(Diisopinocampheyl)borane-mediated reductive aldol reactions of acrylate esters: enantioselective synthesis of anti-aldols.  

PubMed

The (diisopinocampheyl)borane promoted reductive aldol reaction of acrylate esters 4 is described. Isomerization of the kinetically formed Z(O)-enolborinate 5Z to the thermodynamic E(O)-enolborinate 5E via 1,3-boratropic shifts, followed by treatment with representative achiral aldehydes, leads to anti-?-methyl-?-hydroxy esters 9 or 10 with excellent diastereo- (up to ?20:1 dr) and enantioselectivity (up to 87% ee). The results of double asymmetric reactions of 5E with several chiral aldehydes are also presented. PMID:23885946

Allais, Christophe; Nuhant, Philippe; Roush, William R

2013-08-01

385

Stereoselective Synthesis of Saturated Heterocycles via Pd-Catalyzed Alkene Carboetherification and Carboamination Reactions  

PubMed Central

The development of Pd-catalyzed carboetherification and carboamination reactions between aryl/alkenyl halides and alkenes bearing pendant heteroatoms is described. These transformations effect the stereoselective construction of useful heterocycles such as tetrahydrofurans, pyrrolidines, imidazolidin-2-ones, isoxazolidines, and piperazines. The scope, limitations, and applications of these reactions are presented, and current stereochemical models are described. The mechanism of product formation, which involves an unusual intramolecular syn-insertion of an alkene into a Pd-Heteroatom bond is also discussed in detail. PMID:19183704

Wolfe, John P.

2009-01-01

386

Reaction of polyfluorinated imines with trifluoromethyltrimethylsilane. Direct synthesis of N-(perfluoro -t-butyl)amines  

Microsoft Academic Search

The reaction of N-arylimines of hexafluoroacetone and CF3Si(CH3)3 (1) in the presence of CsF results in a 48–84% yield formation of ArN(H)C(CF3)3. The reaction requires an equimolar amount of CsF and rapidly proceeds in solvents such as THF or monoglyme. Interaction of CF3N?C(CF3)2 with excess of 1 leads to the formation of novel amine [(CF3)3C]2NH. Stable salt of this amine

Viacheslav A. Petrov

2000-01-01

387

A mini-review on ammonia decomposition catalysts for on-site generation of hydrogen for fuel cell applications  

Microsoft Academic Search

Due to the drive for better environmental protection and energy conversion efficiency, on-site generation of COx-free hydrogen from ammonia decomposition for fuel cell applications has attracted much attention. The development of high performance solid catalysts is essential for the supply of such hydrogen from ammonia. In this mini-review, we provide a summary of the reaction kinetics of catalytic ammonia decomposition.

S. F. Yin; B. Q. Xu; X. P. Zhou; C. T. Au

2004-01-01

388

Synthesis of nanostructured AlN by solid state reaction of Al and diaminomaleonitrile  

SciTech Connect

The solid state reaction of diaminomaleonitrile (DAMN) with aluminum via both mechanochemical and thermal treatment routes was studied by X-ray diffraction and Fourier transform infrared spectroscopy. During the milling process, the reaction starts with the deammoniation of the DAMN molecules, followed by the formation of nanostructured AlN powder as the main solid product after milling for 7 h. The reactivity of the mixed powder was also investigated during the conventional thermal treatment process using differential scanning calorimetry, derivative thermogravimetry and thermogravimetric analysis. The results reveal that DAMN starts to polymerize at 192 Degree-Sign C by the elimination of the amine groups. Furthermore, increasing the annealing temperature leads to the formation of a nitrogen-containing carbonaceous material with the structure similar to non-crystalline carbon. However, no evidence for the formation of AlN was observed in the annealed samples even at temperatures as high as the Al melting point. - Graphical abstract: AlN nanoparticles obtained after milling of Al and diaminomaleonitrile (DAMN) for 12 h. Highlights: Black-Right-Pointing-Pointer Solid state reaction of diaminomaleonitrile (DAMN) with Al was studied via mechanochemical and thermal treatment routs. Black-Right-Pointing-Pointer Nanocrystalline AlN was successfully synthesized by the mechanochemical process. Black-Right-Pointing-Pointer The C/N material was formed by polymerization of DAMN during the thermal treatment process. Black-Right-Pointing-Pointer No reaction between DAMN and Al was detected during the thermal treatment method.

Rounaghi, S.A., E-mail: s.a.rounaghi@gmail.com [Department of Materials Engineering, Ferdowsi University of Mashhad. P.O. Box no. 91775-1111, Mashhad (Iran, Islamic Republic of); IFW Dresden, Institut fuer Komplexe Materialien, Postfach 27 01 16, Dresden D-01171 (Germany); Eshghi, H., E-mail: heshghi@ferdowsi.um.ac.ir [Department of Chemistry, Ferdowsi University of Mashhad. P.O. Box no. 91775-1436, Mashhad (Iran, Islamic Republic of); Kiani Rashid, A.R.; Vahdati Khaki, J. [Department of Materials Engineering, Ferdowsi University of Mashhad. P.O. Box no. 91775-1111, Mashhad (Iran, Islamic Republic of)] [Department of Materials Engineering, Ferdowsi University of Mashhad. P.O. Box no. 91775-1111, Mashhad (Iran, Islamic Republic of); Samadi Khoshkhoo, M.; Scudino, S. [IFW Dresden, Institut fuer Komplexe Materialien, Postfach 27 01 16, Dresden D-01171 (Germany)] [IFW Dresden, Institut fuer Komplexe Materialien, Postfach 27 01 16, Dresden D-01171 (Germany); Eckert, J. [IFW Dresden, Institut fuer Komplexe Materialien, Postfach 27 01 16, Dresden D-01171 (Germany) [IFW Dresden, Institut fuer Komplexe Materialien, Postfach 27 01 16, Dresden D-01171 (Germany); TU Dresden, Institut fuer Werkstoffwissenschaft, Dresden D-01062 (Germany)

2013-02-15

389

Synthesis and Investigation of Chitosan Derivatives Formed by Reaction with Acyl Chlorides  

Microsoft Academic Search

Chitosan is a linear polysaccharide obtained from chitin deacetylation. Several applications of chitosan have been proposed in specialized literature: water treatment, cosmetic, food additives, development of biomaterials, and mainly drug delivery. In the present paper chitosan was hydrophobized by esterification reaction with acyl chlorides; its derivatives were swelling in water and characterized by C? and H?NMR and infrared spectroscopy. The

Máira R. Rodrigues

2005-01-01

390

Hydrothermal synthesis of Eu3+ doped yttria nanoparticles using a supercritical flow reaction system  

NASA Astrophysics Data System (ADS)

Highly crystalline Eu3+ doped yttria nanoparticle was synthesized by hydrothermal reaction in supercritical water using a continuous flow reaction system (FHT). The reactants of Y(NO3)3/Eu(NO3)3 mixed solution and KOH solution were used as starting materials and that was heated quickly up to 350-450 °C under the pressure of 30 MPa for 0.1-15 s as reaction time. The XRD results revealed that the crystal phase of as-prepared particles was YOOH and converted into cubic-phase Y2O3 after annealing above 550 °C. Primarily particle size of the YOOH was as small as less than 50 nm, keeping after annealing at 800 °C. Effects of reaction time, annealing temperature and Eu doping amount on photoluminescence were examined. The as-prepared particles exhibited red emission without annealing at high temperatures whereas photoluminescent intensity at 612 nm was increased with an increase in the annealing temperature. Photoluminescent intensity was increased with an increase in the Eu doping amount until 4 mol % and saturated at 8 mol %. The photoluminescent property was compared with reference samples via conventional co-precipitation (CP) and batchwise hydrothermal (BHT) methods. The photoluminescent intensity for annealed samples increased in the order: FHT < BHT < CP owing to the increased particle size.

Hayashi, Hiromichi

2012-01-01

391

Recent Developments in Pd-Catalyzed Alkene Aminoarylation Reactions for the Synthesis of Nitrogen Heterocycles  

PubMed Central

This short review describes new developments in Pd-catalyzed aminoarylation reactions between aryl halides and alkenes bearing pendant nitrogen nucleophiles. These transformations provide a novel and powerful method for accessing numerous 3-, 5-, 6-, and 7-membered nitrogen heterocycles. PMID:23243321

Schultz, Danielle M.; Wolfe, John P.

2012-01-01

392

Enantioselective synthesis of succinic acids and ?-lactones via palladium catalysed allylic substitution reactions  

Microsoft Academic Search

The palladium catalysed reaction between non-symmetrical allyl acetates and sodiodimethylmalonate proceeds in high yields and enantioselectivities (up to 99% ee) using a diphenylphosphinoaryl oxazoline ligand. The so-formed substitution products are transformed into enantiomerically enriched succinic acids and also into enantiomerically enriched ?-lactones.

Steven J Coote

1995-01-01

393

Synthesis of (-) Ilimaquinone via a Radical Decarboxylation and Quinone Addition Reaction  

E-print Network

to chromatographically and spectroscopically (1H NMR) homogeneous materials, unless otherwise stated. Reactions were-layer chromatography separations were carried out on 0.25 or 0.50 mm E. Merck silica gel plates (60F- 254). NMR spectra of thiohydroxamic acid derivatives: In a flask protected from the light with aluminum foil at 0 °C was added

Theodorakis, Emmanuel

394

Synthesis and antifungal activities of new pyrazole derivatives via 1,3-dipolar cycloaddition reaction.  

PubMed

A series of cycloadducts--pyrazoles via 1,3-dipolar cycloaddition reactions of generated nitrilimines with N-(4-chloro-2-fluorophenyl)maleimide were described. The novel compounds synthesized were characterized by (1)H NMR, MS, and elemental analysis. The fungicidal tests showed that most of the title compounds exhibit significant fungicidal activities against Corynespora cassiicola. PMID:20486935

Zhang, Chuan-Yu; Liu, Xing-Hai; Wang, Bao-Lei; Wang, Su-Hua; Li, Zheng-Ming

2010-05-01

395

N-heterocyclic carbene-catalyzed internal redox reaction of alkynals: an efficient synthesis of allenoates.  

PubMed

An efficient N-heterocyclic carbene (NHC)-catalyzed internal redox reaction of alkynals that bear a ? leaving group has been developed. This process provides a new access to a range of allenoates in good yields. Preliminary results demonstrate that the enantioselective variant can also be achieved. PMID:22352302

Zhao, Yu-Ming; Tam, Yik; Wang, Yu-Jie; Li, Zigang; Sun, Jianwei

2012-03-16

396

Domino allylic amination/Sonogashira/heterocyclisation reactions: palladium-catalysed three-component synthesis of pyrrolesw  

E-print Network

in fair to good yields in the presence of palladium and copper catalysts under mild reaction conditions. The palladium species acts either as a Sonogashira catalyst9 or as a Lewis acid promoter for the 5-endo dig carbon­iodine bonds as dielectrophile was prepared from buta-2,3-dienoic acid 1 by addition of iodine

Paris-Sud XI, Université de

397

Pseudo-five-component reaction between 3-formylchromones, meldrum's acid, isocyanides and primary arylamines: diversity-oriented synthesis of novel chromone-containing peptidomimetics.  

PubMed

An efficient and practical method has been developed for the diversity-oriented synthesis of chromone-containing tripeptides via pseudo-five-component reaction between 3-formylchromones, Meldrum's acid, isocyanides and primary aromatic amines for the generation of a wide range of structurally interesting and pharmacologically significant compounds at ambient temperature. It is worth mentioning that in the course of this reaction, five new bonds (two C-C bonds, two C-N bonds and one C?O bond) are formed. In the present reaction three amide bonds are newly formed. PMID:21919509

Teimouri, Mohammad Bagher; Akbari-Moghaddam, Peyman; Golbaghi, Golara

2011-11-14

398

Synthesis of polymer-supported dendritic palladium nanoparticle catalysts for Suzuki coupling reaction  

NASA Astrophysics Data System (ADS)

New bead-shaped heterogeneous nanoparticle catalysts viz., amino-terminated poly(amidoamine) (PAMAM) grafted on poly(styrene)-co-Poly(vinylbenzylchloride) (PS-Poly(VBC)) matrices immobilized/stabilized with palladium nanoparticle were prepared by simplified procedure. The first step is the preparation of PS-Poly(VBC) beads by suspension polymerization method. Second, the PAMAM G(0) G(1) and G(2) dendrimers were grafted individually onto the PS-Poly(VBC) matrices via divergent method by repeating two reactions, i.e., Michael addition of methyl acrylate to surface amino groups of aminomethylated PS-Poly(VBC) matrixes followed by amidation of the resulting esters with ethylene diamine. The resulting three types of PAMAM G(0), G(1) and G(2) grafted on PS-Poly(VBC) matrices were complexed individually with PdCl2 and thus yielded the corresponding new bead-shaped heterogeneous nanoparticle catalyst immobilized with PdNPs. The appearance of surface plasmon resonance band noticed at 547 nm in UV confirms the formation of PdNPs. The SEM result shows that the intensity of white patches due to immobilization of PdNPs increases with generation number and XRD reveals that the crystalline nature was decreased against generation number of the PAMAM. The catalytic efficiency of PS-Poly(VBC)-NH2-PdNPs-G(0), G(1) and G(2) catalysts were examined by Suzuki coupling reaction performed in mixture of water/ethanol. The observed reaction yield reveals that the activity was proportional to the generation number of PAMAM grafted onto the PS-Poly(VBC) matrices. The percentage of reaction yield (biphenyl) is sustained to ?70 % even up to five cycles and this in turn confirms the stability of the catalysts. These catalysts can be used to conduct the Suzuki-coupling reaction in continuous mode operation in industrial scale.

Murugan, Eagambaram; Jebaranjitham, J. Nimita; Usha, A.

2012-09-01

399

Thermodynamic and kinetic studies of the liquid phase synthesis of tert-butyl ethyl ether using a reaction calorimeter  

SciTech Connect

The liquid-phase addition of ethanol to isobutene to give tert-butyl ethyl ether (ETBE) on the ion-exchange resin Lewatit K2631 has been studied in a calorimetric reactor. The heat capacity of ETBE and the enthalpy change of the ETBE synthesis reaction in the temperature range 312--333 K have been determined. ETBE heat capacity in the liquid phase has been found to follow the equation C{sub p} = 486.73 {minus} 2.253 (T/K) + 0.00479 (T/K){sup 2}. At 298 K the standard molar reaction enthalpy is {Delta}H{degree} = {minus}32.0 kJ/mol. A determination of the apparent activation energy of 86.5--89.2 kJ/mol has been performed graphically from the plots of heat flow rate versus time. An Eley-Rideal mechanism, with two active sites involved in the rate determining step, has been proved to be correct. From this model an apparent activation energy of 80.6 kJ/mol is deduced. A {minus}3.0 kJ/mol value has been found for the adsorption enthalpy of ethanol. This allows the estimation of the actual gel-phase activation energy of 77.6 kJ/mol.

Sola, L.; Pericas, M.A.; Cunill, F.; Tejero, J. [Univ. de Barcelona (Spain)

1995-11-01

400

An extremely efficient three-component reaction of aldehydes/ketones, amines, and phosphites (Kabachnik-Fields reaction) for the synthesis of alpha-aminophosphonates catalyzed by magnesium perchlorate.  

PubMed

Commercially available magnesium perchlorate is reported as an extremely efficient catalyst for the synthesis of alpha-aminophosphonates. A three-component reaction (3-CR) of an amine, an aldehyde or a ketone, and a di-/trialkyl phosphite (Kabachnik-Fields reaction) took place in one pot under solvent-free conditions to afford the corresponding alpha-aminophosphonates in high yields and short times. The use of solvent retards the rate of the reaction and requires a much longer reaction time than that for neat conditions. The reactions involving an aldehyde, an aromatic amine without any electron-withdrawing substituent, and a phosphite are carried out at rt. The reactions involving cyclic ketones, aromatic amines with an electron-withdrawing substituent, and aryl alkyl ketone (e.g., acetophenone) require longer reaction times at rt or heating. Magnesium perchlorate was found to be superior to other metal perchlorates and metal triflates during the reaction of 4-methoxybenzaldehyde, 2,4-dinitroaniline, and dimethyl phosphite. The catalytic activity of various magnesium compounds was influenced by the counteranion, and magnesium perchlorate was found to be the most effective. The reaction was found to be general with di-/trialkyl phosphites and diaryl phosphite. The Mg(ClO4)2-catalyzed alpha-aminophosphonate synthesis in the present study perhaps represents a true three-component reaction as no intermediate formation of either an imine or alpha-hydroxy phosphonate was observed that indicated the simultaneous involvement of the carbonyl compound, the amine, and the phosphite in the transition state. PMID:17253748

Bhagat, Srikant; Chakraborti, Asit K

2007-02-16

401

Synthesis of Metal Oxide Particles Using Reaction Route from Rare-Earth Metal-EDTA Complexes  

NASA Astrophysics Data System (ADS)

Highly dense, spherical yttria (Y2O3) and erbia (Er2O3) particles were synthesized from their corresponding metal-ethylenediaminetetraacetic (EDTA) complexes. The EDTA·Y·H and EDTA·Er·H complexes were prepared in powdered form. These complexes were used as the staring materials for synthesis of the Y2O3 and Er2O3 particles. The particles were synthesized using an H2-O2 flame produced with a commercial flame spray apparatus. Crystalline structure, surface and cross-sectional morphologies, and elemental distribution of the synthesized particles were investigated. It was confirmed that the crystalline phases of the Y2O3 and Er2O3 particles were homogeneous. In addition, the elemental distribution of the particles was uniform. These results indicate that dense, spherical particles of Y2O3 and Er2O3 have been synthesized with EDTA·Y·H and EDTA·Er·H complexes, respectively.

Komatsu, Keiji; Tsuchiya, Takaaki; Hasebe, Yasuhiro; Sekiya, Tetsuo; Toyama, Ayumu; Nakamura, Atsushi; Akasaka, Hiroki; Saitoh, Hidetoshi

2014-06-01

402

In-situ time resolved synchrotron powder diffraction studies of synthesis and chemical reactions  

SciTech Connect

Equipment for time and temperature dependent powder diffraction has been developed, especially in order to be able to study hydrothermal syntheses of zeolites. The system is very versatile and has so far been used to study e.g. hydrothermal syntheses of zeolites and aluminophosphates, syntheses of layered phosphates, formation of Sorel cements, dehydration and phase transformations of zeolites, solid state synthesis of lanthanum manganites, ion exchange of zeolites using molten salt, and oxidation/reduction of lanthanum manganites at high temperatures. The sample is contained in quartz capillaries and is heated using a stream of hot air. External pressure can be applied allowing hydrothermal syntheses at temperatures up to 200 C to be performed. Controlled atmosphere is obtained by flowing gas or a mixture of gases through the capillary.

Norby, P.

1995-09-01

403

Synthesis of YAG phosphor particles with excellent morphology by solid state reaction  

NASA Astrophysics Data System (ADS)

Cerium doped yttrium aluminum garnet (YAG:Ce) has been chosen as WLED phosphors for its appropriate spectral property. However, YAG powders synthesized by several methods do not satisfy commercial requirements in mobility, size distribution, luminescent intensity, etc. With flux added in the synthesis, well-shaped crystallites can nucleate and grow in the wetted micro domains. High temperature compensates the adverse effect of intermediate product on particle size. The final products are phosphor powders composed of uniformly distributed large particles. Preferred orientation in the XRD patterns confirms that the isolated particles are single crystals other than agglomeration of fine grains. This kind of phosphors has a better performance in WLED devices. This work will improve the commercial production of WLED phosphors.

Song, Zhen; Liao, Jing; Ding, Xianlin; Liu, Xiaolang; Liu, Quanlin

2013-02-01

404

Fischer-Tropsch Synthesis: Characterization and Reaction Testing of Cobalt Carbide  

SciTech Connect

Hydrogenation of carbon monoxide was investigated for cobalt carbide synthesized from Co{sub 3}O{sub 4} by CO carburization in a fixed-bed reactor. The cobalt carbide synthesized was characterized by BET surface area, X-ray diffraction, scanning electron microscopy, X-ray absorption near edge spectroscopy, and extended X-ray absorption fine structure spectroscopy. The catalysts were tested in the slurry phase using a continuously stirred tank reactor at P = 2.0 MPa, H{sub 2}/CO = 2:1 in the temperature range of 493-523 K, and with space velocities varying from 1 to 3 Nl h{sup -1} g{sub cat}{sup -1}. The results strongly suggest that a fraction of cobalt converts to a form with greater metallic character under the conditions employed. This was more pronounced on a Fischer-Tropsch synthesis run conducted at a higher temperature (523 versus 493 K).

Khalid S.; Mohandas J.C.; Gnanamani M.K.; Jacobs G.; Ma W.; Ji Y.; Davis B.H.

2011-08-15

405

Synthesis of novel 2H,5H-Dihydrofuran-3-yl Ketones via ISNC reactions  

PubMed Central

Unique 1-[2H,5H-dihydrofur-3-yl]ketones have been synthesized from propargylic nitroethers via intramolecular cycloadditions involving silyl nitronates. Various substituent groups were placed on the 2 and 5 positions of the dihydrofuran rings. We examined the scope of the long-range coupling in proton NMR of the oxo-dihydrofuran products. The identities of the diastereomers resulting from the Michael Addition/cycloaddition reactions were tentatively assigned for the first time. CAChe MNDO PM5 and CONFLEX programs were engaged to assist with the identification of these stereoisomers. The reaction times and conditions for these oxo-dihydrofurans were found to be different than that of the published dihydrofuranals, which led us to propose a different mechanism. PMID:20161382

Grandbois, Matthew L.; Betsch, Kelsie J.; Buchanan, William D.; Duffy-Matzner, Jetty L.

2009-01-01

406

Synthesis of bistetrahydroquinolines as potential anticholinesterasic agents by double Diels-Alder reactions.  

PubMed

The tetrahydroquinoline ring system is a unit found in many biologically active natural products and pharmacologically relevant therapeutic agents. A new series of bistetrahydroquinolines (bis-THQs) was synthesized using imino Diels-Alder reactions between dialdehydes, anilines and N-vinyl-2-pyrrolidone (NVP). The notable features of this procedure are mild reaction conditions, greater selectivity and good yields of products. In addition, the inhibitory activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) of some selected derivatives is reported. The feasible binding modes of these active compounds, within AChE and BuChE binding sites, were predicted by molecular docking experiments and their binding affinity was estimated by means of free energy calculations through the MM-GBSA approximation. PMID:24141245

Duarte, Yorley; Gutiérrez, Margarita; Astudillo, Luis; Alzate-Morales, Jans; Valdés, Natalia

2013-01-01

407

Controlled Synthesis of ZnO Microcrystals by a Simple Microwave Reaction Method  

Microsoft Academic Search

A simple microwave reaction method without using additives was employed to synthesize ZnO microcrystals with controllable morphology. Zinc acetate dehydrate was selected as reactants and ethylene glycol-water was solvents. Peanutlike ZnO built up by short nanorods, multi-sphere aggregations, spherelike microcrystals covered by ZnO nanoparticles, and spinous morphology mixed with flake like ZnO were obtained only by change of power and

Lifei Chen; Yu Wei

2010-01-01

408

Coupling of the electroenzymatic reduction of NAD + with a synthesis reaction  

Microsoft Academic Search

Hydrogenase from Alcaligenes eutrophus H16 (E.C. 1.12.1.2) catalyzes the electrochemical reduction of the pyridine cofactor NAD+. Previous studies emphasized the kinetics and thermodynamics of the reaction. We applied hydrogenase to regenerate NADH for the transformation of ?-ketoglutarate into l-glutamate catalyzed by an l-glutamate dehydrogenase. The system was first studied in an electrochemical thin-layer cell. A turnover number (TN) of 450

Jean Cantet; Alain Bergel; Maurice Comtat

1996-01-01

409

Synthesis of Pt 3 Co Alloy Nanocatalyst via Reverse Micelle for Oxygen Reduction Reaction in PEMFCs  

Microsoft Academic Search

Monodispersed, uniformly alloyed Pt3Co alloy nanoparticle electrocatalysts were synthesized via reduction of metallic precursors by sodium borohydride in heptane\\/polyethylene\\u000a glycol dodecylether (Brij)\\/water reverse micelles. These particles were further adsorbed on XC-72R carbon powder, separated\\u000a from micelles, and characterized using X-ray diffraction (XRD), transmission electronic microscopy (TEM). The electrochemical\\u000a activity for the oxygen reduction reaction (ORR) was characterized using a Rotating

Zengcai Liu; Chengfei Yu; Irene A. Rusakova; Daxiang Huang; Peter Strasser

2008-01-01

410

A Thermal Dehydrogenative Diels-Alder Reaction of Styrenes for the Concise Synthesis of Functionalized Naphthalenes  

PubMed Central

Functionalized naphthalenes are valuable building blocks in many important areas. A microwave-assisted, intramolecular dehydrogenative Diels-Alder reaction of styrenyl derivatives to provide cyclopenta[b]naphthalene substructures not previously accessible using existing synthetic methods is described. The synthetic utility of these uniquely functionalized naphthalenes was demonstrated by a single-step conversion of one of these cycloadducts to a fluorophore bearing a structural resemblance to Prodan. PMID:22913473

Kocsis, Laura S.; Benedetti, Erica

2012-01-01

411

Synthesis of S-linked carbohydrate analogues via a Ferrier reaction  

Microsoft Academic Search

In this work, the synthetic utility of the Ferrier reaction to access S-linked disaccharides and S-linked glycoamino acids has been probed. Significantly, entry to a range of 1,4- and 1,6-S-linked disaccharides has been achieved using glycals derived from glucose and galactose, and sulfur containing coupling partners derived from methyl ?-d-glucopyranoside. Access to S-linked glycoamino acids and glycopeptides has also been

David Ellis; Sarah E. Norman; Helen M. I. Osborn

2008-01-01

412

New approaches toward the synthesis of (D-homo) steroid skeletons using Mukaiyama reactions  

Microsoft Academic Search

New, short, and flexible procedures have been developed for syntheses of steroid and D-homo steroid skeletons. A Mukaiyama reaction between the silyl enol ether of 6-methoxytetralone and 2-methyl-2-cyclopentenone or carvone, with transfer of the silyl group to the receiving enone, gave a second silyl enol ether. Addition of a carbocation, generated under Lewis acid conditions from 3-methoxy-2-butenol, 3-ethoxy-3-phenyl-2-propenol or 3-methoxy-2-propenol

Florence C. E. Sarabèr; Alexander Baranovsky; Ben J. M. Jansen; Maarten A. Posthumus; Aede de Groot

2006-01-01

413

Catalytic enantioselective synthesis of atropisomeric biaryls: a cation-directed nucleophilic aromatic substitution reaction.  

PubMed

A catalytic enantioselective nucleophilic aromatic substitution reaction which yields axially chiral biaryl derivatives in excellent yields with e.r.?values of up to 97:3 has been developed. This process uses a chiral counterion to direct the addition of thiophenolate to a prochiral dichloropyrimidine by a tandem desymmetrization/kinetic resolution mechanism. The products can be derivatized to a range of atropisomeric structures without any reduction in enantioenrichment, thus offering access to unexplored chiral biaryl architectures. PMID:25257677

Armstrong, Roly J; Smith, Martin D

2014-11-17

414

Reaction Synthesis of Shock-Densified Titanium-Silicon Powder Mixtures  

NASA Astrophysics Data System (ADS)

The reaction behavior of shock-densified intermetallic-forming powder mixture compacts was studied to investigate fabrication of net-shaped materials with fine-grained microstructures. Compacts of similar density were also made by uniaxial pressing at 50,000 psi ( ~0.78 GPa) to compare their reaction behavior with those made by shock compression. The uniaxially-pressed samples showed large amount of porosity as compared to the shocked samples, which remained nearly dense. In addition the shocked sample had a finer grain size ( ~6 ?m) and microhardness values ~20% higher than the statically pressed samples. Shock-compression was also used to make functionally graded compacts, consisting of four layers of Ti-Si and Ti-Al powder mixtures with amounts varying as follows: 100% Ti-Si (impact surface), 80-20, 60-40, and 40-60 vol%. In this presentation, the shock-induced and shock-assisted (post-shock) reaction behavior of the monolithic and functionally-graded powder mixtures will be presented.

Namjoshi, S. A.; Thadhani, N. N.

1997-07-01

415

The Ammonia Dimer Revisited  

NASA Astrophysics Data System (ADS)

The conclusion from microwave spectra by Nelson, Fraser, and Klemperer that the ammonia dimer has a nearly cyclic structure led to much debate about the issue of whether (NH_3)_2 is hydrogen bonded. This structure was surprising because most {ab initio} calculations led to a classical, nearly linear, hydrogen-bonded structure. An obvious explanation of the discrepancy between the outcome of these calculations and the microwave data which led Nelson {et al.} to their ``surprising structure'' might be the effect of vibrational averaging: the electronic structure calculations focus on finding the minimum of the intermolecular potential, the experiment gives a vibrationally averaged structure. Isotope substitution studies seemed to indicate, however, that the complex is nearly rigid. Additional data became available from high-resolution molecular beam far-infrared spectroscopy in the Saykally group. These spectra, displaying large tunneling splittings, indicate that the complex is very floppy. The seemingly contradictory experimental data were explained when it became possible to calculate the vibration-rotation-tunneling (VRT) states of the complex on a six-dimensional intermolecular potential surface. The potential used was a simple model potential, with parameters fitted to the far-infrared data. Now, for the first time, a six-dimensional potential was computed by high level {ab initio} methods and this potential will be used in calculations of the VRT states of (NH_3)_2 and (ND_3)_2. So, we will finally be able to answer the question whether the conclusions from the model calculations are indeed a valid explanation of the experimental data. D. Nelson, G. T. Fraser, and W. Klemperer J. Chem. Phys. 83 6201 (1985) J. G. Loeser, C. A. Schmuttenmaer, R. C. Cohen, M. J. Elrod, D. W. Steyert, R. J. Saykally, R. E. Bumgarner, and G. A. Blake J. Chem. Phys. 97 4727 (1992) E. H. T. Olthof, A. van der Avoird, and P. E. S. Wormer J. Chem. Phys. 101 8430 (1994) E. H. T. Olthof, A. van der Avoird, P. E. S. Wormer, J. G. Loeser, and R. J. Saykally J. Chem. Phys. 101 8443 (1994)

Dawes, Richard; Van Der Avoird, Ad

2012-06-01

416

Synthesis of terephthalic acid via Diels-Alder reactions with ethylene and oxidized variants of 5-hydroxymethylfurfural  

PubMed Central

Terephthalic acid (PTA), a monomer in the synthesis of polyethylene terephthalate (PET), is obtained by the oxidation of petroleum-derived p-xylene. There is significant interest in the synthesis of renewable, biomass-derived PTA. Here, routes to PTA starting from oxidized products of 5-hydroxymethylfurfural (HMF) that can be produced from biomass are reported. These routes involve Diels-Alder reactions with ethylene and avoid the hydrogenation of HMF to 2,5-dimethylfuran. Oxidized derivatives of HMF are reacted with ethylene over solid Lewis acid catalysts that do not contain strong Brønsted acids to synthesize intermediates of PTA and its equally important diester, dimethyl terephthalate (DMT). The partially oxidized HMF, 5-(hydroxymethyl)furoic acid (HMFA), is reacted with high pressure ethylene over a pure-silica molecular sieve containing framework tin (Sn-Beta) to produce the Diels-Alder dehydration product, 4-(hydroxymethyl)benzoic acid (HMBA), with 31% selectivity at 61% HMFA conversion after 6 h at 190 °C. If HMFA is protected with methanol to form methyl 5-(methoxymethyl)furan-2-carboxylate (MMFC), MMFC can react with ethylene in the presence of Sn-Beta for 2 h to produce methyl 4-(methoxymethyl)benzenecarboxylate (MMBC) with 46% selectivity at 28% MMFC conversion or in the presence of a pure-silica molecular sieve containing framework zirconium (Zr-Beta) for 6 h to produce MMBC with 81% selectivity at 26% MMFC conversion. HMBA and MMBC can then be oxidized to produce PTA and DMT, respectively. When Lewis acid containing mesoporous silica (MCM-41) and amorphous silica, or Brønsted acid containing zeolites (Al-Beta), are used as catalysts, a significant decrease in selectivity/yield of the Diels-Alder dehydration product is observed. PMID:24912153

Pacheco, Joshua J.; Davis, Mark E.

2014-01-01

417

Low temperature synthesis of LnOF rare-earth oxyfluorides through reaction of the oxides with PTFE  

SciTech Connect

Highlights: Black-Right-Pointing-Pointer Low temperature synthesis of LnOF rare-earth oxyfluorides from Ln{sub 2}O{sub 3} and PTFE (CF{sub 2}). Black-Right-Pointing-Pointer Rhombohedral LnOF is the major phase and forms as nanocrystals, 29-103 nm. Black-Right-Pointing-Pointer Expected lanthanide contraction observed in lattice parameters and bond lengths. Black-Right-Pointing-Pointer TbOF orders antiferromagnetically at 10 K and has a metamagnetic transition at 1.8 T. Black-Right-Pointing-Pointer GdOF orders antiferromagnetically at 5 K, other LnOF are paramagnetic. -- Abstract: A low temperature solid-state synthesis route, employing polytetrafluoroethylene (PTFE) and the rare-earth oxides, for the formation of the LnOF rare-earth oxyfluorides (Ln = Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er), is reported. With the exception of LaOF, which forms in a tetragonal variant, rhomobohedral LnOF is found to be the major product of the reaction. In the case of PrOF, a transition from the rhombohedral to the cubic fluorite phase is observed on heating in air to 500 Degree-Sign C. X-ray diffraction shows the expected lanthanide contraction in the lattice parameters and bond lengths. Magnetic susceptibility measurements show antiferromagnetic-like ordering in TbOF, T{sub m} = 10 K, with a metamagnetic transition at a field {mu}{sub 0}H{sub t} = 1.8 T at 2 K. An antiferromagnetic transition, T{sub N} = 4 K, is observed in GdOF. Paramagnetic behavior is observed above 2 K in PrOF, NdOF, DyOF, HoOF and ErOF. The magnetic susceptibility of EuOF is characteristic of Van Vleck paramagnetism.

Dutton, S.E., E-mail: sdutton@princeton.edu [Department of Chemistry, Princeton University, Princeton, NJ 08544 (United States); Hirai, D.; Cava, R.J. [Department of Chemistry, Princeton University, Princeton, NJ 08544 (United States)] [Department of Chemistry, Princeton University, Princeton, NJ 08544 (United States)

2012-03-15

418

Synthesis of terephthalic acid via Diels-Alder reactions with ethylene and oxidized variants of 5-hydroxymethylfurfural.  

PubMed

Terephthalic acid (PTA), a monomer in the synthesis of polyethylene terephthalate (PET), is obtained by the oxidation of petroleum-derived p-xylene. There is significant interest in the synthesis of renewable, biomass-derived PTA. Here, routes to PTA starting from oxidized products of 5-hydroxymethylfurfural (HMF) that can be produced from biomass are reported. These routes involve Diels-Alder reactions with ethylene and avoid the hydrogenation of HMF to 2,5-dimethylfuran. Oxidized derivatives of HMF are reacted with ethylene over solid Lewis acid catalysts that do not contain strong Brønsted acids to synthesize intermediates of PTA and its equally important diester, dimethyl terephthalate (DMT). The partially oxidized HMF, 5-(hydroxymethyl)furoic acid (HMFA), is reacted with high pressure ethylene over a pure-silica molecular sieve containing framework tin (Sn-Beta) to produce the Diels-Alder dehydration product, 4-(hydroxymethyl)benzoic acid (HMBA), with 31% selectivity at 61% HMFA conversion after 6 h at 190 °C. If HMFA is protected with methanol to form methyl 5-(methoxymethyl)furan-2-carboxylate (MMFC), MMFC can react with ethylene in the presence of Sn-Beta for 2 h to produce methyl 4-(methoxymethyl)benzenecarboxylate (MMBC) with 46% selectivity at 28% MMFC conversion or in the presence of a pure-silica molecular sieve containing framework zirconium (Zr-Beta) for 6 h to produce MMBC with 81% selectivity at 26% MMFC conversion. HMBA and MMBC can then be oxidized to produce PTA and DMT, respectively. When Lewis acid containing mesoporous silica (MCM-41) and amorphous silica, or Brønsted acid containing zeolites (Al-Beta), are used as catalysts, a significant decrease in selectivity/yield of the Diels-Alder dehydration product is observed. PMID:24912153

Pacheco, Joshua J; Davis, Mark E

2014-06-10

419

Fluoridonitrosyl complexes of technetium(I) and technetium(II). Synthesis, characterization, reactions, and DFT calculations.  

PubMed

A mixture of [Tc(NO)F5](2-) and [Tc(NO)(NH3)4F](+) is formed during the reaction of pertechnetate with acetohydroxamic acid (Haha) in aqueous HF. The blue pentafluoridonitrosyltechnetate(II) has been isolated in crystalline form as potassium and rubidium salts, while the orange-red ammine complex crystallizes as bifluoride or PF6(-) salts. Reactions of [Tc(NO)F5](2-) salts with HCl give the corresponding [Tc(NO)Cl4/5](-/2-) complexes, while reflux in neat pyridine (py) results in the formation of the technetium(I) cation [Tc(NO)(py)4F](+), which can be crystallized as hexafluoridophosphate. The same compound can be synthesized directly from pertechnetate, Haha, HF, and py or by a ligand-exchange procedure starting from [Tc(NO)(NH3)4F](HF2). The technetium(I) cation [Tc(NO)(NH3)4F](+) can be oxidized electrochemically or by the reaction with Ce(SO4)2 to give the corresponding Tc(II) compound [Tc(NO)(NH3)4F](2+). The fluorido ligand in [Tc(NO)(NH3)4F](+) can be replaced by CF3COO(-), leaving the "[Tc(NO)(NH3)4](2+) core" untouched. The experimental results are confirmed by density functional theory calculations on [Tc(NO)F5](2-), [Tc(NO)(py)4F](+), [Tc(NO)(NH3)4F](+), and [Tc(NO)(NH3)4F](2+). PMID:24797021

Balasekaran, Samundeeswari Mariappan; Spandl, Johann; Hagenbach, Adelheid; Köhler, Klaus; Drees, Markus; Abram, Ulrich

2014-05-19

420

Thermal phenomena under microwave field in the organic synthesis processes: Application to the Diels Alder reaction  

SciTech Connect

The influence of the microwave heating on chemical reactions were investigated. The kinetic of the Diels Alder reaction were studied under microwave irradiation at a frequency of 2.45 GHz in a single mode cavity and were compared to the kinetic obtained by a conventional heating. Experiments were carried out in a liquid solvent in order to have a better control of the medium temperature measurement. In a second part, the presence of a catalytic solid phase was introduced. Some thermal fluctuations which are due to an heterogeneity of the electric field were detected in the medium. They reduce the precision of the results and cause problems of experimental reproducibility. A thermoluminescent material allow a good visualization of these phenomena. In addition, the profiles of the electric field intensity were modelled by a 2D finite elements method in the reactor in the presence of a solvent. Despite the small size of the sample and the use of a monomode cavity which both limited the heterogeneities of the medium temperature, the authors showed a great heterogeneity of the electric field intensity and as a result the heterogeneity of the temperature in their sample. In order to avoid these phenomena which induce a lack of reproducibility, a stirring device was developed. The values of the kinetics obtained under the 2 heating modes with the introduction of the stirring device. So, it induces a good control of the medium temperature. All those investigations prompted the authors to the conclusion that there is no difference between microwave heating and a classical heating in the studied reaction.

Saillard, R.; Poux, M.; Audhuy-Peaudecerf, M.

1996-12-31

421

Reaction between lawsone and aminophenol derivatives: Synthesis, characterization, molecular structures and antiproliferative activity  

NASA Astrophysics Data System (ADS)

Reaction between two bioreductive reactants lawsone (2-hydroxy-1,4-napthoquinone) and derivatives 2-aminophenol without catalyst is reported. The reaction between lawsone and 4-chloro-2-aminophenol leads to formation of red colored major product 1A:[2-[(5-chloro-hydroxyphenyl)amino]naphthalene-1,4-dione] and fluorescent orange colored minor compound 1B:[10-chloro-benzo[?]phenoxazine-5-one]. Molecular structure of 1A and 1B were determined by single crystal X-ray diffraction. Two mechanisms were proposed to the formation of red 1A and 1B. ‘Ortho-para’ tautomeric equilibrium was observed in DMSO-d6 solution in 1A, which was revealed by 1H, 13C NMR and LC-MS studies. Molecules of 1A formed dimers via Nsbnd H⋯O interaction and polymeric chain of dimers was formed by Osbnd H⋯O interactions. Cl⋯Cl interactions were observed between the polymeric chains of dimers in 1A. Molecules of 1B show Cl⋯N interaction. Antiproliferative properties is studied for 1A-5A compounds (obtained by the reaction of lawsone with 2-amino-4-methylphenol;2A, 2-aminophenol;3A, 3-aminophenol;4A and 4-aminophenol;5A) and evaluated against two cancer cell lines, THP1 (human monocytic leukemia cells) and COLO205 (colorectal adenocarcinoma) and one normal cell line, HEK293T (human embryonic kidney). The values of 50% inhibitory concentration (IC50) of compounds 1A-5A was determined using XTT assay. The cytotoxic effects of compounds 2A and 3A were observed against COLO205 and compounds 4A and 5A on THP1 were observed to be higher in comparison to their effect on HEK293T cell lines.

Kathawate, Laxmi; Joshi, Pranya V.; Dash, Tapan Kumar; Pal, Sanjima; Nikalje, Milind; Weyhermüller, Thomas; Puranik, Vedavati G.; Konkimalla, V. Badireenath; Salunke-Gawali, Sunita

2014-10-01

422

Versatile synthesis of amino acid functionalized nucleosides via a domino carboxamidation reaction  

PubMed Central

Summary Functionalized oligonucleotides have recently gained increased attention for incorporation in modified nucleic acid structures both for the design of aptamers with enhanced binding properties as well as the construction of catalytic DNA and RNA. As a shortcut alternative to the incorporation of multiple modified residues, each bearing one extra functional group, we present here a straightforward method for direct linking of functionalized amino acids to the nucleoside base, thus equipping the nucleoside with two extra functionalities at once. As a proof of principle, we have introduced three amino acids with functional groups frequently used as key-intermediates in DNA- and RNAzymes via an efficient and straightforward domino carboxamidation reaction. PMID:25383128

Gheerardijn, Vicky; Van den Begin, Jos

2014-01-01

423

1,3-Diferrocenyl-1,3-alkadienes in diene synthesis reactions  

SciTech Connect

Stable 1,3-diferrocenyl-1,3-alkadienes, which form Diels-Alder adducts with N-substituted maleimides, have been prepared. Methyldiferrocenylbutadien participates in a cycloaddition reaction less readily than 1,3-diferrocenyl-1,3-butadiene. Adducts of 1,3-diferrocenyl-1,3-butadiene with N-substituted maleimides are dehydrogenated on Al/sub 2/O/sub 3/ or SiO/sub 2/ with subsequent formation of cyclohexadiene and benzene derivatives; protonation-deprotonation induces isomerization with transposition of the double bond.

Pushin, A.N.; Klimova, E.I.; Sazanova, V.A.

1987-11-10

424

Lanthanide Triflate-Catalyzed Carbon-Carbon Bond-Forming Reactions in Organic Synthesis  

Microsoft Academic Search

Versatile carbon-carbon bond-forming reactions using lanthanide triflates (Ln(OTf)3) as catalysts are discussed. Lanthanide triflates are new types of Lewis acids different from typical Lewis acids such as\\u000a AlCl3, BF3, SnCl4, etc. While most Lewis acids are decomposed or deactivated in the presence of water, lanthanide triflates are stable and\\u000a works as Lewis acids in water solutions. Many nitrogen-containing compounds such

Sh? Kobayashi

425

Stereoselective Synthesis of 4'-Selenonucleosides via Seleno-Michael Reaction as Potent Antiviral Agents.  

PubMed

Based on the hypothesis that the bulky selenium atom, with 4p orbitals, can sterically hinder the approach of a cellular kinase to 5'-OH for phosphorylation, 4'-selenonucleosides with one-carbon homologation were designed and synthesized via a novel seleno-Michael reaction, with the stereoselectivity controlled by steric effects. 5'-Homo-4'-selenonucleosides (n = 2) demonstrated potent antiherpes simplex virus (HSV-1) activity, indicating that the bulky selenium atom might play a key role in preventing phosphorylation by cellular kinases, resulting in no antiviral activity. PMID:25340622

Sahu, Pramod K; Kim, Gyudong; Yu, Jinha; Ahn, Ji Yoon; Song, Jayoung; Choi, Yoojin; Jin, Xing; Kim, Jin-Hee; Lee, Sang Kook; Park, Sunghyouk; Jeong, Lak Shin

2014-11-01

426

Synthesis of Enantiomerically Enriched Imidazolidin-2-Ones via Asymmetric Pd-Catalyzed Alkene Carboamination Reactions  

PubMed Central

A catalyst composed of Pd2(dba)3 and (S)-Siphos-PE is effective for the enantioselective coupling of N-allyureas with aryl bromides to afford 4-substituted imidazolidin-2-ones with up to 95% ee. Added water leads to significantly improved enantioselectivities with electron-poor aryl halide substrates. The mechanism of these transformations is discussed, and evidence is presented which suggests that, in contrast to other asymmetric alkene carboaminations, C–C bond-forming reductive elimination is the enantiodetermining step of these reactions. PMID:22936415

Hopkins, Brett A.

2012-01-01

427

Amperometric detection and electrochemical oxidation of aliphatic amines and ammonia on silver-lead oxide thin-film electrodes  

SciTech Connect

This thesis comprises three parts: Electrocatalysis of anodic oxygen-transfer reactions: aliphatic amines at mixed Ag-Pb oxide thin-film electrodes; oxidation of ammonia at anodized Ag-Pb eutectic alloy electrodes; and temperature effects on oxidation of ethylamine, alanine, and aquated ammonia.

Ge, Jisheng

1996-01-08

428

Branched-chain amino acids and ammonia metabolism in liver disease: therapeutic implications.  

PubMed

The rationale for recommendation of branched-chain amino acids (BCAA; valine, leucine, and isoleucine) in treatment of liver failure is based on their unique pharmacologic properties, stimulatory effect on ammonia detoxification to glutamine (GLN), and decreased concentrations in liver cirrhosis. Multiple lines of evidence have shown that the main cause of the BCAA deficiency in liver cirrhosis is their consumption in skeletal muscle for synthesis of glutamate, which acts as a substrate for ammonia detoxification to GLN and that the BCAA administration to patients with liver failure may exert a number of positive effects that may be more pronounced in patients with marked depression of BCAA levels. On the other hand, due to the stimulatory effect of BCAA on GLN synthesis, BCAA supplementation may lead to enhanced ammonia production from GLN breakdown in the intestine and the kidneys and thus exert harmful effects on the development of hepatic encephalopathy. Therefore, to enhance therapeutic effectiveness of the BCAA in patients with liver injury, their detrimental effect on ammonia production, which is negligible in healthy people and/or patients with other disorders, should be avoided. In treatment of hepatic encephalopathy, simultaneous administration of the BCAA (to correct amino acid imbalance and promote ammonia detoxification to GLN) with ?-ketoglutarate (to inhibit GLN breakdown to ammonia in enterocytes) and/or phenylbutyrate (to enhance GLN excretion by the kidneys) is suggested. Attention should be given to the type of liver injury, gastrointestinal bleeding, signs of inflammation, and the dose of BCAA. PMID:23756281

Holecek, Milan

2013-10-01

429

Synthesis of biodiesel fuel from safflower oil using various reaction parameters.  

PubMed

Biodiesel fuel is gaining more and more importance because of the depletion and uncontrollable prices of fossil fuel resources. The use of vegetable oil and their derivatives as alternatives for diesel fuel is the best answer and as old as Diesel Engine. Chemically biodiesel fuel is the mono alkyl esters of fatty acids derived from renewable feed stocks like vegetable oils and animal fats. Safflower oil contains 75-80% of linoleic acid; the presence of this unsaturated fatty acid is useful in alleviating low temperature properties like pour point, cloud point and cold filter plugging point. In this paper we studied the effect of various parameters such as temperature, molar ratio (oil to alcohol), and concentration of catalyst on synthesis of biodiesel fuel from safflower oil. The better suitable conditions of 1:6 molar ratio (oil to alcohol), 60 degrees C temperature and catalyst concentration of 2% (by wt. of oil) were determined. The finally obtained biodiesel fuel was analyzed for fatty acid composition by GLC and some other properties such as flash point, specific gravity and acid value were also determined. From the results it was clear that the produced biodiesel fuel was with in the recommended standards of biodiesel fuel with 96.8% yield. PMID:17693692

Meka, Pavan Kumar; Tripathi, Vinay; Singh, R P

2006-01-01

430

Synthesis and solvent-dependent photochromic reactions of porphyrin-spiropyran hybrid compounds.  

PubMed

Porphyrin(Por)-spiropyran(SP) hybrid compounds, including Por-SP dyad, Por-SP2 triad, and Por-SP4 pentad, were prepared and characterized by (1)H NMR, MALDI-TOF MS and UV-Vis spectroscopies. Upon 350 nm UV irradiation of Por-SPn (n=1, 2, 4) in dichloromethane, unusual red-shifted absorption spectra were observed with the colour change from pink into green. Probably due to the protonation of core nitrogens in porphyrin ring, their absorption maxima in dichloromethane were shifted from 418 (Soret band), 515, 550, 590, 645 (four Q bands) nm into 450 and 665 nm. Also, fluorescence maxima were also shifted from 650 and 715 nm to 692 nm. In the other hands, upon irradiation with 350nm UV light in THF, the colour changed from pink into violet and absorption band at 590 nm increased and the fluorescence spectra showed the decrease of 650 and 715 nm bands and increase of 600-640 nm band, due to the normal ring-opening reaction of spiropyran moiety into merocyanine. In the dark, original absorption and fluorescence spectra were recovered very slowly in dichloromethane, but quickly in THF. The reversible photochromic reactions of Por-SPn (n=1, 2, 4) in dichloromethane and THF were investigated by observing absorption and fluorescence spectral changes during UV irradiation or standing in the dark. PMID:24036185

Hur, Dae Young; Park, Tae Jong; Shin, Eun Ju

2014-01-01

431

Synthesis and solvent-dependent photochromic reactions of porphyrin-spiropyran hybrid compounds  

NASA Astrophysics Data System (ADS)

Porphyrin(Por)-spiropyran(SP) hybrid compounds, including Por-SP dyad, Por-SP2 triad, and Por-SP4 pentad, were prepared and characterized by 1H NMR, MALDI-TOF MS and UV-Vis spectroscopies. Upon 350 nm UV irradiation of Por-SPn (n = 1, 2, 4) in dichloromethane, unusual red-shifted absorption spectra were observed with the colour change from pink into green. Probably due to the protonation of core nitrogens in porphyrin ring, their absorption maxima in dichloromethane were shifted from 418 (Soret band), 515, 550, 590, 645 (four Q bands) nm into 450 and 665 nm. Also, fluorescence maxima were also shifted from 650 and 715 nm to 692 nm. In the other hands, upon irradiation with 350 nm UV light in THF, the colour changed from pink into violet and absorption band at 590 nm increased and the fluorescence spectra showed the decrease of 650 and 715 nm bands and increase of 600-640 nm band, due to the normal ring-opening reaction of spiropyran moiety into merocyanine. In the dark, original absorption and fluorescence spectra were recovered very slowly in dichloromethane, but quickly in THF. The reversible photochromic reactions of Por-SPn (n = 1, 2, 4) in dichloromethane and THF were investigated by observing absorption and fluorescence spectral changes during UV irradiation or standing in the dark.

Hur, Dae Young; Park, Tae Jong; Shin, Eun Ju

2014-01-01

432

Riley oxidation: A forgotten name reaction for synthesis of selenium nanoparticles  

SciTech Connect

A simple wet chemical method, involving reaction of acetone with selenium dioxide, has been developed, to synthesize polyvinyl alcohol-stabilized selenium nanoparticles. The method is capable of producing nanoparticles in the size range of about 100-300 nm, under ambient conditions. The synthesized nanoparticles can be separated easily from the aqueous sols by a high-speed centrifuge, and can be re-dispersed in aqueous medium by a sonicator. The effect of concentrations of selenium dioxide, acetone and PVA on the size of the selenium nanoparticles has been studied. The size of the selenium nanoparticles has been found to increase with increase in the reaction time as well as the concentration of selenium dioxide, while it decreases with increase in the concentration of the stabilizer, PVA. The synthesized selenium nanoparticles have been characterized by UV-visible optical absorption spectroscopy, X-ray diffraction, energy dispersive X-ray analysis, differential scanning calorimetry, atomic force microscopy, scanning electron microscopy and transmission electron microscopy techniques.

Shah, Chetan P.; Dwivedi, Charu; Singh, Krishan K. [Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India)] [Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India); Kumar, Manmohan, E-mail: manmoku@barc.gov.in [Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India)] [Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India); Bajaj, Parma N. [Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India)] [Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India)

2010-09-15

433

Solid-phase reaction synthesis of mesostructured tungsten disulfide material with a high specific surface area  

SciTech Connect

Highlights: {yields} WS{sub 2} material was synthesized through solid-phase reaction. {yields} (NH{sub 4}){sub 2}WS{sub 4} as precursor and n-octadecylamine as template. {yields} WS{sub 2} material has high specific surface area (145.9 m{sup 2}/g). {yields} The whole preparation process is simple, convenient, green and clean. -- Abstract: A mesostructured tungsten disulfide (WS{sub 2}) material was prepared through a solid-phase reaction utilizing ammonium tetrathiotungstate as the precursor and n-octadecylamine as the template. The as-synthesized WS{sub 2} material was characterized by X-ray powder Diffraction (XRD), Low-temperature N{sub 2} Adsorption (BET method), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The characterization results indicate that the WS{sub 2} material has the typical mesopore structure (3.7 nm) with a high specific surface area (145.9 m{sup 2}/g), and large pore volume (0.18 cm{sup 3}/g). This approach is novel, green and convenient. The plausible mechanism for the formation of the mesostructured WS{sub 2} material is discussed herein.

An, Gaojun, E-mail: angaojun2003@yahoo.com.cn [Beijing POL Research Institute, Beijing 102300 (China)] [Beijing POL Research Institute, Beijing 102300 (China); Lu, Changbo; Xiong, Chunhua [Beijing POL Research Institute, Beijing 102300 (China)] [Beijing POL Research Institute, Beijing 102300 (China)

2011-09-15

434

Synthesis of Y1Ba2Cu3O(sub x) superconducting powders by intermediate phase reaction  

NASA Technical Reports Server (NTRS)

One of the more striking problems for the synthesis of the Y1Ba2Cu3Ox compound is the high-temperature decomposition of the BaCO3. This compound is present as raw material or as an intermediate compound in chemical processes such as amorphous citrate, coprecipitation oxalate, sol-gel process, acetate pyrolisis, etc. This fact makes difficult the total formation reaction of the Y1Ba2Cu3Ox phase and leads to the presence of undesirable phases such as the BaCuO2 phase, the 'green phase', Y2BaCuO5 and others. Here, a new procedure to overcome this difficulty is studied. The barium cation is previously combined with yttrium and/or copper to form intermediate compounds which can react between them to give Y1Ba2Cu3Ox. BaY2O4 and BaCu2O3 react according to the equation BaY2O4+3BaCu2O3 yields 2Y1Ba2Cu3Ox. BaY2O4 is a stable compound of the Y2O3-BaO system; BaCu2O3 is an intimate mixture of BaCuO2 and uncombined CuO. The reaction kinetics of these phases have been established between 860 and 920 C. The phase evolution has been determined. The crystal structure of the Y1Ba2Cu3Ox obtained powder was studied. According to the results obtained from the kinetics study the Y1Ba2Cu3Ox the synthesis was performed at temperatures of 910 to 920 C for short treatment times (1 to 2 hours). Pure Y1Ba2Cu3Ox was prepared, which develops orthorombic type I structure despite of the cooling cycle. Superconducting transition took place at 91 K. The sintering behavior and the superconducting properties of sintered samples were studied. Density, microstructure and electrical conductivity were measured. Sintering densities higher than 95 percent D(sub th) were attained at temperatures below 940 C. Relatively fine grained microstructure was observed, and little or no-liquid phase was detected.

Moore, C.; Fernandez, J. F.; Recio, P.; Duran, P.

1990-01-01

435

Colorimetric Analysis of Ammonia in Water.  

National Technical Information Service (NTIS)

An accurate, reliable method of determing concentration of ammonia in water solution was developed using colorimetric techniques. The procedure involves formation of a colored complex of ammonia with 2,5-dimethoxyoxolane and (E)-p-dimethylamino-cinnamalde...

F. W. Carson, R. L. Gross

1977-01-01

436

(Phenoxyimidazolyl-salicylaldimine)iron complexes: synthesis, properties and iron catalysed ethylene reactions.  

PubMed

The reaction of 2-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L1), 2,4-di-tert-butyl-6-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L2) or 4-tert-butyl-2-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L3) with iron(ii) precursors produced either iron(ii) or iron(iii) complexes, depending on the nature of the anions in the iron(ii) precursor and the ligand. When the anion is chloride and the ligand L1, the product is [(L1)2Fe][FeCl4] (1), but when the anion is triflate (OTf(-)) and the ligand is L2, the product is [(L2)2Fe][OTf]2 (2). With iron(ii) halides and tert-butyl groups on the phenoxy ligands L2 and L3, the iron(iii) complexes [(L2)FeX2] {where X = Cl (3), Br (4) and I = (5)} and [(L3)FeCl2] (6) were formed. Complexes 1-6 were characterised by a combination of elemental analyses, IR spectroscopy and mass spectrometry; and in selected cases (3 and 4) by single crystal X-ray crystallography. The crystal structures of 3 and 4 indicated that the iron(ii) precursors oxidised to iron(iii) in forming complexes 3-6; an observation that was corroborated by the magnetic properties and the (57)Fe Mössbauer spectra of 3 and 4. The iron(iii) complexes 3-6 were used as pre-catalysts for the oligomerisation and polymerisation of ethylene. Products of these ethylene reactions depended on the solvent used. In toluene ethylene oligomerised mainly to 1-butene and was followed by the 1-butene alkylating the solvent to form butyl-toluenes via a Friedel-Crafts alkylation reaction. In chlorobenzene, ethylene oligomerised mainly to a mixture of C4-C12 alkenes. Interestingly small amounts of butyl-chlorobenzenes and hexyl-chlorobenzenes were also formed via a Friedel-Crafts alkylation with butenes and hexenes from the oligomerisation of ethylene. PMID:25111396

Yankey, Margaret; Obuah, Collins; Guzei, Ilia A; Osei-Twum, Emmanuel; Hearne, Giovanni; Darkwa, James

2014-10-01

437

Synthesis of boron nitride by self-propagating reactions at high pressure  

SciTech Connect

Peculiarities of the formation of BN in a self-propagating reaction between LiBF{sub 4} and Li{sub 3}N have been studied under a wide range of p,T conditions within the region of thermodynamic stability of cBN. Boron nitride crystallized mainly in the form of highly ordered hBN (1,700--2,100 K), of mesographitic BN (2,200--3,000 K), or of turbostratic BN (>3,000 K). Cubic boron nitride was obtained with a low yield (up to 14 vol%) as a result of precipitation from the metastable eutectic liquid in the BN-Li{sub 3}N system. These results give further evidence for an alternative metastable behavior in the BN phase formation under high pressures.

Solozhenko, V.L.; Will, G. [Univ. of Bonn (Germany). Mineralogical Inst.; Turkevich, V.Z. [Ukrainian National Academy of Sciences, Kiev (Ukraine). V.N. Bakul Inst. for Superhard Materials

1996-10-01

438

Preparative synthesis of C-(alpha-D-glucopyranosyl)-alkenes and -alkadienes: Diels-Alder reaction.  

PubMed

The reaction of 2,3,4,6-tetra-O-benzyl-1-O-(p-nitrobenzoyl)-alpha-D-glucopyranose with (E)-penta-2,4-dienyltrimethylsilane and boron trifluoride etherate in acetonitrile afforded stereoselectively (E)-5-(tetra-O-benzyl-alpha-D-glucopyranosyl)-1,3-pentadiene in good yield. The readily available penta-O-benzoyl-alpha-D-glucopyranose reacted with allyltrimethylsilane in the presence of boron trifluoride etherate in acetonitrile to give 3-(tetra-O-benzoyl-alpha-D-glucopyranosyl)-1-propene and its beta anomer in yields of 60% and 2.3%, respectively. Diels-Alder cycloaddition of maleic anhydride to diene 1 afforded the adduct cis,cis-3-(tetra-O-benzyl-alpha-D-glucopyranosylmethyl)cyclohex -4-ene- 1,2-dicarboxylic anhydride in high yield. PMID:2582461

de Gracia Garcia Martin, M; Horton, D

1989-08-15