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1

Using aqueous ammonia in hydroaminomethylation reactions: ruthenium-catalyzed synthesis of tertiary amines.  

PubMed

The direct synthesis of tertiary amines from ammonia and olefins is presented. Using a combination of Ru3 (CO)12 and 2-phosphino-substituted imidazole ligand as catalyst system allows for hydroaminomethylation reactions of bulk aliphatic and functionalized olefins. Tertiary amines are obtained in an atom-efficient domino process in moderate to good isolated yields (45-76%) with excellent regioselectivities (n/iso up to 99:1). PMID:25223274

Wu, Lipeng; Fleischer, Ivana; Zhang, Min; Liu, Qiang; Franke, Robert; Jackstell, Ralf; Beller, Matthias

2014-12-01

2

Glow Discharge Enhanced Chemical Reaction: Application in Ammonia Synthesis and Hydrocarbon Gas Cleanup  

E-print Network

Two different plasma enhanced processing technologies were investigated in this study: ammonia synthesis from steam and nitrogen, and hydrocarbon gas clean up. Ammonia is a common sanitizer in swimming pool and fish tank, changing the p...

Ming, Pingjia

2014-06-05

3

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

4

Catalytic Organometallic Reactions of Ammonia  

PubMed Central

Until recently, ammonia had rarely succumbed to catalytic transformations with homogeneous catalysts, and the development of such reactions that are selective for the formation of single products under mild conditions has encountered numerous challenges. However, recently developed catalysts have allowed several classes of reactions to create products with nitrogen-containing functional groups from ammonia. These reactions include hydroaminomethylation, reductive amination, alkylation, allylic substitution, hydroamination, and cross-coupling. This Minireview describes examples of these processes and the factors that control catalyst activity and selectivity. PMID:20857466

Klinkenberg, Jessica L.

2012-01-01

5

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

6

Ammonia synthesis using magnetic induction method (MIM)  

NASA Astrophysics Data System (ADS)

The most challenging issues for ammonia synthesis is to get the high yield. New approach of ammonia synthesis by using Magnetic Induction Method (MIM) and the Helmholtz Coils has been proposed. The ammonia detection was done by using Kjeldahl Method and FTIR. The system was designed by using Autocad software. The magnetic field of MIM was vary from 100mT-200mT and the magnetic field for the Helmholtz coils was 14mT. The FTIR result shows that ammonia has been successfully formed at stretching peaks 1097,1119,1162,1236, 1377, and 1464 cm-1. UV-VIS result shows the ammonia bond at 195nm of wavelength. The ammonia yield was increase to 244.72?mole/g.h by using the MIM and six pairs of Helmholtz coils. Therefore this new method will be a new promising method to achieve the high yield ammonia at ambient condition (at 25?C and 1atm), under the Magnetic Induction Method (MIM).

Puspitasari, P.; Razak, J. Abd; Yahya, N.

2012-09-01

7

Ammonia, oxidation leaching of chalcopyrite —reaction kinetics  

Microsoft Academic Search

The reaction for the ammonia, oxidation leaching of chalcopyrite, CuFeS2 + 4NH3 + 17\\/4 O2 + 2 OH- ? Cu(NH3)+2\\u000a 42 + l\\/2Fe2O3 + 2 SO4 + H2O was studied using monosize particles in an intensely stirred reactor under moderate pressures to determine the important\\u000a chemical factors which govern the kinetic response of the system. The reaction kinetics were studied

L. W. Beckstead; J. D. Miller

1977-01-01

8

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

9

Prebiotic Amino Acid Thioester Synthesis: Thiol-Dependent Amino Acid Synthesis from Formose Substrates (Formaldehyde and Glycolaldehyde) and Ammonia  

NASA Astrophysics Data System (ADS)

Formaldehyde and glycolaldehyde (substrates of the formose autocatalytic cycle) were shown to react with ammonia yielding alanine and homoserine under mild aqueous conditions in the presence of thiol catalysts. Since similar reactions carried out without ammonia yielded ?-hydroxy acid thioesters (Weber, 1984a, b), the thiol-dependent synthesis of alanine and homoserine is presumed to occur via amino acid thioesters - intermediates capable of forming peptides (Weber and Orgel 1979). A pH 5.2 solution of 20 mM formaldehyde, 20 mM glycolaldehyde, 20 mM ammonium chloride, 23 mM 3-mercaptopropionic acid, and 23 mM acetic acid that reacted for 35 days at 40°C yielded (based on initial formaldehyde) 1.8% alanine and 0.08% homoserine. In the absence of thiol catalyst, the synthesis of alanine and homoserine was negligible. Alanine synthesis required both formaldehyde and glycolaldehyde, but homoserine synthesis required only glycolaldehyde. At 25 days the efficiency of alanine synthesis calculated from the ratio of alanine synthesized to formaldehyde reacted was 2.1%, and the yield (based on initial formaldehyde) of triose and tetrose intermediates involved in alanine and homoserine synthesis was 0.3 and 2.1%, respectively. Alanine synthesis was also seen in similar reactions containing only 10 mM each of aldehyde substrates, ammonia, and thiol. The prebiotic significance of these reactions that use the formose reaction to generate sugar intermediates that are converted to reactive amino acid thioesters is discussed.

Weber, Arthur L.

1998-06-01

10

Electride support boosts nitrogen dissociation over ruthenium catalyst and shifts the bottleneck in ammonia synthesis  

PubMed Central

Novel approaches to efficient ammonia synthesis at an ambient pressure are actively sought out so as to reduce the cost of ammonia production and to allow for compact production facilities. It is accepted that the key is the development of a high-performance catalyst that significantly enhances dissociation of the nitrogen–nitrogen triple bond, which is generally considered a rate-determining step. Here we examine kinetics of nitrogen and hydrogen isotope exchange and hydrogen adsorption/desorption reactions for a recently discovered efficient catalyst for ammonia synthesis—ruthenium-loaded 12CaO·7Al2O3 electride (Ru/C12A7:e?)—and find that the rate controlling step of ammonia synthesis over Ru/C12A7:e? is not dissociation of the nitrogen–nitrogen triple bond but the subsequent formation of N–Hn species. A mechanism of ammonia synthesis involving reversible storage and release of hydrogen atoms on the Ru/C12A7:e? surface is proposed on the basis of observed hydrogen absorption/desorption kinetics. PMID:25816758

Kitano, Masaaki; Kanbara, Shinji; Inoue, Yasunori; Kuganathan, Navaratnarajah; Sushko, Peter V.; Yokoyama, Toshiharu; Hara, Michikazu; Hosono, Hideo

2015-01-01

11

Electride support boosts nitrogen dissociation over ruthenium catalyst and shifts the bottleneck in ammonia synthesis.  

PubMed

Novel approaches to efficient ammonia synthesis at an ambient pressure are actively sought out so as to reduce the cost of ammonia production and to allow for compact production facilities. It is accepted that the key is the development of a high-performance catalyst that significantly enhances dissociation of the nitrogen-nitrogen triple bond, which is generally considered a rate-determining step. Here we examine kinetics of nitrogen and hydrogen isotope exchange and hydrogen adsorption/desorption reactions for a recently discovered efficient catalyst for ammonia synthesis-ruthenium-loaded 12CaO·7Al2O3 electride (Ru/C12A7:e(-))-and find that the rate controlling step of ammonia synthesis over Ru/C12A7:e(-) is not dissociation of the nitrogen-nitrogen triple bond but the subsequent formation of N-Hn species. A mechanism of ammonia synthesis involving reversible storage and release of hydrogen atoms on the Ru/C12A7:e(-) surface is proposed on the basis of observed hydrogen absorption/desorption kinetics. PMID:25816758

Kitano, Masaaki; Kanbara, Shinji; Inoue, Yasunori; Kuganathan, Navaratnarajah; Sushko, Peter V; Yokoyama, Toshiharu; Hara, Michikazu; Hosono, Hideo

2015-01-01

12

Process for synthesis of ammonia borane for bulk hydrogen storage  

SciTech Connect

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

13

Tungsten nanoparticles from liquid-ammonia-based synthesis.  

PubMed

Tungsten nanoparticles were obtained from liquid-ammonia-based synthesis via reduction of WCl6 with dissolved sodium. The W(0) nanoparticles exhibit a diameter of 1-2 nm and can be dispersed in alkanes, showing a grayish-orange color due to red-shifted plasmon resonance absorption. PMID:24643208

Schöttle, Christian; Bockstaller, Pascal; Gerthsen, Dagmar; Feldmann, Claus

2014-05-01

14

Sources and sinks for ammonia and nitrite on the early Earth and the reaction of nitrite with ammonia  

NASA Technical Reports Server (NTRS)

An analysis of sources and sinks for ammonia and nitrite on the early Earth was conducted. Rates of formation and destruction, and steady state concentrations of both species were determined by steady state kinetics. The importance of the reaction of nitrite with ammonia on the feasibility of ammonia formation from nitrite was evaluated. The analysis considered conditions such as temperature, ferrous iron concentration, and pH. For sinks we considered the reduction of nitrite to ammonia, reaction between nitrite and ammonia, photochemical destruction of both species, and destruction at hydrothermal vents. Under most environmental conditions, the primary sink for nitrite is reduction to ammonia. The reaction between ammonia and nitrite is not an important sink for either nitrite or ammonia. Destruction at hydrothermal vents is important at acidic pH's and at low ferrous iron concentrations. Photochemical destruction, even in a worst case scenario, is unimportant under many conditions except possibly under acidic, low iron concentration, or low temperature conditions. The primary sink for ammonia is photochemical destruction in the atmosphere. Under acidic conditions, more of the ammonia is tied up as ammonium (reducing its vapor pressure and keeping it in solution) and hydrothermal destruction becomes more important.

Summers, D. P.

1999-01-01

15

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

Microsoft Academic Search

Reaction of triose sugars with ammonia under anaerobic conditions yielded autocatalytic products. The autocatalytic behavior\\u000a of the products was examined by measuring the effect of the crude triose–ammonia reaction product on the kinetics of a second\\u000a identical triose–ammonia reaction. The reaction product showed autocatalytic activity by increasing both the rate of disappearance\\u000a of triose and the rate of formation of

Arthur L. Weber

2007-01-01

16

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

PubMed Central

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 N2 separation and H2 production stages. A maximum ammonia production rate of 1.14 × 10?5?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

17

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

18

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

19

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...

20

Reaction synthesis of intermetallics  

SciTech Connect

Exothermicity associated with the synthesis of aluminides was utilized to obtain nickel, iron, and cobalt aluminides. Combustion synthesis, extrusion, and hot pressing were utilized to obtain intermetallics and their composites. Extrusion conditions, reduction ratios, and hot-pressing conditions of the intermetallics and their composites are discussed.

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

1994-12-31

21

ECUT energy data reference series: ammonia synthesis energy-use and capital stock information  

SciTech Connect

Energy requirements for ammonia synthesis totaled 0.55 quadrillion Btu of natural gas in 1980 and 28,500 MMBtu (8.3 x 10/sup 6/ kWh) of electricity. Efficiencies ranged from 0.72 to 0.8 for natural gas and 0.65 for electricity. Ammonia production in 1980 is estimated at 21 million tones. In the year 2000, U.S. ammonia production is estimated to be between 27 to 34 million tones with 19 to 31 million tons being produced using natural gas. A most likely value of 25 million tons of ammonia from natural gas feedstock is projected. As much as 20% of the energy from natural gas fuel could be saved if a more active catalyst could be developed that would reduce the operating pressure of ammonia synthesis to 1 atm.

Young, J.K.; Johnson, D.R.

1984-07-01

22

Liquid composition having ammonia borane and decomposing to form hydrogen and liquid reaction product  

SciTech Connect

Liquid compositions of ammonia borane and a suitably chosen amine borane material were prepared and subjected to conditions suitable for their thermal decomposition in a closed system that resulted in hydrogen and a liquid reaction product.

Davis, Benjamin L; Rekken, Brian D

2014-04-01

23

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

24

Enhancement of Hsp70 synthesis protects common carp, Cyprinus carpio L., against lethal ammonia toxicity.  

PubMed

Exposure to TEX-OE®, a patented extract of the prickly pear cactus (Opuntia ficus indica) containing chaperone-stimulating factor, was shown to protect common carp, Cyprinus carpio L., fingerlings against acute ammonia stress. Survival was enhanced twofold from 50% to 95% after exposure to 5.92?mg?L(-1) NH(3) , a level determined in the ammonia challenge bioassay as the 1-h LD50 concentration for this species. Survival of TEX-OE®-pre-exposed fish was enhanced by 20% over non-exposed controls during lethal ammonia challenge (14.21?mg?L(-1) ?NH(3) ). Increase in the levels of gill and muscle Hsp70 was evident in TEX-OE®-pre-exposed fish but not in the unexposed controls, indicating that application of TEX-OE® accelerated carp endogenous Hsp70 synthesis during ammonia perturbation. Protection against ammonia was correlated with Hsp70 accretion. PMID:22724455

Sung, Y Y; Roberts, R J; Bossier, P

2012-08-01

25

Microwave-assisted synthesis of MgO–CNTs supported ruthenium catalysts for ammonia synthesis  

Microsoft Academic Search

Small and uniform ruthenium nanoparticles (1.3–2.0nm) supported on the mixture of MgO and carbon nanotubes (CNTs) were prepared by microwave irradiation and the promoted Ru\\/MgO–CNTs (K–Ru\\/MgO–CNTs-a) exhibited high activity for ammonia synthesis. The results show that the highest activity of the K–Ru\\/MgO–CNTs-a catalyst is 5631?molh-1g-cat-1 under 0.20MPa at 683K. The activity is 2.2 times as active as that of K–Ru\\/MgO–CNTs-b

Qing-Chi Xu; Jing-Dong Lin; Jun Li; Xian-Zhu Fu; Ying Liang; Dai-Wei Liao

2007-01-01

26

Reactions of rhenium carbonyl halides in an atmosphere of ionized ammonia  

Microsoft Academic Search

1.The ionization of Re(CO)5X in mixture of vapors of Re(CO)5X+ complexes (X=Cl, Br, I) with ammonia proceeds by charge transfer with NH3+ ions at ammonia pressures of ~0.1 torr.2.Information was obtained on the mechanism of the ion-molecule reactions of rhenium carbonyl halide ions using a formal kinetic analysis of high-pressure mass spectrometric method.3.The formation of ammonia-containing ions proceeds by substitution

V. A. Bogdanov; Yu. I. Savel'ev; R. N. Shchelokov

1987-01-01

27

Control of Nitrogen Dioxide in Stack Emission by Reaction with Ammonia  

NASA Technical Reports Server (NTRS)

The development of an acid base gas-phase reaction system which utilizes anhydrous ammonia as the reactant to remove nitrogen dioxide from hydrazine-nitrogen tetroxide rocket combustion exhaust is reported. This reaction reduced NO2 levels in exhaust emissions so that the resulting stack emission is completely white instead of the earlier observed typical reddish-brown coloration. Preliminary analyses indicate the importance of reaction time and ammonia concentration on removal efficiency and elimination of the health hazard to individuals with respiratory problems.

Metzler, A. J.; Stevenson, E. F.

1970-01-01

28

Carboxymethylguargum-silver nanocomposite: green synthesis, characterization and an optical sensor for ammonia detection  

NASA Astrophysics Data System (ADS)

This work describes the preparation of new carboxymethyl guar gum-silver nanocomposite (CMGG/Ag NC) by green synthesis method. For this carboxymethyl guar gum was used as a reducing agent as well as stabilizer. The silver nanoparticles obtained were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV–vis spectroscopy, Fourier transform infrared (FTIR) and energy dispersive x-ray analysis (EDX). The average size of the silver nanoparticles was found of ˜6 nm. Thus, the obtained CMGG/AgNPs NC was examined for optical sensing property for detection of ammonia in aqueous medium. The response time and the detection limit of ammonia in aqueous solution were detected at room temperature. It was concluded that in the future, at this room temperature optical ammonia sensor may be used for medical diagnosis and clinically for detecting low ammonia level (up to 1 ppm) in biological samples for various biomedical applications.

Pal Gupta, Anek; Verma, Devendra Kumar

2014-09-01

29

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.

Deevi, S.C.; Sikka, V.K. [Oak Ridge National Lab., TN (United States)

1995-12-31

30

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

31

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

32

Photochemical synthesis of organic compounds on Jupiter initiated by the photolysis of ammonia  

NASA Technical Reports Server (NTRS)

The photolysis of ammonia in the presence of certain concentrations of hydrogen, helium, and methane was studied at ambient temperatures and at 115 K. The ratio of reacting methane to photolyzed ammonia varies with concentrations and temperature. Reaction products include almost equal amounts of HCN, ethane, and propane accompanied by lesser amounts of hydrazine, n-butane, n-butane isomers, and pentane isomers. Free radical pathways participating in the reactions are discussed. The components of the starting mixture were chosen because they are believed to be present in the upper atmosphere of Jupiter, and the results are examined with reference to the Jovian atmosphere.

Ferris, J. P.; Nakagawa, C.; Chen, C. T.

1977-01-01

33

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

34

The formation of amino acid precursors in the reaction of atomic carbon with water and ammonia at 77 K  

Microsoft Academic Search

When atomic carbon is condensed on a surface at 77 K containing ammonia and water, glycine, N-methylglycine, alanine, beta-alanine, aspartic acid and serine are generated. It is postulated that these reactions may mimic those which occur when an extraterrestrial carbon atom condenses on a frozen surface coated with water and ammonia and may provide a route to extraterrestrial amino acids.

Daniel W. McPherson; Kazi Rahman; Iris Martinez; Philip B. Shevlin

1987-01-01

35

Experimental and theoretical studies of ammonia generation: Reactions of H2 with neutral cobalt nitride clusters.  

PubMed

Ammonia generation through reaction of H(2) with neutral cobalt nitride clusters in a fast flow reactor is investigated both experimentally and theoretically. Single photon ionization at 193 nm is used to detect neutral cluster distributions through time-of-flight mass spectrometry. Co(m)N(n) clusters are generated through laser ablation of Co foil into N(2)/He expansion gas. Mass peaks Co(m)NH(2) (m = 6, 10) and Co(m)NH(3) (m = 7, 8, 9) are observed for reactions of H(2) with the Co(m)N(n) clusters. Observation of these products indicates that clusters Co(m)N (m = 7, 8, 9) have high reactivity with H(2) for ammonia generation. Density functional theory (DFT) calculations are performed to explore the potential energy surface for the reaction Co(7)N + 3?2H(2) ? Co(7)NH(3), and a barrierless, thermodynamically favorable pathway is obtained. An odd number of hydrogen atoms in Co(m)NH(3) (m = 7, 8, 9) probably come from the hydrogen molecule dissociation on two active cobalt nitride clusters based on the DFT calculations. Both experimental observations and theoretical calculations suggest that hydrogen dissociation on two active cobalt nitride clusters is the key step to form NH(3) in a gas phase reaction. A catalytic cycle for ammonia generation from N(2) and H(2) on a cobalt metal catalyst surface is proposed based on our experimental and theoretical investigations. PMID:23020328

Yin, Shi; Xie, Yan; Bernstein, Elliot R

2012-09-28

36

GaN CVD Reactions: Hydrogen and Ammonia Decomposition and the Desorption of Gallium  

SciTech Connect

Isotopic labeling experiments have revealed correlations between hydrogen reactions, Ga desorption, and ammonia decomposition in GaN CVD. Low energy electron diffraction (LEED) and temperature programmed desorption (TPD) were used to demonstrate that hydrogen atoms are available on the surface for reaction after exposing GaN(0001) to deuterium at elevated temperatures. Hydrogen reactions also lowered the temperature for Ga desorption significantly. Ammonia did not decompose on the surface before hydrogen exposure. However, after hydrogen reactions altered the surface, N15H3 did undergo both reversible and irreversible decomposition. This also resulted in the desorption of N2 of mixed isotopes below the onset of GaN sublimation, This suggests that the driving force of the high nitrogen-nitrogen bond strength (226 kcal/mol) can lead to the removal of nitrogen from the substrate when the surface is nitrogen rich. Overall, these findings indicate that hydrogen can influence G-aN CVD significantly, being a common factor in the reactivity of the surface, the desorption of Ga, and the decomposition of ammonia.

Bartram, Michael E.; Creighton, J. Randall

1999-05-26

37

The reaction of monochloramine and hydroxylamine: implications for ammonia?oxidizing bacteria in chloraminated drinking water  

EPA Science Inventory

Drinking water chloramine use may promote ammonia?oxidizing bacteria (AOB) growth because of naturally occurring ammonia, residual ammonia remaining from chloramine formation, and ammonia released from chloramine decay and demand. A rapid chloramine residual loss is often associa...

38

Engineering methylaspartate ammonia lyase for the asymmetric synthesis of unnatural amino acids  

NASA Astrophysics Data System (ADS)

The redesign of enzymes to produce catalysts for a predefined transformation remains a major challenge in protein engineering. Here, we describe the structure-based engineering of methylaspartate ammonia lyase (which in nature catalyses the conversion of 3-methylaspartate to ammonia and 2-methylfumarate) to accept a variety of substituted amines and fumarates and catalyse the asymmetric synthesis of aspartic acid derivatives. We obtained two single-active-site mutants, one exhibiting a wide nucleophile scope including structurally diverse linear and cyclic alkylamines and one with broad electrophile scope including fumarate derivatives with alkyl, aryl, alkoxy, aryloxy, alkylthio and arylthio substituents at the C2 position. Both mutants have an enlarged active site that accommodates the new substrates while retaining the high stereo- and regioselectivity of the wild-type enzyme. As an example, we demonstrate a highly enantio- and diastereoselective synthesis of threo-3-benzyloxyaspartate (an important inhibitor of neuronal excitatory glutamate transporters in the brain).

Raj, Hans; Szyma?ski, Wiktor; de Villiers, Jandré; Rozeboom, Henriëtte J.; Veetil, Vinod Puthan; Reis, Carlos R.; de Villiers, Marianne; Dekker, Frank J.; de Wildeman, Stefaan; Quax, Wim J.; Thunnissen, Andy-Mark W. H.; Feringa, Ben L.; Janssen, Dick B.; Poelarends, Gerrit J.

2012-06-01

39

Carbon-supported cobalt catalyst for ammonia synthesis: Effect of preparation procedure  

Microsoft Academic Search

Supported cobalt catalysts were synthesised, characterised (by H2 TPD, XRD, TEM), and tested in ammonia synthesis at 9.0 MPa (400–470?°C; H2:N2=3:1). Partly graphitised carbon of high surface area (840 m2\\/g), cobalt nitrate, and barium nitrate were used as a support, a precursor of the active phase, and a promoter precursor, respectively. Both cobalt dispersion in the Ba-doped catalyst and, to

Wioletta Raróg-Pilecka; El?bieta Mi?kiewicz; Marcin Matyszek; Zbigniew Kaszkur; Leszek K?pi?ski; Zbigniew Kowalczyk

2006-01-01

40

Effect of ruthenium precursor on hydrogen-treated active carbon supported ruthenium catalysts for ammonia synthesis  

Microsoft Academic Search

Active carbon (A.C.), after treatment at 1123 K with hydrogen for more than 24 h, was found to be very effective as a support for ruthenium catalysis in ammonia synthesis. The activity of barium promoted Ru catalysts supported on this treated A.C. is affected remarkably by the Ru precursor. Ru3(CO)12 was found previously to be the most effective Ru precursor

Zhi-hua Zhong; Ken-ichi Aika

1998-01-01

41

Ammonia gas transport and reactions in unsaturated sediments: Implications for use as an amendment to immobilize inorganic contaminants.  

PubMed

Use of gas-phase amendments for in situ remediation of inorganic contaminants in unsaturated sediments of the vadose zone may be advantageous, but there has been limited development and testing of gas remediation technologies. Treatment with ammonia gas has a potential for use in treating inorganic contaminants (such as uranium) because it induces a high pore-water pH, causing mineral dissolution and subsequent formation of stable precipitates that decrease the mobility of some contaminants. For field application of this treatment, further knowledge of ammonia transport in porous media and the geochemical reactions induced by ammonia treatment is needed. Laboratory studies were conducted to support calculations needed for field treatment design, to quantify advective and diffusive ammonia transport in unsaturated sediments, to evaluate inter-phase (gas/sediment/pore water) reactions, and to study reaction-induced pore-water chemistry changes as a function of ammonia delivery conditions, such as flow rate, gas concentration, and water content. Uranium-contaminated sediment was treated with ammonia gas to demonstrate U immobilization. Ammonia gas quickly partitions into sediment pore water and increases the pH up to 13.2. Injected ammonia gas advection front movement can be reasonably predicted by gas flow rate and equilibrium partitioning. The ammonia gas diffusion rate is a function of the water content in the sediment. Sodium, aluminum, and silica pore-water concentrations increase upon exposure to ammonia and then decline as aluminosilicates precipitate when the pH declines due to buffering. Up to 85% of the water-leachable U was immobilized by ammonia treatment. PMID:25723886

Zhong, L; Szecsody, J E; Truex, M J; Williams, M D; Liu, Y

2015-05-30

42

Long-term real-time monitoring catalytic synthesis of ammonia in a microreactor by VUV-lamp-based charge-transfer ionization time-of-flight mass spectrometry.  

PubMed

With respect to massive consumption of ammonia and rigorous industrial synthesis conditions, many studies have been devoted to investigating more environmentally benign catalysts for ammonia synthesis under moderate conditions. However, traditional methods for analysis of synthesized ammonia (e.g., off-line ion chromatography (IC) and chemical titration) suffer from poor sensitivity, low time resolution, and sample manipulations. In this work, charge-transfer ionization (CTI) with O2(+) as the reagent ion based on a vacuum ultraviolet (VUV) lamp in a time-of-flight mass spectrometer (CTI-TOFMS) has been applied for real-time monitoring of the ammonia synthesis in a microreactor. For the necessity of long-term stable monitoring, a self-adjustment algorithm for stabilizing O2(+) ion intensity was developed to automatically compensate the attenuation of the O2(+) ion yield in the ion source as a result of the oxidation of the photoelectric electrode and contamination on the MgF2 window of the VUV lamp. A wide linear calibration curve in the concentration range of 0.2-1000 ppmv with a correlation coefficient (R(2)) of 0.9986 was achieved, and the limit of quantification (LOQ) for NH3 was in ppbv. Microcatalytic synthesis of ammonia with three catalysts prepared by transition-metal/carbon nanotubes was tested, and the rapid changes of NH3 conversion rates with the reaction temperatures were quantitatively measured with a time resolution of 30 s. The high-time-resolution CTI-TOFMS could not only achieve the equilibrium conversion rates of NH3 rapidly but also monitor the activity variations with respect to investigated catalysts during ammonia synthesis reactions. PMID:24968116

Xie, Yuanyuan; Hua, Lei; Hou, Keyong; Chen, Ping; Zhao, Wuduo; Chen, Wendong; Ju, Bangyu; Li, Haiyang

2014-08-01

43

Photoinduced ring opening reactions and subsequent thermal ring closure reactions in the thymine-ammonia system and related systems.  

PubMed

The photo-induced ring opening reactions of thymine (Thy) and 1-methylthymine (MeT) with ammonia and with methylamine (MA) at basic pH, and the subsequent ring closure reactions of the resulting adducts, have been studied. In the photo-induced reaction of Thy with ammonia, the dominant product is the E form of N-carbamoyl-3-amino-2-methylacrylamide (IIIa). Heating or acid treatment of aqueous IIIa results in rapid formation of Thy as final product, while allowing IIIa to stand at 4 degrees C produces Thy and two isomeric Thy hydrates, namely trans- and cis-6-hydroxy-5,6-dihydrothymine (Ia and IIa). The main products in the other reactions have analogous structures and undergo analogous ring closure reactions. Incubation of IIIa (and similar adducts) in phosphate buffer near pH 7 significantly enhances the rate of hydrate formation; other weak acid/conjugate base buffer systems also increase the rate of hydrate formation. A mechanism leading from opened ring adduct (e.g.IIIa) to hydrates (e.g.Ia and IIa) is proposed; ring closure leads initially to a dihydrothymine intermediate containing a 6-amino moiety, while further reaction with water produces the observed hydrates. The results described may be relevant to understanding the fate of cross-links generated by photo-induced reaction of thymine moieties in DNA with lysine residues in nuclear proteins (e.g. histones) when they are formed in a cellular environment. Decomposition of such cross-links, catalyzed by cellular phosphate, could lead to production of thymine hydrates attached to lysine residues contained in the protein partner and concurrent generation of an apyrimidinic site in the DNA partner. PMID:20714675

Shetlar, Martin D; Chung, Janet; Hom, Kellie

2010-09-24

44

An efficient route for the preparation of activated carbon supported ruthenium catalysts with high performance for ammonia synthesis  

Microsoft Academic Search

An impregnation–precipitation method was developed for the preparation of activated carbon supported ruthenium-based catalysts for ammonia synthesis. The ammonia concentration in the outlet of reactor for the Ba–Ru–K\\/AC catalysts prepared via impregnation–precipitation method is as high as 20.4vol% at 648K, pressure of 10MPa and with a space velocity of 10,000h?1, which is much higher than that of catalysts obtained via

Ying Li; Chonggen Pan; Wenfeng Han; Haifang Chai; Huazhang Liu

2011-01-01

45

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 of vibrationally state-selected ammonia ions with deuterated water is investigated with a quadrupole energies from 0.5 to 10.0 eV (center of mass) and ammonia ion vibrational states 1020-10 and 1122

Zare, Richard N.

46

The formation of amino acid precursors in the reaction of atomic carbon with water and ammonia at 77 K  

Microsoft Academic Search

When atomic carbon is condensed on a surface at 77 K containing ammonia and water, glycine, N-methylglycine, alanine, ?-alanine,\\u000a aspartic acid and serine are generated. It is postulated that these reactions may mimic those which occur when an extraterrestrial\\u000a carbon atom condenses on a frozen surface coated with water and ammonia and may provide a route to extraterrestrial amino\\u000a acids.

Daniel W. Mcpherson; Kazi Rahman; Iris Martinez; Philip B. Shevlin

1987-01-01

47

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

48

Multicomponent reactions for the synthesis of heterocycles.  

PubMed

Multicomponent domino reactions (MDRs) serve as a rapid and efficient tool for the synthesis of versatile heterocycles, particularly those containing structural diversity and complexity, by a one-pot operation. These reactions can dramatically reduce the generation of chemical wastes, costs of starting materials, and the use of energy and manpower. Moreover, the reaction period can be substantially shortened. This Review covers recent advances on multicomponent domino reactions for the construction of five-, six-, and seven-membered heterocyclic skeletons and their multicyclic derivatives. PMID:20922748

Jiang, Bo; Rajale, Trideep; Wever, Walter; Tu, Shu-Jiang; Li, Guigen

2010-11-01

49

Organocatalytic Asymmetric Assembly Reactions: Synthesis of Spirooxindoles via Organocascade Strategies  

E-print Network

Organocatalytic Asymmetric Assembly Reactions: Synthesis of Spirooxindoles via Organocascade in the enantioselective synthesis of spirooxindoles via organocascade strategies. Various organocatalysts with distinct on the enantioselective synthesis of spirooxindoles via organocascade strategies and is organized on the basis of three

Barbas III, Carlos F.

50

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

51

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

52

Competitive gas-solid reactions realized by ball milling of Zr in ammonia gas  

SciTech Connect

Competitive gas-solid reactions have been observed during high-energy ball milling of zirconium metal powder under an ammonia atmosphere at room temperature. The milling processes were investigated by monitoring pressure changes and subsequently analyzing milled powders with x-ray diffraction, thermal analysis, and elemental composition analysis. It is shown that during an early stage of milling, while the pressure is decreasing, a hydridation reaction predominates and leads to the formation of ZrH{sub 2} phase. During further milling the pressure increases again, and corresponds to a nitridation reaction between ZrH{sub 2} and available nitrogen (either excess NH{sub 3} or incorporated nitrogen in the powder) to form ZrN. Hydrogen gas is liberated and complete conversion to ZrN occurs after prolonged milling. The above reaction sequence was confirmed by the nitridation reaction of ZrH{sub 2} ball milled in NH{sub 3} atmosphere. {copyright} {ital 1996 Materials Research Society.}

Chen, Y.; Williams, J.S. [Department of Electronic Materials and Engineering, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, Australian Capital Territory 0200 (Australia)

1996-06-01

53

Surface Science and Catalysis—Studies on the Mechanism of Ammonia Synthesis: The P. H. Emmett Award Address  

Microsoft Academic Search

About 5 years ago a Battelle Colloquium on “The Physical Basis of Heterogeneous Catalysis” was held in honor of Professor Emmett where he presented an introductory talk on ?Fifty Years of Progress in the Study of the Catalytic Synthesis of Ammonia? [1], a field to which he had made significant contributions during this whole period. So why another report on

G. Ertl

1980-01-01

54

Synthesis and Evaluation of Cu-SAPO-34 Catalysts for Ammonia Selective Catalytic Reduction. 1. Aqueous Solution Ion Exchange  

SciTech Connect

SAPO-34 molecular sieves are synthesized using various structure directing agents (SDAs). Cu-SAPO-34 catalysts are prepared via aqueous solution ion exchange. Catalysts are characterized with surface area/pore volume measurements, temperature programmed reduction (TPR), electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectroscopies. Catalytic properties are examined using standard ammonia selective catalytic reduction (NH3-SCR) and ammonia oxidation reactions. During solution ion exchange, different SAPO-34 samples undergo different extent of structural damage via irreversible hydrolysis. Si content within the samples (i.e., Al-O-Si bond density) and framework stress are key factors that affect irreversible hydrolysis. Even using very dilute Cu acetate solutions, it is not possible to generate Cu-SAPO-34 samples with only isolated Cu2+ ions. Small amounts of CuOx species always coexist with isolated Cu2+ ions. Highly active and selective Cu-SAPO-34 catalysts for NH3-SCR are readily generated using this synthesis protocol, even for SAPO-34 samples that degrade substantially during solution ion exchange. High-temperature aging is found to improve the catalytic performance. This is likely due to reduction of intracrystalline mass-transfer limitations via formation of additional porosity in the highly defective SAPO-34 particles formed after ion exchange. The authors gratefully acknowledge the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Office of Vehicle Technologies for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle Memorial Institute under contract number DE-AC05-76RL01830.

Gao, Feng; Walter, Eric D.; Washton, Nancy M.; Szanyi, Janos; Peden, Charles HF

2013-09-06

55

General basic and coordination catalysis in reactions of haloaromatic compounds with ammonia in the presence of copper(I) compounds  

SciTech Connect

This paper presents a study made to detect general basic catalysis by ammonia (reagent) in reactions of ammonolysis of haloaromatic compounds in the presence of Cu/sup +/ ions, as well as to determine the generality of the mechanisms of the catalytic replacement of a halogen atom by an amino group in the anthraquinone and benzene series.

Chumak, V.T.; Shein, S.M.

1985-11-01

56

Catalytic Radical Domino Reactions in Organic Synthesis  

PubMed Central

Catalytic radical-based domino reactions represent important advances in synthetic organic chemistry. Their development benefits synthesis by providing atom- and step-economical methods to complex molecules. Intricate combinations of radical, cationic, anionic, oxidative/reductive, and transition metal mechanistic steps result in cyclizations, additions, fragmentations, ring-expansions, and rearrangements. This Perspective summarizes recent developments in the field of catalytic domino processes. PMID:24587964

Sebren, Leanne J.; Devery, James J.; Stephenson, Corey R.J.

2014-01-01

57

Catalytic Radical Domino Reactions in Organic Synthesis.  

PubMed

Catalytic radical-based domino reactions represent important advances in synthetic organic chemistry. Their development benefits synthesis by providing atom- and step-economical methods to complex molecules. Intricate combinations of radical, cationic, anionic, oxidative/reductive, and transition metal mechanistic steps result in cyclizations, additions, fragmentations, ring-expansions, and rearrangements. This Perspective summarizes recent developments in the field of catalytic domino processes. PMID:24587964

Sebren, Leanne J; Devery, James J; Stephenson, Corey R J

2014-02-01

58

Synthesis of d- and L-phenylalanine derivatives by phenylalanine ammonia lyases: a multienzymatic cascade process.  

PubMed

The synthesis of substituted D-phenylalanines in high yield and excellent optical purity, starting from inexpensive cinnamic acids, has been achieved with a novel one-pot approach by coupling phenylalanine ammonia lyase (PAL) amination with a chemoenzymatic deracemization (based on stereoselective oxidation and nonselective reduction). A simple high-throughput solid-phase screening method has also been developed to identify PALs with higher rates of formation of non-natural D-phenylalanines. The best variants were exploited in the chemoenzymatic cascade, thus increasing the yield and ee?value of the D-configured product. Furthermore, the system was extended to the preparation of those L-phenylalanines which are obtained with a low ee?value using PAL amination. PMID:25728350

Parmeggiani, Fabio; Lovelock, Sarah L; Weise, Nicholas J; Ahmed, Syed T; Turner, Nicholas J

2015-04-01

59

Synthesis of starch-g-lactic acid copolymer with high grafting degree catalyzed by ammonia water.  

PubMed

The study of starch-g-lactic acid copolymer has gained much attention for its completely degradable property, but its intricate synthetic procedure and low graft degree inhibited its further application. In this work, the synthesis of starch-g-lactic acid copolymer was attempted via the catalysis of ammonia water by one-step process, and the structure of starch-g-lactic acid copolymer was characterized by means of IR, (13)C NMR and HMBC. The synthetic conditions were optimized as follows, the starch was activated for 2h at 80°C at first, starch and lactic acid with weight ratios of 1:4 reacted for 4h at 90°C in vacuum. The starch-g-lactic acid copolymer can be finally obtained with graft degree of starch 58.9%. PMID:25542110

Hu, Yingmo; Tang, Mingru

2015-03-15

60

Regenerable adsorbent for removing ammonia evolved from anaerobic reaction of animal urine  

Microsoft Academic Search

The waste gas evolved from biodegradation of animal urine contains ammonia causing environmental concerns. A new and effective method for removing ammonia from such waste gas using reactive adsorption is presented. In the process, activated carbon impregnated with H2SO4(H2SO4\\/C) is employed. Ammonia in the waste gas reacts with H2SO4 on the adsorbent instantaneously and completely to form (NH4)2SO4. The H2SO4\\/C

Liang-hsing CHOU; Ru-in TSAI; Jen-ray CHANG; Maw-tien LEE

2006-01-01

61

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

62

Dechlorination process of active carbon-supported, barium nitrate-promoted ruthenium trichloride catalyst for ammonia synthesis  

Microsoft Academic Search

The effects of temperature and time of reductive dechlorination of RuCl3 to remove negative-effected chlorine and then form metallic Ru on hydrogen-treated active carbon (HTAC) support on catalytic activity for ammonia synthesis were investigated in detail. The purpose was to try to prepare Ru catalyst by using the low-cost RuCl3 as a precursor to replace other high-priced chlorine-free Ru compounds

Hai Sheng Zeng; Koji Inazu; Ken-ichi Aika

2001-01-01

63

Flow synthesis using gaseous ammonia in a Teflon AF-2400 tube-in-tube reactor: Paal-Knorr pyrrole formation and gas concentration measurement by inline flow titration.  

PubMed

Using a simple and accessible Teflon AF-2400 based tube-in-tube reactor, a series of pyrroles were synthesised in flow using the Paal-Knorr reaction of 1,4-diketones with gaseous ammonia. An inline flow titration technique allowed measurement of the ammonia concentration and its relationship to residence time and temperature. PMID:22532036

Cranwell, Philippa B; O'Brien, Matthew; Browne, Duncan L; Koos, Peter; Polyzos, Anastasios; Peña-López, Miguel; Ley, Steven V

2012-08-14

64

Evaluation of revised polymerase chain reaction primers for more inclusive quantification of ammonia-oxidizing archaea and bacteria.  

PubMed

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) fill key roles in the nitrogen cycle. Thus, well-vetted methods for characterizing their distribution are essential for framing studies of their significance in natural and managed systems. Quantification of the gene coding for one subunit of the ammonia monooxygenase (amoA) by polymerase chain reaction is frequently employed to enumerate the two groups. However, variable amplification of sequence variants comprising this conserved genetic marker for ammonia oxidizers potentially compromises within- and between-system comparisons. We compared the performance of newly designed non-degenerate quantitative polymerase chain reaction primer sets to existing primer sets commonly used to quantify the amoA of AOA and AOB using a collection of plasmids and soil DNA samples. The new AOA primer set provided improved quantification of model mixtures of different amoA sequence variants and increased detection of amoA in DNA recovered from soils. Although both primer sets for the AOB provided similar results for many comparisons, the new primers demonstrated increased detection in environmental application. Thus, the new primer sets should provide a useful complement to primers now commonly used to characterize the environmental distribution of AOA and AOB. PMID:25534249

Meinhardt, Kelley A; Bertagnolli, Anthony; Pannu, Manmeet W; Strand, Stuart E; Brown, Sally L; Stahl, David A

2015-04-01

65

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

66

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...

67

Synthesis of (+)-discodermolide by catalytic stereoselective borylation reactions.  

PubMed

The marine natural product (+)-discodermolide was first isolated in 1990 and, to this day, remains a compelling synthesis target. Not only does the compound possess fascinating biological activity, but it also presents an opportunity to test current methods for chemical synthesis and provides an inspiration for new reaction development. A new synthesis of discodermolide employs a previously undisclosed stereoselective catalytic diene hydroboration and also establishes a strategy for the alkylation of chiral enolates. Furthermore, this synthesis of discodermolide provides the first examples of the asymmetric 1,4-diboration of dienes and borylative diene-aldehyde couplings in complex-molecule synthesis. PMID:25045037

Yu, Zhiyong; Ely, Robert J; Morken, James P

2014-09-01

68

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

69

GREEN CHEMICAL SYNTHESIS THROUGH CATALYSIS AND ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

Green chemical synthesis through catalysis and alternate reaction conditions Encompassing green chemistry techniques and methodologies, we have initiated several projects at the National Risk Management Research laboratory that focus on the design and development of chemic...

70

Pivalolactone, 2. Copolyester synthesis via interchange reactions with polypivalolactone  

Microsoft Academic Search

The synthesis of copolyesters via interchange reactions of polypivalolactone (PPVL) with several compounds was studied. The synthetical procedures are two-stage melt processes: in the first stage ester bonds in the polymer chain are cleaved and new groups are incorporated in the polymer chain, while in the second step condensation of the end-groups formed occurs. For the synthesis of copolymers, three

Edze Jan Tijsma; Does van der Leen; Adriaan Bantjes; Ivan Vulic; Gerard Hidde Werumeus Buning

1993-01-01

71

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

NASA Astrophysics Data System (ADS)

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.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. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr04072d

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

2014-11-01

72

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

73

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

74

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

75

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

76

Organic synthesis by quench reactions. [in prebiotic simulation experiment  

NASA Technical Reports Server (NTRS)

Study of the effects of chemical quench reactions on the formation of organic compounds at a water surface under simulated primordial earth conditions. A mixture of gaseous methane and ammonia over a water surface was exposed to an arc discharge between an electrode and the water surface, generating reactive species. Various organic molecules were formed by a subsequent quenching of these species generated on the water surface. The effects of these water-surface quench reactions were assessed by comparing the amounts of synthesized molecules to the amounts which formed during the discharge of an arc above the water level. It is concluded that the quench (or wet) discharge led to faster rates of reactions, higher-molecular-weight organic compounds, and one-order-of-magnitude larger yields than the dry discharge.

Park, W. K.; Hochstim, A. R.; Ponnamperuma, C.

1975-01-01

77

Ammonia synthesis by hydrogenolysis of titanium-nitrogen bonds using proton coupled electron transfer.  

PubMed

The catalytic hydrogenolysis of the titanium-amide bond in (?(5)-C5Me4SiMe3)2Ti(Cl)NH2 to yield free ammonia is described. The rhodium hydride, (?(5)-C5Me5)(py-Ph)RhH (py-Ph = 2-phenylpyridine), serves as the catalyst and promotes N-H bond formation via hydrogen atom transfer. The N-H bond dissociation free energies of ammonia ligands have also been determined for titanocene and zirconocene complexes and reveal a stark dependence on metal identity and oxidation state. In all cases, the N-H BDFEs of coordinated NH3 decreases by >40 kcal/mol from the value in the free gas phase molecule. PMID:25719966

Pappas, Iraklis; Chirik, Paul J

2015-03-18

78

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

79

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

80

Achieving Chemical Equilibrium: The Role of Imposed Conditions in the Ammonia Formation Reaction  

ERIC Educational Resources Information Center

Under conditions of constant temperature T and pressure P, chemical equilibrium occurs in a closed system (fixed mass) when the Gibbs free energy G of the reaction mixture is minimized. However, when chemical reactions occur under other conditions, other thermodynamic functions are minimized or maximized. For processes at constant T and volume V,…

Tellinghuisen, Joel

2006-01-01

81

Synthesis of MTBE during CO hydrogenation: Reaction sites required  

SciTech Connect

Synthesis of methyl tert-butyl ether (MTBE) during carbon monoxide (CO) hydrogenation has been studied with the following reaction schemes: (1) the addition of isobutylene during CO hydrogenation over metal catalysts active for methanol synthesis (Pd/SiO{sub 2} and Li-Pd/SiO{sub 2}) and (2) the addition of isobutylene during CO hydrogenation over a dual bed configuration consisting of Li-Pd/SiO{sub 2} and a zeolite (H-ZSM-5 or HY). The addition of isobutylene during methanol synthesis over the supported Pd catalysts indicated that MTBE cannot be formed on metal sites from a reaction of isobutylene with methanol precursors. However, addition of isobutylene to the syngas feed over a dual bed consisting of a methanol synthesis catalyst and an acid zeolite downstream of the methanol synthesis catalyst showed that MTBE can be synthesized during CO hydrogenation provided acid sites are available. In order to get higher conversions of methanol to MTBE, optimization of the acid catalyst and/or reaction conditions would be required to minimize formation of byproduct hydrocarbons.

Kazi, A.M.; Goodwin, J.G. Jr.; Marcelin, G.; Oukaci, R. [Univ. of Pittsburgh, PA (United States). Dept. of Chemical and Petroleum Engineering

1995-03-01

82

Tetraglyme-mediated synthesis of Pd nanoparticles for dehydrogenation of ammonia borane.  

PubMed

Palladium nanoparticles (PdNPs) were conveniently prepared in tetraglyme (TG) solution using a variety of palladium precursors. At 140 °C, TG promoted Pd(3)(OAc)(6) to produce irregular shaped PdNPs with an average size of 4 nm. When these PdNPs were re-dispersed in TG and used for the dehydrogenation of ammonia borane (AB) at 85 °C, remarkably enhanced catalytic performance was achieved to release 2.3 equiv. of H(2) in 1 h. PMID:22234607

Kim, Sung-Kwan; Kim, Tae-Jin; Kim, Tae-Young; Lee, Gaehang; Park, Joon T; Nam, Suk Woo; Kang, Sang Ook

2012-02-14

83

Iminium ion cascade reaction in the total synthesis of (+)-vincadifformine.  

PubMed

An iminium ion triggered cascade reaction is described in the total synthesis of (+)-vincadifformine by the coupling of 3,3-substituted tetrahydropyridine and indole derivative. The strategy allows simultaneous construction of two new rings, three new sigma bonds, and two new stereogenic centers in one pot with complete stereochemical control. PMID:21815617

Pandey, Ganesh; C, Prasanna Kumara

2011-09-01

84

Combustion synthesis of advanced materials: Part I. Reaction parameters  

Microsoft Academic Search

An explanation of combustion (self propagating high temperature) synthesis (SHS) is given together with a historical perspective of the examination of such exothermic reactions. The application of thermochemical functions has been used to predict theoretically the maximum adiabatic temperature, Tad. This, combined with a knowledge of the ignition temperature, Tig, and the actual combustion temperature, Tc, has been used to

John J. Moore; H. J. Feng

1995-01-01

85

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

86

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

87

Facile single-step ammonia heat-treatment and quenching process for the synthesis of improved Pt/N-graphene catalysts  

NASA Astrophysics Data System (ADS)

In this work, we present a facile route to prepare electrocatalysts for methanol oxidation. The catalyst synthesis route involves the simultaneous reduction and nitrogen doping of graphene oxide (GO) along with the reduction of H2PtCl6 to Pt by a facile ammonia gas heat-treatment and quenching process. The resulting catalysts are characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy while their electrocatalytic activity toward the oxidation of methanol is evaluated by cyclic voltammetry. The obtained Pt/graphene composites consist of crystalline Pt nanoparticles in the range of 1-4 nm which are well-dispersed on the N-doped graphene sheets. The best Pt/N-graphene catalyst composite is obtained after a 5 min ammonia treatment at 800 °C followed by rapid ammonia gas quenching at room temperature. This catalyst demonstrates superior catalytic activity for methanol electro-oxidation, with a peak current density of 0.218 A mgPt-1, which is about five times higher than an undoped (hydrogen treated and quenched) Pt/graphene control catalyst. The excellent electrocatalytic performance of the ammonia quenched catalyst is attributed to the nitrogenous functional groups and dopants in the graphene sheets that are formed during the facile quenching process in ammonia.

Xiong, Bin; Zhou, Yingke; O'Hayre, Ryan; Shao, Zongping

2013-02-01

88

Synthesis of nanoscale particles of Ta and Nb3Al by homogeneous reduction in liquid ammonia  

E-print Network

, nanoscale powder. Processing at such a high temperature results in an undesirably high rate of particle and electrons. In some cases, electron transport is fast and the overall rate of reaction is controlled by ion of the reaction medium can have a dramatic effect on the kinetics which, in turn, affect the nature

Sadoway, Donald Robert

89

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

90

Effect of primary degradation–reaction products from Ammonia Fiber Expansion (AFEX)-treated corn stover on the growth and fermentation of Escherichia coli KO11  

Microsoft Academic Search

The primary degradation–reaction products (DRP) identified in Ammonia Fiber Expansion (AFEX)-pretreated corn stover are acetate, lactate, 4-hydroxybenzaldehyde (4HBD) and acetamide. The effects of these products at a broad concentration range were tested on Escherichia coli KO11, a strain engineered for cellulosic ethanol production. Fermentations using glucose or xylose as the sole carbohydrate source and a sugar mixture of glucose and

Ming W. Lau; Bruce E. Dale

2010-01-01

91

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

92

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

93

Stereoselective synthesis of indolines via organocatalytic thioester enolate addition reactions.  

PubMed

A straightforward stereoselective synthesis route to indolin-3-yl acetates has been developed using organocatalytic addition reactions of monothiomalonates to ortho-bromo nitrostyrenes as the key step. The addition products of this highly stereoselective one-pot addition-deprotection-decarboxylation sequence were easily further converted to the target indolin-3-yl acetates, via an intramolecular Buchwald-Hartwig coupling reaction. The route provided indolin-3-yl acetates bearing tertiary and exocyclic quarternary stereogenic centers in excellent stereoselectivities and overall yields of 34-83%. PMID:25100030

Kolarovic, Andrej; Käslin, Alexander; Wennemers, Helma

2014-08-15

94

Ammonia causes decreased brain monoamines in fathead minnows (Pimephales promelas)  

USGS Publications Warehouse

Hyperammonemia, arising from variety of disorders, leads to severe neurological dysfunction. The mechanisms of ammonia toxicity in brain are not completely understood. This study investigated the effects of ammonia on monoaminergic systems in brains of fathead minnows (Pimephales promelas). Fish serve as a good model system to investigate hyperammonemic effects on brain function since no liver manipulations are necessary to increase endogenous ammonia concentrations. Using high performance liquid chromatography with electrochemical detection, monoamines and some associated metabolites were measured from whole brain homogenate. Adult males were exposed for 48??h to six different concentrations of ammonia (0.01-2.36??mg/l unionized) which bracketed the 96-h LC50 for this species. Ammonia concentration-dependent decreases were found for the catecholamines (norepinephrine and dopamine) and the indoleamine serotonin (5-HT). After an initial increase in the 5-HT precursor 5-hydroxytryptophan it too decreased with increasing ammonia concentrations. There were also significant increases in the 5-HIAA/5-HT and DOPAC/DA ratios, often used as measures of turnover. There were no changes in epinephrine (Epi) or monoamine catabolites (DOPAC, 5-HIAA) at any ammonia concentrations tested. Results suggest that ammonia causes decreased synthesis while also causing increased release and degradation. Increased release may underlie behavioral reactions to ammonia exposure in fish. This study adds weight to a growing body of evidence demonstrating that ammonia leads to dysfunctional monoaminergic systems in brain which may underlie neurological symptoms associated with human disorders such as hepatic encephalopathy. ?? 2007 Elsevier B.V. All rights reserved.

Ronan, P.J.; Gaikowski, M.P.; Hamilton, S.J.; Buhl, K.J.; Summers, C.H.

2007-01-01

95

Structure Determination and Excited State Proton Transfer Reaction of 1-NAPHTHOL-AMMONIA Clusters in the S_{1} State Studied by Uv-Ir Mid-Ir Spectroscopy  

NASA Astrophysics Data System (ADS)

1-naphthol ammonia clusters have been studied long time as a benchmark system of the excited state proton transfer (ESPT) reactions. Understanding the ESPT reaction in this system has still not been fully established. To detect the cluster size dependence of the S_{1} state properties, many researcher extensively investigated such as emission spectra, lifetime, solvents (ammonia) evaporation pattern. Curiously, cluster structure that is fundamental to discuss the reaction has not been determined for the system. Thus we applied an IR spectroscopy to the S_{1} states of the system to determine the cluster structure and to discuss the minimum size inducing the ionic dissociation of the O-H bond in the S_{1} state. IR spectra were recorded not only the O-H and N-H stretching region (3 {?}m) but also the skeletal vibrational region (5.5-10 {?}m). Though O-H and N-H stretching vibrations do not provide useful structural information due to the broadness, the skeletal vibrations hold the sharpness even in the S_{1} states. Changes in the skeletal vibrations due to the ammonia solvation, e.g. C-O stretching and C-O-H bending, will be discussed based on a comparison with theoretical calculations. O. Cheshnovsky and S. Leutwylar, J. Chem. Phys. 1, 4127 (1988). S. K. Kim et al., Chem. Phys. lett. 228, 369 (1994). C. Dedonder-Lardeux et al., Phys. Chem, Chem, Phys. 3, 4316 (2001).

Yoshikawa, Shunpei; Miyazaki, Mitsuhiko; Martin, Weiler; Ishikawa, Haruki; Fujii, Masaaki

2013-06-01

96

Interorgan ammonia metabolism in liver failure.  

PubMed

In the post-absorptive state, ammonia is produced in equal amounts in the small and large bowel. Small intestinal synthesis of ammonia is related to amino acid breakdown, whereas large bowel ammonia production is caused by bacterial breakdown of amino acids and urea. The contribution of the gut to the hyperammonemic state observed during liver failure is mainly due to portacaval shunting and not the result of changes in the metabolism of ammonia in the gut. Patients with liver disease have reduced urea synthesis capacity and reduced peri-venous glutamine synthesis capacity, resulting in reduced capacity to detoxify ammonia in the liver. The kidneys produce ammonia but adapt to liver failure in experimental portacaval shunting by reducing ammonia release into the systemic circulation. The kidneys have the ability to switch from net ammonia production to net ammonia excretion, which is beneficial for the hyperammonemic patient. Data in experimental animals suggest that the kidneys could have a major role in post-feeding and post-haemorrhagic hyperammonemia.During hyperammonemia, muscle takes up ammonia and plays a major role in (temporarily) detoxifying ammonia to glutamine. Net uptake of ammonia by the brain occurs in patients and experimental animals with acute and chronic liver failure. Concomitant release of glutamine has been demonstrated in experimental animals, together with large increases of the cerebral cortex ammonia and glutamine concentrations. In this review we will discuss interorgan trafficking of ammonia during acute and chronic liver failure. Interorgan glutamine metabolism is also briefly discussed, since glutamine synthesis from glutamate and ammonia is an important alternative pathway of ammonia detoxification. The main ammonia producing organs are the intestines and the kidneys, whereas the major ammonia consuming organs are the liver and the muscle. PMID:12020618

Olde Damink, Steven W M; Deutz, Nicolaas E P; Dejong, Cornelis H C; Soeters, Peter B; Jalan, Rajiv

2002-01-01

97

Synthesis of CdS nanostructures using template-assisted ammonia-free chemical bath deposition  

NASA Astrophysics Data System (ADS)

CdS micro- and nano-structures (micro/nanotubes and nanostructured films) were obtained by ammonia-free chemical bath deposition using polymer templates (ion track-etched polycarbonate membranes and poly(styrene-hydroxyethyl methacrylate) nanosphere arrays). The semiconductor structures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), optical absorption, photoluminescence and electrical measurements. The diameters of CdS tubes are between 300 nm and few microns and the lengths are up to tens of micrometers. The SEM images prove that the CdS films are nanostructured due to the deposition on the polymer nanosphere arrays. For both CdS structures (tubes and films) the XRD patterns show a hexagonal phase. The optical studies reveal a band gap value of about 2.5-2.6 eV and a red luminescence at ˜1.77 eV. A higher increase of conductivity is observed for illuminating the CdS nanostructured film when compared to the simple semiconductor film. This is a consequence of the periodic patterning induced by the polymer nanosphere array.

Preda, N.; Enculescu, M.; Gherendi, F.; Matei, E.; Toimil-Molares, M. E.; Enculescu, I.

2012-09-01

98

Thermodynamics of Strecker Synthesis Reactions During Aqueous Alteration of Carbonaceous Chondrite Parent Bodies  

NASA Astrophysics Data System (ADS)

The wide acceptance of the parent body aqueous alteration hypothesis to explain the presence of hydrated silicate minerals on carbonaceous chondrite meteorites has led a number of researchers to investigate the suggestion that some of the organic compounds in these meteorites were produced during the silicate mineral alteration event (Bunch and Chang, 1980; Peltzer et al., 1984; Cronin, 1989; Shock and Schulte, 1990). Much of the interest has focused on the mechanisms of amino acid formation, the most favored of which is Strecker synthesis (Peltzer et al., 1984; Cronin, 1989; Kerridge, 1990). The observation of ammonium-bearing minerals in several carbonaceous chondrites (Zolensky and McSween, 1988), as well as the possible detection of the same minerals on asteroids (King et al., 1992), may allow explicit coupling of Strecker synthesis reactions with mineral alteration by aqueous fluids on meteorite parent bodies. In one path of Strecker synthesis, aldehydes or ketones react with HCN and ammonia in aqueous solution to produce amino acids. In the absence of ammonia in the initial reaction step, Strecker synthesis will produce hydroxy acids. This process has also been invoked to explain the presence of hydroxy acids on carbonaceous chondrites (Peltzer et al., 1984). The potential for Strecker synthesis of amino and hydroxy acids can be evaluated from values of the Gibbs free energy of the overall reactions deltaG (sub)r degrees. At 25 degrees C and 1 bar, calculated values of deltaG (sub)r degrees are negative for many examples of overall Strecker synthesis reactions, indicating that these reactions are energetically favored at these conditions. Oxygen isotope systematics indicate that aqueous alteration of carbonaceous chondrites occurred at temperatures from 0 degrees to ~150 degrees C (Clayton and Mayeda, 1984). Values of deltaG (sub)r degrees for reactions involving aqueous organic compounds can be calculated at elevated temperature using standard state properties from the literature together with equations, data and parameters provided by Shock and Helgeson (1990) and Shock (1992). We have used correlation algorithms developed by Shock and Helgeson (1990) to estimate equation-of-state parameters for aqueous aldehydes and HCN. These data and parameters, together with those for aqueous amino acids from Shock and Helgeson (1990), hydroxy acids from Shock (1992) and NH(sub)3 (aq) from Shock et al. (1989) were used to calculate values of deltaG (sub)r degrees for Strecker synthesis reactions at elevated temperatures. All the reactions we have investigated thus far are energetically favored over the entire range of temperatures considered. These preliminary results suggest that Strecker synthesis during aqueous alteration may account for the amino acids and hydroxy acids observed in carbonaceous chondrites. Testing this hypothesis, however, requires simultaneous solution of mass-action and mass-balance equations, together with constraints on initial activities of aldehydes and HCN in the aqueous phase. The presence of these compounds in interstellar space (Turner, 1989) and their inferred concentrations in comets provide constraints on these variables. Additionally, the coupled equilibria between the amino and hydroxy acids produced by Strecker synethesis allow evaluation of the activity of NH(sub)3 (ag). References: Bunch T. E. and Chang S. (1980) Geochim. Cosmochim. Acta 44, 1543-1577; Clayton R. N. and Mayeda T. K. (1984) Earth Planet. Sci. Lett. 67, 151-161; Cronin J. R. (1989) Adv. Space Res. 9, 5964; Kerridge J. F. (1991) Origins of Life 21, 19-29; King T. V. V., Clark R. N., Calvin W. M., Sherman D. M., and Brown R. H. (1992) Science 255, 1551-1553; Peltzer E. T., Bada J. L., Schlesinger G., and Miller S. L. (1984) Adv. Space Res. 4, 69-74; Shock E. L. (1992) Amer. J. Sci., submitted; Shock E. L. and Helgeson H. C. (1990) Geochim. Cosmochim. Acta 54, 2009-2036; Shock E. L., Helgeson H. C., and Sverjensky D. A. (1989) Geochim. Cosmochim. Acta 53, 2157-2183; Shock E. L and Schulte M. D. (1990) Nature 343, 728-731; Tur

Schulte, M. D.; Shock, E. L.

1992-07-01

99

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.; Müller, P.

2010-01-01

100

Ruthenium catalyzed formation of N-methylformamides from synthesis gas and ammonia  

SciTech Connect

Both RuO/sub 2/.xH/sub 2/O and Ru/sub 3/(CO)/sub 12/ are effective catalyst precursors for the conversion of CO/H/sub 2//NH/sub 3/ mixtures to N-methylformamides and trimethylamine in liquid phase reactor systems. The formation of N-methylated products is enhanced by operating at low NH/sub 3//syngas ratios. The two most plausible mechanisms for the production of N-methylated products involve: a) interception of incipient formaldehyde to form methyl amines and formamides, and b) hydrogenation of formamides to methylated products. Experimental evidence implies that methanol is not involved as a reaction intermediate, but can participate in a parallel reaction when introduced into the reaction mixture.

Marsella, J.A.; Pez, G.P.

1986-03-01

101

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

102

Ammonia-free method for synthesis of CdS nanocrystalline thin films through chemical bath deposition technique  

Microsoft Academic Search

The preparation of thin films of CdS by chemical bath deposition is mostly based on the utilisation of ammonia as a complexing agent for cadmium ions. Here we report on a technique based on sodium citrate dihydrate that eliminates the problems of ammonia volatility and toxicity. The crystallites with a size range of 10–20 nm in diameter with zinc blend

M. Karimi; M. Rabiee; F. Moztarzadeh; M. Bodaghi; M. Tahriri

2009-01-01

103

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, effect 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 reduction of nitrite and the Strecker can be combined to proceed in each other's presence, to yield glycine from a mixture of nitrite, Fe+2, formaldehyde, and cyanide.

Summers, D. P.; Lerner, N.

1998-01-01

104

Domino reaction involving the Bestmann-Ohira reagent and ?,?-unsaturated aldehydes: efficient synthesis of functionalized pyrazoles.  

PubMed

A mild, efficient and rapid domino reaction involving the Bestmann-Ohira reagent (BOR) and ?,?-unsaturated aldehydes has been developed for the synthesis of densely functionalized vinylpyrazoles. This reaction demonstrates the dual reactivity of BOR as a homologation reagent as well as a cycloaddition partner, thus constituting a domino reaction in an operationally simple procedure. The application of this efficient synthesis of pyrazoles has been demonstrated for the synthesis of phosphonyl analogues of pyrrolopyrazole alkaloids. PMID:25476791

Ahamad, Shakir; Gupta, Ashis Kumar; Kant, Ruchir; Mohanan, Kishor

2015-02-01

105

Effects of ammonia on carbon metabolism in photosynthesizing isolated mesophyll cells from Papaver somniferum L  

Microsoft Academic Search

Addition of ammonia to a suspension of photosynthesizing isolated mesophyll cells from P. somniferum quantitatively alters the pattern of carbon metabolism by increasing rates of certain key ratelimiting steps leading to amino-acid synthesis and by decreasing rates of rate-limiting steps in alternative biosynthetic pathways. Of particular importance is the stimulation of reactions mediated by pyruvate kinase and phosphoenolpyruvate carboxylase. The

John S. Paul; Karen L. Cornwell; James A. Bassham

1978-01-01

106

Fischer-Tropsch synthesis in supercritical reaction media  

SciTech Connect

The goal of this research is to thoroughly investigate the feasibility of using supercritical fluid (SCF) solvent medium for carrying out Fischer-Tropsch (FT) synthesis. Research will address the systematic experimental investigations of FT synthesis over supported Fe and Co catalysts in a CSTR and in a fixed-bed reactor at typical synthesis temperatures (240-260[degrees]C). The SCF medium to be employed is n-Hexane (P[sub c] = 29.7 bar; [Tc] = 233.7[degrees]C), while n-Hexadecane will be employed as the liquid reaction medium. Overall conversion, product distribution and catalyst deactivation will be measured in each case for various feed H[sub 2]/CO ratios ranging from 0.5 to 2. Product analyses will be carried out using GC/TCD, GC/FID and GC/MS systems. The fresh and used catalysts will be characterized with respect to active metal dispersion, surface area and pore size distribution.

Subramaniam, B.

1992-10-01

107

Tris(Cyclopentadienyl)Uranium-t-Butyl: Synthesis, reactions, and mechanisms  

SciTech Connect

Compounds (RC[sub 5]H[sub 4])[sub 3]U(t-Bu) were prepared for R = H, Me, Et. Their decomposition products in aromatic solvents are consistent with a radical decomposition pathway induced by solvent-assisted U-C bond homolysis. NMR was used to study the reactions of (RC[sub 5]H[sub 4])[sub 3]UCl with t-BuLi (R = t-Bu, Me[sub 3]Si). Reactions of (MeC[sub 5]H[sub 4])[sub 3]U(t-Bu) with Lewis bases and fluorocarbons were studied. Analogous reaction chemistry between (RC[sub 5]H[sub 4])[sub 3]ThX systems and t-BuLi was also studied, and reactivity differences between U and Th are discussed. Synthesis of sterically crowded (RC[sub 5]H[sub 4])[sub 4]U compounds is next considered. Reaction of the trivalent (RC[sub 5]H[sub 4])[sub 3]U with (RC[sub 5]H[sub 4])[sub 2]Hg results in formation of (RC[sub 5]H[sub 4])[sub 4]U. Steric congestion, cyclopentadienyl ligand exchange, and electron transfer are discussed. (DLC)

Weydert, M.

1993-04-01

108

Tris(Cyclopentadienyl)Uranium-t-Butyl: Synthesis, reactions, and mechanisms  

SciTech Connect

Compounds (RC{sub 5}H{sub 4}){sub 3}U(t-Bu) were prepared for R = H, Me, Et. Their decomposition products in aromatic solvents are consistent with a radical decomposition pathway induced by solvent-assisted U-C bond homolysis. NMR was used to study the reactions of (RC{sub 5}H{sub 4}){sub 3}UCl with t-BuLi (R = t-Bu, Me{sub 3}Si). Reactions of (MeC{sub 5}H{sub 4}){sub 3}U(t-Bu) with Lewis bases and fluorocarbons were studied. Analogous reaction chemistry between (RC{sub 5}H{sub 4}){sub 3}ThX systems and t-BuLi was also studied, and reactivity differences between U and Th are discussed. Synthesis of sterically crowded (RC{sub 5}H{sub 4}){sub 4}U compounds is next considered. Reaction of the trivalent (RC{sub 5}H{sub 4}){sub 3}U with (RC{sub 5}H{sub 4}){sub 2}Hg results in formation of (RC{sub 5}H{sub 4}){sub 4}U. Steric congestion, cyclopentadienyl ligand exchange, and electron transfer are discussed. (DLC)

Weydert, M.

1993-04-01

109

Catalytic synthesis of biologically important metabolites from formaldehyde and ammonia as a putative way of their prebiotic emergence  

NASA Astrophysics Data System (ADS)

The modern `RNA-world' theory considering the primary life as a system of self-replicating informational and catalytic oligomers is the most widespread hypothesis of life's origin. At the same time an alternative major theory antithetic to the genetic one exists. It is based on the primary formation of important metabolites and building blocks of biopolymers and appearance of the primordial autocatalytic cycles in geochemical environment. [1]. Encouraged by this theory, we suggest the putative emergence pathways to biologically relevant metabolites from simple precursors: formaldehyde (FA) and ammonia, which are known to be present in the interstellar space [2]. Based on our earlier [3, 4] and novel findings as well as on the literature data [5, 6] the scheme of conjugate autocatalytic processes including photochemical condensation of FA yielding C-C bond and catalytic formation of pyruvaldehyde, pyruvic acid, sugars, aminoacids catalyzed by minerals (aluminum silicate, phoshates) and by aminoacids themselves is proposed. Acetaldehyde, glyoxal, glycol-and glyceraldehydes (GA and GCA) were identified in this work as products of photolysis of FA aqueous solution with summary selectivity up to 20% and can serve as substrates for the synthesis of more complex organic compounds. In turn, alanine and pyruvic acid are formed during UV-irradiation of aqueous solution of acetaldehyde and ammonium nitrate [6]. Pyruvaldehyde formation from GCA and FA in presence of amino acids was observed by A. Weber [5]. Finally, we revealed the catalytic activity of zeolite HZSM-5-17 in acid form towards formation of pyruvaldehyde from GA and GCA in presence of alanine with the yield about 5%. This observation indicates that the assumption of catalytic activity of silica-alumina towards the synthesis of metabolites could be realistic. Prebiotic synthesis of sugars from lower monosacharides, as we showed earlier, could take place over phosphate catalysts [4]. The substrates and the products of the proposed scheme were detected in the interstellar space and meteorites [7, 8], evidencing of the possibility of its realization either on the Protoeath or in the protoplanet disk supplying the initial compounds for contemporary metabolism. Acknowledgements. The financial support of Program RAS, IP SB RAS N 10 is gratefully acknowledged. References 1. A. Eschenmoser, in "Origin of life. Chemical approach", Eds. P. Herdewijn, M.V. Kisakurek, Wiley-VCH, placeCityZurich, 2008 and refs therein. 2. D.A. Williams, J. Phys. Conf. 6, 1-17, 2005. 3. Pestunova, O., Simonov, A., Snytnikov, V., et al., Adv. Space Res. 36/2, 214-219, 2005. 4. Simonov, A., Pestunova, O., Matvienko, L., et al., Adv. Space Res. 40, 1634-1640, 2007. 5. A.L. Weber, Orig. Life Evol. Biosph. 31, 71-86, 2001. 6. T.A. Telegina, et. al., Journ. Evol. Biochim. i Fiziol. (Rus). 4/8, 429-434, 1977. 7. Hollis, J., Jewell, P., Lovas, F., et al., The Astrophysical Journal 613, L45-L48, 2004 8. Cooper, G., Kimmich, N., Belisle, W., et al., Nature 414(6866), 879, 2001.

Delidovich, Irina; Taran, Oxana; Simonov, Alexander; Parmon, Valentin

110

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.

111

A Stereoselective Synthesis of (?)-Viridiofungin A Utilizing a TiCl4-Promoted Asymmetric Multicomponent Reaction  

PubMed Central

A stereoselective synthesis of (?)-Viridiofungin A is described. The convergent synthesis utilized a unique highly diastereoselective multicomponent reaction between optically active phenyldihydrofuran and an ?-ketoester to provide two chiral centers including a quarternary carbon center in a single step. Other key steps include an acyloxycarbonum ion-mediated tetrahydrofuran ring-opening reaction and a Julia-Kocienski olefination. PMID:22195730

Ghosh, Arun K.; Kass, Jorden

2012-01-01

112

Liquid Ammonia  

Microsoft Academic Search

This is a review of the use of liquid ammonia as a solvent for chemical processes. Among the subjects covered are the physical properties of the solvent that defines it as “water like.” The physical and chemical processes associated with the formation of solutions and the properties of those solutions are also convered. Included is a discussion of metal?ammonia solutions,

J. J. Lagowski

2007-01-01

113

Ammonia Test  

MedlinePLUS

... ammonia are relatively common in newborns, where the level may rise and fall without causing detectible symptoms. An increased ... Back to top 2. When my increased ammonia level has returned to normal, can it rise again? It depends on why it was increased ...

114

Effect of primary degradation-reaction products from Ammonia Fiber Expansion (AFEX)-treated corn stover on the growth and fermentation of Escherichia coli KO11.  

PubMed

The primary degradation-reaction products (DRP) identified in Ammonia Fiber Expansion (AFEX)-pretreated corn stover are acetate, lactate, 4-hydroxybenzaldehyde (4HBD) and acetamide. The effects of these products at a broad concentration range were tested on Escherichia coli KO11, a strain engineered for cellulosic ethanol production. Fermentations using glucose or xylose as the sole carbohydrate source and a sugar mixture of glucose and xylose were conducted to determine how these products and sugar selection affected fermentation performance. Co-fermentation of the sugar mixture exhibited the lowest overall ethanol productivity compared to single-sugar fermentations and was more susceptible to inhibition. Metabolic ethanol yield increased with the increasing initial concentration of acetate. Although these degradation-reaction products (with exception of acetamide) are generally perceived to be inhibitory, organic acids and 4-hydroxybenzaldehyde at low levels stimulated fermentation. Adaptation of cells to these products prior to fermentation increased overall fermentation rate. PMID:20627718

Lau, Ming W; Dale, Bruce E

2010-10-01

115

[UO2(NH3)5]Br2·NH3: synthesis, crystal structure, and speciation in liquid ammonia solution by first-principles molecular dynamics simulations.  

PubMed

Pentaammine dioxido uranium(vi) dibromide ammonia (1/1), [UO2(NH3)5]Br2·NH3, was synthesized in the form of yellow crystals by the reaction of uranyl bromide, UO2Br2, with dry liquid ammonia. The compound crystallizes orthorhombic in space group Cmcm and is isotypic to [UO2(NH3)5]Cl2·NH3 with a = 13.2499(2), b = 10.5536(1), c = 8.9126(1) Å, V = 1246.29(3) Å(3) and Z = 4 at 123 K. The UO2(2+) cation is coordinated by five ammine ligands and the coordination polyhedron can be best described as pentagonal bipyramid. Car-Parrinello molecular dynamics simulations are reported for [UO2(NH3)5](2+) in the gas phase and in liquid NH3 solution (using the BLYP density functional). According to free-energy simulations, solvation by ammonia has only a small effect on the uranyl-NH3 bond strength. PMID:25797497

Woidy, Patrick; Bühl, Michael; Kraus, Florian

2015-04-01

116

Wittig reactions in water. Synthesis of new water-soluble phosphonium salts and their reactions with substituted benzaldehydes  

Microsoft Academic Search

We report the synthesis of new phosphonium salts which are soluble and stable in basic aqueous solution. The Wittig reactions of these phosphonium salts with substituted benzaldehydes in aqueous sodium hydroxide are discussed. These reactions exclude the use of any organic solvents and the products are isolated by a simple filtration.

Matthew G Russell; Stuart Warren

1998-01-01

117

Ammonia synthons for the multicomponent assembly of complex ?-lactams  

PubMed Central

The synthesis of ?-lactams that are unsubstituted at the 1-position (nitrogen) as well as their subsequent N-functionalization is reported. A recently discovered four-component reaction (4CR) is employed with either an ammonia precursor or a protected form of ammonia that can be deprotected in a subsequent synthetic step. These methods represent the first multicomponent assembly of complex lactam structures that are unsubstituted at nitrogen. In addition, two methods for the introduction of nitrogen substituents that are not possible through the original 4CR are reported. X-ray crystallographic analysis of representative structures reveals conformational changes in the core structure that will enable future deployment of this chemistry in the design and synthesis of diverse collections of lactams suitable for the discovery of new biological probes. PMID:21289284

Tan, Darlene Q.; Martin, Kevin S.; Fettinger, James C.; Shaw, Jared T.

2011-01-01

118

Construction and evaluation of an automated flow injection-stopped flow analyser for multipoint reaction rate spectrophotometric methods. Determination of ammonia nitrogen, creatinine and phosphate  

PubMed Central

The construction and evaluation of a fully automated Flow Injection-Stopped Flow (FI-SF) spectrophotometric analyser is described. A microcomputer (Rockwell AIM 65) is used to control the analyser (sample injection, stop and start of the pump) through a suitable interface. Data acquisition is achieved using a 12 bit ADC card and a suitable subroutine in 6502 assembly language, allowing data sampling at a frequency of 7.5 kHz. The measurement interface and software were evaluated using a voltage ramp generator. A precision of 0.02-1.1% RSD (N =10) was obtained for voltage ramps in the range of 1-37 mVs-1. The FI-SF analyser was evaluated in routine analysis by developing FI-SF kinetic spectrophotometric methods for the determination of ammonia nitrogen (20-250 ppm, 0.4-2.5% RSD) based on the Berthelot reaction, creatinine (20-220 ppm, 0.9-3.6% RSD) based on the Jaffé reaction, and phosphate (5-30 ppm, 1.0-3.3% RSD) based on the phosphomolybdenum blue reaction. The reaction rate is measured by linear fitting of multiple absorbance readings vs time. Algorithms for automated estimation of the residence time, the linear range of the reaction curve, and data treatment are presented. PMID:18924905

Georgiou, Constantinos A.

1991-01-01

119

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

120

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

121

Ammonia (GCMP)  

NSDL National Science Digital Library

Ammonia fountain: this is a resource in the collection "General Chemistry Multimedia Problems". In an ammonia fountain, a flask is filled with ammonia gas. A tube from the flask extends into a pan of water that contains phenolphthalein. When a rubber bulb full of water is squeezed, the water squirts into the flask. Water from the pan then is pushed into the flask and the indicator changes color. General Chemistry Multimedia Problems ask students questions about experiments they see presented using videos and images. The questions asked apply concepts from different parts of an introductory course, encouraging students to decompartmentalize the material.

122

Thermal and combined thermal and radiolytic reactions involving nitrous oxide, hydrogen, nitrogen, and ammonia in contact with tank 241-SY-101 simulated waste  

SciTech Connect

Work described in this report was conducted at Pacific Northwest National Laboratory (PNNL) for the Flammable Gas Safety Project, the purpose of which is to develop information needed to support Westinghouse Hanford Company (WHC) in their efforts to ensure the safe interim storage of wastes at the Hanford Site. Described in this report are the results of tests to evaluate the rates of thermal and combined thermal and radiolytic reactions involving flammable gases in the presence of Tank 241-SY-101 simulated waste. Flammable gases generated by the radiolysis of water and by the thermal and radiolytic decomposition of organic waste constituents may themselves participate in further reactions. Examples include the decomposition of nitrous oxide to yield nitrogen and oxygen, the reaction of nitrous oxide and hydrogen to produce nitrogen and water, and the reaction of nitrogen and hydrogen to produce ammonia. The composition of the gases trapped in bubbles in the wastes might therefore change continuously as a function of the time that the gas bubbles are retained.

Bryan, S.A.; Pederson, L.R.

1996-02-01

123

Action Reaction Learning: Analysis and Synthesis of Human Tony Jebara Alex Pentland  

E-print Network

Action Reaction Learning: Analysis and Synthesis of Human Behaviour Tony Jebara Alex Pentland://jebara.www.media.mit.edu/people/jebara/arl Abstract We propose Action­Reaction Learning as an ap­ proach for analyzing and synthesizing human and its reaction by observing time sequences. We apply this method to analyze human interaction

124

Action Reaction Learning: Analysis and Synthesis of Human Tony Jebara Alex Pentland  

E-print Network

Action Reaction Learning: Analysis and Synthesis of Human Behaviour Tony Jebara Alex Pentland://jebara.www.media.mit.edu/people/jebara/arl Abstract We propose Action-Reaction Learning as an ap- proach for analyzing and synthesizing human and its reaction by observing time sequences. We apply this method to analyze human interaction

Jebara, Tony

125

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.

126

A Novel Synthesis of r-Amino Acid Derivatives through Catalytic, Enantioselective Ene Reactions of  

E-print Network

A Novel Synthesis of r-Amino Acid Derivatives through Catalytic, Enantioselective Ene Reactions variants are known.2 However, the corresponding catalytic, enantioselective ene reaction between alkenes, enantioselective imino ene reaction of R-imino ester 1 with alkenes 2a-f catalyzed by Lewis acid complex 3 and show

Lectka, Thomas

127

Effect of incremental urea supplementation of a conventional corn silage-based diet on ruminal ammonia concentration and synthesis of microbial protein.  

PubMed

One primiparous and 3 multiparous lactating Holstein cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square design to determine the efficacy of adding urea to a corn silage-based diet on ruminal fermentation and microbial protein synthesis. Dietary treatments were 0, 0.3, 0.6, and 0.9% urea in diet dry matter (DM); urea was manually top dressed and incorporated into the ration. The basal diet contained (DM basis) 52% forage (with 61% of forage provided as corn silage) and 48% concentrate ingredients. The basal diet was formulated to meet National Research Council (NRC, 2001) requirements for energy and all nutrients except rumen-degradable protein (RDP) and metabolizable protein. Experimental periods lasted 14 d with the first 9 d for adaptation. The basal diet, without urea addition, contained 9.2% RDP in DM and had a predicted RDP balance of -167 g/d (NRC, 2001). There were no effects of dietary treatment on ruminal true digestibility of organic matter or ruminal apparent digestibility of neutral detergent fiber and acid detergent fiber. Total ruminal volatile fatty acid concentrations increased linearly with increasing urea level. Feeding increasing amounts of urea quadratically increased rumen ammonia N concentrations (9.0, 11.9, 12.8, and 17.4 mg/dL at 0, 0.3, 0.6, and 0.9% urea supplementation, respectively), passage of microbial N, and microbial N in duodenal digesta as a percentage of nonammonia N. The results of this study indicate that there were some positive effects of adding urea to the described lactating dairy cow diet, and that microbial protein synthesis was maximized at an average ruminal ammonia N concentration of 12.8 mg/dL when urea was added at 0.6% in diet DM. PMID:18024754

Boucher, S E; Ordway, R S; Whitehouse, N L; Lundy, F P; Kononoff, P J; Schwab, C G

2007-12-01

128

UV – INDUCED SYNTHESIS OF AMINO ACIDS FROM AQUEOUS STERILIZED SOLUTION OF AMMONIUM FORMATE AND AMMONIA UNDER HETROGENEOUS CONDITIONS  

PubMed Central

Irradiation of sterilized aqueous solution of ammonium formate and ammonia with UV light in the presence and or absence of certain inorganic sensitizers for 25 hrs. gave six ninhydrin positive products in appreciable amounts. Out of the six products observed fiver were characterized as lysine, serine, glutemic acid, n-amino butyric acid and leucine. The sensitizing effect of additives on ammonium formate was observed in the order; uranium oxide > ammonium formate > ferric oxide > arsenic oxide. PMID:22556511

Bisht, G.; Bisht, L. S.

1990-01-01

129

Equation of state of ammonia  

NASA Astrophysics Data System (ADS)

Ammonia and water are critical components of extraterrestrial bodies, determining the density and physical properties of the Outer Planets, their moons, and of extrasolar planets. Ammonia is unusual in having a high heat capacity relative to other molecular species. Equations of state (EOS) are presented for ammonia and for mixtures of ammonia and water. Their properties are discussed in terms of chemical compositions that evolve as pressure and temperature are varied. The NH4OH hydrate of ammonia is known to exist as a separate molecular species at pressures above about 5 GPa, and an effort was made to include reaction between NH3 and H2O in the mixture EOS. The EOS are suitable for calculating structures of icy planets and exoplanets, and of impacts. mass-radius relations which bound the possible interpretations of composition and structure for extraterrestrial bodies of unknown composition, such as exoplanets.

Mulford, R.; Swift, D. C.; Hamel, S.

2014-05-01

130

The purine nucleotide cycle. A pathway for ammonia production in the rat kidney.  

PubMed Central

Particle-free extracts prepared from kidney cortex of rat catalyze the formation of ammonia via the purine nucleotide cycle. The cycle generates ammonia and fumarate from aspartate, using catalytic amounts of inosine monophosphate, adenylosuccinate, and adenosine monophosphate. The specific activities of the enzymes of the cycle are 1.27+/-0.27 nmol/mg protein per min (SE) for adenoylosuccinate synthetase, 1.38+/-0.16 for adenylosuccinase, and 44.0+/-3.3 for AMP deaminase. Compared with controls, extracts prepared from kidneys of rats fed ammonium chloride for 2 days show a 60% increase in adenylosuccinate synthetase and a threefold increase in adenylosuccinase activity, and a greater and more rapid synthesis of ammonia and adenine nucleotide from aspartate and inosine monophosphate. Extracts prepared from kidneys of rats fed a potassium-deficient diet show a twofold increase in adenylosuccinate synthetase and a threefold increase in adenylosuccinase activity. In such extracts the rate of synthesis of ammonia and adenine nucleotide from aspartate and inosine monophosphate is also increased. These results show that the reactions of the purine nucleotide cycle are present and can operate in extracts of kidney cortex. The operational capacity of the cycle is accelerated by ammonium chloride feeding and potassium depletion, conditions known to increase renal ammonia excretion. Extracts of kidney cortex convert inosine monophosphate to uric acid. This is prevented by addition of allopurinol of 1-pyrophosphoryl ribose 5-phosphate to the reaction mixture. PMID:821968

Bogusky, R T; Lowenstein, L M; Lowenstein, J M

1976-01-01

131

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

132

Synthesis of pyroglutamic acid derivatives via double Michael addition reactions of alkynones.   

E-print Network

I. Synthesis of pyroglutamic acid derivatives via double Michael reactions of alkynones Pyroglutamic acids and their derivatives are common structural units of widespread chemical significance and they have been heavily ...

Scansetti, Myriam

2009-01-01

133

Green synthesis of silver nanoparticles in xylan solution via Tollens reaction and their detection for Hg2+  

NASA Astrophysics Data System (ADS)

This work reported a facile and green method to prepare highly stable and uniformly distributed Ag nanoparticles (AgNPs), in which a biopolymer xylan was used as the stabilizing and reducing agent via the Tollens reaction under microwave irradiation. Different variables were evaluated to optimize the reaction conditions. Complete characterization was performed using UV-Vis, XRD, TEM, size distribution analysis and XPS. The results revealed that AgNPs were well dispersed with diameters of 20-35 nm due to the packing of xylan. The optimal conditions were as follows: microwave irradiation temperature was 60-70 °C, microwave power was 800 W, microwave time was 30 min, the ratio of xylan to AgNO3 was 50 mg: 0.13 mmol, and ammonia concentration was 2%. In addition, the AgNPs were collected via high-speed centrifugal separation, and the supernatant was tested by HPAEC, GPC, FT-IR, and NMR. By comparing the structure of xylan before and after the reaction, the reaction mechanism was discussed. It was noted that the xylan-AgNPs composites showed high selectivity and sensitivity for Hg2+ detection. The other 15 metal ions used had no obvious effect on the detection of Hg2+, and the limit of detection (LOD) was 4.6 nM, which is lower than the allowed maximum level of 30 nM for drinking water by WHO. In addition, the xylan-AgNPs composites can be applied for Hg2+ detection in real water samples. This study provides a novel way for the high-value utilization of a rich biomass resource, and a green method for the synthesis of AgNPs for the selective and sensitive detection of harmful heavy metals.This work reported a facile and green method to prepare highly stable and uniformly distributed Ag nanoparticles (AgNPs), in which a biopolymer xylan was used as the stabilizing and reducing agent via the Tollens reaction under microwave irradiation. Different variables were evaluated to optimize the reaction conditions. Complete characterization was performed using UV-Vis, XRD, TEM, size distribution analysis and XPS. The results revealed that AgNPs were well dispersed with diameters of 20-35 nm due to the packing of xylan. The optimal conditions were as follows: microwave irradiation temperature was 60-70 °C, microwave power was 800 W, microwave time was 30 min, the ratio of xylan to AgNO3 was 50 mg: 0.13 mmol, and ammonia concentration was 2%. In addition, the AgNPs were collected via high-speed centrifugal separation, and the supernatant was tested by HPAEC, GPC, FT-IR, and NMR. By comparing the structure of xylan before and after the reaction, the reaction mechanism was discussed. It was noted that the xylan-AgNPs composites showed high selectivity and sensitivity for Hg2+ detection. The other 15 metal ions used had no obvious effect on the detection of Hg2+, and the limit of detection (LOD) was 4.6 nM, which is lower than the allowed maximum level of 30 nM for drinking water by WHO. In addition, the xylan-AgNPs composites can be applied for Hg2+ detection in real water samples. This study provides a novel way for the high-value utilization of a rich biomass resource, and a green method for the synthesis of AgNPs for the selective and sensitive detection of harmful heavy metals. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05999a

Luo, Yuqiong; Shen, Suqin; Luo, Jiwen; Wang, Xiaoying; Sun, Runcang

2014-12-01

134

Synthesis of Non-racemic ?-Hydroxyphosphonates via Asymmetric Phospho-Aldol Reaction.  

PubMed

It has been more than 50 years since the first phospho-aldol reactions of dialkyl phosphites were reported. These efficient P-C bond-forming reactions have become the cornerstone of methods for the synthesis of ?-hydroxyphosphonates and, by numerous available substitution reactions, the synthesis of other ?- and ?-substituted phosphonates and phosphonic acids. Much of the interest in ?- and ?-substituted phosphonates and phosphonic acids has been stimulated by reports of their biological activity, which is often dependent upon their absolute and relative stereochemistry. In this chapter, we review diastereoselective and enantioselective additions of dialkyl phosphites to aldehydes and ketones, otherwise called the phospho-aldol, Pudovik or Abramov reactions. PMID:25467537

Spilling, Christopher D; Malla, Raj K

2015-01-01

135

Synthesis of tetrazole-fused glycosides by a tandem fragmentation-cyclization reaction.  

PubMed

The fragmentation of anomeric alkoxyl radicals (ARF) and the subsequent intramolecular cyclization promoted by hypervalent iodine reagents provide an excellent method for the synthesis of tetrazolo-sugars. This new reaction offers additional advantages for the synthesis of these compounds, including the ready availability of the starting materials, experimental simplicity, mild conditions, and good yields. PMID:22694091

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

2012-07-01

136

Asymmetric total synthesis of (-)-scabronine G via intramolecular double Michael reaction and Prins cyclization.  

PubMed

The enantioselective total synthesis of (-)-scabronine G is described. The key features of the present synthesis include the construction of a 5-6 ring system containing two quaternary carbon centers via a diastereoselective intramolecular double Michael reaction and the formation of a seven-membered ring using a Prins cyclization. PMID:21548644

Kanoh, Naoki; Sakanishi, Kohei; Iimori, Emiko; Nishimura, Ken'ichi; Iwabuchi, Yoshiharu

2011-06-01

137

Ammonia formation by metal-ligand cooperative hydrogenolysis of a nitrido ligand  

NASA Astrophysics Data System (ADS)

Bioinspired hydrogenation of N2 to ammonia at ambient conditions by stepwise nitrogen protonation/reduction with metal complexes in solution has experienced remarkable progress. In contrast, the highly desirable direct hydrogenation with H2 remains difficult. In analogy to the heterogeneously catalysed Haber-Bosch process, such a reaction is conceivable via metal-centred N2 splitting and unprecedented hydrogenolysis of the nitrido ligands to ammonia. We report the synthesis of a ruthenium(IV) nitrido complex. The high nucleophilicity of the nitrido ligand is demonstrated by unusual N-C coupling with ?-acidic CO. Furthermore, the terminal nitrido ligand undergoes facile hydrogenolysis with H2 at ambient conditions to produce ammonia in high yield. Kinetic and quantum chemical examinations of this reaction suggest cooperative behaviour of a phosphorus-nitrogen-phosphorus pincer ligand in rate-determining heterolytic hydrogen splitting.

Askevold, Bjorn; Nieto, Jorge Torres; Tussupbayev, Samat; Diefenbach, Martin; Herdtweck, Eberhardt; Holthausen, Max C.; Schneider, Sven

2011-07-01

138

Ammonia formation by metal-ligand cooperative hydrogenolysis of a nitrido ligand.  

PubMed

Bioinspired hydrogenation of N(2) to ammonia at ambient conditions by stepwise nitrogen protonation/reduction with metal complexes in solution has experienced remarkable progress. In contrast, the highly desirable direct hydrogenation with H(2) remains difficult. In analogy to the heterogeneously catalysed Haber-Bosch process, such a reaction is conceivable via metal-centred N(2) splitting and unprecedented hydrogenolysis of the nitrido ligands to ammonia. We report the synthesis of a ruthenium(IV) nitrido complex. The high nucleophilicity of the nitrido ligand is demonstrated by unusual N-C coupling with ?-acidic CO. Furthermore, the terminal nitrido ligand undergoes facile hydrogenolysis with H(2) at ambient conditions to produce ammonia in high yield. Kinetic and quantum chemical examinations of this reaction suggest cooperative behaviour of a phosphorus-nitrogen-phosphorus pincer ligand in rate-determining heterolytic hydrogen splitting. PMID:21697873

Askevold, Bjorn; Nieto, Jorge Torres; Tussupbayev, Samat; Diefenbach, Martin; Herdtweck, Eberhardt; Holthausen, Max C; Schneider, Sven

2011-07-01

139

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

E-print Network

occurs for a wide range of biogenic and anthropogenic aerosols. Aqueous reaction with ammonium ion coefficient a b s t r a c t Filter samples of secondary organic aerosols (SOA) generated from the ozone (O3 in color (limonene SOA). The aqueous phase reactions with dissolved ammonium (NH4 þ ) salts

Nizkorodov, Sergey

140

Green synthesis of silver nanoparticles in xylan solution via Tollens reaction and their detection for Hg(2+).  

PubMed

This work reported a facile and green method to prepare highly stable and uniformly distributed Ag nanoparticles (AgNPs), in which a biopolymer xylan was used as the stabilizing and reducing agent via the Tollens reaction under microwave irradiation. Different variables were evaluated to optimize the reaction conditions. Complete characterization was performed using UV-Vis, XRD, TEM, size distribution analysis and XPS. The results revealed that AgNPs were well dispersed with diameters of 20-35 nm due to the packing of xylan. The optimal conditions were as follows: microwave irradiation temperature was 60-70 °C, microwave power was 800 W, microwave time was 30 min, the ratio of xylan to AgNO3 was 50 mg: 0.13 mmol, and ammonia concentration was 2%. In addition, the AgNPs were collected via high-speed centrifugal separation, and the supernatant was tested by HPAEC, GPC, FT-IR, and NMR. By comparing the structure of xylan before and after the reaction, the reaction mechanism was discussed. It was noted that the xylan-AgNPs composites showed high selectivity and sensitivity for Hg(2+) detection. The other 15 metal ions used had no obvious effect on the detection of Hg(2+), and the limit of detection (LOD) was 4.6 nM, which is lower than the allowed maximum level of 30 nM for drinking water by WHO. In addition, the xylan-AgNPs composites can be applied for Hg(2+) detection in real water samples. This study provides a novel way for the high-value utilization of a rich biomass resource, and a green method for the synthesis of AgNPs for the selective and sensitive detection of harmful heavy metals. PMID:25429650

Luo, Yuqiong; Shen, Suqin; Luo, Jiwen; Wang, Xiaoying; Sun, Runcang

2015-01-14

141

Microwave-assisted organic synthesis and transformations using benign reaction media.  

PubMed

A nonclassical heating technique using microwaves, termed "Bunsen burner of the 21st century", is rapidly becoming popular and is dramatically reducing reaction times. The significant outcomes of microwave (MW)-assisted green chemistry endeavors, which have resulted in the development of synthetic protocols for drugs and fine chemicals synthesis that are relatively more sustainable, are summarized. The use of emerging microwave-assisted chemistry techniques in conjunction with greener reaction media is dramatically reducing chemical waste and reaction times in several organic syntheses and chemical transformations. A brief historic account of our own experiences in developing MW-assisted organic transformations, which involve various benign alternatives, such as solid-supported reagents, and greener reaction media, namely, aqueous, ionic liquid, and solvent-free, for the synthesis of various heterocycles, coupling reactions, oxidation-reduction reactions, and some name reactions are described. Synthesis of Heterocycles. The synthetic chemistry community has been under increased pressure to produce, in an environmentally benign fashion, the myriad of heterocyclic systems required by society in a short span of time, and one of the best options to accelerate these synthetic processes is to use MW technology. The efficient use of the MW heating approach for the synthesis of various heterocyclic compounds in aqueous and solvent-free medium is discussed. Organic Named Reactions. The application of MW chemistry for various named reaction such as the Prins reaction, the Suzuki reaction, the Heck reaction, the Aza-Michael reaction, Trost's gamma-addition, and the Cannizzaro reaction are summarized. Synthesis and Application of Ionic Liquids. Ionic liquids (ILs), being polar and ionic, in character couple with MW irradiation very efficiently and are, therefore, ideal MW-absorbing candidates for expediting chemical reactions. MW-assisted solvent-free synthesis and application of ILs are discussed. Oxidation-Reduction Reactions. MW protocols using mineral oxides such as alumina, silica, and clay to immobilize reagents on such solid supports have been extensively explored under "dry" media conditions. Various solvent-free examples of oxidation reactions are discussed that involve mixing of neat substrates with clay-supported iron(III) nitrate (clayfen) or iodobenzene diacetate (IBD) as an oxidant; some interesting MW reduction protocols using borohydrides are also discussed. Protection-Deprotection Reactions. The protection and deprotection of alcohols and amines are common events in multistep organic syntheses. Various protection and deprotection protocols under MW irradiation are discussed, including tetrahydropyranylation and (benzyloxycarbonyl) (Cbz)-protection, which are the most frequently employed methods. PMID:18419142

Polshettiwar, Vivek; Varma, Rajender S

2008-05-01

142

Synthesis of Isoquinuclidines from Highly Substituted Dihydropyridines via the Diels-Alder Reaction  

PubMed Central

A stereo- and regioselective Diels-Alder reaction for the synthesis of highly substituted isoquinuclidines from dihydropyridines and electron deficient alkenes has been developed. While reactions with activated dienophiles proceed readily under thermal conditions, the use of Lewis acid additives is necessary to facilitate cycloadditions for less reactive alkenes. This procedure affords the target compounds in high yields and diastereoselectivities. PMID:23320852

Martin, Rhia M.; Bergman, Robert G.; Ellman, Jonathan A.

2013-01-01

143

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

144

Intermixing criteria for reaction synthesis of Ni/Al multilayered microfoils  

E-print Network

that the dependence of the ignition temperature for Ni/Al diffusion couples on the heating rate was a result from the reactant had a much smaller effect on reaction propagation than did the conductive heat lossesIntermixing criteria for reaction synthesis of Ni/Al multilayered microfoils Hee Y. Kim a , Dong S

Hong, Soon Hyung

145

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

146

Bifunctional Iminophosphorane Organocatalysts for Enantioselective Synthesis: Application to the Ketimine Nitro-Mannich Reaction  

PubMed Central

The design, synthesis, and development of a new class of modular, strongly basic, and tunable bifunctional Brønsted base/H-bond-donor organocatalysts are reported. These catalysts incorporate a triaryliminophosphorane as the Brønsted basic moiety and are readily synthesized via a last step Staudinger reaction of a chiral organoazide and a triarylphosphine. Their application to the first general enantioselective organocatalytic nitro-Mannich reaction of nitromethane to unactivated ketone-derived imines allows the enantioselective construction of ?-nitroamines possessing a fully substituted carbon atom. The reaction is amenable to multigram scale-up, and the products are useful for the synthesis of enantiopure 1,2-diamine and ?-amino acid derivatives. PMID:24107070

2013-01-01

147

Diffusion of ammonia gas in PDMS characterized by ATR spectroscopy  

NASA Astrophysics Data System (ADS)

The kinetic parameters of a chemo-optical transducer layer sensitive to gaseous ammonia are characterized by means of attenuation total reflection method. The tested layer consists of cross-linked polydimethylsiloxane matrix sensitized by quinoline-based organometallic dye showing the selective chemical reaction with ammonia. Upper and lower limits of the ammonia diffusion coefficient and the ammonia-dye reaction constant are derived from the obtained experimental data and compared with other data available in literature and obtained from computer simulations.

Levinský, Petr; Kalvoda, Ladislav; Aubrecht, Jan; Fojtíková, Jaroslava

2015-01-01

148

Samarium Diiodide-Mediated Reactions in Total Synthesis  

PubMed Central

Introduced by Henri Kagan more than three decades ago, samarium diiodide (SmI2) has found increasing applications in chemical synthesis. This single-electron reducing agent has been particularly useful in C–C bond formations, including those found in total synthesis endeavors. This Review highlights selected applications of SmI2 in total synthesis, with special emphasis on novel transformations and mechanistic considerations. The examples discussed are both illustrative of the power of this reagent in complex molecule construction and inspirational for the design of synthetic strategies toward such targets, both natural and designed. PMID:19714695

Nicolaou, K. C.; Ellery, Shelby P.; Chen, Jason S.

2009-01-01

149

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

150

A theoretical study of the condensation reactions of methyl cation with ammonia, water, hydrogen fluoride and hydrogen sulphide  

NASA Astrophysics Data System (ADS)

Ab initio molecular orbital calculations have been used to study the condensation reactions of CH 3- with NH 3, H 2O, HF and H 2S. Geometry optimization has been carried out at the Hartree—Fock (HF) level with the split-valence plus d-polarization 6-31G* basis set and improved relative energies obtained from calculations which employ the split-valence plus dp-polarization 6-31G** basis set with electron correlation incorporated via Moller—Plesset perturbation theory terminated at third order (MP3). Zero-point vibrational energies have also been determined and taken into account in deriving relative energies. The structures of the intermediates CH 3XH - (X = NH 2, OH, F and SH) have been obtained and dissociation of these intermediates into CH 2X + + H 2 on the one hand, and CH 3- + HX on the other, has been examined. It is found that for those species for which the methyl condensation reaction is observed to have an appreciable rate (X = NH 2 and SH), the transition structure for hydrogen elimination from CH 3XH - lies significantly lower in energy than the reactants CH 3- + HX (by 75 and 70 kJ mol -1 respectively). On the other hand, for those species for which the methyl condensation reaction is not observed (X = OH and F), the transition structure for H 2 elimination lies higher in energy than CH 3- + HX (by 6 and 87 kJ mol -1 respectively).

Nobes, Ross H.; Radom, Leo

1983-01-01

151

Enabling electrochemical reduction of nitrogen to ammonia at ambient conditions through rational catalyst design.  

PubMed

Commercial design of a sustainable route for on-site production of ammonia represents a potential economic and environmental breakthrough. In an analogous process to the naturally occurring enzymatic mechanism, synthesis of ammonia could be achieved in an electrochemical cell, in which electricity would be used to reduce atmospheric nitrogen and water into ammonia at ambient conditions. To date, such a process has not been realized due to slow kinetics and low faradaic efficiencies. Although progress has been made in this regard, at present there exists no device that can produce ammonia efficiently from air and water at room temperature and ambient pressure. In this work, a scheme is presented in which electronic structure calculations are used to screen for catalysts that are stable, active and selective towards N2 electro-reduction to ammonia, while at the same time suppressing the competing H2 evolution reaction. The scheme is applied to transition metal nitride catalysts. The most promising candidates are the (100) facets of the rocksalt structures of VN and ZrN, which show promise of producing ammonia in high yield at low onset potentials. PMID:25446373

Abghoui, Younes; Garden, Anna L; Hlynsson, Valtýr Freyr; Björgvinsdóttir, Snædís; Ólafsdóttir, Hrefna; Skúlason, Egill

2015-02-01

152

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

PubMed Central

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

2011-01-01

153

Preparation of Carbon Nanotubes (CNTs)Cordierite Monoliths by Catalytic Chemical Vapor Deposition as Catalyst Supports for Ammonia Synthesis  

Microsoft Academic Search

Tunable carbon nanotubles (CNTs)-coated monoliths as catalyst supports were prepared by catalytic chemical vapor deposition\\u000a (CCVD) over deposited cobalt on cordierite. The influence of the preparation conditions such as the cobalt nitrate loading\\u000a on the cordierite monoliths, the flow rate of reaction gases, reaction time and temperature on CNTs yield, thermal properties\\u000a and structural features of the resulting materials were

Binbin Gong; Rong Wang; Bingyu Lin; Feng Xie; Xiujin Yu; Kemei Wei

2008-01-01

154

Ammonia toxicity under hyponatremic conditions in astrocytes: De novo synthesis of amino acids for the osmoregulatory response  

Microsoft Academic Search

This study investigates how the metabolic activity and de novo synthesis of amino acids from glucose correlate with changes in intracellular organic osmolytes involved in astrocytic volume regulation during hyperammonemia and hyponatremia. Multinuclear (1H-, 31P-, 13C-) NMR spectra were recorded to quantify water-soluble metabolites, the cellular energy state, as well as the incorporation of [1-13C]glucose into amino acids of primary

Claudia Zwingmann; Dieter Leibfritz

2005-01-01

155

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

156

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

157

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

PubMed

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

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

2013-08-01

158

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

E-print Network

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... , reflux 48 h 675 43% 12% 24% 1. PPTS, EtOH 2. (COCl) 2 , DMSO, NEt 3 3. [(MeO) 2 P(O)CH 2 ]Li, -78 ?C 4. TPAP, NMO, sieves 5. Ba(OH) 2 ?8H 2 O, 55% overall Scheme 2 11 12 The cascade reaction substrate 4 was prepared using standard methodology (Scheme...

Golden, Jennifer E.; Aubé , Jeffrey

2002-01-01

159

Fischer-Tropsch synthesis in supercritical reaction media  

SciTech Connect

Our goals for this quarter were to complete construction of the reactor and analytical units for carrying out Fischer-Tropsch (F-T) synthesis in liquid (n-hexadecane) and in supercritical n-hexane phases. Progress during this quarter was slower than expected.

Subramaniam, B.; Bochniak, D.; Snavely, K.

1993-01-01

160

Lewis Acid and/or Lewis Base catalyzed [3+2] cycloaddition reaction: Synthesis of pyrazoles and pyrazolines  

E-print Network

1 Lewis Acid and/or Lewis Base catalyzed [3+2] cycloaddition reaction: Synthesis of pyrazoles is reported. All the reactions were carried out under no strong bases/acids, solvent free conditions+2] cycloaddition reaction strategy to form five membered ring systems through the reaction partners of 1,3-dipoles

Paris-Sud XI, Université de

161

Organocatalytic asymmetric cascade reactions of 7-vinylindoles: diastereo- and enantioselective synthesis of C7-functionalized indoles.  

PubMed

The first catalytic asymmetric cascade reaction of 7-vinylindoles has been established by the rational design of such substrates. Cascade reactions with isatin-derived 3-indolylmethanols in the presence of a chiral phosphoric acid derivative allow the diastereo- and enantioselective synthesis of C7-functionalized indoles as well as the construction of cyclopenta[b]indole and spirooxindole frameworks (all >95:5 d.r., 94->99?% ee). This approach not only addresses the great challenge of the catalytic asymmetric synthesis of C7-functionalized indoles, but also provides an efficient method for constructing biologically important cyclopenta[b]indole and spirooxindole scaffolds with excellent optical purity. Investigation of the reaction pathway and activation mode has suggested that this cascade reaction proceeds through a vinylogous Michael addition/Friedel-Crafts process, in which dual H-bonding activation of the two reactants plays a crucial role. PMID:25521722

Shi, Feng; Zhang, Hong-Hao; Sun, Xiao-Xue; Liang, Jing; Fan, Tao; Tu, Shu-Jiang

2015-02-16

162

Design, synthesis, and carbon-heteroatom coupling reactions of organometallic nickel(IV) complexes.  

PubMed

Homogeneous nickel catalysis is used for the synthesis of pharmaceuticals, natural products, and polymers. These reactions generally proceed via nickel intermediates in the Ni(0), Ni(I), Ni(II), and/or Ni(III) oxidation states. In contrast, Ni(IV) intermediates are rarely accessible. We report herein the design, synthesis, and characterization of a series of organometallic Ni(IV) complexes, accessed by the reaction of Ni(II) precursors with the widely used oxidant S-(trifluoromethyl)dibenzothiophenium triflate. These Ni(IV) complexes undergo highly selective carbon(sp(3))-oxygen, carbon(sp(3))-nitrogen, and carbon(sp(3))-sulfur coupling reactions with exogenous nucleophiles. The observed reactivity has the potential for direct applications in the development of nickel-catalyzed carbon-heteroatom coupling reactions. PMID:25766226

Camasso, Nicole M; Sanford, Melanie S

2015-03-13

163

Quinones as dienophiles in the Diels-Alder reaction: history and applications in total synthesis.  

PubMed

In the canon of reactions available to the organic chemist engaged in total synthesis, the Diels-Alder reaction is among the most powerful and well understood. Its ability to rapidly generate molecular complexity through the simultaneous formation of two carbon-carbon bonds is almost unrivalled, and this is reflected in the great number of reported applications of this reaction. Historically, the use of quinones as dienophiles is highly significant, being the very first example investigated by Diels and Alder. Herein, we review the application of the Diels-Alder reaction of quinones in the total synthesis of natural products. The highlighted examples span some 60?years from the landmark syntheses of morphine (1952) and reserpine (1956) by Gates and Woodward, respectively, through to the present day examples, such as the tetracyclines. PMID:24446164

Nawrat, Christopher C; Moody, Christopher J

2014-02-17

164

Synthesis of Single-Crystalline Niobate Nanorods via Ion-Exchange Based on Molten-Salt Reaction  

E-print Network

Synthesis of Single-Crystalline Niobate Nanorods via Ion-Exchange Based on Molten-Salt Reaction by employing hydrothermal reaction2 or templates,3 molten-salt syn- thesis,4 and composite- exchange approach for the synthesis of single-crystal sodium and calcium niobates nanorods based on molten-salt

Wang, Zhong L.

165

Synthesis of Programmable Reaction-Diffusion Fronts Using DNA Catalyzers  

NASA Astrophysics Data System (ADS)

We introduce a DNA-based reaction-diffusion (RD) system in which reaction and diffusion terms can be precisely and independently controlled. The effective diffusion coefficient of an individual reaction component, as we demonstrate on a traveling wave, can be reduced up to 2.7-fold using a self-assembled hydrodynamic drag. The intrinsic programmability of this RD system allows us to engineer, for the first time, orthogonal autocatalysts that counterpropagate with minimal interaction. Our results are in excellent quantitative agreement with predictions of the Fisher-Kolmogorov-Petrovskii-Piscunov model. These advances open the way for the rational engineering of pattern formation in pure chemical RD systems.

Zadorin, Anton S.; Rondelez, Yannick; Galas, Jean-Christophe; Estevez-Torres, André

2015-02-01

166

Synthesis of biaryls via decarboxylative Pd-catalyzed cross-coupling reaction.  

PubMed

[reaction: see text] A simple and efficient route to biaryls via Pd-catalyzed decarboxylative cross-couplings of arene carboxylic acids and aryl iodides is reported. The PdCl2/AsPh3 catalytic system in the presence of Ag2CO3 in DMSO was found to be particularly efficient to perform this transformation. This reaction can be extended to the synthesis of various biaryls, including sterically hindered biaryls, with yields ranging from 58% to 90%. PMID:17411063

Becht, Jean-Michel; Catala, Cédric; Drian, Claude Le; Wagner, Alain

2007-04-26

167

Iodine catalyzed one-pot five-component reactions for direct synthesis of densely functionalized piperidines  

Microsoft Academic Search

A simple and convenient one-pot multicomponent reaction (MCR) has been developed for the synthesis of highly functionalized piperidines catalyzed by molecular iodine. This strategy demonstrated five-component reactions of 1,3-dicarbonyl compounds, amines and aromatic aldehydes in methanol using 10 mol % of iodine at room temperature. This methodology provides an alternative approach for easy access of highly and fully substituted piperidines in moderate

Abu T. Khan; Kranthi K. R. Bannuru

2010-01-01

168

Efficient synthesis and reactions of 1,2-dipyrrolylethynes  

PubMed Central

Various dipyrroles possess important motifs for construction of pyrrole-containing pigments. A series of 1,2-dipyrrolylethynes (4a–d) has been efficiently synthesized using an improved one-pot double Sonagashira coupling from trimethylsilylethyne and various 2-iodopyrroles. The resulting 1,2-dipyrrolylethynes were further transformed into novel indolyl-, ethenyl- and carboranyl-dipyrroles (5–7) using the Larock indole synthesis, stereoselective catalytic hydrogenation, or B10H14. Indolyl-dipyrroles were found to selectively bind fluoride ions using one pyrrolic and the indolyl NHs, whereas the carboranyl- and ethenyl-dipyrroles are potentially valuable precursors for the synthesis of porphyrin isomers and expanded pigments. PMID:21822371

Tanui, Hillary K.; Hao, Erhong; Ihachi, Moses I.; Fronczek, Frank R.; Smith, Kevin M.; Vicente, M. Graça H.

2011-01-01

169

Synthesis of 4- and 6-azaindoles via the Fischer reaction.  

PubMed

Contrary to the common idea that Fischer indole cyclization often cannot be effectively applied to the synthesis of the corresponding azaindoles, we show that this approach can be actually very efficient for the formation of 4- and 6-azaindoles bearing an electron-donating group on the starting pyridylhydrazines. Two 4-azaindole natural product analogues were synthesized in a few steps and very good overall yields. PMID:19839585

Jeanty, Matthieu; Blu, Jérôme; Suzenet, Franck; Guillaumet, Gérald

2009-11-19

170

Treatment of ammonia contaminated water by ozone and hydrogen peroxide  

SciTech Connect

The present research concerns kinetics of oxidation of ammonia by ozone and ozone-hydrogen peroxide mixtures in alkaline solutions. Experiments were carried out at 15 to 35{degrees}C in solutions with pH values varying from 8 to 10 utilizing a stopped-flow spectrophotometer system. Fractions of free ammonia present in acidic and neutral solutions are negligible, and the reaction is very slow. This confirms that only free ammonia can react with ozone in the aqueous phase. The reaction proceeds at moderate rates in the alkaline solutions requiring four moles of ozone to react with each mole of ammonia. The free ammonia is oxidized and converted completely to nitrate in the solutions. The overall reaction between ammonia and ozone is second order with first order in each reactant. The reaction rate constant increases with temperature and pH value of the solution. The average activation energy is 59 Kcal/gmol for all systems investigated at different pH values. The results of the kinetic experiments suggest that the reaction is predominated by the direct oxidation between ammonia and ozone molecules, and that the hydroxyl radical reactions play insignificant roles in the ozonation process. The oxidation rate of ammonia is enhanced considerably in the presence of hydrogen peroxide and ozone mixtures. The formation of hydroxyl radical from interactions between ozone and hydrogen peroxide and the subsequent free radical reactions of ammonia seem important in controlling the destruction rate of free ammonia, as suggested by the results of this study.

Yuan, F.; Hill, D.O.; Kuo, C.H. [Mississippi State Univ., MS (United States)

1995-12-31

171

Glutamine versus Ammonia Utilization in the NAD Synthetase Family  

PubMed Central

NAD is a ubiquitous and essential metabolic redox cofactor which also functions as a substrate in certain regulatory pathways. The last step of NAD synthesis is the ATP-dependent amidation of deamido-NAD by NAD synthetase (NADS). Members of the NADS family are present in nearly all species across the three kingdoms of Life. In eukaryotic NADS, the core synthetase domain is fused with a nitrilase-like glutaminase domain supplying ammonia for the reaction. This two-domain NADS arrangement enabling the utilization of glutamine as nitrogen donor is also present in various bacterial lineages. However, many other bacterial members of NADS family do not contain a glutaminase domain, and they can utilize only ammonia (but not glutamine) in vitro. A single-domain NADS is also characteristic for nearly all Archaea, and its dependence on ammonia was demonstrated here for the representative enzyme from Methanocaldococcus jannaschi. However, a question about the actual in vivo nitrogen donor for single-domain members of the NADS family remained open: Is it glutamine hydrolyzed by a committed (but yet unknown) glutaminase subunit, as in most ATP-dependent amidotransferases, or free ammonia as in glutamine synthetase? Here we addressed this dilemma by combining evolutionary analysis of the NADS family with experimental characterization of two representative bacterial systems: a two-subunit NADS from Thermus thermophilus and a single-domain NADS from Salmonella typhimurium providing evidence that ammonia (and not glutamine) is the physiological substrate of a typical single-domain NADS. The latter represents the most likely ancestral form of NADS. The ability to utilize glutamine appears to have evolved via recruitment of a glutaminase subunit followed by domain fusion in an early branch of Bacteria. Further evolution of the NADS family included lineage-specific loss of one of the two alternative forms and horizontal gene transfer events. Lastly, we identified NADS structural elements associated with glutamine-utilizing capabilities. PMID:22720044

Shatalin, Konstantin; Gelfand, Mikhail S.; Osterman, Andrei L.; Sorci, Leonardo

2012-01-01

172

Glutamine versus ammonia utilization in the NAD synthetase family.  

PubMed

NAD is a ubiquitous and essential metabolic redox cofactor which also functions as a substrate in certain regulatory pathways. The last step of NAD synthesis is the ATP-dependent amidation of deamido-NAD by NAD synthetase (NADS). Members of the NADS family are present in nearly all species across the three kingdoms of Life. In eukaryotic NADS, the core synthetase domain is fused with a nitrilase-like glutaminase domain supplying ammonia for the reaction. This two-domain NADS arrangement enabling the utilization of glutamine as nitrogen donor is also present in various bacterial lineages. However, many other bacterial members of NADS family do not contain a glutaminase domain, and they can utilize only ammonia (but not glutamine) in vitro. A single-domain NADS is also characteristic for nearly all Archaea, and its dependence on ammonia was demonstrated here for the representative enzyme from Methanocaldococcus jannaschi. However, a question about the actual in vivo nitrogen donor for single-domain members of the NADS family remained open: Is it glutamine hydrolyzed by a committed (but yet unknown) glutaminase subunit, as in most ATP-dependent amidotransferases, or free ammonia as in glutamine synthetase? Here we addressed this dilemma by combining evolutionary analysis of the NADS family with experimental characterization of two representative bacterial systems: a two-subunit NADS from Thermus thermophilus and a single-domain NADS from Salmonella typhimurium providing evidence that ammonia (and not glutamine) is the physiological substrate of a typical single-domain NADS. The latter represents the most likely ancestral form of NADS. The ability to utilize glutamine appears to have evolved via recruitment of a glutaminase subunit followed by domain fusion in an early branch of Bacteria. Further evolution of the NADS family included lineage-specific loss of one of the two alternative forms and horizontal gene transfer events. Lastly, we identified NADS structural elements associated with glutamine-utilizing capabilities. PMID:22720044

De Ingeniis, Jessica; Kazanov, Marat D; Shatalin, Konstantin; Gelfand, Mikhail S; Osterman, Andrei L; Sorci, Leonardo

2012-01-01

173

Synthesis of heterocyclic [3.3.3]propellanes via a sequential four-component reaction.  

PubMed

A highly chemoselective heteroannulation protocol for the synthesis of unreported polysubstituted heterocyclic [3.3.3]propellanes has been developed by sequential four-component reaction of ninhydrin, malononitrile, primary amines, and dialkyl acetylenedicarboxylates under mild conditions in water. To the best of our knowledge, there are no previous reports for the synthesis of these classes of heterocyclic [3.3.3]propellanes. The merit of this sequential Knoevenagel condensation/enamine formation/Michael addition/cyclization sequence is highlighted by its high atom-economy, excellent yields, the use of water as reaction media, and the efficiency of production without the use of any activator or metal promoters. This synthesis serves as a nice addition to group-assistant-purification (GAP) chemistry in which purification via chromatography and recrystallization can be avoided, and the pure products were obtained simply by washing the crude products with 95% ethanol. PMID:22480382

Alizadeh, Abdolali; Rezvanian, Atieh; Zhu, Long-Guan

2012-05-01

174

Parallel DNA polymerase chain reaction: Synthesis of two different PCR products from a DNA template  

PubMed Central

Conventionally, in a polymerase chain reaction (PCR), oligonucleotide primers bind to the template DNA in an antiparallel complementary way and the template DNA is amplified as it is. Here we describe an approach in which the first primer binds in a parallel complementary orientation to the single-stranded DNA, leading to synthesis in a parallel direction. Further reactions happened in a conventional way leading to the synthesis of PCR product having polarity opposite to the template used. This is the first study showing that synthesis of DNA can happen also in a parallel direction. We report that from a single-stranded DNA template, two different but related PCR products can be synthesized. PMID:25653847

Bhardwaj, Vikash; Sharma, Kulbhushan

2014-01-01

175

Efficient synthesis of C-N-coupled heterobiaryls by sequential N-h functionalization reactions.  

PubMed

C-N-coupled heterobiaryls were synthesized by sequential N-H functionalization reactions: stereoselective rhodium-catalyzed N-H insertion, followed by regioselective palladium-catalyzed C-H amination. Because of the good substrate scope and excellent selectivity, the developed method presents a novel approach for the synthesis of heterobiaryls, which are potent antibiotics. PMID:25830922

Lee, Dong Jin; Yoo, Eun Jeong

2015-04-17

176

A novel rhodium-catalyzed domino-hydroformylation-reaction for the synthesis of sulphonamides.  

PubMed

An efficient and highly selective method for the synthesis of sulphonamides by a domino hydroformylation-reductive sulphonamidation reaction has been developed. Various olefins and sulphonamides are converted into the desired products in good yields and with excellent selectivities in the presence of a rhodium/Naphos catalyst. PMID:25712242

Dong, Kaiwu; Fang, Xianjie; Jackstell, Ralf; Beller, Matthias

2015-03-10

177

Synthesis and Reactions of Tungsten Alkylidene Complexes That Contain the 2,6-Dichlorophenylimido Ligand  

E-print Network

Synthesis and Reactions of Tungsten Alkylidene Complexes That Contain the 2,6-Dichlorophenylimido Institute of Technology, Cambridge, Massachusetts 02139 ReceiVed October 30, 2006 Tungsten alkylidene alkylidene bisalkoxide complexes of molybdenum or tungsten of the type M(NR)(CHR)(OR)2 are now established

Müller, Peter

178

Reaction engineering: The supercritical water hydrothermal synthesis of nano-particles  

Microsoft Academic Search

Supercritical water hydrothermal synthesis (scWHS) is a relatively simple and environmentally friendly process for the production of potentially valuable metal oxide nanoparticles. However, it has never found industrial application to date due to poor process reliability, reproducibility and control. This paper presents the conclusions of collaborative work between chemical engineers and chemists that attempts to optimise the reaction engineering of

Edward Lester; Paul Blood; Joanne Denyer; Donald Giddings; Barry Azzopardi; Martyn Poliakoff

2006-01-01

179

Stereoselective synthesis of precursors of the macrolide antibiotics via reactions of sulfur ylides with chiral aldehydes  

Microsoft Academic Search

Reactions of stabilized sulfur ylides with chiral aldehydes provided epoxides with high stereoselectivity. The opening of the resulting epoxides with lithium dimethyl cuprate gave 2-methyl-3-hydroxy amides which represent potentially useful building blocks for the synthesis of macrolide natural products. These amides were transformed into chiral aldehydes, with a methyl group in the ?-position, and were reacted, in a iterative process,

F. Jorge López-Herrera; Francisco Sarabia-García; Gracia María Pedraza-Cebrián; María Soledad Pino-González

1999-01-01

180

Reaction under ball-milling: solvent-, ligand-, and metal-free synthesis of unsymmetrical diaryl chalcogenides.  

PubMed

A convenient, efficient, and general procedure for the synthesis of diaryl chalcogenides including sulfides, selenides and tellurides has been developed by the reaction of diazonium tetrafluoroborates and diaryl dichalcogenides on the surface of alumina under ball-milling without any solvent or metal. A wide range of functionalized diaryl chalcogenides are obtained in high purity by this procedure. PMID:24116379

Mukherjee, Nirmalya; Chatterjee, Tanmay; Ranu, Brindaban C

2013-11-01

181

Multistep One-Pot Reactions Combining Biocatalysts and Chemical Catalysts for Asymmetric Synthesis  

E-print Network

Multistep One-Pot Reactions Combining Biocatalysts and Chemical Catalysts for Asymmetric Synthesis Carl A. Denard, John F. Hartwig,*, and Huimin Zhao*,,§ Department of Chemical and Biomolecular of chemical catalysts. Over the last 20 years, research in this area has provided us with proof of concept

Zhao, Huimin

182

The Photochemical Synthesis, Kinetics, and Reactions of Nitrosomethane Dimer: A Physical-Organic Experiment.  

ERIC Educational Resources Information Center

Provides background information procedures, and results for the photochemical synthesis and reactions of nitrosomethane dimer. The experiments described have shown a high degree of reliability with student use and are suggested to illustrate some problems of physical and organic photochemistry. (Author/JN)

Kozubek, H.; And Others

1982-01-01

183

One-pot synthesis of core-shell Cu@SiO2 nanospheres and their catalysis for hydrolytic dehydrogenation of ammonia borane and hydrazine borane  

PubMed Central

Ultrafine copper nanoparticles (Cu NPs) within porous silica nanospheres (Cu@SiO2) were prepared via a simple one-pot synthetic route in a reverse micelle system and characterized by SEM, TEM, EDX, XRD, N2 adsorption-desorption, CO-TPD, XPS, and ICP methods. The characterized results show that ultrafine Cu NPs with diameter of around 2?nm are effectively embedded in the center of well-proportioned spherical SiO2 NPs of about 25?nm in diameter. Compared to commercial SiO2 supported Cu NPs, SiO2 nanospheres supported Cu NPs, and free Cu NPs, the synthesized core-shell nanospheres Cu@SiO2 exhibit a superior catalytic activity for the hydrolytic dehydrogenation of ammonia borane (AB, NH3BH3) and hydrazine borane (HB, N2H4BH3) under ambient atmosphere at room temperature. The turnover frequencies (TOF) for the hydrolysis of AB and HB in the presence of Cu@SiO2 nanospheres were measured to be 3.24 and 7.58?mol H2 (mol Cu min)?1, respectively, relatively high values for Cu nanocatalysts in the same reaction. In addition, the recycle tests show that the Cu@SiO2 nanospheres are still highly active in the hydrolysis of AB and HB, preserving 90 and 85% of their initial catalytic activity even after ten recycles, respectively. PMID:25534772

Yao, Qilu; Lu, Zhang-Hui; Zhang, Zhujun; Chen, Xiangshu; Lan, Yaqian

2014-01-01

184

One-pot synthesis of core-shell Cu@SiO2 nanospheres and their catalysis for hydrolytic dehydrogenation of ammonia borane and hydrazine borane  

NASA Astrophysics Data System (ADS)

Ultrafine copper nanoparticles (Cu NPs) within porous silica nanospheres (Cu@SiO2) were prepared via a simple one-pot synthetic route in a reverse micelle system and characterized by SEM, TEM, EDX, XRD, N2 adsorption-desorption, CO-TPD, XPS, and ICP methods. The characterized results show that ultrafine Cu NPs with diameter of around 2 nm are effectively embedded in the center of well-proportioned spherical SiO2 NPs of about 25 nm in diameter. Compared to commercial SiO2 supported Cu NPs, SiO2 nanospheres supported Cu NPs, and free Cu NPs, the synthesized core-shell nanospheres Cu@SiO2 exhibit a superior catalytic activity for the hydrolytic dehydrogenation of ammonia borane (AB, NH3BH3) and hydrazine borane (HB, N2H4BH3) under ambient atmosphere at room temperature. The turnover frequencies (TOF) for the hydrolysis of AB and HB in the presence of Cu@SiO2 nanospheres were measured to be 3.24 and 7.58 mol H2 (mol Cu min)-1, respectively, relatively high values for Cu nanocatalysts in the same reaction. In addition, the recycle tests show that the Cu@SiO2 nanospheres are still highly active in the hydrolysis of AB and HB, preserving 90 and 85% of their initial catalytic activity even after ten recycles, respectively.

Yao, Qilu; Lu, Zhang-Hui; Zhang, Zhujun; Chen, Xiangshu; Lan, Yaqian

2014-12-01

185

One-pot synthesis of core-shell Cu@SiO2 nanospheres and their catalysis for hydrolytic dehydrogenation of ammonia borane and hydrazine borane.  

PubMed

Ultrafine copper nanoparticles (Cu NPs) within porous silica nanospheres (Cu@SiO2) were prepared via a simple one-pot synthetic route in a reverse micelle system and characterized by SEM, TEM, EDX, XRD, N2 adsorption-desorption, CO-TPD, XPS, and ICP methods. The characterized results show that ultrafine Cu NPs with diameter of around 2 nm are effectively embedded in the center of well-proportioned spherical SiO2 NPs of about 25 nm in diameter. Compared to commercial SiO2 supported Cu NPs, SiO2 nanospheres supported Cu NPs, and free Cu NPs, the synthesized core-shell nanospheres Cu@SiO2 exhibit a superior catalytic activity for the hydrolytic dehydrogenation of ammonia borane (AB, NH3BH3) and hydrazine borane (HB, N2H4BH3) under ambient atmosphere at room temperature. The turnover frequencies (TOF) for the hydrolysis of AB and HB in the presence of Cu@SiO2 nanospheres were measured to be 3.24 and 7.58 mol H2 (mol Cu min)(-1), respectively, relatively high values for Cu nanocatalysts in the same reaction. In addition, the recycle tests show that the Cu@SiO2 nanospheres are still highly active in the hydrolysis of AB and HB, preserving 90 and 85% of their initial catalytic activity even after ten recycles, respectively. PMID:25534772

Yao, Qilu; Lu, Zhang-Hui; Zhang, Zhujun; Chen, Xiangshu; Lan, Yaqian

2014-01-01

186

Ammonia synthons for the multicomponent assembly of complex gamma-lactams.  

PubMed

The synthesis of ?-lactams that are unsubstituted at the 1-position (nitrogen) as well as their subsequent N-functionalization is reported. A recently discovered four-component reaction (4CR) is employed with either an ammonia precursor or a protected form of ammonia that can be deprotected in a subsequent synthetic step. These methods represent the first multicomponent assembly of complex lactam structures that are unsubstituted at nitrogen. In addition, two methods for the introduction of nitrogen substituents that are not possible through the original 4CR are reported. X-ray crystallographic analysis of representative structures reveals conformational changes in the core structure that will enable future deployment of this chemistry in the design and synthesis of diverse collections of lactams suitable for the discovery of new biological probes. PMID:21289284

Tan, Darlene Q; Martin, Kevin S; Fettinger, James C; Shaw, Jared T

2011-04-26

187

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

188

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

189

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

190

Synthesis of amide-type fluoroalkene dipeptide isosteres by an intramolecular redox reaction.  

PubMed

We previously achieved NHC-mediated preparation of ester-type fluoroalkene dipeptide isosteres (ES-FADIs, 4) by an intramolecular redox reaction. In the present study, a cyanide ion-mediated reaction was successfully applied to the conversions of gamma,gamma-difluoro-alpha,beta-enoylsilane 1 or 2 to amide-type fluoroalkene isosteres (AM-FADIs, 5 or 6). The use of catalytic cyanide ion allowed synthesis of chiral auxiliary incorporated FADI 15b which was then subjected to a diastereoselective alpha-alkylation reaction to yield alpha-substituted FADIs 17. Furthermore, the presented amidation protocol was used for straightforward incorporation of FADI into peptidyl resin. PMID:19331368

Yamaki, Yoko; Shigenaga, Akira; Li, Jinglan; Shimohigashi, Yasuyuki; Otaka, Akira

2009-05-01

191

Organocatalytic Michael and Friedel-Crafts reactions in enantioselective synthesis of biologically active compounds  

NASA Astrophysics Data System (ADS)

Recent applications of organocatalytic Michael and Friedel-Crafts reactions in enantioselective synthesis of biologically active compounds: natural products, pharmaceutical agents and plant protection agents are reviewed. The key mechanisms of stereoinduction, types of organocatalysts and reagents used in these reactions are considered. The material is classified according to the type of newly formed bonds incorporating the asymmetric carbon atom, and the information for the most numerous C-C coupling reactions is systematized according to the natures of the electrophile and the nucleophile. The bibliography includes 433 references. Dedicated to Academician O M Nefedov on the occasion of his 80th birthday.

Maltsev, O. V.; Beletskaya, Irina P.; Zlotin, Sergei G.

2011-11-01

192

MICROWAVE EFFECTS IN ORGANIC SYNTHESIS: MECHANISTIC AND REACTION MEDIUM CONSIDERATIONS  

EPA Science Inventory

The scope of applications of microwave irradiation relates to a wide spectrum of organic syntheses with numerous benefits (reduction in reaction times, improved purity of products and better yields) encompassing advantages of both thermal and (or) specific non-purely thermal effe...

193

Prebiotic synthesis of histidine  

NASA Technical Reports Server (NTRS)

The prebiotic formation of histidine (His) has been accomplished experimentally by the reaction of erythrose with formamidine followed by a Strecker synthesis. In the first step of this reaction sequence, the formation of imidazole-4-acetaldehyde took place by the condensation of erythrose and formamidine, two compounds that are known to be formed under prebiotic conditions. In a second step, the imidazole-4-acetaldehyde was converted to His, without isolation of the reaction products by adding HCN and ammonia to the reaction mixture. LC, HPLC, thermospray liquid chromatography-mass spectrometry, and tandem mass spectrometry were used to identify the product, which was obtained in a yield of 3.5% based on the ratio of His/erythrose. This is a new chemical synthesis of one of the basic amino acids which had not been synthesized prebiotically until now.

Shen, C.; Yang, L.; Miller, S. L.; Oro, J.

1990-01-01

194

A new direct single-molecule observation method for DNA synthesis reaction using fluorescent replication protein A.  

PubMed

Using a single-stranded region tracing system, single-molecule DNA synthesis reactions were directly observed in microflow channels. The direct single-molecule observations of DNA synthesis were labeled with a fusion protein consisting of the ssDNA-binding domain of a 70-kDa subunit of replication protein A and enhanced yellow fluorescent protein (RPA-YFP). Our method was suitable for measurement of DNA synthesis reaction rates with control of the ss?DNA form as stretched ss?DNA (+flow) and random coiled ss?DNA (-flow) via buffer flow. Sequentially captured photographs demonstrated that the synthesized region of an ss?DNA molecule monotonously increased with the reaction time. The DNA synthesis reaction rate of random coiled ss?DNA (-flow) was nearly the same as that measured in a previous ensemble molecule experiment (52 vs. 50 bases/s). This suggested that the random coiled form of DNA (-flow) reflected the DNA form in the bulk experiment in the case of DNA synthesis reactions. In addition, the DNA synthesis reaction rate of stretched ss?DNA (+flow) was approximately 75% higher than that of random coiled ss?DNA (-flow) (91 vs. 52 bases/s). The DNA synthesis reaction rate of the Klenow fragment (3'-5'exo-) was promoted by DNA stretching with buffer flow. PMID:24625741

Takahashi, Shunsuke; Kawasaki, Shohei; Miyata, Hidefumi; Kurita, Hirofumi; Mizuno, Takeshi; Matsuura, Shun-ichi; Mizuno, Akira; Oshige, Masahiko; Katsura, Shinji

2014-01-01

195

Synthesis of functionalized chromones through sequential reactions in aqueous media.  

PubMed

An efficient sequential four-component reaction of chromone carbaldehydes, Meldrum's acid, 4-hydroxyl coumarin or 6-methyl-4-hydroxyl-pyrone and primary alcohols is reported which leads to 5a-i in aqueous media. Replacing the primary alcohol with isopropyl alcohol and tert-butyl alcohol results in different products 10 and 11. The environmentally friendly features, good to high yields and easy work-up are advantages of this approach. PMID:24968923

Mehrparvar, Saber; Balalaie, Saeed; Rabbanizadeh, Mahnaz; Rominger, Frank; Ghabraie, Elmira

2014-08-14

196

Synthesis, structure and a nucleophilic coordination reaction of Germanetellurones.  

PubMed

?-Diketiminato cyclopentadienyl and ferrocenylethynyl germylenes LGeR (L = HC[C(Me)N-2,6-iPr2C6H3]2, R = Cp () and C[triple bond, length as m-dash]CFc ()) were prepared and utilized to synthesize the Ge[double bond, length as m-dash]Te bond species. Reactions of , , and LGeC[triple bond, length as m-dash]CPh () with an excess of Te powder proceeded in toluene under reflux successfully yielded germanetellurone L(R)GeTe (R = Cp (), C[triple bond, length as m-dash]CFc (), and C[triple bond, length as m-dash]CPh ()). Further reaction of with GeCl2·dioxane at -78 °C resulted in L(Cp)GeTe(GeCl2) (), the first example of a germylene germanetellurone adduct. Both compounds and contain two isomers that are generated by the simultaneous 1,2-H- and 1,3-H-shifts over the Cp ring at the Ge atom. The reactions of L(Me)GeE with AuC6F5·SC4H8 at room temperature led to pentafluorophenyl gold(i) germanethione and germaneselone compounds L(Me)GeE(AuC6F5) (E = S () and Se ()). The formation of compounds exhibits a rare nucleophilic coordination reaction pathway by the Ge[double bond, length as m-dash]E (E = S, Se, Te) bond towards the metal-containing Lewis acidic species. The structures of compounds , , and are studied by the NMR and/or IR spectroscopy and X-ray crystallography. PMID:24985929

Li, Bin; Li, Yan; Zhao, Na; Chen, Yuefei; Chen, Yujue; Fu, Gang; Zhu, Hongping; Ding, Yuqiang

2014-08-21

197

Synthesis of potential drug metabolites by a modified Udenfriend reaction  

Microsoft Academic Search

Several drugs (clozapine, chlorpromazine, imipramine, buspirone, diltiazem, and propranolol) were subjected to modified Udenfriend conditions (Fe2+\\/Mn2+\\/EDTA\\/ascorbic acid\\/O2). From each reaction, one to four oxidation products were obtained in 1–8% overall yield. Many of these products (9 out of 14) have been reported to be metabolites of the parent drugs in vivo. The products resulted mainly from aromatic hydroxylation, and are

Roger Slavik; Jens-Uwe Peters; Rudolf Giger; Markus Bürkler; Eric Bald

2011-01-01

198

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

199

Synthesis of chemically-modified single-walled carbon nanotubes by counter-current ammonia gas injection into the induction thermal plasma process  

NASA Astrophysics Data System (ADS)

Pristine single-walled carbon nanotubes (SWCNTs) are poorly dispersible and insoluble in many solvents and need to be chemically modified prior to their use in many applications. This work is focused on the investigation of the synthesis of chemically modified SWCNTs material through an in situ approach. The main objectives of the presented research are: 1) to explore the in situ chemical process during the synthesis of SWCNT and 2) to closely examine the effect of a reactive environment on SWCNTs. Effects of the catalyst type and content on the SWCNTs final product, synthesized by induction thermal plasma (ITP), were studied to replace toxic cobalt (Co) in the feedstock. In this regard, three different catalyst mixtures (i.e. Ni-Y2O3, Ni-Co-Y2O3, and Ni-Mo-Y2O3) were used. Experimental results showed that the catalyst type affects the quality of the SWCNT final product. Similar quality SWCNTs can be produced when the same amount of Co was replaced by Ni. Moreover, the results observed in this experimental work were further explained by thermodynamic calculation results. Thermogravimetry (TG) was used throughout the work to characterize the SWCNTs product. TG was firstly standardized by studying the effects of three main instrumental parameters (temperature ramp, TR, initial mass of the sample, IM, and gas flow rate, FR) on the Tonset and full-width half maximum (FWHM) obtained from TG and derivative TG graphs of carbon black, respectively. Therefore, a two-level factorial statistical design was performed. The statistical analysis showed that the effect of TR, IM, and to a lower extent, FR, is significant on FWHM and insignificant on Tonset. A methodology was then developed based upon the SWCNTs synthesis using the ITP system, through an in situ chemistry approach. Ammonia (NH3) was selected and counter-currently injected into the ITP reactor at three different flow rates and by four different nozzle designs. Numerical simulation indicated a better mixing of NH3 in the ITP reactor when a certain nozzle was used. The experimental results showed the increase of D-band intensity in the Raman spectra of SWCNT samples upon the NH3 injection. NH3 could increase the nitrogen content of the SWCNTs final product up to 10 times. The SWCNTs sample treated with 15 vol% NH3 showed an enhanced dispersibility in Dimethylformamide and Isopropanol. Onion-like and planar carbon nanostructures were also observed. Complementary characterization on the SWCNT samples treated by 15 vol% NH3 indicated the surface modification of nanotubes. Metallic tubes showed a higher reactivity with NH3 than semiconducting ones. The model including the reactor thermo-flow field and NH3 thermal decomposition kinetics suggested a two-step SWCNT surface modification in which nanotubes firstly react with H and NH2 intermediates and later, NH3 chemisorbs on the nanotubes. The model also suggested that the intermediate species, like NNH and N2H2, play a role primarily in driving the NH3 decomposition rather than the chemical modification of SWCNTs. Keywords: Single-walled carbon nanotube, Induction thermal plasma, Thermogravimetry, Kinetic, Computational fluid dynamic, Thermodynamic, modification, Functionalization

Shahverdi, Ali

200

Synthesis of new cellulose ethers using Suzuki-Miyaura reactions.  

PubMed

Cellulose ethers are functionalized biopolymers that are industrially produced through drastic conditions employing gaseous reactants with a high risk of industrial accident. The cellulose ethers that are commercially available generally bear short carbon-chains. In this work, an alternative method using non-gaseous chemicals is proposed. It relies on the use of the Suzuki-Miyaura reaction employing mild, moisture- and air-stable conditions. Relatively innocuous reagents are used for this step, which allows the formation of a wide range of cellulose ethers bearing various functional groups with different chain-length. PMID:25458272

Goncalves, Cédric; Favre, Camille; Feuardant, Pierre; Klein, Sarah; Vaca-Garcia, Carlos; Cecutti, Christine; Thiébaud-Roux, Sophie; Vedrenne, Emeline

2015-02-13

201

Fullerenes: Synthesis, separation, characterization, reaction chemistry, and applications -- A review  

SciTech Connect

The recently discovered third allotrope of carbon, the fullerenes, area subject of very active research, particularly for chemists. They have a closed-cage structure, made by interlocking pentagonal and hexagonal panels, and are the only soluble form of carbon. In this review an attempt has been made to summarize ongoing fullerene research. The review covers methods of fullerene production and separation, mechanisms leading to closed-cage structure formation, structural characterization, reaction chemistry, and applications of this novel material. The emerging directions of research are also discussed.

Singh, H.; Srivastava, M. [Indian Inst. of Petroleum, Dehradun (India)

1995-11-01

202

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

203

Synthesis of bicyclic proline derivatives by the aza-cope-mannich reaction: formal synthesis of (±)-acetylaranotin.  

PubMed

Herein we suggest an approach to oxygenated bicyclic amino acids based on an aza-Cope-Mannich rearrangement. Seven distinct amino acid scaffolds analogous to the natural products were prepared on a gram scale with precise control of stereochemistry. Successful implementation of our strategy resulted in the formal synthesis of acetylaranotin. PMID:25631763

Belov, Dmitry S; Ratmanova, Nina K; Andreev, Ivan A; Kurkin, Alexander V

2015-03-01

204

Reaction design, discovery, and development as a foundation to function-oriented synthesis.  

PubMed

Convergent C-C bond-forming reactions define the fabric of organic synthesis and, when applied in complex molecule synthesis, can have a profound impact on efficiency by decreasing the longest linear sequence of transformations required to convert simple starting materials to complex targets. Despite their well-appreciated strategic significance, campaigns in natural product synthesis typically embrace only a small suite of reactivity to achieve such bond construction (i.e., nucleophilic addition to polarized ?-bonds, nucleophilic substitution, cycloaddition, and metal-catalyzed "cross-coupling"), therefore limiting the sites at which convergent coupling chemistry can be strategically employed. In our opinion, it is far too often that triumphs in the field are defined by chemical sequences that do not address the challenges associated with discovery, development, and production of natural product-inspired agents. We speculated that advancing an area of chemical reactivity not represented in the few well-established strategies for convergent C-C bond formation may lead to powerful new retrosynthetic relationships that could simplify approaches to the syntheses of a variety of different classes of natural products. Our studies ultimately embraced the pursuit of strategies to control the course of metallacycle-mediated "cross-coupling" between substrates containing sites of simple ?-unsaturation (ubiquitous functionality in organic chemistry including alkenes, alkynes, allenes, aldehydes, and imines, among others). In just eight years since our initial publication in this area, we have defined over 20 stereoselective intermolecular C-C bond-forming reactions that provide access to structural motifs of relevance for the synthesis of polyketides, fatty acids, alkaloids, and terpenes, while doing so in a direct and stereoselective fashion. These achievements continue to serve as the foundation of my group's activity in natural product and function-oriented synthesis, where our achievements in reaction development are challenged in the context of complex targets. Among our early efforts, we achieved the most concise synthesis of a benzoquinone ansamycin ever described (macbecin I), and moved beyond this achievement to explore the role of our chemistry in function-oriented synthesis targeting the discovery of natural product-inspired Hsp90 inhibitors. These later efforts have led to the discovery of a uniquely selective benzoquinone ansamycin-inspired Hsp90 inhibitor that lacks the problematic quinone present in the natural series. This achievement was made possible by a concise chemical synthesis pathway that had at its core the application of metallacycle-mediated cross-coupling chemistry. PMID:25668752

Micalizio, Glenn C; Hale, Sarah B

2015-03-17

205

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.

206

Synthesis of most polyene natural product motifs using just twelve building blocks and one coupling reaction  

PubMed Central

The inherent modularity of polypeptides, oligonucleotides, and oligosaccharides has been harnessed to achieve generalized building block-based synthesis platforms. Importantly, like these other targets, most small molecule natural products are biosynthesized via iterative coupling of bifunctional building blocks. This suggests that many small molecules also possess inherent modularity commensurate with systematic building block-based construction. Supporting this hypothesis, here we report that the polyene motifs found in >75% of all known polyene natural products can be synthesized using just 12 building blocks and one coupling reaction. Using the same general retrosynthetic algorithm and reaction conditions, this platform enabled the synthesis of a wide range of polyene frameworks covering all of this natural product chemical space, and first total syntheses of the polyene natural products asnipyrone B, physarigin A, and neurosporaxanthin ?-D-glucopyranoside. Collectively, these results suggest the potential for a more generalized approach for making small molecules in the laboratory. PMID:24848233

Woerly, Eric M.; Roy, Jahnabi; Burke, Martin D.

2014-01-01

207

Enantioselective Synthesis of Tetrahydroquinolines, Tetrahydroquinoxalines, and Tetrahydroisoquinolines via Pd-Catalyzed Alkene Carboamination Reactions.  

PubMed

A catalyst composed of Pd2(dba)3 and (S)-Siphos-PE provides excellent results in Pd-catalyzed alkene carboamination reactions between aniline derivatives bearing pendant alkenes and aryl or alkenyl halides. These transformations generate tetrahydroquinolines and tetrahydroquinoxalines that contain quaternary carbon stereocenters with high levels of asymmetric induction. In addition this catalyst also effects the asymmetric synthesis of tetrahydroisoquinolines via related transformations of 2-allylbenzylamines. In contrast to most other approaches to the asymmetric synthesis of these compounds, which frequently involve functional group interconversion or a single C-C or C-N bond-forming event, the carboamination reactions generate both a C-N bond, a C-C bond, and a stereocenter. PMID:25431650

Hopkins, B A; Wolfe, J P

2014-12-01

208

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

209

Stereoselective synthesis of functionalized trisubstituted olefins via palladium(0)-catalyzed cross-coupling reaction.  

PubMed

[reaction: see text]. A highly flexible and stereoselective protocol for the synthesis of branched (E)- and (Z)-trisubstituted alkenes has been developed. The key steps are hydrozirconation-iodination of (1-alkynyl)trimethylsilane followed by Negishi-type cross-coupling. The resultant (Z)-vinyl silane is iododesilylated and subjected to a second cross-coupling reaction to give the trisubstituted olefin. Model studies aimed at the construction of the C14-C15 (Z)-trisubstituted olefin of discodermolide and the C8-C9 (Z)-trisubstituted olefin of callystatin A and analogues are also described. PMID:11594814

Arefolov, A; Langille, N F; Panek, J S

2001-10-18

210

Low-Temperature Synthesis of Actinide Tetraborides by Solid-State Metathesis Reactions  

SciTech Connect

The synthesis of actinide tetraborides including uranium tetraboride (UB,), plutonium tetraboride (PUB,) and thorium tetraboride (ThB{sub 4}) by a solid-state metathesis reaction are demonstrated. The present method significantly lowers the temperature required to {approx_equal}850 C. As an example, when UCl{sub 4}, is reacted with an excess of MgB{sub 2}, at 850 C, crystalline UB, 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, product is purified by washing water and drying.

Lupinetti, Anthony J.; Garcia, Eduardo; Abney, Kent D.

2004-12-14

211

Recent contributions from the asymmetric aza-Michael reaction to alkaloids total synthesis.  

PubMed

This review focuses on recent applications of the aza-Michael reaction in alkaloids total synthesis with a special emphasis on stereoselectivity. The report highlights achievements and challenges over the past five years and describes stereoselective intra- and inter-molecular conjugate addition of nitrogen-containing nucleophiles, including tandem and cascade processes. Total asymmetric syntheses of natural scaffolds, such as pyrrolidine, piperidine and "izidine" families, are depicted. Multi-step syntheses of highly challenging natural products are further detailed, assessing the scope of the stereocontrolled aza-Michael reaction as a powerful tool in alkaloid chemistry. PMID:23896828

Amara, Zacharias; Caron, Joachim; Joseph, Delphine

2013-09-01

212

Synthesis of naphthalene amino esters and arylnaphthalene lactone lignans through tandem reactions of 2-alkynylbenzonitriles.  

PubMed

Tandem reaction of 2-alkynylbenzonitriles with a Reformatsky reagent turned out to be a novel and efficient approach toward 1-aminonaphthalene-2-carboxylates. Interestingly, with 2-(3-hydroxyprop-1-ynyl)benzonitriles as the substrates, a more sophisticated cascade process occurred to give 9-aminonaphtho[2,3-c]furan-1(3H)-ones in good yields. By using this tandem reaction as a key step, a concise and versatile synthetic strategy for the total synthesis of arylnaphthalene lactone lignans has been developed. PMID:24733055

He, Yan; Zhang, Xinying; Fan, Xuesen

2014-05-30

213

Benzannulation via the reaction of ynamides and vinylketenes. application to the synthesis of highly substituted indoles.  

PubMed

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; Danheiser, Rick L

2013-09-20

214

Analysis of Instability in an Industrial Ammonia Reactor  

E-print Network

point for this study was an incident in an industrial plant, where the ammonia synthesis reactor became the reactor beds combined with the positive feedback caused by the preheater. Introduction The starting pointAnalysis of Instability in an Industrial Ammonia Reactor John C. Morud and Sigurd Skogestad Dept

Skogestad, Sigurd

215

Biaryl synthesis via decarboxylative Pd-catalyzed reactions of arenecarboxylic acids and diaryliodonium triflates.  

PubMed

A novel simple and efficient synthesis of biaryls via a Pd-catalyzed decarboxylative cross-coupling reaction of arenecarboxylic acids and diaryliodonium triflates is described. The PdCl2/DPEphos catalytic system in the presence of Ag2CO3 in DMSO was found to be the most efficient. Various biaryls, including sterically hindered biaryls, were synthesized with yields ranging from 37 to 85%. PMID:18553969

Becht, Jean-Michel; Le Drian, Claude

2008-07-17

216

Diversity-oriented synthesis of dihydrobenzoxazepinones by coupling the Ugi multicomponent reaction with a Mitsunobu cyclization  

PubMed Central

Summary An operationally simple protocol for the synthesis of 2,3-dihydrobenzo[f][1,4]oxazepin-3-ones, based on an Ugi reaction of an ortho-(benzyloxy)benzylamine, glycolic acid, an isocyanide and an aldehyde, followed by an intramolecular Mitsunobu substitution was developed. The required ortho-(benzyloxy)benzylamines have been in situ generated from the corresponding azides, in turn prepared in high yields from salicylic derivatives. PMID:24605140

Moni, Lisa; Banfi, Luca; Basso, Andrea; Brambilla, Alice

2014-01-01

217

Cycloaddition reactions of thiazolidine derivatives. An approach to the synthesis of new functionalized heterocyclic systems  

Microsoft Academic Search

A one-pot procedure for the synthesis of two functionalized tricyclic systems having structures of benzo[g]isoquinoline-5,10-dione and dihydrothieno[2,3-b]naphto-4,9-dione (DTNQ) is described. These new series were synthesized from cycloaddition reactions between naphthoquinone and arylthiazolidine derivatives, the latter acting, respectively, as highly reactive N-arylidenedehydroalanine ethyl esters (2-AD) or as amino ester nucleophilic species.

Isabel M Gomez-Monterrey; Pietro Campiglia; Orazio Mazzoni; Ettore Novellino; M. Vittoria Diurno

2001-01-01

218

Asymmetric synthesis of fully substituted cyclopentane-oxindoles through an organocatalytic triple Michael domino reaction.  

PubMed

An efficient, highly stereoselective asymmetric synthesis of fully functionalized cyclopentanes bearing an oxindole moiety and several other functional groups in one pot has been developed. Key step is an organocatalytic triple Michael domino reaction forming three C-C bonds and six stereocenters, including a quaternary one. Starting from equimolar amounts of simple substrates, a high molecular complexity can be reached after a Wittig olefination in one pot. The new protocol can easily be scaled up to gram amounts. PMID:25470781

Zou, Liang-Hua; Philipps, Arne R; Raabe, Gerhard; Enders, Dieter

2015-01-12

219

Cerium ammonium nitrate-catalyzed multicomponent reaction for efficient synthesis of functionalized tetrahydropyridines.  

PubMed

A highly atom-economic one-pot synthesis of functionalized tetrahydropyridines by a multicomponent condensation reaction of ?-keto ester, two equivalents of aromatic aldehyde, and two equivalents of amine in the presence of a catalytic amount of cerium ammonium nitrate (CAN) is reported. In this way, a series of pharmacologically interesting substituted piperidine derivatives were obtained in moderate to good yields at room temperature. PMID:21395344

Wang, Hong-Juan; Mo, Li-Ping; Zhang, Zhan-Hui

2011-03-14

220

Pd-catalyzed arylation reactions with phenol diazonium salts: application in the synthesis of diarylheptanoids.  

PubMed

The first total synthesis of the natural product (3S,7R)-5,6-dehydro-de-O-methyl centrolobine and various analogues is reported, using a highly regio- and diastereoselective Mizoroki-Heck reaction of phenol diazonium salts and enantiopure dihydropyrans. The assigned relative configuration was confirmed by single-crystal X-ray structure analysis, but a revision of the absolute configuration is proposed based on polarimetric measurement. PMID:21434690

Schmidt, Bernd; Hölter, Frank; Kelling, Alexandra; Schilde, Uwe

2011-05-01

221

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

222

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

223

Witting Reaction Using a Stabilized Phosphorus Ylid: An Efficient and Stereoselective Synthesis of Ethyl Trans-Cinnamate  

ERIC Educational Resources Information Center

An instructive experiment for the synthesis of ethyl trans-cinnamate, a pleasant smelling ester used in perfumery and flavoring by the reaction of benzaldehyde with the stable ylid triphenylphosphorane is described. The synthesis, workup and characterization of trans-cinnamate may be accomplished in a single laboratory session with commonly…

Speed, Traci J.; Mclntyre, Jean P.; Thamattoor, Dasan M.

2004-01-01

224

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.

225

Nickel-catalyzed monoarylation of ammonia.  

PubMed

Structurally diverse (hetero)aryl chloride, bromide, and tosylate electrophiles were employed in the Ni-catalyzed monoarylation of ammonia, including chemoselective transformations. The employed JosiPhos/[Ni(cod)2 ] catalyst system enables the use of commercially available stock solutions of ammonia, or the use of ammonia gas in these reactions, thereby demonstrating the versatility and potential scalability of the reported protocol. Proof-of-principle experiments established that air-stable [(JosiPhos)NiCl2 ] precatalysts can be employed successfully in such transformations. PMID:25573662

Borzenko, Andrey; Rotta-Loria, Nicolas L; MacQueen, Preston M; Lavoie, Christopher M; McDonald, Robert; Stradiotto, Mark

2015-03-16

226

Prebiotic synthesis of imidazole-4-acetaldehyde and histidine  

NASA Technical Reports Server (NTRS)

The prebiotic synthesis of imidazole-4-acetaldehyde and imidazole-4-glycol from erythrose and formamidine has been demonstrated as well as the prebiotic synthesis of imidazole-4-ethanol and imidazole-4-glycol from erythrose, formaldehyde, and ammonia. The maximum yields of imidazole-4-acetaldehyde, imidazole-4-ethanol, and imidazole-4-glycol obtained in these reactions are 1.6, 5.4, and 6.8 percent respectively, based on the erythrose. Imidazole-4-acetaldehyde would have been converted to histidine on the primitive earth by a Strecker synthesis, and several prebiotic reactions would convert imidazole-4-glycol and imidazole-4-ethanol to imidazole-4-acetaldehyde.

Shen, Chun; Oro, J.; Yang, Lily; Miller, Stanley L.

1987-01-01

227

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

SciTech Connect

Methanol synthesis from CO and H{sub 2} 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{sup ¯}) 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 H{sub 2} 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, E-mail: johannes.frenzel@theochem.rub.de; Marx, Dominik [Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780 Bochum (Germany)

2014-09-28

228

Primary and secondary reaction pathways in ruthenium-catalyzed hydrocarbon synthesis  

SciTech Connect

Residence time studies show that n-paraffins, {alpha}-olefins, and cis-2-olefins are primary products during hydrocarbon synthesis on Ru catalysts. Their formation, as well as that of branched isomers, is consistent with previously proposed surface reactions of alkyl groups on metal surfaces. Secondary hydrogenation and hydrogenolysis of {alpha}-olefins are inhibited by the water product of the synthesis step. However, {alpha}-olefin readsorption and surface chain initiation and cis-to-trans isomerization take place as secondary reactions. The decrease in {alpha}-olefin readsorption and surface chain initiation and cis-to-trans isomerization take place as secondary reactions. The decrease in {alpha}-olefin readsorption and surface chain initiation and cis-to-trans isomerization take place as secondary reactions. The decrease in {alpha}-olefin readsorption and surface chain initiation and cis-to-trans isomerization take place as secondary reactions. The decrease in {alpha}-olefin selectivity with increasing CO conversion and molecular size reflects the greater extent of readsorption as bed and pore residence times of {alpha}-olefin increase. Readsorption of {alpha}-olefins and chain initiation increases with molecular size because the rate of removal of olefins from liquid-filled catalyst pores is decreased due to intraparticle diffusion limitations. This diffusion-enhanced olefin readsorption accounts for the observed deviations of carbon number distributions from those predicted by Flory polymerization kinetics. Chain growth probability increases with chain length until an asymptotic value is reached. Readsorption decreases the contribution of termination via hydrogen abstraction to chain growth kinetics. In effect, differences in selectivity between small and large hydrocarbons are due to the increasing influence of pore residence times and the decreasing influence of bed residence times on secondary reactions as olefin size increases.

Madon, R.J.; Reyes, S.C.; Iglesia, E. (Exxon Research and Engineering Co., Annandale, NJ (United States))

1991-10-03

229

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

230

Evaluating reaction pathways of hydrothermal abiotic organic synthesis at elevated temperatures and pressures using carbon isotopes  

NASA Astrophysics Data System (ADS)

Experiments were performed to better understand the role of environmental factors on reaction pathways and corresponding carbon isotope fractionations during abiotic hydrothermal synthesis of organic compounds using piston cylinder apparatus at 750 °C and 5.5 kbars. Chemical compositions of experimental products and corresponding carbon isotopic values were obtained by a Pyrolysis-GC-MS-IRMS system. Alkanes (methane and ethane), straight-chain saturated alcohols (ethanol and n-butanol) and monocarboxylic acids (formic and acetic acids) were generated with ethanol being the only organic compound with higher ?13C than CO2. CO was not detected in experimental products owing to the favorable water-gas shift reaction under high water pressure conditions. The pattern of ?13C values of CO2, carboxylic acids and alkanes are consistent with their equilibrium isotope relationships: CO2 > carboxylic acids > alkanes, but the magnitude of the fractionation among them is higher than predicted isotope equilibrium values. In particular, the isotopic fractionation between CO2 and CH4 remained constant at ?31‰, indicating a kinetic effect during CO2 reduction processes. No "isotope reversal" of ?13C values for alkanes or carboxylic acids was observed, which indicates a different reaction pathway than what is typically observed during Fischer-Tropsch synthesis under gas phase conditions. Under constraints imposed in experiments, the anomalous 13C isotope enrichment in ethanol suggests that hydroxymethylene is the organic intermediate, and that the generation of other organic compounds enriched in 12C were facilitated by subsequent Rayleigh fractionation of hydroxymethylene reacting with H2 and/or H2O. Carbon isotope fractionation data obtained in this study are instrumental in assessing the controlling factors on abiotic formation of organic compounds in hydrothermal systems. Knowledge on how environmental conditions affect reaction pathways of abiotic synthesis of organic compounds is critical for understanding deep subsurface ecosystems and the origin of organic compounds on Mars and other planets.

Fu, Qi; Socki, Richard A.; Niles, Paul B.

2015-04-01

231

Reaction parameters for the synthesis of n,n-dimethyl Fatty hydrazides from oil.  

PubMed

Hydrazide derivatives have been synthesized from methyl esters, hydrazones and vegetable oils. They are important due to their diverse applications in pharmaceutical products, detergents as well as in oil and gas industries. The chemical synthesis of fatty hydrazides is well-established; however, only a few publications described the synthesis of fatty hydrazide derivatives, particularly, when produced from refined, bleached and deodorized palm olein. Here, the synthesis and characterization of N,N-dimethyl fatty hydrazides are reported. The N,N-dimethyl fatty hydrazides was successfully synthesized from fatty hydrazides and dimethyl sulfate in the presence of potassium hydroxide with the molar ratio of 1:1:1, 6 hours reaction time and 80? reaction temperature in ethanol. The product yield and purity were 22% and 89%, respectively. The fatty hydrazides used were synthesized from refined, bleached and deodorized palm olein with hydrazine monohydrate at pH 12 by enzymatic route. Fourier transform infrared, gas chromatography and nuclear magnetic resonance (NMR) spectroscopy techniques were used to determine the chemical composition of N,N-dimethyl fatty hydrazides. Proton NMR confirmed the product obtained were N,N-dimethyl fatty hydrazides. PMID:25519290

Ahmad, Norashikin; Azizul Hasan, Zafarizal Aldrin; Hassan, Hazimah Abu; Ahmad, Mansor; Zin Wan Yunus, Wan Md

2015-01-01

232

Synthesis of Acyclic r, -Unsaturated Ketones via Pd(II)-Catalyzed Intermolecular Reaction of Alkynamides and Alkenes  

E-print Network

Synthesis of Acyclic r, -Unsaturated Ketones via Pd(II)-Catalyzed Intermolecular Reaction ketone.3 Here we describe the development of an analogous intermolecular oxidative coupling reaction between alkynamides and terminal alkenes to generate acyclic R, -unsat- urated ketones4 (eq 1). Our

Liu, David R.

233

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

E-print Network

................................................... 40 1.3.2 Acceleration of the MBH Reaction............................. 41 1.3.3 NMR Studies of Complex TMEDA?MgI2 .................. 44 1.3.4 Enantioselective MBH Reaction ................................. 46 1.3.5 Synthesis... AND OUTLOOK.................................................. 156 REFERENCES...................................................................................................... 160 APPENDIX A 1H NMR AND 13C NMR SPECTRA...

Bugarin Cervantes, Alejandro

2011-08-08

234

Lipid synthesis under hydrothermal conditions by Fischer-Tropsch-type reactions  

NASA Technical Reports Server (NTRS)

Ever since their discovery in the late 1970's, mid-ocean-ridge hydrothermal systems have received a great deal of attention as a possible site for the origin of life on Earth (and environments analogous to mid-ocean-ridge hydrothermal systems are postulated to have been sites where life could have originated or Mars and elsewhere as well). Because no modern-day terrestrial hydrothermal systems are free from the influence of organic compounds derived from biologic processes, laboratory experiments provide the best opportunity for confirmation of the potential for organic synthesis in hydrothermal systems. Here we report on the formation of lipid compounds during Fischer-Tropsch-type synthesis from aqueous solutions of formic acid or oxalic acid. Optimum synthesis occurs in stainless steel vessels by heating at 175 degrees C for 2-3 days and produces lipid compounds ranging from C2 to > C35 which consist of n-alkanols, n-alkanoic acids, n-alkenes, n-alkanes and alkanones. The precursor carbon sources used are either formic acid or oxalic acid, which disproportionate to H2, CO2 and probably CO. Both carbon sources yield the same lipid classes with essentially the same ranges of compounds. The synthesis reactions were confirmed by using 13C labeled precursor acids.

McCollom, T. M.; Ritter, G.; Simoneit, B. R.

1999-01-01

235

Pyranoside-into-furanoside rearrangement: new reaction in carbohydrate chemistry and its application in oligosaccharide synthesis.  

PubMed

Great interest in natural furanoside-containing compounds has challenged the development of preparative methods for their synthesis. Herein a novel reaction in carbohydrate chemistry, namely a pyranoside-into-furanoside (PIF) rearrangement permitting the transformation of selectively O-substituted pyranosides into the corresponding furanosides is reported. The discovered process includes acid-promoted sulfation accompanied by rearrangement of the pyranoside ring into a furanoside ring followed by solvolytic O-desulfation. This process, which has no analogy in organic chemistry, was shown to be a very useful tool for the synthesis of furanoside-containing complex oligosaccharides, which was demonstrated by synthesizing disaccharide derivatives ?-D-Galp-(1?3)-?-D-Galf-OPr, 3-O-s-lactyl-?-D-Galf-(1?3)-?-D-Glcp-OPr, and ?-L-Fucf-(1?4)-?-D-GlcpA-OPr related to polysaccharides from the bacteria Klebsiella pneumoniae and Enterococcus faecalis and the brown seaweed Chordaria flagelliformis. PMID:25319316

Krylov, Vadim B; Argunov, Dmitry A; Vinnitskiy, Dmitry Z; Verkhnyatskaya, Stella A; Gerbst, Alexey G; Ustyuzhanina, Nadezhda E; Dmitrenok, Andrey S; Huebner, Johannes; Holst, Otto; Siebert, Hans-Christian; Nifantiev, Nikolay E

2014-12-01

236

A General Strategy for Nanohybrids Synthesis via Coupled Competitive Reactions Controlled in a Hybrid Process.  

PubMed

A new methodology based on core alloying and shell gradient-doping are developed for the synthesis of nanohybrids, realized by coupled competitive reactions, or sequenced reducing-nucleation and co-precipitation reaction of mixed metal salts in a microfluidic and batch-cooling process. The latent time of nucleation and the growth of nanohybrids can be well controlled due to the formation of controllable intermediates in the coupled competitive reactions. Thus, spatiotemporal-resolved synthesis can be realized by the hybrid process, which enables us to investigate nanohybrid formation at each stage through their solution color changes and TEM images. By adjusting the bi-channel solvents and kinetic parameters of each stage, the primary components of alloyed cores and the second components of transition metal doping ZnO or Al2O3 as surface coatings can be successively formed. The core alloying and shell gradient-doping strategy can efficiently eliminate the crystal lattice mismatch in different components. Consequently, varieties of gradient core-shell nanohybrids can be synthesized using CoM, FeM, AuM, AgM (M = Zn or Al) alloys as cores and transition metal gradient-doping ZnO or Al2O3 as shells, endowing these nanohybrids with unique magnetic and optical properties (e.g., high temperature ferromagnetic property and enhanced blue emission). PMID:25818342

Wang, Rongming; Yang, Wantai; Song, Yuanjun; Shen, Xiaomiao; Wang, Junmei; Zhong, Xiaodi; Li, Shuai; Song, Yujun

2015-01-01

237

A General Strategy for Nanohybrids Synthesis via Coupled Competitive Reactions Controlled in a Hybrid Process  

PubMed Central

A new methodology based on core alloying and shell gradient-doping are developed for the synthesis of nanohybrids, realized by coupled competitive reactions, or sequenced reducing-nucleation and co-precipitation reaction of mixed metal salts in a microfluidic and batch-cooling process. The latent time of nucleation and the growth of nanohybrids can be well controlled due to the formation of controllable intermediates in the coupled competitive reactions. Thus, spatiotemporal-resolved synthesis can be realized by the hybrid process, which enables us to investigate nanohybrid formation at each stage through their solution color changes and TEM images. By adjusting the bi-channel solvents and kinetic parameters of each stage, the primary components of alloyed cores and the second components of transition metal doping ZnO or Al2O3 as surface coatings can be successively formed. The core alloying and shell gradient-doping strategy can efficiently eliminate the crystal lattice mismatch in different components. Consequently, varieties of gradient core-shell nanohybrids can be synthesized using CoM, FeM, AuM, AgM (M = Zn or Al) alloys as cores and transition metal gradient-doping ZnO or Al2O3 as shells, endowing these nanohybrids with unique magnetic and optical properties (e.g., high temperature ferromagnetic property and enhanced blue emission). PMID:25818342

Wang, Rongming; Yang, Wantai; Song, Yuanjun; Shen, Xiaomiao; Wang, Junmei; Zhong, Xiaodi; Li, Shuai; Song, Yujun

2015-01-01

238

Fusion reactions and experimental approaches to the synthesis of superheavy nuclei  

SciTech Connect

The question whether the asymmetric actinide based heavy ion reactions could be used for the synthesis of heavy (Z{>=}106) nuclides is essential from the point of view of the study of limitation on fusion, it is also important in such reactions new nuclides close to the magic number N=162 can be produced. Thus as the problem of a hindrance to fusion still remains unsolved the high excitation energy of the compound nucleus looks to be an obvious obstacle to using these reactions. Using the gas-filled recoil separator and electrostatic recoil separator VAS-SILISSA installed at the beam lines of the U-400 heavy ion cyclotron of the FLNR JINR we investigated the fusion reactions leading to 102, 103, 104, 105 and heaviest isotopes of the 106, 108 and 110 elements. The analysis of the measured cross-sections did not reveal any evidence of a hindrance to fusion at the ion bombarding energy close to the Coulomb barrier. {sup 48}Ca+{sup 232}Th{yields}{sup 280}110*, {sup 48}Ca+{sup 238}U{yields}{sup 286}112*, {sup 48}Ca+{sup 244}Pu{yields}{sup 292}114* appear to be the best reactions from the point of view of their cross-sections.

Yeremin, A. V.; Utyonkov, V. K.; Oganessian, Yu. Ts. [Flerov Laboratory of Nuclear Reactions, JINR, 141 980 Dubna, Moscow region (Russian Federation)

1998-02-15

239

Radical Coupling Reactions in Lignin Synthesis: A Density Functional Theory Study  

SciTech Connect

Lignin is a complex, heterogeneous polymer in plant cell walls that provides mechanical strength to the plant stem and confers resistance to degrading microbes, enzymes, and chemicals. Lignin synthesis initiates through oxidative radical-radical coupling of monolignols, the most common of which are p-coumaryl, coniferyl, and sinapyl alcohols. Here, we use density functional theory to characterize radical-radical coupling reactions involved in monolignol dimerization. We compute reaction enthalpies for the initial self- and cross-coupling reactions of these monolignol radicals to form dimeric intermediates via six major linkages observed in natural lignin. The 8-O-4, 8-8, and 8-5 coupling are computed to be the most favorable, whereas the 5-O-4, 5-5, and 8-1 linkages are less favorable. Overall, p-coumaryl self- and cross-coupling reactions are calculated to be the most favorable. For cross-coupling reactions, in which each radical can couple via either of the two sites involved in dimer formation, the more reactive of the two radicals is found to undergo coupling at its site with the highest spin density.

Sangha, A. K.; Parks, J. M.; Standaert, R. F.; Ziebell, A.; Davis, M.; Smith, J. C.

2012-04-26

240

Total Synthesis of Cephalosporolide E via a Tandem Radical/Polar Crossover Reaction. The Use of the Radical Cations under Nonoxidative Conditions in Total Synthesis.  

PubMed

The present work reports the first example of the use of the chemistry of radical cations under nonoxidative conditions in total synthesis. Using a late-stage tandem radical/polar crossover reaction, a highly stereoselective total synthesis of cephalosporolide E (which is typically obtained admixed with cephalosporolide F) was accomplished. The reaction of a phthalimido derivative with triphenyltin radical in refluxing toluene engenders a contact ion-pair (radical cation) that leads, in the first instance, to the cephalosporolide F, which is transformed into the cephalosporolide E via a stereocontrolled spiroketal isomerization promoted by the diphenylphosphate acid that is formed during the tandem transformation. PMID:25642728

Cortezano-Arellano, Omar; Quintero, Leticia; Sartillo-Piscil, Fernando

2015-03-01

241

Efficient lipase-selective synthesis of dilauryl mannoses by simultaneous reaction–extraction system  

Microsoft Academic Search

An efficient method for enzymatic-selective synthesis of dilauryl mannoses was developed using lipase-catalyzed condensation\\u000a of d-mannose and lauric acid in a simultaneous reaction–extraction system. The highest equilibrium conversion of diesters of 51%\\u000a (1,6-diester: 14%; 3,6-diester: 18%; 4,6-diester: 19%) and the total conversion of mono and dilauryl mannoses of 76% were\\u000a achieved at the n-hexane\\/acetonitrile ratio of 1:1, the molar ratio

Wenbin Zhang; Yinjiao Wang; Khizar Hayat; Xiaoming Zhang; Abbas Shabbar; Biao Feng; Chengsheng Jia

2009-01-01

242

Precision synthesis of functional materials via RAFT polymerization and click-type chemical reactions  

NASA Astrophysics Data System (ADS)

The need to tailor polymeric architectures with specific physico-chemical properties via the simplest, cleanest, and most efficient synthetic route possible has become the ultimate goal in polymer synthesis. Recent progress in macromolecular science, such as the discoveries of controlled/"living" free radical polymerization (CRP) methods, has brought about synthetic capabilities to prepare (co)polymers with advanced topologies, predetermined molecular weights, narrow molecular weight distributions, and precisely located functional groups. In addition, the establishment of click chemistry has redefined the selected few highly efficient chemical reactions that become highly useful in post-polymerization modification strategies. Hence, the ability to make well-defined topologies afforded by controlled polymerization techniques and the facile incorporation of functionalities along the chain via click-type reactions have yielded complex architectures, allowing the investigation of physical phenomena which otherwise could not be studied with systems prepared via conventional methods. The overarching theme of the research work described in this dissertation is the fusion of the excellent attributes of reversible addition-fragmentation chain transfer (RAFT) polymerization method, which is one of the CRP techniques, and click-type chemical reactions in the precision of synthesis of advanced functional materials. Chapter IV is divided into three sections. In Section I, the direct RAFT homopolymerization of 2-(acryloyloxy)ethyl isocyanate (AOI) and subsequent post-polymerization modifications are described. The polymerization conditions were optimized in terms of the choice of RAFT chain transfer agent (CTA), polymerization temperature and the reaction medium. Direct RAFT polymerization of AOI requires a neutral CTA, and relatively low reaction temperature to yield AOI homopolymers with low polydispersities. Efficient side-chain functionalization of PAOI homopolymers was achieved via reaction with model amine, thiol and alcohol compounds yielding urea, thiourethane and urethane derivatives, respectively. Reactions with amines and thiols (in the presence of base) were rapid, quantitative and efficient. However, the reaction with alcohols catalyzed by dibutyltin dilaurate (DBTDL) was relatively slow but proceeded to completion. Selective reaction pathways for the addition of difunctional ethanolamine and mercaptoethanol were also investigated. A related strategy is described in Section II wherein a hydroxyl-containing diblock copolymer precursor was transformed into a library of functional copolymers via two sequential post-polymerization modification reactions. A diblock copolymer scaffold, poly[(N,N-dimethylacrylamide)-b-( N-(2-hydroxyethyl)acrylamide] (PDMA-b-PHEA) was first prepared. The hydroxyl groups of the HEA block were then reacted with 2-(acryloyloxy)ethylisocyanate (AOI) and allylisocyanate (AI) resulting in acrylate- and allyl-functionalized copolymer precursors, respectively. The efficiencies of Michael-type and free radical thiol addition reactions were investigated using selected thiols having alkyl, aryl, hydroxyl, carboxylic acid, amine and amino acid functionalities. The steps of RAFT polymerization, isocyanate-hydroxyl coupling and thiol-ene addition are accomplished under mild conditions, thus offering facile and modular routes to synthesize functional copolymers. The synthesis and solution studies of pH- and salt-responsive triblock copolymer are described in Section III. This system is capable of forming self-locked micellar structures which may be controlled by changing solution pH as well as ionic strength. A triblock copolymer containing a permanently hydrophilic poly(N,N-dimethylacrylamide) (PDMA) outer block, a salt-sensitive zwitterionic poly(3[2-(N-methylacrylamido)ethyl dimethylammonio]propanesulfonate) (PMAEDAPS) middle block and a pH-responsive 3-acrylamido-3-methylbutanoic acid (PAMBA) core block was synthesized using aqueous RAFT polymerization. A facile formation of "self-locking&quo

Flores, Joel Diez

2011-12-01

243

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

244

Facile synthesis of ultrathin magnetic iron oxide nanoplates by Schikorr reaction  

PubMed Central

In this work, a very facile one-pot hydrothermal synthesis approach has been developed for the preparation of ultrathin magnetite nanoplates. The hydrothermal procedure was performed by aging ferrous hydroxide under anaerobic conditions, which is known as Schikorr reaction. Ethylene glycol (EG), which was introduced to the reaction as another solvent, played a critical role in the formation process of these nanoplates. Typically, hexagonal Fe3O4 nanoplates with a thickness of 10 to 15 nm and a side length of 150 to 200 nm have been synthesized with EG/H2O = 1:1 in experiments. Our data suggest that the thickness of Fe3O4 nanoplates decreases, and the shape of the nanoplate becomes more irregular when the concentration of EG increases. The as-prepared Fe3O4 nanoplates were highly crystallized single crystals and exhibited large coercivity and specific absorption rate coefficient. PMID:23294626

2013-01-01

245

Novel vapor phase reactions for the synthesis and modification of carbon nanotubes and inorganic nanowires.  

PubMed

Several vapor phase methods have been developed for the preparation and modification of carbon nanotubes and inorganic nanowires. Thus, nebulized spray pyrolysis has been employed for the synthesis of carbon nanotubes and metal nanowires. Multi-walled carbon nanotubes (MWNTs) with fairly uniform diameters and aligned nanotube bundles have been obtained by nebulized spray pyrolysis using solutions of organometallics such as ferrocene in hydrocarbon solvents. Single-crystalline nanowires of zinc, cadmium, cobalt, and lead are obtained by the decomposition of metal acetates. By reacting acid-treated carbon nanotubes with vapors of metal halides, followed by reaction with water and calcination chemically-bonded oxide layers can be obtained on the nanotubes. A similar procedure has been employed to prepare chemically-bonded oxide layers on Al2O3, ZnO, and silicon nanowires by the reaction of the metal halides with the surface hydroxyl groups present on these nanowire surfaces. PMID:17654926

Govindaraj, A; Vivekchand, S R C; Rao, C N R

2007-06-01

246

Multicomponent reactions and ionic liquids: a perfect synergy for eco-compatible heterocyclic synthesis.  

PubMed

The efficiency of a chemical synthesis can be nowadays measured, not only by parameters like selectivity and overall yield, but also by its raw material, time, human resources and energy requirements, as well as the toxicity and hazard of the chemicals and the protocols involved. The development of multicomponent reactions (MCRs) in the presence of task-specific ionic liquids (ILs), used not only as environmentally benign reaction media, but also as catalysts, is a new approach that meet with the requirements of sustainable chemistry. The aim of this tutorial review is to highlight the synergistic effect of the combined use of MCRs and ILs for the development of new eco-compatible methodologies for heterocyclic chemistry. PMID:20963207

Isambert, Nicolas; Sanchez Duque, Maria del Mar; Plaquevent, Jean-Christophe; Génisson, Yves; Rodriguez, Jean; Constantieux, Thierry

2011-03-01

247

The design and synthesis of artificial photosynthetic antennas, reaction centres and membranes.  

PubMed Central

Artificial antenna systems and reaction centres synthesized in our laboratory are used to illustrate that structural and thermodynamic factors controlling energy and electron transfer in these constructs can be modified to optimize performance. Artificial reaction centres have been incorporated into liposomal membranes where they convert light energy to vectorial redox potential. This redox potential drives a Mitchellian, quinone-based, proton-transporting redox loop that generates a Deltamu H(+) of ca. 4.4 kcal mol(-1) comprising DeltapH ca. 2.1 and Deltapsi ca. 70 mV. In liposomes containing CF(0)F(1)-ATP synthase, this system drives ATP synthesis against an ATP chemical potential similar to that observed in natural systems. PMID:12437888

Moore, T A; Moore, A L; Gust, D

2002-01-01

248

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

249

Vulcanism, mercury-sensitized photo-reactions and abiogenetic synthesis - A theoretical treatment  

NASA Technical Reports Server (NTRS)

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 1P1 and 6 3P1 resonance states and the high vapor pressure (greater than 0.001 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 a proposal that Hg-sensitized ultraviolet photo-reactions may have played a significant part in abiogenetic organic synthesis on the primative earth.

Siegel, S. M.; Siegel, B. Z.

1976-01-01

250

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

251

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

252

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

253

Enzymatic synthesis of amoxicillin: avoiding limitations of the mechanistic approach for reaction kinetics.  

PubMed

A recurrent doubt that occurs to the enzyme-kinetics modeler is, When should I stop adding parameters to my mechanistic model in order to fit a non-conventional behavior? This problem becomes more and more involving when the complexity of the reaction network increases. This work intends to show how the use of artificial neural networks may circumvent the need of including an overwhelming number of parameters in the rate equations obtained through the classical, mechanistic approach. We focus on the synthesis of amoxicillin by the reaction of p-OH-phenylglycine methyl ester and 6-aminopenicillanic acid, catalyzed by penicillin G acylase immobilized on glyoxyl-agarose, at 25 degrees C and pH 6.5. The reaction was carried on a batch reactor. Three kinetic models of this system were compared: a mechanistic, a semi-empiric, and a hybrid-neural network (NN). A semi-empiric, simplified model with a reasonable number of parameters was initially built-up. It was able to portray many typical process conditions. However, it either underestimated or overestimated the rate of synthesis of amoxicillin when substrates' concentrations were low. A more complex, full-scale mechanistic model that could span all operational conditions was intractable for all practical purposes. Finally, a hybrid model, that coupled artificial neural networks (NN) to mass-balance equations was established, that succeeded in representing all situations of interest. Particularly, the NN could predict with accuracy reaction rates for conditions where the semi-empiric model failed, namely, at low substrate concentrations, a situation that would occur, for instance, at the end of a fed-batch industrial process. PMID:12378603

Gonçalves, Luciana R B; Sousa, Ruy; Fernandez-Lafuente, Roberto; Guisan, Jose M; Giordano, Raquel L C; Giordano, Roberto C

2002-12-20

254

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

255

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

PubMed

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

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

2014-01-01

256

Fischer-Tropsch synthesis in supercritical reaction media. Progress report, July 10, 1992--September 30, 1992  

SciTech Connect

The goal of this research is to thoroughly investigate the feasibility of using supercritical fluid (SCF) solvent medium for carrying out Fischer-Tropsch (FT) synthesis. Research will address the systematic experimental investigations of FT synthesis over supported Fe and Co catalysts in a CSTR and in a fixed-bed reactor at typical synthesis temperatures (240-260{degrees}C). The SCF medium to be employed is n-Hexane (P{sub c} = 29.7 bar; {Tc} = 233.7{degrees}C), while n-Hexadecane will be employed as the liquid reaction medium. Overall conversion, product distribution and catalyst deactivation will be measured in each case for various feed H{sub 2}/CO ratios ranging from 0.5 to 2. Product analyses will be carried out using GC/TCD, GC/FID and GC/MS systems. The fresh and used catalysts will be characterized with respect to active metal dispersion, surface area and pore size distribution.

Subramaniam, B.

1992-10-01

257

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...

258

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

259

Synthesis of nanocrystalline yttrium iron garnet by low temperature solid state reaction  

SciTech Connect

In this work, nanocrystalline yttrium iron garnet powders were produced by low temperature solid state reaction. The phase evolution during the procedure was determined from the thermogravimetric and differential thermal analysis, and the x-ray diffraction patterns. The results of transmission electron microscopy indicated that the prepared powders exhibited grain size at the nano-level of 20 {approx} 40 nm. Dense ceramics with a theoretical density of around 98% were obtained from the prepared powders after sintering at 1280 deg. C, a relative low sintering temperature compared with conventional ceramic processes, and the saturation magnetizations of sintered samples were also determined. - Research Highlights: {yields}No sol or gel form during the synthesis processing using nitrates and citric acid as raw materials. {yields}The synthesis method needs a low heating temperature (700 deg. C) compared with conventional solid state reaction. {yields}The product is a single phase with homogeneous size distribution and nano grains (20 {approx} 40 nm) confirmed by TEM. {yields}Dense YIG ceramic can be sintered at a low temperature (1280 deg. C) compared with that in conventional processing.

Yu Hongtao, E-mail: yuhongtao@swust.edu.cn; Zeng Liwen; Lu Chao; Zhang Wenbo; Xu Guangliang

2011-04-15

260

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

261

Streamlined ammonia removal from wastewater using biological deammonification process  

Technology Transfer Automated Retrieval System (TEKTRAN)

In this work we evaluated biological deammonification process to more economically remove ammonia from livestock wastewater. The process combines partial nitritation (PN) and anammox. The anammox is a biologically mediated reaction that oxidizes ammonia (NH4+) and releases di-nitrogen gas (N2) unde...

262

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

263

?-Hydroxy-?-lactones as nucleophiles in the Nicholas reaction for the synthesis of oxepene rings. Enantioselective formal synthesis of (-)-isolaurepinnacin and (+)-rogioloxepane A.  

PubMed

The enantioselective formal synthesis of (-)-isolaurepinnacin and (+)-rogioloxepane A has been achieved. The key steps are an intermolecular Nicholas reaction with a ?-hydroxy-?-lactone as the nucleophile, to form branched linear ethers, and an olefin ring-closing metathesis to obtain the oxepene core. PMID:24573686

Rodríguez-López, Julio; Ortega, Nuria; Martín, Victor S; Martín, Tomás

2014-04-11

264

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

265

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

266

Rapid synthesis of highly functionalised ?-amino amides and medium ring lactones using multicomponent reactions of amino alcohols and isocyanides.  

PubMed

Four-component reactions between amino alcohols, aldehydes, isocyanides and thiols proceed rapidly under microwave or conventional heating at 60 °C in methanol. The reaction is successful with a wide range of components and gives access to potentially drug-like products containing amine, amide and thioether functionality in moderate to excellent yield. The reaction conditions are also applicable to the synthesis of a range of 8-10 membered medium ring lactones via three-component reactions of amino alcohols, isocyanides and acid-aldehydes. Incorporation of L-prolinol as the amino alcohol component in each case gives access to multicomponent products with moderate to high diastereoselectivity. PMID:22076284

Bachman, Martin; Mann, Sam E; Sheppard, Tom D

2012-01-01

267

Ammonium accumulation during a silicate-limited diatom bloom indicates the potential for ammonia emission events  

E-print Network

be disproportionately important for air­sea ammonia flux. Once in the atmosphere, ammonia neutralizes acidity in neutralization reactions, particularly with acidic sulfate aerosol. It has been shown that new particle formation and Galloway, 1993). As the predominant naturally occurring base in the atmosphere, ammonia is important

Hansell, Dennis

268

Preparation of double-doped BaCeO 3 and its application in the synthesis of ammonia at atmospheric pressure  

Microsoft Academic Search

Perovskite-type oxides BaCe0.90Sm0.10O3?? (BCS) and BaCe0.80Gd0.10Sm0.10O3?? (BCGS) were synthesized by the sol–gel method and characterized by thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Using the sintered samples as solid electrolytes and silver–palladium alloy as electrodes, ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in a solid-state proton-conducting cell reactor. The

ZhiJie Li; RuiQuan Liu; JiDe Wang; Zheng Xu; YaHong Xie; BenHui Wang

2007-01-01

269

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...

270

Ring Walking/Oxidative Addition Reactions for the Controlled Synthesis of Conjugated Polymers  

SciTech Connect

Power conversion efficiencies of plastic solar cells depend strongly on the molecular weight characteristics of the semiconducting polymers used for their fabrication. The synthesis of these materials typically relies on transition metal mediated catalytic reactions. In many instances, the ideal structures cannot be attained because of deficiencies in these reactions, particularly when it comes to being able to achieve high number average molecular weights and narrow molecular weight distributions. Another important conjugated polymer structure of interest is one in which a single functional group is attached at the end group of the chain. Such systems would be ideal for modifying surface properties at interfaces and for labeling biomolecular probes used in fluorescent biosensors. To respond to the challenges above, our efforts have centered on the design of homogenous transition metal complexes that are easy to prepare and effective in carrying out living, or quasi-living, condensative chain polymerization reactions. The key mechanistic challenge for the success of this reaction is to force the insertion of one monomer unit at a time via a process that involves migration of the transition metal-containing fragment to one terminus of the polymer chain. Chain growth characteristics are therefore favored when the metal does not dissociate from the newly formed reductive elimination product. We have proposed that dissociation is disfavored by the formation of a Ï?-complex, in which the metal can sample various locations of the electronically delocalized framework, a process that we term â??ring-walkingâ?, and find the functionality where oxidative addition takes place. Success has been achieved in the nickel-mediated cross coupling reaction of Grignard reagents with aromatic halides by using bromo[1,2-bis(diphenylphosphino)ethane]phenylnickel. This reagent can yield poly(thiophene)s (one of the most widely used type of polymer in plastic solar cells) with excellent stereoregularity and molecular weight distributions with polydispersities that are consistent with a living polymerization sequence. Another important objective of this program concerned the use of these new catalysts and improved mechanistic insight for the synthesis of specific polymeric materials with prespecified properties.

Bazan, Guillermo C

2012-04-03

271

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

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

2012-01-01

272

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

273

Study of the temperature-programmed reaction synthesis of early transition metal carbide and nitride catalyst materials from oxide precursors  

Microsoft Academic Search

The synthesis of high surface area carbide and nitride materials from binary and ternary oxides of vanadium, niobium, tantalum, molybdenum, and tungsten, suitable for use as catalysts for a wide range of reactions, has been investigated via the temperature-programmed reaction (TPRe) method, in various gas mixtures. TPRe of oxides in CHâ\\/Hâ, CâHâ\\/Hâ, or NHâ yield materials with surface areas >

John B. Claridge; Andrew P. E. York; Attila J. Brungs; Malcolm L. H. Green

2000-01-01

274

Toward safer methodologies for the synthesis of polyheterocyclic systems: intramolecular arylation of arenes under Mizoroki-Heck reaction conditions.  

PubMed

[reaction: see text] A straightforward synthesis of ibudilast-related pyrazolo[1,5-f]phenanthridines is accomplished by a tandem amine-exchange/heterocyclization of arylenaminones followed by an intramolecular biaryl coupling of the so-formed diarylpyrazoles. The direct, environmentally convenient ring-closure of the latter pyrazole intermediates, which show a close resemblance to the antiinflammatory drug celecoxib, is efficiently performed under Mizoroki-Heck reaction conditions. PMID:12659582

Hernández, Susana; SanMartin, Raul; Tellitu, Imanol; Domínguez, Esther

2003-04-01

275

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). PMID:25278634

Joie, Céline; Deckers, Kristina; Enders, Dieter

2014-01-01

276

AMMONIA CONCENTRATIONS IN PINK SALMON, ONCORHYNCHUS GORBUSCHA,  

E-print Network

Agency [EPA] 1974). The EPA method was modified by stabilizing the heat source during the reaction from the gravel is critical for survival ofyoung salmon. The young salmon have a higher rate the end of yolk absorption excrete ammonia at a higher rate than eggs or early alevins (Rice and Stokes

277

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

278

Design and Synthesis of a Photoswitchable Gated Hemicarcerand and Computational Investigations of Stereoselective Organic Reactions  

E-print Network

catalyze the enantioselective allylboration reaction betweenenantioselective allylboration and propargylation reactions.enantioselective catalysis development for allylboration and propargylation reactions.

Wang, Hao

2013-01-01

279

Development of an Asymmetric Trimethylenemethane Cycloaddition Reaction: Application in the Enantioselective Synthesis of Highly Substituted Carbocycles  

PubMed Central

A protocol for the enantioselective [3+2] cycloaddition of trimethylenemethane with electron-deficient olefins has been developed. The synthesis of novel phosphoramidite ligands was critical in this effort, and the preparation and reactivity of these ligands is detailed. The evolution of the ligand design, commencing with acyclic amine-derived phosphoramidites and leading to cyclic pyrrolidine and azetidine structures is discussed. The conditions developed to effect an asymmetric TMM reaction using 2-trimethylsilylmethyl allyl acetate were shown to be tolerant of a wide variety of alkene acceptors, providing the desired methylenecyclopentanes with high levels of enantioselectivity. The donor scope was also explored and substituted systems were tolerated, including one bearing a nitrile moiety. These donors were reactive with unsaturated acylpyrroles, giving the product cyclopentane rings bearing three stereocenters in high enantioselectivity and complete diastereoselectivity. PMID:21936576

Trost, Barry M.; Silverman, Steven M.; Stambuli, James P.

2011-01-01

280

Synthesis of metal-semiconductor core-shell nanoparticles using electrochemical surface-limited reactions.  

PubMed

We report the synthesis of Au/CuI and Au/CdS core-shell nanoparticle (NP) thin films using codeposition and electrochemical atomic layer deposition (EC-ALD). Au nanoparticle films were prepared on glassy carbon supports by depositing alternating layers of poly(diallyl dimethylammonium)-stabilized Au nanoparticles and CoP(2)W(17)O(61)(8-) polyoxometallate interlayers. From there, CuI was deposited onto the surface of Au nanoparticles using electrochemical atomic layer deposition, while CdS films were grown by an atom-by-atom codeposition method. The semiconductor-Au core-shell nanoparticles were characterized by electrochemistry, photoluminescence spectroscopy, and Raman spectroscopy. Our results indicate that the semiconductors deposit onto the AuNP surface by surface limited electrochemical reactions. PMID:19063617

Gu, Chaokang; Xu, Hui; Park, Minseo; Shannon, Curtis

2009-01-01

281

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

282

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

283

The hydroboration reaction as a key for a straightforward synthesis of new MRI-NCT agents.  

PubMed

In this study the hydroboration reaction has been exploited to produce in only four steps a new lipophilic GdBNCT/MRI agent (). As a matter of fact, the formation of a new B-C bond to link the decaborane with the lipophilic moiety greatly simplifies the synthesis of with respect to the previously reported dual agents. The complexes obtained ( and ) have been fully characterised from the relaxometric point of view and, after disaggregation with HP?CD, both isomers display high affinity for low density lipoproteins (LDLs) that can be exploited as specific carriers of these therapeutic and diagnostic agents for tumour cells. The LDL loading capacity is different for the two isomers. In fact, LDL can be loaded with 75 and 300 units of and , respectively, and for this reason, the isomer results to be the best candidate to perform MRI guided BNCT. PMID:25645198

Boggio, Paolo; Toppino, Antonio; Geninatti Crich, Simonetta; Alberti, Diego; Marabello, Domenica; Medana, Claudio; Prandi, Cristina; Venturello, Paolo; Aime, Silvio; Deagostino, Annamaria

2015-03-01

284

Synthesis and reactions of 7-fluoro-4-methyl-6-nitro-2-oxo-2H-1-benzopyran-3-carboxylic acid: a novel scaffold for combinatorial synthesis of coumarins.  

PubMed

7-Fluoro-4-methyl-6-nitro-2-oxo-2H-1-benzopyran-3-carboxylic acid has been prepared as a novel scaffold for combinatorial synthesis of coumarins. The scaffold has three points of diversity. The optimal conditions for its reactions with different nucleophiles in solid phase were obtained. Sixteen coumarin derivatives with different structures were designed and synthesized in solid phase to demonstrate its application as a scaffold for combinatorial synthesis of coumarins. Thirteen of these derivatives were obtained in high yields. Many of these model compounds fluoresce. Combinatorial libraries constructed with this novel scaffold may have interesting biological or physical properties. PMID:14714994

Song, Aimin; Zhang, Jinhua; Lam, Kit S

2004-01-01

285

Library-friendly synthesis of fluorinated ketones through functionalized hydration of alkynes and investigation of the reaction mechanism  

Microsoft Academic Search

A library-friendly synthesis of ?-substituted-?-fluoroketones through functionalized hydration of alkynes in one pot under mild conditions is reported. The ready availability of alkynes and organoboronic acids makes this reaction quite attractive. We also studied the key intermediate—a fluorinated cationic gold species—using in situ NMR spectroscopy and ESI-high resolution mass spectrometry.

Bo Xu; Weibo Wang; Gerald B. Hammond

2011-01-01

286

Synthesis and application of task-specific ionic liquids used as catalysts and\\/or solvents in organic unit reactions  

Microsoft Academic Search

This paper took various types of the task-specific ionic liquids as the main to review their synthesis and application to organic unit reactions from the point of view of development and practical utility. The economical task-specific ionic liquids were also brought forward.

Caibo Yue; Dong Fang; Lin Liu; Ting-Feng Yi

2011-01-01

287

Microwave-Enhanced Organic Syntheses for the Undergraduate Laboratory: Diels-Alder Cycloaddition, Wittig Reaction, and Williamson Ether Synthesis  

ERIC Educational Resources Information Center

Microwave heating enhanced the rate of three reactions typically performed in our undergraduate organic chemistry laboratory: a Diels-Alder cycloaddition, a Wittig salt formation, and a Williamson ether synthesis. Ninety-minute refluxes were shortened to 10 min using a laboratory-grade microwave oven. In addition, yields improved for the Wittig…

Baar, Marsha R.; Falcone, Danielle; Gordon, Christopher

2010-01-01

288

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

289

Synthesis of Polyhydroxylated Piperidine and Pyrrolidine Peptidomimetics via One-Pot Sequential Lactam Reduction/Joullié-Ugi Reaction.  

PubMed

A direct approach to the synthesis of polyhydroxylated piperidine and pyrrolidine peptidomimetics is described. The presented strategy is based on one-pot reduction of sugar-derived lactams with Schwartz's reagent followed by a multicomponent Ugi-Joullié reaction. PMID:25768203

Szcze?niak, Piotr; Maziarz, El?bieta; Stecko, Sebastian; Furman, Bart?omiej

2015-04-01

290

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....

291

Synthesis of 6-(Arylthio)phenanthridines by Copper-Catalyzed Tandem Reactions of 2-Biaryl Isothiocyanates with Diaryliodonium Salts.  

PubMed

A novel copper-catalyzed tandem C-S/C-C bond-forming reaction of 2-biaryl isothiocyanates with diaryliodonium salts was developed. This is the first general approach to synthesize phenanthridines from 2-biaryl isothiocyanates. This methodology has been successfully applied to the synthesis of trisphaeridine. PMID:25719267

Guo, Weisi; Li, Shoulei; Tang, Lin; Li, Ming; Wen, Lirong; Chen, Chao

2015-03-01

292

Control of chemical reactions and synthesis by low-energy electrons.  

PubMed

Controlling the outcome of reactions is a central issue of chemical research. Physical tools can achieve this if they are able to precisely dissociate specific bonds of a molecule. However, to control synthesis, such tools must induce the formation of new bonds between two reactants to yield a more complex product. In the ideal case of an atom efficient synthesis, this product would contain all or at least most of the initial material. An electron beam is a physical tool that is capable of preparing molecules in reactive states or, at low electron energies, of initiating highly selective bond dissociation. The resulting fragments in turn can react with other molecules to yield stable products. This tutorial review focuses in particular on such low-energy electron-initiated molecular syntheses and their applications in the modification of surfaces. It thus emphasizes strategies towards the controlled and predictable formation of more complex products from small reactants initiated by interaction with low-energy electrons either through selective bond dissociation or formation of specific reactive molecular species. However, selective bond dissociation is not always desirable. This is briefly illustrated by the case of electron beam induced deposition where additional strategies may be required to control product formation. PMID:24088739

Böhler, Esther; Warneke, Jonas; Swiderek, Petra

2013-12-21

293

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.

294

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

295

Diastereoselective [2+2]-cycloaddition reactions of unsymmetrical cyclic ketenes with imines: synthesis of modified prolines and theoretical study of the reaction mechanism.  

PubMed

The synthesis of enantiomerically pure modified proline derivatives was achieved by using spiro beta-lactams as starting material that were prepared in turn by the [2+2]-cycloaddition of unsymmetrical cyclic ketenes with optically active imines. A theoretical study of the [2+2]-cycloaddition reaction, using density-functional methods, gave insights on the origin of the observed stereoselectivity of the Staudinger reaction. The spiro beta-lactams were transformed in the N-Boc derivatives and subjected to nucleophilic ring opening, affording the corresponding enantiomerically pure modified proline derivatives, isolated as orthogonally protected compounds. PMID:15471445

Macías, Alberto; Alonso, Eduardo; Del Pozo, Carlos; Venturini, Alessandro; González, Javier

2004-10-15

296

Effect of the reaction temperature on the transglycosylation reactions catalyzed by the cyclodextrin glucanotransferase from Bacillus macerans for the synthesis of large-ring cyclodextrins  

Microsoft Academic Search

The synthesis of cyclodextrins with from 6 to more than 50 glucose units by cyclodextrin glucanotransferase (CGTase, EC 2.4.1.19) from Bacillus macerans was investigated. Analysis of the synthesized cyclic ?-1,4-glucan products showed that a higher yield of large-ring cyclodextrins were obtained with a reaction temperature of 60 °C compared to 40 °C. The yield of large-ring cyclodextrins obtained at 60

Qingsheng Qi; Xiaoyan She; Tomohiro Endo; Wolfgang Zimmermann

2004-01-01

297

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

298

Chemical pathways for the formation of ammonia in Hanford wastes  

SciTech Connect

This report reviews chemical reactions leading to the formation of ammonia in Hanford wastes. The general features of the chemistry of the organic compounds in the Hanford wastes are briefly outlined. The radiolytic and thermal free radical reactions that are responsible for the initiation and propagation of the oxidative degradation reactions of the nitrogen-containing complexants, trisodium HEDTA and tetrasodium EDTA, are outlined. In addition, the roles played by three different ionic reaction pathways for the oxidation of the same compounds and their degradation products are described as a prelude to the discussion of the formation of ammonia. The reaction pathways postulated for its formation are based on tank observations, laboratory studies with simulated and actual wastes, and the review of the scientific literature. Ammonia derives from the reduction of nitrite ion (most important), from the conversion of organic nitrogen in the complexants and their degradation products, and from radiolytic reactions of nitrous oxide and nitrogen (least important). Reduction of nitrite ions is believed to be the most important source of ammonia. Whether by radiolytic or thermal routes, nitrite reduction reactions proceed through nitrogen dioxide, nitric oxide, the nitrosyl anion, and the hyponitrite anion. Nitrite ion is also converted into hydroxylamine, another important intermediate on the pathway to form ammonia. These reaction pathways additionally result in the formation of nitrous oxide and molecular nitrogen, whereas hydrogen formation is produced in a separate reaction sequence.

Stock, L.M.; Pederson, L.R.

1997-09-01

299

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

300

Multicomponent versus domino reactions: One-pot free-radical synthesis of ?-amino-ethers and ?-amino-alcohols  

PubMed Central

Summary Following an optimized multicomponent procedure, an aryl amine, a ketone, and a cyclic ether or an alcohol molecule are assembled in a one-pot synthesis by nucleophilic radical addition of ketyl radicals to ketimines generated in situ. The reaction occurs under mild conditions by mediation of the TiCl4/Zn/t-BuOOH system, leading to the formation of quaternary ?-amino-ethers and -alcohols. The new reaction conditions guarantee good selectivity by preventing the formation of secondary products. The secondary products are possibly derived from a competitive domino reaction, which involves further oxidation of the ketyl radicals. PMID:25670994

Rossi, Bianca; Prosperini, Simona

2015-01-01

301

Removal of ammonia solutions used in catalytic wet oxidation processes.  

PubMed

Ammonia (NH(3)) is an important product used in the chemical industry, and is common place in industrial wastewater. Industrial wastewater containing ammonia is generally either toxic or has concentrations or temperatures such that direct biological treatment is unfeasible. This investigation used aqueous solutions containing more of ammonia for catalytic liquid-phase oxidation in a trickle-bed reactor (TBR) based on Cu/La/Ce composite catalysts, prepared by co-precipitation of Cu(NO(3))(2), La(NO(3))(2), and Ce(NO(3))(3) at 7:2:1 molar concentrations. The experimental results indicated that the ammonia conversion of the wet oxidation in the presence of the Cu/La/Ce composite catalysts was determined by the Cu/La/Ce catalyst. Minimal ammonia was removed from the solution by the wet oxidation in the absence of any catalyst, while approximately 91% ammonia removal was achieved by wet oxidation over the Cu/La/Ce catalyst at 230 degrees C with oxygen partial pressure of 2.0 MPa. Furthermore, the effluent streams were conducted at a liquid hourly space velocity of under 9 h(-1) in the wet catalytic processes, and a reaction pathway was found linking the oxidizing ammonia to nitric oxide, nitrogen and water. The solution contained by-products, including nitrates and nitrites. Nitrite selectivity was minimized and ammonia removal maximized when the feed ammonia solution had a pH of around 12.0. PMID:12781232

Hung, Chang Mao; Lou, Jie Chung; Lin, Chia Hua

2003-08-01

302

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

PubMed

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

2008-10-01

303

Biogenic synthesis of calcium oxalate crystal by reaction of calcium ions with spinach lixivium.  

PubMed

In this paper, we report a biogenic synthesis protocol for preparation of calcium oxalate (CaC2O4, CaOx) crystal at room temperature by a simple protein-mediated reaction of aqueous Ca2+ ions with the C2O4(2-) ions spontaneously released from spinach. The aggregation of calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) with a rod-like morphology was mainly formed in the spinach root lixivium, and the proportion of COM crystal in the aggregation increased with the concentration of Ca2+ ions increasing, however, spindle-shaped crystal was mainly obtained in the spinach leaf lixivium and the content of COM in the product was higher than that obtained in the root lixivium with the similar concentration of Ca2+ ions. COM phase disappeared and only COD crystal with morphology of tetragonal bipyramidal prisms presented in the product when the leaf lixivium was replaced by the leaf broth. The biomolecules such as proteins with molecular weight of 31kDa liberated from the spinach root are negative-charged, which played important roles for the control of CaOx crystal growth in the root lixivium corresponding to the changes of protein secondary structures after reaction with Ca2+ ions. This research was potentially important for unraveling the biomineralization mechanism of CaOx crystal. PMID:20399625

Li, Shi-Kuo; Xie, An-Jian; Shen, Yu-Hua; Yu, Xue-Rong; Hu, Gang

2010-07-01

304

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

305

The Pauson-Khand Reaction as a New Entry to the Synthesis of Bridged Bicyclic Heterocycles: Application to the Enantioselective Total Synthesis of (?)-Alstonerine  

PubMed Central

The first application of the Pauson-Khand reaction (PKR) to the synthesis of azabridged bicyclic structures is described. Compounds containing azabicyclo[3.3.1]nonane and azabicyclo[3.2.1]octane rings fused to cyclopentenones were efficiently constructed via the PKR of cis-2,6-disubstituted N-acyl piperidine enyne substrates, many of which can be readily prepared from 4-methoxypyridine in a few steps. Moreover, the PKR of cis-2,6-disubstituted piperazine enynes allowed the preparation of diazabicyclo[3.3.1]nonanes fused to cyclopentenones. This new strategy for the synthesis of azabridged bicyclic frameworks was exploited as a key step in a concise, enantioselective total synthesis of the macroline alklaoid (?)-alstonerine. PMID:19122869

Miller, Kenneth A.; Shanahan, Charles S.; Martin, Stephen F.

2008-01-01

306

Monodisperse metal nanoparticle catalysts on silica mesoporous supports: synthesis, characterizations, and catalytic reactions  

SciTech Connect

The design of high performance catalyst achieving near 100% product selectivity at maximum activity is one of the most important goals in the modern catalytic science research. To this end, the preparation of model catalysts whose catalytic performances can be predicted in a systematic and rational manner is of significant importance, which thereby allows understanding of the molecular ingredients affecting the catalytic performances. We have designed novel 3-dimensional (3D) high surface area model catalysts by the integration of colloidal metal nanoparticles and mesoporous silica supports. Monodisperse colloidal metal NPs with controllable size and shape were synthesized using dendrimers, polymers, or surfactants as the surface stabilizers. The size of Pt, and Rh nanoparticles can be varied from sub 1 nm to 15 nm, while the shape of Pt can be controlled to cube, cuboctahedron, and octahedron. The 3D model catalysts were generated by the incorporation of metal nanoparticles into the pores of mesoporous silica supports via two methods: capillary inclusion (CI) and nanoparticle encapsulation (NE). The former method relies on the sonication-induced inclusion of metal nanoparticles into the pores of mesoporous silica, whereas the latter is performed by the encapsulation of metal nanoparticles during the hydrothermal synthesis of mesoporous silica. The 3D model catalysts were comprehensively characterized by a variety of physical and chemical methods. These catalysts were found to show structure sensitivity in hydrocarbon conversion reactions. The Pt NPs supported on mesoporous SBA-15 silica (Pt/SBA-15) displayed significant particle size sensitivity in ethane hydrogenolysis over the size range of 1-7 nm. The Pt/SBA-15 catalysts also exhibited particle size dependent product selectivity in cyclohexene hydrogenation, crotonaldehyde hydrogenation, and pyrrole hydrogenation. The Rh loaded SBA-15 silica catalyst showed structure sensitivity in CO oxidation reaction. In addition, Pt-mesoporous silica core-shell structured NPs (Pt{at}mSiO{sub 2}) were prepared, where the individual Pt NP is encapsulated by the mesoporous silica layer. The Pt{at}mSiO{sub 2} catalysts showed promising catalytic activity in high temperature CO oxidation. The design of catalytic structures with tunable parameters by rational synthetic methods presents a major advance in the field of catalyst synthesis, which would lead to uncover the structure-function relationships in heterogeneous catalytic reactions.

Somorjai, G.A.

2009-09-14

307

Chemical pathways for the formation of ammonia in Hanford wastes  

SciTech Connect

This report reviews chemical reactions leading to the formation of ammonia in Hanford wastes. The general features of the chemistry of the organic compounds in the Hanford wastes are briefly outlined. The radiolytic and thermal free radical reactions that are responsible for the initiation and propagation of the oxidative degradation reactions of the nitrogen-containing complexants, trisodium HEDTA and tetrasodium EDTA, are outlined. In addition, the roles played by three different ionic reaction pathways for the oxidation of the same compounds and their degradation products are described as a prelude to the discussion of the formation of ammonia. The reaction pathways postulated for its formation are based on tank observations, laboratory studies with simulated and actual wastes, and the review of the scientific literature. Ammonia derives from the reduction of nitrite ion (most important), from the conversion of organic nitrogen in the complexants and their degradation products, and from radiolytic reactions of nitrous oxide and nitrogen (least important).

Stock, L.M.; Pederson, L.R.

1997-12-01

308

Ammonia Release on ISS  

NASA Technical Reports Server (NTRS)

Crew: Approximately 53% metabolic load Product of protein metabolism Limit production of ammonia by external regulation NOT possbile Payloads Potential source Scientific experiments Thorough safety review ensures sufficient levels of containment

Macatangay, Ariel

2009-01-01

309

Ammonia Clouds on Jupiter  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] Click on the image for movie of Ammonia Ice Clouds on Jupiter

In this movie, put together from false-color images taken by the New Horizons Ralph instrument as the spacecraft flew past Jupiter in early 2007, show ammonia clouds (appearing as bright blue areas) as they form and disperse over five successive Jupiter 'days.' Scientists noted how the larger cloud travels along with a small, local deep hole.

2007-01-01

310

Synthesis of ordered mesoporous crystalline CuS and Ag2S materials via cation exchange reaction.  

PubMed

Cation exchange reaction is a strong tool for the synthesis of new ionic nanomaterials. Most of them are isolated nanoparticles with simple geometric features, such as nanodots, nanorods and nanospheres. In this work, we demonstrated that ordered mesoporous CdS with a complex cubic Ia3d gyroidal 3D bicontinuous porous structure and large particle size can be successfully converted to crystalline CuS and Ag2S materials via cation exchange reaction without destroying the well-defined nanostructure. The change in crystal structure is an important factor for a successful conversion when the reaction is carried out without the presence of a silica template. In addition, the cation exchange reaction is sufficient for a complete compositional conversion, even when the mesostructured CdS precursor is embedded inside a mesoporous silica matrix. Our results indicate that cation exchange reaction may be applied to highly complex nanostructures with extremely large particle sizes. PMID:25684647

Wang, Jun; Xu, Weiming; Bao, Haifeng; Shi, Yifeng

2015-02-26

311

Formation and reaction of ammonium sulfate salts on V 2O 5\\/AC catalyst during selective catalytic reduction of nitric oxide by ammonia at low temperatures  

Microsoft Academic Search

The formation rate and reaction rate of ammonium sulfate salts on V2O5\\/AC catalyst during selective catalytic reduction (SCR) of NO with NH3 at low temperatures were studied using elemental analysis, transient response, and TPR methods. In the presence of SO2 and H2O, ammonium sulfate salts deposit on the surface of the V2O5\\/AC catalyst, block the pores of the catalyst, and

Zhanggen Huang; Zhenping Zhu; Zhenyu Liu; Qingya Liu

2003-01-01

312

A photoisomerization-coupled asymmetric Stetter reaction: application to the total synthesis of three diastereomers of (?)-cephalimysin A  

PubMed Central

The total synthesis of 8-epi, 8,9-epi, and 9-epi-(?)-cephalimysin A is described. Our catalytic enantioselective synthesis takes advantage of a novel tandem photoisomerization/Stetter reaction. The approach provides rapid access to the desired spirofuranone lactam core in good yield and excellent enantioselectivity. A late stage oxidation strategy allows for flexible access to three of the four diastereomers of cephalimysin A. Access to the epimers provides further support for the correction of the initially proposed relative stereochemistry of cephalimysin A. PMID:24224080

Lathrop, Stephen P.

2013-01-01

313

Improving The Efficiency Of Ammonia Electrolysis For Hydrogen Production  

NASA Astrophysics Data System (ADS)

Given the abundance of ammonia in domestic and industrial wastes, ammonia electrolysis is a promising technology for remediation and distributed power generation in a clean and safe manner. Efficiency has been identified as one of the key issues that require improvement in order for the technology to enter the market phase. Therefore, this research was performed with the aim of improving the efficiency of hydrogen production by finding alternative materials for the cathode and electrolyte. 1. In the presence of ammonia the activity for hydrogen evolution reaction (HER) followed the trend Rh>Pt>Ru>Ni. The addition of ammonia resulted in lower rates for HER for Pt, Ru, and Ni, which have been attributed to competition from the ammonia adsorption reaction. 2. The addition of ammonia offers insight into the role of metal-hydrogen underpotential deposition (M-Hupd) on HER kinetics. In addition to offering competition via ammonia adsorption it resulted in fewer and weaker M-Hupd bonds for all metals. This finding substantiates the theory that M-Hupd bonds favor HER on Pt electrocatalyst. However, for Rh results suggest that M-Hupd bond may hinder the HER. In addition, the presence of unpaired valence shell electrons is suggested to provide higher activity for HER in the presence of ammonia. 3. Bimetals PtxM1-x (M = Ir, Ru, Rh, and Ni) offered lower overpotentials for HER compared to the unalloyed metals in the presence of ammonia. The activity of HER in the presence of ammonia follows the trend Pt-Ir>Pt-Rh>Pt-Ru>Pt-Ni. The higher activity of HER is attributed to the synergistic effect of the alloy, where ammonia adsorbs onto the more electropositive alloying metal leaving Pt available for Hupd formation and HER to take place. Additionally, this supports the theory that the presence of a higher number of unpaired electrons favors the HER in the presence of ammonia. 4. Potassium polyacrylate (PAA-K) was successfully used as a substitute for aqueous KOH for ammonia electrolysis. PAA-K allowed for a wider operating potential for the electrolytic cell while increasing the rate for HER at lower cell voltages. The conversion of ammonia improved from 16 % to 25 %, while the current efficiency for the consumption of ammonia increased from 92 +/- 1 % to 97 +/- 2 % by using PAA-K in lieu of KOH. The use of PAA-K also prevented the crossover of the hydrogen produced to the anode side, unlike aqueous KOH.

Palaniappan, Ramasamy

314

Development of a Suzuki Cross-Coupling Reaction between 2-Azidoarylboronic Pinacolate Esters and Vinyl Triflates To Enable the Synthesis of [2,3]-Fused Indole Heterocycles  

PubMed Central

The scope and limitations of a Suzuki reaction between 2-azidoarylboronic acid pinacolate esters and vinyl triflates are reported. This cross-coupling reaction enables the regioselective synthesis of indoles after a subsequent RhII2-catalyzed sp2-C–H bond amination reaction. PMID:24571492

2015-01-01

315

Ammonia diffusion through Nalophan™ bags.  

PubMed

The aim of the work is to verify the diffusion rate of ammonia through the Nalophan™ film that constitutes the sampling bag, considering storage times ranging from 1 to 26 h. The ammonia decay over time was evaluated using gas-chromatography for the quantification of ammonia concentration inside the bag. The research assesses the roles of both of ammonia and water concentration gradients at the polymeric film interface on the diffusion process. The results show that both the ammonia concentration gradient and, in a less pronounced way, the water concentration gradient are the main 'engines' of ammonia diffusion. Double bags seem to represent a simple solution for preventing ammonia losses during storage. Another interesting result concerns the role of the bag surface on the ammonia diffusion rate: the higher the surface/volume (S/V) ratio, the higher the ammonia diffusion rate through the polymeric film. PMID:24552718

Sironi, Selena; Eusebio, Lidia; Dentoni, Licinia; Capelli, Laura; Del Rosso, Renato

2014-01-01

316

Microwave enhanced palladium catalysed coupling reactions: a diversity-oriented synthesis approach to functionalised flavones.  

PubMed

Microwave enhanced diversity-oriented synthesis (MEDOS) using palladium catalysed protocols is introduced as a powerful new strategy for the synthesis of systematically modified small molecules and is highlighted by application to functionalised flavones. PMID:17345738

Fitzmaurice, Richard J; Etheridge, Zac C; Jumel, Emelie; Woolfson, Derek N; Caddick, Stephen

2006-12-14

317

Absolute asymmetric synthesis in enantioselective autocatalytic reaction networks: theoretical games, speculations on chemical evolution and perhaps a synthetic option.  

PubMed

The Soai reaction and the Viedma deracemization of racemic conglomerate crystal mixtures are experimental pieces of evidence of the ability of enantioselective autocatalytic coupled networks to yield absolute asymmetric synthesis. Thermodynamically open systems or systems with non-uniform energy distributions may lead to chiral final states and, in systems able to come into thermodynamic equilibrium with their surroundings, to kinetically controlled absolute asymmetric synthesis. The understanding of network parameters and of the thermodynamic scenarios that may lead to spontaneous mirror symmetry breaking (SMSB) could assist in the development of new methods for asymmetric synthesis and enantioselective polymerizations (e.g., replicators), and to frame reasonable speculations on the origin of biological homochirality. PMID:25352056

Ribó, Josep M; Blanco, Celia; Crusats, Joaquim; El-Hachemi, Zoubir; Hochberg, David; Moyano, Albert

2014-12-22

318

Synthesis of Ultrastable Copper Sulfide Nanoclusters via Trapping the Reaction Intermediate: Potential Anticancer and Antibacterial Applications.  

PubMed

Copper-based nanomaterials have broad applications in electronics, catalysts, solar energy conversion, antibiotics, tissue imaging, and photothermal cancer therapy. However, it is challenging to prepare ultrasmall and ultrastable CuS nanoclusters (NCs) at room temperature. In this article, a simple method to synthesize water-soluble, monodispersed CuS NCs is reported based on the strategy of trapping the reaction intermediate using thiol-terminated, alkyl-containing short-chain poly(ethylene glycol)s (HS-(CH2)11-(OCH2CH2)6-OH, abbreviated as MUH). The MUH-coated CuS NCs have superior stability in solutions with varied pH values and are stable in pure water for at least 10 months. The as-prepared CuS NCs were highly toxic to A549 cancer cells at a concentration of higher than 100 ?M (9.6 ?g/mL), making them be potentially applicable as anticancer drugs via intravenous administration by liposomal encapsulation or by direct intratumoral injection. Besides, for the first time, CuS NCs were used for antibacterial application, and 800 ?M (76.8 ?g/mL) CuS NCs could completely kill the E. coli cells through damaging the cell walls. Moreover, the NCs synthesized here have strong near-infrared (NIR) absorption and can be used as a candidate reagent for photothermal therapy and photoacoustic imaging. The method of trapping the reaction intermediate for simple and controlled synthesis of nanoclusters is generally applicable and can be widely used to synthesize many metal-based (such as Pt, Pd, Au, and Ag) nanoclusters and nanocrystals. PMID:25785786

Wang, Hong-Yin; Hua, Xian-Wu; Wu, Fu-Gen; Li, Bolin; Liu, Peidang; Gu, Ning; Wang, Zhifei; Chen, Zhan

2015-04-01

319

Analysis of instability in an industrial ammonia John C. Morud Sigurd Skogestad  

E-print Network

of the instability is the positive feedback from the heat recycle caused by the feed-e uent heat exchanger. We rstAnalysis of instability in an industrial ammonia reactor John C. Morud Sigurd Skogestad Chemical was an incident in an industrial plant, where the ammonia synthesis reactor became unstable with rapid temperature

Skogestad, Sigurd

320

Analysis of instability in an industrial ammonia John C. Morud Sigurd Skogestad \\Lambda  

E-print Network

point of this work was an incident in an industrial ammonia fixed bed synthesis reactor in GermanyAnalysis of instability in an industrial ammonia reactor John C. Morud Sigurd Skogestad \\Lambda, 1998 Revised version Submitted for publication in AIChE Journal 1 Abstract The starting point

Skogestad, Sigurd

321

Lessons from the Total Synthesis of (±) Phalarine: Insights Into the Mechanism of the Pictet–Spengler Reaction  

PubMed Central

The furanobisindole alkaloid, phalarine, possesses a unique structural framework within the alkaloid family of natural products. Our laboratory recently disclosed the racemic total synthesis of phalarine, featuring an efficient azaspiroindolenine rearrangement; this achievement is revisited in detail. Upon completion of the first-generation total synthesis, we explored some interesting mechanism-level issues with regard to the key azaspiroindolenine rearrangement. These investigations provided valuable insights into the mechanism of racemization during the azaspiroindolenine rearrangement en route to synthetic phalarine. In addition, in the course of these studies, we demonstrated the Pictet–Spengler capture reaction for C2-aryl indoles, and successfully isolated the elusive azaspiroindolenine intermediate of the Pictet–Spengler reaction. Key insights into the remarkably subtle stereoelectronics that govern this rearrangement for C2-arylated indoles are discussed. PMID:20711493

Trzupek, John D.; Li, Chaomin; Chan, Collin; Crowley, Brendan M.; Heimann, Annekatrin C.; Danishefsky, Samuel J.

2010-01-01

322

Ammonia formation from the reactions of H atoms with N atoms trapped in a solid N2 matrix at 10-30 K  

NASA Astrophysics Data System (ADS)

The reactions of H atoms with N atoms trapped in an N2 matrix were studied. The N2 matrix, containing N atoms, was formed by depositing plasma-activated N2 gas over the surface of a cryocooler at 10-30 K. The deposited active nitrogen was reacted with H atoms by spraying plasma-activated hydrogen gas over the surface of the deposited sample. It was found that the H atoms diffuse inside the N2 matrix and react with N atoms to form NH3 molecules. The diffusion of H atoms in N2 and H2O matrices at 10-30 K and the absence of H subtraction from NH3 by H atoms were confirmed by an electron spin resonance experiment.

Hiraoka, K.; Yamashita, A.; Yachi, Y.; Aruga, K.; Sato, T.; Muto, H.

1995-04-01

323

Reaction pathways and catalyst requirements in the synthesis of isobutanol from CO and H{sub 2}  

SciTech Connect

The synthesis of isobutanol and methanol from CO/H{sub 2} on K-Cu-Mg-CeO{sub x} catalysts is inhibited by CO{sub 2}, one of the reaction products. Alcohol coupling reactions show that CO{sub 2} decreases the rates of both alcohol dehydrogenation and base-catalyzed chain growth condensation reactions. Basic site density and reactivity were determined using a {sup 12}CO{sub 2}/{sup 13}CO{sub 2} isotopic transient technique. Addition of K to Cu-Mg-CeO{sub x} increases both basic site density and strength, but influences weakly the rate of base-catalyzed alcohol coupling reactions. Cu enhances the rates of alcohol dehydrogenation, and Ce increases Cu dispersion and stabilizes high surface area MgO. The cross-coupling reactions of acetaldehyde and {sup 13}C-labeled methanol produce singly-labeled propionaldehyde, suggesting that it forms by the condensation of acetaldehyde and a reactive intermediate derived from methanol. Isobutyraldehyde, a precursor to isobutanol, forms via the condensation of propionaldehyde and reactive C{sub 1} species resulting from methanol. Temperature-programmed surface reaction studies of preadsorbed ethanol have shown that CO decreases the rate of base-catalyzed self-condensation reactions of ethanol to acetone, possibly due to the poisoning of basic and metal sites by the CO{sub 2} formed from CO by water-gas shift or Boudouard reactions.

Xu, M.; Stephens, B.L.; Gines, M.J.L.; Iglesia, E. [Univ. of California, Berkeley, CA (United States). Dept. of Chemical Engineering

1996-12-31

324

Synthesis of a Library of “Lead-Like” ?-Lactams by a One Pot, Four-Component Reaction  

PubMed Central

The synthesis of a pilot scale library of 116 structurally diverse ?-lactams is reported. The library core structure emanates from a ?-lactam forming one-pot, four-component reaction of ammonium acetate, p-methoxythiophenol, p-methoxybenzaldehyde and maleic anhydride. Structural diversity then arises from amide coupling, thioaryl cleavage, N-functionalization and heterocycle forming reactions on this core structure. Computational analysis reveals that the library contains molecular properties and shape diversity suitable for drug lead and biological probe discovery. PMID:23682712

Martin, Kevin S.; Di Maso, Michael J.; Fettinger, James C.

2013-01-01

325

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

326

Myocardial synthesis of prostaglandin-like substances and coronary reactions to cardiostimulation and to hypoxia.  

PubMed Central

1 Continuous recording of cardiac contractions and coronary flow from isolated perfused hearts of rats permitted the study of coronary reactions to: (a) cardiostimulation induced by single doses or slow infusions of noradrenaline, CaCl2, glucagon or electrically induced tachycardia; (b) short interruptions of coronary inflow (hypoxia). 2 Except during tachycardia the heart rate was kept constant at 210 beats/min by electrical pacing. 3 Metabolic coronary vasodilatation (MCD) resulting from cardiac hyperactivity induced by noradrenaline, Ca2+, tachycardia or glucagon was inhibited by administration of prostaglandin E2. Reactive hyperaemia response to hypoxia was unaffected by prostaglandin administration. 4 Inhibition of MCD could also be obtained by prolonged infusion with arachidonic acid (1.6 X 10(-7) M), presumably by its conversion into prostaglandin-like substance since arachidonic acid failed to block MCD in hearts from rats pretreated with non-steroidal anti-inflammatory drugs (indomethacin, naproxen, phenylbutazone). 5 Reactive hyperaemia was unaffected either by arachidonic acid or by blockade of the synthesis of prostaglandin-like substances by anti-inflammatory drugs. 6 Since prostaglandin synthetase inhibition does not prevent but may enhance MCD, we do not advocate prostaglandin-like substances as agents directly responsible for the coronary vasodilatation that follows cardiac hyperactivity. 7 We postulate that cardiac overproduction of prostaglandins may lead to a failure in the adaptive coronary flow response to cardiac hyperactivity (coronary insufficiency?). PMID:760893

Sunahara, F A; Talesnik, J

1979-01-01

327

Synthesis of Dehydroluciferin by Firefly Luciferase: Effect of Dehydroluciferin, Coenzyme A and Nucleoside Triphosphates on the Luminescent Reaction  

Microsoft Academic Search

The formation of dehydroluciferin (L) from luciferin (LH2) in the reaction catalyzed by firefly luciferase (EC 1.13.12.7) has been studied. The E·LH2-AMP complex may follow two different pathways: towards production of light and towards the synthesis of the E·L-AMP complex. This last step has an inhibitory effect on light emission as molecules of the enzyme are trapped in a light

Rui Fontes; Alexey Dukhovich; Antonio Sillero; Maria A. Günther Sillero

1997-01-01

328

Sequential decarboxylative azide–alkyne cycloaddition and dehydrogenative coupling reactions: one-pot synthesis of polycyclic fused triazoles  

PubMed Central

Summary Herein, we describe a one-pot protocol for the synthesis of a novel series of polycyclic triazole derivatives. Transition metal-catalyzed decarboxylative CuAAC and dehydrogenative cross coupling reactions are combined in a single flask and achieved good yields of the respective triazoles (up to 97% yield). This methodology is more convenient to produce the complex polycyclic molecules in a simple way. PMID:25670973

Bharathimohan, Kuppusamy; Ponpandian, Thanasekaran; Bhuvanesh, Nattamai

2014-01-01

329

Synthesis of diverse indene derivatives from 1-diazonaphthalen-2(1H)-ones via thermal cascade reactions.  

PubMed

A sequential Wolff rearrangement of 1-diazonaphthalen-2(1H)-ones followed by trapping of the ketene intermediate with primary and aromatic amines or alcohols and phenols in the presence of various aldehydes generates 1H-indene-3-carboxamides or 1H-indene-3-carboxylates. This constitutes an unprecedented three-component coupling reaction that allows for the synthesis of functionalized indene derivatives under catalyst-free thermal conditions. PMID:23944353

Somai Magar, Krishna Bahadur; Lee, Yong Rok

2013-09-01

330

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

PubMed Central

Summary 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; Li, Guigen

2014-01-01

331

Regio- and stereoselective synthesis of benzothiazolo-pyrimidinones via an NHC-catalyzed Mannich/lactamization domino reaction.  

PubMed

An NHC-catalyzed regio- and stereoselective Mannich/lactamization domino reaction of N-(benzothiazolyl)imines with ?-chloroaldehydes has been developed. This new protocol provides a facile approach for the asymmetric synthesis of benzothiazolo-pyrimidinones and a pyrrolo[1,2-a]indolone in moderate to good yields (34-78%) and excellent stereoselectivities (87-99% ee, up to >20?:?1 d.r.). PMID:25476422

Ni, Qijian; Song, Xiaoxiao; Xiong, Jiawen; Raabe, Gerhard; Enders, Dieter

2015-01-25

332

Ionic Liquid as Catalyst and Reaction Medium: A Simple and Efficient Procedure for Paal–Knorr Furan Synthesis  

Microsoft Academic Search

The ionic liquid 1-butyl-3-methyl-imidazolium hydrogen sulfate, [bmim]HSO4, efficiently catalyzes Paal–Knorr furan synthesis without any organic solvent. A wide range of aliphatic and aromatic 1,4-diketones easily undergo condensations to form furan derivatives, providing a general and convenient procedure. The Paal–Knorr reaction of ester-substituted 1,4-diketones is first reported. The ionic liquid can be recovered and reused for subsequent runs without any appreciable

Gangqiang Wang; Zhi Guan; Rongchang Tang; Yanhong He

2010-01-01

333

Multicomponent reactions of dimethyl methoxymalonate and dialkyl acetylenedicarboxylate in the presence of N-nucleophiles: one-pot synthesis of 2H-pyridinyl-2-butenedioates in water.  

PubMed

An efficient synthesis of 2H-pyridinyl-2-butenedioate derivatives via reaction of dimethyl methoxymalonate and dialkyl acetylenedicarboxylate in the presence of N-nucleophiles in water as a solvent is described. PMID:19763860

Khalilzadeh, Mohammad A; Hossaini, Zinatossadat; Kharian, Samaneh

2010-08-01

334

Use of a Tandem Prins/Friedel-Crafts Reaction in the Construction of the Indeno-Tetrahydropyridine Core of the Haouamine Alkaloids: Formal Synthesis of (?)-Haouamine A  

PubMed Central

A tandem Prins/Friedel-Crafts reaction useful for the construction of the indeno-tetrahydropyridine core of the haouamine alkaloids and a formal synthesis of (?)-haouamine A are described. PMID:21517105

Fenster, Erik; Fehl, Charlie; Aubé, Jeffrey

2011-01-01

335

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

336

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

337

The suzuki reaction in stereocontrolled polyene synthesis: Retinol (vitamin A), its 9- and\\/or 13-demethyl analogs, and related 9-demethyl-dihydroretinoids  

Microsoft Academic Search

A new synthesis of retinol (vitamin A) and 9- and\\/or 13-demethylretinols, with essentially complete control of regio- and stereochemistry, is described which is based on the thallium-accelerated, palladium-catalyzed cross-coupling reactions of (E)-1-alkenylboronic acids and (E)-1-alkenyl iodides (Suzuki reaction). The procedure has also been extended to the stereocontrolled synthesis of a series of 9-demethyl-dihydroretinoids of potential biological interest.

Alicia Torrado; Beatriz Iglesias; Susana López; Angel R. de Lera

1995-01-01

338

Tamaru's model for ammonia decomposition over titanium oxynitride  

Microsoft Academic Search

Titanium oxynitride TiNxOy was prepared by reaction of titania with flowing ammonia between 890 and 1120 K. Optimized operating conditions led to specific surface areas ranging from 58 to 87 m2 g?1. Kinetics of catalytic ammonia decomposition at 900 K showed that titanium oxynitrides presented a tungsten (or iron)-type behaviour at low hydrogen pressure and a Temkin–Pyzhev behaviour characteristic of

Gérald Djéga-Mariadassou; Chae-Ho Shin; Guy Bugli

1999-01-01

339

Propagation strategy of ammonia fungi  

Microsoft Academic Search

Ammonia fungi invade forest floors immediately after a enrichment disturbance by a large input of ammonium-nitrogen. Latent\\u000a form(s) of the ammonia fungi are spores and\\/or mycelium fragments. Ammonia fungi are characterized by their rapid germination\\u000a stimulated by the presence of ammonium-nitrogen under neutral to weakly alkaline conditions. Each ammonia fungus establishes\\u000a its territory during suppressed combative abilities of other microbes

Akira Suzuki

2009-01-01

340

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

341

Reaction mechanisms and kinetics of the synthesis and decomposition of lithium metazirconate through solid-state reaction  

Microsoft Academic Search

The reaction mechanisms and kinetics describing the formation and surface decomposition of lithium metazirconate pellets (Li2ZrO3) have been investigated during Li2ZrO3 formation via solid-state reaction. Samples were analysed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. A metastable tetragonal Li2ZrO3 phase was synthesised at low temperatures, recrystallizing into a monoclinic structure when the temperature was increased above 800 °C.

Heriberto Pfeiffer; Kevin M. Knowles

2004-01-01

342

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

NASA Astrophysics Data System (ADS)

Supersonic molecular beams have been used to determine the yield of CO from the partial oxidation of CH4 on a Rh(111) catalytic substrate, CH4+(1/2)O2?CO +2H2, as a function of beam kinetic energy. These experiments were done under ultrahigh vacuum conditions with concurrent molecular beams of O2 and CH4, ensuring that there was only a single collision for the CH4 to react with the surface. The fraction of CH4 converted is strongly dependent on the normal component of the incident beam's translational energy, and approaches unity for energies greater than ˜1.3eV. Comparison with a simplified model of the methane-Rh(111) reactive potential gives insight into the barrier for methane dissociation. These results demonstrate the efficient conversion of methane to synthesis gas, CO +2H2, are of interest in hydrogen generation, and have the optimal stoichiometry for subsequent utilization in synthetic fuel production (Fischer-Tropsch or methanol synthesis). Moreover, under the reaction conditions explored, no CO2 was detected, i.e., the reaction proceeded with the production of very little, if any, unwanted greenhouse gas by-products. These findings demonstrate the efficacy of overcoming the limitations of purely thermal reaction mechanisms by coupling nonthermal mechanistic steps, leading to efficient C-H bond activation with subsequent thermal heterogeneous reactions.

Gibson, K. D.; Viste, M.; Sibener, S. J.

2006-10-01

343

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

344

Reaction of the CoII-Substrate Radical Pair Catalytic Intermediate in Coenzyme B12-Dependent Ethanolamine Ammonia-Lyase in Frozen Aqueous Solution from 190 to 217 K  

PubMed Central

The decay kinetics of the aminoethanol-generated CoII-substrate radical pair catalytic intermediate in ethanolamine ammonia-lyase from Salmonella typhimurium have been measured on timescales of <105 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 ? T ? 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 ? 214 K: the decay is monoexponential. The observed first-order rate constants for the monoexponential (kobs,m) and the fast phase of the biexponential decay (kobs,f) adhere to the same linear relation on an lnk versus T?1 (Arrhenius) plot. Thus, kobs,m and kobs,f correspond to the same apparent Arrhenius prefactor and activation energy (logAapp,f (s?1) = 13.0, Ea,app,f = 15.0 kcal/mol), and therefore, a common decay mechanism. We propose that kobs,m and kobs,f represent the native, forward reaction of the substrate through the radical rearrangement step. The slow phase rate constant (kobs,s) for 190 ? T ? 207 K obeys a different linear Arrhenius relation (logAapp,s (s?1) = 13.9, Ea,app,s = 16.6 kcal/mol). In the transition temperature range, kobs,s displays a super-Arrhenius increase with increasing temperature. The change in Ea,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 CoII-substrate radical pair lies below 190 K. PMID:18805934

Zhu, Chen; Warncke, Kurt

2008-01-01

345

Simultaneous synthesis of gold nanoparticle/graphene nanocomposite for enhanced oxygen reduction reaction  

NASA Astrophysics Data System (ADS)

We report here on a novel and facile technique for the simultaneous synthesis of a highly active and stable gold (Au) nanoparticle/reduced graphene oxide (rGO) sheet nanocomposite as an efficient electrocatalyst to facilitate the oxygen reduction reaction (ORR). X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray (EDX) spectroscopy and electrochemical methods were employed to characterize the Au and rGO nanocomposites formed on the electrode surface. The major advantage of the simultaneous synthetic method is the integration of the superb properties of both Au nanoparticles and graphene in a single-step with a 100% usage of the precursors. The Au/rGO nanocomposites exhibited pronounced electrocatalytic performance towards ORR with approximately three times higher than that of Au nanoparticles. The nanocomposites show the ORR onset peak potentials at 0.12 and -0.03 V (vs Ag/AgCl), with reduction peaks at -0.06 and -0.16 V (vs Ag/AgCl) in 0.1 M H2SO4 and KOH media, which is ?120-190 mV more positive than that of Au nanoparticles and a commercial Pt/C catalyst. Moreover, the nanocomposites exhibit excellent methanol tolerance and high durability in comparison with the commercial Pt/C. The new method demonstrated in this study provides an efficient route for the generation of ultrafine and highly dense Au nanoparticles that are homogeneously dispersed on rGO sheets for ORR.

Govindhan, Maduraiveeran; Chen, Aicheng

2015-01-01

346

Fully diastereoselective synthesis of polysubstituted, functionalized piperidines and decahydroquinolines based on multicomponent reactions catalyzed by cerium(IV) ammonium nitrate.  

PubMed

The cerium(IV) ammonium nitrate (CAN)-catalyzed, three-component reaction between primary amines, ?-dicarbonyl compounds, and ?,?-unsaturated aldehydes in ethanol heated to reflux, constitutes a general, one-pot synthesis of 1,4-dihydropyridines. Their reduction with sodium triacetoxyborohydride furnished piperidine derivatives bearing up to five substituents with full diastereoselectivity in a hitherto inaccessible stereochemical arrangement. The reaction proceeded with no significant loss of enantiomeric purity under mild reduction conditions that are compatible with several functional groups that are normally sensitive to reduction. Octahydroquinolin-5-one derivatives, which were prepared by a modified version of the initial multicomponent reaction, were not suitable substrates for the sodium triacetoxyborohydride mediated reduction, but they were transformed into the corresponding decahydroquinolines, including a precursor of the amphibian alkaloid pumiliotoxin?C, by catalytic hydrogenation under a variety of conditions. PMID:24909665

Suryavanshi, Padmakar A; Sridharan, Vellaisamy; Maiti, Swarupananda; Menéndez, J Carlos

2014-07-01

347

reactions  

Microsoft Academic Search

Gene regulatory, signal transduction and metabolic networks are major areas of interest in the newly emerging field of systems biology. In living cells, stochastic dynamics play an important role; however, the kinetic parameters of biochemical reactions necessary for modelling these processes are often not accessible directly through experiments. The problem of estimating stochastic reaction constants from molecule count data measured,

S. Reinker; R. M. Altman; J. Timmer

348

Synthesis of ordered mesoporous crystalline CuS and Ag2S materials via cation exchange reaction  

NASA Astrophysics Data System (ADS)

Cation exchange reaction is a strong tool for the synthesis of new ionic nanomaterials. Most of them are isolated nanoparticles with simple geometric features, such as nanodots, nanorods and nanospheres. In this work, we demonstrated that ordered mesoporous CdS with a complex cubic Ia3d gyroidal 3D bicontinuous porous structure and large particle size can be successfully converted to crystalline CuS and Ag2S materials via cation exchange reaction without destroying the well-defined nanostructure. The change in crystal structure is an important factor for a successful conversion when the reaction is carried out without the presence of a silica template. In addition, the cation exchange reaction is sufficient for a complete compositional conversion, even when the mesostructured CdS precursor is embedded inside a mesoporous silica matrix. Our results indicate that cation exchange reaction may be applied to highly complex nanostructures with extremely large particle sizes.Cation exchange reaction is a strong tool for the synthesis of new ionic nanomaterials. Most of them are isolated nanoparticles with simple geometric features, such as nanodots, nanorods and nanospheres. In this work, we demonstrated that ordered mesoporous CdS with a complex cubic Ia3d gyroidal 3D bicontinuous porous structure and large particle size can be successfully converted to crystalline CuS and Ag2S materials via cation exchange reaction without destroying the well-defined nanostructure. The change in crystal structure is an important factor for a successful conversion when the reaction is carried out without the presence of a silica template. In addition, the cation exchange reaction is sufficient for a complete compositional conversion, even when the mesostructured CdS precursor is embedded inside a mesoporous silica matrix. Our results indicate that cation exchange reaction may be applied to highly complex nanostructures with extremely large particle sizes. Electronic supplementary information (ESI) available: XRD patterns and nitrogen sorption data of the KIT-6 template, CdS precursor and Ag2S and CuS products. See DOI: 10.1039/c4nr07060g

Wang, Jun; Xu, Weiming; Bao, Haifeng; Shi, Yifeng

2015-02-01

349

NMR Study of the Synthesis of Alkyl-Terminated Silicon Nanoparticles from the Reaction of SiCl4 with the Zintl  

E-print Network

. At the heart of this approach for silicon is the reaction of a Zintl salt with silicon tetrachloride SiCl4NMR Study of the Synthesis of Alkyl-Terminated Silicon Nanoparticles from the Reaction of SiCl4 with the Zintl Salt, NaSi Daniel Mayeri, Brian L. Phillips,*, Matthew P. Augustine,*, and Susan M. Kauzlarich

Augustine, Mathew P.

350

Bismuth Subnitrate Catalyzed Efficient Synthesis of 3,4?Dihydropyrimidin?2(1H)?Ones: An Improved Protocol for the Biginelli Reaction  

Microsoft Academic Search

An efficient synthesis of 3,4?dihydropyrimidinones (DHPMs) using bismuth subnitrate as the catalyst for the first time from an aldehyde, ??ketoester, and urea in acetonitrile is described. This new method consistently has the advantage of excellent yields (88–96%) and short reaction times (1.5–4 h) than do classical Biginelli reaction conditions.

Y. Thirupathi Reddy; B. Rajitha; P. Narsimha Reddy; B. Sunil Kumar; V. P. Rao G

2004-01-01

351

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

352

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

353

Toluene Dioxygenase-Catalyzed Synthesis and Reactions of cis-Diol Metabolites Derived from 2- and 3-Methoxyphenols.  

PubMed

Using toluene dioxygenase as biocatalyst, enantiopure cis-dihydrodiol and cis-tetrahydrodiol metabolites, isolated as their ketone tautomers, were obtained from meta and ortho methoxyphenols. Although these isomeric phenol substrates are structurally similar, the major bioproducts from each of these biotransformations were found at different oxidation levels. The relatively stable cyclohexenone cis-diol metabolite from meta methoxyphenol was isolated, while the corresponding metabolite from ortho methoxyphenol was rapidly bioreduced to a cyclohexanone cis-diol. The chemistry of the 3-methoxycyclohexenone cis-diol product was investigated and elimination, aromatization, hydrogenation, regioselective O-exchange, Stork-Danheiser transposition and O-methylation reactions were observed. An offshoot of this technology provided a two-step chemoenzymatic synthesis, from meta methoxyphenol, of a recently reported chiral fungal metabolite; this synthesis also established the previously unassigned absolute configuration. PMID:25756661

Boyd, Derek R; Sharma, Narain D; Malone, John F; McIntyre, Peter B A; McRoberts, Colin; Floyd, Stewart; Allen, Christopher C R; Gohil, Amit; Coles, Simon J; Horton, Peter N; Stevenson, Paul J

2015-04-01

354

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

355

M{prime}-RTaO{sub 4} synthesis: Activation of the precursor oxides by the reaction flux  

SciTech Connect

Studies of the M{prime}-RTaO{sub 4} (R = Gd, Y, Lu) phosphor synthesis reaction show that, contrary to previous views, the flux (e.g., Li{sub 2}SO{sub 4}, LiCl, Na{sub 2}SO{sub 4}) serves as in important reactant. Through a combination of techniques (DTA, TGA, XRPD, and mass balance), the authors find that close to its melting point, the flux reacts exothermically with the blended tantalum and yttrium oxides to give intermediate compounds. These reactive intermediates then combine to make M`-REaO{sub 4} and to regenerate the flux. Thus, the flux serves a dual purpose; it first activates the oxide reaction mixture and then serves as a classical flux in the growth of RTaO{sub 4} crystals. In light of this discovery, a more appropriate term for these flux compounds is catalyst or reactive flux because they facilitate the synthesis of RTaO{sub 4} through chemical reaction.

Hedden, D.B.; Zegarski, W. [DuPont Company, Towanda, PA (United States)] [DuPont Company, Towanda, PA (United States); Torardi, C.C. [DuPont Company, Wilmington, DE (United States)] [DuPont Company, Wilmington, DE (United States)

1995-09-01

356

Synthesis and reactions of 1,1-diamino-2,2-dinitroethylene  

Microsoft Academic Search

Low temperature nitrations of 2-methylimidazole gave in addition to the known 2-methyl-5(4)-nitroimidazole (1), 2-(dinitromethylene)-5,5-dinitro-4-imidazolidinone (3) and parabanic acid (2). The tetranitro compound 3 was also obtained by nitration of 2-methyl-4,5-dihydro-(1H)-5-imidazolone (8). Thermal decomposition of 3 gave 2-(dinitromethylene)-4,5-imidazolidinedione (4) which also was the product from nitration of the new compound 2-methoxy-2-methyl-4,5-imidazolidinedione. Treatment of 4 with aqueous ammonia gave the previously unknown

Abraham Langlet; Ulf Wellmar; Ulf Bemm

1998-01-01

357

Synthesis of superheavy element 120 via {sup 50}Ti+{sup A}Cf hot fusion reactions  

SciTech Connect

Synthesis of superheavy element 120 in terms of the {sup 50}Ti+{sup 249-252}Cf fusion-evaporation reactions is evaluated and discussed. It is found that the reactions of {sup 250,251}Cf({sup 50}Ti,3n){sup 297,298}120 and {sup 251,252}Cf({sup 50}Ti,4n){sup 297,298}120 are relatively favorable with the maximum evaporation-residue cross sections of 0.12, 0.09, 0.11, and 0.25 pb, respectively. However, {sup 252}Cf may be difficult to be target because its spontaneous fission will bring about serious background in the experiment. Fusion probabilities for different target-projectile combinations leading to the formation of surperheavy nucleus {sup 302}120 are estimated with the ''fusion-by-diffusion'' model and presented as a function of the Coulomb parameter Z{sub 1}Z{sub 2}/(A{sub 1}{sup 1/3}+A{sub 2}{sup 1/3}). Among the reactions {sup 50}Ti+{sup 252}Cf, {sup 54}Cr+{sup 248}Cm, {sup 58}Fe+{sup 244}Pu, and {sup 64}Ni+{sup 238}U, the reaction {sup 50}Ti+{sup 252}Cf has the largest fusion probability. Synthesis of superheavy element 120 is of essential importance for determining whether the magic proton shell should be at Z=114 or at higher proton numbers Z=120-126. Therefore, the experiment to produce isotopes with Z=120 in the fusion reactions {sup 50}Ti+{sup 250,251}Cf is of great interest.

Liu, Z. H. [China Institute of Atomic Energy, Beijing 102413 (China); Bao Jingdong [Department of Physics, Beijing Normal University, Beijing 100875 (China); Center of Theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator, Lanzhou 730000 (China)

2009-11-15

358

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

359

Acid-catalyzed domino reactions of tetraarylbut-2-yne-1,4-diols. Synthesis of conjugated indenes and inden-2-ones.  

PubMed

The reaction of tetraarylbut-2-yne-1,4-diols with electron-rich aromatic compounds at room temperature, under p-TsOH catalysis, affords substituted polycyclic aromatic indene derivatives through a domino reaction involving the formation of a cationic allenylium intermediate. This species can undergo a series of competitive intramolecular cascade reactions, leading to a conjugated inden-2-one. This simple method allows the efficient synthesis of substituted indenes and inden-2-ones, in two steps, from aromatic ketones. PMID:24846324

Sousa, Céu M; Berthet, Jerome; Delbaere, Stephanie; Coelho, Paulo J

2014-06-20

360

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

361

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

362

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes  

PubMed Central

Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to the preparation of new organic dyes. Although numerous strategies have been reported to access naphthalene scaffolds, many procedures still present limitations in terms of incorporating functionality, which in turn narrows the range of available substrates. The development of versatile methods for direct access to substituted naphthalenes is therefore highly desirable. The Diels-Alder (DA) cycloaddition reaction is a powerful and attractive method for the formation of saturated and unsaturated ring systems from readily available starting materials. A new microwave-assisted intramolecular dehydrogenative DA reaction of styrenyl derivatives described herein generates a variety of functionalized cyclopenta[b]naphthalenes that could not be prepared using existing synthetic methods. When compared to conventional heating, microwave irradiation accelerates reaction rates, enhances yields, and limits the formation of undesired byproducts. The utility of this protocol is further demonstrated by the conversion of a DA cycloadduct into a novel solvatochromic fluorescent dye via a Buchwald-Hartwig palladium-catalyzed cross-coupling reaction. Fluorescence spectroscopy, as an informative and sensitive analytical technique, plays a key role in research fields including environmental science, medicine, pharmacology, and cellular biology. Access to a variety of new organic fluorophores provided by the microwave-assisted dehydrogenative DA reaction allows for further advancement in these fields. PMID:23609566

Kocsis, Laura S.; Benedetti, Erica; Brummond, Kay M.

2013-01-01

363

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

364

Atmospheric dispersion of ammonia: an ammonia fog model  

SciTech Connect

A simplification to the two-phase ammonia vapor-droplet fog problem has been implemented to study the dispersion of a spill of 40 tons of ammonia. We have circumvented the necessity of adding the partial differential equations for mass, momentum, and energy for the ammonia in the liquid phase by certain assumptions. It is assumed that the ammonia fog behaves as an ideal gas including the droplets. A temperature-dependent molecular weight was introduced to simulate the transition from a vapor-droplet cloud to a pure vapor cloud of ammonia. Likewise, the vaporization of ammonia was spread out over a temperature range. Mass, momentum, energy, and total ammonia is conserved rigorously. The observed features of the ammonia spill simulation have pointed out phenomena that could not be predicted in simpler calculations. Perhaps the most obvious feature is the cloud bifurcation due to the strength of the gravity current relative to the ambient wind. The gravity spreading of the denser ammonia fog significantly perturbs the unidirectional windfield in the vicinity of the spill, setting up complex eddy patterns in the cloud which are enhanced by ground heating and warm dry air entrainment. The lower concentrations appear to lift off by a buoyancy-induced flow. The ammonia cloud, rather than being cigar shaped as assumed in simpler models, ranges from pancake shaped to pear shaped, depending upon the ambient windfield. The fact that the ammonia cloud remains cold, very low, and wide is in qualitative agreement with some of the large-scale ammonia spill accidents. 14 figures.

Kansa, E.J.; Rodean, H.C.; Chan, S.T.; Ermak, D.L.

1983-01-01

365

[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

366

REVISITING NUCLEOPHILIC SUBSTITUTION REACTIONS: MICROWAVE-ASSISTED SYNTHESIS OF AZIDES, THIOCYANATES AND SULFONES IN AQUEOUS MEDIUM  

EPA Science Inventory

A practical, rapid and efficient microwave (MW) promoted synthesis of various azides, thiocyanates and sulfones, is described in aqueous medium. This general and expeditious MW-enhanced nucleophilic substitution approach uses easily accessible starting materials such as halides o...

367

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

368

Combustion of Powder Mixtures Forming Reaction Products - Synthesis of NiAl  

Microsoft Academic Search

Combustion of powder mixtures under adiabatic conditions -Self-propagating High-temperature Synthesis (SHS)-is an efficient and attractive technique to synthesize a host of materials for high technology applications, namely, ceramics, intermetallics, composites and functionally graded materials. Conditions necessary for and general features of this technique are briefly reviewed.Experimental investigations on synthesis of nickel monoaluminide from stoichiometric mixtures of component powders by this

S. K. ROY; A. BISWAS

2001-01-01

369

Microwave-Assisted Organic Synthesis in the Organic Teaching Lab: A Simple, Greener Wittig Reaction  

ERIC Educational Resources Information Center

A greener, microwave-assisted Wittig reaction has been developed for the second-semester organic teaching laboratory. Utilizing this microwave technique, a variety of styrene derivatives have been successfully synthesized from aromatic aldehydes in good yields (41-68%). The reaction not only occurs under neat reaction conditions, but also employs…

Martin, Eric; Kellen-Yuen, Cynthia

2007-01-01

370

Fungal and Plant Phenylalanine Ammonia-lyase  

PubMed Central

L-Phenylalanine is one of the essential amino acids that cannot be synthesized in mammals in adequate amounts to meet the requirements for protein synthesis. Fungi and plants are able to synthesize phenylalanine via the shikimic acid pathway. L-Phenylalanine, derived from the shikimic acid pathway, is used directly for protein synthesis in plants or metabolized through the phenylpropanoid pathway. This phenylpropanoid metabolism leads to the biosynthesis of a wide array of phenylpropanoid secondary products. The first step in this metabolic sequence involves the action of phenylalanine ammonia-lyase (PAL). The discovery of PAL enzyme in fungi and the detection of 14CO2 production from 14C-ring-labeled phenylalanine and cinnamic acid demonstrated that certain fungi can degrade phenylalanine by a pathway involving an initial deamination to cinnamic acid, as happens in plants. In this review, we provide background information on PAL and a recent update on the presence of PAL genes in fungi. PMID:22783113

Hyun, Min Woo; Yun, Yeo Hong; Kim, Jun Young

2011-01-01

371

Generation of allenic/propargylic zirconium complexes and subsequent cross-coupling reactions: a facile synthesis of multisubstituted allenes.  

PubMed

The beta-alkoxide elimination reaction of propargylic ether with Negishi reagent leads to allenes and/or alkynes after hydrolysis. The product distribution is highly dependent on the substitution pattern of starting propargylic ethers; that is, aryl- or alkyl-substituted propargylic ethers favor the allene products, whereas TMS-substituted propargylic ethers afford alkynes. DFT calculations revealed that both the large steric effect and the beta-effect of the TMS group favor the alkyne products, reversing the selectivity. Subsequent coupling reactions of the allenic/propargylic zirconium intermediates with aryl iodides in the presence of Pd(PPh(3))(4)/CuCl provide a straightforward route for the synthesis of multisubstituted allenes. PMID:19921814

Zhang, Hao; Fu, Xiaoping; Chen, Jingjin; Wang, Erjuan; Liu, Yuanhong; Li, Yuxue

2009-12-18

372

The dynamics of ammonia metabolism in man. Effects of liver disease and hyperammonemia.  

PubMed Central

The cyclotron-produced radionuclide, 13N, was used to label ammonia and to study its metabolism in a group of 5 normal subjects and 17 patients with liver disease, including 5 with portacaval shunts and 11 with encephalopathy. Arterial ammonia levels were 52-264 micron. The rate of ammonia clearance from the vascular compartment (metabolism) was a linear function of its arterial concentration: mumol/min = 4.71 [NH3]a + 3.76, r = +0.85, P less than 0.005. Quantitative body scans showed that 7.4 +/- 0.3% of the isotope was metabolized by the brain. The brain ammonia utilization rate, calculated from brain and blood activities, was a function of the arterial ammonia concentration: mumol/min per whole brain = 0.375 [NH3]a - 3.6, r = +0.93, P less than 0.005. Assuming that cerebral blood flow and brain weights were normal, 47 +/- 3% of the ammonia was extracted from arterial blood during a single pass through the normal brains. Ammonia uptake was greatest in gray matter. The ammonia utilization reaction(s) appears to take place in a compartment, perhaps in astrocytes, that includes less than 20% of all brain ammonia. In the 11 nonencephalopathic subjects the [NH3]a was 100 +/- 8 micron and the brain ammonia utilization rate was 32 +/- 3 mumol/min per whole brain; in the 11 encephalopathic subjects these were respectively elevated to 149 +/- 18 micron (P less than 0.01), and 53 +/- 7 mumol/min per whole brain (P less than 0.01). In normal subjects, approximately equal to 50% of the arterial ammonia was metabolized by skeletal muscle. In patients with portal-systemic shunting, muscle may become the most important organ for ammonia detoxification. Muscle atrophy may thereby contribute to the development of hyperammonemic encephalopathy with an associated increase in the brain ammonia utilization rate. Images PMID:429564

Lockwood, A H; McDonald, J M; Reiman, R E; Gelbard, A S; Laughlin, J S; Duffy, T E; Plum, F

1979-01-01

373

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

374

Bronchiectasis following pulmonary ammonia burn  

SciTech Connect

Long-term follow-up of the pulmonary lesions of severe exposure to ammonia in humans has seldom been documented, and development of bronchiectasis continues to be of concern. We studied a previously healthy 30-year-old woman whose lungs at time of necropsy, three years after massive exposure to ammonia fumes, had extensive cylindrical and saccular bronchiectasis. We concluded that massive exposure to ammonia can lead to bronchiectasis. It is not known, however, whether the bronchiectasis resulted from chemical injury by ammonia or from a superimposed bacterial bronchitis.

Hoeffler, H.B.; Schweppe, H.I.; Greenberg, S.D.

1982-12-01

375

Ammonium accumulation during a silicate-limited diatom bloom indicates the potential for ammonia emission events  

E-print Network

). As the predominant naturally occurring base in the atmosphere, ammonia is important in neutralization reactions in the atmosphere, ammonia neutralizes acidity and in doing so plays a potentially significant role in climate, particularly with acidic sulfate aerosol. It has been shown that new particle formation from sulfuric acid gas

Hansell, Dennis

376

Arrhenius equation for modeling feedyard ammonia emissions using temperature and diet crude protein  

Technology Transfer Automated Retrieval System (TEKTRAN)

Temperature controls many processes of ammonia volatilization. For example, urea hydrolysis is an enzymatically catalyzed reaction described by the Arrhenius equation. Diet crude protein (CP) controls ammonia emission by affecting N excretion. Objectives were to use the Arrhenius equation to model a...

377

Application of carbon dioxide towards the development of smart materials, green reaction schemes and metallic nanoparticle synthesis  

NASA Astrophysics Data System (ADS)

Global carbon dioxide (CO2) emissions have steadily risen over the last 50 years, with 34 billion tons of CO2 released in 2009 alone. Its potential as a greenhouse gas has negatively affected of our lives and environment by the resulting ocean acidification and climate change. To mitigate atmospheric CO2, various strategies have been implemented for CO2 separation, capture, storage and use as a chemical feedstock. The use of CO2 in various chemical industries is attractive as its non-flammable, non-toxic, and relatively inert properties have made it an inherently safer alternative to traditional organic solvents, as well as, a greener carbon feedstock. Also, the accessible critical properties, appreciable critical density, high diffusivity and tunable thermophysical properties make liquid and supercritical CO2 an attractive solvent for industrial applications. In recent years, significant progress has been made in the field of tunable solvent media by employing the reversible reaction of CO2 with amines to produce carbamates. This class of compounds possesses ionic properties that are significantly different from their amines resulting in a non-ionic to ionic switching mechanism that provides for switchable solvent properties, reversible surfactants, low molecular weight organogelators and stimuli responsive materials. The focus of this dissertation is therefore the implementation of the reversible CO2—amine reaction for the formation of smart surfaces, greener amine protection mechanisms, and cationic metallic nanoparticle synthesis. Chapter 2 of this dissertation demonstrates the reversible reaction of CO2 with amine-containing self-assembled monolayers to yield "smart" surfaces that undergo a reversible change in structure, charge, and wettability upon reaction with CO2. The formation carbamate esters are also a widely implemented mechanism for amine protection during organic synthesis. However, traditional methods of protection incur increased solvent use and energy consumption due to a separate deprotection reaction. To solve this dilemma, the reversible protection of amines using CO2 induced carbamates was demonstrated in chapter 3; by reducing n-alkyl benzophenone imine and n-phenyl, nalkylurea yields by up to 67% compared to non-protected amines. The applicability of this chemistry to these classes of nucleophilic substitution reactions and has significant potential to alter the way we approach amine protection in organic synthesis. Another research area that has grown popularity over the last decade is the development of metallic nanoparticles, specifically gold nanoparticles (GNPs), due to their size and shape dependent optical and catalytic properties. Chapter 4 of this dissertation demonstrates the successful application of polyethylene imine (PEI) in the synthesis of cationic GNPs, which are of significant interest for biomedical applications. In this work, we investigated the effect of pH, PEI concentration and reduction method on the size and stability of amine-stabilized gold and silver nanoparticles. Furthermore the potential of carbon dioxide as a stabilizing aid through reversible carbamate formation was explored, leading to a decrease in particle size at ambient temperature along with an increase in stability. In summary, this work has demonstrated the great potential of employing the reversible reaction of carbon dioxide with primary and secondary amines as an effective and greener alternative to conventional methods in a diversity of fields that include "smart" materials, organic chemistry, and functional nanomaterials.

Mohammed, Fiaz S.

378

The synthesis of pentadienylium salts via reactions of (5-ethoxy-1,5-diaryl-2,4-pentadienylidene)ethyloxonium perchlorate with hydrazines  

Microsoft Academic Search

Reaction of the readily available (5-ethoxy-1,5-diaryl-2,4-pentadienylidene)ethyloxonium perchlorate 1 with hydrazines, R2NNH2 or RNHNH2,provides a simple and efficient synthesis of previously unknown (5-ethoxy-1,5-diaryl-2,4-pentadienylidene)hydrazinium salt 2a-d. Application of this method to be synthesis of the highly conjugated pentadienylium salt from terephthalic dihydrazide is reported.

François Rivière; Vadim D. Romanenko; Marie-Rose Maziéres; Michel Sanchez; Jean-Gérard Wolf

1996-01-01

379

Methanol synthesis on ZnO(000{overline{1}}). III. Free energy landscapes, reaction pathways, and mechanistic insights  

NASA Astrophysics Data System (ADS)

The interplay of physical and chemical processes in the heterogeneous catalytic synthesis of methanol on the ZnO(000overline{1}) surface with oxygen vacancies is expected to give rise to a complex free energy landscape. A manifold of intermediate species and reaction pathways has been proposed over the years for the reduction of CO on this catalyst at high temperature and pressure conditions as required in the industrial process. In the present study, the underlying complex reaction network from CO to methanol is generated in the first place by using ab initio metadynamics for computational heterogeneous catalysis. After having "synthesized" the previously discussed intermediates in addition to finding novel species, mechanistic insights into this network of surface chemical reactions are obtained based on exploring the global free energy landscape, which is refined by investigating individual reaction pathways. Furthermore, the impact of homolytic adsorption and desorption of hydrogen at the required reducing gas phase conditions is probed by studying such processes using different charge states of the F-center.

Kiss, Janos; Frenzel, Johannes; Nair, Nisanth N.; Meyer, Bernd; Marx, Dominik

2011-02-01

380

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

381

Enantioselective total synthesis of the potent antitumor agent (-)-mucocin using a temporary silicon-tethered ring-closing metathesis cross-coupling reaction.  

PubMed

The enantioselective total synthesis of the annonaceous acetogenin (-)-mucocin (1) was accomplished using a triply convergent 12-step sequence (longest linear sequence) in 13.6% overall yield. This represents the first application of the temporary silicon-tethered (TST) ring-closing metathesis (RCM) cross-coupling reaction and the enantioselective alkyne/aldehyde addition to the synthesis of a complex annonaceous acetogenin. Moreover, all three fragments required for the coupling reactions are conveniently prepared in 5-6 steps from two readily available enantiomerically enriched epoxides. Finally, this synthesis stimulated the development of a new approach for the construction of 3-hydroxy-2,6-disubstituted tetrahydropyrans, using the bismuth tribromide-mediated reductive etherification reaction, which represents a motif that is prevalent in a wide range of pharmacologically significant natural products. PMID:14640634

Evans, P Andrew; Cui, Jian; Gharpure, Santosh J; Polosukhin, Alexei; Zhang, Hai-Ren

2003-12-01

382

System and method for determining an ammonia generation rate in a three-way catalyst  

SciTech Connect

A system according to the principles of the present disclosure includes a rate determination module, a storage level determination module, and an air/fuel ratio control module. The rate determination module determines an ammonia generation rate in a three-way catalyst based on a reaction efficiency and a reactant level. The storage level determination module determines an ammonia storage level in a selective catalytic reduction (SCR) catalyst positioned downstream from the three-way catalyst based on the ammonia generation rate. The air/fuel ratio control module controls an air/fuel ratio of an engine based on the ammonia storage level.

Sun, Min; Perry, Kevin L; Kim, Chang H

2014-12-30

383

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 8 min 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

384

Computational Study of Field Initiated Surface Reactions for Synthesis of Diamond and Silicon  

NASA Technical Reports Server (NTRS)

This project involves using quantum chemistry to simulate surface chemical reactions in the presence of an electric field for nanofabrication of diamond and silicon. A field delivered by a scanning tunneling microscope (STM) to a nanometer scale region of a surface affects chemical reaction potential energy surfaces (PES) to direct atomic scale surface modification to fabricate sub-nanometer structures. Our original hypothesis is that the applied voltage polarizes the charge distribution of the valence electrons and that these distorted molecular orbitals can be manipulated with the STM so as to change the relative stabilities of the electronic configurations over the reaction coordinates and thus the topology of the PES and reaction kinetics. Our objective is to investigate the effect of applied bias on surface reactions and the extent to which STM delivered fields can be used to direct surface chemical reactions on an atomic scale on diamond and silicon. To analyze the fundamentals of field induced chemistry and to investigate the application of this technique for the fabrication of nanostructures, we have employed methods capable of accurately describing molecular electronic structure. The methods we employ are density functional theory (DFT) quantum chemical (QC) methods. To determine the effect of applied bias on surface reactions we have calculated the QC PESs in various applied external fields for various reaction steps for depositing or etching diamond and silicon. We have chosen reactions which are thought to play a role in etching and the chemical vapor deposition growth of Si and diamond. The PESs of the elementary reaction steps involved are then calculated under the applied fields, which we vary in magnitude and configuration. We pay special attention to the change in the reaction barriers, and transition state locations, and search for low energy reaction channels which were inaccessible without the applied bias.

Musgrave, Charles Bruce

1999-01-01

385

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

386

Optical reaction cell and light source for [18F] fluoride radiotracer synthesis  

DOEpatents

An apparatus is disclosed 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-Dglucose. 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. 4 figs.

Ferrieri, R.A.; Schlyer, D.; Becker, R.J.

1998-09-15

387

Synthesis reaction pathway of nitrogen-rich ionic compound N 7H 2 +  

Microsoft Academic Search

The potential energy surface of nitrogen-rich ionic compound N7H2+ synthesized by N5+ and cis-N2H2 was investigated. The structures involved in the PES of N7H2+ were optimized using Hartree–Fork, MP2, hybrid functional theory, and CASSCF methods. The barrier height of synthesis pathway was predicted to be 46.8 kcal\\/mol corrected by ZPVE at the B3LYP\\/6-311++G** level. Such high barrier makes the synthesis

Li Jie Wang; Paul G Mezey

2002-01-01

388

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

389

The Construction of All-Carbon Quaternary Stereocenters by Use of Pd-Catalyzed Asymmetric Allylic Alkylation Reactions in Total Synthesis  

PubMed Central

All-carbon quaternary stereocenters have posed significant challenges in the synthesis of complex natural products. These important structural motifs have inspired the development of broadly applicable palladium-catalyzed asymmetric allylic alkylation reactions of unstabilized non-biased enolates for the synthesis of enantioenriched ?-quaternary products. This microreview outlines key considerations in the application of palladium-catalyzed asymmetric allylic alkylation reactions and presents recent total syntheses of complex natural products that have employed these powerful transformations for the direct, catalytic, enantioselective construction of all-carbon quaternary stereocenters. PMID:24944521

Hong, Allen Y.

2014-01-01

390

Anion-exchange synthesis of nanoporous FeP nanosheets as electrocatalysts for hydrogen evolution reaction.  

PubMed

Nanoporous FeP nanosheets are successfully synthesized via the anion-exchange reaction of inorganic-organic hybrid Fe18S25-TETAH (TETAH = protonated triethylenetetramine) nanosheets with P ions. The as-prepared nanoporous FeP nanosheets exhibit high electrochemical hydrogen evolution reaction activity in acidic medium. PMID:23771125

Xu, You; Wu, Rui; Zhang, Jingfang; Shi, Yanmei; Zhang, Bin

2013-07-28

391

Enantioselective Synthesis of Functionalized Pyrazoles by NHC-Catalyzed Reaction of Pyrazolones with ?,?-Unsaturated Aldehydes.  

PubMed

The N-heterocyclic carbene (NHC)-organocatalyzed enantioselective annulation reaction of pyrazolones with ?,?-unsaturated aldehydes proceeding via the chiral ?,?-unsaturated acyl azolium intermediates under oxidative conditions is presented. The reaction afforded dihydropyranone-fused pyrazoles in moderate to good yields and good er values under operationally simple and base-free conditions. PMID:25723547

Yetra, Santhivardhana Reddy; Mondal, Santigopal; Suresh, Eringathodi; Biju, Akkattu T

2015-03-20

392

An efficient and scalable Ritter reaction for the synthesis of tert-butyl amides.  

PubMed

A scalable procedure for the conversion of nitriles to N-tert-butyl amides via the Ritter reaction was optimized employing tert-butyl acetate and acetic acid. The reaction has a broad scope for aromatic, alkyl, and alpha,beta-unsaturated nitriles. PMID:19245267

Baum, Jean C; Milne, Jacqueline E; Murry, Jerry A; Thiel, Oliver R

2009-03-01

393

Synthesis of highly functionalized ?-aminocyclopentanecarboxylate stereoisomers by reductive ring opening reaction of isoxazolines  

PubMed Central

Summary A rapid and simple procedure was devised for the synthesis of multifunctionalized cyclic ?-amino esters and ?-amino alcohols via the 1,3-dipolar cycloaddition of nitrile oxides to ?-aminocyclopentenecarboxylates. The opening of the isoxazoline reductive ring to the corresponding highly functionalized 2-aminocyclopentanecarboxylates occurred stereoselectively with good yields. PMID:22423276

Nonn, Melinda; Kiss, Loránd; Sillanpää, Reijo

2012-01-01

394

Synthesis of highly functionalized ?-aminocyclopentanecarboxylate stereoisomers by reductive ring opening reaction of isoxazolines.  

PubMed

A rapid and simple procedure was devised for the synthesis of multifunctionalized cyclic ?-amino esters and ?-amino alcohols via the 1,3-dipolar cycloaddition of nitrile oxides to ?-aminocyclopentenecarboxylates. The opening of the isoxazoline reductive ring to the corresponding highly functionalized 2-aminocyclopentanecarboxylates occurred stereoselectively with good yields. PMID:22423276

Nonn, Melinda; Kiss, Loránd; Sillanpää, Reijo; Fülöp, Ferenc

2012-01-01

395

Fischer-Tropsch synthesis in supercritical reaction media. Progress report, October 1, 1992--December 31, 1992  

SciTech Connect

Our goals for this quarter were to complete construction of the reactor and analytical units for carrying out Fischer-Tropsch (F-T) synthesis in liquid (n-hexadecane) and in supercritical n-hexane phases. Progress during this quarter was slower than expected.

Subramaniam, B.; Bochniak, D.; Snavely, K.

1993-01-01

396

“ONE-POT” SYNTHESIS OF TRIARYL PHOSPHATES A REACTION CALORIMETRY APPROACH  

Microsoft Academic Search

Triaryl phosphates were obtained in yields ranging from 85–96× in a “one-pot” synthesis via an alkaline route: an ethanolic solution of sodium hydroxide was added to a solution of substituted phenol in toluene. The mixture was distilled until all ethanol was removed. Phosphorus oxychloride was then added and the toluene was distilled. The triaryl phosphates were characterized by NMR (H

J. F. Cajaiba Da Silva; H. T. Nakayama; C. Costa Neto

1997-01-01

397

Combustion of Powder Mixtures Forming Reaction Products – Synthesis of NiAl  

Microsoft Academic Search

Combustion of powder mixtures under adiabatic conditions–Self-propagating High-temperature Synthesis (SHS)-is an efficient and attractive technique to synthesize a host of materials for high technology applications, namely, ceramics, intermetallics, composites and functionally graded materials. Conditions necessary for and general features of this technique are briefly reviewed.

S. K. ROY; A. BISWAS

2002-01-01

398

Synthesis of 2,4-diarylsubstituted-pyridines through a Ru-catalyzed four component reaction.  

PubMed

A ruthenium-catalyzed one-pot synthesis of 2,4-diarylsubstituted pyridines from acetophenones, ammonium acetate and DMF under an oxygen atmosphere is described. The carbon atom situated at C6 of the pyridine ring comes from the methyl group of DMF and the nitrogen atom comes from ammonium acetate. PMID:25764281

Bai, Yang; Tang, Lichang; Huang, Huawen; Deng, Guo-Jun

2015-03-31

399

THE IMPROVED SYNTHESIS OF CARBONATED SOYBEAN OIL USING SUPERCRITICAL CARBON DIOXIDE AT A REDUCED REACTION TIME  

Technology Transfer Automated Retrieval System (TEKTRAN)

We have demonstrated at improved synthesis of a cyclic carbonate of soybean oil (CSO) utilizing supercritical carbon dioxide (CO2) as the solvent. Because the mutual solubility of supercritical CO2 and oil is significantly higher than that of the gas, our method synthesizes the material in ~1/3 of ...

400

Total synthesis of atrochamins F, H, I, and J through cascade reactions  

PubMed Central

A concise and efficient cascade-based total synthesis of artochamins F, H, I, and J is described. The potential biogenetic connection between artochamin F, or a derivative thereof, and artochamins H, I, and J, through an unusual formal [2+2] cycloaddition process, was shown to be feasible. An alternative mechanism for this transformation is also proposed. PMID:19461992

Nicolaou, K. C.; Lister, Troy; Denton, Ross M.; Gelin, Christine F.

2008-01-01

401

Nitridation of chromium powder in ammonia atmosphere  

NASA Astrophysics Data System (ADS)

CrN powder was synthesized by nitriding Cr metal in ammonia gas flow, and its chemical reaction mechanism and nitridation process were studied. Through thermodynamic calculations, the Cr-N-O predominance diagrams were constructed for different temperatures. Chromium nitride formed at 7002-1200°C under relatively higher nitrogen and lower oxygen partial pressures. Phases in the products were then investigated using X-ray diffraction (XRD), and the Cr2N content varied with reaction temperature and holding time. The results indicate that the Cr metal powder nitridation process can be explained by a diffusion model. Further, Cr2N formed as an intermediate product because of an incomplete reaction, which was observed by high-resolution transmission electron microscopy (HRTEM). After nitriding at 1000°C for 20 h, CrN powder with an average grain size of 63 nm was obtained, and the obtained sample was analyzed by using a scanning electron microscope (SEM).

Li, Ling; Zhen, Qiang; Li, Rong

2015-03-01

402

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

403

Acid-base catalysis of chiral Pd complexes: development of novel catalytic asymmetric reactions and their application to synthesis of drug candidates.  

PubMed

Using the unique character of the chiral Pd complexes 1 and 2, highly efficient catalytic asymmetric reactions have been developed. In contrast to conventional Pd(0)-catalyzed reactions, these complexes function as an acid-base catalyst. Thus active methine and methylene compounds were activated to form chiral palladium enolates, which underwent enantioselective carbon-carbon bond-forming reactions such as Michael reaction and Mannich-type reaction with up to 99% ee. Interestingly, these palladium enolates acted cooperatively with a strong protic acid, formed concomitantly during the formation of the enolates to activate electrophiles, thereby promoting the C-C bond-forming reaction. This palladium enolate chemistry was also applicable to electrophilic enantioselective fluorination reactions, and various carbonyl compounds including beta-ketoesters, beta-ketophosphonates, tert-butoxycarbonyl lactone/lactams, cyanoesters, and oxindole derivatives could be fluorinated in a highly enantioselective manner (up to 99% ee). Using this method, the catalytic enantioselective synthesis of BMS-204352, a promising anti-stroke agent, was achieved. In addition, the direct enantioselective conjugate addition of aromatic and aliphatic amines to alpha,beta-unsaturated carbonyl compound was successfully demonstrated. In this reaction, combined use of the Pd complex 2 having basic character and the amine salt was the key to success, allowing controlled generation of the nucleophilic free amine. This aza-Michael reaction was successfully applied to asymmetric synthesis of the CETP inhibitor torcetrapib. PMID:17015970

Hamashima, Yoshitaka

2006-10-01

404

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...

405

Ammonia Emissions from Dairy Production Systems in Wisconsin  

Technology Transfer Automated Retrieval System (TEKTRAN)

Ammonia (NH3) gas is reactive and is the major basic gas that neutralizes atmospheric acid gases produced from combustion of fossil fuels. This reaction produces an aerosol that is a component of atmospheric haze and is implicated in nitrogen (N) deposition and as a potential human health hazard. T...

406

Kinetic investigation of a solvent-free, chemoenzymatic reaction sequence towards enantioselective synthesis of a ?-amino acid ester.  

PubMed

A solvent-free, chemoenzymatic reaction sequence for the enantioselective synthesis of ?-amino acid esters has been kinetically and thermodynamically characterized. The coupled sequence comprises a thermal aza-Michael addition of cheap starting materials and a lipase catalyzed aminolysis for the kinetic resolution of the racemic ester. Excellent ee values of >99% were obtained for the ?-amino acid ester at 60% conversion. Kinetic constants for the aza-Michael addition were obtained by straightforward numerical integration of second-order rate equations and nonlinear fitting of the progress curves. A different strategy had to be devised for the biocatalytic reaction. Initially, a simplified Michaelis-Menten model including product inhibition was developed for the reaction running in THF as an organic solvent. Activity based parameters were used instead of concentrations in order to facilitate the transfer of the kinetic model to the solvent-free system. Observed solvent effects not accounted for by the use of thermodynamic activities were incorporated into the kinetic model. Enzyme deactivation was observed to depend on the ratio of the applied substrates and also included in the kinetic model. The developed simple model is in very good agreement with the experimental data and allows the simulation and optimization of the solvent-free process. PMID:22275046

Strompen, Simon; Weiss, Markus; Ingram, Thomas; Smirnova, Irina; Gröger, Harald; Hilterhaus, Lutz; Liese, Andreas

2012-06-01

407

The impact of genome analyses on our understanding of ammonia-oxidizing bacteria.  

PubMed

The availability of whole-genome sequences for ammonia-oxidizing bacteria (AOB) has led to dramatic increases in our understanding of these environmentally important microorganisms. Their genomes are smaller than many other members of the proteobacteria and may indicate genome reductions consistent with their limited lifestyle. The genomes have a surprising level of gene repetition including genes for ammonia catabolism, iron acquisition, and insertion sequences. The gene profiles reveal limited genes for catabolism and transport of complex organic compounds, but complete pathways for some other compounds. This led to the observation of chemolithoheterotrophic growth of Nitrosomonas europaea. Genes for sucrose synthesis/degradation were identified. The core metabolic module of aerobic ammonia oxidation, the extraction of electrons from hydroxylamine to generate proton-motive force and reductant, has evolutionary roots in the denitrification inventory of anaerobic sulfur-dependent bacteria. The extension by ammonia monooxygenase provides a mechanism to feed this module using ammonia and O(2). PMID:17506671

Arp, Daniel J; Chain, Patrick S G; Klotz, Martin G

2007-01-01

408

A facile and expeditious microwave-assisted synthesis of 4-aryl-2-ferrocenyl-quinoline derivatives via multi-component reaction  

Microsoft Academic Search

An efficient and rapid route for the synthesis of 4-aryl-2-ferrocenyl-quinoline derivatives through microwave-assisted multi-component reaction of acetylferrocene with aromatic aldehyde and dimedone in the presence of ammonium acetate using DMF as reaction media at 100°C is described. This novel procedure lends itself well to combinatorial methods, providing the target heteropolymetallic compounds in excellent yield without further purification.

Shu-Jiang Tu; Shu Yan; Xu-Dong Cao; Shan-Shan Wu; Xiao-Hong Zhang; Wen-Juan Hao; Zheng-Guo Han; Feng Shi

2009-01-01

409

An enantioselective formal synthesis of 4-demethoxydaunomycin using the catalytic asymmetric ring opening reaction of meso-epoxide with p-anisidine  

Microsoft Academic Search

A catalytic asymmetric formal synthesis of 4-demethoxydaunomycin (3) was achieved using a catalytic asymmetric ring opening reaction of meso-epoxide 9 as a key step. The epoxide opening reaction was promoted by 10mol% of Pr-(R)-BINOL–Ph3P?O complex to give the ?-amino alcohol 11 in 80% yield with 65% enantiomeric excess (ee). Single recrystallization enhanced the enantiomeric purity of the ?-amino alcohol 11

Akihiro Sekine; Takashi Ohshima; Masakatsu Shibasaki

2002-01-01

410

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

411

Insight into methanol synthesis from CO2 hydrogenation on Cu(111): Complex reaction network and the effects of H2O  

SciTech Connect

Methanol synthesis from CO2 hydrogenation on supported Cu catalysts is of considerable importance in the chemical and energy industries. Although extensive experimental and theoretical efforts have been carried out in the past decades, the most fundamental questions such as the reaction mechanisms and the key reaction intermediates are still in debate. In the present work, a comprehensive reaction network for CO2 hydrogenation to methanol on Cu(111) was studied using periodic density functional theory (DFT) calculations. All of the elementary reaction steps in the reaction network were identified in an unbiased way with the dimer method. Our calculation results show that methanol synthesis from direct hydrogenation of formate on Cu(111) is not feasible due to the high activation barriers for some of the elementary steps. Instead, we find that CO2 hydrogenation to hydrocarboxyl (trans-COOH) is kinetically more favorable than formate in the presence of H2O via a unique proton transfer mechanism. The trans-COOH is then converted into hydroxymethylidyne (COH) via dihydroxycarbene (COHOH) intermediates, followed by three consecutive hydrogenation steps to form hydroxymethylene (HCOH), hydroxymethyl (H2COH), and methanol. This is consistent with recent experimental observations [1], which indicate that direct hydrogenation of formate will not produce methanol under dry hydrogen conditions. Thus, both experiment and computational modeling clearly demonstrate the important role of trace amounts of water in methanol synthesis from CO2 hydrogenation on Cu catalysts. The proposed methanol synthesis route on Cu(111) not only provides new insights into methanol synthesis chemistry, but also demonstrates again that spectroscopically observed surface species are often not critical reaction intermediates but rather spectator species. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

Zhao, Yafan; Yang, Yong; Mims, Charles A.; Peden, Charles HF; Li, Jun; Mei, Donghai

2011-05-31

412

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

413

Nickel-catalyzed reaction of thioisatins and alkynes: a facile synthesis of thiochromones.  

PubMed

A new synthetic method for thiochromones was developed by using nickel-catalyzed decarbonylative cycloaddition of readily available thioisatins with alkynes. This reaction proceeded under very mild conditions and has quite high functional group compatibility. PMID:25347619

Inami, Tasuku; Kurahashi, Takuya; Matsubara, Seijiro

2014-11-01

414

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

415

Catalytic esterification of polyoxypropylene glycols applied in reaction injection moulding block copolyamide synthesis  

Microsoft Academic Search

The kinetics of the model reaction between ethylene glycol and N-acetyl-?-caprolactam in the presence of different catalysts was investigated using differential isothermal calorimetry. Tetrabutyl orthotitanate was shown to be the most effective catalyst for the esterification of hydroxyl-containing compounds. It was shown that the reaction proceeded preferably by opening an exocyclic amide bond with the liberation of free ?-caprolactam. The

V. A. Kotelnikov; I. E. Persits; N. N. Surin; L. B. Danilevskaya; H. Sekiguchi; Ch. Bui

1996-01-01

416

Synthesis of trifluoromethyl-containing vicinal diamines by asymmetric decarboxylative mannich addition reactions.  

PubMed

Herein is reported a study of asymmetric decarboxylative Mannich addition reactions between (Ss)-N-t-butylsulfinyl-3,3,3-trifluoroacetaldimine and Schiff bases derived from various aldehydes and lithium 2,2-diphenylglycinate. These reactions proceed with excellent diastereoselectivities and good chemical yields, providing a practical method for preparation of trifluoromethyl-containing vicinal diamines. The procedures can be conducted under convenient conditions, rendering this approach of high synthetic value. PMID:25714116

Wu, Lingmin; Xie, Chen; Mei, Haibo; Dai, Yanling; Han, Jianlin; Soloshonok, Vadim A; Pan, Yi

2015-03-20

417

Synthesis of substituted tetrahydroindoloisoquinoline derivatives via intramolecular Pd-catalyzed alkene carboamination reactions.  

PubMed

Intramolecular Pd-catalyzed alkene carboamination reactions of substituted 2-allyl-N-(2-bromobenzyl)anilines are described. The substrates for these reactions are generated in two steps from readily available 2-allylanilines and 2-bromobenzaldehyde derivatives. The transformations afford substituted tetrahydroindoloisoquinolines, an uncommon class of fused bicyclic heterocycles, in good yield. The mechanism of these transformations is described, and a model that accounts for the observed product stereochemistry is proposed. PMID:24724560

Alicea, Jeremiah; Wolfe, John P

2014-05-01

418

Synthesis of Medium-Bridged Twisted Lactams via Cation–? Control of Regiochemistry of Intramolecular Schmidt Reaction  

PubMed Central

Medium-bridged twisted amides can be synthesized by the intramolecular Schmidt reaction of 2-azidoalkyl ketones. In these reactions, the regiochemistry of the Schmidt reaction is diverted into a typically disfavored pathway by the presence of an aromatic group at the ?-position adjacent to the ketone, which stabilizes the predominantly reactive conformation of the azidohydrin intermediate by engaging in a non-bonded cation–? interaction with the positively charged diazonium cation. This results in the rarely observed rearrangement of the C-C bond distal to the azidoalkyl chain. This reaction pathway also requires the azide-containing tether to be situated in the axial orientation in the key azidohydrin intermediate. Examination of the effect of substitution of aromatic rings on the regiochemistry of the Schmidt reaction shows an increase in the migratory selectivity with more electron-rich aromatic groups. The selectivity is lower when an electron withdrawing substituent is placed on the aromatic ring. The ability of cation–? interactions to act as a controlling element decreases when Lewis acids coordinate to substituents on the aromatic ring. The developed version of the Schmidt reaction provides a direct access to a family of medium-bridged twisted amides with [4.3.1] bicyclic system, compounds which are very difficult to access using other currently available methods. PMID:20095596

Szostak, Michal; Yao, Lei; Aubé, Jeffrey

2010-01-01

419

Stoichiometric Reactions of Acylnickel(II) Complexes with Electrophiles and the Catalytic Synthesis of Ketones.  

PubMed

Acylnickel(II) complexes feature prominently in cross-electrophile coupling (XEC) reactions that form ketones, yet their reactivity has not been systematically investigated. We present here our studies on the reactivity of acylnickel(II) complexes with a series of carbon electrophiles. Bromobenzene, ?-chloroethylbenzene, bromooctane, and iodooctane were reacted with (dtbbpy)Ni(II)(C(O)C5H11)(Br) (1b) and (dtbbpy)Ni(II)(C(O)tolyl)(Br) (1c) to form a variety of organic products. While reactions with bromobenzene formed complex mixtures of ketones, reactions with ?-chloroethylbenzene were highly selective for the cross-ketone product. Reactions with iodooctane and bromooctane also produced the cross-ketone product, but in intermediate yield and selectivity. In most cases the presence or absence of a chemical reductant (zinc) had only a small effect on the selectivity of the reaction. The coupling of 1c with iodooctane (60% yield) was translated into a catalytic reaction, the carbonylative coupling of bromoarenes with primary bromoalkanes (six examples, 60% average yield). PMID:25364092

Wotal, Alexander C; Ribson, Ryan D; Weix, Daniel J

2014-10-27

420

Template-free synthesis of hollow nitrogen-doped carbon as efficient electrocatalysts for oxygen reduction reaction  

NASA Astrophysics Data System (ADS)

In this paper, we report a template-free method to fabricate hollow nitrogen-doped carbon (HNC) by pyrolysis of hollow polyaniline microspheres, which were synthesized by suspension polymerization method. The entire synthesis is simple, environmentally benign, and economic. The oxygen reduction reaction (ORR) activity of the as-prepared HNC catalyst is close to that of the commercial Pt/C catalyst in alkaline media with four electron pathway. Moreover, the HNC shows much better fuel crossover resistance and long-term durability than the commercial Pt/C in alkaline medium. All these features make HNC a potentially promising and suitable substitute for the expensive noble metal catalysts in the next generation alkaline fuel cells.

Wu, Rui; Chen, Siguo; Zhang, Yuanliang; Wang, Yao; Ding, Wei; Li, Li; Qi, Xueqiang; Shen, Xiu; Wei, Zidong

2015-01-01

421

Synthesis and characterization of palladium and palladium-cobalt nanoparticles on Vulcan XC-72R for the oxygen reduction reaction.  

PubMed

A single-source approach was used to synthesize bimetallic nanoparticles on a high-surface-area carbon-support surface. The synthesis of palladium and palladium-cobalt nanoparticles on carbon black (Vulcan XC-72R) by chemical and thermal reduction using organometallic complexes as precursors is described. The electrocatalysts studied were Pd/C, Pd2Co/C, and PdCo2/C. The nanoparticles composition and morphology were characterized using inductively coupled plasma mass spectrophotometer (ICP-MS), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray fluorescence spectroscopy (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. Electrocatalytic activity towards the oxygen reduction reaction (ORR) and methanol tolerance in oxygen-saturated acid solution were determined. The bimetallic catalyst on carbon support synthetized by thermal reduction of the Pd2Co precursor has ORR electrocatalytic activity and a higher methanol tolerance than a Pt/C catalyst. PMID:24102312

Arroyo-Ramírez, Lisandra; Montano-Serrano, Rubenier; Luna-Pineda, Tatiana; Román, Félix R; Raptis, Raphael G; Cabrera, Carlos R

2013-11-27

422

Single-shell carbon-encapsulated iron nanoparticles: synthesis and high electrocatalytic activity for hydrogen evolution reaction.  

PubMed

Efficient hydrogen evolution reaction (HER) through effective and inexpensive electrocatalysts is a valuable approach for clean and renewable energy systems. Here, single-shell carbon-encapsulated iron nanoparticles (SCEINs) decorated on single-walled carbon nanotubes (SWNTs) are introduced as a novel highly active and durable non-noble-metal catalyst for the HER. This catalyst exhibits catalytic properties superior to previously studied nonprecious materials and comparable to those of platinum. The SCEIN/SWNT is synthesized by a novel fast and low-cost aerosol chemical vapor deposition method in a one-step synthesis. In SCEINs the single carbon layer does not prevent desired access of the reactants to the vicinity of the iron nanoparticles but protects the active metallic core from oxidation. This finding opens new avenues for utilizing active transition metals such as iron in a wide range of applications. PMID:25683139

Tavakkoli, Mohammad; Kallio, Tanja; Reynaud, Olivier; Nasibulin, Albert G; Johans, Christoffer; Sainio, Jani; Jiang, Hua; Kauppinen, Esko I; Laasonen, Kari

2015-04-01

423

Ammonia Ice Clouds on Jupiter  

NASA Technical Reports Server (NTRS)

The top cloud layer on Jupiter is thought to consist of ammonia ice, but most of that ammonia 'hides' from spectrometers. It does not absorb light in the same way ammonia does. To many scientists, this implies that ammonia churned up from lower layers of the atmosphere 'ages' in some way after it condenses, possibly by being covered with a photochemically generated hydrocarbon mixture. The New Horizons Linear Etalon Imaging Spectral Array (LEISA), the half of the Ralph instrument that is able to 'see' in infrared wavelengths that are absorbed by ammonia ice, spotted these clouds and watched them evolve over five Jupiter days (about 40 Earth hours). In these images, spectroscopically identified fresh ammonia clouds are shown in bright blue. The largest cloud appeared as a localized source on day 1, intensified and broadened on day 2, became more diffuse on days 3 and 4, and disappeared on day 5. The diffusion seemed to follow the movement of a dark spot along the boundary of the oval region. Because the source of this ammonia lies deeper than the cloud, images like these can tell scientists much about the dynamics and heat conduction in Jupiter's lower atmosphere.

2007-01-01

424

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...

425

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...

426

An efficient synthesis of thiopyrano[5,6- c]coumarin\\/[6,5- c]chromones through intramolecular domino Knoevenagel hetero Diels–Alder reactions  

Microsoft Academic Search

The synthesis of novel polycyclic thiopyrano coumarin\\/chromone frameworks through intramolecular domino Knoevenagel hetero Diels–Alder reactions of 4-hydroxy coumarin and its benzo-analogous with S-prenylated aromatic aldehydes was studied. A high degree of chemoselectivity was achieved by the application of microwave irradiation and a solid support.

Jayadevan Jayashankaran; Rathna Durga R. S. Manian; Raghavachary Raghunathan

2006-01-01

427

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

428

Synthesis of polysubstituted ?-amino cyclohexane carboxylic acids via Diels-Alder reaction using Ni(II)-complex stabilized ?-alanine derived dienes.  

PubMed

This paper describes the design and synthesis of a new class of ?-alanine derived dienes stabilized by Ni(II)-complex. Preliminary study of their Diels-Alder cycloaddition reactions with several types of dienophiles demonstrates their significant synthetic potential for the preparation of various polyfunctional ?-aminocyclohexane carboxylic acids. PMID:23053018

Ding, Xiao; Wang, Hengshuai; Wang, Jiang; Wang, Sinan; Lin, Daizong; Lv, Li; Zhou, Yu; Luo, Xiaomin; Jiang, Hualiang; Aceña, José Luis; Soloshonok, Vadim A; Liu, Hong

2013-02-01

429

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...

430

The possible role of the pre-exponential factor in explaining the increased reaction rates observed during the microwave synthesis of titanium carbide  

Microsoft Academic Search

Reaction rates observed during the microwave synthesis of titanium carbide powder via the carbothermal reduction of the oxide are more than three times faster than those observed during conventional processing at the same temperature. Although not dissimilar to other reports of “microwave effects” in the literature, this result is of interest because the microwave heating mechanism is quite different compared

J. G. P. Binner; N. A. Hassine; T. E. Cross

1995-01-01

431

Parallel synthesis of dihydropyrimidinones using Yb(III)-resin and polymer-supported scavengers under solvent-free conditions. A green chemistry approach to the Biginelli reaction  

Microsoft Academic Search

An efficient synthesis of an array of 3,4-dihydropyrimidin-2-(1H)-ones using solid-supported ytterbium(III) reagent from aldehydes, 1,3-dicarbonyl compounds and urea (Biginelli reaction) under solvent-free conditions is described. Purification of each member of the library was carried out using a cocktail of acid and basic polymer-supported scavengers

Alessandro Dondoni; Alessandro Massi

2001-01-01

432

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

433

Intramolecular cycloaddition reactions of furo[3,4-b]indoles for alkaloid synthesis.  

PubMed

Model studies dealing with the Cu(II)- or Rh(II)-catalyzed carbenoid cyclization/cycloaddition cascade of several ?-diazo indolo amido esters have been carried out as an approach to the alkaloid scandine. The Cu(II)-catalyzed reaction of an ?-diazo indolo diester that contains a tethered oxa-pentenyl side chain was found to give rise to a reactive benzo[c]furan which undergoes a subsequent [4 + 2]-cycloaddition across the tethered ?-bond. The reaction proceeds by the initial generation of a copper carbenoid intermediate which cyclizes onto the adjacent carbonyl group to give a reactive benzo[c]furan which in certain cases can be isolated. Disappointingly, the analogous reaction with the related amido indolo ester failed to take place, even when the tethered ?-bond contained an electron-withdrawing carbomethoxy group. It would seem that the geometric requirements for the intramolecular cycloaddition of the furo[3,4-b]indole system with the tethered ?-bond imposes distinct restrictions upon the bond angles of the reacting centers to prevent the cycloaddition reaction from occurring. However, the incorporation of another carbonyl group on the nitrogen atom of the tethered alkenyl diazo amido indolo ester seemingly provides better orbital overlap between the reacting ?-systems and allows the desired cycloaddition reaction to occur. PMID:24617539

Padwa, Albert; Zou, Yan; Cheng, Bo; Li, Hao; Downer-Riley, Nadale; Straub, Christopher S

2014-04-01

434

Molecular and physiological responses to long-term sublethal ammonia exposure in Atlantic salmon (Salmo salar).  

PubMed

The objective of this study was to determine the underlying physiological and molecular responses to long-term sublethal ammonia exposure in Atlantic salmon (Salmo salar) parr. Previous studies have predominately focused on mechanisms during acute, short-term exposure. For that purpose Atlantic salmon parr were exposed to four ammonia concentrations between 4 and 1800 ?mol l(-1) total ammonia nitrogen (TAN), and subjected to two feeding regimes for 15 weeks. Elevated environmental ammonia and full feeding strength caused an initial increase in plasma ammonia levels ([T(amm)]) after 22 days of exposure, which thereafter declined and remained similar to the control animals towards the end of the study. On the other hand, a progressive decrease in plasma urea levels was evident throughout the entire exposure period and depended on the concentration of environmental ammonia, with the largest decrease in urea levels observed at the highest ammonia concentrations (1700 and 1800 ?mol l(-1) TAN). We hypothesized that the successful adaptation to long-term elevated ammonia levels would involve an increased capacity for carrier-facilitated branchial excretion. This hypothesis was strengthened by the first evidence of an up-regulation of branchial transcription of the genes encoding the Rhesus (Rh) glycoproteins, Rhcg1 and Rhcg2, urea transporter (UT) and aquaporin 3a (Aqp3a), during long-term exposure. Of the Rhesus glycoprotein (Rh) mRNAs, Rhcg1 was up-regulated at all tested ammonia levels, while Rhcg2 showed a concentration-sensitive increase. Increased transcription levels of V-type H(+)-ATPase (H(+)-ATPase) were observed at the highest ammonia concentrations (1700 and 1800 ?mol l(-1) TAN) and coincided with an up-regulation of Rhcg2 at these concentrations. Transcription of UT and Aqp3a was increased after 15 weeks of exposure to low ammonia levels (470 and 480 ?mol l(-1) TAN). A significant increase in brain glutamine (Gln) concentration was observed for full fed Atlantic salmon after 22 days and in fish with restricted feeding after 105 days of exposure to 1800 and 1700 ?mol l(-1) TAN, respectively, without any concomitant decrease in brain glutamate (Glu) concentrations. These results suggest that Gln synthesis is an ammonia detoxifying strategy employed in the brain of Atlantic salmon parr during long-term sublethal ammonia exposure. Full feed strength had an additive effect on plasma [T(amm)], while the restricted feeding regime postponed the majority of the observed physiological and molecular responses. In conclusion, Atlantic salmon parr adapts to the long-term sublethal ammonia concentrations with increased branchial transcription levels of ammonia and urea transporting proteins and ammonia detoxification in the brain. PMID:22898234

Kolarevic, Jelena; Takle, Harald; Felip, Olga; Ytteborg, Elisabeth; Selset, Roger; Good, Christopher M; Baeverfjord, Grete; Asgård, Torbjørn; Terjesen, Bendik Fyhn

2012-11-15

435

Ammonia transport by terrestrial and aquatic insects  

Microsoft Academic Search

Ammonia, an end product from amino acid and nucleic acid metabolism, is highly toxic for most animals. This review will provide an update on nitrogen metabolism in terrestrial and aquatic insects with emphasis on ammonia generation and transport.Aspects that will be discussed include metabolic pathways of nitrogenous compounds, the origin of ammonia and other nitrogenous waste products, ammonia toxicity, putative

Dirk Weihrauch; Andrew Donini; Michael J. O’Donnell

436

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 ...

437

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....

438

Enantioselective Synthesis of Tryptophan Derivatives by a Tandem Friedel – Crafts Conjugate Addition/Asymmetric Protonation Reaction  

PubMed Central

The tandem Friedel–Crafts conjugate addition/asymmetric protonation reaction between 2-substituted indoles and methyl 2-acetamidoacrylate is reported. The reaction is catalyzed by (R)-3,3?-dibromo-BINOL in the presence of stoichiometric SnCl4, and is the first example of a tandem conjugate addition/asymmetric protonation reaction using a BINOL•SnCl4 complex as the catalyst. A range of indoles furnished synthetic tryptophan derivatives in good yields and high levels of enantioselectivity, even on preparative scale. The convergent nature of this transformation should lend itself to the preparation of unnatural tryptophan derivatives for use in a broad array of synthetic and biological applications. PMID:22390403

Kieffer, Madeleine E.; Repka, Lindsay M.; Reisman, Sarah E.

2012-01-01

439

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

440

Evaluation of a commercial packed bed flow hydrogenator for reaction screening, optimization, and synthesis.  

PubMed

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; Doherty, Elizabeth M

2011-01-01

441

A separation-integrated cascade reaction to overcome thermodynamic limitations in rare-sugar synthesis.  

PubMed

Enzyme cascades combining epimerization and isomerization steps offer an attractive route for the generic production of rare sugars starting from accessible bulk sugars but suffer from the unfavorable position of the thermodynamic equilibrium, thus reducing the yield and requiring complex work-up procedures to separate pure product from the reaction mixture. Presented herein is the integration of a multienzyme cascade reaction with continuous chromatography, realized as simulated moving bed chromatography, to overcome the intrinsic yield limitation. Efficient production of D-psicose from sucrose in a three-step cascade reaction using invertase, D-xylose isomerase, and D-tagatose epimerase, via the intermediates D-glucose and D-fructose, is described. This set-up allowed the production of pure psicose (99.9?%) with very high yields (89?%) and high enzyme efficiency (300?g of D-psicose per g of enzyme). PMID:25688873

Wagner, Nina; Bosshart, Andreas; Failmezger, Jurek; Bechtold, Matthias; Panke, Sven

2015-03-27

442

Lithium aminoborohydrides 16. Synthesis and reactions of monomeric and dimeric aminoboranes.  

PubMed

Aminoboranes are synthesized in situ from the reaction of the corresponding lithium aminoborohydrides (LABs) with methyl iodide, trimethylsilylchloride (TMS-Cl), or benzyl chloride under ambient conditions. In hexanes, the reaction using methyl iodide produces aminoborane and methane, whereas in tetrahydro-furan (THF) this reaction produces amine-boranes (R1R2HN:BH3) as the major product. The reaction of iPr-LAB with TMS-Cl or benzyl chloride yields exclusively diisopropylaminoborane [BH2-N(iPr)2] in THF as well as in hexanes at 25 degrees C. Diisopropylaminoborane and dicyclohexylaminoborane exist as monomers due to the steric requirement of the alkyl group. All other aminoboranes studied are not sterically hindered enough to be monomers in solution, but instead exist as a mixture of monomers and dimers. The dimers are four-membered rings formed through boron-nitrogen coordination. In general aminoboranes are not hydroborating reagents. However, monomeric aminoboranes, such as BH2-N(iPr)2, can reduce nitriles in the presence of catalytic amounts of LiBH4. This BH2-N(iPr)2/LiBH4 reducing system also re-duces ketones, aldehydes, and esters. Diisopropylaminoborane, synthesized from iPr-LAB, can be converted into boronic acids by a palladium-catalyzed reaction with aryl bromides. Aminoboranes derived from heterocyclic amines, such as pyrrole, pyrazole, and imidazole, can be prepared by the direct reaction of borane/tetrahydrofuran (BH3:THF) with these heterocyclic amines. It has been reported that pyrazole-derived aminoborane forms a six-membered dimer through boron-nitrogen coordination, where as, pyrrolylborane forms a dimer through boron-hydrogen coordination. Pyrrolylborane monohydroborates both alkenes and alkynes at ambient temperatures. Hydroboration of styrene with pyrrolylborane followed by hydrolysis gives the corresponding boronic acid, 2-phenylethylboronic acid, in 40% yield. Similarly phenylacetylene is mono-hydroborated by pyrrolylborane, to give E-2-phenylethenylboronic acid in 50% yield. PMID:18215062

Pasumansky, Lubov; Haddenham, Dustin; Clary, Jacob W; Fisher, Gary B; Goralski, Christian T; Singaram, Bakthan

2008-03-01

443

Stereocontrolled synthesis of bicyclic sulfamides via Pd-catalyzed alkene carboamination reactions. Control of 1,3-asymmetric induction by manipulating mechanistic pathways.  

PubMed

A new annulation strategy for the synthesis of trans-bicyclic sulfamides is described. The Pd-catalyzed alkene carboamination reactions of 2-allyl and cis-2,5-diallyl pyrrolidinyl sulfamides with aryl and alkenyl triflates afford the fused bicyclic compounds in good yields and with good diastereoselectivity (up to 13:1 dr). Importantly, by employing reaction conditions that favor an anti-aminopalladation mechanism, the relative stereochemistry between the C3 and C4a stereocenters of the products is reversed relative to related Pd-catalyzed carboamination reactions that proceed via syn-aminopalladation. PMID:24916343

Babij, Nicholas R; McKenna, Grace M; Fornwald, Ryan M; Wolfe, John P

2014-06-20

444

Reaction regimes on the synthesis of hollow particles by the Kirkendall effect.  

PubMed

The formation of hollow vs solid particles by means of the oxidation reaction of solid metal particles depends on the differential self-diffusivities of the reactants through the composite shell, the reaction probabilities at each interface, and the concentration and diffusivity of the element in solution. By means of a kinetic model of the oxidation process, we determine the phase diagrams for the geometry of the oxidized particles and propose four shell growth regimes. We experimentally illustrate the different growth scenarios by changing the conditions of oxidation of cadmium spherical crystals using different chalcogen precursors. PMID:19630408

Cabot, Andreu; Ibáñez, Maria; Guardia, Pablo; Alivisatos, A Paul

2009-08-19

445

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

446

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

PubMed Central

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

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

2011-01-01

447

(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

448

A chemical synthesis of 11-methoxy mitragynine pseudoindoxyl featuring the interrupted Ugi reaction  

PubMed Central

A synthesis of 11-methoxy mitragynine pseudoindoxyl, a new member of the mitragynine class of opioid agonists, from a derivative of the Geissman-Waiss lactone is described. An internal attack of an electron-rich aromatic ring on an electrophilic nitrilium ion and a late-stage construction of the functionalized piperidine ring by the method of reductive cyclization are the pivotal transformations; both ring annulations proceed in a highly diastereoselective fashion. The construction of substituted indoxyl frameworks by the interrupted Ugi method offers an attractive alternative to the strategy of oxidatively rearranging indoles. PMID:23878716

Kim, Jimin; Schneekloth, John S.

2013-01-01

449

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

450

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 5