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1

Exergy analysis of industrial ammonia synthesis  

Microsoft Academic Search

Exergy consumption of ammonia production plants depends strongly on the ammonia synthesis loop design. Due to the thermodynamically limited low degree of conversion of hydrogen–nitrogen mixture to ammonia, industrial ammonia synthesis is implemented as recycle process (so-called “ammonia synthesis loop”). Significant quantities of reactants are recycled back to reactor, after the removal of ammonia at low temperatures. Modern ammonia synthesis

Zornitza Kirova-Yordanova

2004-01-01

2

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.

Klinkenberg, Jessica L.

2012-01-01

3

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

4

Reactions of fluoroalkyl-. beta. -ketoesters with ammonia  

SciTech Connect

It has been found that ..beta..-ketoesters containing highly fluorinated substituents (CF/sub 3/, or H(CF/sub 2/)/sub 4/) react with ammonia to give ..beta..-aminocrotonate esters, or under severe conditions, ..beta..-ketoamides. The latter react with a tenfold excess of ammonia to give ..beta..-aminocrotonamides together with acetamide and fluorocarboxamides. Acetoacetic and 4,4-difluoroacetoacetic esters react with ammonia, irrespective of the reaction conditions, to give ..beta..-aminocrotonate and 4,4-difluoro-..beta..-aminocrotonate esters. Using DNMR and dipole moments, it has been shown that rotation of the amino group around the C-N bond in fluorinated ..beta..-aminocrotonate esters is restricted (..delta..Gnumber approx. 50 kJ/mole).

Pashkevich, K.I.; Saloutin, V.I.; Fomin, A.N.; Rudaya, M.N.; Egorova, L.G.

1987-01-20

5

The sugar model: autocatalytic activity of the triose-ammonia reaction.  

PubMed

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 of 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. PMID:17225954

Weber, Arthur L

2007-04-01

6

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

7

Reaction of ketene ions with ammonia  

SciTech Connect

Reactions of ketene ions with NH{sub 3}, ND{sub 3}, H{sub 2}O, and CH{sub 4} were investigated in a selected ion flow tube (SIFT). There were no observable products for H{sub 2}O and CH{sub 4} and no ion/neutral complex stabilization in any of the systems investigated. The ammonia system demonstrated two reaction channels, in agreement with previous FTICR data (1) distonic ion CH{sub 2}NH{sub 3}{sm bullet}{sup +} formation, with a branching ratio of 0.2 and (2) proton transfer, with a branching ratio of 0.8. The overall second-order rate constant for NH{sub 3} is (2.2 {plus minus} 0.15) {times} 10{sup {minus}9} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}, in agreement with the gas kinetic ion-dipole collision rate. Isotope scrambling was studied for primary (CH{sub 2}CO{sup +}) and for secondary (CH{sub 2}NX{sub 3}{sm bullet}{sup +} and NX{sub 4}{sup +}, X = H or D) proton-transfer reactions with ND{sub 3}; CH{sub 2}NH{sub 3}{sm bullet}{sup +} appears to transfer an X{sup +} ion to ND{sub 3} without any scrambling. CH{sub 2}CO{sm bullet}{sup +} undergoes reactions with partial scrambling and NX{sub 4}{sup +} seems to react with almost complete scrambling. The results are compared with these of Adams, Smith, and Henchman on the NH{sub 4}{sup +}/ND{sub 3} system.

Iraqi, M.; Lifshitz, C. (Hebrew Univ. of Jerusalem (Israel)); Reuben, B.G. (South Bank Polytechnic, London (United Kingdom))

1991-10-03

8

Reactions of nitrate salts with ammonia in supercritical water  

Microsoft Academic Search

Reactions involving nitrate salts and ammonia were investigated in supercritical water at temperatures from 450 to 530 C and pressures near 300 bar. Reaction products included nitrite, nitrogen gas, and nitrous oxide. Observed reaction rates and product distributions provided evidence for a free-radical reaction mechanism with NOâ, NO, and NHâ· as the primary reactive species at supercritical conditions. In the

Philip C. Dell'Orco; Earnest F. Gloyna; Steven J. Buelow

1997-01-01

9

Heterogeneous photocatalytic synthesis of ammonia from water and nitrogen  

NASA Astrophysics Data System (ADS)

Photocatalytic synthesis of ammonia from water and nitrogen was performed. Binary wafered catalysts prepared with semiconductor powder (TiO 2, SrTiO 3, CdS or GaP) and platinum black, where the copolymer of ethylene and vinylalcohol was used as a binder, were found to be more effective to yield ammonia than the semiconductor powders alone.

Miyama, Hajime; Fujii, Nobuyuki; Nagae, Yasushi

1980-09-01

10

Structure sensitivity of supported ruthenium catalysts for ammonia synthesis  

Microsoft Academic Search

The catalytic ammonia synthesis activities of four supported ruthenium catalysts are reported. It is seen that Ru\\/MgAl2O4 is more active than two similar Ru\\/C catalysts, which are significantly more active than Ru\\/Si3N4. The activity differences cannot be satisfactorily explained solely by the differences in dispersion. Recent results from single crystal studies and DFT calculations have shown that ammonia synthesis over

Claus J. H Jacobsen; Søren Dahl; Poul L Hansen; Eric Törnqvist; Lone Jensen; Henrik Topsøe; Dorthe V Prip; Pernille B Møenshaug; Ib Chorkendorff

2000-01-01

11

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

NASA Technical Reports Server (NTRS)

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 alpha-hydroxy acid thioesters, the thiol-dependent synthesis of alanine and homoserine is presumed to occur via amino acid thioesters-intermediates capable of forming peptides. 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.

1998-01-01

12

Process for treating gases in the ammonia synthesis. [separation and dehydration of gases leaving synthesis reactor  

Microsoft Academic Search

In the synthesis of ammonia, a process is disclosed for treating the gases flowing from the synthesis reactor wherein those gases flow through a film absorber countercurrent to a cooled aqueous film to extract ammonia which is withdrawn as a strong solution from the absorber and scrubbed gases are combined for recycle with a stream of fresh feed which is

Guadalupi

1977-01-01

13

Process for synthesis of ammonia borane for bulk hydrogen storage  

DOEpatents

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

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

2011-03-01

14

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

15

FTIR characterization of Ru/SiO 2 catalyst for ammonia synthesis  

NASA Astrophysics Data System (ADS)

Carbon monoxide adsorption on a Ru/SiO 2 catalyst was followed by IR spectroscopy to investigate the active sites. Using this catalyst, ammonia synthesis was achieved at 350°C in an N 2/H 2 gas mixture (N 2/H 2?3 : 1) for different reaction times. In addition to NH 3 other NH x ( x=1,2) species were also observed. CO adsorption after NH 3 production was also performed to investigate the change in nature of the active sites. Based on the experimental evidence participation of Ru 0 sites in ammonia synthesis was confirmed and a partial oxidation of the reduced Ru sites during the synthesis was observed.

Sayan, ?.; Kantcheva, M.; Suzer, S.; Uner, D. O.

1999-05-01

16

Importance of ammonia pressure in the kinetics of ammonia synthesis over supported Ru  

Microsoft Academic Search

The reaction of 3:1 hydrogen-nitrogen over (unpromoted) ruthenium on silica gel or ..gamma..-alumina was studied in a flow reactor at 1.2-3.8 cc\\/sec volumetric flow rates and 691°⁻⁵⁷⁴sup 0\\/K, under which conditions the equilibrium ammonia partial pressure varied from 318-1910 Pa. The plot of partial ammonia pressure vs. the logarithm of the reciprocal volumetric flow rate had slopes of 0.64 and

P. R. Holzman; W. K. Shiflett; J. A. Dumesic

1980-01-01

17

Phenylalanine Ammonia Lyase Catalyzed Synthesis of Amino Acids by an MIO-Cofactor Independent Pathway.  

PubMed

Phenylalanine ammonia lyases (PALs) belong to a family of 4-methylideneimidazole-5-one (MIO) cofactor dependent enzymes which are responsible for the conversion of L-phenylalanine into trans-cinnamic acid in eukaryotic and prokaryotic organisms. Under conditions of high ammonia concentration, this deamination reaction is reversible and hence there is considerable interest in the development of PALs as biocatalysts for the enantioselective synthesis of non-natural amino acids. Herein the discovery of a previously unobserved competing MIO-independent reaction pathway, which proceeds in a non-stereoselective manner and results in the generation of both L- and D-phenylalanine derivatives, is described. The mechanism of the MIO-independent pathway is explored through isotopic-labeling studies and mutagenesis of key active-site residues. The results obtained are consistent with amino acid deamination occurring by a stepwise E1 cB elimination mechanism. PMID:24692092

Lovelock, Sarah L; Lloyd, Richard C; Turner, Nicholas J

2014-04-25

18

Direct Spectrophotometric Analysis of Ammonia in Natural Waters by the Phenol-Hypochlorite Reaction.  

National Technical Information Service (NTIS)

The phenol-hypochlorite reaction has been adapted to detect microgram quantities of ammonia natural waters. The procedure does not require that the sample be heated, be alkaline, or that the ammonia be extracted. This method estimates ammonia in waters of...

R. T. Emmet

1968-01-01

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

CONVERSION OF CATTLE FEEDLOT MANURE TO ETHYLENE AND AMMONIA SYNTHESIS GAS  

EPA Science Inventory

An investigation was undertaken to scale-up a partial oxidation reactor to evaluate the potential for producing an ammonia synthesis gas from cattle feedlot residue. The synthesis gas from the reactor can be further processed to produce ammonia using existing, commercial technolo...

21

Reaction synthesis of intermetallics.  

National Technical Information Service (NTIS)

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, redu...

S. C. Deevi V. K. Sikka

1994-01-01

22

Solid-state ammonia sensor based on Berthelot’s reaction  

Microsoft Academic Search

A non-reversible solid-state ammonia sensor based on formation of indophenol blue has been developed. A new optimised reaction conditions found for Berthelot’s reaction allow the sensor to respond to dissolved ammonia in ambient conditions at a much faster reaction rate than previously known. This solid-state colorimetric sensor reaches maximum colour intensity in ?3min at room temperature (?20°C) and responds linearly

King Tong Lau; Steve Edwards; Dermot Diamond

2004-01-01

23

An ammonia-stabilized mixed-cation borohydride: synthesis, structure and thermal decomposition behavior.  

PubMed

We demonstrate the synthesis, crystal structure and thermal decomposition behavior of a novel ammonia-stabilized mixed-cation borohydride where the NH3 groups enable the coexistence of Li and Mg cations as an "assistant". Li2Mg(BH4)4·6NH3, which is comprised of orderly arranged Mg[NH3]6(2+) ammine complexes and Li2[BH4]4(2-) complex anions, was synthesized by the mechanochemical reaction between Mg(BH4)2·6NH3 and LiBH4. This novel compound crystallizes in a tetragonal P4(3)2(1)2 (No. 96) structure with lattice parameters a = b = 10.7656(8) Å and c = 13.843(1) Å with very short dihydrogen bonds, which determine a very low onset temperature of 80 °C for hydrogen release and are also responsible for the nucleation of Li2Mg(BH4)4·3NH3 as a decomposition intermediate. Mechanistic investigations on the thermal decomposition showed that the H(?+)-H(?-) combination in the ammonia-stabilized mixed-cation borohydride was significantly enhanced due to the strengthened Mg-N bonds. Upon heating, 11.02 moles of H2 (equivalent to 11.1 wt%) and 3.07 moles of NH3 are evolved from one mole of Li2Mg(BH4)4·6NH3 with a three-step reaction. The insights into the formation mechanism of ammonia-stabilized mixed-cation borohydride and the role played by NH3 group are very useful as a guideline for the design and synthesis of novel B-N-based materials with high hydrogen content. PMID:24226915

Yang, Yanjing; Liu, Yongfeng; Wu, Hui; Zhou, Wei; Gao, Mingxia; Pan, Hongge

2014-01-01

24

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

25

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

26

Reactions of synthesis gas  

Microsoft Academic Search

The use of synthesis gas (syngas) offers the opportunity to furnish a broad range of environmentally clean fuels and chemicals. There has been steady growth in the traditional uses of syngas. Almost all hydrogen gas is manufactured from syngas and there has been a tremendous spurt in the demand for this basic chemical; indeed, the chief use of syngas is

Irving Wender

1996-01-01

27

Regeneration of ammonia borane spent fuel by direct reaction with hydrazine and liquid ammonia.  

PubMed

Ammonia borane (H(3)N-BH(3), AB) is a lightweight material containing a high density of hydrogen (H(2)) that can be readily liberated for use in fuel cell-powered applications. However, in the absence of a straightforward, efficient method for regenerating AB from dehydrogenated polymeric spent fuel, its full potential as a viable H(2) storage material will not be realized. We demonstrate that the spent fuel type derived from the removal of greater than two equivalents of H(2) per molecule of AB (i.e., polyborazylene, PB) can be converted back to AB nearly quantitatively by 24-hour treatment with hydrazine (N(2)H(4)) in liquid ammonia (NH(3)) at 40°C in a sealed pressure vessel. PMID:21415349

Sutton, Andrew D; Burrell, Anthony K; Dixon, David A; Garner, Edward B; Gordon, John C; Nakagawa, Tessui; Ott, Kevin C; Robinson, J Pierce; Vasiliu, Monica

2011-03-18

28

Regeneration of Ammonia Borane Spent Fuel by Direct Reaction with Hydrazine and Liquid Ammonia  

Microsoft Academic Search

Ammonia borane (H3N-BH3, AB) is a lightweight material containing a high density of hydrogen (H2) that can be readily liberated for use in fuel cell-powered applications. However, in the absence of a straightforward, efficient method for regenerating AB from dehydrogenated polymeric spent fuel, its full potential as a viable H2 storage material will not be realized. We demonstrate that the

Andrew D. Sutton; Anthony K. Burrell; David A. Dixon; Edward B. Garner; John C. Gordon; Tessui Nakagawa; Kevin C. Ott; J. Pierce Robinson; Monica Vasiliu

2011-01-01

29

Conversion of Cattle Feedlot Wastes to Ammonia Synthesis Gas.  

National Technical Information Service (NTIS)

The potential of a process to convert cattle feedlot manure to anhydrous ammonia is studied. Due to the fact that ammonia is currently produced on a large scale using natural gas and air, only the processing associated with a reactor system to convert the...

J. E. Halligan K. L. Herzog H. W. Parker R. M. Sweazy

1974-01-01

30

Conversion of Cattle Feedlot Wastes to Ammonia Synthesis Gas.  

National Technical Information Service (NTIS)

A study was undertaken to determine the potential of a process to convert cattle feedlot manure to anhydrous ammonia. Due to the fact that ammonia is currently produced on a large scale using natural gas and air, only the processing associated with a reac...

H. W. Parker J. E. Halligan K. L. Herzog R. M. Sweazy

1974-01-01

31

N-Doping of Graphene Through Electrothermal Reactions with Ammonia  

Microsoft Academic Search

Graphene is readily p-doped by adsorbates, but for device applications, it would be useful to access the n-doped material. Individual graphene nanoribbons were covalently functionalized by nitrogen species through high-power electrical joule heating in ammonia gas, leading to n-type electronic doping consistent with theory. The formation of the carbon-nitrogen bond should occur mostly at the edges of graphene where chemical

Xinran Wang; Xiaolin Li; Li Zhang; Youngki Yoon; Peter K. Weber; Hailiang Wang; Jing Guo; Hongjie Dai

2009-01-01

32

The influence of phase and morphology of molybdenum nitrides on ammonia synthesis activity and reduction characteristics  

SciTech Connect

The reactivities of a series of ternary and binary molybdenum nitrides have been compared. Data have been obtained for the catalytic synthesis of ammonia at 400 deg. C and ambient pressure using a 3:1 H{sub 2}:N{sub 2} mixture. Amongst the ternary nitrides, the mass normalised activity is in the order Co{sub 3}Mo{sub 3}N>Fe{sub 3}Mo{sub 3}N>>Ni{sub 2}Mo{sub 3}N. For the binary molybdenum nitrides, the ammonia synthesis activity is significantly lower than that of Co{sub 3}Mo{sub 3}N and Fe{sub 3}Mo{sub 3}N and varies in the order {gamma}-Mo{sub 2}N{approx}{beta}-Mo{sub 2}N{sub 0.78}>>{delta}-MoN. Nanorod forms of {beta}-Mo{sub 2}N{sub 0.78} and {gamma}-Mo{sub 2}N exhibit generally similar activities to conventional polycrystalline samples, demonstrating that the influence of catalyst morphology is limited for these two materials. In order to characterise the reactivity of the lattice nitrogen species of the nitrides, temperature programmed reactions with a 3:1 H{sub 2}:Ar mixture at temperatures up to 700 deg. C have been performed. For all materials studied, the predominant form of nitrogen lost was N{sub 2}, with smaller amounts of NH{sub 3} being formed. Post-reaction powder diffraction analyses demonstrated lattice shifts in the case of Co{sub 3}Mo{sub 3}N and Ni{sub 2}Mo{sub 3}N upon temperature programmed reaction with H{sub 2}/Ar. Incomplete decomposition yielding mixtures of Mo metal and the original phase were observed for Fe{sub 3}Mo{sub 3}N and {gamma}-Mo{sub 2}N, whilst {beta}-Mo{sub 2}N{sub 0.78} transforms completely to Mo metal and {delta}-MoN is converted to {gamma}-Mo{sub 2}N. - Graphical abstract: Nanorod {gamma}-Mo{sub 2}N.

Mckay, D. [WestCHEM, Department of Chemistry, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Hargreaves, J.S.J. [WestCHEM, Department of Chemistry, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ (United Kingdom)], E-mail: justinh@chem.gla.ac.uk; Rico, J.L.; Rivera, J.L. [Laboratorio de Catalisis, Facultad de Ingenieria Quimica, UMSNH, Edificio E, C.U., Morelia Mich. (Mexico); Sun, X.-L. [WestCHEM, Department of Chemistry, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Department of Chemical Engineering, Shanghai Institute of Technology, 120 Cao Bao Road, Shanghai 200235 (China)

2008-02-15

33

Understanding the novolak synthesis reaction  

NASA Astrophysics Data System (ADS)

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

Bogan, Leonard E., Jr.

1993-09-01

34

The Inversion Potential of Ammonia: An Intrinsic Reaction Coordinate Calculation for Student Investigation  

ERIC Educational Resources Information Center

A report is presented to describe how students can be empowered to construct the full, double minimum inversion potential for ammonia by performing intrinsic reaction coordinate calculations. This work can be associated with the third year physical chemistry lecture laboratory or an upper level course in computational chemistry.

Halpern, Arthur M.; Ramachandran, B. R.; Glendening, Eric D.

2007-01-01

35

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

36

Kinetic analysis of the reactions catalyzed by histidine and phenylalanine ammonia lyases.  

PubMed

Although both the structures and the reactions of histidine and phenylalanine ammonia lyases (HAL and PAL) are very similar, the former shows a primary kinetic deuterium (D) isotope effect, while the latter does not. In the HAL reaction, the release of ammonia is partially rate-determining and is slower than the release of the product (E)-urocanate (4), whereas in the PAL reaction, the release of (E)-cinnamate (2) is the rate-limiting step. With (2S,3S)-[3-(2)H1]phenylalanine (1a), we determined the kinetic D isotope effects with the PAL mutants Q487A, Y350F, L137 H, and the double mutant L137 H/Q487E. The kH/kD values for the former two were of the same magnitude as with wild-type PAL (1.20+/-0.07), while the exchange of L137 to H almost doubled the effect (kH/kD=2.32+/-0.01). We conclude that L137 is part of the hydrophobic pocket harboring the phenyl group of the substrate/product and is responsible for its strong binding. The stability of the HAL ammonia complex was demonstrated 40 years ago. Here, we show that, in contrast to the former assumption, ammonia in the complex is not covalently bound to the prosthetic electrophile, 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO; 5). We carried out experiments with a mutant enzyme lacking MIO and exhibiting ca. 10(3) times less activity. Nevertheless, the enzyme-ammonia complex was formed, and the mutant behaved upon addition of (E)-[14C]urocanate (4a) like wild-type HAL. We conclude, therefore, that ammonia is bound in the complex by Coulomb forces as ammonium ion and can be released only after (E)-urocanate (4). PMID:17191848

Viergutz, Sandra; Rétey, János

2004-02-01

37

Potassium promoter in industrial ammonia synthesis catalyst: Studies by surface ionization  

Microsoft Academic Search

Industrial ammonia synthesis catalysts, as fresh (pre-reduced and passivated) and used (passivated) flat samples were studied in a molecular beam UHV apparatus, using a surface ionization detector. The desorption of the K promoter from the catalyst at 870–1080 K could be characterized, by measuring angular distributions and simultaneous Arrhenius plots, as a function of the angle around the sample. The

K. Engvall; L. Holmlid; A. Kotarba; J. B. C. Pettersson; P. G. Menon; P. Skaugset

1996-01-01

38

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

39

Purge gas recovery of ammonia synthesis plant by integrated configuration of catalytic hydrogen-permselective membrane reactor and solid oxide fuel cell as a novel technology  

NASA Astrophysics Data System (ADS)

The purge gas emission of ammonia synthesis plant which contains hazardous components is one of the major sources of environmental pollution. Using integrated configuration of catalytic hydrogen-permselective membrane reactor and solid oxide fuel cell (SOFC) system is a new approach which has a great impact to reduce the pollutant emission. By application of this method, not only emission of ammonia and methane in the atmosphere is prevented, hydrogen is produced through the methane steam reforming and ammonia decomposition reactions that take place simultaneously in a catalytic membrane reactor. The pure generated hydrogen by recovery of the purge gas in the Pd-Ag membrane reactor is used as a feed of SOFC. Since water is the only byproduct of the electrochemical reaction in the SOFC, it is recycled to the reactor for providing the required water of the reforming reaction. Performance investigation of the reactor represents that the rate of hydrogen permeation increases with enhancing the reactor temperature and pressure. Also modeling results indicate that the SOFC performance improves with increasing the temperature and fuel utilization ratio. The generated power by recovery of the purging gas stream of ammonia synthesis plant in the Razi petrochemical complex is about 8 MW.

Siavashi, Fakhteh; Saidi, Majid; Rahimpour, Mohammad Reza

2014-12-01

40

Synthese du Nitrate d'Ammonium a Partir d'Ammoniac et d'Acide Nitrique avec Recuperation et Recyclage de l'Azote Mineral (Recovery and Recycling of Ammonia Contained in Gases from Ammonium Nitrate Production).  

National Technical Information Service (NTIS)

The company performs ammonium nitrate synthesis accompanied by recovery and recycling of the ammonia contained in the vapor. The synthesis of ammonium nitrate is carried out in both techniques through a nitric acid reaction on the ammonia. When the reacti...

1981-01-01

41

Effect of Ammonia Reaction Time on the Calytic Poperties of Sputtered Iron-Based Electrocatalyst  

NASA Astrophysics Data System (ADS)

Fe-based electrocatalysts for polymer electrolyte membrane fuel cells (PEMFCs) were produced using a sputter deposition process involving a carbon paper (CP) and a NH3 heat treatment environment. The Fe--N--CP sample reacted with ammonia for 10 min at 950 °C displayed a greater current density than the samples reacted with ammonia for other reaction times. The impedance of the samples treated for 10 min with ammonia shows the highest value, which means much higher ligand formation and lower electric conductivity, which are consistent with the results of cyclic voltammetry (CV). This is directly due to the formation of ligands between the Fe and CP used when exposed to a nitrogen environment. While the current density of the Fe-based electrocatalysts under review did not exceed that of standard Pt/C electrocatalysts, the results herein suggest that nonprecious metal electrodes may be a viable alternative in PEMFCs.

Lee, Ki-Seong; Lee, Minku; Hong, Tae-Whan; Ju, HyunChul; Kim, Whangi; Kim, Dongmin

2013-10-01

42

Mechanism of C-3 hydrogen exchange and the elimination of ammonia in the 3-methylaspartate ammonia-lyase reaction.  

PubMed

The enzyme 3-methylaspartate ammonia-lyase (EC 4.3.1.2) catalyzes the exchange of the C-3 hydrogen of the substrate, (2S,3S)-3-methylaspartic acid, with solvent hydrogen. The mechanism of the exchange reaction was probed using (2S,3S)-3-methylaspartic acid and its C-3-deuteriated isotopomer. Incubations conducted in tritiated water allowed the rate of protium or deuterium wash-out from the substrates to be measured as tritium wash-in. The primary deuterium isotope effects for the exchange under essentially Vmax conditions ( [S] much greater than Km) were 1.6, 1.5, and 1.5 at pH 9.0, 7.6, and 6.5. The deamination reaction, measured spectrophotometrically on the same incubations, showed isotope effects of 1.7, 1.6, and 1.4 at pH 9.0, 7.6, and 6.5, in agreement with the values of DV and D(V/K) reported previously [Botting, N.P., Akhtar, M., Cohen, M.A., & Gani, D. (1988) Biochemistry 27, 2956-2959]. The ratio of the rate of exchange to the rate of deamination, however, varied widely with pH. Together with the identical values of the primary isotope effects for the two reactions, this result indicates that the partition between reaction pathways occurs after the slowest steps in the common part of the reaction coordinate pathway, almost certainly after the cleavage of the C-N bond at the level of the enzyme-ammonia-mesaconic acid complex, and not at the putative carbanion level as was previously suggested. The enzyme requires both K+ and Mg2+ ions for activity, although ammonium ion is also able to bind in the K+ site and act as an activator. Variation of the metal ion concentration alters the magnitude of the primary deuterium isotope effects. The variation of potassium ion concentration causes the most marked changes: at 1.6 mM K+, DV and D(V/K) are 1.7, whereas at 50 mM K+, DV and D(V/K) are reduced to 1.0. The isotope effects are also reduced at low K+ concentration due to the emergence of a slow-acting high K+ affinity monopotassium form of the enzyme. The binding order and role of the metal ion cofactors and their influence in determining the formal mechanism of the reaction is discussed, and the failure of previous workers to observe primary deuterium isotope effects for the deamination process is explained. The product desorption order was tested by product inhibition, alternative product inhibition, and isotope exchange experiments. Ammonia and mesaconic acid debind in a random fashion.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:1531295

Botting, N P; Gani, D

1992-02-11

43

Background Information on Ammonia.  

National Technical Information Service (NTIS)

Information on the synthesis, production, and use of ammonia (7664417) is reviewed. The importance of a catalyst in the process of uniting hydrogen and nitrogen to form ammonia, producers of ammonia between 1961 and 1974, their annual production capacity,...

R. Hartle

1975-01-01

44

Ethylene-enhanced Synthesis of Phenylalanine Ammonia-Lyase in Pea Seedlings 1  

PubMed Central

The effect of ethylene on the development of phenylalanine ammonia-lyase activity in segments excised from the epicotyl apex of pea seedling was studied. Although there was some increase in phenylalanine ammonia-lyase activity in segments not treated with ethylene, a marked increase in phenylalanine ammonia-lyase activity occurred in ethylene-treated tissues during the incubation. The induction period was estimated to be about 6 hours. The activity reached a maxmum at 30 hours and then declined. On withdrawal of ethylene, the increase was sustained for a short period and then stopped. After retreatment with ethylene, the increase was resumed. Addition of CO2 reduced the effect of ethylene. Administration of cycloheximide or actinomycin D at an early period almost completely suppressed the increase in phenylalanine ammonia-lyase activity. However, if these inhibitors were administered at a later period, while phenylalanine ammonia-lyase activity was approaching a maximum, they not only failed to reduce but rather stimulated the activity. These results are consistent with the view that there exist both phenylalanine ammonia-lyase-synthesizing and -inactivating systems, and that the development of both systems may involve de novo synthesis of protein.

Hyodo, Hiroshi; Yang, Shang Fa

1971-01-01

45

Synthesis of Ammonia Borane for Hydrogen Storage Applications  

SciTech Connect

A new synthetic procedure to make the condensed phase hydrogen storage material, ammonia borane (NH3BH3, abbreviated as AB), is described and compared with previous literature procedures. Ammonia borane with a gravimetric density ca. 194 gm H2/kg and a volumetric density ca. 146 H2/liter, is a promising chemical hydrogen storage material for fuel cell powered applications. The work shows that ammonium borohydride, NH4BH4, formed in situ by the metathesis of NH4X and MBH4 salts (M = Na, Li; X = Cl, F) in liquid NH3, can be induced to decompose in an organic ether to yield AB in near quantitative yield. The purity of the AB prepared by this one-pot synthetic strategy is sufficient to meet the thermal stability requirements for on-board hydrogen storage.

Heldebrant, David J.; Karkamkar, Abhijeet J.; Linehan, John C.; Autrey, Thomas

2008-07-05

46

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

47

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

48

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...

49

Synthesis of Ammonia Borane for Hydrogen Storage Applications  

SciTech Connect

A new synthetic procedure to make a condensed phase hydrogen storage material, ammonia borane (AB) is described and compared with previous literature procedures. The work shows that ammonium borohydride, NH4BH4, formed in-situ by the metathesis of NH4X and MBH4 salts (M = Na, Li; X = Cl, F) in liquid NH3, can be induced to decompose in THF to yield AB in near quantitative yield. AB, NH3BH3, gravimetric density ca. 194 gm H2/kg and volumetric density ca. 146 H2/liter is a promising chemical hydrogen storage material for fuel cell powered applications.

Heldebrant, David J.; Karkamkar, Abhijeet J.; Linehan, John C.; Autrey, Thomas

2008-07-01

50

Operation of adsorbers for purifying ammonia synthesis make-up gas  

SciTech Connect

The operation of adsorbers which purify ammonia synthesis make-up gas was assessed theoretically and empirically. A mathematical model predicts that nitrogen adsorption in 13X molecular sieve decreases the effluent flow rate and effluent molecular wight, and increases the effluent temperature at the start of the adsorption step. These interrelated, transient, process changes can greatly disrupt downstream unit operations. Data and observations from commercial ammonia synthesis gas adsorbers agree well with the effects predicted by the model. The effluent temperature rise can be used to monitor the condition of the adsorbent, the effectiveness of the previous thermal regeneration step, and flow distribution in the adsorber. A combination of activated alumina followed by 13X molecular sieve should reduce the transient process changes due to nitrogen adsorption, increase the capacity of the adsorber, and provide greater operating flexibility relative to 13X molecular sieve as the sole adsorbent.

Schoofs, G.R. (Columbia Univ., New York, NY (United States))

1993-04-01

51

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

52

Green synthesis of polysaccharide/gold nanoparticle nanocomposite: an efficient ammonia sensor.  

PubMed

A low cost eco-friendly method for the synthesis of gold nanoparticles (AuNPs) using guar gum (GG) as a reducing agent is reported. The nanoparticles obtained are characterized by UV-vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Based on these results, a potential mechanism for this method of AuNPs synthesis is discussed. GG/AuNPs nanocomposite (GG/AuNPs NC) was exploited for optical sensor for detection of aqueous ammonia based on surface plasmon resonance (SPR). It was found to have good reproducibility, response times of ?10 s and excellent sensitivity with a detection limit of 1ppb (parts-per-billion). This system allows the rapid production of an ultra-low-cost GG/AuNPs NC-based aqueous ammonia sensor. PMID:23544533

Pandey, Sadanand; Goswami, Gopal K; Nanda, Karuna K

2013-04-15

53

Ab Initio Quantum Calculations of Reactions in Astrophysical Ices: Acetaldehyde and Acetone with Ammonia  

NASA Astrophysics Data System (ADS)

Complex organic molecules, including amino acid precursors, have been observed in young stellar objects. Both laboratory and theoretical studies have shown that ice chemistry can play an important role in low-temperature synthetic pathways, with water serving as a catalyst that can significantly enhance reaction rates by lowering barriers or eliminating them altogether. Reactions between carbonyl species and ammonia are particularly promising, as shown in previous studies of the formaldehyde-ammonia reaction. In this study, we explore the reactions of ammonia with two larger carbonyl species, acetaldehyde and acetone, embedded in a water ice cluster. To examine the explicit impact of the water, we gradually increase the size of the cluster from 4H_2O to 12H_2O. Cluster calculations were performed at the MP2/{6-31}+G^{**} or B3LYP/{6-31}+G^{**} level. In order to account for the electrostatic contribution from bulk ice, the Polarizable Continuum Model (PCM) and Isodensity Surface Polarized Continuum Model (IPCM) were used to model reaction field solvation effects. For both acetaldehyde and acetone, the reactant is a charge transfer complex (a partial charge-transfer complex in small clusters and full proton-transfer complex in larger clusters). Rearrangement to amino-hydroxylated products can occur by surmounting a small reaction barrier. Stereo-selectivity is observed in the case of acetaldehyde. P. Ehrenfreund and S. B. Charnley, Ann. Rev. Astron. Astrophys. 38, 427 (2000). W. A. Schutte, L. J. Allamandola, and S. A. Sandford, Science 259, 1143 (1993) W. A. Schutte, L. J. Allamandola, and S. A. Sandford, Icarus 104, 118 (1993) D. E. Woon, Icarus 142, 550 (1999) S. P. Walch, C. W. Bauschicher, Jr., A. Ricca and E. L. O. Bakes, Chem. Phys. Lett, 333, 6 (2001)

Chen, L.; Woon, D. E.

2009-06-01

54

Support Effect and Active Sites on Promoted Ruthenium Catalysts for Ammonia Synthesis  

Microsoft Academic Search

The catalytic activities of three supported, barium-promoted ruthenium catalysts for ammonia synthesis are reported. The three supports are silicon nitride (Si3N4), magnesium aluminum spinel (MgAl2O4), and graphitized carbon (C). The effect of the promoter on the activity is strongly dependent on the choice of support material in accordance with several previous observations. Here, this dependence is ascribed to a difference

Thomas W. Hansen; Poul L. Hansen; Søren Dahl; Claus J. H. Jacobsen

2002-01-01

55

Intracluster reactions in phenylacetylene ammonia clusters initiated through resonant enhanced ionization  

SciTech Connect

Protonated ammonia clusters of specific size are observed to form following the resonant enhanced ionization of phenylacetylene--ammonia clusters PAx(NH/sub 3/)/sub n/ in the 0/sup 0//sub 0/ region of the S/sub 1/--S/sub 0/ transition of the (unclustered) PA. The resonance enhanced absorption of two photons, approx. =8.8 eV total energy, are found to cause intracluster reactions for ngreater than or equal to5. The findings imply that the adiabatic ionization potential of (NH/sub 3/)/sub 4/ is greater than 8.8 eV, while that of (NH/sub 3/)/sub 5/ is (slightly) less.

Breen, J.J.; Tzeng, W.; Kilgore, K.; Keesee, R.G.; Castleman A.W. Jr.

1989-01-01

56

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

DOEpatents

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

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

1982-01-01

57

Synthesis and removal of phenylalanine ammonia-lyase activity in illuminated discs of potato tuber parenchyme.  

PubMed

(1) The synthesis and removal of phenylalanine ammonia-lyase (EC 4.3.1.5) in illuminated discs of potato (Solanum tuberosum cv King Edward) tuber tissue has been investigated by density labelling with deuterium (2H) from deuterium oxide (2H2O) followed by centrifugation to equilibrium in a CsC1 density gradient. (2) Temporal changes in enzyme level have been described in terms of the equation (dE/dt) = ks-kdE where (dE/dt) is the rate of change of enzyme level per unit of tissue (E) with respect to time (t), ks is the rate constant for synthesis of the enzyme and kd is the rate constant for the removal of active enzyme. (3) The optimal concentration of 2H2O was determined by analysis of the relationship between 2H2O concentration, development of enzyme activity and the magnitude of the increase in buoyant density of phenylalanine ammonia-lyase. A concentration of 2H2O of about 40% (v/v) was found to be optimal, allowing achievement of maximal or near maximal increases in the buoyant density of the enzyme without inhibition of the development of enzyme activity, thereby circumventing the major drawback of 2H2O as a source of density label. (4) The overlapping distribution profiles of enzyme activity after density gradient centrifugation were resolved by an iterative method of best fit which allows estimation of the proportions of pre-existing, unlabelled enzyme and newly synthesised, labelled enzyme at the end of the labelling period. This technique has been developed to obtain the rate constants for enzyme synthesis and for removal of active enzyme throughout the period of rapid change in enzyme level. (5) It is demonstrated that the initial rapid increase in phenylalanine ammonia-lyase activity in illuminated discs reflects an increase in the rate constant for enzyme synthesis in the absence of activation of pre-existing enzyme and in the absence of removal of active enzyme. The abrupt transition to a phase of decline in enzyme activity is caused by (a) a reduction in the rate constant for enzyme synthesis and (b) a dramatic increase in the rate constant for removal of active enzyme. The subsequent stabilisation of the enzyme is caused by decay of both rate constants to relatively low levels. (6) The results are consistent with hypothesis that rapid modulation of enzyme levels during tissue differentiation is achieved by simultaneous changesin the rate constants for both enzyme synthesis and for removal of active enzyme. PMID:760822

Lamb, C J; Merritt, T K; Butt, V S

1979-01-18

58

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

59

Synthesis of ?,?-dimethoxyfluoropolyethers: reaction mechanism and kinetics  

Microsoft Academic Search

A new class of hydrofluoropolyethers, the ?,?-dimethoxyfluoropolyethers (DM-FPEs), characterized by the copolymeric structure CH3O(CF2CF2O)n(CF2O)mCH3 has been recently developed. The synthesis of DM-FPEs here described, has been carried out via a new synthetic route which consists of the reaction of a perfluoropolyether diacyl fluoride with methyl fluoroformate in the presence of a metal fluoride. The reaction products are DM-FPEs and carbon

M. Avataneo; U. De Patto; M. Galimberti; G. Marchionni

2005-01-01

60

Synthesis of ammonia and liquid fuel by CH4 and N2 plasmas without catalyst at ambient pressure and temperature  

Microsoft Academic Search

Summary form only given. In this paper, we discuss about the synthesis of ammonia and liquid fuel by CH4 and N2 plasmas without catalyst at ambient pressure and temperature. Key problems of the plasma synthesis: (1) Strong dielectric barrier discharge are formed in micro-gap, which the reduce field is ?400 Td, the average electron energy is ?10 eV, and electron

Mindong Bai; Xiyao Bai; Ning Wang; Dongmei Zhang; Keping Zhan

2004-01-01

61

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

62

DC Conduction in Si3N4 Films Grown by the Pyrolytic Reaction between Silane and Ammonia  

Microsoft Academic Search

The present paper describes experimental studies of the electrical characteristics of silicon nitride films deposited pyrolytically by the reaction between silane and ammonia. The substrates were n- and p-type silicon of various resistivities and also silicon with a tungsten layer on to which the nitride was deposited. The majority of the samples show symmetric behaviour with bias and therefore indicate

Fateh Mohammad Nazar

1978-01-01

63

DFT studies of the conversion of four mesylate esters during reaction with ammonia.  

PubMed

The energetics of the Menshutkin-like reaction between four mesylate derivatives and ammonia have been computed using B3LYP functional with the 6-31+G** basis set. Additionally, MPW1K/6-31+G** level calculations were carried out to estimate activation barrier heights in the gas phase. Solvent effect corrections were computed using PCM/B3LYP/6-31+G** level. The conversion of the reactant complexes into ion pairs is accompanied by a strong energy decrease in the gas phase and in all solvents. The ion pairs are stabilized with two strong hydrogen bonds in the gas phase. The bifurcation at C2 causes a significant activation barrier increase. Also, bifurcation at C5 leads to noticeable barrier height differentiation. Both B3LYP/6-31+G** and MPW1K/6-31+G** activation barriers suggest the reaction 2 (2a?+?NH3) to be the fastest in the gas phase. The reaction 4 is the slowest one in all environments. PMID:23571822

Nowacki, Andrzej; Sikora, Karol; Dmochowska, Barbara; Wi?niewski, Andrzej

2013-08-01

64

Increased urea synthesis and/or suppressed ammonia production in the African lungfish, Protopterus annectens, during aestivation in air or mud.  

PubMed

The objective of this study was to elucidate how the African lungfish, Protopterus annectens, ameliorated ammonia toxicity during 12 or 46 days of aestivation in air or in mud. Twelve days of aestivation in air led to significant increases in contents of urea, but not ammonia, in tissues of P. annectens. The estimated rate of urea synthesis increased 2.7-fold despite the lack of changes in the activities of hepatic ornithine-urea cycle enzymes, but there was only a minor change in the estimated rate of ammonia production. After 46 days of aestivation in air, the ammonia content in the liver decreased significantly and contents of urea in all tissues studied increased significantly, indicating that the fish shifted to a combination of increased urea synthesis (1.4-fold of the day 0 value) and decreased ammonia production (56% of the day 0 value) to defend against ammonia toxicity. By contrast, 12 days of aestivation in mud produced only minor increases in tissue urea contents, with ammonia contents remained unchanged. This was apparently achieved through decreases in urea synthesis and ammonia production (40 and 15%, respectively, of the corresponding day 0 value). Surprisingly, 46 days of aestivation in mud resulted in no changes in tissue urea contents, indicating that profound suppressions of urea synthesis and ammonia production (2.6 and 1.2%, respectively, of the corresponding day 0 value) had occurred. This is the first report on such a phenomenon, and the reduction in ammonia production was so profound that it could be the greatest reduction known among animals. Since fish aestivated in mud had relatively low blood pO(2) and muscle ATP content, they could have been exposed to hypoxia, which induced reductions in metabolic rate and ammonia production. Consequently, fish aestivating in mud had a lower dependency on increased urea synthesis to detoxify ammonia, which is energy intensive, than fish aestivating in air. PMID:18058110

Loong, Ai M; Pang, Cheryl Y M; Hiong, Kum C; Wong, Wai P; Chew, Shit F; Ip, Yuen K

2008-03-01

65

Polytellurides of Mn, Fe, and Zn from mild solvothermal reactions in liquid ammonia.  

PubMed

The reaction of elemental Mn, Fe, and Zn with Te in liquid ammonia at 50 °C leads to the polytellurides [Mn(NH3)6]Te4 (1), [Fe(NH3)6]Te4·NH3 (2), and [Zn(NH3)4]2Te15 (3) in quantitative yield for 1 and 3, and in 30-50% yield for 2. The compounds form black crystals, which are air sensitive and easily lose ammonia without a protective atmosphere of NH3. Compound 3 is semiconducting with a thermal activation energy of 1.2 eV. In the crystal structures of 1 and 2, tetratelluride anions Te4(2-) in gauche conformation with dihedral angles around 90° are present, which are linked to form infinite spiral chains. Compound 3 contains an unusual Te15(4-) polyanion in the form of a bent chain Te7-Te-Te7. The connection between the Te4 groups in 1 and 2 and the two Te7 groups in 3 is achieved via linear Te3 entities, which are strongly asymmetric in 1, almost symmetric in 2, and symmetric in 3 (for 1, Te-Te···Te 174.0°, d1 = 2.87, d2 = 3.25 Å; for 2, Te-Te-Te 178.8°, d1 = 3.01, d2 = 3.09 Å; for 3, Te-Te-Te 180°, d1 = d2 = 3.06 Å). Periodic DFT calculations show that interaction between the Te4(2-) units is negligible in 1 and weak but undoubtedly present in 2. The overlap population amounts to 0.09 in the linear Te3 group of 3. The band structure calculation of 3 gives semiconducting behavior with a band gap of 1.5 eV in fair agreement with experimental data. PMID:23848606

Kysliak, Oleksandr; Marcus, Max; Bredow, Thomas; Beck, Johannes

2013-08-01

66

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

67

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

SciTech Connect

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

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

1994-01-18

68

Structure and reactivity of alumina-supported iron catalysts for ammonia synthesis  

SciTech Connect

Alumina-supported iron catalysts, obtained either by impregnation of iron from a K/sub 4/(Fe(CN)/sub 6/) aqueous solution upon several acid-modified ..gamma..-Al/sub 2/O/sub 3/ samples or by the incipient wetness method, were characterized and their activities for ammonia synthesis at atmospheric pressure and 593 K were studied. Characterization was carried out by temperature-programmed reduction (TPR), kinetics of hydrogen reduction, CO chemisorption, X-ray photoelectron spectroscopy (XPS), IR spectroscopy, and Moessbauer spectroscopy, resulting in the degree of reduction and the dispersion of the metallic phase dependent on the previous acid modification of the ..gamma..-Al/sub 2/O/sub 3/. The XPS surface composition expressed as M 2p/Al 2p (M = Fe, K) gave K 2p/Al 2p > Fe 2p/Al 2p. IR experiments, with NO as probe molecules, exhibited bands for reduced catalysts at 1778 and 1712 cm/sup -1/ whose intensity and position depended on the protonation degree of ..gamma..-Al/sub 2/O/sub 3/ and promoter content, respectively. Moessbauer spectra of the reduced samples showed the presence of surface ..cap alpha..-Fe, superparamagnetic Fe/sup 0/, Fe/sup 2 +/, Fe/sup 3 +/, and ..cap alpha..-Fe/sub 2/O/sub 3/ depending on the catalyst. Finally, the catalytic activity for ammonia synthesis was found to be dependent on the surface structure of the catalyst and hence on the method of preparation.

Sueiras, J.E.; Homs, N.; Ramirez de la Piscina, P.; Gracia, M.; Fierro, J.L.G.

1986-04-01

69

Novel Haloperoxidase Reaction: Synthesis of Dihalogenated Products  

PubMed Central

The enzymatic synthesis of vicinal, dihalogenated products from alkenes and alkynes is described. The enzymatic reaction required an alkene or alkyne, dilute hydrogen peroxide, a haloperoxidase, and molar amounts of halide ions. Vicinal dichloro, dibromo, and diiodo products could be formed. A hydroxyl group on the carbon adjacent to the carbon-carbon double or triple bond lowered the halide ion concentration needed to produce the dihalo product. This reaction offers one explanation for the origin of natural, vicinal, dihalogenated products, such as those found frequently in marine microogranisms.

Geigert, John; Neidleman, Saul L.; Dalietos, Demetrios J.; DeWitt, Susanne K.

1983-01-01

70

Ammonia oxidation catalysis: Hydrogen cyanide, nitric oxide, and hydrogen  

NASA Astrophysics Data System (ADS)

This thesis focuses on ammonia oxidation processes, specifically hydrogen cyanide synthesis and hydrogen generation. This work stemmed from previous investigations into hydrogen addition to ethane partial oxidation, which had revealed that the use of hydrogen with noble metal catalysts could give improved performance in oxidative dehydrogenation. Based on this discovery and simulations of ethylene synthesis reactions, it was hypothesized that hydrogen addition to the Andrussow process for hydrogen cyanide synthesis would also give superior results. By reacting hydrogen, ammonia, methane, and oxygen over a platinum/rhodium gauze catalyst in a millisecond contact time reactor, and then analyzing the product with a gas chromatograph, this hypothesis was tested. It was found that, as the amount hydrogen fed increased, so too did the hydrogen cyanide selectivity. However, the ammonia conversion decreased significantly over the same range, and as a result the overall yield decreased with increasing hydrogen fed. Following these hydrogen cyanide synthesis experiments, work began on a project to generate hydrogen through ammonia reforming. Fuel cell technology necessitates a readily available, inexpensive source of hydrogen; many feel that this hydrogen can be obtained from ammonia. It was hoped that by catalytically oxidizing ammonia, large amounts of hydrogen could be produced at high ammonia conversions. By varying the ammonia/oxygen feed ratio, the catalyst used, and the reactor configuration, it was found that hydrogen yields in excess of 60% could be obtained at ammonia conversions of 99%. This product stream is suitable for use in a P.E.M. fuel cell.

Olschki, David Alexander

71

Microstructure and electrical-optical properties of cesium tungsten oxides synthesized by solvothermal reaction followed by ammonia annealing  

SciTech Connect

Cesium tungsten oxides (Cs{sub x}WO{sub 3}) were synthesized by solvothermal reactions using ethanol and 57.1 vol% ethanol aqueous solution at 200 {sup o}C for 12 h, and the effects of post annealing in ammonia atmosphere on the microstructure and electrical-optical properties were investigated. Agglomerated particles consisting of disk-like nanoparticles and nanorods of Cs{sub x}WO{sub 3} were formed in the pure ethanol and ethanol aqueous solutions, respectively. The samples retained the original morphology and crystallinity after annealing in ammonia atmosphere up to 500 {sup o}C, while a small amount of nitrogen ion were incorporated in the lattice. The as-prepared Cs{sub x}WO{sub 3} sample showed excellent near infrared (NIR) light shielding ability as well as high transparency in the visible light region. The electrical resistivity of the pressed pellets of the powders prepared in pure ethanol and 57.1 vol% ethanol aqueous solution greatly decreased after ammonia annealing at 500 {sup o}C, i.e., from 734 to 31.5 and 231 to 3.58 {Omega} cm, respectively. - Graphical abstract: Cesium tungsten oxides (Cs{sub x}WO{sub 3}) with different morphology were synthesized by solvothermal reaction, and the effects of post-ammonia annealing on the microstructure and electrical-optical properties were investigated.

Liu Jingxiao, E-mail: jxiaoliu@sina.co [Institute of Multidisciplinary Research for Advanced Material, Tohoku University, Sendai 9808577 (Japan); School of Chemistry and Materials, Dalian Polytechnic University, Dalian 116034 (China); Ando, Yoshihiko [Institute of Multidisciplinary Research for Advanced Material, Tohoku University, Sendai 9808577 (Japan); Dong Xiaoli; Shi Fei [School of Chemistry and Materials, Dalian Polytechnic University, Dalian 116034 (China); Yin Shu [Institute of Multidisciplinary Research for Advanced Material, Tohoku University, Sendai 9808577 (Japan); Adachi, Kenji; Chonan, Takeshi [Ichikawa Research Laboratory, Sumitomo Metal Mining Co., Ltd (Japan); Tanaka, Akikazu [Technology Division, Advanced Technology Information Department, Sumitomo Metal Mining Co. (Japan); Sato, Tsugio [Institute of Multidisciplinary Research for Advanced Material, Tohoku University, Sendai 9808577 (Japan)

2010-10-15

72

Use of AlPO-11, SnAPO-11, SAPO-31 and SAPO-41 Elaborated Solid Materials as Catalysts in Ammonia Alkylation Reaction  

NASA Astrophysics Data System (ADS)

The present study deals with the synthesis of octylamines by ammonia alkylation with octanol-1 in gaseous phase using solid microporous materials as AlPO-11, SnAPO-11, SAPO-31 and SAPO-41. They were prepared by hydrothermal process in Teflon steel less reactor under autogenic pressure and at determined temperatures. SAPO-31 material was obtained using HF acid and without fluoride media. The materials have presented a catalytic activity in the study reaction. Primary isomers (MOA) were obtained with better selectivity of about 85 to 99%. Silicium and tin are the origin of the acidity and are responsible to the activity catalytic of SnAPO-11 and SAPO-31 materials.

Khemaissia, Sihem; Nibou, Djamel; Amokrane, Samira; Lebaili, Nemcha

73

Product distributions and rate constants for ion-molecule reactions in water, hydrogen sulfide, ammonia, and methane  

NASA Technical Reports Server (NTRS)

The thermal energy, bimolecular ion-molecule reactions occurring in gaseous water, hydrogen sulfide, ammonia, and methane have been identified and their rate constants determined using ion cyclotron resonance methods. Absolute rate constants were determined for the disappearance of the primary ions by using the trapped ion method, and product distributions were determined for these reactions by using the cyclotron ejection method. Previous measurements are reviewed and compared with the results using the present methods. The relative rate constants for hydrogen-atom abstraction, proton transfer, and charge transfer are also determined for reactions of the parent ions.

Huntress, W. T., Jr.; Pinizzotto, R. F., Jr.

1973-01-01

74

Influence of the temperature of secondary condensation on the energy characteristics in operation of an ammonia-synthesis plant of high unit capacity  

Microsoft Academic Search

Operating experience in an ammonia-synthesis plant of high unit capacity showed that the secondary-condensation unit does not operate efficiently enough, and as a result the cooling temperature of the circulating gas beyond the evaporator fluctuates from +10 to -12°C. The residual content of ammonia in the gas entering the synthesis stage varies with the temperature of secondary condensation, and this

V. T. Efimov; V. I. Atroshchenko; A. K. Babichenko; S. A. Eroshchenkov

1979-01-01

75

Ammonia treatment of wheat straw. 2. Efficiency of microbial protein synthesis, rumen microbial protein pool size and turnover, and small intestinal protein digestion in sheep  

Microsoft Academic Search

Ammonia-treated wheat straw (AWS) was compared with untreated wheat straw (UWS) and untreated wheat straw supplemented with urea (SWS) in an experiment with 6 wether sheep. Microbial protein synthesis increased after ammonia treatment due to the higher intake of rumen degradable organic matter (OM). The efficiency of microbial protein synthesis was low for all diets, averaging 22.1 g N\\/kg apparently

S. J. Oosting; T. C. Viets; S. C. W. Lammers-Wienhoven; Bruchem van J

1993-01-01

76

High efficiency luminescent gallium nitride powders by direct synthesis from gallium metal and ammonia.  

NASA Astrophysics Data System (ADS)

High quality as-synthesized gallium nitride (GaN) powders have been obtained by a complete reaction between high purity gallium metal and ultra high purity ammonia in a horizontal quartz tube reactor at 1100 ºC. Elemental analysis showed that the powders obtained by this method have a stoichiometric nitrogen concentration (16.73 weight hexagonal crystalline structure of the GaN synthesized. Electron microscopy showed that the powders are formed by at least two kinds of particles, small size platelets and large size needles. The GaN powders obtained by this method are light gray and produce high ultra-violet luminescence around 370 nm (3.35 eV, near band-edge emission) when they are excited by accelerated electrons (cathodoluminescence) or by high energy photons (photoluminescence) at room temperature.

Garcia, Rafael; Bell, Abigail; Stevens, Michael; Ponce, Fernando

2003-10-01

77

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

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

78

Synthesis of Ammonia Using CH 4 \\/N 2 Plasmas Based on Micro-Gap Discharge under Environmentally Friendly Condition  

Microsoft Academic Search

The synthesis of ammonia has been studied in methane-nitrogen plasmas using a micro-gap discharge under an environmentally\\u000a friendly condition. The effects of some parameters such as the specific input energy, the discharge gap, the volume ratio\\u000a of CH4\\/N2, the residence time, and the gas temperature on the yield of NH3 and conversion rate of CH4 are discussed in the paper.

Mindong Bai; Zhitao Zhang; Mindi Bai; Xiyao Bai; Honghui Gao

2008-01-01

79

Supported Catalysts with RuM (M = Fe, Co, Ni, Mo) Bimetallic Active Centers for Ammonia Synthesis  

Microsoft Academic Search

Supported Ru-M (M = Fe, Co, Ni, Mo) bimetallic active center catalysts with a potassium promoter for the ammonia synthesis were studied. The activity of the Ru-Co catalyst is the highest, and the activity of the Ru-Mo catalyst is the lowest. When the Ru loading decreases by half (from 4% to 2%), the Ru-Co catalyst with a Co loading of

Zhenwei YANG; Weiming GUO; Jingdong LIN; Daiwei LIAO

2006-01-01

80

Surface heterogeneity and ionization of Cs promoter in carbon-based ruthenium catalyst for ammonia synthesis  

NASA Astrophysics Data System (ADS)

Second-generation ammonia synthesis cesium-doped ruthenium catalyst supported on turbostratic carbon was investigated by the species resolved thermal alkali desorption method (SR-TAD). Energetic barriers for cesium ions (2.86 eV), ground state (1.96 eV) and electronically excited atoms (5.76 eV) desorbing from the Cs-Ru/C catalyst were determined. In the case of ruthenium-free Cs/C system, cesium desorbs as ground state atoms only, with an energy barrier of 2.87 eV. The work functions determined by the thermionic emission of electrons from Cs/C and Cs-Ru/C were of the same value (2.9 eV). It was concluded that ruthenium induces heterogeneous distribution of cesium on the catalyst surface. The promoter stability is reduced on low work function areas and its surface ionization on high work function areas opens the ionic desorption channel. The Cs desorption from the catalyst is discussed in terms of the literature data for the cesium/graphite system.

Kotarba, Andrzej; Dmytrzyk, Jaromir; Raróg-Pilecka, Wioletta; Kowalczyk, Zbigniew

2003-02-01

81

Synthesis, characterization, and magnetic properties of mixed-valence europium-ammonia intercalation compounds of titanium disulfide  

Microsoft Academic Search

Europium-ammonia intercalation compounds of titanium disulfide have been synthesized by reaction of Eu-NH3 solutions with TiS2, characterized by thermogravimetric analysis and powder X-ray diffraction, and investigated by electron paramagnetic resonance, magnetization, and magnetic susceptibility measurements. These materials crystallize in a 3R-type structure in which every layer is occupied by intercalated species. The intercalation of NH3 is accompanied by the formation

S. P. Hsu; W. S. Glaunsinger

1987-01-01

82

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

PubMed Central

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

Cooper, Arthur J. L.

2012-01-01

83

Catalytic Effects of Metal-loaded Membrane-like Alumina Tubes on Ammonia Synthesis in Atmospheric Pressure Plasma by Dielectric Barrier Discharge  

Microsoft Academic Search

Plasma synthesis of ammonia was studied at atmospheric pressure using a dielectric-barrier-discharge-plasma reactor equipped\\u000a with a metal-loaded membrane-like alumina tube as a catalyst between the electrodes. Introducing the pure alumina into N2–H2 plasma resulted in an increase in the ammonia yield and the further improvement was achieved by loading the alumina with\\u000a Ru, Pt, Ni, and Fe. These results clearly

Takanori Mizushima; Kazumi Matsumoto; Hironobu Ohkita; Noriyoshi Kakuta

2007-01-01

84

Increased urea synthesis and\\/or suppressed ammonia production in the African lungfish, Protopterus annectens , during aestivation in air or mud  

Microsoft Academic Search

The objective of this study was to elucidate how the African lungfish, Protopterus annectens, ameliorated ammonia toxicity during 12 or 46 days of aestivation in air or in mud. Twelve days of aestivation in air led\\u000a to significant increases in contents of urea, but not ammonia, in tissues of P. annectens. The estimated rate of urea synthesis increased 2.7-fold despite the

Ai M. Loong; Cheryl Y. M. Pang; Kum C. Hiong; Wai P. Wong; Shit F. Chew; Yuen K. Ip

2008-01-01

85

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

86

Inhibition of glutamine synthesis induces glutamate dehydrogenase-dependent ammonia fixation into alanine in co-cultures of astrocytes and neurons.  

PubMed

It has been previously demonstrated that ammonia exposure of neurons and astrocytes in co-culture leads to net synthesis not only of glutamine but also of alanine. The latter process involves the concerted action of glutamate dehydrogenase (GDH) and alanine aminotransferase (ALAT). In the present study it was investigated if the glutamine synthetase (GS) inhibitor methionine sulfoximine (MSO) would enhance alanine synthesis by blocking the GS-dependent ammonia scavenging process. Hence, co-cultures of neurons and astrocytes were incubated for 2.5h with [U-(13)C]glucose to monitor de novo synthesis of alanine and glutamine in the absence and presence of 5.0 mM NH(4)Cl and 10 mM MSO. Ammonia exposure led to increased incorporation of label but not to a significant increase in the amount of these amino acids. However, in the presence of MSO, glutamine synthesis was blocked and synthesis of alanine increased leading to an elevated content intra- as well as extracellularly of this amino acid. Treatment with MSO led to a dramatic decrease in glutamine content and increased the intracellular contents of glutamate and aspartate. The large increase in alanine during exposure to MSO underlines the importance of the GDH and ALAT biosynthetic pathway for ammonia fixation, and it points to the use of a GS inhibitor to ameliorate the brain toxicity and edema induced by hyperammonemia, events likely related to glutamine synthesis. PMID:21397649

Dadsetan, Sherry; Bak, Lasse K; Sørensen, Michael; Keiding, Susanne; Vilstrup, Hendrik; Ott, Peter; Leke, Renata; Schousboe, Arne; Waagepetersen, Helle S

2011-09-01

87

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...

88

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

89

The Chemistry of Liquid Ammonia.  

ERIC Educational Resources Information Center

The solvent and chemical properties of liquid ammonia are presented. In a certain sense, ammonia is a more versatile solvent than is water because of its ability to solubilize, without reaction, highly negative or reducing species. (Author/BB)

Lagowski, J. J.

1978-01-01

90

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

NASA Technical Reports Server (NTRS)

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

Bosco, S. R.

1982-01-01

91

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

NASA Astrophysics Data System (ADS)

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

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

2005-06-01

92

Green synthesis of biopolymer-silver nanoparticle nanocomposite: an optical sensor for ammonia detection.  

PubMed

Biopolymer used for the production of nanoparticles (NPs) has attracted increasing attention. In the presence article we use aqueous solution of polysaccharide Cyamopsis tetragonaloba commonly known as guar gum (GG), from plants. GG acts as reductive preparation of silver nanoparticles which are found to be <10 nm in size. The uniformity of the NPs size was measured by the SEM and TEM, while a face centered cubic structure of crystalline silver nanoparticles was characterized using powder X-ray diffraction technique. Aqueous ammonia sensing study of polymer/silver nanoparticles nanocomposite (GG/AgNPs NC) was performed by optical method based on surface plasmon resonance (SPR). The performances of optical sensor were investigated which provide the excellent result. The response time of 2-3 s and the detection limit of ammonia solution, 1 ppm were found at room temperature. Thus, in future this room temperature optical ammonia sensor can be used for clinical and medical diagnosis for detecting low ammonia level in biological fluids, such as plasma, sweat, saliva, cerebrospinal liquid or biological samples in general for various biomedical applications in human. PMID:22750580

Pandey, Sadanand; Goswami, Gopal K; Nanda, Karuna K

2012-11-01

93

Synthesis and characterization of polyaniline–carboxylated PVC composites: Application in development of ammonia sensor  

Microsoft Academic Search

Polyaniline (PAni) and carboxylated polyvinyl chloride (PVC) composites were synthesized and studied for their structural, electrical and electrochemical properties and used as a novel material for development of an ammonia gas sensor. Processible conducting composites were prepared by introducing carboxylated PVC in the PAni matrix under vigorous stirring and sonication conditions. Self-standing films of these electroactive and homogeneous composites were

Vandana Singh; Swati Mohan; G. Singh; P. C. Pandey; Rajiv Prakash

2008-01-01

94

Consecutive isocyanide-based multicomponent reactions: synthesis of cyclic pentadepsipeptoids.  

PubMed

The synthesis of six cyclic depsipeptoids inspired by the natural depsipeptide sansalvamide A is described. An efficient and fast synthetic strategy was developed using a combination of consecutive isocyanide-based multicomponent reactions (Ugi and Passerini reactions). This methodology can be used to access a variety of cyclic oligodepsipeptoids. PMID:24991252

Barreto, Angélica de Fátima S; Vercillo, Otilie E; Wessjohann, Ludger A; Andrade, Carlos Kleber Z

2014-01-01

95

Consecutive isocyanide-based multicomponent reactions: synthesis of cyclic pentadepsipeptoids  

PubMed Central

Summary The synthesis of six cyclic depsipeptoids inspired by the natural depsipeptide sansalvamide A is described. An efficient and fast synthetic strategy was developed using a combination of consecutive isocyanide-based multicomponent reactions (Ugi and Passerini reactions). This methodology can be used to access a variety of cyclic oligodepsipeptoids.

Barreto, Angelica de Fatima S; Vercillo, Otilie E; Wessjohann, Ludger A

2014-01-01

96

Reaction mechanism of platinum dimer cation with ammonia based on the relativistic density functional study  

NASA Astrophysics Data System (ADS)

The gas-phase reactions between Pt2+ and NH3 have been investigated using the relativistic density functional approach (ZORA-PW91/TZ2P). The quartet and doublet potential energy surfaces of Pt2+ + NH3 have been explored. The minimum energy reaction path proceeds through the following steps: Pt2+(4?u) + NH3 ? q-1 ? d-2 ? d-3 ? d-4 ? d-Pt2NH+ + H2. In the whole reaction pathway, the step of d-2 ? d-3 is the rate-determining step with a energy barrier of 36.1 kcal/mol, and exoergicity of the whole reaction is 12.0 kcal/mol. When Pt2NH+ reacts with NH3 again, there are two rival reaction paths in the doublet state. One is degradation of NH4+ and another is loss of H2. In the case of degradation of NH4+, the activation energy is only 3.4 kcal/mol, and the overall reaction is exothermic by 8.9 kcal/mol. Thus, this reaction is favored both thermodynamically and kinetically. However, in the case of loss of H2, the rate-determining step's energy barrier is 64.3 kcal/mol and the overall reaction is endothermic by 8.5 kcal/mol, so it is difficult to take place. Predicted relative energies and barriers along the suggested reaction paths are in reasonable agreement with experimental observations.

Xu, Dan; Chen, Xian-Yang; Wang, Shu-Guang

97

Catalytic asymmetric synthesis of ?-butenolides by direct vinylogous reactions.  

PubMed

The ?-butenolide structural motif is a prominent feature in many bioactive natural products and drugs. This short review summarizes catalytic asymmetric synthesis of ?-butenolides through direct vinylogous reactions by metal complexes and organocatalysts. In light of building chiral ?-tertiary and quaternary carbon centers of butenolides, three synthetic strategies are included: 1) the reactions with furanone derivatives as nucleophiles, 2) olefination of ?,?- disubstituted butenolides and 3) the reactions by using ?,?-disubstituted butenolides as nucleophiles. PMID:23544459

Yan, Lin; Wu, Xiaohong; Liu, Hongjun; Xie, Liangying; Jiang, Zhiyong

2013-05-01

98

Multicomponent reactions of isocyanides in the synthesis of heterocycles  

NASA Astrophysics Data System (ADS)

The latest achievements in the field of isocyanide-based multicomponent reactions for the synthesis of heterocycles are generalized. The attention is focused on the intramolecular Ugi reactions of oxocarboxylic acids and the reactions of diaza nucleophiles developed in recent years. The data on the biological activities of the products are presented and the advantages of this method as a convenient and effective tool of medicinal chemistry are demonstrated.

Ivachtchenko, Aleksandr V.; Ivanenkov, Ya A.; Kysil, Vladimir M.; Krasavin, Mikhail Yu; Ilyin, Aleksei P.

2010-11-01

99

Ester synthesis in lipase-catalyzed reactions  

Microsoft Academic Search

This review discusses the myriad of reaction systems employed in ester production catalyzed by lipases. Enzyme behavior in reaction systems is a consequence of certain structural patterns typical of lipases. Water has a profound effect on the lipase behavior either directly by affecting the hydration of the enzyme or indirectly by changing the nature of the reaction media and\\/or enzyme

Ahmad R. M Yahya; William A Anderson; Murray Moo-Young

1998-01-01

100

EXAFS-XANES evidence of in situ cesium reduction in Cs-Ru/C catalysts for ammonia synthesis.  

PubMed

We present here a X-ray absorption spectroscopy (XAS) investigation on the local chemical order and electronic structure of Cs and Ba, promoters of the Ru/C catalysts for ammonia synthesis that attracted interest because of highly increased productivity. The role of the promoters is still largely unclear, although indirect evidence for Cs partial reduction has been obtained by this and other groups. Our XAS analysis with in situ H(2) reduction directly supports the partial Cs reduction in the promoted Ru/C catalysts, depending on the presence of Ru and on the graphitization degree of the support. Higher coordination of Ba was observed with respect to Cs in the reduced samples, without evidence of heavy atoms (Ru, Cs, and Ba) in the surroundings. Because of the strong electropositive nature of Cs, direct experimental evidence of its partial reduction is of outstanding significance also for other applications. PMID:21434615

Rossetti, Ilenia; Sordelli, Laura; Ghigna, Paolo; Pin, Sonia; Scavini, Marco; Forni, Lucio

2011-04-18

101

Reaction synthesis and formation mechanism of barium hexaboride  

Microsoft Academic Search

The synthesis and formation mechanism of BaB6 powder by the reaction of BaCO3 with B4C and carbon was investigated systematically in the present study. The influences of heating temperature and holding time on the reaction products were studied by X-ray diffractometry, and the morphologies of BaB6 were investigated by scanning electron microscopy. The interaction in the BaCO3–B4C–C system by which

Guanghui Min; Shuqi Zheng; Zengda Zou; Huashun Yu; Jiande Han

2003-01-01

102

Selective synthesis of isobutanol by means of the Guerbet reaction  

Microsoft Academic Search

The synthesis of isobutanol (iBuOH) from methanol\\/n-propanol (MeOH\\/PrOH) mixtures has been studied by the Guerbet reaction in the presence of either supported or homogeneous nickel-based\\/sodium methoxide (MeONa) catalytic systems. The catalysts performances were studied as a function of reaction parameters, such as pre-activation or not of the nickel component, temperature, MeONa\\/Ni molar ratio, gaseous atmosphere (H2 or N2) and the

Carlo Carlini; Alessandro Macinai; Mario Marchionna; Marilena Noviello; Anna Maria Raspolli Galletti; Glauco Sbrana

2003-01-01

103

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

104

Synthesis of neoproteoglycans using the transglycosylation reaction as a reverse reaction of endo-glycosidases  

PubMed Central

A method for the synthesis of carbohydrate chains (glycosaminoglycans) and their coupling to peptides was investigated using proteoglycans. Glycosidases generally catalyze a hydrolytic reaction, but can also mediate the reverse reaction, which in this case is a transglycosylation. In the transglycosylation reaction of bovine testicular hyaluronidase, which is an endoglycosidase, glycosaminoglycans (hyaluronan and chondroitin sulfates) release disaccharide (uronic acid-N-acetylhexosamine) moieties from non-reducing terminal sites, and then the liberated disaccharides are transferred immediately to the non-reducing termini of other glycosaminoglycan chains. Using such continuous reactions, it is possible to synthesize glycosaminoglycan chains according to a specific design. It then becomes possible to transfer glycosaminoglycan chains synthesized on a peptide to other peptides using the transglycosylation reaction of endo-?-xylosidase acting on the linkage region between a peptide and glycosaminoglycan chains of proteoglycans. We believe this approach will open a new field for the synthesis of homogeneous proteoglycans or their corresponding analogues.

ENDO, Masahiko; KAKIZAKI, Ikuko

2012-01-01

105

A Theoretical Investigation of the Plausibility of Reactions Between Ammonia and Carbonyl Species (Formaldehyde, Acetaldehyde, and Acetone) in Interstellar Ice Analogs at Ultracold Temperatures  

NASA Technical Reports Server (NTRS)

We have reexamined the reaction between formaldehyde and ammonia, which was previously studied by us and other workers in modestly sized cluster calculations. Larger model systems with up to 12H2O were employed, and reactions of two more carbonyl species, acetaldehyde and acetone, were also carried out. Calculations were performed at the B3LYP/6-31+G** level with bulk solvent effects treated with a polarizable continuum model; limited MP2/6-31+G** calculations were also performed. We found that while the barrier for the concerted proton relay mechanism described in previous work remains modest, it is still prohibitively high for the reaction to occur under the ultracold conditions that prevail in dense interstellar clouds. However, a new pathway emerged in more realistic clusters that involves at least one barrierless step for two of the carbonyl species considered here: ammonia reacts with formaldehyde and acetaldehyde to form a partial charge transfer species in small clusters (4H2O) and a protonated hydroxyamino intermediate species in large clusters (9H2O, 12H2O); modest barriers that decrease sharply with cluster size are found for the analogous processes for the acetone-NH3 reaction. Furthermore, if a second ammonia replaces one of the water molecules in calculations in the 9H2O clusters, deprotonation can occur to yield the same neutral hydroxyamino species that is formed via the original concerted proton relay mechanism. In at least one position, deprotonation is barrierless when zero-point energy is included. In addition to describing the structures and energetics of the reactions between formaldehyde, acetaldehyde, and acetone with ammonia, we report spectroscopic predictions of the observable vibrational features that are expected to be present in ice mixtures of different composition.

Chen, Lina; Woon, David E.

2011-01-01

106

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

SciTech Connect

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

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

2011-12-15

107

Ammonia-treated Ordered Mesoporous Carbons as Catalytic Materials for Oxygen Reduction Reaction  

SciTech Connect

Polymer electrolyte membrane fuel cells (PEMFCs) have been considered as promising alternative power sources for many mobile and stationary applications. Compared to the fast hydrogen oxidation at the anode, the sluggish oxygen reduction reaction (ORR) at the cathode requires high-performance catalysts. Currently, platium (Pt) nanoparticles supported on high surface area carbons remain the best catalysts for ORR. However, both instability and high cost of Pt-based catalysts represent two main obstacles limiting the commercial applications of PEMFCs. The instability of supported Pt catalysts is mainly due to the corrosion of carbon support under operation conditions and the agglomation and detachment of Pt particles, leading to a decrease in catalytic surface areas. Development of corrosion resistant supports and enhancement of the interactions between Pt and supports are two strategies to improve the cathode long-term activity.

Wang, Xiqing; Lee, Je Seung; Zhu, Qing; Liu, Jun; Wang, Yong; Dai, Sheng

2010-04-13

108

Computational study of TNT synthesis in solvated nitration reaction systems  

NASA Astrophysics Data System (ADS)

Mononitrotoluene (MNT) was incorporated into solvated reaction systems and was subjected to subsequent nitration (electrophilic and free radical substitution) to obtain corresponding dinitrotoluene (DNT) and trinitrotoluene (TNT) products. In the electrophilic nitration system, the energy barrier of the reaction to produce o,p-dinitrotoluene from p-nitrotoluene was found to decrease from 62.7 to 14.7 kJ/mol to 9.2 kJ/mol in solventless, hydrated, and methanol-solvated molecular reaction systems, respectively. Further nitration to produce TNT in related solventless and solvated systems also led to a stepwise decreasing trend in the required energy, from 297.6 to 118.6 kJ/mol to 42.8 kJ/mol. Comparative synthesis using ·NO2 as the nitrating reagent to obtain o,p-DNT or TNT in the hydrated system shows a lower reaction energy barrier than that of the same reaction in the solventless system.

Liu, Min-Hsien; Cheng, Ken-Fa; Chen, Cheng; Hong, Yaw-Sun

109

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

110

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

111

The Identification of the Reaction Products Formed by the Oxidation of Aqueous Ammonia with Potassium Ferrate VI.  

National Technical Information Service (NTIS)

An exploratory study was undertaken to determine the feasibility of using potassium ferrate VI to oxidize ammonia in the secondary effluent from water treatment plants. The method shows good potential in that the major oxidation product, elemental nitroge...

G. W. Buttwin

1972-01-01

112

Wide range ammonia concentration analyzer utilizing a new principle of photoelectrochemical reaction at a nanoporous TiO2 photoanode.  

PubMed

It was successfully demonstrated that ammonia concentration in water can be determined easily with a remarkably wide dynamic range of 5 orders of magnitude by measuring the photocurrent generated by ammonia in a photoelectrochemical cell composed of a nanoporous TiO(2) photoanode, an O(2)-reducing Pt cathode and a UV-LED (ultra-violet light-emitting-diode) light source. PMID:20448917

Suzuki, Takashi; Ueno, Hirohito; Nemoto, Junichi; Fujii, Yuki; Hoshino, Mikio; Kaneko, Masao

2009-08-01

113

Tests of ammonia synthesis catalysts on an industrial nitrogen-hydrogen mixture  

Microsoft Academic Search

Impurities in the hydrocarbon feedstock for the production of nitrogen-hydrogen mixture (NHM) for industrial NHâ synthesis are known to poison the SA-1 industrial catalyst. The catalytic activity for some new catalysts, MV-5B, M-3S, and MV-1S, more resistant to poisoning was determined. The equipment and experimental procedure for various tests on the catalysts are described. Catalysts of particle sizes of 0.5-2.6

B. S. Zhirnov; V. E. Elizarev; Z. I. Cherepakhina; S. S. Lachinov; S. A. Akhmetov

1980-01-01

114

Selective synthesis of isobutanol by means of the Guerbet reaction  

Microsoft Academic Search

The synthesis of isobutanol (iBuOH) from mixtures of methanol (MeOH) and n-propanol (PrOH), via the Guerbet reaction, has been studied. Heterogeneous copper based catalytic systems, in combination with soluble sodium methoxide (MeONa) as basic component, were employed. In particular, copper-Raney and copper chromite were tested as metal components. The effect of the relative amount of MeONa with respect to the

Carlo Carlini; Marco Di Girolamo; Mario Marchionna; Marilena Noviello; Anna Maria Raspolli Galletti; Glauco Sbrana

2002-01-01

115

Synthesis of primary aromatic amides by aminocarbonylation of aryl halides using formamide as an ammonia synthon.  

PubMed

Primary aromatic amides were prepared by a palladium-catalyzed aminocarbonylation reaction of aryl halides in high yields (70-90%) using formamide as the amine source. The reactions require a palladium catalyst in combination with a nucleophilic Lewis base such as imidazole or 4-(dimethylamino)pyridine (DMAP). Aryl, heteroaryl, and vinyl bromides and chlorides were converted to the primary amides under mild conditions (5 bar, 120 degrees C) using 1 mol % of a palladium-phosphine complex. Best results were obtained in dioxane using triphenylphosphine as the ligand and DMAP as the base. For activated aryl bromides, a phosphine-to-palladium ratio of 2:1 was sufficient, but less reactive aryl bromides or aryl chlorides required ligand-to-palladium ratios up to 8:1 in order to stabilize the catalyst and achieve full conversion. The influence of catalyst, base, solvent, pressure, and temperature was studied in detail. The mechanism of the reaction could be clarified by isolating and identifying the reaction intermediates. In addition, methylamides and dimethylamides were prepared by the same method using N-methylformamide and N,N-dimethylformamide as the amine source. PMID:11397169

Schnyder, A; Beller, M; Mehltretter, G; Nsenda, T; Studer, M; Indolese, A F

2001-06-15

116

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

117

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

NASA Astrophysics Data System (ADS)

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

Bhandari, Pushpak

118

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

119

Pressure-reaction synthesis of titanium composite materials  

DOEpatents

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

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

1993-01-01

120

Fischer-Tropsch synthesis in supercritical reaction media  

SciTech Connect

The reactor configuration has been modified to handle tows both in the upflow and downflow directions. For comparison to bubble column operation, an upflow mode of operation will be used. For comparison to trickle-bed operation, a downflow mode will be employed. Thus, this modification allows the most flexibility for studying the effects of liquid and supercritical reaction media on the Fischer-Tropsch synthesis reaction and permits comparisons of our experimental results with previous work. A stainless steel reactor tube was ordered. This unit along with three other pieces of tubing (greater than 1/4in. i. d.) are to be sent to Alon Processing Co. for alonizing (passivating) the internal surface. This process had been employed by Huff and Satterfield (1983) to ensure that the stainless steel surfaces are catalytically inert at high temperatures (> 200[degree]C).

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

1993-04-01

121

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

122

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

123

Integrated optic ammonia sensor  

Microsoft Academic Search

Most of the disadvantages that exist with electrochemical devices (e.g., short lifetimes, difficult to miniaturize, need of reference electrodes) can be avoided by using optical sensors. Smock et al. describe a device incorporating a ninhydrin coated fused silica rod that could detect ammonia vapor at concentrations below 100 ppb, however, the reaction is irreversible. Guiliani et al. describe a reversible

Rainer Klein; Edgar I. Voges

1993-01-01

124

Mechanism of the reaction of nitric oxide, ammonia, and oxygen over vanadia catalysts. 2. Isotopic transient studies with oxygen-18 and nitrogen-15  

SciTech Connect

The mechanism of nitric oxide reduction with ammonia to form N/sub 2/, H/sub 2/O and N/sub 2/O both in the presence and in the absence of O/sub 2/ over the following series of catalysts, unsupported V/sub 2/O/sub 5/, V/sub 2/O/sub 5/ on TiO/sub 2/, V/sub 2/O/sub 5/ on SiO/sub 2//Al/sub 2/O/sub 3/, and V/sub 2/O/sub 5/ on Al/sub 2/O/sub 3/, has been investigated with the aid of labeled O/sub 2/ and labeled NH/sub 3/ at 400/sup 0/C. The behavior of ammonia was studied both in the presence and in the absence of O/sub 2/. The presence of labeled O/sub 2/ gives extra information about the product distribution and the reaction mechanism. Evidence is given that ammonia does not react with O/sub 2/ or O from any source during the reaction, but that nitrogen and nitrous oxide were produced by a reaction involving all three species, NO, NH/sub 3/, and/or O/sub 2/. Nitrous oxide and water are both formed at two different sites of the catalyst. A series of transient tracing studies were performed in a plug-flow reactor using /sup 15/NH/sub 3/ and /sup 18/O/sub 2/. Both /sup 15/NN and /sup 15/NNO were produced on the unsupported V/sub 2/O/sub 5/, V/sub 2/O/sub 5/ on TiO/sub 2/, V/sub 2/O/sub 5/ on SiO/sub 2//Al/sub 2/O/sub 3/, and V/sub 2/O/sub 5/ on Al/sub 2/O/sub 3/ with very high selectivities. The mechanism of the reaction of NO, NH/sub 3/, and O/sub 2/, proposed in a previous paper, is further evaluated on the basis of this new experimental evidence.

Janssen, F.J.J.G.; van den Kerkhof, F.M.G.; Bosch, H.; Ross, J.R.H.

1987-12-31

125

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

PubMed Central

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

Stahl, David A.

2013-01-01

126

Electrooxidation of ammonia in waste water  

Microsoft Academic Search

A study was undertaken of the electro-oxidation of ammonia as a possible new method of ammonia removal during waste-water treatment. Reaction rates were measured in the concentration range of 1.2×10-4 M to 1×10-2 M ammonia and at pH values of 5–13. The influence of the polarization rate (0.05–0.5 V min-1) and the ammonia concentrations on the oxidation peak current were

L. Marin?i?; F. B. Leitz

1978-01-01

127

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.

128

Ammonia Regulation of Carbon Metabolism in Photosynthesizing Leaf Discs 1  

PubMed Central

Alfalfa (Medicago sativa L., var. El Unico) leaf discs, floating on buffer containing NH4Cl and photosynthesizing with 14CO2, produced more labeled amino acid and less sucrose than did control discs (no added NH4Cl). The level of pyruvate increased and that of phosphoenolpyruvate decreased. These and other changes in levels of labeled compounds led us to conclude that pyruvate kinase was activated by ammonia, resulting in increased transfer of photosynthetically incorporated carbon to synthesis of amino acid skeletons at the expense of sucrose synthesis. Carbon flow through enzymes catalyzing the anaplerotic reactions was apparently stimulated.

Platt, Steven G.; Plaut, Zvi; Bassham, James A.

1977-01-01

129

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.

Ghosh, Arun K.; Kass, Jorden

2012-01-01

130

A stereoselective synthesis of (-)-viridiofungin A utilizing a TiCl(4)-promoted asymmetric multicomponent reaction.  

PubMed

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 acyloxycarbonium ion-mediated tetrahydrofuran ring-opening reaction and a Julia-Kocienski olefination. PMID:22195730

Ghosh, Arun K; Kass, Jorden

2012-01-20

131

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.

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

2011-01-01

132

Photodissociation of pyrrole-ammonia clusters by velocity map imaging: mechanism for the H-atom transfer reaction.  

PubMed

The photodissociation dynamics of pyrrole-ammonia clusters (PyH·(NH(3))(n), n = 2-6) has been studied using a combination of velocity map imaging and non-resonant detection of the NH(4)(NH(3))(n-1) products. The excited state hydrogen-atom transfer mechanism (ESHT) is evidenced through delayed ionization and presents a threshold around 236.6 nm, in agreement with previous reports. A high resolution determination of the kinetic energy distributions (KEDs) of the products reveals slow (?0.15 eV) and structured distributions for all the ammonia cluster masses studied. The low values of the measured kinetic energy rule out the existence of a long-lived intermediate state, as it has been proposed previously. Instead, a direct N-H bond rupture, in the fashion of the photodissociation of bare pyrrole, is proposed. This assumption is supported by a careful analysis of the structure of the measured KEDs in terms of a discrete vibrational activity of the pyrrolyl co-fragment. PMID:21076731

Rubio-Lago, L; Amaral, G A; Oldani, A N; Rodríguez, J D; González, M G; Pino, G A; Bañares, L

2011-01-21

133

Comment on ``on the role of promoters in promoted iron catalysts used in the industrial synthesis of ammonia''  

NASA Astrophysics Data System (ADS)

In a recent paper, Vandervell and Waugh presented the results of N 2 and H 2 temperature-programmed desorption (TPD) measurements performed on active industrial ammonia catalysts in a flow reactor system. This comment discusses some possible problems involved in the interpretation of their data.

Muhler, M.; Nielsen, Lars Pleth; Fastrup, B.

1991-06-01

134

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) [San Francisco, CA

1998-01-01

135

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

136

Solid-state reaction synthesis of boron carbonitride nanotubes  

NASA Astrophysics Data System (ADS)

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

Mo, Libin; Chen, Yongjun; Luo, Lijie

2010-07-01

137

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

138

Reactions of aromatic hydrocarbons with nucleophilic reagents in liquid ammonia. VII. Direction of hydroxylation of 3-substituted (Cl, Br, I, NO/sub 2/) nitrobenzenes with potassium hydroxide  

SciTech Connect

The reaction of 3-chloro-, 3-bromo-, and 3-iodonitrobenzenes with potassium hydroxide and oxygen in liquid ammonia (-33/sup 0/C) leads to the formation of nitrohalogenophenols, corresponding to substitution of the hydrogen atom at the ortho and para positions of the ring in relation to the nitro group by a hydroxy group. In the case of the last two substrates it also leads to the corresponding 2-halo-geno-3',4'-dinitrodiphenylamines. In view of the fact that substituted diphenylamines are formed under the same conditions as a result of the reaction of 3-nitro-aniline with 3-halogenonitrobenzenes it is suggested that 3-bromo- and 3-iodonitrobenzenes are partly converted into 3-nitroaniline through the intermediate formation of 3-nitrodehydrobenzene. During dehydroxylation in the absence of oxygen the proportion of the phenols corresponding to substitution of the hydrogen atom at the para position to the nitro group by the hydroxy group increases, and the degree of transformation of the initial compounds decreases. 2,4-dinitrophenol is formed with a low yield during the reaction of 1,3-nitrobenzene and potassium hydroxide in the presence of oxygen or in an atmosphere of argon.

Malykhin, E.V.; Kolesnichenko, G.A.; Shteingarts, V.D.

1986-09-20

139

Facile and fast synthesis of single-crystalline fractal zinc structures through a solution phase reaction and their conversion to zinc oxide.  

PubMed

We report a novel method for the synthesis of fractal Zn structures through a solution phase reaction. An Al-film-deposited substrate was immersed in an aqueous ammonia solution containing Zn ions and maintained at 95 degrees C for 5 min. After the reaction, the Al-deposited side of the substrate was found to be covered with fractal Zn structures. These Zn structures are highly oriented, and the Zn(002) planes are parallel to the substrate. They are single-crystalline and the average thickness of the plates is approximately 50 nm. On the basis of our results, we propose a mechanism for the spontaneous growth of such fractal Zn structures. Single-crystalline fractal ZnO structures can also be obtained by calcination of the as-synthesized fractal Zn crystals at 500 degrees C for 5 h in air. These fractal ZnO structures are highly oriented and inherit their morphologies from the Zn structures. PMID:19453111

Cho, Seungho; Kim, Semi; Kim, Hye-Jin; Lee, Bo Ram; Lee, Kun-Hong

2009-09-01

140

Method and apparatus for manufacturing ammonia synthesis gas from a stream of gas rich in hydrogen and a stream of nitrogen  

SciTech Connect

Difficulties associated with the operational stability of a conventional cryogenic plant for manufacturing ammonia synthesis gas from a stream rich in hydrogen and a stream of nitrogen are reduced by using three heat exchangers in place of the conventional single heat exchanger. In use, the first heat exchanger, which is preferably arranged with its cold end uppermost, is used to cool the stream of nitrogen to a temperature which: (A) if the nitrogen is above its critical pressure is between 8 and 28/sup 0/ C. Above its critical temperature; O (B) if the nitrogen is below its critical pressure is between 3 and 9/sup 0/ C. Above its dew point part of the nitrogen leaving the first heat exchanger is passed downwardly through a third heat exchanger where it is further cooled before being introduced into a nitrogen wash column where it acts as reflux. The third heat exchanger is cooled by vapor leaving the top of the nitrogen wash column.

McNeil, B.A.

1982-06-29

141

Polystyrenesulfonate-catalyzed synthesis of novel pyrroles through Paal-Knorr reaction  

PubMed Central

Background The classical Paal-Knorr reaction is one of the simplest and most economical methods for the synthesis of biologically important and pharmacologically useful pyrrole derivatives. Results Polystyrenesulfonate-catalyzed simple synthesis of substituted pyrroles following Paal-Knorr reaction has been accomplished with an excellent yield in aqueous solution. This method also produces pyrroles with multicyclic polyaromatic amines. Conclusions The present procedure for the synthesis of N-polyaromatic substituted pyrroles will find application in the synthesis of potent biologically active molecules.

2012-01-01

142

Copper/TEMPO catalysed synthesis of nitriles from aldehydes or alcohols using aqueous ammonia and with air as the oxidant.  

PubMed

Copper/TEMPO catalysts can be used to prepare nitriles from aldehydes or alcohols using aqueous ammonia. Readily accessible methods were developed that enable standard glassware to be used with air as the source of O2. It was further shown that, at higher temperatures in a pressurised reactor under limiting oxygen conditions (8% O2), catalyst loadings of 1 mol% could be employed. PMID:23719631

Dornan, Laura M; Cao, Qun; Flanagan, James C A; Crawford, James J; Cook, Matthew J; Muldoon, Mark J

2013-07-11

143

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.

Bhanushali, Mayur; Zhao, Cong-Gui

2011-01-01

144

Experimental study of reactions of the buckministerfullerene cations C[sub 60][sup [center dot]+], C[sub 60][sup 2+], and C[sub 60][sup [center dot]3+] with ammonia and amines in the gas phase  

Microsoft Academic Search

Results of SIFT experiments are reported for ion-molecule reactions initated by C[sub 60][sup [center dot]+], C[sub 60][sup 2+], C[sub 60][sup [center dot]3+] in ammonia, methylamine, ethylamine, dimethylamine, and trimethylamine at 294 [+-] 2 K in helium gas at a pressure of 0.35 [+-] 0.02 Torr. The main features of the observed reactions can be described in terms of adduct formation

G. Javahery; S. Petrie; H. Wincel; J. Wang; D. K. Bohme

1993-01-01

145

Reaction Route of GaN Powder Formation via Sintering Gallium Ethylenediamine Tetraacetic Acid Complexes in Ammonia  

NASA Astrophysics Data System (ADS)

The thermal decomposition behaviours of gallium ethylenediamine tetraacetic acid (Ga-EDTA) complex (Ga[(OOCCH2)2-N-CH2-CH2-N-(CH2COO)2]NH4) powders were investigated by thermogravimetric and differential thermal analysis (TG/DTA) under a flow of various ambient gas. It is found that the thermal stability of Ga-EDTA complexes is not much influenced by the ambient gases. In the case of ammonia ambient, with increasing the temperature, the mass loss undergoes four steps due to thermal decomposition and release of organic groups, resulting in Ga-iminodiacetate (IMDA), Ga-glycinate, and other Ga-related compounds, followed by the formation of GaN and carbon elimination. X-ray diffraction (XRD) patterns of the residue revealed that the temperature of GaN crystallization ranged from about 600 to 1100 °C and that the crystal quality improved with temperature. GaN powders of high crystal quality was obtained at 1100 °C.

Liu, Yu-Huai; Koide, Shinya; Miyake, Hideto; Hiramatsu, Kazumasa; Nakamura, Atsushi; Nambu, Nobuyoshi

2007-12-01

146

Petrochemical developments\\/ammonia: coal versus gas  

Microsoft Academic Search

An analytical study has shown that the direct conversion of coal with oxygen to a synthesis gas by the Koppers-Totzek (K-T) process is much more economical than the indirect conversion of coal to SNG and reforming of the latter (mixed with natural gas) to make synthesis gas. In either case, the synthesis gas can be used to make ammonia or

Hess

1976-01-01

147

Biomimetic synthesis of Pd nanocatalysts for the Stille coupling reaction.  

PubMed

Here we report on the biomimetic synthesis of Pd nanoparticles for use as models of green catalytic systems. The nanomaterials are synthesized using peptides isolated via phage-display techniques that are specific to Pd surfaces. Using this synthetic strategy, peptide-functionalized Pd nanoparticles of 1.9 +/- 0.3 nm in diameter are produced, which are soluble and stable in aqueous solutions. Once characterized, these biobased materials were then used as catalysts to drive the formation of C-C bonds using the Stille coupling reaction. Under the conditions of an aqueous solvent at room temperature, quantitative product yields were achieved within 24.0 h employing catalyst loadings of > or = 0.005 mol % of Pd. Additionally, high TOF values of 3207 +/- 269 mol product x (mol Pd x h)(-1) have been determined for these materials. The catalytic reactivity was then examined over a set of substrates with substitutions for both functional group and halide substituents, demonstrating that the peptide-based Pd nanoparticles are reactive toward a variety of functionalities. Taken together, these bioinspired materials represent unique model systems for catalytic studies to elucidate ecologically friendly reactive species and conditions. PMID:19422199

Pacardo, Dennis B; Sethi, Manish; Jones, Sharon E; Naik, Rajesh R; Knecht, Marc R

2009-05-26

148

Screening of electrocatalysts for direct ammonia fuel cell: Ammonia oxidation on PtMe (Me: Ir, Rh, Pd, Ru) and preferentially oriented Pt(1 0 0) nanoparticles  

Microsoft Academic Search

Ammonia has attracted attention as a possible fuel for direct fuel cells since it is easy to handle and to transport as liquid or as concentrated aqueous solution. However, on noble metal electrodes ammonia oxidation is a sluggish reaction and the electrocatalyst needs to be improved for developing efficient ammonia fuel cells. In this work, ammonia electrooxidation reaction on 3–4-nm

F. J. Vidal-Iglesias; J. Solla-Gullón; V. Montiel; J. M. Feliu; A. Aldaz

2007-01-01

149

First enantioselective total synthesis of (+)-(R)-Pinnatolide using an asymmetric domino allylation reaction.  

PubMed

An efficient total synthesis of (+)-(R)-Pinnatolide is described. As a key step an asymmetric multicomponent domino allylation reaction of methyl levulinate is used to form the quaternary stereogenic center in a highly selective way. PMID:22853329

Tietze, Lutz F; Wolfram, Thomas; Holstein, Julian J; Dittrich, Birger

2012-08-17

150

An improved Larock synthesis of quinolines via a Heck reaction of 2-bromoanilines and allylic alcohols.  

PubMed

A modified Larock method has been developed for the one-pot synthesis of substituted quinolines via a Heck reaction of 2-bromoanilines and allylic alcohols followed by dehydrogenation with diisopropyl azodicarboxylate (DIAD). PMID:21469650

Stone, Matthew T

2011-05-01

151

A Concise Approach to the Synthesis of opp-Dibenzoporphyrins through the Heck Reaction  

SciTech Connect

A concise approach to the synthesis of functionalized opp-dibenzoporphyrins is described. In this method, introduction of alkenyl groups to the porphyrin periphery through the vicinal 2-fold Heck reaction, 6- electrocyclization, and subsequent aromatization occur in one pot.

Deshpande, Rohit [Miami University, Oxford, OH; Jiang, Lin [Miami University, Oxford, OH; Schmidt, Gregory [Miami University, Oxford, OH; Rakovan, John [Miami University, Oxford, OH; Wang, Xiaoping [ORNL; Wheeler, Kraig [Eastern Illinois University; Wang, Hong [Miami University, Oxford, OH

2009-01-01

152

Studies on the Reaction Mechanism and Product Distribution of the Fischer-Tropsch Synthesis Process.  

National Technical Information Service (NTIS)

Experimental and theoretical studies on the reaction mechanism, products, and catalyst of the Fischer-Tropsch synthesis process are described. The author's many own product spectra obtained with iron base catalysts (with strongly varying pressures, temper...

M. Ritschel

1983-01-01

153

A novel synthesis of tert-leucine via a Leuckart type reaction  

Microsoft Academic Search

An efficient synthesis of racemic tert-leucine from trimethylpyruvic acid using a Leuckart type reaction is described. A facile resolution of an intermediate with ?-methylbenzylamine allows entry into either (R)-or (S)-tert-leucine.

Brian M. Adger; Ulrich C. Dyer; Ian C. Lennon; Peter D. Tiffin; Simon E. Ward

1997-01-01

154

Efficient synthesis of tetrasubstituted thiophenes by reaction of benzoyl isothiocyanates, ethyl bromopyruvate and enaminones  

Microsoft Academic Search

An efficient synthesis of ethyl 2-(4-acetyl-5-benzoylamino-3-methyl-2-thienyl)-2-oxoacetates is described via reaction between benzoyl isothiocyanates and ethyl bromopyruvate in the presence of enaminones.

Issa Yavari; Zinatossadat Hossaini; Maryam Sabbaghan

2008-01-01

155

Addition of water, methanol, and ammonia to Al3O3- clusters: Reaction products, transition states, and electron detachment energies  

NASA Astrophysics Data System (ADS)

Products of reactions between the book and kite isomers of Al3O3- and three important molecules are studied with electronic structure calculations. Dissociative adsorption of H2O or CH3OH is highly exothermic and proton-transfer barriers between anion-molecule complexes and the products of these reactions are low. For NH3, the reaction energies are less exothermic and the corresponding barriers are higher. Depending on experimental conditions, Al3O3- (NH3) coordination complexes or products of dissociative adsorption may be prepared. Vertical electron detachment energies of stable anions are predicted with ab initio electron propagator calculations and are in close agreement with experiments on Al3O3- and its products with H2O and CH3OH. Changes in the localization properties of two Al-centered Dyson orbitals account for the differences between the photoelectron spectra of Al3O3- and those of the product anions.

Guevara-García, Alfredo; Martínez, Ana; Ortiz, J. V.

2005-06-01

156

Efficient synthesis of fluorophosphonylated alkyles by ring-opening reaction of cyclic sulfates.  

PubMed

Ring-opening reactions of functionalized 1,2-cyclic sulfates and oxetanes with the phosphonodifluoromethyl carbanion are reported. This approach allows an easy access to fluorinated beta-hydroxyphosphonates that are building blocks in the synthesis of acyclic nucleosides. Synthesis of precursors of nucleoside phosphorylase inhibitors from these alcohols is described. PMID:18666773

Diab, Sonia Amel; Sene, Aboubacary; Pfund, Emmanuel; Lequeux, Thierry

2008-09-01

157

Copper-catalyzed synthesis of primary arylamines via cascade reactions of aryl halides with amidine hydrochlorides.  

PubMed

We have developed an efficient method for the synthesis of primary arylamines from aryl halides using amidine hydrochlorides as the ammonia surrogates. The protocol uses 10 mol % CuI as the catalyst, 20 mol % L-proline as the ligand, Cs2CO3 as the base, and DMF as the solvent and proceeds the sequential coupling of aryl halides with amidine hydrochlorides and hydrolysis of intermediates to give the target products. This is a convenient, inexpensive, and practical approach to primary arylamines. PMID:18662031

Gao, Xiaoting; Fu, Hua; Qiao, Renzhong; Jiang, Yuyang; Zhao, Yufen

2008-09-01

158

Applications of Multicomponent Reactions to the Synthesis of Diverse Heterocyclic Scaffolds  

PubMed Central

The sequencing of multicomponent reactions (MCRs) and subsequent cyclization reactions is a powerful stratagem for the rapid synthesis of diverse heterocyclic scaffolds. The optimal MCR is sufficiently flexible that it can be employed to generate adducts bearing a variety of functional groups that may then be selectively paired to enable different cyclization manifolds, thereby leading to a diverse collection of products. The growing interest in diversity-oriented synthesis has led to increased attention to this paradigm for library synthesis, which has inspired many advances in the design and implementation of MCRs for the construction of diverse heterocyclic scaffolds.

Sunderhaus, James D.

2009-01-01

159

Reaction engineering principles of combustion synthesis of advanced materials  

NASA Astrophysics Data System (ADS)

A mathematical model of solid-solid combustion synthesis and gas-solid combustion synthesis is formulated and the governing equations are numerically solved. The stability of solid-solid combustion is briefly discussed. Results of numerical simulations of the two types of combustion are summarized.

Gatica, Jorge E.; Dandekar, Hemant W.; Viljoen, Hendrik J.; Hlavacek, Vladimir

160

Ruthenium complex-catalyzed synthesis of carbamates by dehydrogenative reaction of formamides with alcohols  

Microsoft Academic Search

In the presence of a catalytic amount of RuCl2(PPh3)3, various alkyl N-arylcarbamates are obtained in 23–82% yields by dehydrogenative reaction of N-aryl substituted formamides with alcohols. The present reaction offers an alternative method for phosgene- and carbon monoxide-free synthesis of carbamates.

Shinji Kotachi; Teruyuki Kondo; Yoshihisa Watanabe

1993-01-01

161

Synthesis of Triarylmethane and Xanthene Dyes Using Electrophilic Aromatic Substitution Reactions  

ERIC Educational Resources Information Center

The synthesis of dyes has long been a popular topic in organic chemistry laboratory experiments because it allows students to see first hand that reactions learned in class can be used to make compounds with useful applications. In this experiment electrophilic aromatic substitution reactions are used to synthesize several triarylmethane and…

McCullagh, James V.; Daggett, Kelly A.

2007-01-01

162

Everyday Chemical Reactions: A Writing Assignment to Promote Synthesis of Concepts and Relevance in Chemistry  

Microsoft Academic Search

Capturing the interest of students in required chemistry courses is a problem for which many solutions have been proposed and described. The solution proposed here is the use of a writing assignment on everyday chemical reactions. Students select their own organic reaction and apply concepts learned throughout the semester to understanding it. The assignment requires the synthesis of many concepts

Abby L. Parrill

2000-01-01

163

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

PubMed Central

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

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

2012-01-01

164

Combustion Synthesis Reactions in Cold-Rolled Ni/Al and Ti/Al Multilayers  

NASA Astrophysics Data System (ADS)

In this article, a cold rolling method was developed to fabricate Ni/Al and Ti/Al multilayer foils, and the combustion synthesis reactions in the cold-rolled foils were investigated. Combustion synthesis reactions were initiated by heating one end of the cold-rolled foil in a flame for several seconds. The Ni/Al foils went through three reaction stages. The first reaction stage was a displacement of reaction zone with Al3Ni as the reaction product. During the second stage, the part of the foil in the flame underwent thermal explosion. In the last stage, the heat released by thermal explosion triggered a self-propagating high-temperature synthesis (SHS) reaction across the foil that resulted in the formation of AlNi. In contrast, the Ti/Al foils experienced only two reaction stages. First, a displacement of the reaction zone propagated across the foil with formation of Al3Ti at the Ti/Al interface. Then a thermal explosion reaction occurred in the part of foil that was heated in the flame, resulting in many different phases in the reacted foil.

Qiu, Xiaotun; Liu, Ranran; Guo, Shengmin; Graeter, Jesse Harris; Kecskes, Laszlo; Wang, Jiaping

2009-07-01

165

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.

2013-01-01

166

Bifunctional iminophosphorane organocatalysts for enantioselective synthesis: application to the ketimine nitro-Mannich reaction.  

PubMed

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

Núñez, Marta G; Farley, Alistair J M; Dixon, Darren J

2013-11-01

167

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

PubMed Central

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

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

2008-01-01

168

Modeling the reaction synthesis of shock-densified titanium-silicon powder mixture compacts  

Microsoft Academic Search

The reaction behavior of shock-consolidated Ti-Si powder mixture compacts, densified at 5 to 7 GPa pressure, was investigated\\u000a to determine conditions required for solid-state reaction synthesis leading to the formation of dense Ti5Si3 intermetallic compounds with fine-grained microstructure. It was observed that at temperatures greater than 1000 C, the\\u000a heat released following reaction initiation in the solid state exceeds the

S. A. Namjoshi; N. N. Thadhani

2000-01-01

169

One-pot Synthesis of Lactams Using Domino Reactions: Combination of Schmidt Reaction with Sakurai and Aldol Reactions  

PubMed Central

A series of domino reactions in which the intramolecular Schmidt reaction is combined with either a Sakurai reaction, an aldol reaction, or both is reported. The Sakurai reaction of an allylsilane with an azido-containing enone under Lewis acidic conditions followed by protonation of the resulting titanium enolate species allowed for a subsequent intramolecular Schmidt reaction. Alternatively, the intermediate titanium enolate could undergo an aldol reaction, followed by the intramolecular Schmidt reaction to form lactam products with multiple stereogenic centers. The stereochemical features of the titanium enolate aldol reaction with several 3-azidoaldehyde substrates during this domino process is discussed.

Huh, Chan Woo; Somal, Gagandeep K.; Katz, Christopher E.; Pei, Huaxing; Zeng, Yibin; Douglas, Justin T.; Aube, Jeffrey

2009-01-01

170

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

171

Quantitative relationship between phenylalanine ammonia-lyase levels and phenylpropanoid accumulation in transgenic tobacco identifies a rate-determining step in natural product synthesis.  

PubMed Central

Phenylalanine ammonia-lyase (PAL) catalyzes the first step in phenylpropanoid synthesis. The role of PAL in pathway regulation was investigated by measurement of product accumulation as a function of enzyme activity in a collection of near-isogenic transgenic tobacco plants exhibiting a range of PAL levels from wild type to 0.2% of wild type. In leaf tissue, PAL level is the dominant factor regulating accumulation of the major product chlorogenic acid and overall flux into the pathway. In stems, PAL at wild-type levels contributes, together with downstream steps, in the regulation of lignin deposition and becomes the dominant, rate-determining step at levels 3- to 4-fold below wild type. The metabolic impact of elevated PAL levels was investigated in transgenic leaf callus that overexpressed PAL. Accumulation of the flavonoid rutin, the major product in wild-type callus, was not increased, but several other products accumulated to similarly high levels. These data indicate that PAL is a key step in the regulation of overall flux into the pathway and, hence, accumulation of major phenylpropanoid products, with the regulatory architecture of the pathway poised so that downstream steps control partitioning into different branch pathways. Images

Bate, N J; Orr, J; Ni, W; Meromi, A; Nadler-Hassar, T; Doerner, P W; Dixon, R A; Lamb, C J; Elkind, Y

1994-01-01

172

The interaction at the solid\\/liquid interface of 2,4-dichlorophenoxyacetic acid with silica modified by reaction with ammonia gas  

Microsoft Academic Search

A method for the attachment of ammonia to modified silica gel has been developed. In the first step, tetraethylorthosilicate and (3-glycidoxypropyl)trimethoxysilane were co-condensed in the presence of n-dodecylamine, a neutral surfactant template, to produce a modified mesoporous silica. The epoxy group incorporated into the mesoporous silica was opened by ammonia gas thus introducing amine chelate groups covalently bound to the

Alexandre G. S. Prado; Edimar DeOliviera

2005-01-01

173

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

PubMed

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

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

2007-05-24

174

Studies on the synthesis of pectenotoxin II: synthesis of a C(11)-C(26) fragment precursor via [3 + 2]-annulation reactions of chiral allylsilanes.  

PubMed

[see reaction]. A synthesis of tetracycle 2 corresponding to the C(11)-C(26) fragment of pectenotoxin II is described. The synthesis features two highly stereoselective [3 + 2]-annulation reactions of chiral allylsilanes, generated via allylboration of aldehydes with the chiral gamma-silylallylborane 4 or the gamma-silylallylboronate 19, for construction of the highly substituted C and E rings. PMID:11405752

Micalizio, G C; Roush, W R

2001-06-14

175

Self-sustained high-temperature reactions: initiation, propagation and synthesis  

Microsoft Academic Search

Self-Propagating High-Temperature Synthesis (SHS), also called combustion synthesis is an exothermic and self-sustained reaction between the constituents, which has assumed significance for the production of ceramics and ceramic-metallic materials (cermets), because it is a very rapid processing technique without the need of complex furnaces. However, one of the drawbacks of this route is the high porosity of the final product

M. Martinez Pacheco

2007-01-01

176

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.

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

2011-01-01

177

Synthesis and minisci reactions of organotrifluoroborato building blocks.  

PubMed

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

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

2013-05-01

178

Synthesis and Minisci Reactions of Organotrifluoroborato Building Blocks  

PubMed Central

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

Presset, Marc; Fleury-Bregeot, Nicolas; Oehlrich, Daniel

2013-01-01

179

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.

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

2012-01-01

180

Ready synthesis of free N-H 2-arylindoles via the copper-catalyzed amination of 2-bromo-arylacetylenes with aqueous ammonia and sequential intramolecular cyclization.  

PubMed

A wide range of free N-H 2-arylindoles were synthesised via the copper(II)-catalyzed amination of 2-bromo-arylacetylenes with aqueous ammonia and sequential intramolecular cyclization. The convenience and atom economy of aqueous ammonia, and the low cost of the copper catalytic system make this protocol readily superior in practical application. PMID:21584339

Wang, Huifeng; Li, Yaming; Jiang, Linlin; Zhang, Rong; Jin, Kun; Zhao, Defeng; Duan, Chunying

2011-07-01

181

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

182

Selective synthesis of isobutanol by means of the Guerbet reaction  

Microsoft Academic Search

The synthesis of isobutanol via the Guerbet condensation between methanol and ethanol was studied by using sodium methoxide (MeONa) as soluble basic component and copper-based catalysts as heterogeneous dehydrogenating\\/hydrogenating metal species. The effect of the nature of the catalyst and the relative amount of its individual components with respect to the reacting alcohols as well as of temperature on productivity

Carlo Carlini; Marco Di Girolamo; Alessandro Macinai; Mario Marchionna; Marilena Noviello; Anna Maria Raspolli Galletti; Glauco Sbrana

2003-01-01

183

Induction of Hypozincemia and Hepatic Metallothionein Synthesis in Hypersensitivity Reactions.  

National Technical Information Service (NTIS)

Recent evidence indicates that hypersensitivity reactions, produced in rats by the administration of a protein antigen, alters plasma zinc and iron homeostasis by depressing concentrations of these trace minerals. Studies were performed to determine if hy...

P. Z. Sobocinski W. J. Canterbury E. C. Hauer F. A. Beall

1978-01-01

184

Porous silicon ammonia gas sensor  

NASA Astrophysics Data System (ADS)

A planar optical waveguide is manufactured by the functionnalisation of oxidised mesoporous silicon with Bromothymol Blue to achieve a sensitive ammonia sensor suitable for low gas concentrations. The propagated light intensity is measured at the output of the waveguide. The sensitivity at low concentrations and the short time of reaction of the sensor are enhanced by a confinement effect of the gas molecules inside the pores. The dependence of the output signal with gas concentration is demonstrated. When the ammonia flow is stopped, the reversibility of the initial characteristics of the propagated light is naturally obtained with the disappearance of the gas molecules.

Chaillou, A.; Charrier, J.; Lorrain, N.; Sarret, M.; Haji, L.

2006-03-01

185

Reaction synthesis of TiB 2–TiC composites with enhanced toughness  

Microsoft Academic Search

In situ toughened TiB2–TiCx composites were fabricated using reaction synthesis of B4C and Ti powders at high temperatures. The resulting materials possessed very high relative densities and well developed TiB2 plate-like grains, leading to a rather high fracture toughness, up to 12.2 MPa?m1\\/2. The microstructure was examined by means of XRD, SEM, TEM and EDAX. The reaction products mainly consisted

G. Wen; S. B. Li; B. S. Zhang; Z. X. Guo

2001-01-01

186

RNA-peptide conjugate synthesis by inverse-electron demand Diels-Alder reaction.  

PubMed

Here we report an efficient method for the synthesis of RNA-peptide conjugates by inverse-electron demand Diels-Alder reaction. Various dienophiles were enzymatically incorporated into RNA and reacted with a chemically synthesized diene-modified peptide. The Diels-Alder reaction proceeds with near-quantitative yields in aqueous solution with stoichiometric amounts of reactants, even at low micromolar concentrations. PMID:24871687

Ameta, Sandeep; Becker, Juliane; Jäschke, Andres

2014-06-11

187

Hydrogen-bond-mediated cascade reaction involving chalcones: facile synthesis of enantioenriched trisubstituted tetrahydrothiophenes.  

PubMed

A bifunctional squaramide catalyzed sulfa-Michael/aldol cascade reaction between 1,4-dithiane-2,5-diol and chalcones with a low catalyst loading has been developed. Trisubstituted tetrahydrothiophenes with three contiguous stereogenic centers are obtained in a highly stereocontrolled manner. Additionally, a remarkable temperature effect on reaction efficiency was observed and a synthetically potential gram-synthesis was also conducted. PMID:22313116

Ling, Jun-Bing; Su, Yu; Zhu, Hai-Liang; Wang, Guan-Yu; Xu, Peng-Fei

2012-02-17

188

Diversity synthesis using the complimentary reactivity of rhodium(II)- and palladium(II)-catalyzed reactions.  

PubMed

Rhodium(II)-catalyzed reactions of aryldiazoacetates can be conducted in the presence of iodide, triflate, organoboron, and organostannane functionality, resulting in the formation of a variety of cyclopropanes or C-H insertion products with high stereoselectivity. The combination of the rhodium(II)-catalyzed reaction with a subsequent palladium(II)-catalyzed Suzuki coupling offers a novel strategy for diversity synthesis. PMID:16839138

Ni, Aiwu; France, Jessica E; Davies, Huw M L

2006-07-21

189

Chemical and Physical Properties of Copper-Based Catalysts for CO Shift Reaction and Methanol Synthesis  

Microsoft Academic Search

The modern low-pressure methanol synthesis catalysts are based on copper-containing systems such as Cu\\/ZnO\\/Al2O3 and Cu\\/ZnO\\/Cr2O3 with various compositions. These catalysts are also highly active for the low-temperature CO shift reaction. For both reactions the nature of the active sites is still an open question.

Giovanna Ghiotti; Flora Boccuzzi

1987-01-01

190

One-pot synthesis of olefins from aromatic ketones via tandem consecutive hydrogenation–dehydration reactions  

Microsoft Academic Search

In this work, the synthesis of aromatic olefins from the corresponding ketones via tandem consecutive hydrogenation–dehydration reactions was studied. The conversion of acetophenone (AP) to styrene (STY) was used as model reaction. Initially, the liquid-phase hydrogenation of AP to 1-phenylethanol (PHE), using cyclohexane as solvent, was investigated at 363K and 10bar over Ni, Co, Cu, Pd and Pt supported on

Nicolás M. Bertero; Carlos R. Apesteguía; Alberto J. Marchi

2011-01-01

191

Enantioselective Synthesis of the ABC Ring Motif of Norzoanthamine Based on Asymmetric Robinson Annulation Reactions  

PubMed Central

An enantioselective strategy for the synthesis of tetracyclic motif 5, representing the northern fragment of norzoanthamine, is presented. Key to the strategy is the use of two asymmetric Robinson annulation reactions that produce the tricyclic ABC ring system with excellent stereoselectivity. Further functionalization at the periphery of the C ring produces compound 5 containing six contiguous stereocenters of the natural product.

Nguyen, Thong X.; Dakanali, Marianna; Trzoss, Lynnie; Theodorakis, Emmanuel A.

2011-01-01

192

Solvent-free synthesis of functionalized thiazoles using multicomponent reaction of isothiocyanates.  

PubMed

An efficient synthesis of thiazoles is described via an one-pot reaction between acid chlorides, ammonium thiocyanate tetramethylguanidine and ?-bromocarbonyl compounds under solvent-free conditions without using any catalyst. The method offers several advantages including high yields of products and an easy work-up procedure at room temperature in excellent yield. PMID:23721069

Sayyed-Alangi, Seyyedeh Zahra; Hossaini, Zinatossadat; Rostami-Charati, Faramarz; Sajjadi-Ghotabadi, Hadi

2013-11-01

193

Synthesis and Investigation of Nanomaterials by Homogeneous Nonaqueous Solution Phase Reactions  

Microsoft Academic Search

The objective of this Ph.D. study is to explore an important and fertile research topic on the methods for synthesis of nanomaterials by homogeneous nonaqueous solution phase reaction. Research in this work focuses on synthesizing several kinds of nanomaterials in different environments and structure, including spherical nanoparticles, nanowires and core-shell structure composites We first synthesized metallic nanomaterials in this system,

Zhihui Ban

2005-01-01

194

Solid phase synthesis of hydantoins by thermal cyclization and screening of reaction conditions using APOS 1200.  

PubMed

A novel strategy for solid-phase synthesis of hydantoins with high optical purity is described using a thermal pH-neutral cyclization and simultaneous release from resin. Hereby even hydantoins bearing a pH-sensitive side chain (protection) are available. The reaction conditions are well screened applying the parallel organic synthesizer APOS 1200. PMID:10729901

Karnbrock, W; Deeg, M; Gerhardt, J; Rapp, W

1998-01-01

195

Coupling reaction and azeotropic distillation for the synthesis of glycerol carbonate from glycerol and dimethyl carbonate  

Microsoft Academic Search

A new process, coupling reaction and azeotropic distillation was proposed for the synthesis of glycerol carbonate (GC) from glycerol (G) and dimethyl carbonate (DMC). The bench scale experimental investigation was systematically conducted for this new process. With calcium oxide (CaO) as the solid catalyst, the high yield of glycerol carbonate can be obtained at a low molar ratio of dimethyl

Jiabo Li; Tao Wang

2010-01-01

196

Diastereoselective synthesis of (±)-heliotropamide by a one-pot, four-component reaction.  

PubMed

The first synthesis of heliotropamide is reported. The preparation of this 2-oxopyrrolidine (?-lactam) natural product relied on a diastereoselective one-pot, four-component reaction (4CR) for the assembly of the core structure. On the basis of chemical shift correlation and NOESY experiments, the previously unknown alkene geometry of heliotropamide is assigned as E. PMID:21062051

Younai, Ashkaan; Chin, Gregory F; Shaw, Jared T

2010-12-01

197

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

198

Redox reactions in liquid plasma during iron oxide and oxide-hydroxide nanoparticles synthesis  

Microsoft Academic Search

A new synthesis method of iron oxide and iron oxide-hydroxide nanoparticles by pulsed liquid plasma process is presented. The redox reaction rates in liquid phase depend on the relative number densities of oxygen and hydrogen atoms produced in plasma gas phase and on the injected energy per pulse. The oxidation rate was higher than the reduction one in both regimes

M. A. Bratescu; N. Saito; O. Takai

199

Organocatalytic cascade reactions: diversity-oriented synthesis for the construction of hydroisoquinoline scaffolds.  

PubMed

The organocatalytic enantioselective synthesis of highly functionalized hydroisoquinolines by trienamine-mediated [4+2]-cycloaddition/nucleophilic ring-closing reaction cascade sequence of cyanoacrylamides with 2,4-dienals is presented. The corresponding cycloadducts are formed in high yields and excellent stereoselectivities. Moreover, a series of transformations demonstrate the synthetic application of the obtained hydroisoquinolines. PMID:24769648

Gómez, Clarisa Villegas; Cruz, David Cruz; Mose, Rasmus; Jørgensen, Karl Anker

2014-06-01

200

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

Microsoft Academic Search

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

Ç?nar Öncel; Yuda Yürüm

2006-01-01

201

Enantioselective synthesis of both enantiomers of vicinal norbornanediamines through the Leuckart reaction of 2-norbornanones  

Microsoft Academic Search

The reaction of 2-norbornanones bearing an amine derivative in the bridgehead position with formamide and formic acid yields enantiomerically pure 1,2-norbornane diamides. These compounds are excellent precursors of chiral vicinal diamines, which have been increasingly used due to their numerous applications in medicinal chemistry and asymmetric synthesis. The rigid structure of the norbornane framework allows the study of conformational equilibrium

Antonio Garc??a Mart??nez; Enrique Teso Vilar; Amelia Garc??a Fraile; Paloma Mart??nez-Ruiz

2001-01-01

202

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

NASA Astrophysics Data System (ADS)

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

Namjoshi, Shantanu Ashok

203

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

204

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

205

Synthesis of boron nitride powders  

NASA Astrophysics Data System (ADS)

In the materials science community there is much interest in the development of new, efficient approaches for preparing ceramic powders having properties or performance characteristics not found with powders produced by traditional metallurgical synthesis methods. In this regard, aerosol-based syntheses are finding general acceptance for the preparation of non-metal and metal oxide powders. In contrast, much less effort has been given to aerosol-type syntheses for non-oxide powders despite potentially useful benefits. This dissertation describes the application of two chemical systems in aerosol assisted vapor phase synthesis (AAVS) for the preparation of spherical morphology boron oxynitride, BNxOy, powders that are subsequently converted to spherical morphology boron nitride in a second nitridation step. Chapter 1 describes the AAVS synthesis of BNxOy powders using a reaction of an aqueous boric acid containing aerosol with ammonia at 1000°C. The effect of reactor tube material, total gas flow rate, ammonia concentration, boric acid concentration, and urea addition to the boric acid aerosol on the percent oxygen composition is described. The resulting BNxOy powders contain significant amounts of oxygen that require replacement in a second stage nitridation reaction at elevated temperature under ammonia. The influences of the reaction temperature profile, crucible geometry and transformation additive on final oxygen composition and powder crystallinity are described. Chapter 2 outlines the formation of BNxOy powders from an AAVS reaction between the boron precursor (MeO)3B and ammonia. The formation of the powders is studied as a function of total gas flow rate and ammonia concentration. In all cases the resulting powders contain lower levels of oxygen compared to powders produced from aqueous boric acid aerosols. The conversion of the BNxOy powders in the second stage nitridation reaction with ammonia is examined as a function of crucible geometry, temperature profile and ammonia flow rate. In support of this process, the molecular reaction between (MeO)3B and NH3 was reexamined. The adduct, (MeO)3B·NH3, was isolated and its molecular structure determined by single crystal X-ray diffraction techniques. The results of these studies provide guidance for more detailed studies that should result in industrial scale synthesis of spherical morphology BN which currently is not formed by standard metallurgical syntheses. This new material has potential applications in several areas including the formation of BN loaded organic polymer composites.

Dreissig, Dirk Horst

2002-09-01

206

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...

207

Synthesis of transactinide nuclei in cold fusion reactions using radioactive beams  

NASA Astrophysics Data System (ADS)

Chances of synthesis of transactinide nuclei in cold fusion reactions (one-neutron-out reactions) using radioactive beams are evaluated. Because in most of the cases intensities of radioactive beams are significantly less than those of the stable beams, reactions with the greatest radioactive-beam intensities for the particular elements are considered. The results are compared with the recent ones obtained by Loveland [Phys. Rev. CPRVCAN0556-281310.1103/PhysRevC.76.014612 76, 014612 (2007)], who investigated the same nuclei.

Smola?czuk, Robert

2010-06-01

208

Synthesis of calix[4]arene alkylamine derivatives as new phase-transfer catalysts for esterification reaction  

Microsoft Academic Search

This study reports the synthesis of calix[4]arene-based phase-transfer catalysts derived from the reaction of 5,17-di-tert-butyl-25,27,26,28-tetrahydroxycalix[4]arene with N-ethylpiperazine, diallylamine or 4-benzylpiperidine. The catalytic efficiency of the calix[4]arenes alkylamine derivatives was evaluated by carrying out the ester-forming reaction of alkali metal carboxylates (sodium butyrate or sodium caprylate) with p-nitrobenzyl bromide. It has been observed that the ester-forming reaction of alkali metal carboxylates

Ezgi Akceylan; Mustafa Yilmaz

2011-01-01

209

Intramolecular Pd(II)-catalyzed oxidative biaryl synthesis under air: reaction development and scope.  

PubMed

New reaction conditions for intramolecular palladium(II)-catalyzed oxidative carbon-carbon bond formation under air are described. The use of pivalic acid as the reaction solvent, instead of acetic acid, results in greater reproducibility, higher yields, and broader scope. This includes the use of electron-rich diarylamines as illustrated in the synthesis of three naturally occurring carbazole products: Murrayafoline A, Mukonine, and Clausenine. A variety of side products have also been isolated, casting light on competing reaction pathways and revealing new reactivity with palladium(II) catalysis. PMID:18543991

Liégault, Benoît; Lee, Doris; Huestis, Malcolm P; Stuart, David R; Fagnou, Keith

2008-07-01

210

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

PubMed

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

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

2014-01-01

211

Acyl Iodides in Organic Synthesis: VI. Reactions with Vinyl Ethers  

Microsoft Academic Search

Reactions of acetyl iodide with butyl vinyl ether, 1,2-divinyloxyethane, phenyl vinyl ether, 1,4-di-vinyloxybenzene, and divinyl ether were studied. Vinyl ethers derived from aliphatic alcohols (butyl vinyl ether and 1,2-divinyloxyethane) react with acetyl iodide in a way similar to ethyl vinyl ether, i.e., with cleavage of both O–Csp2 and Alk–O ether bonds. From butyl vinyl ether, a mixture of vinyl iodide,

M. G. Voronkov; A. A. Trukhina; N. N. Vlasova

2004-01-01

212

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

213

Synthesis of nanosized silicon particles by a rapid metathesis reaction  

SciTech Connect

A solid-state rapid metathesis reaction was performed in a bed of sodium silicofluoride (Na{sub 2}SiF{sub 6}) and sodium azide (NaN{sub 3}) powders diluted with sodium fluoride (NaF), to produce silicon nanoparticles. After a local ignition of Na{sub 2}SiF{sub 6}+4NaN{sub 3}+kNaF mixture (here k is mole number of NaF), the reaction proceeded in a self-sustaining combustion mode developing high temperatures (950-1000 deg. C) on very short time scales (a few seconds). Silicon nanoparticles prepared by the combustion process was easily separated from the salt byproducts by simple washing with distilled water. The structural and morphological studies on the nanoparticles were carried out using X-ray diffractometer (XRD) and field emission scanning electron microscope (FESEM). The mean size of silicon particles calculated from the FESEM image was about 37.75 nm. FESEM analysis also shows that the final purified product contains a noticeable amount of silicon fibers, dendrites and blocks, along with nanoparticles. The mechanism of Si nanostructures formation is discussed and a simple model for interpretation of experimental results is proposed. - Graphical abstract: Silicon nanoparticles 37.75 nm in mean diameter was obtained by rapid metathesis reaction performed in Na{sub 2}SiF{sub 6}+4NaN{sub 3} powder bed diluted with NaF.

Won, C.W. [RASOM, Chungnam National University, Yuseong, Daejeon 305-764 (Korea, Republic of); Nersisyan, H.H., E-mail: haykrasom@hotmail.co [RASOM, Chungnam National University, Yuseong, Daejeon 305-764 (Korea, Republic of); Won, H.I. [RASOM, Chungnam National University, Yuseong, Daejeon 305-764 (Korea, Republic of); Lee, H.H. [Korea Research Institute of Chemical Technology, Daejeon 305-600 (Korea, Republic of)

2009-11-15

214

Catalytic activity of systems based on coordination cyanides of copper, iron, ruthenium, and osmium in the reaction of ammonia synthesis  

Microsoft Academic Search

The purpose of the present investigation was to study the catalytic activity of systems based on cyano complexes of iron and its electronic analogs (ruthenium and osmium), and on coordination copper cyanides of the composition KâFe(Cu(CN)â)â and KFe(Cu(CN)â). The catalyst activities under 200 atm pressure were determined in an apparatus at space velocity of 15,000 h⁻¹ in the temperature range

Zh. I. Tkachenko; L. I. Pavlenko; Yu. A. Lyubchenko

1980-01-01

215

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

216

A New Direct Single-Molecule Observation Method for DNA Synthesis Reaction Using Fluorescent Replication Protein A  

PubMed Central

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.

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

2014-01-01

217

Synthesis and reactions of the oxides of hexafluoropropylene trimers  

SciTech Connect

By the oxidation of the hexafluoropropylene trimers with an aqueous solution of sodium hypochlorite in the presence of acetonitrile the following ..cap alpha..-oxides were obtained: 2,3-Epoxyperfluoro-3-isopropyl-4-methylpentane and 2,3-epoxyperfluoro-3-ethyl-2,4-dimethylpentane. According to the /sup 19/F NMR data, the epoxidation takes place stereoselectively with the formation of only one conformer of the ..cap alpha..-oxide in each case. The determining effect of the steric factors on the reactivity of the oxides of hexafluoropropylene trimers in reaction with nucleophiles was demonstrated.

Zapevalov, A.Ya.; Filyakova, T.I.; Peschanskii, N.V.; Kodess, M.I.; Kolenko, I.P.

1986-03-10

218

The pathway of ammonia assimilation in the silkworm, Bombyx mori  

Microsoft Academic Search

Ammonia can easily be assimilated into amino acids and used for silk-protein synthesis in the silkworm, Bombyx mori. To determine the metabolic pathway of ammonia assimilation, silkworm larvae were injected with methionine sulfoximine (MS), a specific inhibitor of glutamine synthetase (GS). Activity of GS in the fat body 2h after treatment with 400?g MS decreased to less than 10% of

Chikara Hirayama; Kotaro Konno; Hiroshi Shinbo

1997-01-01

219

Optimized extract preparation methods and reaction conditions for improved yeast cell-free protein synthesis.  

PubMed

Cell-free protein synthesis (CFPS) has emerged as a powerful platform technology to help satisfy the growing demand for simple, affordable, and efficient protein production. In this article, we describe a novel CFPS platform derived from the popular bio-manufacturing organism Saccharomyces cerevisiae. By developing a streamlined crude extract preparation protocol and optimizing the CFPS reaction conditions we were able to achieve active firefly luciferase synthesis yields of 7.7?±?0.5?µg?mL(-1) with batch reactions lasting up to 2?h. This duration of synthesis is the longest ever reported for a yeast CFPS batch reaction. Furthermore, by removing extraneous processing steps and eliminating expensive reagents from the cell-free reaction, we have increased relative product yield (µg protein synthesized per $ reagent cost) over an alternative commonly used method up to 2000-fold from ?2?×?10(-4) to ?4?×?10(-1) ?µg?$(-1) , which now puts the yeast CPFS platform on par with other eukaryotic CFPS platforms commercially available. Our results set the stage for developing a yeast CFPS platform that provides for high-yielding and cost-effective expression of a variety of protein therapeutics and protein libraries. PMID:23832321

Hodgman, C Eric; Jewett, Michael C

2013-10-01

220

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

221

Synthesis of nanosized silicon particles by a rapid metathesis reaction  

NASA Astrophysics Data System (ADS)

A solid-state rapid metathesis reaction was performed in a bed of sodium silicofluoride (Na 2SiF 6) and sodium azide (NaN 3) powders diluted with sodium fluoride (NaF), to produce silicon nanoparticles. After a local ignition of Na 2SiF 6+4NaN 3+ kNaF mixture (here k is mole number of NaF), the reaction proceeded in a self-sustaining combustion mode developing high temperatures (950-1000 °C) on very short time scales (a few seconds). Silicon nanoparticles prepared by the combustion process was easily separated from the salt byproducts by simple washing with distilled water. The structural and morphological studies on the nanoparticles were carried out using X-ray diffractometer (XRD) and field emission scanning electron microscope (FESEM). The mean size of silicon particles calculated from the FESEM image was about 37.75 nm. FESEM analysis also shows that the final purified product contains a noticeable amount of silicon fibers, dendrites and blocks, along with nanoparticles. The mechanism of Si nanostructures formation is discussed and a simple model for interpretation of experimental results is proposed.

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

2009-11-01

222

Synthesis of temperature-responsive anion exchanger via click reaction.  

PubMed

The temperature-responsive anion exchanger was synthesized by immobilizing the poly(N-isopropylacrylamide) (PNIPAM), a kind of the temperature-responsive polymer, on the external surface of mesoporous silica via click reaction. The structure of this synthesized composite was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), elemental analysis, and nitrogen adsorption experiment. The amount of PNIPAM immobilized on the external surface of mesoporous silica, which was calculated from the weight loss measured by thermogravimetry, increased from 5.3 wt.% to 12.9 wt.% (dry) depending on the amount of PNIPAM added in the click reaction. The adsorption-desorption behavior of methyl orange (MO) ions in this synthesized anion exchanger was affected by the temperature of aqueous solution: the MO ions were adsorbed and desorbed reversibly and repeatedly with changing the pH of the solution at 25 °C, while the amount of adsorbed MO ions remained nearly constant at about 0.05 mmol/g independent of the pH of the solution at 40 °C. Also, the amount of PNIPAM immobilized on the mesoporous silica influenced the adsorption rate of MO ions, suggesting that the adsorption rate in this composite is controlled by the diffusion of MO ions through the PNIPAM layer. PMID:22446148

Murakami, Kenji; Yu, Xue; Kato, Takahiro; Inoue, Yukihiko; Sugawara, Katsuyasu

2012-06-15

223

Synthesis of tertiary propargylamines via a rationally designed multicomponent reaction of primary amines, formaldehyde, arylboronic acids and alkynes.  

PubMed

A novel approach for the synthesis of tertiary propargylamines is achieved through a Cu(OAc)2-catalyzed multicomponent reaction of primary amines, formaldehyde, arylboronic acids and alkynes, where a combination of PBM and A(3)-coupling reactions is involved in this new multicomponent reaction. PMID:24969221

Wang, Jiayi; Shen, Qiaoying; Li, Pinzhen; Peng, Yanqing; Song, Gonghua

2014-08-14

224

Experimental study of reactions of the buckministerfullerene cations C[sub 60][sup [center dot]+], C[sub 60][sup 2+], and C[sub 60][sup [center dot]3+] with ammonia and amines in the gas phase  

SciTech Connect

Results of SIFT experiments are reported for ion-molecule reactions initated by C[sub 60][sup [center dot]+], C[sub 60][sup 2+], C[sub 60][sup [center dot]3+] in ammonia, methylamine, ethylamine, dimethylamine, and trimethylamine at 294 [+-] 2 K in helium gas at a pressure of 0.35 [+-] 0.02 Torr. The main features of the observed reactions can be described in terms of adduct formation and charge transfer and are in line with the known electron recombination energies of these three fullerene cations. Higher order reactions of the adduct ions display both further adduct formation and proton transfer. Addition is the only primary product channel observed with C[sub 60][sup [center dot]+]. The apparent bimolecular rate coefficient for adduct formation increases systematically from a low value of less than 1 [times] 10[sup [minus]12] cm[sup 3] molecule[sup [minus]1] s[sup [minus]1] (with NH[sub 3]) to a value which appears to saturate at about 1 [times] 10[sup [minus]9] cm[sup 3] molecule[sup [minus]1] s[sup [minus]1], the collision rate coefficient, with decreasing ionization energy of the added amine. C-N bond formation is proposed for these addition reactions and a model is presented which accounts for the trend in the rate coefficients. Secondary adducts were observed to form rapidly with ammonia and all of the amines except trimethylamine and are attributed to the formation of a proton bond. Charge transfer was observed to compete with addition in the reactions of the C[sub 60][sup 2+] dication with the amines (NH[sub 3] reacted exclusively by addition), increasing in relative importance with decreasing ionization energy of the amine. 31 refs., 5 figs., 3 tabs.

Javahery, G.; Petrie, S.; Wincel, H.; Wang, J.; Bohme, D.K. (York Univ., North York, Ontario (Canada))

1993-06-30

225

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.

226

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

227

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

228

Synthesis of most polyene natural product motifs using just 12 building blocks and one coupling reaction  

NASA Astrophysics Data System (ADS)

The inherent modularity of polypeptides, oligonucleotides and oligosaccharides has been harnessed to achieve generalized 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 both the synthesis of a wide range of polyene frameworks that covered all of this natural-product chemical space and the 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 to making small molecules in the laboratory.

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

2014-06-01

229

Synthesis of most polyene natural product motifs using just 12 building blocks and one coupling reaction.  

PubMed

The inherent modularity of polypeptides, oligonucleotides and oligosaccharides has been harnessed to achieve generalized 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 both the synthesis of a wide range of polyene frameworks that covered all of this natural-product chemical space and the first total syntheses of the polyene natural products asnipyrone B, physarigin A and neurosporaxanthin b-D-glucopyranoside. Collectively, these results suggest the potential for a more generalized approach to making small molecules in the laboratory. PMID:24848233

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

2014-06-01

230

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

PubMed

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

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

2013-10-11

231

Synthesis of cyclopentadiene-fused chromanones via one-pot multicomponent reactions.  

PubMed

We have developed one-pot method for the synthesis of functionalized novel cyclopentadiene-fused chromanone scaffolds. A variety of 4-oxo-2,4-dihydrocyclopenta[c]chromene-1,2-dicarboxylates were obtained in moderate to good yields via condensation of 2-hydroxybenzaldehydes and ethyl acetoacetate with 1:1 acetylenecarboxylate-isocyanides in toluene. These reactions presumably proceed via reaction of the in situ generated 3-acetyl-2H-chromen-2-ones with acetylenecarboxylate-isocyanide zwitterionic intermediates through Michael addition/intramolecular cyclization and double [1,5] acyl shift rearrangement cascade. PMID:23387378

Ghandi, Mehdi; Ghomi, Ali-Tabatabaei; Kubicki, Maciej

2013-03-15

232

Copper-supported catalysts in methanol synthesis and water gas shift reaction  

Microsoft Academic Search

The comparative studies of physicochemical properties of Cu-support catalysts (support = ZnO, Al2O3, Cr2O3, ZnAl2O4, FeAlO3, or CrAl3O6) and their catalytic activity in methanol synthesis and water gas shift reaction were the main goal of this work. The promotion\\u000a effect of copper addition in both reaction was proved. The formation of spinel type structure CuCr2O4, ZnAl2O4 and binary oxide CrAl3O6,

T. P. Maniecki; P. Mierczy?ski; W. K. Jó?wiak

2010-01-01

233

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

234

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

PubMed

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

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

2012-01-01

235

Synthesis of Superheavy Nuclei in 48CA-INDUCED Reactions  

NASA Astrophysics Data System (ADS)

Thirty-four new nuclides with Z = 104-116, 118 and N = 161-177 have been synthesized in the complete-fusion reactions of 238U, 237Np, 242,244Pu, 243Am, 245,248Cm, and 249Cf targets with 48Ca beams. The masses of evaporation residues were identified through measurements of the excitation functions of the xn-evaporation channels and from cross bombardments. The decay properties of the new nuclei agree with those of previously known heavy nuclei and with predictions from different theoretical models. A discussion of self-consistent interpretations of all observed decay chains originating from the parent isotopes 282,283112, 282113, 286-289114, 287,288115, 290-293116, and 294118 is presented. Decay energies and lifetimes of the neutron-rich superheavy nuclei as well as their production cross sections indicate a considerable increase in the stability of nuclei with an increasing number of neutrons, which agrees with the predictions of theoretical models concerning the decisive dependence of the structure and radioactive properties of superheavy elements on their proximity to the nuclear shells with N = 184 and Z = 114.

Oganessian, Yu. Ts.; Utyonkov, V. K.; Lobanov, Yu. V.; Abdullin, F. Sh.; Polyakov, A. N.; Sagaidak, R. N.; Shirokovsky, I. V.; Tsyganov, Yu. S.; Voinov, A. A.; Gulbekian, G. G.; Bogomolov, S. L.; Gikal, B. N.; Mezentsev, A. N.; Iliev, S.; Subbotin, V. G.; Sukhov, A. M.; Subotic, K.; Zagrebaev, V. I.; Vostokin, G. K.; Itkis, M. G.; Moody, K. J.; Patin, J. B.; Shaughnessy, D. A.; Stoyer, M. A.; Stoyer, N. J.; Wilk, P. A.; Kenneally, J. M.; Landrum, J. H.; Wild, J. F.; Lougheed, R. W.

2008-11-01

236

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

PubMed

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; Riva, Renata

2014-01-01

237

Highly diastereoselective synthesis of 1-carbamoyl-4-aminoindoloazepinone derivatives via the Ugi reaction.  

PubMed

A one-pot procedure for the highly diastereoselective synthesis of 1-carbamoyl-4-amino-1,2,4,5-tetrahydroindolo[2,3-c]azepin-3-one derivatives is described. Using 2-formyl-L-tryptophan as a bifunctional building block, a catalyst-free Ugi-three-component reaction (Ugi-3CR) was developed to present trisubstituted indoloazepinones in good yields and excellent diastereomeric excess. PMID:24160404

Jida, Mouhamad; Betti, Cecilia; Urbanczyk-Lipkowska, Zofia; Tourwé, Dirk; Ballet, Steven

2013-11-15

238

Stereoselective synthesis of 2,5-disubstituted morpholines using a palladium-catalyzed hydroamination reaction.  

PubMed

A palladium-catalyzed hydroamination reaction is the key step in a stereoselective synthesis of 2,5-disubstituted and 2,3,5-trisubsituted morpholines from carbamate-protected aziridines. Aziridines are selectively attacked at the more substituted position by unsaturated alcohol nucleophiles using Lewis acid catalysts. Palladium-catalyzed hydroamination of the resulting aminoalkenes gives morpholines as a single diastereomer in excellent yield. PMID:23784260

McGhee, Alicia; Cochran, Brian M; Stenmark, Torrey A; Michael, Forrest E

2013-08-01

239

Direct synthesis of ?-hydroxy-?-amino acids via diastereoselective decarboxylative aldol reaction.  

PubMed

A straightforward metal-free synthesis of anti-?-hydroxy-?-amino acids is described. The organic base-mediated decarboxylative aldol reaction of cheap, readily available ?-amidohemimalonates with various aldehydes afforded under very mild conditions anti-?-hydroxy-?-amido esters in high yields and complete diastereoselectivity. Simple one-pot subsequent transformations enabled the corresponding anti-?-hydroxy-?-amino acids or in a few examples their syn diastereomers to be obtained directly using epimerization conditions. PMID:24188057

Singjunla, Yuttapong; Baudoux, Jérôme; Rouden, Jacques

2013-11-15

240

Enzymatic Synthesis of Biodiesel from Transesterification Reactions of Vegetable Oils and Short Chain Alcohols  

Microsoft Academic Search

Biodiesel synthesis by alcoholysis of three vegetable oils (soybean, sunflower and rice bran) catalyzed by three commercial\\u000a lipases (Novozym 435, Lipozyme TL-IM and Lipozyme RM-IM), and the optimization of the enzymes stability over repeated batches\\u000a is described. The effects of the molar ratio of alcohol to oil and the reaction temperature with methanol, ethanol, propanol\\u000a and butanol were also studied.

Rafael Costa Rodrigues; Giandra Volpato; Keiko Wada; Marco Antônio Záchia Ayub

2008-01-01

241

Methanol synthesis and water-gas shift reactions on Raney copper catalysts  

Microsoft Academic Search

The use of Raney copper to catalyse the synthesis of methanol and the water-gas shift reaction is reviewed. The preparation of Raney copper and Raney copper-zinc alloys together with their leaching to form active catalysts is first considered. The production of methanol is promoted by copper and the major—but not the only—role of zinc oxide involves the production of higher

M. S. Wainwright; D. L. Trimm

1995-01-01

242

Diels-alder reactions of styrylcyclohexenones: an efficient procedure for the synthesis of substituted dehydrodecaline derivatives.  

PubMed

The Diels-Alder reaction of styrylcyclohex-2-enone derivatives 1 with N-phenylmaleimide was shown to be an efficient pathway for the synthesis of substituted dehydrodecaline derivatives. At elevated temperatures, mixtures of endo/exo adducts were formed, while in the presence of TiCl4 exclusive formation of the endo stereoisomer was observed. Spectroscopic analysis and X-ray crystallography confirmed the formation of the endo adducts. PMID:24062124

Abaee, M Saeed; Mojtahedi, Mohammad M; Rezaei, M Taghi; Khavasi, Hamid Reza

2011-09-01

243

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

244

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

NASA Astrophysics Data System (ADS)

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

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

245

Brh2 promotes a template-switching reaction enabling recombinational bypass of lesions during DNA synthesis  

PubMed Central

Accumulating evidence for Rad51-catalyzed DNA strand invasion during double-strand break repair features a 3? single-stranded tail as the preferred substrate for reaction, but paradoxically the preferred substrate in model reactions in vitro is the 5? end. Here we examined the Rad51-promoted 5? end invasion reaction in the presence of Brh2, the BRCA2-family protein in Ustilago maydis. Using plasmid DNA and a homologous duplex oligonucleotide with 5? protruding single-stranded tail as substrates, we found that Brh2 can stimulate Rad51 to promote formation of a four-stranded complement-stabilized D-loop. In this structure the incoming recessed complementary strand of the oligonucleotide has switched partners and can now prime DNA synthesis using the recipient plasmid DNA as template, circumventing a lesion that blocks elongation when the 5? protruding tail serves as template for fill-in synthesis. We propose that template switching promoted by Brh2 provides a mechanism for recombination-mediated bypass of lesions blocking synthesis during DNA replication.

Mazloum, Nayef; Holloman, William K.

2009-01-01

246

Side-chain migration reactions and ring B aromatization in labdanes: scope and limitations. Synthesis of isofregenedane type tetrahydronaphthalenic diterpenes  

Microsoft Academic Search

The reaction of bicyclic diterpenes with an allylic oxygenated function or an equivalent functionality on ring B in the presence of I2\\/benzene afforded a simple and rapid synthesis of tetrahydronaphthalenic diterpenes of the isofregenedane class.

I. S Marcos; P Basabe; M Laderas; D D??ez; A Jorge; J. M Rodilla; R. F Moro; A. M Lithgow; I. G Barata; J. G Urones

2003-01-01

247

Enantioselective synthesis of (s)- and (R)-tolterodine by asymmetric hydrogenation of a coumarin derivative obtained by a Heck reaction.  

PubMed

An efficient and short enantioselective synthesis of (S)- and (R)-tolterodine was performed by asymmetric hydrogenation of a coumarin intermediate, easily obtained by a Heck reaction from inexpensive and commercially available starting materials. PMID:17625882

Ulgheri, Fausta; Marchetti, Mauro; Piccolo, Oreste

2007-08-01

248

Two-step synthesis of hexaammonium triptycene: an air-stable building block for condensation reactions to extended triptycene derivatives.  

PubMed

A simple two-step synthesis of an air-stable hexaammoniumtriptycene is introduced, which can be used for a variety of transformations by condensation reactions, e.g., to benzimidazole, benzotriazole, and quinoxaline derivatives in high yields. PMID:21688800

Mastalerz, Michael; Sieste, Stefanie; Ceni?, Mila; Oppel, Iris M

2011-08-01

249

One-pot synthesis of functionalized thioureas by reaction of benzoyl isothiocyanates, secondary amines, and alkyl propiolates  

Microsoft Academic Search

An efficient one-pot synthesis of functionalized thioureas is described via three-component reaction of benzoyl isothiocyanates, secondary amines, and alkyl propiolates in the presence of triphenylphosphine\\u000a (20?mol%).

Issa Yavari; S. Zahra Sayyed-Alangi; Maryam Sabbaghan; Rahimeh Hajinasiri; Nasir Iravani

2008-01-01

250

Elucidation of reaction network and effective control of carbon number distribution in the three phase Fischer–Tropsch synthesis  

Microsoft Academic Search

Reactions over olefins introduced during FT synthesis have been studied in a trickle bed reactor. Incorporation of 1-olefins into a growing alkyl chain could remarkably enhance the selectivity up to around 90% in heavy wax or middle distillate from syngas and could decrease the yields of lighter hydrocarbons with a higher CO conversion compared to the conventional FT synthesis. Results

Xiaohao Liu; Xiaohong Li; Yoshifumi Suehiro; Kaoru Fujimoto

2007-01-01

251

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

252

Applications of Skyrme energy-density functional to fusion reactions for synthesis of superheavy nuclei  

SciTech Connect

The Skyrme energy-density functional approach has been extended to study massive heavy-ion fusion reactions. Based on the potential barrier obtained and the parametrized barrier distribution the fusion (capture) excitation functions of a lot of heavy-ion fusion reactions are studied systematically. The average deviations of fusion cross sections at energies near and above the barriers from experimental data are less than 0.05 for 92% of 76 fusion reactions with Z{sub 1}Z{sub 2}<1200. For the massive fusion reactions, for example, the {sup 238}U-induced reactions and {sup 48}Ca+{sup 208}Pb, the capture excitation functions have been reproduced remarkably well. The influence of structure effects in the reaction partners on the capture cross sections is studied with our parametrized barrier distribution. By comparing the reactions induced by double-magic nucleus {sup 48}Ca and by {sup 32}S and {sup 35}Cl, the ''threshold-like'' behavior in the capture excitation function for {sup 48}Ca-induced reactions is explored and an optimal balance between the capture cross section and the excitation energy of the compound nucleus is studied. Finally, the fusion reactions with {sup 36}S, {sup 37}Cl, {sup 48}Ca, and {sup 50}Ti bombarding {sup 248}Cm, {sup 247,249}Bk, {sup 250,252,254}Cf, and {sup 252,254}Es, as well as the reactions leading to the same compound nucleus with Z=120 and N=182, are studied further. The calculation results for these reactions are useful for searching for the optimal fusion configuration and suitable incident energy in the synthesis of superheavy nuclei.

Wang Ning; Scheid, Werner [Institute for Theoretical Physics at Justus-Liebig-University, D-35392 Giessen (Germany); Wu Xizhen; Liu Min [China Institute of Atomic Energy, Beijing 102413 (China); Li Zhuxia [China Institute of Atomic Energy, Beijing 102413 (China); Institute of Theoretical Physics, Chinese Academic of Science, Beijing 100080 (China); Nuclear Theory Center of National Laboratory of Heavy Ion Accelerator, Lanzhou 730000 (China)

2006-10-15

253

Copper-catalyzed intramolecular tandem reaction of (2-halogenphenyl)(3-phenyloxiran-2-yl)methanones: synthesis of (Z)-aurones.  

PubMed

A convenient and efficient method for the copper-catalyzed synthesis of (Z)-aurones via intramolecular tandem reaction of (2-halogenphenyl)(3-phenyloxiran-2-yl)methanones is reported. Moreover, a plausible mechanism for the formation of (Z)-aurones is proposed. This is the first report on the synthesis of (Z)-aurones through copper-catalyzed Ullmann coupling reaction employing epoxides as substrates. PMID:24735197

Weng, Yiyi; Chen, Qixu; Su, Weike

2014-05-01

254

Synthesis of Dichlorophenylphosphine via a Friedel-Crafts Reaction in [Et4N]Br-XAlCl3 Ionic Liquids  

Microsoft Academic Search

The Friedel-Crafts reaction of phosphorus trichloride and benzene in [Et4N]Br-XAlCl3 ([Et4N]Br = tetraethylammonium bromide) ionic liquids (ILs) was investigated for the clean synthesis of dichlorophenylphosphine (DCPP). A simple product isolation procedure was achieved, and the effects of IL's composition, reaction time, and quantity on this reaction were studied. The [Et4N]Br-XAlCl3 ILs gave this reaction a green character. From the isolation

Yu-Yong Wu; Li-Sheng Wang; Zhong-Wei Wang

2005-01-01

255

Facile solvothermal synthesis of porous cubic Cu microparticles as copper catalysts for Rochow reaction.  

PubMed

Porous cubic Cu microparticles were synthesized by a facile solvothermal method using Cu(CH(3)COO)(2)·H(2)O as the Cu precursor and NaOH in a solution containing ethanol, ethylene glycol, and water. The synthesis conditions were investigated and a growth process of porous cubic Cu microparticles was proposed. The catalytic properties of the porous Cu microparticles as model copper catalysts for Rochow reaction were explored. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, temperature-programmed reduction, and nitrogen adsorption. It was found that the morphology and structure of the porous cubic Cu microparticles are highly dependent on the reaction time and temperature as well as on the amount of reactants added. Compared to the commercial Cu microparticles with irregular morphology and dense internal structure, porous cubic Cu microparticles show much higher dimethyldichlorosilane selectivity and Si conversion via Rochow reaction, which are attributed to the enhanced formation of active Cu(x)Si phase and gas transportation in the presence of the pore system within microparticles, demonstrating the significance of the pore structure of the copper catalysts in catalytic reactions of organosilane synthesis. PMID:22364243

Zhang, Zailei; Che, Hongwei; Wang, Yingli; She, Xilin; Sun, Jin; Gunawan, Poernomo; Zhong, Ziyi; Su, Fabing

2012-03-01

256

A novel one-step method for the synthesis of C-5-substituted Omicron6,5'-cyclopyrimidine nucleoside analogues in ammonia water.  

PubMed

A novel one-step method for preparing C-5-substituted Omicron(6),5'-cyclopyrimidine nucleoside analogues is reported. This method employs molecular iodine to mediate the cyclization from the 5'-Omicron-hydroxyl group of the sugar ring and C-6 at the position of the nitrogen base in ammonia water under mild conditions without any other aprotic organic solvent. PMID:18302414

Qu, Gui-Rong; Ren, Bo; Niu, Hong-Ying; Mao, Zhi-Jie; Guo, Hai-Ming

2008-03-21

257

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

258

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

259

Catalytic dehydrocoupling/dehydrogenation of N-methylamine-borane and ammonia-borane: synthesis and characterization of high molecular weight polyaminoboranes.  

PubMed

The catalytic dehydrocoupling/dehydrogenation of N-methylamine-borane, MeNH(2)·BH(3) (7), to yield the soluble, high molecular weight poly(N-methylaminoborane) (8a), [MeNH-BH(2)](n) (M(W) > 20?000), has been achieved at 20 °C using Brookhart's Ir(III) pincer complex IrH(2)POCOP (5) (POCOP = [?(3)-1,3-(OPtBu(2))(2)C(6)H(3)]) as a catalyst. The analogous reaction with ammonia-borane, NH(3)·BH(3) (4), gave an insoluble product, [NH(2)-BH(2)](n) (8d), but copolymerization with MeNH(2)·BH(3) gave soluble random copolymers, [MeNH-BH(2)](n)-r-[NH(2)-BH(2)](m) (8b and 8c). The structures of polyaminoborane 8a and copolymers 8b and 8c were further analyzed by ultrahigh resolution electrospray mass spectrometry (ESI-MS), and 8a, together with insoluble homopolymer 8d, was also characterized by (11)B and (1)H solid-state NMR, IR, and wide-angle X-ray scattering (WAXS). The data indicate that 8a-8c are essentially linear, high molecular weight materials and that the insoluble polyaminoborane 8d possesses a similar structure but is of lower molecular weight (ca. 20 repeat units), presumably due to premature precipitation during its formation. The yield and molecular weight of polymer 8a was found to be relatively robust toward the influence of different temperatures, solvents, and adduct concentrations, while higher catalyst loadings led to higher molecular weight materials. It was therefore unexpected that the polymerization of 7 using 5 was found to be a chain-growth rather than a step-growth process, where high molecular weights were already attained at about 40% conversion of 7. The results obtained are consistent with a two stage polymerization mechanism where, first, the Ir catalyst 5 dehydrogenates 7 to afford the monomer MeNH?BH(2) and, second, the same catalyst effects the subsequent polymerization of this species. A wide range of other catalysts based on Ru, Rh, and Pd were also found to be effective for the transformation of 7 to polyaminoborane 8a. For example, polyaminoborane 8a was even isolated from the initial stage of the dehydrocoupling/dehydrogenation of 7 with [Rh(?-Cl)(1,5-cod)](2) (2) as the catalyst at 20 °C, a reaction reported to give the N,N,N-trimethyl borazine, [MeN-BH](3), under different conditions (dimethoxyethane, 45 °C). The ability to use a variety of catalysts to prepare polyaminoboranes suggests that the synthetic strategy should be applicable to a broad range of amine-borane precursors and is a promising development for this new class of inorganic polymers. PMID:20806956

Staubitz, Anne; Sloan, Matthew E; Robertson, Alasdair P M; Friedrich, Anja; Schneider, Sven; Gates, Paul J; Schmedt auf der Günne, Jörn; Manners, Ian

2010-09-29

260

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

261

Multicomponent reactions of ammonium thiocyanate, acyl chlorides, alkyl bromides, and enaminones: a facile one-pot synthesis of thiophenes.  

PubMed

An efficient synthesis of thiophene derivatives is described via one-pot reaction between ammonium thiocyanate, acyl chlorides, ?-halocarbonyls, and enaminones under solvent-free conditions at 65 °C. The mild reaction conditions and high yields of the products exhibit the good synthetic advantage of these methods. PMID:21695452

Hossaini, Zinatossadat; Rostami-Charati, Faramarz; Soltani, Samira; Mirzaei, Anwar; Berijani, Kayhaneh

2011-11-01

262

A reexamination of Biginelli-like multicomponent condensation reaction: one-pot regioselective synthesis of spiro heterobicyclic rings.  

PubMed

A pseudo four-component reaction is described, leading to the efficient regioselective synthesis of sigma symmetric spiro heterobicyclic rings using aldehydes and urea in the presence of cyclic beta-diester or beta-diamides such as Meldrum's acid or barbituric acid derivatives. The reaction needs no added catalyst and proceeds solvent-free conditions at 80 degrees C. PMID:15209166

Shaabani, Ahmad; Bazgir, Ayoob; Bijanzadeh, Hamid Reza

2004-01-01

263

Synthesis of benzimidazoles by potassium tert-butoxide-promoted intermolecular cyclization reaction of 2-iodoanilines with nitriles.  

PubMed

The synthesis of benzimidazoles by intermolecular cyclization reaction of 2-iodoanilines with nitriles has been developed. These reactions proceeded without the aid of any transition metals or ligands and just using KOBu(t) as the base. A variety of substituted benzimidazole derivatives can be synthesized by the approach. PMID:24081201

Xiang, Shi-Kai; Tan, Wen; Zhang, Dong-Xue; Tian, Xian-Li; Feng, Chun; Wang, Bi-Qin; Zhao, Ke-Qing; Hu, Ping; Yang, Hua

2013-11-14

264

Thermo-electrochemical modeling of ammonia-fueled solid oxide fuel cells considering ammonia thermal decomposition in the anode  

Microsoft Academic Search

Ammonia (NH3) is a promising hydrogen carrier and a possible fuel for use in Solid Oxide Fuel Cells (SOFCs). In this study, a 2D thermo-electrochemical model is developed to investigate the heat\\/mass transfer, chemical (ammonia thermal decomposition) and electrochemical reactions in a planar SOFC running on ammonia. The model integrates three sub-models: (1) an electrochemical model relating the current density–voltage

Meng Ni

2011-01-01

265

Reaction site-driven regioselective synthesis of AChE inhibitors.  

PubMed

The enzyme-directed synthesis is an emerging fragment-based lead discovery approach in which the biological target is able to assemble its own multidentate ligands from a pool of building blocks. Here, we report for the first time the use of the human acetylcholinesterase (AChE) as an enzyme for the design and synthesis of new potent heterodimeric huprine-based inhibitors. Both the specific click chemistry site within the protein and the regioselectivity of the Huisgen cycloaddition observed suggest promising alternatives in the design of efficient mono- and dimeric ligands of AChE. Finally, a detailed computational modelling of the click reaction was conducted to further understand the origin of this TGS selectivity. PMID:24216754

Oueis, Emilia; Santoni, Gianluca; Ronco, Cyril; Syzgantseva, Olga; Tognetti, Vincent; Joubert, Laurent; Romieu, Anthony; Weik, Martin; Jean, Ludovic; Sabot, Cyrille; Nachon, Florian; Renard, Pierre-Yves

2014-01-01

266

Oxygen Isotope Exchange between Metabolites and Water during Biochemical Reactions Leading to Cellulose Synthesis.  

PubMed

Cellulose was produced heterotrophically from different carbon substrates by carrot tissue cultures and Acetobacter xylinum (a cellulose-producing bacterium) and by castor bean seeds germinated in the dark, in each case in the presence of water having known concentration of oxygen-18 ((18)O). We used the relationship between the amount of (18)O in the water and in the cellulose that was synthesized to determine the number and (18)O content of the substrate oxygens that exchanged with water during the reactions leading to cellulose synthesis. Our observations support the hypothesis that oxygen isotope ratios of plant cellulose are determined by isotopic exchange occurring during hydration of carbonyl groups of the intermediates of cellulose synthesis. PMID:16665045

Sternberg, L da S; Deniro, M J; Savidge, R A

1986-10-01

267

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

268

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

269

Synthesis of ?-lactams by transition metal promoted Staudinger reactions: alternative synthetic approaches from transition metal enhanced organocatalysis to in situ, highly reactive intermediate synthesis and catalytic tandem reactions.  

PubMed

The development of new types of ?-lactam antibiotics is a relevant field of contemporary pharmaceutical research. Although many types of antibiotics are available on the market and widely used, ?-lactam antibiotics are considered to be one of the best choice as they are highly effective while having reasonable safety profiles. The wide application however has led to the appearance of resistant bacteria suppressing their efficacy. In the last decade fewer and fewer new antibiotics have been launched into the market, however more and more multiresistant germs have appeared posing significant threats especially to patients who are suffering from chronic diseases and have weakened immune systems. The development of new, highly efficient antibiotics is now direly needed. One of the options to accelerate ?-lactam antibiotic research is the development of alternative robust, convenient, versatile and cheap synthetic procedures in which the ?-lactam molecules can be easily synthesized with the desired diastereoselectivity. The most general way to introduce diastereoselectivity in the chemical reactions is the application of chiral catalyst systems. While there are several systems for the synthesis of ?-lactams the transition metal assisted Staudinger reaction--[2 + 2] cycloaddition between a ketene and an imine--remained the most simple and most versatile methodology. The motivation behind this brief review is to draw the chemical community's attention to the relevance and applicability of transition metal promoted Staudinger reactions in ?-lactam based antibiotic development. This article summarizes the most relevant pioneer works completed on this field in order to open new ideas for the forthcoming organometallic systems based bioactive material development. PMID:23925443

Tuba, Robert

2013-09-28

270

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

PubMed

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

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

2012-01-01

271

Organic Compounds in Meteorites: They may have formed in the solar nebula, by catalytic reactions of carbon monoxide, hydrogen, and ammonia.  

PubMed

Organic compounds in meteorites seem to have formed by catalytic reactions of CO, H2, and NH3 in the solar nebula, at 360 degrees to 400 degrees K and (4 to 10) x 10-6 atm. The onset of these reactions was triggered by the formation of suitable catalysts (magnetite, hydrated silicates) at these temperatures. These reactions may be a source of prebiotic carbon compounds on the inner planets, and interstellar molecules. PMID:17772148

Anders, E; Hayatsu, R; Studier, M H

1973-11-23

272

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

PubMed Central

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

Mitachi, Katsuhiko; Mohan, Priya; Siricilla, Shajila

2014-01-01

273

Synthesis of borondipyrromethene (BODIPY)-labeled sphingosine derivatives by cross-metathesis reaction.  

PubMed

A new efficient and flexible synthesis of fluorescently labeled sphingosine derivatives from commercially available Garner aldehyde (8) is described. For this, appropriate alkenylated borondipyrromethene (BODIPY) dyes were synthesized and used for the first time in a cross-metathesis reaction, the key step of the approach. The labeled sphingosines with appropriate chain length were accepted as substrates by sphingosine kinases (SPHKs), yielding the corresponding phosphorylated products. One of these derivatives (11d) was identified as the first reported selective substrate for SPHK-1. PMID:17249735

Peters, Carsten; Billich, Andreas; Ghobrial, Michael; Högenauer, Klemens; Ullrich, Thomas; Nussbaumer, Peter

2007-03-01

274

Study on reaction rates for methanol synthesis from carbon monoxide, carbon dioxide, and hydrogen  

Microsoft Academic Search

The reaction rates for methanol synthesis from carbon monoxide, carbon dioxide, and hydrogen over a copper-zinc-based catalyst were measured under the following conditions: temperature, 210-300°C; pressure, 4-10 MPa, feed gas composition Hâ\\/CO 2.7-720, Hâ\\/COâ, 4.3-120, COâ\\/CO, 0.05-180 (in moles). It was concluded that direct methanol production from COâ takes place under the above conditions in addition to the two well-known

M. Takagawa; M. Ohsugi

1987-01-01

275

Synthesis of BaTi 4O 9 ceramics by reaction-sintering process  

Microsoft Academic Search

Synthesis of BaTi4O9 ceramics by a reaction-sintering process was investigated. The mixture of raw materials for stoichiometric BaTi4O9 were pressed and sintered into ceramics without any calcination stage involved. Pure BaTi4O9 phases were obtained at 1150–1280°C. High-sintered density, 98.2–99.5% of theoretical value (4.533g\\/cm3), can be obtained for pellets sintered at 1200–1280°C for 2–6h. Some rod-shaped grains 3–7?m in the longitudinal

Yi-Cheng Liou; Chi-Ting Wu; Ko-Hao Tseng; Tzu-Chin Chung

2005-01-01

276

Ion-molecule condensation reactions: a mechanism for organic synthesis in ionized reducing atmospheres.  

PubMed

The CH3+ ion, formed in ionized methane, undergoes consecutive eliminative condensation reactions with methane to form the carbonium ions C2H5+, i-C3H7+ and t-C4H9+. At T smaller than 500 degrees K, NCH4 greater than 10(16) cm-3 these ions react with NH3 in competitive condensation -- H+ transfer reactions, e.g. C2H5 + NH3 M leads to C2H5NH3+ leads to NH4+ + C2H4 At particle densities of NCH4 smaller than 10(16) cm-3 proton transfer is the only significant reaction channel. At NCH4 greater than 10(17) cm-3 condensation constitutes 5--20% of the overall reactions. The product of the condensation reaction further associates with CO2 to form C2H5NH3+ . CO2; the atomic composition of this cluster ion is identical with the protonated amino acid alanine. The carbonium ions i-C3H7+ and t-C4H9+ condense also with HCN to yield protonated isocyanides. HCNH% also appears to condense with HCN at T greater than 570 degrees K, and form cluster ions with HCN at lower temperatures. The rate constants of the condensation reactions vary with temperature and pressure in a complex manner. Under conditions similar to those on Titan at an altitude of 100 km (T = 100--150 degrees K, NCH4 approximately 10(18) cm-3), with a methane atmosphere containing 1% H2 and traces of NH3 and H2O, ion-molecule condensation reactions followed by H+ transfer are expected to lead to the atmospheric synthesis of C2H6, C3H8, CH3OH, C2H5OH and the terminal ions NH4+, CH3NH3+ and C2H5NH3+. At higher temperatures (250 degrees K smaller than T smaller than 400 degrees K), the synthesis of i-C4H10, i-C3H7OH and t-C4H9OH and of the ions i-C3H7NH3+ and t-C4H9NH3+ is also expected. Electron recombination of the terminal ions may yield amines, imines and nitriles. Cycles of protonation and dissociative recombination of the alkanes and alcohols produced in condensation reactions will also produce unsaturated hydrocarbons, ketones and aldehydes in the ionized atmosphere. PMID:752132

Meot-Ner, M

1978-12-01

277

Reaction chemistry/nanocrystal property relations in the hot injection synthesis, the role of the solute solubility.  

PubMed

Various literature studies show that increasing the concentration of free acid in the hot injection synthesis of colloidal nanocrystals raises the diameter of the resulting nanocrystals. We analyze this reaction chemistry/nanocrystal property relation by combining reaction simulations with an experimental study on a particular CdSe nanocrystal synthesis. We find that increasing the free acid concentration has the same effect on a real synthesis as raising the solute solubility in the simulations. Both lead to larger sizes and a deterioration of the size dispersion at constant reaction rate. Since free acids are used to coordinate the cation precursors in these syntheses, this leads to a meaningful link between a parameter in reaction simulations and the composition of an experimental reaction mixture. We thus explain the increase of the nanocrystal size with the acid concentration as resulting from an enhanced consumption of the solute by nanocrystal growth, which reduces the number of nanocrystals formed. This link between a simulation parameter and the composition of the reaction mixture provides a rational basis to further explore and understand reaction chemistry/nanocrystal property relations in the hot injection synthesis. PMID:23320536

Abe, Sofie; Capek, Richard K; De Geyter, Bram; Hens, Zeger

2013-02-26

278

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

279

Synthesis and Structure Characterization of Boron-Nitrogen Containing Phenol Formaldehyde Resin  

Microsoft Academic Search

A boron-nitrogen modified phenol formaldehyde resin (BNPFR) was prepared from phenol, formalin, ammonia water, n-butyl alcohol, boric acid, and paraformaldehyde. The reaction mechanism and structure of BNPFR during the synthesis and curing process were investigated by FTIR, NMR. The thermal stability was determined by thermogravimetric analysis. The results showed that borate, ether linkage, methylene bridges, and hexatomic ring containing coordinate

Jungang Gao; Xiaohui Su; Liya Xia

2005-01-01

280

Fischer-Tropsch synthesis in supercritical reaction media. Progress report, January 1, 1993--March 31, 1993  

SciTech Connect

The reactor configuration has been modified to handle tows both in the upflow and downflow directions. For comparison to bubble column operation, an upflow mode of operation will be used. For comparison to trickle-bed operation, a downflow mode will be employed. Thus, this modification allows the most flexibility for studying the effects of liquid and supercritical reaction media on the Fischer-Tropsch synthesis reaction and permits comparisons of our experimental results with previous work. A stainless steel reactor tube was ordered. This unit along with three other pieces of tubing (greater than 1/4in. i. d.) are to be sent to Alon Processing Co. for alonizing (passivating) the internal surface. This process had been employed by Huff and Satterfield (1983) to ensure that the stainless steel surfaces are catalytically inert at high temperatures (> 200{degree}C).

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

1993-04-01

281

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

282

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

283

Facile synthesis of ultrathin magnetic iron oxide nanoplates by Schikorr reaction.  

PubMed

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

Ma, Ming; Zhang, Yu; Guo, Zhirui; Gu, Ning

2013-01-01

284

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) [Los Alamos, NM; Garcia, Eduardo (Los Alamos, NM) [Los Alamos, NM; Abney, Kent D. (Los Alamos, NM) [Los Alamos, NM

2004-12-14

285

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.

2013-01-01

286

Clickable periodic mesoporous organosilicas: synthesis, click reactions, and adsorption of antibiotics.  

PubMed

Pharmaceutical antibiotics are not easily removed from water by conventional water-treatment technologies and have been recognized as new emerging pollutants. Herein, we report the synthesis of clickable azido periodic mesoporous organosilicas (PMOs) and their use as adsorbents for the adsorption of antibiotics. Ethane-bridged PMOs, functionalized with azido groups at different densities, were synthesized by the co-condensation of 1,2-bis(trimethoxysilyl)ethane (BTME) and 3-azidopropyltrimethoxysilane (AzPTMS), in the presence of nonionic-surfactant triblock-copolymer P123, in an acidic medium. Four different alkynes were conjugated to azide-terminated PMOs by means of an efficient click reaction. The clicked PMOs showed improved adsorption capacity (241??g?g(-1)) for antibiotics (ciprofloxacin hydrochloride) compared with azido-functionalized PMOs because of the enhanced ?-? stacking interactions. These results indicate that click reactions can introduce multifunctional groups onto PMOs, thus demonstrating the great potential of PMOs for environmental applications. PMID:24488956

Gao, Jinsuo; Zhang, Xueying; Xu, Shutao; Tan, Feng; Li, Xinyong; Zhang, Yaobin; Qu, Zhenping; Quan, Xie; Liu, Jian

2014-02-10

287

Palladium-Catalyzed Coupling of Ammonia with Aryl Chlorides, Bromides, Iodides and Sulfonates: A General Method for the Preparation of Primary Arylamines  

PubMed Central

We report that the complex generated from Pd[P(o-tol)3]2 and the alkylbisphosphine CyPF-t-Bu is a highly active and selective catalyst for the coupling of ammonia with aryl chlorides, bromides, iodides, and sulfonates. The couplings of ammonia with this catalyst conducted with a solution of ammonia in dioxane form primary arylamines from a variety of aryl electrophiles in high yields. Catalyst loadings as low as 0.1 mol % were sufficient for reactions of many aryl chlorides and bromides. In the presence of this catalyst, aryl sulfonates also coupled with ammonia for the first time in high yields. A comparison of reactions in the presence of this catalyst versus those in the presence of existing copper and palladium systems revealed a complementary, if not broader substrate scope. The utility of this method to generate amides, imides and carbamates is illustrated by a one-pot synthesis of a small library of these carbonyl compounds from aryl bromides and chlorides. Mechanistic studies show that Pd[P(o-tol)3]2 and CyPF-t-Bu generate a more active and general catalyst than that generated from CyPF-t-Bu and palladiun(II) precursors because of the low concentration of active catalyst that is generated from the combination of palladium(II), ammonia and base.

Vo, Giang D.

2010-01-01

288

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...

289

Method for forming ammonia  

DOEpatents

A method for forming ammonia is disclosed and which includes the steps of forming a plasma; providing a source of metal particles, and supplying the metal particles to the plasma to form metal nitride particles; and providing a substance, and reacting the metal nitride particles with the substance to produce ammonia, and an oxide byproduct.

Kong; Peter C. (Idaho Falls, ID) [Idaho Falls, ID; Pink, Robert J. (Pocatello, ID) [Pocatello, ID; Zuck, Larry D. (Idaho Falls, ID) [Idaho Falls, ID

2008-08-19

290

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 (J) 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

291

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

292

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.

Meshram, Jyotsna

2014-01-01

293

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

294

Synthesis and reaction temperature-tailored self-assembly of copper sulfide nanoplates  

NASA Astrophysics Data System (ADS)

Nanostructured copper sulfides have attracted much attention due to their unique electronic and optical properties and potential applications in many areas. This article presents a high-temperature precursor-injection method to synthesize covellite copper sulfide (CuS) nanoplates by using oleylamine as capping ligands. The synthesized CuS nanoplates were found to be self-assembled into face-to-face one-dimensional columnar arrays with the longest column of 0.75 ?m. Further studies showed that the reaction temperature has strong effects on the size, size distribution and the self-assembly behaviors of the CuS nanoplates. The self-assembly behaviors were found to be tuned by the reaction temperature. In the range of 140-180 °C, the face-to-face self-assembly is formed over the entire substrate, whereas only edge-to-edge arrangements were observed at the reaction temperature of 200 °C. As the temperature further increases, the product exhibits a mixture of large and small nanocrystals and there is not any presence of self-assembly. The present study highlights the size-controlled synthesis of copper sulfide nanoplates and their self-assembly behaviors dependent on reaction temperature.

Wu, Haibin; Chen, Wei

2011-12-01

295

Cross-coupling reaction of saccharide-based alkenyl boronic acids with aryl halides: the synthesis of bergenin.  

PubMed

A convenient synthetic pathway enabling D-glucal and D-galactal pinacol boronates to be prepared in good isolated yields was achieved. Both pinacol boronates were tested in a series of cross-coupling reactions under Suzuki-Miyaura cross-coupling conditions to obtain the corresponding aryl, heteroaryl, and alkenyl derivatives in high isolated yields. This methodology was applied to the formal synthesis of the glucopyranoside moiety of papulacandin?D and the first total synthesis of bergenin. PMID:24590755

Parkan, Kamil; Pohl, Radek; Kotora, Martin

2014-04-01

296

A synthesis of (+/-)-sparteine.  

PubMed

In a synthesis of racemic sparteine, Diels-Alder reaction between dimethyl bromomesaconate 14 and dicyclopentenyl 4, followed by cyclopropane formation, set up the stereochemistry at C-1 and C-5 as S and R, respectively, in a meso intermediate 8. The stereochemistry at C-2 and C-4 was then secured by a moderately diastereoselective protonation of the bis-enolate 17 derived from the diester 8 by reductive cleavage with lithium in liquid ammonia. The C=C in the racemic diester 19 was ozonolysed and the diketone converted by Beckmann rearrangement into the bis-lactam . Reduction of the bis-lactam with lithium aluminium hydride and intramolecular nucleophilic displacement gave racemic sparteine 1. Some ideas for making this synthesis amenable to a synthesis of enantiomerically enriched sparteine are presented. PMID:15827657

Buttler, Thomas; Fleming, Ian; Gonsior, Sabine; Kim, Bo-Hye; Sung, A-Young; Woo, Hee-Gweon

2005-04-21

297

A concise and diversity-oriented strategy for the synthesis of benzofurans and indoles via Ugi and Diels-Alder reactions.  

PubMed

A one-pot synthesis of diverse benzofurans and indoles from readily available starting materials was achieved via the sequential Ugi four-component reaction, intramolecular Diels-Alder reaction, and oxidative aromatization. PMID:16283808

Lu, Kui; Luo, Tuoping; Xiang, Zheng; You, Zejin; Fathi, Reza; Chen, Jiahua; Yang, Zhen

2005-01-01

298

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...

299

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

300

Organic reaction pathways in the nonaqueous synthesis of metal oxide nanoparticles.  

PubMed

Nonaqueous-solution routes to metal oxide nanoparticles are a valuable alternative to the known aqueous sol-gel processes, offering advantages such as high crystallinity at low temperatures, robust synthesis parameters and ability to control the crystal growth without the use of surfactants. In the first part of the review we give a detailed overview of the various solution routes to metal oxides in organic solvents, with a strong focus on surfactant-free processes. In most of these synthesis approaches, the organic solvent plays the role of the reactant that provides the oxygen for the metal oxide, controls the crystal growth, influences particle shape, and, in some cases, also determines the assembly behavior. We have a closer look at the following reaction systems in this order: 1) metal halides in alcohols, 2) metal alkoxides, acetates, and acetylacetonates in alcohols, 3) metal alkoxides in ketones, and 4) metal acetylacetonates in benzylamine. All these systems offer some peculiarities with respect to each other, providing many possibilities to control and tailor the particle size and shape, as well as the surface and assembly properties. In the second part we present general mechanistic principles for aqueous and nonaqueous sol-gel processes, followed by the discussion of reaction pathways relevant for nanoparticle formation in organic solvents. Depending on the system several mechanisms have been postulated: 1) alkyl halide elimination, 2) elimination of organic ethers, 3) ester elimination, 4) C--C bond formation between benzylic alcohols and alkoxides, 5) ketimine and aldol-like condensation reactions, 6) oxidation of metal nanoparticles, and 7) thermal decomposition methods. PMID:16927442

Niederberger, Markus; Garnweitner, Georg

2006-09-25

301

N-alkylation of amino acid residues by chloromethyl groups. A potential side reaction in the solid phase peptide synthesis.  

PubMed

A serious side reaction in the peptide synthesis on the Merrifield resin was observed during attempts to synthesize the TMV fragment, Asn-Pro-Thr-Thr-Ala (101--105). The side reaction is consistent with N-alkylation of the amino groups by the residual chloromethyl groups on the resin, which lowers the total yield and complicates evaluation of monitoring data during the synthesis. It is shown that several amino acids can be N-alkylated in different positions in the peptide chain and in different solvents. The extent of N-alkylation is in some cases 50%. PMID:700919

Christensen, M; Schou, O

1978-09-01

302

Development of high performance Cu\\/ZnO-based catalysts for methanol synthesis and the water-gas shift reaction  

Microsoft Academic Search

Our group’s studies on Cu\\/ZnO-based catalysts for methanol synthesis via hydrogenation of CO2 and for the water-gas shift reaction are reviewed. Effects of ZnO contained in supported Cu-based catalysts on their activities for several reactions were investigated. The addition of ZnO to Cu-based catalyst supported on Al2O3, ZrO2 or SiO2 improved its specific activity for methanol synthesis and the reverse

Masahiro Saito; Kazuhisa Murata

2004-01-01

303

Palladium-catalyzed tandem reaction of 2-hydroxyarylacetonitriles with sodium sulfinates: one-pot synthesis of 2-arylbenzofurans.  

PubMed

The first example of the palladium-catalyzed one-pot synthesis of 2-arylbenzofurans in moderate to excellent yields via a tandem reaction of 2-hydroxyarylacetonitriles with sodium sulfinates is reported. A plausible mechanism for the formation of 2-arylbenzofurans involving desulfinative addition and intramolecular annulation reactions is proposed. Moreover, the present synthetic route to benzofurans could be readily scaled up to the gram quantity without any difficulty. Thus, the method represents a convenient and practical strategy for synthesis of benzofuran derivatives. PMID:24824918

Chen, Jiuxi; Li, Jianjun; Su, Weike

2014-06-28

304

Getting a theoretical handle on fullerene ions: Quantum chemical calculations on the reactions of C60+, C602+ and C603+ with ammonia  

NASA Astrophysics Data System (ADS)

Hybrid density functional theory calculations at the B3-LYP/6-31G** level of theory are used to explore the interactions between singly, doubly, and triply charged fullerene cations and ammonia. The calculations illuminate (and generally support) several aspects of the previously-reported experimental results for these systems. Primary adduct formation is exothermic but is hindered by an energetically costly localized distortion of the fullerene cage at the site of addition, as the `chosen' carbon atom shifts from strained sp2 to sp3 coordination. The 50-75 kJ mol-1 `deformation energy' is substantially larger than the residual strength of the bond between C60+ and NH3. Although the deformation energy rises with increasing fullerene ion charge state, it does so less steeply than does the electrostatic attraction between C60n+ and NH3, so that the overall bond strength to NH3 is progressively and substantially larger for the di- and tricationic adduct ions. For all charge states, a proton-bound structure is found to be the energetically preferred secondary adduct, but for dicationic and tricationic adducts formation of a secondary adduct is significantly less exothermic than proton transfer. It appears that the failure of C60+ to add measurably to nucleophiles weaker than NH3 arises because such nucleophiles are not able to overcome the required deformation energy to effect bond formation. We find also that, in contrast to a simple electrostatically-driven model of `handle' formation (in which it was proposed that the most strongly bound doubly-derivatized fullerene dications would be those for which the `handles' were most widely separated across the fullerene framework) the lowest-energy double-handled adducts are in fact those for which the remaining resonance stabilization is greatest, with electrostatic considerations apparently taking a back seat on the question of relative stability. Similar considerations appear to apply to the double-handled tricationic adducts.

Petrie, Simon

2006-09-01

305

Oxidation of Ammonia in Water by Ferrates (VI) and (IV).  

National Technical Information Service (NTIS)

The objective of the exploratory study was to determine the feasibility of application of ferrates (VI) to oxidation of ammonia to elemental nitrogen in pure water solutions and sewage treatment plant secondary effluent. Two competing reactions, the oxida...

K. Svanks

1976-01-01

306

Enzymology of the oxidation of ammonia to nitrite by bacteria.  

PubMed

The enzymes which catalyze the oxidation of ammonia to nitrite by autotrophic bacteria are reviewed. A comparison is made with enzymes which catalyze the same reactions in methylotrophs and organotrophic heterotrophic bacteria. PMID:9049018

Hooper, A B; Vannelli, T; Bergmann, D J; Arciero, D M

1997-02-01

307

Supercritical hydrothermal synthesis and in situ organic modification of indium tin oxide nanoparticles using continuous-flow reaction system.  

PubMed

ITO nanoparticles were synthesized hydrothermally and surface modified in supercritical water using a continuous flow reaction system. The organic modification of the nanoparticles converted the surface from hydrophilic to hydrophobic, making the modified nanoparticles easily dispersible in organic solvent. The addition of a surface modifier into the reaction system impacted the crystal growth and particle size as well as dispersion. The particle size was 18 nm. Highly crystalline cubic ITO with a narrow particle size distribution was obtained. The advantages of short reaction time and the use of a continuous reaction system make this method suitable for industrial scale synthesis. PMID:22132931

Lu, Jinfeng; Minami, Kimitaka; Takami, Seiichi; Shibata, Masatoshi; Kaneko, Yasunobu; Adschiri, Tadafumi

2012-01-01

308

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

309

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

310

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

311

Biological design principles of complex feedback modules in the E. coli ammonia assimilation system.  

PubMed

To synthesize natural or artificial life, it is critically important to understand the design principles of how biochemical networks generate particular cellular functions and evolve complex systems in comparison with engineering systems. Cellular systems maintain their robustness in the face of perturbations arising from environmental and genetic variations. In analogy to control engineering architectures, the complexity of modular structures within a cell can be attributed to the necessity of achieving robustness. To reveal such biological design, the E. coli ammonia assimilation system is analyzed, which consists of complex but highly structured modules: the glutamine synthetase (GS) activity feedback control module with bifunctional enzyme cascades for catalyzing reversible reactions, and the GS synthesis feedback control module with positive and negative feedback loops. We develop a full-scale dynamic model that unifies the two modules, and we analyze its robustness and fine tuning with respect to internal and external perturbations. The GS activity control is added to the GS synthesis module to improve its transient response to ammonia depletion, compensating the tradeoffs of each module, but its robustness to internal perturbations is lost. These findings suggest some design principles necessary for the synthesis of life. PMID:22035079

Masaki, Koichi; Maeda, Kazuhiro; Kurata, Hiroyuki

2012-01-01

312

Enantioselective, Iridium-Catalyzed Monoallylation of Ammonia  

PubMed Central

Highly enantioselective, iridium-catalyzed monoallylations of ammonia are reported. These reactions occur with electron-neutral, -rich, and -poor cinnamyl carbonates, alkyl and trityloxy-substituted allylic carbonates, and dienyl carbonates in moderate to good yields and excellent enantioselectivities. This process is enabled by the use of an iridium catalyst that does not require a Lewis acid for activation and that is stable toward a large excess of ammonia. This selective formation of primary allylic amines allows for one-pot syntheses of heterodiallylamines and allylic amides that are not otherwise accessible via iridium-catalyzed allylic amination without the use of blocking groups and protective group manipulations.

Pouy, Mark J.; Stanley, Levi M.; Hartwig, John F.

2009-01-01

313

Reactor for removing ammonia  

DOEpatents

Disclosed is a device for removing trace amounts of ammonia from a stream of gas, particularly hydrogen gas, prepared by a reformation apparatus. The apparatus is used to prevent PEM "poisoning" in a fuel cell receiving the incoming hydrogen stream.

Luo, Weifang (Livermore, CA); Stewart, Kenneth D. (Valley Springs, CA)

2009-11-17

314

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

315

PEG-embedded KBr3: A recyclable catalyst for multicomponent coupling reaction for the efficient synthesis of functionalized piperidines  

PubMed Central

Summary PEG-embedded potassium tribromide ([K+PEG]Br3 ?) was found to be an efficient and recyclable catalyst for the synthesis of functionalized piperidines in high yields in a one step, three component coupling between aldehyde, amine and ?-keto ester. At the end of the reaction the [K+PEG]Br3 ? was readily regenerated from the reaction mixture by treating the residue containing [K+PEG]Br? with molecular bromine.

Verma, Sanny

2011-01-01

316

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.

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

2013-01-01

317

Efficient catalyst-free four-component synthesis of novel ?-aminoethers mediated by a Mannich type reaction.  

PubMed

Herein, it is provided an efficient and one-pot procedure for the synthesis of novel and diversely substituted ?-aminoethers in good yields through a four-component process by treatment of benzylamines with polyformaldehyde and activated alkenes in aliphatic alcohols acting both as solvent and as etherificant agents. Reactions proceeded via a Mannich-type reaction, where the formation of iminium ions and aminals was identified as the key intermediates to obtain the target products. PMID:23167924

Abonia, Rodrigo; Castillo, Juan; Insuasty, Braulio; Quiroga, Jairo; Nogueras, Manuel; Cobo, Justo

2013-01-14

318

Densification process of TiCx–Ni composites formed by self-propagating high-temperature synthesis reaction  

Microsoft Academic Search

Densification behaviour of the TiC-Ni system formed by self-propagating high-temperature synthesis (SHS) were studied to develop\\u000a the structural metal-matrix composites. The composites were prepared by two routes: (1) consolidation during the SHS reaction,\\u000a and (2) consolidation process after the SHS reaction. The final phases of the stoichiometric reactant mixture of titanium\\u000a and graphite with 50 wt% nickel produced by simultaneous

YONG CHOI; J. K. LEE; M. E MULLINS

1997-01-01

319

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

320

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

321

Mechanisms of renal ammonia production and protein turnover.  

PubMed

Renal synthesis and excretion of ammonia are critical for efficient removal of acids from the body. Besides the rate of ammonia production, the intrarenal distribution of produced ammonia is a crucial step in the renal regulation of acid-base balance. Various acid-base disorders are associated not only with changes in ammonia production but also with its distribution between the urine and the renal veins. The final effect of ammonia production on acid-base balance largely depends on the events that determine the distribution of ammonia produced between urine and blood. Several factors, among which urine pH, urine flow, total ammonia production "per se" and renal blood flow may affect the percent of ammonia excreted into urines in humans with different acid-base disturbances. Among these factors, urine pH is the most important. An additional effect of stimulated ammoniagenesis is kidney hypertrophy. In tubule epithelial cells, the associated increase in ammonia production, rather than the acidosis per se, is responsible for favoring tubular hypertrophy. This effect is related to the inhibition of protein degradation, owing to changes in lysosomal pH and cathepsin activity, without effects on cell cycle. Both changes of PI-3 kinase pathway and the suppression of chaperone-mediated autophagy are candidate mechanism for ammonia-mediated inhibition of protein degradation in tubule cells. Available data in humans indicate that the response of kidney to metabolic acidosis includes both changes in amino acid uptake and suppression of protein degradation. The latter effect is associated with the increase in ammonia excretion and partition into the urine. PMID:19083087

Garibotto, Giacomo; Verzola, Daniela; Sofia, Antonella; Saffioti, Stefano; Menesi, Fadya; Vigo, Emanuela; Tarroni, Alice; Deferrari, Giacomo; Gandolfo, Maria Teresa

2009-03-01

322

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

323

Elongase Reactions as Control Points in Long-Chain Polyunsaturated Fatty Acid Synthesis  

PubMed Central

Background ?6-Desaturase (Fads2) is widely regarded as rate-limiting in the conversion of dietary ?-linolenic acid (18:3n-3; ALA) to the long-chain omega-3 polyunsaturated fatty acid docosahexaenoic acid (22:6n-3; DHA). However, increasing dietary ALA or the direct Fads2 product, stearidonic acid (18:4n-3; SDA), increases tissue levels of eicosapentaenoic acid (20:5n-3; EPA) and docosapentaenoic acid (22:5n-3; DPA), but not DHA. These observations suggest that one or more control points must exist beyond ALA metabolism by Fads2. One possible control point is a second reaction involving Fads2 itself, since this enzyme catalyses desaturation of 24:5n-3 to 24:6n-3, as well as ALA to SDA. However, metabolism of EPA and DPA both require elongation reactions. This study examined the activities of two elongase enzymes as well as the second reaction of Fads2 in order to concentrate on the metabolism of EPA to DHA. Methodology/Principal Findings The substrate selectivities, competitive substrate interactions and dose response curves of the rat elongases, Elovl2 and Elovl5 were determined after expression of the enzymes in yeast. The competitive substrate interactions for rat Fads2 were also examined. Rat Elovl2 was active with C20 and C22 polyunsaturated fatty acids and this single enzyme catalysed the sequential elongation reactions of EPA?DPA?24:5n-3. The second reaction DPA?24:5n-3 appeared to be saturated at substrate concentrations not saturating for the first reaction EPA?DPA. ALA dose-dependently inhibited Fads2 conversion of 24:5n-3 to 24:6n-3. Conclusions The competition between ALA and 24:5n-3 for Fads2 may explain the decrease in DHA levels observed after certain intakes of dietary ALA have been exceeded. In addition, the apparent saturation of the second Elovl2 reaction, DPA?24:5n-3, provides further explanations for the accumulation of DPA when ALA, SDA or EPA is provided in the diet. This study suggests that Elovl2 will be critical in understanding if DHA synthesis can be increased by dietary means.

Gregory, Melissa K.; Gibson, Robert A.; Cook-Johnson, Rebecca J.; Cleland, Leslie G.; James, Michael J.

2011-01-01

324

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.

2013-01-01

325

A new synthesis of TATB using inexpensive starting materials and mild reaction conditions  

SciTech Connect

TATB is currently manufactured in US by nitration of the expensive TCB to give 2,4,6-trichloro-1,3,5-trinitrobenzene which is then aminated to yield TATB. Elevated temperatures (150 C) are required for both reactions. There is a need for a more economical synthesis of TATB that also addresses current environmental issues. We have recently found that 1,1,1-trimethylhydrazinium iodide (TMHI) allows the amination of nitroarenes at ambient temperature via Vicarious Nucleophilic Substitution of hydrogen. TMHI reacts with picramide in presence of strong base (NaOMe or t-BuOK) to give TATB in over 95% yield. TMHI and picramide can be obtained from either inexpensive starting materials or surplus energetic materials from demilitarization activities, such as the 30,000 metric tons of UDMH (surplus rocket propellant) from the former Soviet Union.

Mitchell, A.R.; Pagoria, P.F.; Schmidt, R.D.

1996-04-01

326

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.

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

2011-01-01

327

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.

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

2009-01-01

328

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

PubMed Central

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

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

2004-01-01

329

Synthesis of isotopically labeled P-site substrates for the ribosomal peptidyl transferase reaction  

PubMed Central

Isotopomers of the ribosomal P-site substrate, the trinucleotide peptide conjugate CCA-pcb,1 have been designed and synthesized in 26–350020steps. These include individual isotopic substitution at the ?-proton, carbonyl carbon, and carbonyl oxygen of the amino acid, the O2' and O3' of the adenosine, and a remote label in the N3 and N4 of both cytidines. These isotopomers were synthesized by coupling cytidylyl-(3'5')-cytidine phosphoramidite isotopomers, as the common synthetic intermediates, with isotopically substituted A-Phe-cap-biotin (A-pcb). The isotopic enrichment is higher than 99% for 1-13C (Phe), 2-2H (Phe), and 3,4-15N2 (cytidine), 93% for 2'/3'- 18O (adenosine), and 64% for 1-18O (Phe). A new synthesis of highly enriched [1-18O2] phenylalanine has been developed. The synthesis of [3'-18O] adenosine was improved by Lewis acid aided regioselective ring opening of the epoxide and by an economical SN2-SN2 method with high isotopic enrichment (93%). Such substrates are valuable for studies of the ribosomal peptidyl transferase reaction by complete kinetic isotope effect analysis and of other biological processes catalyzed by nucleic acid related enzymes, including polymerases, reverse transcriptases, ligases, nucleases, and ribozymes.

Zhong, Minghong

2010-01-01

330

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.

331

Fischer-Tropsch synthesis in supercritical reaction media. Progress report, October 1, 1993--December 31, 1993  

SciTech Connect

Construction of the automated high pressure reactor unit was completed. Testing of the reactor and trial runs are currently in progress. An HP 5890 GC/FID system interfaced with an BP 3365 Chemstation is now in place for analysis of F-T synthesis products. Calibration methods are currently under development. The pressure transducers were successfully calibrated using high precision Heise gauges. Figure 1 shows the linearity of the transducer response. The HPLC pump, used for pumping n-hexane was also tested and calibrated. The agitated sand bath surrounding the reactor (meant for absorbing the high heat of reaction produced in Fischer-Tropsch synthesis) was assembled in place and successfully tested. The entire system was tested to withstand the operating pressures and to be free of leaks. A cold wax trap was fabricated and added to the existing setup. This is similar in nature to the hot wax trap and will serve to collect condensables from the product stream not collected in the hot wax trap and from the GC exhaust stream. Pressure control (using the stepping-motor-driven micrometering valve) and temperature control tests are currently in progress aimed at establishing the control parameters. Thereafter, the experimental investigations consisting of the blank runs and sub-, near-, and supercritical experiments will be commenced. Progress was made in the development of both on-line and off-line analyses. Off-line analysis determines retention times (compound identification) and response factors (quantitative analysis).

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

1994-01-01

332

Reactions of selected 1-olefins and ethanol added during the Fischer-Tropsch synthesis: Topical report  

SciTech Connect

The effects of addition during synthesis of C/sub 2/, C/sub 4/, C/sub 6/, C/sub 10/ or C/sub 20/, normal 1-olefins, was studied in a continuous well-stirred liquid phase reactor. Studies were at 248/sup 0/C and 0.78 to 1.48 MPa, using a reduced fused magnetite catalyst containing potassium. Incorporation of these olefins into growing chains could be detected, but was relatively minor. Instead the olefin was hydrogenated to the corresponding paraffin or isomerized to the 2-olefin. Excluding ethylene, which is unusually reactive, the reactivity of the olefins increased with molecular weight. Disappearance of all added species was much less at low synthesis conversions than at high, attributed to competitive adsorption with CO. The reactions of added ethanol were also studied. Ethanol or ethylene decreased the hydrogenation capabilities of the catalyst as reflected in decreased formation of CH/sub 4/ and increased olefin/paraffin ratio of the products. Neither addition affected the chain growth probability, ..cap alpha... 21 refs., 11 figs., 5 tabs.

Hanlon, R.T.; Satterfield, C.N.

1987-10-30

333

Addition of water, methanol, and ammonia to Al{sub 3}O{sub 3}{sup -} clusters: Reaction products, transition states, and electron detachment energies  

SciTech Connect

Products of reactions between the book and kite isomers of Al{sub 3}O{sub 3}{sup -} and three important molecules are studied with electronic structure calculations. Dissociative adsorption of H{sub 2}O or CH{sub 3}OH is highly exothermic and proton-transfer barriers between anion-molecule complexes and the products of these reactions are low. For NH{sub 3}, the reaction energies are less exothermic and the corresponding barriers are higher. Depending on experimental conditions, Al{sub 3}O{sub 3}{sup -} (NH{sub 3}) coordination complexes or products of dissociative adsorption may be prepared. Vertical electron detachment energies of stable anions are predicted with ab initio electron propagator calculations and are in close agreement with experiments on Al{sub 3}O{sub 3}{sup -} and its products with H{sub 2}O and CH{sub 3}OH. Changes in the localization properties of two Al-centered Dyson orbitals account for the differences between the photoelectron spectra of Al{sub 3}O{sub 3}{sup -} and those of the product anions.

Guevara-Garcia, Alfredo; Martinez, Ana; Ortiz, J.V. [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico (UNAM), Circuito Exterior s/n, Ciudad Universitaria, P.O. Box 70-360, Coyoacan 04510, Distrito Federal Mexico (Mexico); Department of Chemistry, Kansas State University, Manhattan, Kansas 66506-3701 (United States)

2005-06-01

334

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

PubMed

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

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

2013-04-25

335

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....

336

A stereoselective synthesis of (+)-physoperuvine using a tandem aza-Claisen rearrangement and ring closing metathesis reaction.  

PubMed

A stereoselective synthesis of (+)-physoperuvine, a tropane alkaloid from Physalis peruviana Linne has been developed using a one-pot tandem aza-Claisen rearrangement and ring closing metathesis reaction to form the key amino-substituted cycloheptene ring. PMID:19532981

Zaed, Ahmed M; Swift, Michael D; Sutherland, Andrew

2009-07-01

337

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

338

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

339

Novel application of Leuckart-Wallach reaction for synthesis of tetrahydro-1,4-benzodiazepin-5-ones library.  

PubMed

A novel and efficient strategy has been developed to synthesize privileged tetrahydro-1,4-benzodiazepines with excellent yields and purities; this synthetic pathway was established by the revitalization of the Leuckart-Wallach (LW) reaction via solid-phase synthesis. PMID:17851604

Lee, Sung-Chan; Park, Seung Bum

2007-09-28

340

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

341

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

342

Synthesis of spiro[dihydropyridine-oxindoles] via three-component reaction of arylamine, isatin and cyclopentane-1,3-dione  

PubMed Central

Summary A fast and convenient protocol for the synthesis of novel spiro[dihydropyridine-oxindole] derivatives in satisfactory yields was developed by the three-component reactions of arylamine, isatin and cyclopentane-1,3-dione in acetic acid at room temperature. On the other hand the condensation of isatin with two equivalents of cyclopentane-1,3-dione gave 3,3-bis(2-hydroxy-5-oxo-cyclopent-1-enyl)oxindole in high yields. The reaction mechanism and substrate scope of this novel reaction is briefly discussed.

Sun, Yan; Sun, Jing

2013-01-01

343

Use of carbonyl group addition--elimination reactions for synthesis of nucleic acid conjugates.  

PubMed

This review outlines the synthesis of covalent conjugates of oligonucleotides and their analogues that are obtained by reactions of carbonyl compounds with various nucleophiles such as primary amines, N-alkoxyamines, hydrazines, and hydrazides. The products linked by imino, oxime, hydrazone, or thiazolidine groups are shown to be useful intermediates for a wide range of chemical biology applications. Methods for their preparation, isolation, purification, and analysis are highlighted, and the comparative stabilities of the respective linkages are evaluated. The relative merits of incorporation of a carbonyl group, particularly an aldehyde group, into either the oligonucleotide or the ligand parts are considered. Examples of harnessing of aldehyde-nucleophile coupling for the labeling of nucleic acids are given, as well as their conjugation to various biomolecules (e.g. peptides and small molecule ligands), site-specific cross-linking of oligonucleotides to nucleic acid-binding proteins, assembly of multibranched supramolecular structures, and immobilization on functionalized surfaces. Future perspectives of bioconjugation and complex molecular engineering via carbonyl group addition-elimination reactions in nucleic acids chemistry are discussed. PMID:15898711

Zatsepin, Timofei S; Stetsenko, Dmitry A; Gait, Michael J; Oretskaya, Tatiana S

2005-01-01

344

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.

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

2008-01-01

345

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

346

Ammonia in comet P/Halley  

NASA Technical Reports Server (NTRS)

In comet P/Halley the abundances of ammonia relative to water reported in the literature differ by about one order of magnitude from roughly 0.1% up to 2%. Different observational techniques seem to have inherent systematic errors. Using the ion mass channels m/q = 19 amu/e, 18 amu/e and 17 amu/e of the Neutral Mass Spectrometer experiment aboard the spacecraft Giotto, we derive a production rate of ammonia of (1.5(sub -0.7)(sup +0.5))% relative to water. Inside the contact surface we can explain our data by a nuclear source only. The uncertainty in our abundance of ammonia is primarily a result of uncertainties in some key reaction coefficients. We discuss in detail these reactions and the range of error indicated results from extreme assumptions in the rate coefficients. From our data, even in the worst case, we can exclude the ammonia abundance to be only of the order of a few per mill.

Meier, R.; Eberhardt, P.; Krankowsky, D.; Hodges, R. R.

1994-01-01

347

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.

Lathrop, Stephen P.

2013-01-01

348

Synthesis of 2-monoacylglycerols and structured triacylglycerols rich in polyunsaturated fatty acids by enzyme catalyzed reactions.  

PubMed

This paper studies the synthesis of structured triacylglycerols (STAGs) by a four-step process: (i) obtaining 2-monoacylglycerols (2-MAGs) by alcoholysis of cod liver oil with several alcohols, catalyzed by lipases Novozym 435, from Candida antartica and DF, from Rhizopus oryzae, (ii) purification of 2-MAGs, (iii) formation of STAGs by esterification of 2-MAGs with caprylic acid catalyzed by lipase DF, from R. oryzae, and (iv) purification of these STAGs. For the alcoholysis of cod liver oil, absolute ethanol, ethanol 96% (v/v) and 1-butanol were compared; the conditions with ethanol 96% were then optimized and 2-MAG yields of around 54-57% were attained using Novozym 435. In these 2-MAGs, DHA accounted for 24-31% of total fatty acids. In the operational conditions this lipase maintained a stable level of activity over at least 11 uses. These results were compared with those obtained with lipase DF, which deactivated after only three uses. The alcoholysis of cod liver oil and ethanol 96% catalyzed by Novozym 435 was scaled up by multiplying the reactant amounts 100-fold and maintaining the intensity of treatment constant (IOT=3g lipase h/g oil). In these conditions, the 2-MAG yield attained was about 67%; these 2-MAGs contained 36.6% DHA. The synthesized 2-MAGs were separated and purified from the alcoholysis reaction products by solvent extraction using solvents of low toxicity (ethanol and hexane); 2-MAG recovery yield and purity of the target product were approximately 96.4% and 83.9%, respectively. These 2-MAGs were transformed to STAGs using the optimal conditions obtained in a previous work. After synthesis and purification, 93% pure STAGs were obtained, containing 38% DHA at sn-2 position and 60% caprylic acid (CA) at sn-1,3 positions (of total fatty acids at these positions), i.e. the major TAG is the STAG with the structure CA-DHA-CA. PMID:22759534

Rodríguez, Alicia; Esteban, Luis; Martín, Lorena; Jiménez, María José; Hita, Estrella; Castillo, Beatriz; González, Pedro A; Robles, Alfonso

2012-08-10

349

Organic reaction systems: using microcapsules and microreactors to perform chemical synthesis.  

PubMed

The appetite for complex organic molecules continues to increase worldwide, especially in rapidly developing countries such as China, India, and Brazil. At the same time, the cost of raw materials and solvent waste disposal is also growing, making sustainability an increasingly important factor in the production of synthetic life-saving/improving compounds. With these forces in mind, our group is driven by the principle that how we synthesize a molecule is as important as which molecule we choose to synthesize. We aim to define alternative strategies that will enable more efficient synthesis of complex molecules. Drawing our inspiration from nature, we attempt to mimic (1) the multicatalytic metabolic systems within cells using collections of nonenzyme catalysts in batch reactors and (2) the serial synthetic machinery of fatty acid/polyketide biosynthesis using microreactor systems. Whether we combine catalysts in batch to prepare an active pharmaceutical ingredient (API) or use microreactors to synthesize small or polymeric molecules, we strive to understand the mechanism of each reaction while also developing new methods and techniques. This Account begins by examining our early efforts in the development of novel catalytic materials and characterization of catalytic systems and how these observations helped forge our current models for developing efficient synthetic routes. The Account progresses through a focused examination of design principles needed to develop multicatalyst systems using systems recently published by our group as examples. Our systems have been successfully applied to produce APIs as well as new synthetic methods. The multicatalyst section is then juxtaposed with our work in continuous flow multistep synthesis. Here, we discuss the design principles needed to create multistep continuous processes using examples from our recent efforts. Overall, this Account illustrates how multistep organic routes can be conceived and achieved using strategies and techniques that mimic biological systems. PMID:23072456

Longstreet, Ashley R; McQuade, D Tyler

2013-02-19

350

Effect of nitrogen doping on oxygen vacancies of titanium dioxide supported vanadium pentoxide for ammonia-SCR reaction at low temperature.  

PubMed

A V2O5/N-doped TiO2 catalyst has been developed by partly substituting the lattice oxygen of TiO2 support with nitrogen, which showed a remarkable increase in activity for the reduction of NO with NH3 at low temperature. The catalyst was characterized by Brunauer-Emmett-Teller (BET), transmission electron microscope (TEM), photoluminescence (PL), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR). The results demonstrated that N doping cannot noticeably change the microscopic features but dramatically enhanced the formation of surface oxygen vacancies, which can play a vital role in the formation of superoxide ions to improve the SCR activity. The catalyst with [N]/[Ti]=1.0×10(-2) showed the highest NO removal efficiency in the SCR reaction at low temperature. Furthermore, the V1TiN1.0 catalyst showed better resistance to SO2 and H2O during the SCR of NO. PMID:23664293

Li, Hongyu; Zhang, Shule; Zhong, Qin

2013-07-15

351

Gas Generator Research and Development, BI-GAS Process. A Study of Ammonia Consuming Bacteria.  

National Technical Information Service (NTIS)

One of the problems encountered in operating the BI-GAS Pilot Plant has been the excessive production of ammonia in the synthesis gas from the gasifier. The contract with the Indiana Borough Sewage Plant limits the concentration of ammonia nitrogen in the...

1979-01-01

352

The Ammonia-Soda Process.  

ERIC Educational Resources Information Center

This article is a condensed version of a commentary written to accompany a set of slides which describes the ammonia-soda process used by the ammonia-soda plant at Northwich of the United Kingdom. (HM)

Tingle, M.

1979-01-01

353

Liberation of ammonia by cyanobacteria  

SciTech Connect

Photoheterotrophic nitrogen-fixing cyanobacteria release ammonia when treated with methionine sulfoximine (MSX) to inhibit nitrogen incorporation into protein. This released ammonia can be derived from recently fixed nitrogen (nitrogen atmosphere) or endogenous reserves (argon atmosphere). Anaerobic ammonia release requires light and is stimulated by the photosystem II herbicides DCMU and Atrazine, regardless of the source of ammonia. As much as one quarter of the total cellular nitrogen can be released as ammonia by cyanbacteria treated with MSX and DCMU under argon in light. Chromatography of cell extracts indicates that virtually all cellular proteins are degraded. DCMU and Atrazine, at very low concentration, inhibit sustained uptake of the ammonia analog /sup 14/C methylamine. These data indicate that the herbicides interrupt ammonia uptake and retention by the cells, and support a role for photosystem II in ammonia metabolism.

Newton, J.W.

1986-04-01

354

Formation of Adenine by Electron Irradiation of Methane, Ammonia, and Water  

Microsoft Academic Search

The possibility of the synthesis of heterocyclic bases from mixtures of ; primitive gases was investigated. Results are reported on the synthesis of ; adenine by electron irradiation of a mixture of methane, ammonia, and water. ; Carbon-14 was used as a tracer. An inverse relation between the amount of ; adenine synthesis and amount of hydrogen gas present was

Cyril Ponnamperuma; Richard M. Lemmon; Ruth Mariner; Melvin Calvin

1963-01-01

355

Reaction Routes for the Synthesis of CuInSe2 Using Bilayer Compound Precursors  

SciTech Connect

The reaction pathways and phase evolution during synthesis of CuInSe{sub 2} (CIS) by a novel bilayer approach were investigated using in situ high-temperature X-ray diffraction. Two bilayer precursor structures, glass/Mo/{gamma}-In{sub 2}Se{sub 3}/{beta}-CuSe + {beta}-Cu{sub 2}Se/Se and glass/Mo/{gamma}-In{sub 2}Se{sub 3}/{beta}-Cu{sub 2}Se/Se, were examined in this study. Temperature ramp experiments revealed that the phase transformation sequence for each bilayer precursor qualitatively follows that predicted by the phase diagram and that the onset temperatures for decomposition of the sub-binary compounds depend on the Se partial pressure. Measurement of the isothermal rate of formation of CuInSe{sub 2} at six temperatures in the range 260 to 310 C for the {gamma}-In{sub 2}Se{sub 3}/{beta}-CuSe + {beta}-Cu{sub 2}Se/Se bilayer suggests relatively slow nucleation followed by diffusion-limited reaction with estimated activation energy of 162({+-}7) and 225 ({+-}16) kJ/mol from Avrami and parabolic models, respectively. Interestingly, the measured activation energy for the same precursor in a 4 mol % H{sub 2}/He ambient (108 ({+-}8) kJ/mol) was lower than that observed in pure N{sub 2} (158 ({+-}16) kJ/mol). The results of isothermal measurements in the temperature range 250 to 300 C for the {gamma}-In{sub 2}Se{sub 3}/{beta}-Cu{sub 2}Se/Se precursor film in an inert ambient are consistent with one-dimensional diffusion-limited growth with estimated activation energy from the Avrami and parabolic models of 194 ({+-}10) and 203 ({+-}12) kJ/mol, respectively.

Krishnan, Rangarajan [University of Florida; Wood, David [University of Florida; Chaudhari, Vaibhav U. [University of Florida; Payzant, E Andrew [ORNL; Noufi, Rommel [National Renewable Energy Laboratory (NREL); Rozeveld, Steve [Dow Chemical Company, The; Kim, Woo Kyoung [Yeungnam University, Korea; Anderson, Timothy J [University of Florida

2012-01-01

356

Effects of S-adenosylmethionine decarboxylase, polyamines, amino acids, and weak bases (amines and ammonia) on development and ribosomal RNA synthesis in Xenopus embryos.  

PubMed

We have been studying control mechanisms of gene expression in early embryogenesis in a South African clawed toad Xenopus laevis, especially during the period of midblastula transition (MBT), or the transition from the phase of active cell division (cleavage stage) to the phase of extensive morphogenesis (post-blastular stages). We first found that ribosomal RNA synthesis is initiated shortly after MBT in Xenopus embryos and those weak bases, such as amines and ammonium ion, selectively inhibit the initiation and subsequent activation of rRNA synthesis. We then found that rapidly labeled heterogeneous mRNA-like RNA is synthesized in embryos at pre-MBT stage. We then performed cloning and expression studies of several genes, such as those for activin receptors, follistatin and aldolases, and then reached the studies of S-adenosylmethionine decarboxylase (SAMDC), a key enzyme in polyamine metabolism. Here, we cloned a Xenopus SAMDC cDNA and performed experiments to overexpress the in vitro-synthesized SAMDC mRNA in Xenopus early embryos, and found that the maternally preset program of apoptosis occurs in cleavage stage embryos, which is executed when embryos reach the stage of MBT. In the present article, we first summarize results on SAMDC and the maternal program of apoptosis, and then describe our studies on small-molecular-weight substances like polyamines, amino acids, and amines in Xenopus embryos. Finally, we summarize our studies on weak bases, especially on ammonium ion, as the specific inhibitor of ribosomal RNA synthesis in Xenopus embryonic cells. PMID:20013010

Shiokawa, Koichiro; Aso, Mai; Kondo, Takeshi; Takai, Jun-Ichi; Yoshida, Junki; Mishina, Takamichi; Fuchimukai, Kota; Ogasawara, Tsukasa; Kariya, Taro; Tashiro, Kosuke; Igarashi, Kazuei

2010-02-01

357

Synthesis and in vitro characterization of a preactivated thiomer via polymerization reaction.  

PubMed

The objective of this study was to synthesize 6-(2-acryloylamino-ethyldisulfanyl)-nicotinic acid (ACENA) for subsequent copolymerization with acrylic acid (AA) as a new method for synthesis of preactivated thiomers. Copolymerization reactions of ACENA and AA with different molar ratios were performed and the molecular weight (M(w)) values of the resulting copolymers were calculated and reported from 3046 to 3271 Da. The disulfide bond content values in the polymer chain were determined from 400 to 544 ?mol disulfide bond per gram polymer. The transport enhancement ratio for 0.5% (m/v) solution of poly(acrylic acid) (PAA) was 1.1 using sodium fluorescein (Na-Flu) as model drug, in Ussing-type chambers, whereas it was over 1.9 for 0.5% (m/v) solution of ACENA and AA copolymers. Resazurin cell-viability test showed no significant toxicity for the polymers. Copolymerization of AA and disulfide-bond-containing monomers can open new horizons for the preparation of preactivated thiomers taking the better controllability and the huge variety of available monomers and combinations thereof into account. PMID:22913323

Solhi, Laleh; Schönbichler, Stefan A; Dünnhaupt, Sarah; Barthelmes, Jan; Friedl, Heike; Huck, Christian W; Bernkop-Schnürch, Andreas

2012-10-01

358

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

359

Methanol synthesis on ZnO(0001). II. Structure, energetics, and vibrational signature of reaction intermediates  

NASA Astrophysics Data System (ADS)

A rigorous characterization of a wealth of molecular species adsorbed at oxygen defects on ZnO(0001) is given. These defects represent the putative active sites in methanol synthesis from CO and H2. The oxidation state of the ZnO catalyst and thus the preferred charge state and the reactivity of the oxygen vacancies depend on the gas phase temperature and pressure conditions. Considering charge states of oxygen vacancies relevant at the reducing conditions of the industrial process, i.e., F++/H2, F0, F0/H2, and F--, as well as the F++ center which is abundant at UHV conditions and therefore important to allow for comparison with surface science experiments, we have investigated the structure, energetics, and vibrational frequencies of an exhaustive catalog of reaction intermediates using electronic structure calculations. After having identified the characteristic adsorption modes of CO, formate, formic acid, hydroxymethylene, formyl, formaldehyde, dioxomethylene, hydroxymethyl, hydroxymethoxide, methoxide, as well as methanol itself, the thermodynamic stability of all species with respect to the charge state of the oxygen vacancy and their electronic stabilization is discussed in detail and summarized in an energy level diagram.

Kiss, Janos; Frenzel, Johannes; Meyer, Bernd; Marx, Dominik

2013-07-01

360

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

PubMed

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

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

2013-01-01

361

Efficient Synthesis of Secondary Alkyl Fluorides via Suzuki Cross-Coupling Reaction of 1-Halo-1-fluoroalkanes.  

PubMed

Organofluorine compounds have found extensive applications in various areas of science. Consequently, the development of new efficient and selective methods for their synthesis is an important goal in organic chemistry. Here, we present the first Suzuki cross-coupling reaction which utilizes dihalo compounds for the preparation of secondary alkyl fluorides. Namely, an unprecedented use of simple 1-halo-1-fluoroalkanes as electrophiles in Csp(3)-Csp(3) and Csp(3)-Csp(2) cross-couplings allows for the formal site-selective incorporation of F-group in the alkyl chain with no adjacent activating functional groups. Highly effective approach to the electrophilic substrates, 1-halo-1-fluoroalkanes, via iododecarboxylation of the corresponding ?-fluorocarboxylic acids is also presented. The conceptually new route to organofluorides was used for the facile preparation of biomedically valuable compounds. In addition, we demonstrated that an asymmetric version of the developed reaction for the stereoconvergent synthesis of chiral secondary alkyl fluorides is feasible. PMID:24958322

Jiang, Xiaojian; Sakthivel, Sekarpandi; Kulbitski, Kseniya; Nisnevich, Gennady; Gandelman, Mark

2014-07-01

362

Carbohydrate-steroid conjugation by Ugi reaction: one-pot synthesis of triple sugar/pseudo-peptide/spirostane hybrids.  

PubMed

The one-pot synthesis of novel molecular chimeras incorporating sugar, pseudo-peptide, and steroidal moieties is described. For this, a new carbohydrate-steroid conjugation approach based on the Ugi four-component reaction was implemented for the ligation of glucose and chacotriose to spirostanic steroids. The approach proved wide substrate scope, as both mono and oligosaccharides functionalized with amino, carboxy, and isocyano groups were conjugated to steroidal substrates in an efficient, multicomponent manner. Two alternative strategies based on the hydrazoic acid variant of the Ugi reaction were employed for the synthesis of tetrazole-based chacotriose-diosgenin conjugates resembling naturally occurring spirostan saponins. This is the first time that triple sugar/pseudo-peptide/steroid hybrids are produced, thus opening up an avenue of opportunities for applications in drug discovery and biological chemistry. PMID:22925772

Rivera, Daniel G; Pérez-Labrada, Karell; Lambert, Liudmila; Dörner, Simon; Westermann, Bernhard; Wessjohann, Ludger A

2012-10-01

363

Composition-Controlled Synthesis of Bimetallic PdPt Nanoparticles and Their Electrocatalysis for Methanol Oxidation Reaction  

SciTech Connect

PdPt alloy nanoparticles (NPs) are promising catalysts for various chemical reactions because of the presence of powerful catalytic components of Pt and Pd on the surface of one nanostructure. In this paper, we report a facile synthesis of polyhedral PdPt alloy NPs via coreduction of Pd(acac){sub 2} (acac = acetylacetonate) and Pt(acac)2 with morpholine borane in oleylamine at 90 and 180 C. In the synthesis, the molar ratio of the two metal precursors added in the reaction mixture was carried over to the final PdPt NP product, and compositions of the PdPt NPs were readily tuned from Pd{sub 88}Pt{sub 12} to Pd{sub 34}Pt{sub 66}. These PdPt NPs show the composition-dependent catalytic activity for methanol oxidation, with NPs in 40-60 atomic % Pt exhibiting the superior activity and durability.

Liu, Yi [Brown University; Chi, Miaofang [ORNL; Mazumder, Vismadeb [Brown University; More, Karren Leslie [ORNL; Sun, Shouheng [Brown University

2011-01-01

364

Regioselective synthesis of 1,2-dihydroquinolines by a solvent-free MgBr2-catalyzed multicomponent reaction.  

PubMed

A highly efficient and regioselective synthesis of 1,2-dihydroquinolines via a multicomponent reaction between an aniline and two ketones is described. This reaction was catalyzed by magnesium bromide and carried out under solvent-free conditions. When the reaction was performed by using 3-substituted anilines and nonsymmetrically substituted ketones, principally a single product was found among the four expected regioisomers. A variety of anilines and ketones, including cyclic ketones, were evaluated providing a series of 1,2-dihydroquinolines with diverse substitution patterns. A study of the mechanism is discussed. There is evidence of the in situ formation of the imine as a result of the reaction between the aniline and one of the ketones, before annulation to the heterocyclic ring. PMID:24044723

Gutiérrez, Rsuini U; Correa, Hans C; Bautista, Rafael; Vargas, José Luis; Jerezano, Alberto V; Delgado, Francisco; Tamariz, Joaquín

2013-10-01

365

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

PubMed Central

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

Chen, Ming; Roush, William R.

2012-01-01

366

A facile and efficient ultrasound-assisted synthesis of novel dispiroheterocycles through 1,3-dipolar cycloaddition reactions.  

PubMed

A facile and efficient one-pot three-component procedure for synthesis of novel dispirooxindolecyclo[pyrrolo[1,2-c]thiazole-6,5'-thiazolidine] derivatives without any catalysts under ultrasonic condition has been developed. Combining with the advantages of sonochemistry, such as mild reaction conditions, good yield and short reaction times, we have made a progress on construction of novel disiproheterocyclic compounds via the 1,3-dipolar cycloaddition of azomethine ylides. Several experiments were especially carried out for investigating the acceleration mechanism of ultrasound on the cycloaddition. PMID:21855389

Hu, Yu; Zou, Yi; Wu, Hui; Shi, Daqing

2012-03-01

367

The diene-transmissive hetero-Diels-Alder reaction of 2-vinyl ?,?-unsaturated aldimines: stereoselective synthesis of hexahydroquinazolin-2-ones.  

PubMed

Stereoselective synthesis of hexahydroquinazolin-2(1H)-ones has been achieved through the application of the diene-transmissive hetero-Diels-Alder methodology to 2-vinyl-1-aza-1,3-butadienes. The cross-conjugated 1-azatriene underwent an initial hetero-Diels-Alder reaction on the 1-aza-1,3-butadiene system with tosyl isocyanate to afford the [4 + 2] mono-cycloadduct pyrimidinone. The second Diels-Alder reaction on the electron-rich 1-amino-1,3-diene unit of the mono-cycloadduct with dienophiles provided hexahydroquinazolin-2(1H)-ones with high stereoselectivity. PMID:24710814

Kobayashi, Satoru; Kudo, Kenji; Ito, Ai; Hirama, Satoru; Otani, Takashi; Saito, Takao

2014-05-28

368

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

PubMed Central

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

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

2012-01-01

369

Synthesis of a library of "lead-like" ?-lactams by a one pot, four-component reaction.  

PubMed

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; Shaw, Jared T

2013-07-01

370

One-pot synthesis of S-alkyl dithiocarbamates via the reaction of N-tosylhydrazones, carbon disulfide and amines.  

PubMed

A new, convenient and efficient transition metal-free synthesis of S-alkyl dithiocarbamates through one-pot reaction of N-tosylhydrazones, carbon disulfide and amines is reported. Tosylhydrazones derived from various aromatic and aliphatic ketones or aldehydes were tested and gave dithiocarbamates in good to excellent yields. The tosylhydrazones can be generated in situ without isolation, which provides a simpler one-pot method to synthesize dithiocarbamates via the reaction of carbonyl compounds, carbon disulfide and amines in the presence of 4-methylbenzenesulfonohydrazide. PMID:23863979

Sha, Qiang; Wei, Yun-Yang

2013-09-14

371

Chemical synthesis of cross-linked polyaniline by a novel solvothermal metathesis reaction of p-dichlorobenzene with sodium amide  

Microsoft Academic Search

We reported the chemical synthesis of cross-linked polyaniline (PANI) by a novel solvothermal metathesis reaction of p-dichlorobenzene (C6H4Cl2) with sodium amide (NaNH2) in benzene at 220°C. In this method, the aniline monomer and complicated treatment were needless and the yield of final products was over 50%. The as-synthesized brown samples were NMP-soluble but water-insoluble; and they were characterized by XRD,

Qixun Guo; Chengqi Yi; Lei Zhu; Qing Yang; Yi Xie

2005-01-01

372

Synthesis of a new class of carborane-containing star-shaped molecules via silicon tetrachloride promoted cyclotrimerization reactions.  

PubMed

Symmetrical star-shaped molecules with carborane clusters on the periphery have been synthesized in good yields via silicon tetrachloride mediated cyclotrimerization reactions of 9-benzyl derivatives of carboranes with acetyl group substitution on the benzene ring. Facile functionalization of these symmetrical core structures with 1-iodoheptane and trivinylchlorosilane produce compounds which could be used as liquid crystalline substances and precursors for synthesis of higher order carbosilane dendrons. PMID:18465864

Dash, Barada Prasanna; Satapathy, Rashmirekha; Maguire, John A; Hosmane, Narayan S

2008-06-01

373

A model for a countercurrent gas—solid—solid trickle flow reactor for equilibrium reactions. The methanol synthesis  

Microsoft Academic Search

The theoretical background for a novel, countercurrent gas—solid—solid trickle flow reactor for equilibrium gas reactions is presented. A one-dimensional, steady-state reactor model is developed. The influence of the various process parameters on the reactor performance is discussed. The physical and chemical data used apply to the case of low-pressure methanol synthesis from CO and H2 with an amorphous silica—alumina as

K. R. Westerterp; M. Kuczynski

1987-01-01

374

Synthesis of [60]fullerene-fused tetrahydroazepinones and azepinonimines via Cu(OAc)2-promoted N-heteroannulation reaction.  

PubMed

A convenient and efficient Cu(OAc)2-mediated N-heteroannulation reaction of [60]fullerene with N-sulfonylated o-amino-aromatic methyl ketones or O-alkyl oximes has been reported for the synthesis of novel and scarce [60]fullerene-fused tetrahydroazepinones and -azepinonimines in a highly selective manner. Moreover, a possible mechanism involving two pathways is proposed on the basis of the experimental observations. PMID:24476125

Liu, Tong-Xin; Zhang, Zhenbei; Liu, Qingfeng; Zhang, Pengling; Jia, Penghao; Zhang, Zhiguo; Zhang, Guisheng

2014-02-01

375

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

Microsoft Academic Search

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

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

2005-01-01

376

Asymmetric synthesis of trisubstituted tetrahydrothiophenes bearing a quaternary stereocenter via double Michael reaction involving dynamic kinetic resolution.  

PubMed

The stereoselective synthesis of highly functionalized tetrahydrothiophenes bearing three contiguous stereocenters, one of them quaternary, can be achieved by reacting trans-?-cyano-?,?-unsaturated ketones and trans-tert-butyl 4-mercapto-2-butenoate in the presence of a readily available amine thiourea. The products are obtained in high yield, good diastereoselectivity, and excellent enantioselectivity. The overall formation of tetrahydrothiophenes occurs via a cascade double Michael reaction involving a highly efficient process of dynamic kinetic resolution. PMID:23786495

Meninno, Sara; Croce, Gianluca; Lattanzi, Alessandra

2013-07-01

377

Reaction between triphenylphosphine and aromatic amines in the presence of diethyl azodicarboxylate: an efficient synthesis of aryliminophosphoranes under neutral and mild conditions  

Microsoft Academic Search

An efficient synthesis of aryliminophosphoranes is described. A mixture of an aromatic amine, diethyl azodicarboxylate and triphenylphosphine undergo a Mitsonobu type reaction at ambient temperature in dry dichloromethane to afford aryliminophosphoranes in excellent yields.

Mehdi Adib; Ehsan Sheikhi; Azadeh Deljoush

2011-01-01

378

Synthesis of (+)-Bullatacin via the Highly Diastereoselective [3+2] Annulation Reaction of a Racemic Aldehyde and a Non-Racemic Allylsilane  

PubMed Central

A total synthesis of (+)-bullatacin has been accomplished via a diastereoselective [3+2] annulation reaction of the highly enantiomerically enriched allylsilane 3 and racemic aldehyde 4, which provides the key bis-tetrahydrofuran fragment 15 with ? 20 : 1 ds.

Tinsley, Jennifer M.; Mertz, Eric; Chong, Pek Y.; Rarig, Robert-Andre F.; Roush, William R.

2008-01-01

379

Synthesis and properties of 2-acetylthiamin pyrophosphate: an enzymatic reaction intermediate  

SciTech Connect

The synthesis of 2-acetylthiamin pyrophosphate (acetyl-TPP) is described. The synthesis of this compound is accomplished at 23/sup 0/C by the oxidation of 2-(1-hydroxyethyl) thiamin pyrophosphate using aqueous chromic acid as the oxidizing agent under conditions where Cr(III) coordination to the pyrophosphoryl moiety and hydrolysis of both the pyrophosphate and acetyl moieties were prevented. Although the chemical properties exhibited by acetyl-TPP are similar to those of the 2-acetyl-3,4-dimethylthiazolium ion examined by Lienhard, significant differences exist because of the pyrimidine ring in acetyl-TPP. Characterization of acetyl-TPP by ultraviolet spectroscopy, /sup 1/H NMR, /sup 13/C NMR, and /sup 31/P NMR provided evidence that the compound in aqueous solution exists as an equilibrium mixture of keto, hydrate, and intramolecular carbinolamine forms. The equilibria for the hydration and carbinolamine formation reactions at pD 1.3 as determined by /sup 1/H NMR are strongly dependent on the temperature, showing an increase in the hydrate and carbinolamine forms at the expense of the keto form with decreasing temperature. The concentration of keto form also decreases with increasing pH. Acetyl-TPP is stable in aqueous acid but rapidly deacetylates at higher pH to form acetate and thiamin pyrophosphate. Trapping of the acetyl moiety in aqueous solution occurs efficiently with 1.0 M hydroxylamine at pH 5.5-6.5 to form acetohydroxamic acid and to a much smaller extent with 1.0 M 2-mercaptoethanol at pH 4.0 and 5.0 to form thio ester. Transfer of the acetyl group to 0.5 M dihydrolipoic acid at pH 5.0 and 1.0 M phosphate dianion at pH 7.0 is not observed to any significant extent in water. The kinetic and thermodynamic reactivity of acetyl-TPP with water and other nucleophiles is compatible with a hypothetical role for acyl-TPPs as enzymatic acyl-transfer intermediates.

Gruys, K.J.; Halkides, C.J.; Frey, P.A.

1987-12-01

380

Enantio- and diastereoselective synthesis of piperidines by coupling of four components in a "one-pot" sequence involving diphenylprolinol silyl ether mediated Michael reaction.  

PubMed

An efficient, asymmetric, four-component, one-pot synthesis of highly substituted piperidines with excellent diastereo- and enantioselectivity was established through the diphenylprolinol silyl ether mediated Michael reaction of aldehyde and nitroalkene, followed by the domino aza-Henry reaction/hemiaminalization reaction and a Lewis acid mediated allylation or cyanation reaction. All carbons of the piperidine ring are substituted with different groups, and its five contiguous stereocenters are completely controlled in both relative and absolute senses. PMID:20853903

Urushima, Tatsuya; Sakamoto, Daisuke; Ishikawa, Hayato; Hayashi, Yujiro

2010-10-15

381

Applied reaction dynamics: efficient synthesis gas production via single collision partial oxidation of methane to CO on Rh111.  

PubMed

Supersonic molecular beams have been used to determine the yield of CO from the partial oxidation of CH4 on a Rh111 catalytic substrate, CH4+12O2-->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 approximately 1.3 eV. Comparison with a simplified model of the methane-Rh111 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. PMID:17029475

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

2006-10-01

382

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 ~1.3 eV. 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

383

Micro ammonia sensor  

SciTech Connect

A micro ammoniasensor, consisting of an ISFET covered with a dry membrane which is made from nonactin and substituted poly-..gamma..-methyl-L-glutamate (PMG) is described. The gate output voltage of the micro ammonia sensor increased with NH/sub 4/OH addition. The response time of the sensor was 2 min at 30/sup 0/C, and the sensor exhibited superior selectivity for NH/sub 4//sup +/ compared to a pH sensitive ISFET.

Kubo, I.; Karube, I.; Moriizumi, T.

1986-01-01

384

Phase- and shape-controlled synthesis of cadmium hydroxyl chloride microstructures via an ammonia-assisted conversion of 1D CdQCl (Q=quinoline) complex microwires  

NASA Astrophysics Data System (ADS)

In this paper we reported a NH3·H2O-assisted solvothermal route for successful synthesis of cadmium hydroxyl chlorides (Cdx(OH)yClz) microstructures with different phases and shapes, employing 1D CdQCl (Q=quinoline) complex microwires as the precursor. Experiments contained two processes: firstly, CdQCl complex microwires with 500-600 nm in diameter and several hundreds of micrometers in length were prepared by the complexation between CdCl2·2.5H2O and quinoline at room temperature; then, CdQCl microwires were solvothermally treated at 150 °C for 10 h in the presences of different amounts of NH3·H2O to produce Cdx(OH)yClz microstructures with various phases and shapes. The as-obtained precursor and Cdx(OH)yClz microstructures were characterized by scanning electron microscopy, transmission electron microscopy, Infrared spectrometry and X-ray powder diffraction. Experiments showed that hexagonal Cd(OH)Cl was obtained from water-methanol system, while rhombohedral Cd4(OH)5Cl3 from methanol system. Also, it was found that the shapes of Cdx(OH)yClz could be tuned by the amounts of NH3·H2O. Furthermore, the UV diffuse reflection and photoluminescence spectra of the precursor and Cdx(OH)yClz were also investigated.

Wang, Xin; Ni, Yonghong; Hong, Jianming

2013-11-01

385

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

386

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

387

Synthesis of diaryl ketones via a phosphine-free Fukuyama reaction.  

PubMed

The synthesis of unsymmetrical diaryl ketones via the Fukuyama coupling of thioesters and organozinc reagents is described. Typically, the synthesis of diaryl ketones using this methodology provides low yields. The simple complex, Pd(dba)(2), was found to convert a variety of aryl thioesters to diaryl ketones in good yields. PMID:22037521

Kunchithapatham, Kamala; Eichman, Chad C; Stambuli, James P

2011-12-21

388

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

PubMed Central

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

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

2013-01-01

389

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

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

390

Synthesis of potato starch sulfate and optimization of the reaction conditions  

Microsoft Academic Search

Potato starch sulfate was obtained by the reaction between potato starch and chlorosulfonic acid in pyridine. It was characterized by FT-IR and SEM. The reaction conditions were studied systematically, which included the volume ratio of pyridine to chlorosulfonic acid, reaction temperature and time in preparing sulfating agent process, and the ratio of starch mass to chlorosulfonic acid volume, reaction temperature

Dapeng Cui; Mingzhu Liu; Lan Wu; Yinghui Bi

2009-01-01

391

Synthesis of guanosine and its derivatives from 5-amino-1-beta-D-ribofuranosyl-4-imidazolecarboxamide. III. Formation of a novel cycloimidazole nucleoside and its cleavage reactions.  

PubMed Central

A new cycloimidazole nucleoside, 5-(1 inch -benzamido-1 inch-hydroxymethylene) amino-2', 1 inch-anhydro-1-beta-D-ribofuranosyl-4-imidazolecarboxamide (III) was synthesized by reaction of 5-amino-1-beta-D-ribofuranosyl-4-imidazolecarboxamide (AICA-riboside) with benzoyl isothiocyanate followed by methylation with methyl iodide. The structure of III was elucidated on the basis of its nmr spectra and chemical reactions. Of special interest are reactions of III with various nucleophiles. For example, guanosine (IX) was obtained by amination of III wtih ammonia in 72% yield. Analogous reactions of III with methylamine and dimethylamine gave N2-methylguanosine (X) and N2-dimethylguanosine (XI), respectively. Refluxing of III in alkaline solution afforded xanthosine (VII). The probable mechanism of formation and facile ring-opening of III is also discussed.

Okutsu, M; Yamazaki, A

1976-01-01

392

Antiinflammatory peptides (antiflammins) inhibit synthesis of platelet- activating factor, neutrophil aggregation and chemotaxis, and intradermal inflammatory reactions  

PubMed Central

Synthetic peptides corresponding to the region of highest similarity between human lipocortin I and rabbit uteroglobin inhibit phospholipase A2 and show potent antiinflammatory activity on the carrageenan-induced rat footpad edema. The peptide HDMNKVLDL (antiflammin-2) inhibits the synthesis of platelet-activating factor (PAF) induced by TNF or phagocytosis in rat macrophages and human neutrophils, and by thrombin in vascular endothelial cells. The peptide MQMKKVLDS (antiflammin-1) is less inhibitory than antiflammin-2 for macrophages and not inhibitory for neutrophils after a 5-min preincubation. This finding suggests that antiflammin-1 is inactivated by neutrophils secretory products, possibly oxidizing agents. Synthesis of PAF is inhibited by antiflammin- 2 without an appreciable lag, but this inhibition is reversed when neutrophils or macrophages are washed and incubated in fresh medium. Therefore, antiflammins must be continuously present to inhibit PAF synthesis. Antiflammins block activation of the acetyltransferase required for PAF synthesis, suggesting that this enzyme is another target for the inhibitory activity of antiflammins. These peptides inhibit neutrophil aggregation and chemotaxis induced by complement component C5a. Antiflammin-2 suppresses the increase in vascular permeability and the leukocyte infiltration induced in rats by an Arthus reaction or by intradermal injection of rTNF and C5a.

1990-01-01

393

Gas–liquid–liquid reaction engineering: the Koch synthesis of pivalic acid from iso- and tert-butanol; Reaction kinetics and the effect of a dispersed second-liquid phase  

Microsoft Academic Search

In gas–liquid–liquid reaction systems with fast parallel and consecutive reactions the effects of mass transfer and mixing on the product yield can be significant. The Koch synthesis of pivalic acid, using sulfuric acid as catalyst, was chosen to study these effects. Reaction kinetics and the effect of the catalyst-phase composition have been investigated by using isobutanol as reactant. For studying

D. W. F. Brilman; W. P. M. van Swaaij; G. F. Versteeg

1999-01-01

394

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

PubMed

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

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

2010-06-01

395

Synthesis of 2,8-dioxabicyclo[3.3.1]nonane derivatives via a sequential Knoevenagel condensation and hetero-Diels-Alder reaction in an aqueous medium.  

PubMed

Utilizing aldehyde-substituted vinylogous carbonates and 1,3-diketones, a simple protocol is presented for the synthesis of 2,8-dioxabicyclo[3.3.1]nonane derivatives via Knoevenagel condensation followed by a hetero-Diels-Alder reaction under green reaction conditions. The structure of a key product is unequivocally confirmed by X-ray crystallography. PMID:24147553

Srinivas, Venu; Koketsu, Mamoru

2013-11-15

396

Synthesis of phenol derivatives from cyclohex-2-enones bearing an alkyne through Lewis acid-catalyzed enolization and intramolecular Alder-Rickert reaction.  

PubMed

A cationic rhodium(I) complex- or In(OTf)(3)-catalyzed synthesis of phenol derivatives from cyclohex-2-enone having an ethoxycarbonyl-substituted alkyne has been achieved. This reaction proceeds via enolization and an intramolecular Alder-Rickert reaction. PMID:23003109

Kinbara, Atsushi; Yamagishi, Takehiro; Hanzawa, Naoko; Kawashima, Etsuko; Miyaoka, Hiroaki

2012-10-19

397

Direct synthesis of 3,4-dihydro-2 H-pyrido[1,2- a]pyrimidines, by addition reactions with 2-aminopyridines  

Microsoft Academic Search

Reaction of 2-aminopyridines with formaldehyde and electron rich alkenes permits synthesis of pyridopyrimidines by formation of imines and subsequent addition to the alkenes in a formal aza Diels Alder reaction. The structure of the cyclic amidine products is confirmed by single crystal X-ray analysis on a neutral amidine isolated from an aminopyridine substituted with an electron withdrawing trifluoromethyl group and

John M Mellor; Glynn D Merriman; Helen Rataj; Gillian Reid

1996-01-01

398

Catalytic Asymmetric Synthesis of 3,3'-Diaryloxindoles as Triarylmethanes with a Chiral All-Carbon Quaternary Center: Phase-Transfer-Catalyzed SN Ar Reaction.  

PubMed

Catalytic asymmetric synthesis of unsymmetrical triarylmethanes with a chiral all-carbon quaternary center was achieved by using a chiral bifunctional quaternary phosphonium bromide catalyst in the SN Ar reaction of 3-aryloxindoles under phase-transfer conditions. The presence of a urea moiety in the chiral phase-transfer catalyst was important for obtaining high enantioselectivity in this reaction. PMID:24802937

Shirakawa, Seiji; Koga, Kenta; Tokuda, Takashi; Yamamoto, Kenichiro; Maruoka, Keiji

2014-06-10

399

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

NASA Astrophysics Data System (ADS)

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

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

1998-03-01

400

SYNTHESIS THROUGH REACTIONS OF NUCLEOPHILES WITH ACRYLONITRILES; PART 13: A DIRECT ONE-POT SYNTHESIS OF THIAZOLOPYRIDINES  

Microsoft Academic Search

Several new thiazolopyridines have been synthesized by a one-pot method through the ternary condensation of aldehydes with malononitrile and thioglycolic acid. Structure and reaction pathway are also reported.

F. F. Abdel-latif; Y. S. Mohammed; H. Abdel-ghani; E. Kh. Ahmed; E. H. El-gawish

1993-01-01

401

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.

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

2011-01-01

402

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.

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

2014-01-01

403

Biogenic synthesis of palladium nanoparticles using Pulicaria glutinosa extract and their catalytic activity towards the Suzuki coupling reaction.  

PubMed

Green synthesis of nanomaterials finds the edge over chemical methods due to its environmental compatibility. Herein, we report a facile and eco-friendly method for the synthesis of palladium (Pd) nanoparticles (NPs) using an aqueous solution of Pulicaria glutinosa, a plant widely found in a large region of Saudi Arabia, as a bioreductant. The as-prepared Pd NPs were characterized using ultraviolet-visible (UV-vis) spectroscopy, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transform-infrared spectroscopy (FT-IR). The hydroxyl groups of the plant extract (PE) molecules were found mainly responsible for the reduction and growth of Pd NPs. FT-IR analysis confirmed the dual role of the PE, both as a bioreductant as well as a capping ligand, which stabilizes the surface of Pd NPs. The crystalline nature of the Pd NPs was identified using XRD analysis which confirmed the formation of a face-centered cubic structure (JCPDS: 87-0641, space group: Fm3m (225)). Furthermore, the as-synthesized Pd NPs demonstrated excellent catalytic activity towards the Suzuki coupling reaction under aqueous and aerobic conditions. Kinetic studies of the catalytic reaction monitored using GC confirmed that the reaction completes in less than 5 minutes. PMID:24619034

Khan, Mujeeb; Khan, Merajuddin; Kuniyil, Mufsir; Adil, Syed Farooq; Al-Warthan, Abdulrahman; Alkhathlan, Hamad Z; Tremel, Wolfgang; Tahir, Muhammad Nawaz; Siddiqui, Mohammed Rafiq H

2014-06-28

404

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

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

1979-01-01

405

Cell-free Protein Synthesis in a Microchamber Revealed the Presence of an Optimum Compartment Volume for High-order Reactions.  

PubMed

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

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

2014-06-20

406

Atmospheric Dispersion of Ammonia: An Ammonia Fog Model.  

National Technical Information Service (NTIS)

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 ener...

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

1983-01-01

407

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...

408

Alleviating versus stimulating effects of bicarbonate on the growth of Vallisneria natans under ammonia stress.  

PubMed

Bicarbonate plays a crucial role in limiting the growth of submersed aquatic macrophytes in eutrophic lakes, and high ammonia is often toxic to macrophytes. In order to evaluate the combined effect of HCO3 (-) and total ammonia (i.e., the total of NH3 and NH4 (+)) on submersed macrophytes Vallisneria natans, the growth and physiological response of V. natans in the presence of HCO3 (-) and ammonia were studied. The results showed that with the increase of ammonia, morphological parameters of V. natans declined. In contrast, increased HCO3 (-) concentration stimulated the growth of V. natans, especially when the NH4 (+)-N/NO3 (-)-N ratio was 1:7. High ammonia concentration induced excess free amino acids (FAA) accumulation and soluble carbohydrates (SC) depletion in plant tissues. However, the elevated HCO3 (-) promoted the synthesis of SC and rendered the decrease of FAA/SC ratio. The results also suggested that HCO3 (-) could partially alleviate the stress of ammonia, as evidenced by the decrease of FAA/SC ratio and the growth enhancement of V. natans when the ammonia concentration was 0.58 mg?L(-1). Given the fact that HCO3 (-) is probably the dominant available carbon source in most eutrophic lakes, the ability of V. natans to use HCO3 (-) for SC synthesis may explain the alleviating effect of HCO3 (-) on V. natans under ammonia stress. PMID:23381797

Dou, Yanyan; Wang, Baozhong; Chen, Liangyan; Yin, Daqiang

2013-08-01

409

Enantioselective palladium-catalyzed total synthesis of vitamin e by employing a domino Wacker-Heck reaction.  

PubMed

An enantioselective total synthesis of vitamin E in which a novel palladium-catalyzed domino reaction was employed as the key step is described. This reaction allows the formation of the chiral chroman framework and the concurrent introduction of part of the side chain of vitamin E. The sequence comprises an enantioselective Wacker cyclization and a subsequent Heck reaction. Accordingly, reaction of alkenylphenol 12 with methyl vinyl ketone (13) in the presence of catalytic amounts of Pd(OTFA)(2) (TFA = trifluoroacetate), the enantiopure ligand (S,S)-Bn-BOXAX (8 b; Bn = benzyl, BOXAX = 2,2'-bis(oxazolyl)-1,1'-binaphthyl, and p-benzoquinone (9) as an oxidant gives access to chiral chroman 10 with an enantioselectivity of 97 % ee in 84 % yield. Chroman 10 is then converted into 24 by an aldol condensation reaction with (3R)-3,7-dimethyloctanal (11). Subsequent 1,2-addition of methyllithium, elimination of water, and hydrogenation yields vitamin E. PMID:17001611

Tietze, Lutz F; Stecker, Florian; Zinngrebe, Julia; Sommer, Konrad M

2006-11-24

410

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

411

The copper catalysed reaction of sodium methoxide with aryl bromides : a mechanistic study leading to a facile synthesis of anisole derivatives  

Microsoft Academic Search

The copper catalysed reaction of unactivated aryl bromides with sodium methoxide has been investigated by studying a number of parameters (copper catalyst, cosolvent, concentration and relative ratio of the reactants, additives and aryl bromide substituents) which influence this reaction. The ipso-substitution reaction was found to proceed via an intimate electron transfer mechanism involving a cuprate-like intermediate, Na[Cu(OMe){2}]. A convenient synthesis

G. van Koten; Koten van G; D. M. Grove; T. Kuilman; O. G. Piekstra; L. A. Hulshof; R. A. Sheldon

1989-01-01

412

Synthesis of (±)-cis-clavicipitic acid by a Rh(I)-catalyzed intramolecular imine reaction.  

PubMed

A new and short synthesis of racemic cis-clavicipitic acid was achieved by taking advantage of the double nucleophilic character of indole-4-pinacolboronic ester. Key to the success of the synthesis were an efficient and selective C-3 indole Friedel-Crafts alkylation and the development of an unprecedented intramolecular rhodium-catalyzed 1,2-addition of an aryl pinacolboronic ester to an unactivated imine. PMID:24605802

Bartoccini, Francesca; Casoli, Mariangela; Mari, Michele; Piersanti, Giovanni

2014-04-01

413

Application of a Catalytic Asymmetric Povarov Reaction using Chiral Ureas to the Synthesis of a Tetrahyroquinoline Library  

PubMed Central

A 2328-membered library of 2,3,4-trisubstituted tetrahydroquinolines was produced using a combination of solution- and solid-phase synthesis techniques. A tetrahydroquinoline (THQ) scaffold was prepared via an asymmetric Povarov reaction using cooperative catalysis to generate three contiguous stereogenic centers. A matrix of 4 stereoisomers of the THQ scaffold was prepared to enable the development of stereo/structure-activity relationships (SSAR) upon biological testing. A sparse matrix design strategy was employed to select library members to be synthesized with the goal of generating a diverse collection of tetrahydroquinolines with physicochemical properties suitable for downstream discovery.

Gerard, Baudouin; O'Shea, Morgan Welzel; Donckele, Etienne; Kesavan, Sarathy; Akella, Lakshmi B.; Xu, Hao; Jacobsen, Eric N.; Marcaurelle, Lisa A.

2012-01-01

414

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

PubMed

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

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

2009-08-01

415

Microwave-assisted four-component, one-pot condensation reaction: an efficient synthesis of annulated pyridines.  

PubMed

A one-pot, effective synthesis of pyridines by a modified Kröhnke procedure is described. Polysubstituted annulated pyridines were synthesized in high yields by four-component, one-pot cyclocondensation reactions of N-phenacylpyridinium bromide, aromatic aldehydes, acetophenones or cyclic ketones in the presence of ammonium acetate and acetic acid, assisted by microwave irradiation. In this procedure, cyclic ketones with two alpha-CH(2) groups yield annulated pyridines with additional alpha-benzylidene groups, which are derived in situ from double aldol condensation of cyclic ketones with two moles of aromatic aldehydes. PMID:17340010

Yan, Chao-Guo; Cai, Xi-Mei; Wang, Qi-Fang; Wang, Ting-Yu; Zheng, Ming

2007-03-21

416

Copper-catalyzed synthesis of benzimidazoles via cascade reactions of o-haloacetanilide derivatives with amidine hydrochlorides.  

PubMed

We have developed an efficient method for the synthesis of benzimidazoles via cascade reactions of o-haloacetoanilide derivatives with amidine hydrochlorides. The protocol uses 10 mol % CuBr as the catalyst, Cs2CO3 as the base, and DMSO as the solvent, and no ligand is required. The procedure proceeds via the sequential coupling of o-haloacetoanilide derivatives with amidines, hydrolysis of the intermediates (amides), and intramolecular cyclization with the loss of NH3 to give 2-substituted 1H-benzimidazoles. PMID:18754576

Yang, Daoshan; Fu, Hua; Hu, Liming; Jiang, Yuyang; Zhao, Yufen

2008-10-01

417

In-situ hot pressing\\/solid-liquid reaction synthesis of dense titanium silicon carbide bulk ceramics  

Microsoft Academic Search

An in-situ hot pressing\\/solid-liquid reaction process was developed for the synthesis of dense polycrystalline Ti3SiC2 ceramics using Ti, Si, and graphite powders as starting materials. The present work demonstrated that this process was one\\u000a of the most effective and simple methods for the preparation of dense bulk Ti3SiC2 materials. Lattice constants of a=3.068 and c=17.645 are calculated for Ti3SiC2 made

Y. Zhou; Zhimei Sun; Shengqi Chen; Y. Zhang

1998-01-01

418

Extending Pummerer reaction chemistry. Synthesis of (+/-)-dibromophakellstatin by oxidative cyclization of an imidazole derivative.  

PubMed

The diastereoselective oxidative cyclization of a dihydrooroidin derivative is reported. The thioimidate product formed by application of a new variant of the Pummerer reaction serves as a precursor to dibromophakellstatin. [reaction: see text] PMID:15727477

Feldman, Ken S; Skoumbourdis, Amanda P

2005-03-01

419

Ammonia Removal in a Pond System and in a Stripping Tower.  

National Technical Information Service (NTIS)

The mode of ammonia removal from ponds is described by a model of a first-order, chemical reaction, independently of the operational conditions of the pond system. Enhanced ammonia removal was observed at extended retention times owing to biological ammon...

M. Ronen L. R. J. Vanvuuren

1977-01-01

420

Determination of ammonia in beers by pervaporation flow injection analysis and spectrophotometric detection  

Microsoft Academic Search

A pervaporation flow injection (PFI) method is described for the determination of ammonia in beers. After injecting the sample into a NaOH donor solution, ammonia and other volatiles are transferred in the pervaporation unit from the donor stream to an acceptor stream containing sodium salicylate and nitroprusside, which subsequently mixes with alkaline sodium dichloroisocyanurate to allow the classical Berthelot reaction

Lijuan Wang; Terence J. Cardwell; Robert W. Cattrall; Maria D. Luque de Castro; Spas D. Kolev

2003-01-01

421

Effect of acetylene and ammonia as reburn fuel additions to methane in nitric oxide reburning  

Microsoft Academic Search

Presented in this paper are the computational results of NO reburning with (a) a combination of methane and acetylene and (b) a combination of methane and ammonia. An updated reaction mechanism that was more comprehensive in terms of predicting the ammonia and isocyanic acid oxidation chemistry was employed to run the CKINTERP program. Using the binary file created by executing

S. K. Kumpaty; V. P. Nokku; K. Subramanian

1996-01-01

422

27 CFR 21.96 - Ammonia, aqueous.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 2013-04-01 false Ammonia, aqueous. 21.96 Section 21...Specifications for Denaturants § 21.96 Ammonia, aqueous. (a) Alkalinity. Strongly alkaline to litmus. (b) Ammonia content. 27 to 30...

2013-04-01

423

Ambient Ammonia Measurements in Coastal Southeastern Virginia.  

National Technical Information Service (NTIS)

Results are presented from a measurement program to test an in situ ammonia measurement technique and to document the temporal and spatial variability associated with ammonia. The ammonia data were accumulated for two sites in coastal Southeastern Virgini...

C. N. Harward W. A. McClenny J. M. Hoell J. A. Williams B. S. Williams

1981-01-01

424

Facile synthesis of functionalized tetrahydroquinolines via domino Povarov reactions of arylamines, methyl propiolate and aromatic aldehydes  

PubMed Central

Summary In the presence of p-toluenesulfonic acid as catalyst the domino reaction of arylamines, methyl propiolates and aromatic aldehydes in ethanol proceeded smoothly to give polysubstituted 1,2,3,4-tetrahydroquinolines in moderate yields. The reaction is believed to involve the Povarov reaction of in situ generated ?-enamino ester with the in situ formed aromatic imine.

Sun, Jing; Gao, Hong; Wu, Qun

2012-01-01

425

Efficient synthesis of (+/-)-erysotramidine using an NBS-promoted cyclization reaction of a hexahydroindolinone derivative.  

PubMed

An NBS-promoted intramolecular electrophilic aromatic substitution reaction of a hexahydroindolinone derivative was used to assemble the tetracyclic core of the erythrinane skeleton. The resulting cyclized product was transformed into (+/-)-erysotramidine in three additional steps. The cyclization reaction is also successful using variously substituted aryl and furanyl bicyclic lactams under acidic conditions. [reaction: see text] PMID:14682766

Lee, Hyoung Ik; Cassidy, Michael P; Rashatasakhon, Paitoon; Padwa, Albert

2003-12-25

426

Studies on the synthesis of 2 & 4-picoline-correlation of acidity with the catalytic activity  

Microsoft Academic Search

Systematic studies carried out at C.F.R.I. pertainining to catalytic vapour phase synthesis of pyridine bases, namely 2 & 4-picolines through cyclodehydrogenation reaction of acetaldehyde and ammonia have been described. Metal oxide modified amorphous silica- alumina and crystalline alumino-silicate namely ZSM-5 zeolites were found to be active and selective catalysts towards the formation of the lower pyridines bases. The method of

Sisir K. Roy; Banikar Ghosh; Shyam K. Roy

1998-01-01

427

Synthesis and spectroscopic structural studies of the adducts formed in the reaction of aminopyridines with TCNQ  

NASA Astrophysics Data System (ADS)

The adducts 7,7-dicyano-8,8-di- m-aminopyridilequinodimethane and 7,7-dicyano-8,8-di- p-aminopyridilequinodimethane are formed by the reaction of the electron donors 3-aminopyridine (3APY) and 4-aminopyridine (4APY), respectively, with the ?-acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ). The reactions were studied using electronic, infrared and mass spectral and thermal measurements. The results indicate that the aminopyridines undergo rapid N-substitution by TCNQ forming the reaction products and HCN molecules. A general mechanism for the reactions as well as the structures of the reaction products are proposed.

AlQaradawi, Siham Y.; Nour, E. M.

2006-08-01

428

Ammonia caramels: Specifications and analysis  

Microsoft Academic Search

Twenty three UK commercially produced ammonia caramels and eight experimentally produced ammonia caramels have been analysed by a range of physical and chemical tests, which include solids content, nitrogen levels, colour intensity and pH. A statistical treatment of the results is reported.

A. L. Patey; G. Shearer; M. E. Knowles; W. H. B. Denner

1985-01-01

429

Ammonia caramels: specifications and analysis.  

PubMed

Twenty three UK commercially produced ammonia caramels and eight experimentally produced ammonia caramels have been analysed by a range of physical and chemical tests, which include solids content, nitrogen levels, colour intensity and pH. A statistical treatment of the results is reported. PMID:4018316

Patey, A L; Shearer, G; Knowles, M E; Denner, W H

1985-01-01

430

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.

431

Novel one-pot synthesis of diverse ?,?-unsaturated ?-ketoesters by thermal cascade reactions of diazodicarbonyl compounds and enol ethers: transformation into substituted 3,5-diketoesters.  

PubMed

Sequential Wolff rearrangement of ?-diazo-?-ketoesters followed by trapping of the ketene intermediates with enol ethers generated a variety of ?,?-unsaturated ?-ketoesters. This method involves a novel thermal cascade reaction and allows the synthesis of ?,?-unsaturated ?-ketoesters with trans-stereochemistry under catalyst-free conditions. The synthesized compounds were further transformed into novel 3,5-diketoesters, which were used for the synthesis of naturally occurring 2-pyrone and 1-naphthoic acid ester. PMID:24841124

Pandit, Rameshwar Prasad; Lee, Yong Rok

2014-06-01

432

Prebiotic synthesis of imidazole-4-acetaldehyde and histidine  

NASA Astrophysics Data System (ADS)

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 products were identified by TLC, HPLC, and LC-MS by comparison with authentic samples. The maximum yields of imidazole-4-acetaldehyde, imidazole-4-ethanol, and imidazole-4-glycol obtained in these reactions are 1.6, 5.4, 6.8% 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; Yang, Lily; Miller, Stanley L.; Oró, J.

1987-09-01

433

Pyrolysis of monohalobenzenes in an ammonia atmosphere  

SciTech Connect

Gas-phase pyrolysis of monohalobenzenes was studied in a flow tubular reactor in the presence of ammonia at a pressure equal to atmospheric in the temperature range from 600 to 1,000 C, contact time 4 s. The major pyrolysis products are C{sub 6}H{sub 6}, NH{sub 4}{sup +}HlG{sup {minus}}, and HCN; benzonitrile and biphenyl are formed to a minor extent. Formation of hydrogen cyanide becomes appreciable above 800 C. Dehalogenation presumably proceeds by a chain mechanism and involves hydrogen atoms. The process is of interest as a model reaction in connection with the problem of utilization of toxic industrial wastes.

Kashin, A.N.; Maiorov, O.V.; Ivanova, G.G. [Lomonosov Moscow State Univ. (Russian Federation)

1996-05-01

434

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

SciTech Connect

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

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

2013-01-01

435

Chemically reduced graphene oxide for ammonia detection at room temperature.  

PubMed

Chemically reduced graphene oxide (RGO) has recently attracted growing interest in the area of chemical sensors because of its high electrical conductivity and chemically active defect sites. This paper reports the synthesis of chemically reduced GO using NaBH4 and its performance for ammonia detection at room temperature. The sensing layer was synthesized on a ceramic substrate containing platinum electrodes. The effect of the reduction time of graphene oxide (GO) was explored to optimize the response, recovery, and response time. The RGO film was characterized electrically and also with atomic force microscopy and X-ray photoelectron spectroscopy. The sensor response was found to lie between 5.5% at 200 ppm (parts per million) and 23% at 2800 ppm of ammonia, and also resistance recovered quickly without any application of heat (for lower concentrations of ammonia). The sensor was exposed to different vapors and found to be selective toward ammonia. We believe such chemically reduced GO could potentially be used to manufacture a new generation of low-power portable ammonia sensors. PMID:23856001

Ghosh, Ruma; Midya, Anupam; Santra, Sumita; Ray, Samit K; Guha, Prasanta K

2013-08-14

436

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

437

An efficient synthesis of symmetric and unsymmetric bis-(?-aminoamides) via Ugi multicomponent reaction.  

PubMed

A library of symmetrical and unsymmetrical bis-(?-aminoamides) has been prepared starting from symmetrical secondary diamines by using a double Ugi four-component reaction. A sacrifical Mumm rearrangement, thanks to the use of 2-hydroxymethyl benzoic acid, is necessary to suppress the competing split-Ugi reaction, increasing the yield and simplifying the purification step. The scope, the reaction conditions, and the role of water in trapping the nitrilium intermediate are also discussed. PMID:23150900

La Spisa, Fabio; Feo, Alberto; Mossetti, Riccardo; Tron, Gian Cesare

2012-12-01

438

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

439

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

440

High-pressure catalytic reactions over single-crystal metal surfaces  

NASA Astrophysics Data System (ADS)

Studies dealing with high-pressure catalytic reactions over single-crystal surfaces are reviewed. The coupling of an apparatus for the measurement of reaction kinetics at elevated pressures with an ultrahigh vacuum system for surface analysis allows detailed study of structure sensitivity, the effects of promoters and inhibitors on catalytic activity, and, in certain cases, identification of reaction intermediates by post-reaction surface analysis. Examples are provided which demonstrate the relevance of single-crystal studies for modeling the behaviour of high-surface-area supported catalysts. Studies of CO methanation and CO oxidation over single-crystal surfaces provide convincing evidence that these reactions are structure insensitive. For structure-sensitive reactions (ammonia synthesis, alkane hydrogenolysis, alkane isomerization, water-gas shift reaction, etc.) model single-crystal studies allow correlations to be established between surface structure and catalytic activity. The effects of both electronegative (S and P) and electropositive (alkali metals) impurities upon the catalytic activity of metal single crystals for ammonia synthesis, CO methanation, alkane hydrogenolysis, ethylene epoxidation and water-gas shift are discussed. The roles of "ensemble" and "ligand" effects in bimetallic catalysts are examined in light of data obtained using surfaces prepared by vapor-depositing one metal onto a crystal face of a dissimilar metal.

Rodriguez, JoséA.; Wayne Goodman, D.

1991-11-01

441

Expanding the scope of PNA-encoded synthesis (PES): Mtt-protected PNA fully orthogonal to fmoc chemistry and a broad array of robust diversity-generating reactions.  

PubMed

Nucleic acid-encoded libraries are emerging as an attractive and highly miniaturized format for the rapid identification of protein ligands. An important criterion in the synthesis of nucleic acid encoded libraries is the scope of reactions that can be used to introduce molecular diversity and devise divergent pathways for diversity-oriented synthesis (DOS). To date, the protecting group strategies that have been used in peptide nucleic acid (PNA) encoded synthesis (PES) have limited the choice of reactions used in the library synthesis to just a few prototypes. Herein, we describe the preparation of PNA monomers with a protecting group combination (Mtt/Boc) that is orthogonal to Fmoc-based synthesis and compatible with a large palette of reactions that have been productively used in DOS (pall