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1

Ammonia Synthesis  

Microsoft Academic Search

\\u000a Ammonia production is a very energy- and capital-intensive industry as it requires high temperature (400–500°C) and also high\\u000a pressure (150–300 bar) for its daily operations. Two moles of ammonia are obtained by reacting one mole of nitrogen and three\\u000a moles of hydrogen gases in the presence of conventional catalyst which is magnetite. The process to produce ammonia is known\\u000a as

Noorhana Yahya; Poppy Puspitasari; Krzysztof Koziol; Pavia Guiseppe

2

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

3

Temperature controlled ammonia synthesis process  

SciTech Connect

A process is described for the synthesis of ammonia carried out at a pressure greater than 100 atmospheres which process comprises passing a mixture of gases in continuous flow through apparatus so as to carry out the following steps: (a) passing at least a portion of an ammonia feed syngas through a heat exchanger to increase its temperature; (b) passing the feed syngas from (a) through a first ammonia synthesis catalyst bed to obtain an effluent; (c) passing at least a portion of the effluent from (b) through the heat exchanger of (a) to decrease the temperature of the effluent; (d) passing the effluent from (c) through a series of at least two additional ammonia synthesis catalysts beds and then subsequent to each bed through a high temperature heat sink to decrease the temperature of the effluent and to obtain a final product effluent; and (c) recovering ammonia from the final product effluent of the series in (d).

Grotz, B.J. Jr.

1986-11-25

4

Apparatus for ammonia synthesis  

SciTech Connect

Apparatus is described for the synthesis of ammonia, comprising: a first vertical synthesis reactor comprising a first reactor shell and a first catalyst bed contained in a first catalyst holder positioned within and spaced apart from the first reactor shell to provide a first annulus between the first catalyst holder and the first reactor shell to allow feed gas to enter the first catalyst bed; a second vertical synthesis reactor comprising a second reactor shell and a second catalyst bed contained in a second catalyst holder positioned within and spaced apart from the second reactor shell to provide a second annulus between the second catalyst holder and second reactor shell to allow feed gas to enter the second catalyst bed; a gas-gas heat exchanger; a first coupling means for coupling the bottom end of the first reactor to the gas-gas heat exchanger, the first coupling means having a first conduit between the fist annulus and the gas-gas heat exchanger for passage of feed to the first catalyst bed and a second conduit to pass effluent from the first catalyst bed to the gas-gas heat exchanger; a second heat exchanger comprising an exchanger shell having disposed therein a first tube bundle and a second tube bundle disposed in an interior portion of the exchanger shell inside of the first tube bundle; a second coupling means for coupling the bottom end of the second reactor to the second heat exchanger, the second coupling means having a third conduit between the second annulus and the outlet of the first tube bundle for passage of feed to the second catalyst bed and a fourth conduit to pass effluent from the second catalyst bed to the second tube bundle; and a fifth conduit to pass effluent from the gas-gas heat exchanger to the inlet of the first tube bundle.

Grotz, B.J.

1993-08-17

5

Development of ammonia synthesis  

Microsoft Academic Search

Ammonia production is a high energy and capital-intensive industry as it obliges high temperature (400–500°C) and also high pressure (150–300 bar) for its daily processes. Two moles of ammonia are obtained by reacting one mole of nitrogen and three moles of hydrogen gases in the existence of conventional catalyst which are magnetite (Fe3O4). The process to produce ammonia is known

Poppy Puspitasari; Noorhana Yahya

2011-01-01

6

Sugar-driven prebiotic synthesis of ammonia from nitrite.  

PubMed

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

Weber, Arthur L

2010-03-07

7

The Ammonia Synthesis Reaction: An Exception to the Le Chatelier Principle and Effects of Nonideality  

ERIC Educational Resources Information Center

Le Chatelier's principle states that the further addition of a particular component will cause the reaction to shift in the direction that reduces the total number of moles of the system. However, the addition of one reactant [N[subscript 2

Uline, Mark J.; Corti, David S.

2006-01-01

8

Mechanism of formation of ammonia synthesis catalyst  

SciTech Connect

The formation of ammonia synthesis catalyst by the reduction of magnetite by hydrogen at 450/sup 0/C has been studied using electron microscopy, X-ray energy dispersive and electron energy loss analysis, and including in situ reduction experiments in a gas reaction cell in an electron microscope. The reaction is characterized by a cellular mechanism of reduction leading to the formation of a periodic network of iron crystallites and pores without any significant volume change. The iron nucleates epitaxially on the oxide, and minor elements, notably aluminum, initially in solution in the oxide, partition to the iron crystallite surfaces. Elements present in intercrystalline ferrite and glassy phases remain essentially immobile during reduction with the exception of potassium which migrates rapidly to the iron surfaces.

Pennock, G.M.; Flower, H.M.; Andrew, S.P.S.

1987-01-01

9

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

2007-01-17

10

Reaction mechanisms in peptide synthesis. Part 1. Semiquantitative characteristics of the reactivity of 2-methyl-5(4H)-oxazolone with water and ammonia in the gas phase and weakly polar media.  

PubMed

2,4-Dialkyl-5(4H)-oxazolones are well-recognized intermediates in some aminolysis reactions in peptide synthesis. Using the MOPAC molecular orbital programs, detailed geometric and energetic characteristics of the elementary reaction pathways for the additions of water and ammonia to 2-methyl-5(4H)-oxazolone have been determined at the AM1 level. The results demonstrate that the additions must be parsed into a two-step mechanism involving formation of the alpha-hydroxyimine followed by tautomerization to the parent N-acetylamino acid or amide. PMID:1818092

Ciarkowski, J; Chen, F M; Benoiton, N L

1991-12-01

11

COâ removal from ammonia synthesis gas with SELEXOL Solvent Process  

Microsoft Academic Search

The high cost of energy which has prevailed since the 70's has forced ammonia producers to seek new methods to save energy and lower the ammonia production cost. The purpose of this paper is to discuss the use of SELEXOL Solvent Process for treatment of ammonia synthesis gas and discuss a patented SELEXOL process scheme which permits substantially 100% carbon

Shah

1987-01-01

12

Ammonia Synthesis from First-Principles Calculations  

NASA Astrophysics Data System (ADS)

The rate of ammonia synthesis over a nanoparticle ruthenium catalyst can be calculated directly on the basis of a quantum chemical treatment of the problem using density functional theory. We compared the results to measured rates over a ruthenium catalyst supported on magnesium aluminum spinel. When the size distribution of ruthenium particles measured by transmission electron microscopy was used as the link between the catalyst material and the theoretical treatment, the calculated rate was within a factor of 3 to 20 of the experimental rate. This offers hope for computer-based methods in the search for catalysts.

Honkala, K.; Hellman, A.; Remediakis, I. N.; Logadottir, A.; Carlsson, A.; Dahl, S.; Christensen, C. H.; Nørskov, J. K.

2005-01-01

13

Palladium-catalyzed synthesis of indoles via ammonia cross-coupling-alkyne cyclization.  

PubMed

The synthesis of indoles via the metal-catalyzed cross-coupling of ammonia is reported for the first time; the developed protocol also allows for the unprecedented use of methylamine or hydrazine as coupling partners. These Pd/Josiphos-catalyzed reactions proceed under relatively mild conditions for a range of 2-alkynylbromoarenes. PMID:21594239

Alsabeh, Pamela G; Lundgren, Rylan J; Longobardi, Lauren E; Stradiotto, Mark

2011-05-18

14

Reactions of Hydrogen Atoms with Hydrazine, Ammonia, and Nitrous Oxide  

Microsoft Academic Search

Reactions of hydrogen atoms with hydrazine, ammonia, and nitrous oxide have been investigated in a flow system employing a mass spectrometer for the measurements of the steady-state concentrations of the gases. It is shown that reaction with hydrazine proceeds through the mechanism: N2H4+H=H2+N2H3,k1=3.5×1011e?2000?RTmole?1cc sec?1;2N2H3=2NH3+N2,k2⩾3×1012 mole?1cc sec?1 (at 150∘C). The mechanism of the reactions of hydrogen atoms with ammonia or nitrous

M. Schiavello; G. G. Volpi

1962-01-01

15

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

16

Growth of organic microspherules in sugar-ammonia reactions.  

PubMed

Reaction of small sugars of less than four carbons with ammonia in water yielded organic microspherules generally less than ten microns in size. The time course of microspherule growth was examined for the D-erythrose-ammonia reaction that yielded microspherules attached to the glass walls of containers. Measurements were made of the elemental composition and infrared spectrum of the microspherule material. These viscose semi-solid microspherules are viewed as possible containers for prebiotic catalytic processes relevant to the origin of life. PMID:16254690

Weber, Arthur L

2005-12-01

17

Mechanochemical synthesis of ammonia upon titanium dispersion  

Microsoft Academic Search

We have found a new method for synthesizing ammonia which proceeds in the course of vibration dispersion of titanium. The dispersion was carried out in air with an eccentric vibration mill with a power density of 10 W\\/g. The barrels were cooled with liquid nitrogen every 3 min of milling. The powder of titanium iodide (purity 99.9%) was preliminarily annealed

T. S. Ivanova; A. G. Lipson; V. A. Kuznetsov; A. K. Buryak; M. P. Glazunov; V. V. Gubin

1993-01-01

18

Investigation of manganese-doped iron ammonia synthesis catalysts  

Microsoft Academic Search

The iron catalysts for ammonia synthesis doped with manganese in amounts up to 3wt.% has been investigated. The addition of manganese oxide did not influence the distribution of other promoters in the catalyst precursors, manganese oxide itself was entirely incorporated into phases of iron oxides, its concentration in the wustite phase was about twice that in the magnetite phase.At concentrations

Micha? J. Figurski; Walerian Arabczyk; Zofia Lendzion-Bielu?; Stanis?aw Lenart

2004-01-01

19

Ammonia synthesis process and apparatus for use therein  

US Patent & Trademark Office Database

A method for synthesis of ammonia includes compressing a synthesis gas containing hydrogen and nitrogen in a multi-stage (50, 56 and 57) centrifugal compressor. The synthesis gas is compressed to a pressure of from about 800 to 900 psia in the first stage (50) of the compressor, and withdrawn therefrom and subjected to cooling and dehydration by contact with liquid ammonia in a dehydrator (54). The cooled, dehydrated synthesis gas is then returned to the compressor and introduced into the second stage (56) thereof. Because of this interstage cooling and dehydration, compressor speed may be reduced and significant savings in power consumption are attained because of the favorable effect of the dehydrator (54) on the last two stages (56, 57) of the compressor. Additional power saving is realized because refrigeration requirements for the synthesis loop are reduced. Apparatus to carry out the process includes a centrifugal compressor fitted with a synthesis gas outlet (2, 4 and 6) connecting the discharge of the first stage (50) of the compressor with the synthesis gas inlet of the dehydrator (54), and a synthesis gas intermediate inlet (8) connecting the inlet of the second stage (56) of the compressor in flow communication with the synthesis gas outlet of the dehydrator (54).

2004-11-02

20

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...

21

Reactions of orthophthalaldehyde with ammonia and 2-aminoethanol.  

PubMed

Reactions of orthophthalaldehyde (OPA) with amines are used in the determination of amino acids and in applications of OPA as a biocide. To contribute to the understanding of processes involved, the reactions of OPA with ammonia, which are conveniently slow, were studied. In a set of rapidly established equilibria, the 1,3-dihydroxyindole and the product of its dehydration are formed (Scheme 1). The individual equilibria were identified and equilibrium constants determined using DC polarography and UV spectra. The ring closure involves the carbinolamine; the imine formation is a side reaction. Both the ring formation and the dehydration of the carbinolamine are generally acid catalyzed. In the finally established overall equilibria between OPA and the isoindole derivative, the concentrations of intermediates are negligible. The same applies to the reaction of OPA with 2-aminoethanol, in which the initial formation of a carbinolamine and of an imine are too fast to be followed. Very slow reactions taking place during periods of hours or days, which probably result in the formation of dimeric species, have also been observed. This contribution demonstrates the advantages of combinations of polarographic and spectrophotometric techniques in the investigation of complex reactions of some organic compounds. PMID:18843407

Kulla, Eliona; Zuman, Petr

2008-08-29

22

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

Microsoft Academic Search

When bis(dinitrogen) complexes of molybdenum and tungsten are treated with an excess of strong acid, with few exceptions, a complex containing the hydrazido(2-) ligand has been identified either as a product in the reaction or as an intermediate on the way to the formation of ammonia and hydrazine. In the case of those molybdenum complexes that produce ammonia, the stoichiometry

G. E. Bossard; T. Adrian George; Daniel B. Howell; Lenore M. Koczon; Richard K. Lester

1983-01-01

23

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

PubMed Central

The N?N bond (225?kcal mol?1) in dinitrogen is one of the strongest bonds in chemistry therefore artificial synthesis of ammonia under mild conditions is a significant challenge. Based on current knowledge, only bacteria and some plants can synthesise ammonia from air and water at ambient temperature and pressure. Here, for the first time, we report artificial ammonia synthesis bypassing N2 separation and H2 production stages. A maximum ammonia production rate of 1.14 × 10?5?mol m?2 s?1 has been achieved when a voltage of 1.6?V was applied. Potentially this can provide an alternative route for the mass production of the basic chemical ammonia under mild conditions. Considering climate change and the depletion of fossil fuels used for synthesis of ammonia by conventional methods, this is a renewable and sustainable chemical synthesis process for future.

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

2013-01-01

24

Iron single crystals as ammonia synthesis catalysts: effect of surface structure on catalyst activity  

Microsoft Academic Search

The activity of three iron single-crystal faces with respect to their ability to catalyze ammonia synthesis was investigated. At 798 K and a total pressure of 20 atm of a stoichiometric mixture of hydrogen and nitrogen, the relative rates of ammonia formation were found to be 418:25:1 for Fe(111), Fe(100), and Fe(110) samples, respectively. The activation energy for ammonia synthesis

N. D. Spencer; R. C. Schoonmaker; G. A. Somorjai

1982-01-01

25

CO/sub 2/ removal from ammonia synthesis gas with SELEXOL Solvent Process  

SciTech Connect

The high cost of energy which has prevailed since the 70's has forced ammonia producers to seek new methods to save energy and lower the ammonia production cost. The purpose of this paper is to discuss the use of SELEXOL Solvent Process for treatment of ammonia synthesis gas and discuss a patented SELEXOL process scheme which permits substantially 100% carbon dioxide recovery. This paper also describes: the SELEXOL Process Technology; treating of Ammonia Synthesis Gas; philosophy; high CO/sub 2/ Recovery Process; 100% CO2 Recovery Process; cost and Utility Requirement; plant Performance Data.

Shah, V.A.

1987-01-01

26

Role of the aerosol phase state in ammonia/amines exchange reactions.  

PubMed

The exchange reaction of ammonia in (NH4)2SO4 with an amine and the corresponding reverse reaction of amines in aminium sulfates with ammonia were investigated using an electrodynamic balance coupled with a Raman spectrometer. The temporal changes in particle mass, chemical composition, and phase state were simultaneously monitored. When the salt particles were in an aqueous state at elevated relative humidities (RHs), the exchange of ammonia/amine vapors in the particle phase was reversible. The exchange rates of aqueous particles were in general higher than those of their corresponding solid counterparts. An aqueous phase was essential for the effective displacement of ammonia and amines. Aminium salts in different phase states and with different evaporation characteristics showed remarkably different reaction behaviors in ammonia vapor. The less compact amorphous aminium sulfate solids were more susceptible to ammonia exchange than the crystalline solids. The aminium salts in a liquid state exhibited substantial amine evaporation at <3% RH and formed acidic bisulfate. Under ammonia exposure, these acidic aminium droplets underwent both neutralization and displacement reactions. Stable solid salts containing ammonium, aminium, sulfate, and bisulfate were formed and hindered further reactions. The result suggests that ambient aminium sulfates may be acidic. Overall, the phase states of the ammonium and aminium salt particles crucially determine the heterogeneous reaction rates and final product properties and identities. PMID:23668831

Chan, Lap P; Chan, Chak K

2013-05-24

27

Biocatalytic enantioselective synthesis of N-substituted aspartic acids by aspartate ammonia lyase.  

PubMed

The gene encoding aspartate ammonia lyase (aspB) from Bacillus sp. YM55-1 has been cloned and overexpressed, and the recombinant enzyme containing a C-terminal His(6) tag has been purified to homogeneity and subjected to kinetic characterization. Kinetic studies have shown that the His(6) tag does not affect AspB activity. The enzyme processes L-aspartic acid, but not D-aspartic acid, with a K(m) of approximately 15 mM and a k(cat) of approximately 40 s(-1). By using this recombinant enzyme in the reverse reaction, a set of four N-substituted aspartic acids were prepared by the Michael addition of hydroxylamine, hydrazine, methoxylamine, and methylamine to fumarate. Both hydroxylamine and hydrazine were found to be excellent substrates for AspB. The k(cat) values are comparable to those observed for the AspB-catalyzed addition of ammonia to fumarate ( approximately 90 s(-1)), whereas the K(m) values are only slightly higher. The products of the enzyme-catalyzed addition of hydrazine, methoxylamine, and methylamine to fumarate were isolated and characterized by NMR spectroscopy and HPLC analysis, which revealed that AspB catalyzes all the additions with excellent enantioselectivity (>97 % ee). Its broad nucleophile specificity and high catalytic activity make AspB an attractive enzyme for the enantioselective synthesis of N-substituted aspartic acids, which are interesting building blocks for peptide and pharmaceutical synthesis as well as for peptidomimetics. PMID:18844200

Weiner, Barbara; Poelarends, Gerrit J; Janssen, Dick B; Feringa, Ben L

2008-01-01

28

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

29

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

SciTech Connect

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

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

1983-07-06

30

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

31

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

32

Metabolic properties of a mixed culture of aerobic ammonia oxidizers and its optimal reaction conditions.  

PubMed

The aerobic ammonia oxidation is an important process for nitrogen removal from wastewater with high ammonia concentration. Here, we investigated the metabolic properties of a mixed culture of aerobic ammonia oxidizers and determined its optimal reaction conditions. The maximum specific rate of NO(2)(-)-N formation of the culture was 14.9 mg N mg(protein)(-1) d(-1). The ammonia oxidation capacity was positively correlated with the microbial biomass concentration. Haldane model showed that the half-saturation constant (K(s)) for NH(4)(+)-N of the culture was 78.5 mg L(-1), and the inhibition constant (K(i)) for NH(4)(+)-N was 393.4 mg L(-1). The acetic acid and beef extract had significant inhibitory effects on ammonia oxidation, while there was little effect of methanol and glucose on ammonia oxidation. Orthogonal experiments with range analysis, variance analysis, factor contribution analysis and response surface analysis confirmed the optimal reaction conditions for ammonia oxidation to be 30-32 °C, pH 7.8-8.0, and 150-200 mg L(-1) NH(4)(+)-N concentration. PMID:22100242

Shen, Li-dong; Chen, Peng; He, Fan-zhong; Hu, An-hui; Zheng, Ping; Xu, Xiang-yang; Hu, Bao-lan

2011-10-31

33

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

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

34

Reaction synthesis of titanium aluminides  

Microsoft Academic Search

The formation of titanium aluminides from the elemental powders has been investigated. A traditional powder metallurgy route of compaction (by cold isostatic pressing, hot pressing or hot extrusion) followed by heat treatment was compared with the novel technique of hot extrusion reaction synthesis (HERS). The products from these different production methods were characterised by x-ray diffraction and microscopy (light and

E. K. Y. Fu; R. D. Rawlings; H. B. McShane

2001-01-01

35

Direct aldol and tandem Mannich reactions in room temperature ammonia solutions  

Microsoft Academic Search

An economical, simple, and efficient direct aldol reaction via the double activation of both aldehydes and ketones by ammonia has been developed. An unprecedented tandem Mannich reaction was observed when hydroxybenzaldehydes, pyrrole-2-carboxyaldehyde, and indole-3-carboxyaldehyde were employed to afford 2,2-dimethyl-6-aryl-4-pyrilidinones in moderate to good yields.

Lichun Feng; Lijin Xu; Kimhung Lam; Zhongyuan Zhou; C. W. Yip; Albert S. C. Chan

2005-01-01

36

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

37

Ammonia inhibits long-term potentiation via neurosteroid synthesis in hippocampal pyramidal neurons.  

PubMed

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

Izumi, Y; Svrakic, N; O'Dell, K; Zorumski, C F

2012-12-29

38

The kinetics and mechanisms of aromatic nucleophilic substitution reactions in liquid ammonia.  

PubMed

The rates of aromatic nucleophilic substitution reactions in liquid ammonia are much faster than those in protic solvents indicating that liquid ammonia behaves like a typical dipolar aprotic solvent in its solvent effects on organic reactions. Nitrofluorobenzenes (NFBs) readily undergo solvolysis in liquid ammonia and 2-nitrofluorobenzene is about 30 times more reactive than the 4-substituted isomer. Oxygen nucleophiles, such as alkoxide and phenoxide ions, readily displace fluorine of 4-NFB in liquid ammonia to give the corresponding substitution product with little or no competing solvolysis product. Using the pK(a) of the substituted phenols in liquid ammonia, the Brønsted ?(nuc) for the reaction of 4-NFB with para-substituted phenoxides is 0.91, indicative of the removal of most of the negative charge on the oxygen anion and complete bond formation in the transition state and therefore suggests that the decomposition of the Meisenheimer ?-intermediate is rate limiting. The aminolysis of 4-NFB occurs without general base catalysis by the amine and the second-order rate constants generate a Brønsted ?(nuc) of 0.36 using either the pK(a) of aminium ion in acetonitrile or in water, which is also interpreted in terms of rate limiting breakdown of the Meisenheimer ?-intermediate. Nitrobenzene and diazene are formed as unusual products from the reaction between sodium azide and 4-NFB, which may be due to the initially formed 4-nitroazidobenzene decomposing to give a nitrene intermediate, which may then give diazene or be trapped by ammonia to give the unstable hydrazine which then yields nitrobenzene. PMID:21417418

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

2011-03-31

39

[Development of efficient methods for synthesis of nitrogen-containing compounds using carbamates, acylhydrazines, and ammonia].  

PubMed

For the efficient synthesis of divergent nitrogen-containing compounds of pharmaceutical and agricultural importance, the development of efficient, complementary, and new synthetic methodologies is essential. One of the key subjects is how to introduce nitrogen atoms in to organic molecules. This review summaries our recent efforts on this issue, focusing on the use of carbamates, acylhydrazines, and ammonia as nitrogen sources. PMID:17139157

Sugiura, Masaharu

2006-12-01

40

STUDY ON THE PRECIPITATION OF AMMONIUM URANATES. I. REACTION BETWEEN URANYL NITRATE AND AMMONIA  

Microsoft Academic Search

The mechanism of the precipitation and the composition of the ; precipitate which results from the reaction between uranyl nitrate and ammonia ; were studied by potentiometric, conductometric, and analytical methods. It is ; shown that the ammonium diuranate is not obtained as has been reponted in the ; literature. At the beginning a precipitate with the compoisition (NHâ)\\/sub ;

C. Dragulescu; I. Julean

1959-01-01

41

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

42

Analytical and Experiment Study on the Chemical Reaction Kinetics of Composite Adsorbent–Ammonia Working Pair  

Microsoft Academic Search

An iso-volumetric test unit was built to test the adsorption and desorption performances of a consolidated composite adsorbent (mixture of CaCl2 and expanded graphite) with ammonia as the working fluid. The reaction kinetics and heat transfer performance of the consolidated adsorbent were studied and two reaction orders [8\\/4 and 4\\/2] were considered in this study. The influences of the refrigerant

Su Ling Li; Jing Yi Wu; Zai Zhong Xia; Ru Zhu Wang

2010-01-01

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

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

45

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

PubMed

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

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

2012-09-28

46

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

47

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

NASA Astrophysics Data System (ADS)

Ammonia generation through reaction of H2 with neutral cobalt nitride clusters in a fast flow reactor is investigated both experimentally and theoretically. Single photon ionization at 193 nm is used to detect neutral cluster distributions through time-of-flight mass spectrometry. ComNn clusters are generated through laser ablation of Co foil into N2/He expansion gas. Mass peaks ComNH2 (m = 6, 10) and ComNH3 (m = 7, 8, 9) are observed for reactions of H2 with the ComNn clusters. Observation of these products indicates that clusters ComN (m = 7, 8, 9) have high reactivity with H2 for ammonia generation. Density functional theory (DFT) calculations are performed to explore the potential energy surface for the reaction Co7N + 3/2H2 --> Co7NH3, and a barrierless, thermodynamically favorable pathway is obtained. An odd number of hydrogen atoms in ComNH3 (m = 7, 8, 9) probably come from the hydrogen molecule dissociation on two active cobalt nitride clusters based on the DFT calculations. Both experimental observations and theoretical calculations suggest that hydrogen dissociation on two active cobalt nitride clusters is the key step to form NH3 in a gas phase reaction. A catalytic cycle for ammonia generation from N2 and H2 on a cobalt metal catalyst surface is proposed based on our experimental and theoretical investigations.

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

2012-09-01

48

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

49

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

2013-01-16

50

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

PubMed

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). PMID:22614383

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

2012-04-29

51

Homoaromatics as intermediates in the substitution reactions of 1,2,4,5-tetrazines with ammonia and hydrazine  

Microsoft Academic Search

This thesis describes some nucleophilic substitution reactions between the red 1,2,4,5-tetrazines and hydrazine-hydrate or ammonia. Special attention was paid to the occurrence of the S

A. D. Counotte-Potman

1981-01-01

52

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

53

Intracluster reactions: The formation of hydrazine complexes from ammonia clusters following ArF excimer laser excitation  

Microsoft Academic Search

We have found a novel intracluster reaction proceeding in large ammonia or ammonia\\/argon clusters upon excitation with ArF excimer laser radiation which leads to the formation of unprotonated and prototaned hydrazine clusters, (N2H4)+n and (N2H4)nH+ (n=1–4). To our knowledge it is the first time that the production of bareclustersofadifferentchemicalspecies has been observed as a result of an intracluster reaction. Besides

Matthias Färber; Friedrich Huisken

1996-01-01

54

Updating turbine of synthesis gas compression unit for ammonia production  

Microsoft Academic Search

In this article an examination has been made of the problems that arise during operation of the R32\\/15-9.9\\/4.1 type of steam\\u000a turbine of the synthesis gas compressor of the enterprise Minudobreniya in Rossosh, Russia, due to high vibration levels that\\u000a cause emergency stoppage of the unit on account of failure of the standard sliding (plain) support bearings. The causes of

V. G. Getsman; K. V. Gordienko; P. V. Lebedev; V. S. Martsinkovskii; I. E. Kukharev; V. I. Yurko; I. V. Ovseiko

2010-01-01

55

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

SciTech Connect

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

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

1996-10-01

56

Synthesis and degradation of phenylalanine ammonia-lyase of Rhodosporidium toruloides.  

PubMed

The regulation of the enzyme phenylalanine ammonia-lyase (PAL), which is of potential use in oral treatment of phenylketonuria, was investigated. Antiserum against PAL was prepared and was shown to be monospecific for the enzyme by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The native enzyme and two inactive mutant forms of the enzyme were purified to homogeneity by immunoaffinity chromatography, using anti-PAL immunoglobulin G-Sepharose 4B. Both mutant enzymes contained intact prosthetic groups. The formation of PAL catalytic activity after phenylalanine was added to yeast cultures was paralleled by the appearance of enzyme antigen. During induction, uptake of [3H]leucine into the enzyme was higher than uptake into total protein. Our results are consistent with de novo synthesis of an enzyme induced by phenylalanine, rather than activation of a proenzyme. The half-lives of PAL and total protein were similar in both exponential and stationary phase cultures. No metabolite tested affected the rate of enzyme degradation. Glucose repressed enzyme synthesis, whereas ammonia reduced phenylalanine uptake and pool size and so may repress enzyme synthesis through inducer exclusion. The synthesis of enzyme antigen by a mutant unable to metabolize phenylalanine indicated that this amino acid is the physiological inducer of the enzyme. PMID:7068528

Gilbert, H J; Tully, M

1982-05-01

57

First-principles study of ammonia synthesis on a supported iron nanocluster  

NASA Astrophysics Data System (ADS)

Possibility of ammonia synthesis on a MgO(100) supported iron nanocluster has been studied using density functional theory. The N2 molecules were sequentially adsorbed on the Fe7/MgO(100) and the most favorable adsorption geometries and dissociation pathways investigated. The first two N2 molecules were found to dissociate easily upon adsorption, producing nitrogen atoms which bind strongly to the cluster. The third N2 molecule adsorbs in a favorable molecular state without dissociating. Adding H atoms one by one to the adsorbed N2 molecule we found that two H atoms are required to break the molecule and then, after adding another two H atoms, the first ammonia is formed. The process is accompanied with a small energy barrier and the microscopic mechanism is similar to the one proposed for the biological nitrogen fixation.

Sljivancanin, Zeljko; Pasquarello, Alfredo

2005-03-01

58

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

NASA Astrophysics Data System (ADS)

When atomic carbon is condensed on a surface at 77 K containing ammonia and water, glycine, N-methylglycine, alanine, ?-alanine, aspartic acid and serine are generated. It is postulated that these reactions may mimic those which occur when an extraterrestrial carbon atom condenses on a frozen surface coated with water and ammonia and may provide a route to extraterrestrial amino acids. Experiments designed to elucidate the mechanisms of amino acid formation under these conditions have been carried out.

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

1987-09-01

59

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

Microsoft Academic Search

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

ADAM STASZKIEWICZ; JAN CHMURA

2002-01-01

60

Removal of boron from wastewater by the hydroxyapatite formation reaction using acceleration effect of ammonia.  

PubMed

The mechanism was discussed for the removal of boron by the hydroxyapatite (HAp) formation reaction using Ca(OH)(2) and (NH(4))(2)HPO(4) in room temperature. Time required to remove boron was 20 min by adding Ca(OH)(2) and (NH(4))(2)HPO(4) for the remaining boron to below 1mg/L. The removal rate of boron was controlled by the HAp precipitate formation and the presence of ammonia. From the XRD patterns and SEM images, HAp could be confirmed in the precipitate product. The reaction between borate ions and calcium hydroxide was accelerated by dehydration with ammonia; the borate-calcium hydroxide compound coprecipitated with resulting HAp. Although the removal of boron decreased in the presence of sulfate, phosphate, and aluminum, these effects could be prevented by adding excess Ca(OH)(2). Interference of fluoride ions was eliminated by adding Al(3+). Sodium alpha-olefin sulfonate was the most effective coagulant for HAp precipitation. The proposed boron removal method has several advantages about treating time and ability of boron removal. The method was successfully applied to the real hot spring wastewater. PMID:22981286

Yoshikawa, Eishi; Sasaki, Atsushi; Endo, Masatoshi

2012-08-25

61

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

SciTech Connect

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

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

1988-08-24

62

Compositional effects in Ru, Pd, Pt, and Rh-doped mesoporous tantalum oxide catalysts for ammonia synthesis.  

PubMed

A series of early metal-promoted Ru-, Pd-, Pt-, and Rh-doped mesoporous tantalum oxide catalysts were synthesized using a variety of dopant ratios and dopant precursors, and the effects of these parameters on the catalytic activity of NH3 synthesis from H2 and N2 were explored. Previous studies on this system supported an unprecedented mechanism in which N-N cleavage occurred at the Ta sites rather than on Ru. The results of the present study showed, for all systems, that Ba is a better promoter than Cs or La and that the nitrate is a superior precursor for Ba than the isopropoxide or the hydroxide. 15N-labeling studies showed that residual nitrate functions as the major ammonia source in the first hour but that it does not account for the ammonia produced after the nitrate is completely consumed. Ru3(CO)12 proved to be a better Ru precursor than RuCl(3).3H2O, and an almost linear increase in activity with increasing Ru loading level was observed at 350 degrees C (623 K). However, at 175 degrees C (448 K), the increase in Ru had no effect on the reaction rate. Pd functioned with comparable rates to Ru, while Pt and Rh functioned far less efficiently. The surprising activities for the Pd-doped catalysts, coupled with XPS evidence for low-valent Ta in this catalyst system, support a mechanism in which cleavage of the N-N triple bond occurs on Ta rather than the precious metal because the Ea value for N-N cleavage on Pd is 2.5 times greater than that for Ru, and the 9.3 kJ mol-1 Ea value measured previously for the Ru system suggests that N-N cleavage cannot occur at the Ru surface. PMID:17497850

Yue, Chaoyang; Qiu, Longhui; Trudeau, Michel; Antonelli, David

2007-05-12

63

Relationship between ammonia sensing properties of polyaniline nanostructures and their deposition and synthesis methods.  

PubMed

The ammonia absorption properties of polyaniline nanostructures are studied in terms of sensitivity, response and recovery times and stability. These characteristics are obtained by measuring, at room temperature, the absorbance variations at 632 nm. The nanostructures are synthesized either by interfacial or rapid or dropwise polymerizations with the oxidant-to-monomer mole ratio equals to 0.5 or 1. The influence of the deposition method (in-situ or drop-coating technique) as well as the nature of the dopant (HCl, CSA or I(2)) on the gas detection properties are also studied. The results show a strong dependence of the morphology on the deposition method, the in-situ technique leads to the best sensitivity and response time. For this deposition method, the nanostructures sensitivity, response time and regeneration rate depend on the synthesis method, the dopant and the mole ratio. The ageing effect after 8 months under ambient conditions and the mechanism of interaction between the polyaniline nanostructures and ammonia molecules are also presented. PMID:22769037

Kebiche, H; Debarnot, D; Merzouki, A; Poncin-Epaillard, F; Haddaoui, N

2012-06-14

64

Investigation of various promoted catalysts for ammonia synthesis by means of Mossbauer spectroscopy  

SciTech Connect

Mossbauer spectra are given for various promoted unreduced catalysts for ammonia synthesis, and their distinctive features are examined in comparison with the spectra of magnetite. A trend is noted toward increases in the specific surface and the specific metal surface of the reduced catalysts with increasing value of quadrupole splitting in the partial spectrum due to trivalent iron ions in tetragedral coordination in the unreduced specimens. The present work was aimed at studying the interaction of the primary promoters Al/sub 2/O/sub 3/ and K/sub 2/O with magnetite in unreduced catalysts by means of Mossbauer spectroscopy, and also at an examination of the effect of this interaction on the formation of surface in the reduced catalysts.

Peev, T.M. (Burgas Higher Chemical Tech. Inst., Bulgaria); Krylova, A.V.; Morozov, V.V.

1982-04-01

65

The Chinese soft-shelled turtle, Pelodiscus sinensis, decreases nitrogenous excretion, reduces urea synthesis and suppresses ammonia production during emersion.  

PubMed

The objective of this study was to examine the effects of 6 days of emersion on nitrogen metabolism and excretion in the Chinese soft-shelled turtle, Pelodiscus sinensis. Despite having a soft shell with a cutaneous surface that is known to be water permeable, P. sinensis lost only ~2% of body mass and was able to maintain its hematocrit and plasma osmolality, [Na(+)] and [Cl(-)] during 6 days of emersion. During emersion, it ameliorated water loss by reducing urine output, which led to a reduction (by 29-76%) in ammonia excretion. In comparison, there was a more prominent reduction (by 82-99%) in urea excretion during emersion due to a lack of water to flush the buccopharyngeal epithelium, which is known to be the major route of urea excretion. Consequently, emersion resulted in an apparent shift from ureotely to ammonotely in P. sinensis. Although urea concentration increased in several tissues, the excess urea accumulated could only account for 13-22% of the deficit in urea excretion. Hence, it can be concluded that a decrease (~80%) in urea synthesis occurred in P. sinensis during the 6 days of emersion. Indeed, emersion led to significant decreases in the activity of some ornithine-urea cycle enzymes (argininosuccinate synthetase/argininosuccinate lyase and arginase) from the liver of P. sinensis. As a decrease in urea synthesis occurred without the accumulation of ammonia and total free amino acids, it can be deduced that ammonia production through amino acid catabolism was suppressed with a proportional reduction in proteolysis in P. sinensis during emersion. Indeed, calculated results revealed that there could be a prominent decrease (~88%) in ammonia production in turtles after 6 days of emersion. In summary, despite being ureogenic and ureotelic in water, P. sinensis adopted a reduction in ammonia production, instead of increased urea synthesis, as the major strategy to ameliorate ammonia toxicity and problems associated with dehydration during terrestrial exposure. PMID:23348951

Ip, Yuen K; Lee, Serene M L; Wong, Wai P; Chew, Shit F

2013-01-24

66

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

67

A controlled atmosphere in situ X-ray diffraction study of the activation and performance of ammonia synthesis catalysts derived from CeRu sub 2 , CeCo sub 2 , and CeFe sub 2  

Microsoft Academic Search

High active ammonia synthesis catalysts derived from cerium intermetallic alloy precursors CeRuâ, CeCoâ, and CeFeâ have been studied by in situ powder X-ray diffraction (XRD) with concurrent analysis of catalytic activity. The reaction was investigated at pressures of up to 50 bar and at temperatures up to 550°C. Precursor activation was carried out in pure hydrogen, Nâ\\/Hâ, and CO\\/Hâ under

A. P. Walker; T. Rayment; R. M. Lambert

1989-01-01

68

Cross-linked enzyme aggregates of phenylalanine ammonia lyase: novel biocatalysts for synthesis of L-phenylalanine.  

PubMed

Cross-linked enzyme aggregates of phenylalanine ammonia lyase (PAL-CLEAs) from Rhodotorula glutinis were prepared. The effects of the type of aggregating agent, its concentration, and that of cross-linking agent were studied. PAL-CLEAs production was most effective using ammonium sulfate (40 % saturation), followed by cross-linking for 1 h with 0.2 % (v/v) glutaraldehyde. Moreover, the storage and operational stability of the resulting PAL-CLEAs were also investigated. Compared to the free enzyme, the PAL-CLEAs exhibited the expected increased stability of the enzyme against various deactivating conditions such as pH, temperature, denaturants, and organic solvents and showed higher storage stability than its soluble counterpart. Additionally, the reusability of PAL-CLEAs with respect to the biotransformation of L-phenylalanine was evaluated. PAL-CLEAs could be recycled at least for 12 consecutive batch reactions without dramatic activity loss, which should dramatically increase the commercial potential of PAL for synthesis of L: -phenylalanine. To the best of our knowledge, this is the first report of immobilization of PAL as cross-linked enzyme aggregates. PMID:22622644

Cui, Jian-Dong; Zhang, Si; Sun, Li-Mei

2012-05-24

69

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

70

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

SciTech Connect

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

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

2009-02-15

71

Isotopic transient analysis of ammonia synthesis over Ru\\/MgO catalysts promoted by cesium, barium, or lanthanum  

Microsoft Academic Search

The global and intrinsic kinetics of ammonia synthesis over ruthenium supported on MgO (?2 wt% Ru) and promoted with Cs, Ba, or La were examined at 3 atm and various dihydrogen pressures with steady-state and isotopic transient measurements. Steady-state, global measurements revealed that Cs–Ru\\/MgO was strongly inhibited by dihydrogen whereas Ba–Ru\\/MgO and La–Ru\\/MgO were weakly inhibited by the reactant. However, the

Stacey E Siporin; Robert J Davis

2004-01-01

72

Reaction Zone Structure of Gaseous Hydrogen Chloride Jets Submerged in Aqueous Ammonia Solutions.  

National Technical Information Service (NTIS)

A theoretical investigation of the structure of a turbulent, gaseous, reacting hydrogen chloride jet submerged in an aqueous ammonia bath was conducted. This particular combination of reactants has been found to produce a highly dynamic, rapidly fluctuati...

S. H. Chan P. J. Janke T. R. Shen R. S. Amano H. D. Shin

1986-01-01

73

Tritium Secondary Kinetic Isotope Effect on Phenylalanine Ammonia-Lyase-Catalyzed Reaction  

Microsoft Academic Search

The mechanism by which phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) catalyzes the reversible elimination of ammonia from phenylalanine yielding (E)-cinnamic acid has gained much attention in the recent years. Dehydroalanine is essential for the catalysis. It was assumed that this prostetic group acts as the electrophile, leading to a covalently bonded enzyme–intermediate complex with quarternary nitrogen of phenylalanine. Recently, an alternative

Andrzej Lewandowicz; Jacek Jemielity; Marianna Ka?ska; Jerzy Zo?; Piotr Paneth

1999-01-01

74

Multicomponent reactions for the synthesis of functionalized imidazoles.  

PubMed

An efficient synthesis of functionalized tetrahydroimidazoles via a one-pot tandem reaction between ninhydrin, primary alkylamines, arylisocyanates or arylisothiocyanates, acetylenic esters and triphenylphosphine is described. PMID:23713458

Seyfi, Samereh; Hossaini, Zinatossadat; Rostami-Charati, Faramarz

2013-09-01

75

Synthesis and photocatalytic performances of BiVO4 by ammonia co-precipitation process  

NASA Astrophysics Data System (ADS)

This paper reports the preparation and photocatalytic performance of Bismuth vanadate (BiVO4) by a facile and inexpensive approach. An amorphous BiVO4 was first prepared by a co-precipitation process from aqueous solutions of Bi(NO3)3 and NH4VO3 using ammonia. Followed by heating treatment at various temperatures, the amorphous phase converted to crystalline BiVO4 with a structure between monoclinic and tetragonal scheelite. The crystallization of BiVO4 occurred at about 523 K, while the nanocrystalline BiVO4 were formed with a heat-treatment of lower than 673 K. However, when the heat-treatment was carried out at 773 K, the accumulation of nanocrystals to bulk particles was observed. The photocatalytic performances of the materials were investigated by O2 evolution under visible-light, and MB decomposition under solar simulator. The results demonstrated that the crystalline structure is still the vital factor for the activities of both reactions. However, the crystallinity of BiVO4 gives a major influence on the activity of O2 evolution, whereas the surface area, plays an important role for photocatalytic MB decomposition.

Yu, Jianqiang; Zhang, Yan; Kudo, Akihiko

2009-02-01

76

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

NASA Astrophysics Data System (ADS)

Cesium tungsten oxides (CsxWO3) were synthesized by solvothermal reactions using ethanol and 57.1 vol% ethanol aqueous solution at 200 °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 CsxWO3 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 °C, while a small amount of nitrogen ion were incorporated in the lattice. The as-prepared CsxWO3 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 °C, i.e., from 734 to 31.5 and 231 to 3.58 ? cm, respectively.

Liu, Jing-Xiao; Ando, Yoshihiko; Dong, Xiao-Li; Shi, Fei; Yin, Shu; Adachi, Kenji; Chonan, Takeshi; Tanaka, Akikazu; Sato, Tsugio

2010-10-01

77

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

PubMed

The waste gas evolved from biodegradation of animal urine contains ammonia causing environmental concerns. A new and effective method for removing ammonia from such waste gas using reactive adsorption is presented. In the process, activated carbon impregnated with H2SO4(H2SO4/C) is employed. Ammonia in the waste gas reacts with H2SO4 on the adsorbent instantaneously and completely to form (NH4)2SO4. The H2SO4/C adsorbent is high in NH3 adsorption capacity and regenerable. The NH3 removal capacity of this regenerable adsorbent is more than 30 times that of the adsorbents used normally in the industry. The spent H2SO4/C is regenerated by flowing low-pressure steam through the adsorbent bed to remove the (NH4)2SO4 from the adsorbent. The regeneration by-product is concentrated (NH4)2SO4 solution, which is a perfect liquid fertilizer for local use. Re-soaking the activated carbon with H2SO4 solution rejuvenates the activity of the adsorbent. Thus the H2SO4/C can be reused repeatedly. In the mechanism of this reactive adsorption process, trace of H2O in the waste gas is a required, which lends itself to treating ammonia gas saturated with moisture from biodegradation of animal urine. PMID:17294961

Chou, Liang-hsing; Tsai, Ru-in; Chang, Jen-ray; Lee, Maw-tien

2006-01-01

78

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

79

Process for synthesizing ammonia  

SciTech Connect

In a continuous ammonia synthesis process in which a synthesis gas mixture containing nitrogen and hydrogen is passed sequentially over two or more catalyst beds containing ammonia synthesis catalyst to produce a gaseous effluent from each of the catalyst beds containing ammonia and unreacted nitrogen and hydrogen, the improvements is described which comprises cooling the gaseous effluent from the first of the catalyst beds, before the effluent enters the second catalyst bed, by heat exchange in a stream superheater to control the temperature of the effluent entering the second catalyst bed to a desired level.

Grotz, B.J.

1988-05-17

80

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

81

Oxetane synthesis through the Paternò-Büchi reaction.  

PubMed

The Paternò-Büchi reaction is a photochemical reaction between a carbonyl compound and an alkene to give the corresponding oxetane. In this review the mechanism of the reaction is discussed. On this basis the described use in the reaction with electron rich alkenes (enolethers, enol esters, enol silyl ethers, enanines, heterocyclic compounds has been reported. The stereochemical behavior of the reaction is particularly stressed. We pointed out the reported applications of this reaction to the synthesis of naturally occuring compounds. PMID:24043139

D'Auria, Maurizio; Racioppi, Rocco

2013-09-16

82

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

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

83

Infrared studies of the surface and gas phase reactions leading to the growth of titanium nitride thin films from tetrakis (dimethylamido) titanium and ammonia  

Microsoft Academic Search

In this paper, the reaction of tetrakis (dimethylamido) titanium (Ti(NME[sub 2])[sub 4]) with ammonia is studied in the gas phase and on titanium disilicide, aluminum, and copper surfaces using infrared spectroscopy. In the gas phase the main product of this reaction, dimethylamine, forms rapidly even at 300 K, and a fine yellow powder is deposited on the windows of the

Lawrence H. Dubois; B. R. Zegarski; G. S. Girolami

1992-01-01

84

Theoretical studies of possible processes for the interstellar production of phosphorus compounds. Reaction of P sup + with ammonia  

SciTech Connect

A theoretical study of the reaction of P{sup +} with ammonia, as a possible source of interstellar phosphorus-nitrogen compounds, has been carried out. The geometries of the possible products of this reaction, (HNP){sup +} and (H{sub 2}NP){sup +}, as well as of the relevant species on the triplet (H{sub 3}NP){sup +} potential energy surface have been optimized at the Hartree-Fock level. Relative energies were obtained through correlated calculations at the fourth-order Moller-Plesset theory. Calculations demonstrate that PNH{sup +} is the lowest lying (HNP){sup +} triplet state, with HPN{sup +} lying 50 kcal/mol higher at the correlated level. In the case of the (H{sub 2}NP){sup +} system, PNH{sub 2}{sup +} is found to be the ground state with trans-HPNH{sup +} and H{sub 2}PN{sup +} lying 44 and 93 kcal/mol, respectively, higher in energy at the correlated level. The PNH{sub 3}{sup +} ion-molecule complex is the lowest lying triplet (H{sub 3}NP){sup +} structure by a relatively high value, i.e. 40 kcal/mol. The stability order of this system is PNH{sub 3}{sup +} > HPNH{sub 2}{sup +} > H{sub 2}PNH{sup +} > H{sub 3}PN{sup +}. The reaction of P{sup +} with ammonia has been found to be endothermic in all cases except for the production of PNH{sub 2}{sup +}. In addition, two different mechanisms for producing PNH{sub 2}{sup +} that are barrier free have been found. Therefore, the reaction of P{sup +} with NH{sub 3}, leading to PNH{sub 2}{sup +}, seems to be a plausible interstellar process, since it is exothermic and also proceeds with no activation barrier.

Largo, A.; Barrientos, C. (Universidad de Oviedo (Spain)); Fores, J.R. (Universidad de Valladolid (Spain)); Ugalde, J.M. (Euskal Herriko Unibertsitatea (Spain))

1991-01-01

85

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

86

Electroactive mesoporous tantalum oxide catalysts for nitrogen activation and ammonia synthesis.  

PubMed

A new mesoporous Ta oxide catalyst for conversion of dinitrogen to ammonia shows strong evidence for a novel mechanism involving low valent Ta on the surface, supporting recent work in organometallic chemistry using low valent early transition metals for dinitrogen cleavage. PMID:16767235

Yue, Chaoyang; Trudeau, Michel; Antonelli, David

2006-02-20

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

Activating effect of scandium in the catalytic synthesis of ammonia and the investigation of this effect using the contact potential difference method and the Moessbauer effect  

Microsoft Academic Search

It has been found that the superheating of scandium oxide-promoted iron catalysts for the synthesis of ammonia gives rise to a significant increase in both their specific and total activities. On prolonged superheating the specific catalytic activity is reduced almost to the initial value. The activity changes correlate with changes in the electron work function: the highest activity corresponds to

L. A. Rudnitskii; P. D. Rabina; A. A. Melikyan; V. P. Korneev; L. D. Kuznetsov; T. V. Saprykina; A. M. Alekseev

1976-01-01

89

A Kinetic Study of the Assimilation of [15N]-ammonia and the Synthesis of Amino Acids in an Exponentially Growing Culture of Candida utilis  

Microsoft Academic Search

Ammonium phosphate labelled with 15N has been used in a single quantitative experiment to trace the pathways of ammonia assimilation and amino acid synthesis in food yeast. Methods have been developed and are briefly described, whereby the free amino acids and amides, and the amino acid residues of the proteins, may be extracted from the yeast, separated by ion-exchange chromatography,

A. P. Sims; B. F. Folkes

1964-01-01

90

Synthesis of hexagonal gold nanoparticles using a microfluidic reaction system  

Microsoft Academic Search

A new microfluidic reaction system capable of mixing, transporting and reacting is developed for the synthesis of gold nanoparticles. It allows for a rapid and a cost-effective approach to accelerate the synthesis of gold nanoparticles. The microfluidic reaction chip is made from micro-electro-mechanical-system technologies which integrate a micro-mixer, micro-pumps, a micro-valve, micro-heaters and a micro temperature sensor on a single

Chen-Hsun Weng; Chih-Chia Huang; Chen-Sheng Yeh; Huan-Yao Lei; Gwo-Bin Lee

2008-01-01

91

Reactions of synthesis of heavy nuclei: Brief summary and outlook  

SciTech Connect

The possible reactions of synthesis of extremely heavy nuclei with almost closed proton and neutron shells are analyzed on the basis of current experimental and theoretical data on the properties of the isotopes of superheavy elements. It has been shown that advances in obtaining extremely heavy nuclei for which microscopic models predict an increase in stability require further investigations of the mechanism of synthesis reactions. Direct and model experiments aimed at solving this problem are discussed.

Oganessian, Yu. Ts. [Joint Institute for Nuclear Research (Russian Federation)], E-mail: luda.rom@jinr.ru

2006-06-15

92

Using first principles to predict bimetallic catalysts for the ammonia decomposition reaction.  

PubMed

The facile decomposition of ammonia to produce hydrogen is critical to its use as a hydrogen storage medium in a hydrogen economy, and although ruthenium shows good activity for catalysing this process, its expense and scarcity are prohibitive to large-scale commercialization. The need to develop alternative catalysts has been addressed here, using microkinetic modelling combined with density functional studies to identify suitable monolayer bimetallic (surface or subsurface) catalysts based on nitrogen binding energies. The Ni-Pt-Pt(111) surface, with one monolayer of Ni atoms residing on a Pt(111) substrate, was predicted to be a catalytically active surface. This was verified using temperature-programmed desorption and high-resolution electron energy loss spectroscopy experiments. The results reported here provide a framework for complex catalyst discovery. They also demonstrate the critical importance of combining theoretical and experimental approaches for identifying desirable monolayer bimetallic systems when the surface properties are not a linear function of the parent metals. PMID:20489718

Hansgen, Danielle A; Vlachos, Dionisios G; Chen, Jingguang G

2010-04-25

93

Control of synthesis of functional mRNA coding for phenylalanine ammonia-lyase from Rhodosporidium toruloides.  

PubMed

The regulation of functional mRNA coding for phenylalanine ammonia-lyase (PAL) from Rhodosporidium toruloides was investigated. Polyadenylic acid [poly(A)]-containing RNA was an efficient template for in vitro translation in rabbit reticulocyte lysate. Non-poly(A)-containing RNA did not stimulate in vitro protein synthesis. Several lines of experimental evidence indicate that mRNA from R. toruloides directs PAL synthesis in reticulocyte lysate: (i) the major radioactive product in immunoprecipitates when lysates, incubated with yeast poly(A)-containing RNA, were reacted with PAL-antiserum had the same molecular weight as native PAL (75,000); (ii) this major radioactive product competes with authentic PAL for binding to PAL-antiserum; and (iii) partial proteolytic peptide maps of the in vitro translation product were very similar to those of native PAL. The levels of functional mRNA coding for PAL, when R. toruloides was grown in different physiological conditions, were determined by quantitation of PAL synthesized in vitro when RNA was added to reticulocyte lysate. Functional PAL mRNA was six times higher in yeast grown on phenylalanine compared with glucose-phenylalanine minimal medium. No functional PAL mRNA was detected in yeast grown on glucose-ammonia minimal medium in the presence or absence of phenylalanine. These observed changes in functional PAL mRNA were similar to levels of PAL catalytic and antigenic activity. The kinetics of functional PAL mRNA synthesis and degradation were studied. Maximum levels of functional PAL mRNA were observed within 60 min of transfer to PAL-inducing growth conditions. Poly(A)-containing RNA and functional PAL mRNA were rapidly degraded when cells were transferred from phenylalanine to glucose-ammonia minimal medium, with half-lives of 25 and 10 min, respectively. Thus, it is suggested that the alterations in the amount of PAL in cells of R. toruloides grown in different physiological conditions primarily result from alteration in the amount of functional mRNA coding for the enzyme. PMID:6826518

Gilbert, H J; Stephenson, J R; Tully, M

1983-03-01

94

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

95

A truly green synthesis of ?-aminonitriles via Strecker reaction  

PubMed Central

Background The classical Strecker reaction is one of the simplest and most economical methods for the synthesis of racemic ?-aminonitriles (precursor of ?-amino acids) and pharmacologically useful compounds. Results Indium powder in water is shown to act as a very efficient catalyst for one-pot, three-component synthesis of ?-aminonitriles from diverse amines, aldehydes and TMSCN. This general rapid method is applicable to a wide range of amines and aldehydes and produces products in excellent yield. Conclusions The present one-pot, three-component environmentally benign procedure for the synthesis of ?-aminonitriles will find application in the synthesis of complex biologically active molecules.

2011-01-01

96

Microwave synthesis of large few-layer graphene sheets in aqueous solution of ammonia  

Microsoft Academic Search

Few-layer graphene (FLG) sheets with sizes exceeding several micrometers have been synthesized by exfoliation of expanded\\u000a graphite in aqueous solution of ammonia under microwave irradiation, with an overall yield approaching 8 wt.%. Transmission\\u000a electron microscopy (in bright-field and dark-field modes) together with electron diffraction patterns and atomic force microscopy\\u000a confirmed that this graphene material consisted mostly of mono-, bi- or

Izabela Janowska; Kambiz Chizari; Ovidiu Ersen; Spyridon Zafeiratos; Driss Soubane; Victor Da Costa; Virginie Speisser; Christine Boeglin; Matthieu Houllé; Dominique Bégin; Dominique Plee; Marc-Jacques Ledoux; Cuong Pham-Huu

2010-01-01

97

Organocatalytic cascade reactions as a new tool in total synthesis  

NASA Astrophysics Data System (ADS)

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

Grondal, Christoph; Jeanty, Matthieu; Enders, Dieter

2010-03-01

98

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

ERIC Educational Resources Information Center

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

Tellinghuisen, Joel

2006-01-01

99

Microwave initiated reactions: Pechmann coumarin synthesis, Biginelli reaction, and acylation  

Microsoft Academic Search

An energy-efficient protocol has been developed for solvent-free reactions that are mildly exothermic but not spontaneous. The exothermic reaction mixture—on several g-scale—is exposed for about 30s to low power (about 200W) microwaves and then the microwave oven is switched off. After this short burst of energy, the exothermic reaction gets initiated and proceeds on its own to completion. A number

Maghar S. Manhas; Subhendu N. Ganguly; Somdatta Mukherjee; Amit K. Jain; Ajay K. Bose

2006-01-01

100

Enzyme Catalysis of Synthesis Reactions in Non-Aqueous Solvents by Reversal of Nominally Hydrolytic Reactions.  

National Technical Information Service (NTIS)

This project is an extension of an effort to develop new methods of chemical synthesis by using hydrolytic enzymes to catalyze condensations , the reverse of usual hydrolysis reactions. In conventional aqueous media the thermodynamic equilibrium of hydrol...

L. G. Butler R. G. Squires F. Reithel

1974-01-01

101

Computational investigation of the histidine ammonia-lyase reaction: a modified loop conformation and the role of the zinc(II) ion  

Microsoft Academic Search

Possible reaction intermediates of the histidine ammonia-lyase (HAL) reaction were investigated within the tightly closed\\u000a active site of HAL from Pseudomonas putida (PpHAL). The closed structure of PpHAL was derived from the crystal structure of PpHAL inhibited with l-cysteine, in which the 39–80 loop including the catalytically essential Tyr53 was replaced. This modified loop with closed\\u000a conformation was modeled using

Amalia-Laura Seff; Sarolta Pilbák; Ioan Silaghi-Dumitrescu; László Poppe

102

Gas–liquid absorption reaction between (NH 4) 2SO 3 solution and SO 2 for ammonia-based wet flue gas desulfurization  

Microsoft Academic Search

In order to investigate the characteristics of the reaction between ammonium sulfite, the main desulfurizing solution, and the flue-gas-contained sulfur dioxide during the process of ammonia-based WFGD (wet flue gas desulfurization) in a power plant, the gas–liquid absorption reaction between sulfur dioxide and an ammonium sulfite solution was studied in a stirred tank reactor. The experimental results indicate that the

Xiang Gao; Honglei Ding; Zhen Du; Zuliang Wu; Mengxiang Fang; Zhongyang Luo; Kefa Cen

2010-01-01

103

Kinetics of reactions occurring during polyurethane synthesis  

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

104

Synthesis of heterocyclic compounds using radical reactions  

Microsoft Academic Search

A generalised radical reaction has been used to synthesise heterocyclic compounds which could serve as ligands for drug discovery. Attempt also have been made to rationalise the formation of oxidation products formed during TBTH reaction.

A. K. Ganguly; C. H. Wang; M. David; P. Bartner; T. M. Chan

2002-01-01

105

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

106

Controllable synthesis of silver nanoparticle-decorated reduced graphene oxide hybrids for ammonia detection.  

PubMed

We demonstrate controllable fabrication of Ag nanoparticle (NP)-decorated reduced graphene oxide (RGO/Ag) hybrids and their application for fast and selective detection of ammonia at room temperature. Ag NPs greatly improved the sensitivity of RGO. The response time (6 s) and recovery time (10 s) are comparable with our previous Ag NP-decorated multiwalled carbon nanotube (MWCNT/Ag) NH3 sensors; however, the sensitivity is about twice that of MWCNT/Ag hybrids. We found that the loading density of NPs greatly affects the sensing performance of RGO/Ag hybrids and a proper NP loading leads to maximum sensitivity. PMID:23527378

Cui, Shumao; Mao, Shun; Wen, Zhenhai; Chang, Jingbo; Zhang, Yang; Chen, Junhong

2013-05-21

107

Ammonia toxicity, tolerance, and excretion  

Microsoft Academic Search

Ammonia is an unusual toxicant in that it is produced by, as well as being poisonous to, animals. In aqueous solution ammonia has two species, NH3 and NH4+, total ammonia is the sum of [NH3] + [NH4+] and the pK of this ammonia\\/ammonium ion reaction is around 9.5. The NH3\\/NH4+ equilibrium both internally in animals and in ambient water depends

Y. K. Ip; S. F. Chew; D. J. Randall

2001-01-01

108

Thermodynamic analysis of reactions in the system methane-ammonia-oxygen  

SciTech Connect

At the present time, the chief method for industrial production of hydrogen cyanide is oxidative ammonolysis of methane (OAM) by the reaction of CH{sub 4}, NH{sub 3}, and air over a platinum catalyst at elevated temperatures. The object of the present work was to determine the energetically most favorable mechanism for the formation of hydrogen cyanide in the oxidative ammonolysis of methane based on a thermodynamic analysis of reactions in the system CH{sub 4}-NH{sub 3}-O{sub 2}, and this is both opportune and of current interest. 9 refs., 1 fig., 4 tabs.

Grin`, G.I.; Trusov, N.V.; Dmitriev, N.M.

1992-02-20

109

Synthesis of pentafluorophenylmethylamines via silicon Mannich reaction.  

PubMed

[reaction: see text] The three-component coupling of aldehydes, secondary amines, and methoxytris(pentafluorophenyl)silane, MeOSi(C(6)F(5))(3), affording pentafluorophenylmethylamines has been described. The generation of the five-coordinate silicate intermediate is believed to be the key feature responsible for the efficiency of the reaction. PMID:15987168

Dilman, Alexander D; Belyakov, Pavel A; Korlyukov, Alexander A; Struchkova, Marina I; Tartakovsky, Vladimir A

2005-07-01

110

A controlled atmosphere in situ X-ray diffraction study of the activation and performance of ammonia synthesis catalysts derived from CeRu sub 2 , CeCo sub 2 , and CeFe sub 2  

SciTech Connect

High active ammonia synthesis catalysts derived from cerium intermetallic alloy precursors CeRu{sub 2}, CeCo{sub 2}, and CeFe{sub 2} have been studied by in situ powder X-ray diffraction (XRD) with concurrent analysis of catalytic activity. The reaction was investigated at pressures of up to 50 bar and at temperatures up to 550{degree}C. Precursor activation was carried out in pure hydrogen, N{sub 2}/H{sub 2}, and CO/H{sub 2} under various regimes of temperature and pressure. It is found that the formation of active catalysts depends upon the presence of cerium hydride and transition metal crystallites in the ultimate material, although there is no correlation between XRD-derived metal areas and chemical rates. The corresponding transition metal/cerium dioxide catalysts have a much lower activity for ammonia synthesis. The special activity of the hydride-based catalysts may arise from an intimate interaction between the support phase and the ultradispersed transition metal particles.

Walker, A.P.; Rayment, T.; Lambert, R.M. (Univ. of Cambridge (England))

1989-05-01

111

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

NASA Astrophysics Data System (ADS)

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

Arashiba, Kazuya; Miyake, Yoshihiro; Nishibayashi, Yoshiaki

2011-02-01

112

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

PubMed

The synthesis of transition metal-dinitrogen complexes and the stoichiometric transformation of their coordinated dinitrogen into ammonia and hydrazine have been the subject of considerable research, with a view to achieving nitrogen fixation under ambient conditions. Since a single example in 2003, no examples have been reported of the catalytic conversion of dinitrogen into ammonia under ambient conditions. The dimolybdenum-dinitrogen complex bearing PNP pincer ligands was found to work as an effective catalyst for the formation of ammonia from dinitrogen, with 23 equiv. of ammonia being produced with the catalyst (12 equiv. of ammonia are produced based on the molybdenum atom of the catalyst). This is another successful example of the catalytic and direct conversion of dinitrogen into ammonia under ambient reaction conditions. We believe that the results described in this Article provide valuable information with which to develop a more effective nitrogen-fixation system under mild reaction conditions. PMID:21258384

Arashiba, Kazuya; Miyake, Yoshihiro; Nishibayashi, Yoshiaki

2010-12-05

113

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

Microsoft Academic Search

The kinetics of the synthesis of ammonia from its elements over Fe\\/TiOâ, and hydrazine-pretreated alkali-promoted Fe\\/TiOâ catalysts was studied in a flow microreactor at 101 kPa pressure. The kinetic model was modified to account for deactivation of supported catalyst particles by Ostwald ripening. Pretreatment of Fe\\/TiOâ with hydrazine increased the ammonia synthesis turnover frequency by more than an order of

A. Jr. Nobile; V. V. Brunt; M. W. Jr. Davis

1991-01-01

114

Effects of carbon dioxide emission, kinetically-limited reactions, and diffusive transport on ammonia emission from manure  

Technology Transfer Automated Retrieval System (TEKTRAN)

Volatilization of ammonia (NH3) from animal manure causes significant loss of fixed N from livestock operations. Ammonia emission from manure is the culmination of biological, chemical, and physical processes, all of which are well-understood. In this work, we present a speciation and transport mode...

115

Synthesis reaction of metatitanate BaTiO 3  

Microsoft Academic Search

Thermogravimetric and X-ray diffraction analysis of the reaction mixture, during the synthesis of barium metatitanate BaTiO3 from BaCO3 and TiO2 allowed clarification of the transformation time and the role of the reaction environment: in air, the occurrence of BaTiO3 is in competition with that of orthotitanate Ba2TiO4. The latter forms between 25 and 95% of the transformation of the initial

A. Beauger; J. C. Mutin; J. C. Niepce

1983-01-01

116

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

117

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

118

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

2009-05-28

119

Reaction of Sn4(4-) in liquid ammonia: the formation of Rb6[(?(2)-Sn4)Zn(?(3)-Sn4)]·5NH3.  

PubMed

The reaction of Rb4Sn4 with ZnPh2 in liquid ammonia in the presence of [2.2.2]-cryptand yielded crystals of Rb6[(?(2)-Sn4)Zn(?(3)-Sn4)]·5NH3, which could be characterized by single crystal X-ray diffraction. This is the first example of a successful solution reaction of the highly charged tetrahedral Sn4(4-) anions. The homoleptic [E4ZnE4](6-) complex (E = tetrel element) was previously known only for E[double bond, length as m-dash]Ge and Si/Ge. PMID:24067942

Fendt, Franziska; Koch, Carina; Gärtner, Stefanie; Korber, Nikolaus

2013-10-22

120

Regioselective Reactions for Programmable Resveratrol Oligomer Synthesis  

PubMed Central

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

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

2011-01-01

121

Shock-induced chemical reactions and synthesis of binary compounds  

SciTech Connect

The results of an experimental program on shock-induced chemical reactions and synthesis of binary compounds are presented. Binary powder mixture systems that are investigated include: (1) intermetallic forming compounds (e.g., Ni--Al, Ni--Si, Nb--Si, etc.) associated with large negative heats of reaction; and (2) isomorphous (e.g., Ni--Cu) and fully immiscible (e.g., Nb--Cu) systems associated with zero (or positive) heat of reaction. The extent of shock induced chemical reactions and the type of shock synthesized compounds formed in these systems are observed to be dependent on (i) shock-loading condition, (ii) the relative volumetric distribution of the mixture constituents, and (iii) differences in respective material properties which affect relative particle flow. 5 refs., 9 figs.

Thadhani, N.N.; Advani, A.; Song, I.; Dunbar, E.; Grebe, A. (New Mexico Inst. of Mining and Technology, Socorro, NM (USA). Center for Explosives Technology Research); Graham, R.A. (Sandia National Labs., Albuquerque, NM (USA))

1990-01-01

122

Synthesis, Characterization, and Reactions of Mono and Bicyclic Phostones  

Microsoft Academic Search

Improved methods for the synthesis of 5- and 6-membered ring phostones 2 and 1 as well as original preparations of bicyclic phostones 4 (n=1,2) have been successfully executed. The preparation of the 4-membered ring 3 was more elusive, but the observed products indicated its presence as an intermediate which underwent further transformations. Reaction of 1 with 2,2,6,6-tetramethylpiperidide at low temperature,

Sheldon E. Cremer; Anthony G. Sommese; Oscar Rodriguez

1993-01-01

123

Synthesis of mesoporous silica-pillared clay by intragallery ammonia-catalyzed hydrolysis of tetraethoxysilane using quaternary ammonium surfactants as gallery templates  

Microsoft Academic Search

Mesoporous silica-pillared montmorillonite (MMT) materials were synthesized by intragallery ammonia-catalyzed hydrolysis tetraethoxysilane (TEOS). The reaction involved hydrolysis and condensation of tetraethoxysilane in the presence of intragallery surfactants templates. Powder X-ray diffraction (XRD), N2 adsorption–desorption isotherms, scanning electron microscopy (SEM) and Fourier transform infra-red (FT-IR) spectra were employed to characterize the mesoporous silica-pillared montmorillonite. These novel materials exhibited reflections corresponding to

Baoshan Li; Huihui Mao; Xiao Li; Wei Ma; Zhenxing Liu

2009-01-01

124

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

SciTech Connect

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

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

1980-09-10

125

Electrocatalytic study of ammonia synthesis and methane dimerization in high temperature solid electrolyte cells  

NASA Astrophysics Data System (ADS)

The present report covers the first year of the three year project. The work is funded 50-50 by the National Science Foundation and the Department of Energy. The NSF support started on February 15, 1989 while the DOE support started on September 15, 1989. This created some minor difficulties in the budget distribution but hopefully within the second year everything will be smoothed out. The personnel involved in the project includes the principal investigator (M. Stoukides) who devotes 25 to 30 percent of his time during the year. Douglas Eng is going to work as a research scientist in the project on a full-time basis. Dr. Eng worked under the P.I. in the area of methane oxidation and he is probably the most qualified person for this position. Mr. Po-Hung Chiang has started working as a Ph.D. candidate in the H(sup +) solid electrolyte aided study of methane dimerization. Mr. Hyatham Algahtang, a new graduate student, is the most favorite candidate for the study of NH3 synthesis. He is already examining preliminary aspects of the project. Most of the equipment required for this research was in operating condition in the laboratory. Additional equipment purchased included a Lindberg furnace that could reach as high as 1500 C for fabrication of the solid electrolyte and a Rosemount Analytical hydrogen analyzer for continuous measurement of the concentration of hydrogen on either the cathodic or the anodic side.

Stoukides, M.

1990-01-01

126

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

PubMed

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

Kajimoto, T

2000-01-01

127

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

Microsoft Academic Search

The reactions of anhydrous HBr and HCl with trans-(Mo(Nâ)â(triphos)(PRâ)), where triphos = PhP(CHâCHâPPhâ)â(PRâ = PPhâ(1), PMePhâ (2)), in tetrahydrofuran (THF) solution to produce ammonia and in benzene solution to produce hydrazine and ammonia have been examined. Complex 1 reacted with HBr in THF to produce 1.5 mol of Nâ\\/mol of 1 and routinely ca. 0.72 mol of NHâ\\/mol of 1,

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

1985-01-01

128

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

NASA Astrophysics Data System (ADS)

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

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

129

Liquid Ammonia  

Microsoft Academic Search

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

J. J. Lagowski

2007-01-01

130

Synthesis of differentially substituted hexaethynylbenzenes based on tandem Sonogashira and Negishi cross-coupling reactions.  

PubMed

[reaction: see text] Synthesis of polyethynyl-substituted aromatic compounds was achieved efficiently by the use of the Negishi cross-coupling reaction, and this method, coupled with the Sonogashira reaction, was applied to the synthesis of differentially substituted hexaethynylbenzenes from chloroiodobenzenes. PMID:11463331

Sonoda, M; Inaba, A; Itahashi, K; Tobe, Y

2001-07-26

131

Efficient intramolecular general-acid catalysis of the reactions of alpha-effect nucleophiles and ammonia oxide with a phosphate triester.  

PubMed

The S(N)2(P) reactions with alpha-effect nucleophiles of the cationic form 1.H(+) of phosphate triester diethyl 8-(N,N-dimethylamino)-1-naphthyl phosphate are catalyzed by the neighboring dimethylammonium group, with accelerations as high as 10(6). Hydroxylamine and its N-methyl and N,N-dimethyl derivatives, which react through oxygen, we presume by way of the zwitterionic ammonia oxide tautomers, are of special interest. The alpha-effect and the efficient general-acid catalysis in this system are mutually reinforcing. The alpha-effect is greater for the reactions of the triester than for the corresponding mono- and diesters and qualitatively different for hydroxylamines RR'NOH, where the likely role of the ammonia oxide tautomer NH(3)(+)-O(-) is evaluated by ab initio calculations. The initial phosphorus-containing product NH(2)OPO(OEt)(2) reacts further with hydroxylamine to generate diethyl phosphate and diimide, identified by its disproportionation to hydrazine and N(2) and its reducing potential. PMID:19159237

Kirby, Anthony J; Tondo, Daniel W; Medeiros, Michelle; Souza, Bruno S; Priebe, Jacks P; Lima, Marcelo F; Nome, Faruk

2009-02-11

132

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

133

Iminium Ion Cascade Reactions: Stereoselective Synthesis of Quinolizidines and Indolizidines  

PubMed Central

A novel iminium ion cascade reaction has been developed that allows for the stereoselective synthesis of a variety of substituted aza-fused bicycles. The combination of amino allylsilanes and aldehydes (or ketones) was used to synthesize a number of quinolizidines and indolizidines in an one-pot reaction sequence. This technology has been used to effect the facile syntheses of several indolizidine and quinolizidine natural products including, (±)-epilupinine, (±)-tashiromine, and (?)-epimyrtine. Substrate scope has been examined varying the type of amino allylsilanes (primary, secondary and conjugated) and carbonyl compounds (aldehydes and ketones) to give a variety of fused ring structures. Varying the components chosen allows for the inclusion of synthetically useful functional groups at different positions on the core structure. The methodology has been used to construct the tricyclic core structures present in the cylindricine family and halichlorine.

Amorde, Shawn M.; Jewett, Ivan T.; Martin, Stephen F.

2009-01-01

134

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.

135

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

PubMed

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

Nakagawa, Tatsunori; Stahl, David A

2013-08-30

136

Fischer-Tropsch synthesis in supercritical reaction media  

SciTech Connect

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

Subramaniam, B.

1992-10-01

137

Ammonia poisoning  

MedlinePLUS

Ammonia gas Some household cleaners Some liniments Some fertilizers Note: This list may not be all-inclusive. ... pulse, breathing rate, and blood pressure. Blood and urine tests will be done. The patient may receive: ...

138

A study on the reaction characteristics of vanadium-impregnated natural manganese oxide in ammonia selective catalytic reduction.  

PubMed

This study investigated the effect of adding vanadium (V) to natural manganese oxide (NMO) in ammonia (NH3) selective catalytic reduction (SCR). The addition of V to NMO decreased the catalytic activity at low temperatures by blocking the active site. However, the enhancement of catalytic activity was achieved by controlling NH3 oxidation at high temperatures. From the NH3 temperature programmed desorption and oxygen on/off test, it was confirmed that the amount of Lewis acid site and active lattice oxygen of the catalyst affects the catalytic performance at low temperature. PMID:21608495

Kim, Sung Su; Lee, Sang Moon; Park, Kwang Hee; Kwon, Dong Wook; Hong, Sung Chang

2011-05-01

139

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

PubMed

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

Hristov, A N; Ropp, J K

2003-07-01

140

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

SciTech Connect

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

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

1996-02-01

141

Synthesis of highly functionalized phenylalanine derivatives via cross-enyne metathesis reactions  

Microsoft Academic Search

A new method for the synthesis of constrained phenylalanine derivatives is described. In this regard, the simple synthesis of acyclic diene building blocks embodying an ?-amino acid moiety has been achieved. The diene building blocks have been prepared by cross enyne-metathesis reaction as a key step. The Diels–Alder reaction of the dienes with a dienophile such as dimethyl acetylenedicarboxilate (DMAD)

Sambasivarao Kotha; Somnath Halder; Enugurthi Brahmachary

2002-01-01

142

A unified approach for the simultaneous synthesis of reaction, energy, and separation systems  

Microsoft Academic Search

Previous studies on process integration have generally considered reaction and separation as processes that occur sequentially in a flowsheet. In this paper, a unified formalism is presented for the synthesis of reaction-separation systems, while ensuring optimal energy management. The synthesis model stems from a target-based approach for reactor networks due to an earlier study. It is shown that, by postulating

S. Balakrishna; L. T. Biegler

1993-01-01

143

Synthesis of the integrastatin nucleus using the Ramberg-Bäcklund reaction.  

PubMed

[reaction: see text] The first synthesis of the tetracyclic nucleus of the Integrastatins, natural products that have been shown to selectively inhibit HIV-1 integrase, is reported. Key steps of this synthesis involve a novel cis-selective Ramberg-Bäcklund reaction and an unusual Lewis acid-promoted cyclization step. PMID:14602020

Foot, Jonathan S; Giblin, Gerard M P; Taylor, Richard J K

2003-11-13

144

Synthesis reactions and radioactive properties of transactinoid elements  

NASA Astrophysics Data System (ADS)

It is well known that the heaviest elements of the periodic table have been synthesized in the cold fusion of magic nuclei of Pb with Z less than 26 ions. Because of dynamic limitations for fusion under strong Coulomb interaction of nuclei, the cross-sections of cold fusion reactions diminish exponentially with growing compound nucleus atomic number. For element Z = 110 produced in the reaction Pb-208(Ni-62,n)(sub 271)110, the expected cross-section is 10(exp -36) sq cm. In still more asymmetric reactions, when isotopes of actinoid elements irradiated with relatively light ions (Z less than or equal 12) are used as the target material, the compound nuclei possess an excitation energy of approx. 50 MeV. At this energy the nuclear shell effects are strongly suppressed and, as a result, in the case of hot compound nuclei of transactinoid elements the fission barrier is practically absent. The transition of these nuclei into the ground state depends strongly on the dynamic properties of the system with respect to the fission degree of freedom. Experimental studies were going on in two directions: (1) determination of the fission time by measuring the prefission neutrons (of Cf-Fm nuclei) in a wide interval of excitation energies; (2) direct synthesis of known nuclides with Z = 102-105 in reactions with ions of Ne-22, Mg-26, Al-27 and P-31 when final nuclei are produced in the ground state after the evaporation of five or six neutrons from the excited compound nuclei (E(sub x) = 50-60 MeV). The dependence of the reaction cross-section (HI, 5-6n) on the atomic number of the compound nucleus in different target-ion combinations points to the possibility of synthesizing new elements in hot fusion reactions. The advantage of these reactions arises from the use of neutron-rich nuclei like Cm-248 and Cf-249 which allows us to synthesize nuclei close to the deformed shell N = 162, for which a considerable growth of stability against spontaneous fission is predicted. Experimental set-ups and methods of detecting rare events of formation and decay of transactinide nuclei are described.

Oganessian, Yu. Ts.

1994-10-01

145

Laccase-generated quinones in naphthoquinone synthesis via Diels–Alder reaction  

Microsoft Academic Search

The tandem synthesis of naphthoquinones was conducted from the reaction of laccase-generated quinones and acyclic dienes via Diels–Alder reaction. This reaction was carried out under mild condition in aqueous medium and yielded naphthoquinones up to 80%. In addition, the effect of solvent was also investigated and water was shown to be optimal for this reaction.

Suteera Witayakran; Abdullah Zettili; Arthur J. Ragauskas

2007-01-01

146

Phosphatidylethanolamine synthesis by castor bean endosperm : a base exchange reaction.  

PubMed

A base exchange reaction for synthesis of phosphatidylethanolamine by the endoplasmic reticulum of castor bean (Ricinus comminus L. var Hale) endosperm has been examined. The calculated Michaelis-Menten constant of the enzyme for ethanolamine was 5 micromolar and the optimal pH was 7.8 in the presence of 2 millimolar CaCl(2). l-Serine, N-methylethanolamine and N,N-dimethylethanolamine all reduced ethanolamine incorporation, while d-serine and myo-inositol had little effect. These inhibitions of ethanolamine incorporation were found to be noncompetitive and ethanolamine also noncompetitively inhibited l-serine incorporation by exchange. The activity of the ethanolamine base exchange enzyme was affected by several detergents, with the best activity being obtained with the zwitterionic defjtergent 3-3-cholamidopropyl) dimethylammonio-2-hydroxyl-1-propanesulfonate. PMID:16667427

Shin, S; Moore, T S

1990-05-01

147

Effects of ammonia\\/silica molar ratio on the synthesis and structure of bimodal mesopore silica xerogel  

Microsoft Academic Search

A surfactant-templated silica xerogel with high pore volume, high porosity and narrow bimodal mesopore size distribution (designated as BMS) was synthesized by a judiciously controlled two-phase sol–gel processing under basic conditions. The properties of BMS silica mesostructure and the effect of ammonia\\/silica molar ratio on the resultant silica structure and morphology were assessed using various analytical techniques such as XRD,

Xiaozhong Wang; Wenhuai Li; Guangshan Zhu; Shilun Qiu; Dongyuan Zhao; Bing Zhong

2004-01-01

148

Integration of a turbine expander with an exothermic reactor loop—Flow sheet development and application to ammonia production  

Microsoft Academic Search

This paper investigates the direct integration of a gas turbine power cycle with an ammonia synthesis loop. Such a loop represents a typical reactor–separator system with a recycle stream and cold separation of the product from the recycle loop. The hot reaction products are expanded directly instead of raising steam in a waste heat boiler to drive a steam turbine.

I. L. Greeff; J. A. Visser; K. J. Ptasinski; F. J. J. G. Janssen

2003-01-01

149

Excited Singlet State Intermolecular Proton Transfer Reaction, Jet-Cooled Clusters, 1-naphthol/Ammonia, Mass Resolved Excitation, Threshold Photo-ionization, Emission Spectroscopy, Water Cluster Systems, Cluster Geometry  

National Technical Information Service (NTIS)

The excited singlet state intermolecular proton transfer reaction in jet-cooled clusters of 1-naphthol/ammonia and water is investigated employing mass resolved excitation, threshold photo-ionization, and emission spectroscopy. The 1-naphthol(NH3)3 cluste...

E. R. Bernstein S. Li S. K. Kim

1991-01-01

150

Infrared studies of the surface and gas phase reactions leading to the growth of titanium nitride thin films from tetrakis (dimethylamido) titanium and ammonia  

SciTech Connect

In this paper, the reaction of tetrakis (dimethylamido) titanium (Ti(NME[sub 2])[sub 4]) with ammonia is studied in the gas phase and on titanium disilicide, aluminum, and copper surfaces using infrared spectroscopy. In the gas phase the main product of this reaction, dimethylamine, forms rapidly even at 300 K, and a fine yellow powder is deposited on the windows of the IR cell. Under ultrahigh vacuum conditions there is no reaction between Ti(NMe[sub 2])[sub 4] and NH[sub 3] on any of the three surfaces studied at temperatures between 300 and 650 K. Heating pure Ti(NMe[sub 2])[sub 4] to temperatures [gt] 550K in the gas phase, leads to species that contain Ti-N-C metallacycles and N=C double bonds. The thermal decomposition of Ti(NMe[sub 2])[sub 4] on both TiSi[sub 2] and Al surfaces at temperatures up to 650 K yields films that contain titanium, nitrogen, and a significant amount of carbon. No decomposition is observed on copper; instead, molecular desorption occurs below 400 K. The authors' observations are compared with the known thermal chemistry of titanium dialkylamides in solution.

Dubois, L.H.; Zegarski, B.R. (AT and T Bell Labs., Murray Hill, NJ (United States)); Girolami, G.S. (Illinois Univ., Urbana, IL (United States). Materials Research Lab.)

1992-12-01

151

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

152

Reaction synthesis of Ni-Al based particle composite coatings  

SciTech Connect

Electrodeposited metal matrix/metal particle composite (EMMC) coatings were produced with a nickel matrix and aluminum particles. By optimizing the process parameters, coatings were deposited with 20 volume percent aluminum particles. Coating morphology and composition were characterized using light optical microscopy (LOM), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). Differential thermal analysis (DTA) was employed to study reactive phase formation. The effect of heat treatment on coating phase formation was studied in the temperature range 415 to 1,000 C. Long-time exposure at low temperature results in the formation of several intermetallic phases at the Ni matrix/Al particle interfaces and concentrically around the original Al particles. Upon heating to the 500--600 C range, the aluminum particles react with the nickel matrix to form NiAl islands within the Ni matrix. When exposed to higher temperatures (600--1,000 C), diffusional reaction between NiAl and nickel produces ({gamma})Ni{sub 3}Al. The final equilibrium microstructure consists of blocks of ({gamma}{prime})Ni{sub 3}Al in a {gamma}(Ni) solid solution matrix, with small pores also present. Pore formation is explained based on local density changes during intermetallic phase formation and microstructural development is discussed with reference to reaction synthesis of bulk nickel aluminides.

SUSAN,DONALD F.; MISIOLEK,WOICECK Z.; MARDER,ARNOLD R.

2000-02-11

153

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

SciTech Connect

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

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

2011-12-05

154

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

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

155

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

156

Methanol and ammonia from biomass  

Microsoft Academic Search

A wide variety of petrochemicals can be produced from wood first converting the wood to synthesis gas, which can then be converted to either methanol or ammonia and further processed to produce the desired chemical product. Some of the chemical derivatives that can be produced from these two basic intermediate products are summarized. Pacific Northwest Laboratory is currently developing a

E. G. Baker; L. K. Mudge; M. D. Brown

1984-01-01

157

Sorption of ammonia by copper-titanium chloride films  

SciTech Connect

This work studies the kinetics of ammonia by copper-titanium chloride films. The course of the reaction was studied with the aid of a piezoelectric quartz microbalance. An illustration shows the kinetics of ammonia sorption, and it is concluded that the kinetics of ammonia sorption by copper-titanium chloride films conform to a parabolic law and is determined by diffusion of ammonia into the films. The IR absorption spectra of the products of reaction of the films with ammonia indicate formation of complex compounds, ammines. It is also concluded that copper-titanium chloride films can be used as ammonia-sensitive coatings in piezoresonance transducers.

Kol'tsov, S.I.; Dobruskin, V.K.; Kurashvili, S.E.

1985-09-01

158

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

159

Mechanisms of renal ammonia production and protein turnover  

Microsoft Academic Search

Renal synthesis and excretion of ammonia are critical for efficient removal of acids from the body. Besides the rate of ammonia\\u000a production, the intrarenal distribution of produced ammonia is a crucial step in the renal regulation of acid-base balance.\\u000a Various acid-base disorders are associated not only with changes in ammonia production but also with its distribution between\\u000a the urine and

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

2009-01-01

160

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

Microsoft Academic Search

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

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

2005-01-01

161

Enantioselective total synthesis of ?-lactonic marine natural products, (+)-tanikolide and (?)-malyngolide, via RCM reaction  

Microsoft Academic Search

Enantioselective total synthesis of ?-lactonic marine natural products, (+)-tanikolide and (?)-malyngolide isolated from Lyngbya majuscula, was achieved by using the Sharpless asymmetric epoxidation and a ring-closing metathesis, as key reactions.

Hirotake Mizutani; Masayuki Watanabe; Toshio Honda

2002-01-01

162

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

163

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

164

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

2008-07-31

165

Synthesis of alkaloidal compounds using an electrochemical reaction as a key step  

Microsoft Academic Search

This review describes application of electroorganic reactions to synthesis of some key skeletons which are commonly found in natural alkaloids and some key intermediates which are useful materials for formation of the alkaloidal structures. The methods of synthesis are classified into three categories, namely, (1) Oxidative coupling, (2) Oxidative activation of the position to the nitrogen atom of amines and

Tatsuya Shono

166

Novel reaction route for dimethyl carbonate synthesis from CO 2 and methanol  

Microsoft Academic Search

Direct synthesis of dimethyl carbonate from CO2 and methanol was investigated at near supercritical conditions using nickel acetate as the catalyst. It was demonstrated that dimethyl carbonate could be produced as the unique product at such low temperature as 305 K and the yield was 12 times higher than that at non-supercritical conditions. The synthesis was sensitive to the reaction

Tiansheng Zhao; Yizhuo Han; Yuhan Sun

2000-01-01

167

Heteroatom directed aromatic lithiation reactions for the synthesis of condensed heterocyclic compounds  

Microsoft Academic Search

Heteroatom directed aromatic lithiation reaction is now widely used for the synthesis of condensed heterocyclic compounds. New synthesis of condensed heterocyclic compounds are now known which can provide compounds not readily available by the usual acid catalysed methods. In this chapter these newer methods and their applications to several natural products are presented. Also presented, in some cases, are other

Nurani Sivaramakrishna Narasimhan; Raghao Shivaram Mali

168

The enzymatic synthesis of glucosylmyristate as a reaction model for general considerations on ‘sugar esters’ production  

Microsoft Academic Search

‘Sugar esters’ are non-ionic biodegradable surfactant which are potentially attractive for the cosmetic and food market. Unfortunately, the formation of by-products by chemical synthesis affects the quality of the surfactant. Enzymatic synthesis is a promising and environmentally friendly approach preventing this problem but requiring a proper setting up of the reaction system (membrane reactor, azeotropic mixture, pervaporation system, etc.) for

F. Cauglia; P. Canepa

2008-01-01

169

Quality Improvement for Ammonia Emission Inventory  

Microsoft Academic Search

Ammonia gas reactions in the atmosphere are a significant source of PM2.5. Due to the increasing concentration of PM2.5 in atmosphere, the need for improved ammonia emission inventories has become an increasingly important air quality issue. A comparison is shown of ammonia inventory data from CMU (Carnegie Mellon University) based on the years 1996 and 1997, and NET99 (EPA's National

Joshua Fu; Yunhee Kim; Wayne Davis; Terry Miller

170

The plakotenins: biomimetic Diels-Alder reactions, total synthesis, structural investigations, and chemical biology.  

PubMed

The total synthesis of plakotenin, a cytotoxic marine natural product, using a biomimetic Diels-Alder reaction is described in detail. Two approaches were used, whereby the Diels-Alder reaction occurs at different stages of the synthesis. Homo- and nor-plakotenin, related natural products, were also prepared, as well as iso-plakotenin, a diastereoisomer of plakotenin. The syntheses prove the relative and absolute stereochemistry of the latter. The chemical biology of the plakotenins was investigated on selected compounds. PMID:23037572

Bourcet, Emmanuel; Kaufmann, Larissa; Arzt, Stephanie; Bihlmeier, Angela; Klopper, Wim; Schepers, Ute; Bräse, Stefan

2012-10-04

171

Click Reaction: Highly Efficient Synthesis of 2,3-Dihydroquinazolin-4(1H)-ones  

Microsoft Academic Search

In this work, condensation reaction of 2-aminobenzamide with various alkyl, aryl, and alicyclic aldehydes or ketones to 2,3-dihydroquinazolin-4(1H)-one derivatives in the presence of a catalytic amount of ammonium chloride in ethanol at room temperature is described. This reaction can be classified as a click chemical synthesis because of its high yields, short reaction times, and green and efficient reaction medium.

Ahmad Shaabani; Ali Maleki; Hamid Mofakham

2008-01-01

172

Phenylalanine ammonia-lyase in tobacco. Molecular cloning and gene expression during the hypersensitive reaction to tobacco mosaic virus and the response to a fungal elicitor.  

PubMed Central

A tobacco (Nicotiana tabacum L. cv Samsun NN) cDNA clone coding the enzyme phenylalanine ammonia-lyase (PAL) was isolated from a cDNA library made from polyadenylated RNA purified from tobacco mosaic virus (TMV)-infected leaves. Southern analysis indicated that, in tobacco, PAL is encoded by a small family of two to four unclustered genes. Northern analysis showed that PAL genes are weakly expressed under normal physiological conditions, they are moderately and transiently expressed after wounding, but they are strongly induced during the hypersensitive reaction to TMV or to a fungal elicitor. Ribonuclease protection experiments confirmed this evidence and showed the occurrence of two highly homologous PAL messengers originating from a single gene or from two tightly co-regulated genes. By in situ RNA-RNA hybridization PAL transcripts were shown to accumulate in a narrow zone of leaf tissue surrounding necrotic lesions caused by TMV infection or treatment with the fungal elicitor. In this zone, no cell specificity was observed and there was a decreasing gradient of labeling from the edge of necrosis. Some labeling was also found in various cell types of young, healthy stems and was shown to accumulate in large amounts in the same cell types after the deposition of an elicitor solution at the top of the decapitated plant.

Pellegrini, L; Rohfritsch, O; Fritig, B; Legrand, M

1994-01-01

173

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

NASA Astrophysics Data System (ADS)

Improved data on biosphere-atmosphere exchange are fundamental to understanding the production and fate of ammonia (NH3) in the atmosphere. The GRAMINAE Integrated Experiment combined novel measurement and modelling approaches to provide the most comprehensive analysis of the interactions to date. Major inter-comparisons of micrometeorological parameters and NH3 flux measurements using the aerodynamic gradient method and relaxed eddy accumulation (REA) were conducted. These showed close agreement, though the REA systems proved insufficiently precise to investigate vertical flux divergence. Grassland management had a large effect on fluxes: Emissions increased after grass cutting (-50 to 700 ng m-2 s-1 NH3) and after N-fertilization (0 to 3800 ng m-2 sammonia emission from leaf litter are identified as a priority for future research.

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

2009-01-01

174

Reaction of aromatic compounds with nucleophilic reagents in liquid ammonia. VIII. The origin of the oxygen atom of the hydroxy group in the products from the hydroxylation of 1-nitronaphthalene with alkali and molecular oxygen  

SciTech Connect

In the reaction of 1-nitronaphthalene with K/sup 18/OH and /sup 16/O/sub 2/ in liquid ammonia 1-nitro-2- and 4-nitro-1-naphthols labeled with the /sup 18/O isotope in the hydroxyl group are formed. The ratio of the isomers and the content of the /sup 18/O isotope depend on the ratio of 1-nitronaphthalene and alkali, on the temperature, and on the presence of moisture in the ammonia. The amount of the /sup 18/O isotope in the hydroxylation products indicates that in contrast to the analogous reaction of nitrobenzene and its derivatives the hydroxy function of the products in this case is formed not only from the alkali but also to a significant degree form the oxygen of the O/sub 2/.

Malykhin, E.V.; Shteingarts, V.D.

1987-10-20

175

Silicon-modified metal-ammonia reduction of fluorene  

SciTech Connect

The metal-ammonia reduction of aromatic and polynuclear aromatic compounds, known as the Birch reduction when alcohols are employed as proton sources, represents an important method for the synthesis of hydroaromatic compounds. The regiochemistry of this reduction is dictated primarily by the electron density distribution in the anionic intermediates. The authors have been exploring methods for regiochemical control in this reaction and have shown that a trimethylsilyl group can be used to alter regiochemistry, and, after its subsequent removal, afford a misoriented Birch reduction product.

Smith, W.K.; Hardin, J.N.; Rabideau, P.W. (Indiana Univ.-Purdue Univ., Indianapolis (United States))

1990-08-31

176

Sub-2 nm SnO{sub 2} nanocrystals: A reduction/oxidation chemical reaction synthesis and optical properties  

SciTech Connect

A simple reduction/oxidation chemical solution approach at room temperature has been developed to synthesize ultrafine SnO{sub 2} nanocrystals, in which NaBH{sub 4} is used as a reducing agent instead of mineralizers such as sodium hydroxide, ammonia, and alcohol. The morphology, structure, and optical property of the ultrafine SnO{sub 2} nanocrystals have been characterized by high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), differential scanning calorimetry and thermogravimetric analysis (DSC-TGA), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectroscopy. It is indicated that the uniform tetragonal ultrafine SnO{sub 2} nanocrystals with the size below 2 nm have been fabricated at room temperature. The band gap of the ultrafine SnO{sub 2} nanocrystals is about 4.1 eV, exhibiting 0.5 eV blue shift from that of the bulk SnO{sub 2} (3.6 eV). Furthermore, the mechanism for the reduction/oxidation chemical reaction synthesis of the ultrafine SnO{sub 2} nanocrystals has been preliminary presented.

Zhang Hui; Du Ning; Chen Bindi; Cui Tianfeng [State Key Lab of Silicon Materials and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Yang Deren [State Key Lab of Silicon Materials and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China)], E-mail: mseyang@zju.edu.cn

2008-11-03

177

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

Microsoft Academic Search

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

Claudia Zwingmann; Dieter Leibfritz

2005-01-01

178

Synthesis of mesoporous silica-pillared clay by intragallery ammonia-catalyzed hydrolysis of tetraethoxysilane using quaternary ammonium surfactants as gallery templates.  

PubMed

Mesoporous silica-pillared montmorillonite (MMT) materials were synthesized by intragallery ammonia-catalyzed hydrolysis tetraethoxysilane (TEOS). The reaction involved hydrolysis and condensation of tetraethoxysilane in the presence of intragallery surfactants templates. Powder X-ray diffraction (XRD), N(2) adsorption-desorption isotherms, scanning electron microscopy (SEM) and Fourier transform infra-red (FT-IR) spectra were employed to characterize the mesoporous silica-pillared montmorillonite. These novel materials exhibited reflections corresponding to a basal spacing of 4.76-5.62 nm, a uniform pore size of 3.75-4.51 nm and large surface areas of 597.2-712.4 m(2)/g. And the porous structure and physical properties of silica-pillared montmorillonite derivatives remained stable after heating for 5 h at 700 degrees C in air. Our results indicate that surfactants play a decisive role in pore formation, because they act as micelle-like template during the hydrolysis of TEOS. These mesoporous silica-pillared montmorillonite materials exhibit excellent catalytic activity and selectivity for coker gas oil cracking reaction in comparison to normal MCM-41 and Al-MCM-41. PMID:19394630

Li, Baoshan; Mao, Huihui; Li, Xiao; Ma, Wei; Liu, Zhenxing

2009-04-02

179

Synthesis and Decomposition of Zinc Iodide: Model Reactions for Investigating Chemical Change in the Introductory Laboratory  

Microsoft Academic Search

The purpose of this article is to discuss two colorful reactions not widely used by chemical educators in high schools or college chemistry laboratories: The synthesis of zinc iodide from its elements, zinc and iodine, and the subsequent decomposition of zinc iodide back into its elements. These reactions are important for chemistry teachers to know about because they can be

Stephen Demeo

1995-01-01

180

Synthesis of glycerol carbonate from glycerol and dimethyl carbonate by transesterification: Catalyst screening and reaction optimization  

Microsoft Academic Search

The synthesis of glycerol carbonate from glycerol and dimethyl carbonate by transesterification is reported. Firstly, a catalyst screening has been performed by studying the influence of different basic and acid homogeneous and heterogeneous catalysts on reaction results. Catalytic activity is extremely low for acidic catalysts indicating that reaction rate is very slow. On the contrary, high conversions and yields are

José R. Ochoa-Gómez; Olga Gómez-Jiménez-Aberasturi; Belén Maestro-Madurga; Amaia Pesquera-Rodríguez; Camilo Ramírez-López; Leire Lorenzo-Ibarreta; Jesús Torrecilla-Soria; María C. Villarán-Velasco

2009-01-01

181

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

182

Design and synthesis of chiral ligands for use in stereoselective atropisomeric biaryl coupling reactions  

Microsoft Academic Search

A new chiral ligand design program was initiated for the stereoselective synthesis of sterically hindered systems, such as atropisomeric biaryls. The concept of helical-sense discrimination was investigated, for use in the Pd-based Suzuki coupling reaction. A new set of design principles was established for chiral ligands for use in these reactions; 1) the ligand must contain a defined helical twist

Mary J Gresser

2007-01-01

183

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

184

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

Microsoft Academic Search

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

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

2009-01-01

185

Mesoporous aluminosilicate nanocage-catalyzed three-component coupling reaction: an expedient synthesis of ?-aminophosphonates  

Microsoft Academic Search

Here we demonstrate for the first time the synthesis of ?-aminophosphonates through the three-component coupling reaction of aldehydes, amines, and diethyl phosphite by using highly acidic 3D mesoporous aluminosilicate nanocage catalyst, which gave excellent yield with a high selectivity in a short reaction time due to its high acidity, 3D pores, and a huge space in the nanocages.

Ajayan Vinu; Pranjal Kalita; Veerappan V. Balasubramanian; Hamid Oveisi; Tamil Selvan; Ajayan Mano; Murugulla A. Chari; B. V. Subba Reddy

2009-01-01

186

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

187

Hydrothermal synthesis of anatase TiO2 nanorods with high crystallinity using ammonia solution as a solvent.  

PubMed

Anatase TiO2 nanorods with high crystallinity were synthesized using ammonia solution (28%) as a solvent by through the hydrothermal method. The X-ray diffraction pattern confirmed the product's anatase phase and high crystallinity, and the transmission electron microscope (TEM) image demonstrated the unique morphologies of the two ends of the TiO2 nanorods (two tringle-horn shapes and one round-horn shape), whose lengths and widths were within the ranges of 200-300 and 60-110 nm, respectively. The high-resolution TEM image clearly displayed the crystal lattices of the (101) planes lying along the direction of the lengthes of the TiO2 nanorods. The energy dispersive X-ray spectrum of a TiO2 nanorod revealed the presence of about 4 atm% nitrogen element as a trace in the anatase TiO2 nanorod. The Raman spectrum of the TiO2 nanorods also showed the typical bands of anatase TiO2 and very weak peaks resulting from the TiN first-order defect-induced Raman scattering. The UV-vis diffuse-reflectance spectra showed a slight red shift (about 3 nm) of the anatase TiO2 nanorods compared with P25, which probably resulted from the trace of TiN on the surfaces of the anatase TiO2 nanorods. A three-stage-process mechanism model is proposed for the formation of the nanorods: Rhombus crystallites bounded by four {101} faces are first formed through anisotropic growth, then longer rhombus crystallites are grown via oriented attachment, finally, nanorods with a unique morphology are self-assembled by Van Der Waals forces. PMID:22121648

Zhang, Dong Ri; Cha, Hyun Gil; Kang, Young Soo

2011-07-01

188

Ozonation of water: kinetics of oxidation of ammonia by ozone and hydroxyl radicals  

Microsoft Academic Search

A laboratory study showed that ozone-initiated oxidation of ammonia in water can result from the direct reaction of ozone with ammonia as well as from the reactions of hydroxyl radicals formed upon ozone decomposition. The direct reaction of ozone predominated at pH < 9, but in the presence of low concentrations of free ammonia, it is a slow reaction. At

Juerg Hoigne; Heinz Bader

1978-01-01

189

Room temperature formation of ammonia by oxidizing hydrogenated cerium nanoparticles in the air.  

PubMed

Ammonia formation was observed when hydrogenated cerium nanoparticles prepared by hydrogen plasma-metal reaction (HPMR) were exposed to the air at room temperature. This novel phenomenon represents a successful example of room temperature cleavage of dinitrogen and may find application in low temperature synthesis of ammonia under thermodynamically favorable conditions. A possible mechanism is also proposed. We suggest that the oxidation of cerium hydride offers chemical force to drive the hydrogen atoms out of the lattice. The monoatomic H released to the surface is highly active and readily reacts with N2 to yield ammonia. Some surface processes, which we know little about at the moment, are likely to be involved so as to lower the energy barrier of nitrogen dissociation. Further investigation is required to elucidate the detailed mechanism. PMID:16573143

Zhang, Yaohua; Liu, Tong; Wang, Zhong; Li, Yan; Li, Xingguo

2006-03-01

190

Novel Synthesis of Methyl Ketones Based on the Blaise Reaction  

Microsoft Academic Search

A facile two-step synthesis of methyl ketones from alkyl nitriles via the Blaise conversion of nitriles into ?-keto esters and acid-mediated hydrolysis followed by decarboxylation of the resulting ?-keto esters is described.

H. Surya Prakash Rao; K. Padmavathy; K. Vasantham; Shaik Rafi

2009-01-01

191

Organocatalytic cascade reactions as a new tool in total synthesis  

Microsoft Academic Search

The total synthesis of natural products and biologically active compounds, such as pharmaceuticals and agrochemicals, has reached an extraordinary level of sophistication. We are, however, still far away from the 'ideal synthesis' and the state of the art is still frequently hampered by lengthy protecting-group strategies and costly purification procedures derived from the step-by-step protocols. In recent years several new

Christoph Grondal; Matthieu Jeanty; Dieter Enders

2010-01-01

192

The enzymatic synthesis of glucosylmyristate as a reaction model for general considerations on 'sugar esters' production.  

PubMed

'Sugar esters' are non-ionic biodegradable surfactant which are potentially attractive for the cosmetic and food market. Unfortunately, the formation of by-products by chemical synthesis affects the quality of the surfactant. Enzymatic synthesis is a promising and environmentally friendly approach preventing this problem but requiring a proper setting up of the reaction system (membrane reactor, azeotropic mixture, pervaporation system, etc.) for the control of the water activity so that the enzyme efficiency is often negatively affected. In this paper, the synthesis of glucosylmyristate by Novozym 435 is taken as a model to illustrate the general features of the 'sugar esters' synthesis, with particularly regard to the influence on the synthesis of the pre-reaction treatment of the enzyme and reaction mixture, water adsorbents, reaction solvents, products and reagents. The aim is reached by placing the water adsorbents in contact with the enzyme preparation, so that high dehydration efficiency is achieved and the other factors affecting the kinetic of the synthesis are better highlighted. PMID:17399984

Cauglia, F; Canepa, P

2007-03-30

193

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

194

Construction of functional group reactivity database under various reaction conditions automatically extracted from reaction database in a synthesis design system.  

PubMed

To be able to estimate the reactivity of functional groups under certain reaction conditions, we have stored three types of data: (1) data of change or destruction of the functional groups by the conditions of the reaction conditions; (2) data showing no influence of the reaction conditions on the functional groups; and (3) data showing the relative reactivity of two functional groups in the presence of certain reaction conditions. These three types of data, considered together, form entities that are referenced as "interaction data". These interaction data are used in a synthesis design system called SYNSUP. A new module in our system has been constructed that automatically generates interaction data from the reaction databases. From 15 265 reactions in the database, our program selected 2763 useful reactions with yields of > or =90% and one functional group change. From these useful reactions, data regarding 465 interferences, 815 cases of inert functional groups (under the reaction conditions), and 62 relative rate data could be extracted. In addition, with the use of multiple relative rate datasets, the reactivity of more than two functional groups could be deduced. PMID:20187659

Tanaka, Akio; Okamoto, Hideho; Bersohn, Malcolm

2010-03-22

195

Formation of apatite oxynitrides by the reaction between apatite-type oxide ion conductors, La8+xSr2-x(Si/Ge)6O26+x/2, and ammonia  

NASA Astrophysics Data System (ADS)

Following growing interest in the use of ammonia as a fuel in solid oxide fuel cells (SOFCs), we have investigated the possible reaction between the apatite silicate/germanate electrolytes, La8+xSr2-x(Si/Ge)6O26+x/2, and NH3 gas. We examine how the composition of the apatite phase affects the reaction with ammonia. For the silicate series, the results showed a small degree of N incorporation at 600 °C, while at higher temperatures (800 °C), substantial N incorporation was observed. For the germanate series, partial decomposition was observed after heating in ammonia at 800 °C, while at the lower temperature (600 °C), significant N incorporation was observed. For both series, the N content in the resulting apatite oxynitride was shown to increase with increasing interstitial oxide ion content (x/2) in the starting oxide. The results suggest that the driving force for the nitridation process is to remove the interstitial anion content, such that for the silicates the total anion (O+N) content in the oxynitrides approximates to 26.0, the value for an anion stoichiometric apatite. For the germanates, lower total anion contents are observed in some cases, consistent with the ability of the germanates to accommodate anion vacancies. The removal of the mobile interstitial oxide ions on nitridation suggests problems with the use of apatite-type electrolytes in SOFCs utilising NH3 at elevated temperatures.

Orera, A.; Headspith, D.; Apperley, D. C.; Francesconi, M. G.; Slater, P. R.

2009-12-01

196

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

197

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

2007-04-25

198

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

199

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

200

Characterization of a thermostable methylaspartate ammonia lyase from Carboxydothermus hydrogenoformans.  

PubMed

Methylaspartate ammonia lyase (MAL; EC 4.3.1.2) catalyzes the reversible addition of ammonia to mesaconate to give (2S,3S)-3-methylaspartate and (2S,3R)-3-methylaspartate as products. MAL is of considerable biocatalytic interest because of its potential use for the asymmetric synthesis of substituted aspartic acids, which are important building blocks for synthetic enzymes, peptides, chemicals, and pharmaceuticals. Here, we have cloned the gene encoding MAL from the thermophilic bacterium Carboxydothermus hydrogenoformans Z-2901. The enzyme (named Ch-MAL) was overproduced in Escherichia coli and purified to homogeneity by immobilized metal affinity chromatography. Ch-MAL is a dimer in solution, consisting of two identical subunits (?49 kDa each), and requires Mg(2+) and K(+) ions for maximum activity. The optimum pH and temperature for the deamination of (2S,3S)-3-methylaspartic acid are 9.0 and 70°C (k (cat)?=?78 s(-1) and K (m)?=?16 mM). Heat inactivation assays showed that Ch-MAL is stable at 50°C for >4 h, which is the highest thermal stability observed among known MALs. Ch-MAL accepts fumarate, mesaconate, ethylfumarate, and propylfumarate as substrates in the ammonia addition reaction. The enzyme also processes methylamine, ethylamine, hydrazine, hydroxylamine, and methoxylamine as nucleophiles that can replace ammonia in the addition to mesaconate, resulting in the corresponding N-substituted methylaspartic acids with excellent diastereomeric excess (>98% de). This newly identified thermostable MAL appears to be a potentially attractive biocatalyst for the stereoselective synthesis of aspartic acid derivatives on large (industrial) scale. PMID:22005738

Raj, Hans; Puthan Veetil, Vinod; Szymanski, Wiktor; Dekker, Frank J; Quax, Wim J; Feringa, Ben L; Janssen, Dick B; Poelarends, Gerrit J

2011-10-18

201

Dihydroazolopyrimidines with a nodal nitrogen atom: Synthesis, reactions, tatutomerism (review)  

Microsoft Academic Search

The published data on methods of synthesis of dihydro derivatives of azolopyrimidines with a nodal nitrogen atom are generalized; their applicability is comparatively analyzed. The chemical properties of dihydroazolopyrimidine systems are examined; the intra- and intermolecular factors that determine the position of imine—enamine tautomeric equilibrium are analyzed.

S. M. Desenko

1995-01-01

202

Fischer-Tropsch synthesis in supercritical reaction media  

SciTech Connect

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

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

1993-01-01

203

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

2013-04-17

204

Synthesis of reactive distillation systems with multiple equilibrium chemical reactions  

Microsoft Academic Search

The authors describe a procedure to determine the feasibility of separating mixtures with multiple equilibrium chemical reactions by reactive distillation. The method involves describing the system in terms of new composition coordinates which represent the reactive system in a lower dimensional composition space. The justification for these new variables is that when equilibrium chemical reactions occur in a mixture, the

Sophie Ung; Michael F. Doherty

1995-01-01

205

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

PubMed

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

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

2013-07-25

206

Facile synthesis of photo-cleavable polymers via Passerini reaction.  

PubMed

Passerini three-component reaction and multicomponent polymerization (MCP) were demonstrated to be facile methods for the preparation of photo-cleavable polymers, photo- and redox-dually cleavable polymers, as well as block copolymers. PMID:23945608

Li, Lei; Lv, An; Deng, Xin-Xing; Du, Fu-Sheng; Li, Zi-Chen

2013-08-27

207

Synthesis of the decalin core of codinaeopsin via an intramolecular Diels-Alder reaction.  

PubMed

We describe the synthesis of the decalin core of codinaeopsin (1), a tryptophan-polyketide hybrid natural product with promising antimalarial activity (IC50 4.7 ?M, against Plasmodium falciparum), via an intramolecular Diels-Alder (IMDA) reaction. A convergent synthesis was developed to prepare the precursors for the IMDA reaction in 10 steps. The exo cycloadducts were derived from thermal, IMDA reactions of the substrates containing a Weinreb amide or ester conjugated dienophile, and the endo adducts were from Lewis acid promoted reactions of the substrates with a formyl group. Both exo and endo products of the IMDA were exclusively isolated and characterized by NMR spectroscopy. One endo cycloadduct was further confirmed with X-ray crystallography. Theoretical calculations reveal the influence of the substituents of the decalin core on the IMDA process. PMID:23649407

Ramanathan, Mani; Tan, Chun-Jui; Chang, Wen-Jung; Tsai, Hui-Hsu Gavin; Hou, Duen-Ren

2013-06-21

208

Low-temperature synthesis of LiBH4 by gas-solid reaction.  

PubMed

The solvent-free synthesis of LiBH(4) from LiH in a borane atmosphere at 120 degrees C and ambient pressures is demonstrated. The source of borane is a milled LiBH(4)/ZnCl(2) mixture, in which Zn(BH(4))(2) is generated by a metathesis reaction. The yield of the reaction of about 74 % LiBH(4) shows that a bulk reaction is taking place upon borane absorption by LiH. This indicates that the formation of B-H bonds is the limiting step for the formation of LiBH(4) from the elements. Therefore, the use of diborane as a starting reactant allows one to circumvent the reaction barrier for the B-B bond dissociation and explains the rather moderate synthesis conditions. PMID:19373797

Friedrichs, Oliver; Borgschulte, Andreas; Kato, Shunsuke; Buchter, Florian; Gremaud, Robin; Remhof, Arndt; Züttel, Andreas

2009-01-01

209

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

210

Chemoselective Michael reactions on pyroglutamates. Expeditious synthesis of spiro-bis-?-lactams as ?-turn peptidomimetics  

Microsoft Academic Search

Starting from pyroglutamic acid, the synthesis of spiro-bis-?-lactams, using as key step a chemoselective Michael reaction of pyroglutamates is reported. Thus, the reaction of N-BOC-l-methyl pyroglutamate with LiHMDS gives the enolates at C4 which react with several Michael acceptors. On the other hand, N-benzyl-l-methyl pyroglutamate reacts under the same conditions, to give the ester enolate which reacts with Michael acceptors

Miguel F Braña; Mar??a Garranzo; Beatriz de Pascual-Teresa; Javier Pérez-Castells; Mar??a Rosario Torres

2002-01-01

211

Efficient synthesis of hydroxyl isoindolones by a pd-mediated c?h activation/annulation reaction.  

PubMed

Radical reaction: A convenient synthesis of hydroxyl isoindolones by a Pd-catalyzed C?H activation/annulation reaction with near "click chemistry" efficiency is presented (see scheme; TBHP=tert-butyl hydrogen peroxide). This methodology features short reaction times (10-30?min), high atom economy, wide substrate scope (22 examples), and good reaction yields (up to 93?%). PMID:23843382

Yu, Qingzhen; Zhang, Nana; Huang, Jianhui; Lu, Shaonan; Zhu, Yi; Yu, Xiaoxiao; Zhao, Kang

2013-07-10

212

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

213

A catalytic multicomponent coupling reaction for the enantioselective synthesis of spiroacetals.  

PubMed

The first multicomponent catalytic asymmetric synthesis of spiroacetals has been described. Hybrid molecules comprising a spiroacetal scaffold (a natural-product inspired scaffold) and an ?-amino acid motif (a privileged fragment) are easily available through a gold phosphate-catalysed one-pot three component coupling reaction of alkynols, anilines and glyoxylic acid. PMID:23435368

Cala, Lara; Mendoza, Abraham; Fañanás, Francisco J; Rodríguez, Félix

2013-04-01

214

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

215

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

216

Synthesis and reaction of phthaloyl peroxide derivatives, potential organocatalysts for the stereospecific dihydroxylation of alkenes  

Microsoft Academic Search

To improve the synthesis and reactivity of phthaloyl peroxide derivatives a method has been developed using sodium percarbonate and phthaloyl chlorides. The reactions of the new phthaloyl peroxide derivatives with trans-stillbene as well as the improved reactivity of 3,4-dichlorophthaloyl peroxide with a variety of alkenes are reported.

Changxia Yuan; Abram Axelrod; Michael Varela; Laura Danysh; Dionicio Siegel

2011-01-01

217

Synthesis, characterisation, and oxygen atom transfer reactions involving the first gold(i)-alkylperoxo complexes.  

PubMed

The synthesis of a new class of organogold species containing a peroxo moiety is reported. Complexes [Au(IPr)(OO(t)Bu)] and [Au(SIPr)(OO(t)Bu)] have been synthesised via a straightforward methodology using the parent gold(i) hydroxide complexes as synthons. These complexes have been successfully used in oxygen-transfer reactions to triphenylphosphine. PMID:24107923

Collado, Alba; Gómez-Suárez, Adrián; Oonishi, Yoshihiro; Slawin, Alexandra M Z; Nolan, Steven P

2013-10-22

218

Possible genotoxicity of melanin synthesis intermediates: Tyrosinase reaction products interact with DNA in vitro  

Microsoft Academic Search

The actual cellular target of the cytotoxic intermediates of melanin synthesis is not yet known. In the present paper it is shown that eukaryotic DNA binds in vitro to soluble reaction products of tyrosinase (EC 1.14.18.1) and is physically modified, as ascertained by the following criteria: (a) buoyant density in cesium chloride density gradients; (b) polyacrylamide gel electrophoresis: (c) deoxyribonuclease

M. Miranda; D. Botti; M. Cola

1984-01-01

219

Intramolecular Alkene Carboamination Reactions for the Synthesis of Enantiomerically Enriched Tropane Derivatives  

PubMed Central

The synthesis of tropane derivatives via intramolecular Pd-catalyzed alkene difunctionalization reactions is described. Enantiopure N-aryl-?-aminoalkenes bearing an aryl or alkenyl halide adjacent to the amino group were converted to benzo- or cycloalkenyl-fused tropane products in good yield and with no loss of enantiopurity.

Schultz, Danielle M.; Wolfe, John P.

2011-01-01

220

Synthesis and reactions of some new pyrrolylthieno[2,3-D]quinoxaline and pyrrolopyrazinothienoquinoxalines.  

PubMed

The synthesis of 3-pyrrolyl-2-substituted thieno[2,3-b]quinoxalines from the precursor 3-amino derivatives are described. Synthesized compounds were subjected to reactions with other reagents to synthesize poly-fused heterocyclic incorporated thienoquinoxaline moiety. Some of the synthesized compounds were screened for their antibacterial and antifungal activities. PMID:23342493

Geies, Ahmed A; Elossaily, Yasser A; Moustafa, Osama Sh

221

Tandem ring-closing metathesis/isomerization reactions for the total synthesis of violacein.  

PubMed

A series of 5-substituted 2-pyrrolidinones was synthesized through a one-pot ruthenium alkylidene-catalyzed tandem RCM/isomerization/nucleophilic addition sequence. The intermediates resulting from RCM/isomerization showed reactivity toward electrophiles in aldol condensation reactions which provided a new entry for the total synthesis of the antileukemic natural product violacein. PMID:23550830

Petersen, Mette T; Nielsen, Thomas E

2013-04-03

222

Fabrication and simultaneous bonding of metal matrix composite by combustion synthesis reaction  

Microsoft Academic Search

The combustion synthesis and bonding of TiB2\\/Cu composite were simultaneously performed in a single process. The heat of reaction of TiB2 formation was high enough to form the bonded interface between the composite and an aluminum rod. Intermetallic compounds consisting of copper and aluminum were observed at the interface.

Y. J. Kwon; M. Kobashi; T. Choh; N. Kanetake

2004-01-01

223

Construction materials for reaction unit in the liquid-phase synthesis of propylene oxide  

Microsoft Academic Search

The main components of the reaction medium in equipment for the synthesis of propylene oxide by liquid-phase oxidation of gaseous propylene with peracetic acid are propylene, peracetic acid, ethyl acetate, acetic acid, propylene oxide, carbon dioxide, oxygen, methane, and propylene glycol acetates. The operating conditions of the equipment and content of the main components of the medium are shown. Results

V.-I. D. Zaritskii; V. I. D

1987-01-01

224

Highly stereoselective synthesis of trisubstituted cyclohexanols using a guanidine-catalyzed tandem Henry-Michael reaction.  

PubMed

A highly diastereoselective (dr >99:1) and enantioselective (ee value up to 98%) synthesis of trisubstituted cyclohexanols was achieved by using a tandem Henry--Michael reaction between nitromethane and 7-oxo-hept-5-enals catalyzed by the Misaki-Sugimura guanidine. PMID:23544418

Dai, Qipu; Huang, Huicai; Zhao, John Cong-Gui

2013-04-09

225

A convenient route for the synthesis of hydroxyapatite through a novel microwave-mediated metathesis reaction  

Microsoft Academic Search

Microwave synthesis of ceramics offers the advantage of efficient transformation of energy and heating throughout the volume efficiently in a shorter period. In this communication, we report the first example of a novel metathesis reaction performed in the presence of microwave irradiation. Nanocrystaline particles of hydroxyapatite (HAP) could be readily synthesized by microwave treatment of calcium chloride (CaCl2) and sodium

Purnendu Parhi; A. Ramanan; Alok R. Ray

2004-01-01

226

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

227

Synthesis of (2-alkylthiothiazolin-5-yl)methyl dodecanoates via tandem radical reaction.  

PubMed

A series of (2-alkylthiothiazolin-5-yl)methyl dodecanoates was synthesized from various alkyl N-allylcarbamodithioates and dilauroyl peroxide via a tandem radical hydrogen-abstraction-cyclization-substitution/combination reaction with a 5-exo-trig radical cyclization as a key step. The current route is the first, convenient, and efficient synthesis of (2-alkylthiothiazolin-5-yl)methanol derivatives. PMID:23857510

Kakaei, Saeed; Xu, Jiaxi

2013-09-01

228

Organoberyllium compounds and their chemical reactions. XI. Synthesis of diacetylhydrobenzoins  

SciTech Connect

The authors previously determined that the reaction of aromatic aldehydes with acylhaloberyllium in ethyl acetate lead to the formation of stilbene. In this same vein they have found that the final products of this reaction can include not only stilbenes but also diacetylhydrobenzoin and that the product is determined by the nature of the solvent. In this paper they determine that while ethyl acetate indeed leads to the stilbene the use of an ether--diethyl or diisopropyl--leads to diacetylhydrobenzoin. NMR spectroscopy is used to ascertain the structure of the product.

Lapkin, I.I.; Sinani, S.V.

1987-08-10

229

Synthesis of various shapes of titanate nanoparticles via hydrothermal reaction  

NASA Astrophysics Data System (ADS)

Various shapes and aspect ratio of titanate nanoparticles have been synthesized via a one-pot synthetic method involving an autoclave system using irregularly shaped anatase nanopowder. The influence of reaction conditions such as raw material concentration, temperature, pressure and reaction time to the particle morphology have been studied systematically. The particles were characterized by FESEM, EDX, TEM, HRTEM and XRD. Ultrahigh aspect ratio titanate particles with the length of up to hundreds of micrometers have been observed. The XRD result shows that the nanorods synthesized are of mixed phases.

Tan, Kim Song; Riley, Jason

2012-11-01

230

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

231

Synthesis of three kinds of GaN nanowires through Ga2O3 films’ reaction with ammonia  

NASA Astrophysics Data System (ADS)

A new method was employed to obtain GaN nanowires (NWs). In this method, SiC films were deposited with radio frequency (r.f.) magnetron sputtering onto silicon substrates and annealed at high temperature, and then Ga2O3 films were deposited on top of the SiC intermediate layers and annealed in NH3 atmosphere. SiC layer was used to reduce thermal and lattice mismatch between GaN and Si, and improve NWs’ quality. After Ga2O3 films reacted with NH3, a great quantity of GaN NWs with the shape of birch trunks and stalactites were found by transmission electron microscopy (TEM). At the same time, a few very even and uniform pillarlike NWs were observed. The electron diffraction patterns (EDP) show that birch trunk-shaped and pillarlike NWs are all single-crystalline structures. These NWs were also analyzed with the assistance of X-ray diffraction (XRD), Fourier transformed infrared spectra (FTIR) and high-resolution transmission electron microscopy (HRTEM) to show their properties.

Dong, Zhihua; Xue, Chengshan; Zhuang, Huizhao; Wang, Shuyun; Gao, Haiyong; Tian, Deheng; Wu, Yuxin; He, Jianting; Liu, Yi'An

2005-03-01

232

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...

233

Synthesis of phenyl-adducted cyclodextrin through the click reaction  

Microsoft Academic Search

A new derivative of ?-cyclodextrin (CD) has been made incorporating the phenyl group through the use of click reaction. The resulting product suggests a self-association phenomenon through the formation of inclusion compound between the phenyl group and CD. The product has been characterized by 1H and 13C NMR spectroscopy.

Atanu Biswas; H. N. Cheng; G. W. Selling; J. L. Willett; D. F. Kendra

2009-01-01

234

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

235

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

236

Synthesis of layered sodium lanthanum selenide through ion exchange reactions  

SciTech Connect

Layered hexagonal KLaSe2 ({alpha}-NaFeO{sub 2}-type) was synthesized using the reactive flux method and analyzed by powder XRD to determine its lattice constants (space group R-3m, a = 4.40508(5) A, c = 22.7838(5) A). NaLaSe{sub 2}, which normally crystallizes as a disordered rock salt structure with mixed Na+/La + 3 sites, was synthesized through a solid state ion exchange reaction at 585 deg. C from a 1:3 molar ratio mixture of KLaSe{sub 2}:NaI. The product of this reaction was hexagonally layered NaLaSe{sub 2} (space group R-3m, a = 4.3497(3) A, c = 20.808(2) A) isostructural to KLaSe{sub 2}. This product was analyzed by comparison with members of the set of solid solutions Na{sub (1-x)}K{sub (x)}LaSe{sub 2} to confirm that the extent ion exchange in this reaction was complete. Cubic (disordered) NaLaSe{sub 2} was also reacted with KI to yield the poorly crystalline hexagonally layered product with the approximate formula Na{sub 0.79}K{sub 0.21}LaSe{sub 2}.

Butts, Laura J.; Strickland, Nicholas [Department of Chemistry, Texas State University - San Marcos, 601 University Drive, San Marcos, TX 78666 (United States); Martin, Benjamin R. [Department of Chemistry, Texas State University - San Marcos, 601 University Drive, San Marcos, TX 78666 (United States)], E-mail: bmartin@txstate.edu

2009-04-02

237

Formation of apatite oxynitrides by the reaction between apatite-type oxide ion conductors, La{sub 8+x}Sr{sub 2-x}(Si/Ge){sub 6}O{sub 26+x/2}, and ammonia  

SciTech Connect

Following growing interest in the use of ammonia as a fuel in solid oxide fuel cells (SOFCs), we have investigated the possible reaction between the apatite silicate/germanate electrolytes, La{sub 8+x}Sr{sub 2-x}(Si/Ge){sub 6}O{sub 26+x/2,} and NH{sub 3} gas. We examine how the composition of the apatite phase affects the reaction with ammonia. For the silicate series, the results showed a small degree of N incorporation at 600 deg. C, while at higher temperatures (800 deg. C), substantial N incorporation was observed. For the germanate series, partial decomposition was observed after heating in ammonia at 800 deg. C, while at the lower temperature (600 deg. C), significant N incorporation was observed. For both series, the N content in the resulting apatite oxynitride was shown to increase with increasing interstitial oxide ion content (x/2) in the starting oxide. The results suggest that the driving force for the nitridation process is to remove the interstitial anion content, such that for the silicates the total anion (O+N) content in the oxynitrides approximates to 26.0, the value for an anion stoichiometric apatite. For the germanates, lower total anion contents are observed in some cases, consistent with the ability of the germanates to accommodate anion vacancies. The removal of the mobile interstitial oxide ions on nitridation suggests problems with the use of apatite-type electrolytes in SOFCs utilising NH{sub 3} at elevated temperatures. - Graphical abstract: In this paper we show that heating the apatite-type electrolytes La{sub 8+x}Sr{sub 2-x}(Si/Ge){sub 6}O{sub 26+x/2} in NH{sub 3} at high temperatures leads to nitridation of the electrolyte, with the level of nitridation increasing with increasing x.

Orera, A. [School of Chemistry, University of Birmingham, Birmingham B15 2TT (United Kingdom); Headspith, D. [Department of Chemistry, University of Hull, Cottingham Road, Hull (United Kingdom); Apperley, D.C. [Department of Chemistry, Durham University, South Road, Durham DH1 3LE (United Kingdom); Francesconi, M.G. [Department of Chemistry, University of Hull, Cottingham Road, Hull (United Kingdom); Slater, P.R., E-mail: p.r.slater@bham.ac.u [School of Chemistry, University of Birmingham, Birmingham B15 2TT (United Kingdom)

2009-12-15

238

Formamide-based prebiotic synthesis of nucleobases: a kinetically accessible reaction route.  

PubMed

Synthesis of nucleobases in nonaqueous environments is an alternative way for the emergence of terrestrial life, which could solve the fundamental problem connected to the hydrolytic instability of nucleic acid components in an aqueous environment. In this contribution, we present a plausible reaction route for the prebiotic synthesis of nucleobases in formamide, which does not require participation of the formamide trimer and aminoimidazole-carbonitrile intermediates. The computed activation energy of the proposed pathway is noticeably higher than that of the HCN-based synthetic route, but it is still feasible under the experimental conditions of the Saladino synthesis. We show that, albeit both the pyrimidine and purine ring formation utilizes the undissociated form of formamide, the dehydration product of formamide, HCN, may also play a key role in the mechanism. The rate determining step of the entire reaction path is the cyclization of the diaza-pentanimine precursor. The subsequent formation of the imidazole ring proceeds with a moderate activation energy. Our calculations thus demonstrate that the experimentally suggested reaction path without the involvement of aminoimidazole-carbonitrile intermediates is also a viable alternative for the nonaqueous synthesis of nucleobases. PMID:22129168

Šponer, Judit E; Mládek, Arnošt; Šponer, Ji?í; Fuentes-Cabrera, Miguel

2011-12-14

239

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

PubMed

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

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

2003-03-01

240

Tandem reactions for streamlining synthesis: enantio- and diastereoselective one-pot generation of functionalized epoxy alcohols.  

PubMed

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

Hussain, Mahmud M; Walsh, Patrick J

2008-08-01

241

Single-step ugi multicomponent reaction for the synthesis of phosphopeptidomimetics.  

PubMed

This article describes the design and optimization of an effective microwave-assisted multicomponent reaction to produce a novel class of phosphopeptidomimetic compounds. When using aminophosphonic acids (?, ?, ?), aldehydes, and isocyanides as reactants and alcohols as solvents, these building blocks are merged to functionalized amido-aminophosphonate structures in a novel Ugi-type one-pot transformation reaction. A high level of structural diversity can be achieved with this synthetic approach, providing a platform for the production of functionalized building blocks for novel bioactive molecules. The general scope of this multicomponent synthetic protocol is explored by variation of reaction parameters together with an evaluation of a diverse set of reaction substrates. The applicability of this reaction has been demonstrated by the synthesis of 17 distinct compounds giving yields in the range of 20-92%. PMID:24053467

Gargano, Andrea F G; Buchinger, Stefanie; Kohout, Michal; Lindner, Wolfgang; Lämmerhofer, Michael

2013-10-08

242

Ammonia Concentration in Porcine Ovarian Developing Follicles  

Microsoft Academic Search

An experiment was conducted to investigate pH, osmolality, and the concentration of ammonia, total protein, glutamine and glutamic acid in follicular fluid at different developmental stages (<2, 3-4 and 5-6 mm in diameter) and serum of porcine. The concentrations of ammonia and total protein content were determined with the catalyzed indophenols reaction and the Bradford assay method and read on

K. M. A. Tareq; Ryuichiro Obata; A. G. Miah; Ko-ichi Hammano; Hirotada Tsujii

2005-01-01

243

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

244

Hydrodenitrogenation chemistry. I. Cleavage of alkylcarbon-nitrogen bonds, methane and ammonia formation in the HDN reaction of 1,2,3,4-tetrahydroquinoline with a nickel oxide catalyst supported on silica/alumina  

SciTech Connect

The hydrodenitrogenation reaction (HDN) is one of the most important industrial processes used in the refining of petroleum feedstocks and involves the removal of the nitrogen atom, as ammonia, from polynuclear heteroaromatic nitrogen compounds at high temperatures and high pressures of hydrogen gas (350-500/sup 0/C and 2000 psi). It is interesting to note that most of the reported heterogeneous catalysts require the complete hydrogenation of both the nitrogen heterocyclic ring and the aromatic ring before carbon-nitrogen bond cleavage can occur. A major breakthrough in the technical and economic aspects of the HDN reaction would take place if, in fact a catalyst could be found that would selectively cleave the C-N bond din the saturated nitrogen ring and subsequently produce ammonia, without substantial reduction of the aromatic rings, at lower temperatures as well as lower pressures of hydrogen gas. In this note, the authors report on a highly loaded nickel oxide catalyst (50% by weight Ni), supported on silica/alumina, that will effectively provide some of the criteria for an ideal HDN catalyst. 8 references.

Fish, R.H.; Thormodsen, A.D.; Moore, R.S.; Perry, D.L.; Heinemann, H.

1986-11-01

245

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

246

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

247

Silver-catalyzed tandem synthesis of naphthyridines and thienopyridines via three-component reaction.  

PubMed

An efficient approach for the silver-catalyzed regioselective tandem synthesis of highly functionalized 1,2-dihydrobenzo[1,6]naphthyridines 6a-z and 7a-e by the reaction of ortho-alkynylaldehydes 3a-n with amines 4a-d and ketones 5a-c/active methylene compounds 5d-g, under mild reaction conditions, is described. The scope of the developed chemistry was successfully extended for the direct synthesis of 1,2-dihydrobenzo[4,5]thieno[2,3-c]pyridines 8a-e, which is known as the sulfur analogue of ?-carbolines. Naphthyridines 6a-z and thienopyridines 8a-e were obtained via dual activation concept using l-proline as organocatalyst; however, naphthyridines 7a-e were synthesized without using organocatalyst. The reaction shows selective N-C bond formation on the more electrophilic alkynyl carbon, resulting in the regioselective 6-endo-dig-cyclized products. Reactivity behavior of electron-deficient and electron-rich ortho-alkynylaldehydes in the synthesis of naphthyridines and thienopyridine by three-component reaction is supported by the control experiment. PMID:23565804

Verma, Akhilesh K; Kotla, Siva K Reddy; Choudhary, Deepak; Patel, Monika; Tiwari, Rakesh K

2013-04-17

248

Combustion synthesis of advanced materials: Studies of the influence of gravity and reaction kinetics  

NASA Astrophysics Data System (ADS)

Combustion synthesis is an attractive technique to synthesize a wide variety of advanced materials that include powders and near-net shape products of ceramics, intermetallics, composites and functionally gradient materials. It is also considered to be a valuable method for space applications, because of low energy requirements and simple equipment. However, it is necessary to understand how microgravity influences the combustion mechanism and properties of the synthesized materials. In this work, combustion synthesis experiments were conducted both in normal and in low-gravity conditions, using a unique setup designed and developed for this purpose. Microgravity experiments were done in NASA Lewis Research Center using Drop Tower which provided 2.2 s of 10-5 g level, as well as on-board DC-9 aircraft (20 s of 10-2 g). It was clearly demonstrated that gravity plays an important role during combustion synthesis. It significantly influences both the combustion and structure formation processes. It was also shown that microgravity conditions allow the synthesis of materials with improved micro- and macrostructures. The study of chemical reaction kinetics in combustion synthesis systems is of critical importance. The measurement of kinetic parameters (especially activation energy) and a comparison with known elementary processes provides an insight into the controlling step of the mechanism. In this work, a computer-assisted electrothermography method was developed to determine the intrinsic kinetics of reactions under conditions similar to those realized during combustion synthesis of materials. This technique was applied to investigate the kinetics and other features associated with the reaction of titanium with nitrogen at 1 atm pressure. It was shown that at temperatures below the melting point of titanium, the reaction follows parabolic rate law. The obtained activation energy value is in good agreement with literature data. At higher temperatures, however, the reaction mechanism is different due to faster diffusion of nitrogen in molten titanium. Mathematical treatment of experimentally obtained heat generation curves allowed to estimate the diffusion coefficient of nitrogen in molten titanium. In addition, the reaction rate was shown to depend strongly on the heating rate.

Pelekh, Aleksey Yevgeuyevich

249

THE PRODUCTION OF CHEMICALS FROM REACTORS. PART VI. ANHYDROUS HYDRAZINE FROM THE PILE AND FISSION FRAGMENT IRRADIATION OF LIQUID AMMONIA  

Microsoft Academic Search

Experiments are described on the synthesis of hydrazine liquid ammonia ; under pile radiation and fission fragbombardment. The yields of hydrazfne were ; found to respectively 0.11 and 1.10 molecules per 100 ev deposited in the ammonia. ; (auth);

D. A. Landsman; C. M. Noble

1961-01-01

250

Stereoselective synthesis of 4-dehydroxydiversonol employing enantioselective palladium-catalysed domino reactions.  

PubMed

The stereoselective synthesis of 4-dehydroxydiversonol (4) employing enantioselective palladium-catalysed domino processes such as the domino Wacker-Heck and the domino Wacker-carbonylation reaction for the formation of the central chroman moiety is described. Thus, reaction of 8 with palladium(II) trifluoroacetate [Pd(OTFA)2] in the presence of carbon monoxide, methanol and the 2,2'- bis(oxazolin-2-yl)-1,1'-binaphthyl (BOXAX) ligand 17 led to 19 in 80% yield and 96% ee. Similarly, the chroman 7 was prepared using 8 and methyl acrylate (9) as starting material. Hydrogenation of the double bond, oxidation of the benzylic methylene group and intramolecular acylation of chromanone 6 provided the tetrahydroxanthenone core 5, from which the synthesis of 4 was completed. The relative configuration of 4 could be established by crystal structure analysis. PMID:18698572

Tietze, Lutz F; Spiegl, Dirk A; Stecker, Florian; Major, Julia; Raith, Christian; Grosse, Christian

2008-01-01

251

A biomimetic domino reaction for the concise synthesis of capreomycidine and epicapreomycidine.  

PubMed

The non-proteinogenic amino acids capreomycidine and epicapreomycidine are constituents of antibiotically active natural products, but the synthesis of these unusual cyclic guanidine derivatives is challenging. The biosynthesis of capreomycidine has therefore been employed as a guideline to develop a concise biomimetic synthesis of both epimeric amino acids. The resulting domino-guanidinylation-aza-Michael-addition reaction provides the most convenient access to these amino acids in racemic form. Attempts to dissect the domino reaction into two separate transformations for a stereocontrolled version of this synthetic approach have also been made. The synthesized didehydro-arginine derivatives with urethane-protected guanidine moieties did not undergo the aza-Michael-addition anymore. These results may have wider implications for the 1,4-addition of guanidines to ?,?-unsaturated carbonyl compounds, particularly to didehydro amino acids. PMID:22619064

Büschleb, Martin; Granitzka, Markus; Stalke, Dietmar; Ducho, Christian

2012-05-23

252

EFFECT OF VFA ON AMMONIA UTILIZATION FOR AMINO ACID AND UREA SYNTHESIS BY RUMINAL EPITHELIAL AND DUODENAL MUCOSAL CELLS ISOLATED FROM GROWING SHEEP  

Technology Transfer Automated Retrieval System (TEKTRAN)

The objective was to determine effects of VFA on the extent of assimilation of ammonia N into amino acids and urea by isolated ruminal epithelial (REC) and duodenal mucosal cells (DMC) in short-term incubations. Cells were isolated from growing Polypay ram lambs (n=4) fed a mixed forage-concentrate ...

253

Silicon-based cross-coupling reactions in the total synthesis of natural products.  

PubMed

Unlike other variants of transition-metal-catalyzed cross-coupling reactions, those based on organosilicon donors have not been used extensively in natural product synthesis. However, recent advances such as: 1) the development of mild reaction conditions, 2) the expansion of substrate scope, 3) the development of methods to stereoselectively and efficiently introduce the silicon-containing moiety, 4) the development of a large number of sequential processes, and 5) the advent of bifunctional bis(silyl) linchpin reagents, signify the coming of age of silicon-based cross-coupling reactions. The following case studies illustrate how silicon-based cross-coupling reactions play a strategic role in constructing carbon-carbon bonds in selected target molecules. PMID:20333628

Denmark, Scott E; Liu, Jack H-C

2010-04-12

254

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

2013-02-14

255

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

DOEpatents

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

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

2004-12-14

256

Synthesis and Decomposition of Zinc Iodide: Model Reactions for Investigating Chemical Change in the Introductory Laboratory  

NASA Astrophysics Data System (ADS)

The purpose of this article is to discuss two colorful reactions not widely used by chemical educators in high schools or college chemistry laboratories: The synthesis of zinc iodide from its elements, zinc and iodine, and the subsequent decomposition of zinc iodide back into its elements. These reactions are important for chemistry teachers to know about because they can be performed by introductory students to understand different aspects of chemical change such as the concepts of reaction, compound, bonding, excess and limiting reactants, an empirical formula, balanced chemical equation, the conservation of matter and energy, the Law of the Conservation of Mass, and the Law of Constant Composition. These concepts, in turn, are important because they are fundamental to chemistry, are widely taught by chemistry teachers, and are deceptively difficult for introductory chemistry students to understand. The synthesis of zinc iodide has many scientific advantages over current syntheses of binary compounds from elements such as the syntheses of copper sulfide and magnesium oxide. For example, zinc iodide can be synthesized to 1% of theoretical mass in less than a half an hour and can be readily analyzed qualitatively as well as quantitatively by two different titrations. As a set of reactions, the synthesis and decomposition of zinc iodide is safe to perform, reliable, inexpensive, and does not pose a threat to the environment. The author has developed a small collection of teacher activities describing the synthesis and decomposition of zinc iodide. The activities are innovative because they contain improvements not found in the existing literature. Appropriate for high school and first year college chemistry teachers, all of the activities contain detailed procedures and discussions as well as safety and disposal requirements.

Demeo, Stephen

1995-09-01

257

Organic Reactions in Ionic Liquids: Gewald Synthesis of 2?Aminothiophenes Catalyzed by Ethylenediammonium Diacetate  

Microsoft Academic Search

Ionic liquids based on 1?butyl?3?methylimidazolium tetrafluoroborate (BmimBF4) and 1?butyl?3?methylimidazolium hexafluorophosphate (BmimPF6) were used as reusable alternatives to volatile organic solvents (VOCs) for ethylenediammonium diacetate (EDDA) catalyzed Gewald synthesis of 2?aminothiophenes. Significant rate enhancement and improvement of the yield were observed. The ionic liquids containing catalyst EDDA were recycled several times with no decreases in yields and reaction rates.

Yi Hu

2004-01-01

258

Highly Diastereoselective Pd-Catalyzed Carboetherification Reactions of Acyclic Internal Alkenes. Stereoselective Synthesis of Polysubstituted Tetrahydrofurans  

PubMed Central

A highly diastereoselective synthesis of substituted tetrahydrofurans bearing stereocenters at C2 and C1? via Pd-catalyzed carboetherification reactions of acyclic internal alkenes is described. Use of an improved catalyst composed of Pd2(dba)3/S-Phos provides products with up to >20:1 dr. The stereoselective preparation of tetrahydrofurans containing three stereocenters, including a molecule structurally related to simplakidine A, is also reported.

Ward, Amanda F.; Wolfe, John P.

2010-01-01

259

Laccase from Basidiomycetous Fungus–Catalyzed Synthesis of Substituted Benzopyranocoumarins via Domino Reaction  

Microsoft Academic Search

The present investigation provides a simple and convenient route to organic synthesis of substituted benzopyranocoumarin, which is important because it is a probable HIV protease inhibitor. The reaction of ?,?-unsaturated derivatives of coumarins with catechol or 1,4-hydroquinones was catalyzed using laccase in an aqueous medium. Quinones, generated in situ by the oxidation of the corresponding catechol or 1,4-hydroquinones, underwent a

Mazaahir Kidwai; Roona Poddar; Sarika Diwaniyan; Ramesh Chander Kuhad

2011-01-01

260

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

261

p-Toluene Sulfonic Acid–Catalyzed, Solvent-Free Synthesis of Symmetrical Bisamides by Reaction Between Aldehydes and Amides  

Microsoft Academic Search

Reaction between aldehydes and amides catalyzed by p-toluene sulfonic acid in solvent-free conditions provided a simple and efficient one-pot route for the synthesis of symmetrical bisamide derivatives in excellent yields.

Mohammad Anary-Abbasinejad; Mohammad H. Mosslemin; Alireza Hassanabadi; Safiyeh Tajik Safa

2010-01-01

262

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

SciTech Connect

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

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

1985-10-23

263

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

264

Asymmetric Palladium-Catalyzed Carboamination Reactions for the Synthesis of Enantiomerically Enriched 2-(Arylmethyl)- and 2-(Alkenylmethyl) pyrrolidines  

PubMed Central

The enantioselective synthesis of 2-(arylmethyl)- and 2-(alkenylmethyl)pyrrolidine derivatives via Pd-catalyzed alkene carboamination reactions is described. These transformations generate enantiomerically enriched products with up to 94% ee from readily available alkenyl or aryl bromides and N-boc-pent-4-enylamines. The application of this method to a concise asymmetric synthesis of (?)-tylophorine is also discussed.

Mai, Duy N.; Wolfe, John P.

2010-01-01

265

Synthesis of Dibenzoxepine Lactams via a Cu-Catalyzed One-Pot Etherification/Aldol Condensation Cascade Reaction: Application toward the Total Synthesis of Aristoyagonine.  

PubMed

A general synthesis of dibenzoxepine lactams has been developed using a one-pot Cu-catalyzed etherification/aldol condensation cascade reaction. The reaction of 4-hydroxyisoindolin-1-one with a wide range of 2-bromobenzaldehydes in the presence of a copper catalyst provided various aristoyagonine derivatives in good yields. PMID:24000941

Lim, Hye Sun; Choi, Young Lok; Heo, Jung-Nyoung

2013-09-03

266

General and efficient synthesis of 2-alkylcarbapenems: synthesis of dethiacarba analogs of Clinically Useful carbapenems via palladium-catalyzed cross-coupling reaction  

Microsoft Academic Search

Palladium-catalyzed cross-coupling reaction of carbapenem-2-yl triflate with alkylborane gave 2-alkylcarbapenem in good yield. The usefulness of this reaction was demonstrated by the synthesis of highly functionalized 2-alkylcarbapenems, dethiacarba analogs of imipenem, panipenem, biapenem, meropenem, and S-4661.

Yukitoshi Narukawa; Koichi Nishi; Hiroshi Onoue

1997-01-01

267

DABCO?Catalyzed Efficient Synthesis of Naphthopyran Derivatives via One?Pot Three?Component Condensation Reaction at Room Temperature  

Microsoft Academic Search

Diazabicyclo[2.2.2]octane (DABCO) has been used as a mild and efficient catalyst for synthesis of 2?amino?3?cyano naphthopyran derivatives via a one?pot three?component reaction of aromatic aldehydes, naphthols, and malononitrile at room temperature. The short reaction times, easy workup, good to excellent yields, and mild reaction conditions make this domino Knoevenagel–Michael reaction both practical and attractive.

Saeed Balalaie; Sorour Ramezanpour; Morteza Bararjanian; Jürgen H. Gross

2008-01-01

268

Modelling of equilibrium limited hydrogenation reactions carried out in H + conducting solid oxide membrane reactors  

Microsoft Academic Search

A model is prepared for the hydrogenation reactions of ammonia and methanol synthesis that are carried out in solid electrolyte cell-reactors. Hydrogen is supplied in the form of H+ through the proton conducting wall and the thermodynamic activity of hydrogen on the catalyst surface is controlled electrochemically. Under certain conditions, the yield of the cell-reactor is orders of magnitude higher

E. Panagos; I. Voudouris; M. Stoukides

1996-01-01

269

Process for ammonia syngas manufacture  

SciTech Connect

This patent describes an improved process for reforming hydrocarbons to obtain a synthesis gas containing an approximately stoichiometric amount of hydrogen and nitrogen from which ammonia may be formed in which a hydrocarbon is reacted with steam and air in a reforming operation to obtain a first effluent. This effluent consists of hydrogen, nitrogen and carbon monoxide. The carbon monoxide is reacted in a shift conversion stage to produce a second effluent consisting of hydrogen, nitrogen, and carbon dioxide. The improved process has the additional steps of separating the second effluent into a first stream and a second stream. The first stream is reacted with air in a fuel cell to produce a byproduct stream and a product stream which is passed through a de-oxygenation stage to produce a purified stream. The second stream and the purified stream is passed into a pressure swing adsorption unit in which the synthesis gas and a waste fuel stream are separated.

Jungerhans, R.R.J.

1986-03-25

270

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

SciTech Connect

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

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

1994-11-01

271

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

272

Synthesis of nanocrystalline silicon carbonitride films by remote plasma enhanced chemical vapor deposition using the mixture of hexamethyldisilazane with helium and ammonia  

Microsoft Academic Search

The silicon carbonitride films were synthesised by remote plasma enhanced chemical vapor deposition (RPECVD) using a mixture of ammonia, helium and hexamethyldisilazane Si2NH(CH3)6 as the volatile single-source precursor. Different analysis techniques such as IR, Raman spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, EDS, scanning electron microscopy, high-resolution electron microscopy, selective area electron diffraction and X-ray diffraction using synchrotron radiation were used to

N. I. Fainer; Yu. M. Rumyantsev; A. N. Golubenko; M. L. Kosinova; F. A. Kuznetsov

2003-01-01

273

Synthesis and reactions of a nucleoside derivative of phosphoric sulfonic anhydride. Studies related to the mechanisms of coupling reactions in the chemical synthesis of oligodeoxyribonucleotides by phosphotriester procedures.  

PubMed Central

The synthesis of a model compound, diphenylphosphoric toluene-p-sulfonic anhydride, an arylsubstituted phosphoric sulfonic mixed anhydride, is described. Using the same procedure a thymidyl substituted derivative was prepared. The phosphoric sulfonic anhydride is the presumed intermediate in oligonucleotide coupling reactions involving phosphodiester activation by arenesulfonyl derivatives. This mixed anhydride reacts with a variety of nucleophiles. It can be converted to phophotriester derivatives in the presence of simple alcohols. Phosphotriester formation using the 5'-hydroxyl of a thymidine derivative requires additionally a catalyst such as N-methylimidazole. The reactive intermediate produced upon the addition of N-methylimidazole to the phosphoric sulfonic anhydride has been observed spectroscopically using 31P-NMR.

Dabkowski, W; Skrzypczynski, Z; Michalski, J; Piel, N; McLaughlin, L W; Cramer, F

1984-01-01

274

Selective inhibition of the bacterial translocase reaction in peptidoglycan synthesis by mureidomycins.  

PubMed Central

Mureidomycins (MRDs) A and C inhibited strongly the formation of undecaprenyl pyrophosphoryl N-acetylmuramyl-pentapeptide (lipid intermediate I), which is an intermediate in bacterial peptidoglycan synthesis (50% inhibitory concentration [IC50] of MRD A, 0.05 microgram/ml). However, they did not inhibit the formation of dolichyl pyrophosphoryl N-acetylglucosamine (Dol-p-p-GlcNAc), dolichyl phosphoryl glucose, or dolichyl phosphoryl mannose, the precursors for mammalian glycoprotein synthesis, or the formation in Bacillus subtilis of lipid-linked N-acetylglucosamine for teichoic acid synthesis (IC50s, > 100 micrograms/ml). In contrast, tunicamycin (TCM) inhibited strongly the formation of Dol-p-p-GlcNAc (IC50, 0.03 microgram/ml) but inhibited weakly the formation of bacterial lipid intermediate I (IC50, 44 micrograms/ml). When the effects of MRDs A and C and TCM on the growth of mammalian cells were compared, MRDs did not show any toxicity, even at 1,000 micrograms/ml, whereas TCM inhibited the growth of BALB/3T3 cells at 10 micrograms/ml. On the basis of these results, it was concluded that MRDs are the first specific and potent inhibitors of the translocase reaction in bacterial peptidoglycan synthesis, showing a high level of toxicity against bacteria and a low level of toxicity against mammalian cells. A specific inhibitor of translocase could be a potent antibiotic with highly selective toxicity.

Inukai, M; Isono, F; Takatsuki, A

1993-01-01

275

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

PubMed

Ever since their discovery in the late 1970's, mid-ocean-ridge hydrothermal systems have received a great deal of attention as a possible site for the origin of life on Earth (and environments analogous to mid-ocean-ridge hydrothermal systems are postulated to have been sites where life could have originated or Mars and elsewhere as well). Because no modern-day terrestrial hydrothermal systems are free from the influence of organic compounds derived from biologic processes, laboratory experiments provide the best opportunity for confirmation of the potential for organic synthesis in hydrothermal systems. Here we report on the formation of lipid compounds during Fischer-Tropsch-type synthesis from aqueous solutions of formic acid or oxalic acid. Optimum synthesis occurs in stainless steel vessels by heating at 175 degrees C for 2-3 days and produces lipid compounds ranging from C2 to > C35 which consist of n-alkanols, n-alkanoic acids, n-alkenes, n-alkanes and alkanones. The precursor carbon sources used are either formic acid or oxalic acid, which disproportionate to H2, CO2 and probably CO. Both carbon sources yield the same lipid classes with essentially the same ranges of compounds. The synthesis reactions were confirmed by using 13C labeled precursor acids. PMID:10227201

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

1999-03-01

276

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); Pink, Robert J. (Pocatello, ID); Zuck, Larry D. (Idaho Falls, ID)

2008-08-19

277

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...

278

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

PubMed Central

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

Fischer, Carolin

2011-01-01

279

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

PubMed

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

Fischer, Carolin; Koenig, Burkhard

2011-01-14

280

APPLICATION OF A SYSTEMATIC APPROACH FOR DETERMINING POSSIBLE REACTION MECHANISMS: METHANOL SYNTHESIS AND ANODIC OXIDATION OF ZINC  

Microsoft Academic Search

A systematic enumeration of possible reaction mechanisms consistent with a given set of chemical species and elementary steps is useful in guiding research in heterogeneous reaction systems which are encountered in catalysis and electrochemistry. In this paper, the synthesis of methanol by catalytic hydrogenation of carbon monoxide and the anoidic oxidation of zinc in alkaline solutions are presented as two

JORGE L. VALDES; CECILIA Y. MAK; JOHN HAPPEL; HUK Y. CHEH

1985-01-01

281

Total synthesis of (-)-FR182877 through tandem IMDA-IMHDA reactions and stereoselective transition-metal-mediated transformations.  

PubMed

Intelligent design: The total synthesis of the cytotoxic (-)-FR182877 relies on 1) tandem Diels-Alder reactions to close rings A-D (see scheme), 2) a palladium-mediated 7-exo-trig reaction, and 3) an iridium-mediated isomerization followed by epimerization and stereoselective reduction. PMID:19226590

Tanaka, Natsumi; Suzuki, Takahiro; Matsumura, Takehiko; Hosoya, Yosuke; Nakada, Masahisa

2009-01-01

282

One-pot synthesis of 4-methylisoquinolines via a sequential Pd-catalyzed Heck reaction and intramolecular cyclization.  

PubMed

An efficient, one-pot synthesis of 4-methylisoquinolines via a cascade Pd-catalyzed Heck reaction, intramolecular cyclization and isomerization has been developed. This reaction has a wide range of substrates with various functional groups, and the corresponding products have been obtained in good yields. PMID:24068319

Tian, Yulin; Qi, Jianguo; Sun, Chenbin; Yin, Dali; Wang, Xiaojian; Xiao, Qiong

2013-10-01

283

Metal-free transannulation reaction of indoles with nitrostyrenes: a simple practical synthesis of 3-substituted 2-quinolones.  

PubMed

3-Substituted 2-quinolones are obtained via a novel, metal-free transannulation reaction of 2-substituted indoles with 2-nitroalkenes in polyphosphoric acid. The reaction can be used in conjunction with the Fisher indole synthesis offering a practical three-component heteroannulation methodology to produce 2-quinolones from arylhydrazines, 2-nitroalkenes and acetophenone. PMID:23999797

Aksenov, Alexander V; Smirnov, Alexander N; Aksenov, Nicolai A; Aksenova, Inna V; Frolova, Liliya V; Kornienko, Alexander; Magedov, Igor V; Rubin, Michael

2013-09-17

284

Determination of the activity of diamine oxidases, urease and histidine ammonia-lyase by enzymatic assay of ammonia  

Microsoft Academic Search

The activities of diamine oxidases (DAO) from submaxillary glands, parotid glands and kidneys, from human serum during the pregnancy and from pig serum and of DAO from pea seedlings and the activities of urease and histidine ammonia-lyase have been determined by measuring NH4+ released from the corresponding substrates. Ammonia has been determined with the aid of glutamate dehydrogenase reaction in

W. Lorenz; J. Kusche; H. Hahn; E. Werle

1968-01-01

285

Tandem overman rearrangement and intramolecular amidomercuration reactions. stereocontrolled synthesis of cis- and trans-2,6-dialkylpiperidines.  

PubMed

[reaction: see text] Hg(II)-mediated tandem Overman rearrangement and intramolecular amidomercuration reactions were proven to provide a convenient tool for the stereoselective synthesis of cis- and trans-2,6-disubstituted piperidines. Thus, upon treatment with Hg(OTFA)(2) in THF, the trichloroacetimidate 1 directly transformed into the 2,6-dialkyl piperidine 2 with almost exclusive trans selectivity. The amiodomercuration reaction of the carbamate 7 by Hg(OTFA)(2) in nitromethane showed an excellent cis selectivity. Also reported is the stereoselective synthesis of solenopsin A and isosolenopsin A. PMID:15330589

Singh, Om V; Han, Hyunsoo

2004-09-01

286

Modelling for the optimization of the reaction chamber in silicon nanoparticle synthesis by a radio-frequency induction thermal plasma  

NASA Astrophysics Data System (ADS)

The optimization of the reaction chamber for the silicon nanoparticle synthesis process by a radio-frequency induction thermal plasma is addressed using a plasma thermo-fluid-dynamic model coupled with electromagnetic field equations and with a moment model for nanoparticle transport. Various reaction chamber geometries composed of two parts—a conical top and a cylindrical bottom—are evaluated in terms of the yield of the synthesis process, the presence of recirculation flow patterns that may affect the uniformity of the produced nanoparticles and the size distribution of nanoparticles at the chamber outlet. Turbulent diffusion is suggested as the physical phenomenon that leads to nanoparticle deposition onto the walls of the reaction chamber. The injection of a suitable gas along the walls of the reaction chamber at the axial position, where the nanoparticle nucleation takes place, is proven to be effective in increasing the synthesis process yield.

Colombo, V.; Ghedini, E.; Gherardi, M.; Sanibondi, P.

2012-10-01

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

Biochemical Characterization of the Arabidopsis Biotin Synthase Reaction. The Importance of Mitochondria in Biotin Synthesis1  

PubMed Central

Biotin synthase, encoded by the bio2 gene in Arabidopsis, catalyzes the final step in the biotin biosynthetic pathway. The development of radiochemical and biological detection methods allowed the first detection and accurate quantification of a plant biotin synthase activity, using protein extracts from bacteria overexpressing the Arabidopsis Bio2 protein. Under optimized conditions, the turnover number of the reaction was >2 h?1 with this in vitro system. Purified Bio2 protein was not efficient by itself in supporting biotin synthesis. However, heterologous interactions between the plant Bio2 protein and bacterial accessory proteins yielded a functional biotin synthase complex. Biotin synthase in this heterologous system obeyed Michaelis-Menten kinetics with respect to dethiobiotin (Km = 30 ?m) and exhibited a kinetic cooperativity with respect to S-adenosyl-methionine (Hill coefficient = 1.9; K0.5 = 39 ?m), an obligatory cofactor of the reaction. In vitro inhibition of biotin synthase activity by acidomycin, a structural analog of biotin, showed that biotin synthase reaction was the specific target of this inhibitor of biotin synthesis. It is important that combination experiments using purified Bio2 protein and extracts from pea (Pisum sativum) leaf or potato (Solanum tuberosum) organelles showed that only mitochondrial fractions could elicit biotin formation in the plant-reconstituted system. Our data demonstrated that one or more unidentified factors from mitochondrial matrix (pea and potato) and from mitochondrial membranes (pea), in addition to the Bio2 protein, are obligatory for the conversion of dethiobiotin to biotin, highlighting the importance of mitochondria in plant biotin synthesis.

Picciocchi, Antoine; Douce, Roland; Alban, Claude

2001-01-01

289

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

290

Fusion reactions and experimental approaches to the synthesis of superheavy nuclei  

NASA Astrophysics Data System (ADS)

The question whether the asymmetric actinide based heavy ion reactions could be used for the synthesis of heavy (Z>=106) nuclides is essential from the point of view of the study of limitation on fusion, it is also important in such reactions new nuclides close to the magic number N=162 can be produced. Thus as the problem of a hindrance to fusion still remains unsolved the high excitation energy of the compound nucleus looks to be an obvious obstacle to using these reactions. Using the gas-filled recoil separator [1] and electrostatic recoil separator VAS-SILISSA [2] installed at the beam lines of the U-400 heavy ion cyclotron of the FLNR JINR we investigated the fusion reactions leading to 102, 103, 104, 105 and heaviest isotopes of the 106, 108 and 110 elements. The analysis of the measured cross-sections did not reveal any evidence of a hindrance to fusion at the ion bombarding energy close to the Coulomb barrier. 48Ca+232Th-->280110*, 48Ca+238U-->286112*, 48Ca+244Pu-->292114* appear to be the best reactions from the point of view of their cross-sections.

Yeremin, A. V.; Utyonkov, V. K.; Oganessian, Yu. Ts.

1998-02-01

291

Fusion reactions and experimental approaches to the synthesis of superheavy nuclei  

SciTech Connect

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

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

1998-02-15

292

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

PubMed

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

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

2012-10-21

293

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

SciTech Connect

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

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

2012-04-26

294

Exploration of click reaction for the synthesis of modified nucleosides as chitin synthase inhibitors  

Microsoft Academic Search

Click reaction approach toward the synthesis of two sets of novel 1,2,3-triazolyl linked uridine derivatives 19a–19g and 21a–21g was achieved by Cu(I)-catalyzed 1,3-dipolar cycloaddition of 5?-azido-5?-deoxy-2?,3?-O-(1-methylethylidene)uridine (17) with propargylated ether of phenols 18a–18g and propargylated esters 20a–20g. Structure of one of the representative compound 19d was unambiguously confirmed by X-ray crystallography. Chitin synthase inhibition study of all these compounds 19a–19g

Preeti M. Chaudhary; Sayalee R. Chavan; Fazal Shirazi; Meenakshi Razdan; Prachi Nimkar; Shailaja P. Maybhate; Anjali P. Likhite; Rajesh Gonnade; Braja G. Hazara; Mukund V. Deshpande; Sunita R. Deshpande

2009-01-01

295

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

296

A facile synthesis of N-benzyl-4-acetylproline via a tandem cationic aza-Cope rearrangement-Mannich reaction  

Microsoft Academic Search

N-Benzyl-4-acetylproline can be prepared from N-(2-hydroxy-2-methyl)but-3-enyl-N-benzylamine and glyoxylic acid via a tandem cationic aza-Cope rearrangement-Mannich reaction. This reaction represents the first example of such a mechanism being utilised for the synthesis of functionalised proline derivatives. In addition the reaction requires only mild conditions and a good yield of amino acid product is obtained without any need for purification.

Andrew Cooke; Jonathan Bennett; Emma McDaid

2002-01-01

297

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

298

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

299

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

PubMed Central

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

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

2002-01-01

300

Palladium-catalyzed alkene carboamination reactions for the synthesis of substituted piperazines  

PubMed Central

A strategy for the stereoselective preparation of enantiomerically enriched cis-2,6-disubstituted piperazines from amino acid precursors is described. The target compounds are generated in 95–99% ee with good to excellent levels of diastereoselectivity (usually 14:1 to >20:1) using Pd-catalyzed carboamination reactions between aryl or alkenyl halides and substituted ethylenediamine derivatives to form the heterocyclic rings. The synthesis requires only 4–5 steps from commercially available amino acids, and allows for the modular construction of piperazines bearing different substituents at N1, N4, C2, and C6. The use of this strategy for the construction of 2,3-disubstituted piperazines, fused bicyclic piperazines, and tetrahydroquinoxalines is also reported. In addition, the mechanism of the key carboamination reactions are discussed, and new models that predict and explain the stereochemical outcome of these transformations are presented.

Nakhla, Josephine S.; Schultz, Danielle M.; Wolfe, John P.

2009-01-01

301

Alkaline Earth metallocenes coordinated with ester pendants: synthesis, structural characterization, and application in metathesis reactions.  

PubMed

A variety of ester-substituted cyclopentadiene derivatives have been synthesized by one-pot reactions of 1,4-dilithio-1,3-butadienes, CO, and acid chlorides. Direct deprotonation of the ester-substituted cyclopentadienes with Ae[N(SiMe3 )2 ]2 (Ae=Ca, Sr, Ba) efficiently generated members of a new class of heavier alkaline earth (Ca, Sr, Ba) metallocenes in good to excellent yields. Single-crystal X-ray structural analysis demonstrated that these heavier alkaline earth metallocenes incorporated two intramolecularly coordinated ester pendants and multiply-substituted cyclopentadienyl ligands. The corresponding transition metal metallocenes, such as ferrocene derivatives and half-sandwich cyclopentadienyl tricarbonylrhenium complexes, could be generated highly efficiently by metathesis reactions. The multiply-substituted cyclopentadiene ligands bearing an ester pendant, and the corresponding heavier alkaline earth and transition-metal metallocenes, may have further applications in coordination chemistry, organometallic chemistry, and organic synthesis. PMID:23934787

Li, Heng; Zhang, Wen-Xiong; Xi, Zhenfeng

2013-08-09

302

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

303

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

304

Enantioselective organocatalytic intramolecular Diels-Alder reactions. The asymmetric synthesis of solanapyrone D.  

PubMed

The first direct enantioselective organocatalytic intramolecular Diels-Alder reaction has been accomplished. The use of iminium catalysis has provided a new catalytic strategy for the enantioselective [4 + 2] cycloisomerization of a wide variety of tethered diene-enal systems. The use of imidazolidinones 1 and 2 as the asymmetric catalysts has been found to mediate the enantioselective construction of [4.4.0] and [4.3.0] ring systems. Application of this methodology to the highly efficient asymmetric synthesis of the marine metabolite solanpyrone D has also been accomplished. A diverse spectrum of aldehyde substrates can also be accommodated in this new organocatalytic transformation. Importantly, this technology has been utilized to execute the first enantioselective, catalytic Type II IMDA reaction. PMID:16104734

Wilson, Rebecca M; Jen, Wendy S; Macmillan, David W C

2005-08-24

305

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

306

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

PubMed

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

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

2002-12-20

307

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

SciTech Connect

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

Subramaniam, B.

1992-10-01

308

Monitoring ammonia to assess halitosis  

Microsoft Academic Search

Objective. This study examined the applicability of ammonia monitoring for assessing halitosis. Study Design. The actual degree of halitosis was determined by using an organoleptic test in 61 subjects aged 28 ± 10 years (mean ± SD). Levels of volatile sulfur compounds and ammonia were determined by using gas chromatography and ammonia monitoring, respectively. Levels of ammonia and methyl mercaptan

Akiko Amano; Yasuo Yoshida; Takahiko Oho; Toshihiko Koga

2002-01-01

309

Enzymology of the oxidation of ammonia to nitrite by bacteria  

Microsoft Academic Search

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.

Alan B. Hooper; Todd Vannelli; David J. Bergmann; David M. Arciero

1997-01-01

310

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

311

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

312

Ammonia Production Systems Integration.  

National Technical Information Service (NTIS)

Conceptual designs of 11 mobile ammonia fuel production systems were prepared. These systems represent various combinations of total electric power to the system, mobility class, electrical power frequency, and cooling medium. This report presents a descr...

B. N. Thomson G. E. Hook N. T. Mills R. A. Coval R. M. Reinstrom

1966-01-01

313

Acylation of acetals and related geminal systems. The use of this reaction in the synthesis of phospholipids  

NASA Astrophysics Data System (ADS)

The practical significance of acylation of acetals, orthoesters, and their aza-analogues (oxazolines) in fine organic synthesis is considered. Attention is mainly focused on the application of this reaction to the design of glycerophosphatides and other types of phospholipids. The use of acylation of these geminal alkoxides and oxazolines makes it possible to optimise the strategy of the synthesis of polyfunctional ester systems. The bibliography includes 76 references.

Nifantiev, Edward E.; Predvoditelev, Dmitrii A.

1997-01-01

314

Synthesis, Reactions, and Selected PhysicoChemical Properties of 1,3-and 1,2-Tetrachalcogenafulvalenes  

Microsoft Academic Search

This review describes the synthesis of 1,3-tetrachalcogenafulvalenes and 1,2-tretrathiafulvalenes, the chemical transformation of substituents, reactions of the ring system, and the synthesis of polymers with 1,3-tetrathiafulvalene units in the backbone and in the side chain. 1,2-And 1,3-tetrachalcogenafulvalenes synthesized until now and selected properties (melting point, u.v.-vis. absorption data and oxidation potential) are recorded in appropriate tables. The literature until the

G. Schukat; A. M. Richter; E. Fanghänel

1987-01-01

315

A Detailed Kinetic Study of Ammonia Oxidation  

Microsoft Academic Search

A comprehensive study of ammonia oxidation in laminar flames and Sow reactors using detailed chemical kinetic modelling is reported. A flat premixed NH3\\/NO flame and counterflow CO\\/O2\\/N2 and CH4\\/O2\\/N2 diffusion flames doped with ammonia have been studied along with NH3\\/NO\\/O2 and NH3\\/NO\\/O2\\/C2H6 flow reactors. Available kinetic data has been reviewed and a detailed reaction mechanism for the C\\/N system is

R. P. LINDSTEDT; F. C. LOCKWOOD; M. A. SELIM

1995-01-01

316

Control of catalytic hydrotreating selectivity with ammonia  

SciTech Connect

The hydrogenation of phenanthrene in the presence of 24 kPa of ammonia was studied during the hydrodenitrogenation (HDN) of quinoline on a sulfided NiMo/Al{sub 2}O{sub 3} catalyst at 360{degrees}C, 6.9 MPa total H{sub 2} pressure in a vapor phase tubular reactor. Ammonia, through competitive adsorption, reduced the formation of phenanthrene hydrogenated products and the hydrocracking of 9,10-dihydrophenanthrene to biphenyl. The effects occur largely when the HDN reactions are substantially completed. 6 refs., 8 figs., 1 tab.

Satterfield, C.N.; Lee, C.M.

1991-01-01

317

Titan's Ammonia Feature  

NASA Astrophysics Data System (ADS)

NH3 has long been considered an important component in the formation and evolution of the outer planet satellites. NH3 is particularly important for Titan, since it may serve as the reservoir for atmospheric nitrogen. A brightening seen on Titan starting in 2004 may arise from a transient low-lying fog or surface coating of ammonia. The spectral shape suggests the ammonia is anhydrous, a molecule that hydrates quickly in the presence of water.

Smythe, W.; Nelson, R.; Boryta, M.; Choukroun, M.

2011-10-01

318

Equine infectious anemia virus and human immunodeficiency virus DNA synthesis in vitro: characterization of the endogenous reverse transcriptase reaction.  

PubMed Central

The endogenous reverse transcriptase reaction of equine infectious anemia virus (EIAV) has been studied, and conditions allowing synthesis of full-length minus-strand DNA have been determined. In contrast to results reported for other retroviruses, synthesis of EIAV full-length minus-strand DNA was not impaired by high concentrations of Nonidet P-40, a nonionic detergent used to make the virion envelope permeable. All components of the reaction were titrated for maximum synthesis of complete minus strands, and a time course under the standardized conditions was determined. Minor subgenomic bands were observed in some cases, and both the size and proportion varied with reaction conditions. Conditions established for full-length EIAV DNA synthesis also allowed full-genome-length human immunodeficiency virus type 1 DNA synthesis. The human immunodeficiency virus type 1 DNA product contained a greater proportion of reverse transcripts that were shorter than the complete virus genome. Also in contrast to EIAV, the endogenous synthesis of high-molecular-weight human immunodeficiency virus type 1 DNA was drastically reduced at Nonidet P-40 concentrations above 0.02%. These results indicated that a detergent-stable core is not a property shared by all lentiviruses. The EIAV virion synthetic machinery is unusually stable and provides a convenient system for further in vitro study of reverse transcription. Images

Borroto-Esoda, K; Boone, L R

1991-01-01

319

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

ERIC Educational Resources Information Center

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

Sauvage, Xavier; Delaude, Lionel

2008-01-01

320

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

ERIC Educational Resources Information Center

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

Sauvage, Xavier; Delaude, Lionel

2008-01-01

321

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

322

One pot three component reaction for the rapid synthesis of pyrrolo[1,2-a]benzimidazoles.  

PubMed

An efficient strategy for the synthesis of pyrrolo[1,2-a]-benzimidazole (PBI) linked to an ionic liquid (ILs) as a soluble support under microwave irradiation was explored. The key intermediate benzimidazoles were synthesized via N-acylation followed by cyclodehydration of IL-supported methyl-3-amino-4-(isobutylamino) benzoate. The synthesis of the IL-bound PBI was performed by one-pot three-component condensation under microwave dielectric heating, which involved a Knoevenagel condensation and a [4+1]-cycloaddition reaction. The reaction was monitored directly by means of (1)H NMR. All final products were obtained in good yield and high purity after precipitation. PMID:23529678

Hsu, Wei-Shun; Paike, Vijaykumar; Sun, Chung-Ming

2013-03-26

323

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

324

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

325

Resolution of the paradox of ammonia and hydroxylamine as substrate analogues for the water-oxidation reaction catalyzed by photosystem II  

SciTech Connect

The O/sub 2/-evolving center of photosystem II (PSII) contains a Mn tetramer complex that serves as the catalyst for the H/sub 2/O-oxidation reaction. In a ligand-substitution reaction thought to be analogous to the substrate-binding reaction, NH/sub 3/ coordinates to the Mn complex only after formation of the S/sub 2/ state, which then exhibits an altered S/sub 2/-state multiline electron paramagnetic resonance (EPR) signal. The free-base form of hydroxylamine binds to a Cl/sup -/-binding site prior to reacting with the Mn complex; subsequently, hydroxylamine probably reduces the Mn complex from the S/sub 1/ state to the S..sqrt../sub 1/ state through an outer-sphere electron-transfer mechanism. The rate of hydroxylamine's reaction with the Mn complex is reduced about 17-fold with each added N-methyl substituent, showing that the binding site is sterically selective for small ligands. NH/sub 3/ also binds to the O/sub 2/-evolving center in the S/sub 1/ state in a manner inversely dependent on the Cl/sup -/ concentration, causing the Mn complex to exhibit a g = 4.1 EPR signal in lieu of the multiline EPR signal in the S/sub 2/ state. The results suggest that primary amines and hydroxylamines bind to the O/sub 2/-evolving center in the S/sub 1/ state at the same Cl/sup -/-binding site. Thus, two ligand-binding sites exist in the O/sub 2/-evolving center. One site is located on the Mn complex and is restricted to binding NH/sub 3/ and presumably H/sub 2/O. This site is assigned to the substrate-binding site. A second site is identified as the Cl/sup -/-binding site; primary amines and hydroxylamines compete with Cl/sup -/ for coordination to this site. In view of the finding that hydroxylamines bind to the Cl/sup -/-binding site, they conclude that hydroxylamines should not be considered as substrate analogues for the H/sub 2/O-oxidation reaction catalyzed by PSII.

Beck, W.F.; Brudvig, G.W.

1988-03-02

326

Total synthesis of actinobolin from d-glucose by way of the stereoselective three-component coupling reaction  

Microsoft Academic Search

The total synthesis of (?)-actinobolin 3, an antipode of the natural product, starting from d-glucose is described. A three-component coupling reaction of functionalized cyclohexenone (+)-6 derived from d-glucose by way of Ferrier's carbocyclization reaction, with vinyl cuprate and 2-alkoxypropanal 7 effectively constructed the carbon framework of 3 in a highly stereoselective manner. In an aldol process of the three-component coupling

Satoshi Imuta; Hiroki Tanimoto; Miho K. Momose; Noritaka Chida

2006-01-01

327

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

328

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

PubMed

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

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

2003-04-01

329

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

Microsoft Academic Search

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·3B2O3·3.5H2O. Effects of stirring speed, presence of baffles, amount of seed, particle size and purity of zinc oxide, and mole ratio of H3BO3:ZnO on the zinc borate formation reaction were

Mert Kilinç; Gaye Ö. Çakal; Sertan Yesil; Göknur Bayram; Inci Eroglu; Saim Özkar

2010-01-01

330

Facile synthesis of fully substituted dihydro-?-carbolines via Brønsted acid promoted cascade reactions of ?-indolyl propargylic alcohols with nitrones.  

PubMed

A straightforward synthesis of fully substituted ?-carbolines via Brønsted acid promoted cyclizations of ?-indolyl propargylic alcohols with nitrones is described. The use of nitrones bearing alkenyl or electron-rich aryl groups as the R(4) substituent dramatically switches the reaction pathway to afford tetrasubstituted alkenes and amines, which is assumed to proceed through a rearrangement reaction involving N-O bond cleavage and 1,2-migration of the R(4) group to an adjacent nitrogen atom. PMID:23145995

Wang, Lu; Xie, Xin; Liu, Yuanhong

2012-11-12

331

Synthesis of biaryl imino/keto carboxylic acids via aryl amide directed C-H activation reaction.  

PubMed

A novel Pd-catalysed C-H activation reaction for the synthesis of biaryl imino/keto carboxylic acids is developed. This reaction underwent aryl amide directed C-H activation ortho-acylation followed by ring closing and ring opening processes to give a range of biaryl imino/keto carboxylic acids. Our methodology features the utilization of a cheap and green oxidant (TBHP) as well as readily available aldehydes. PMID:24013806

Zhang, Nana; Yu, Qingzhen; Chen, Ruixue; Huang, Jianhui; Xia, Yeqing; Zhao, Kang

2013-10-21

332

The mechanism of ammonia production and the effect of mechanical work load on proteolysis and amino acid catabolism in isolated perfused rat heart.  

PubMed Central

The effect of mechanical work load on net proteolysis, amino acid catabolism and ammonia production was studied in isolated perfused beating or K+-arrested hearts. Net proteolysis was about 16 mumol/g dry wt. during 1h and was not affected by the mechanical work. The combined catabolic rate of the major amino acids was 7.1 mumol/g dry wt. in the beating heart and 2.1 mumol/g dry wt. in the arrested heart during the 1 h experimental period. The main differences lay in the deamination of aspartate plus glutamate, which was inhibited by 60% during low energy consumption, and in net alanine synthesis, which was increased by 94%. The ammonia production plus its conversion into amide nitrogen was 9.2 and 3.4 mumol/g dry wt. in the beating and arrested heart respectively during 1 h. The decrease in the total adenine nucleotide pool during the 1 h perfusion was very low, 1.0 and 0.5 mumol/g dry wt. in the beating and arrested hearts respectively, and did not contribute significantly to ammonia production. Thus ammonia production is dependent on the cellular energy state, whereas net proteolysis is not. The maximal capacities of the purine nucleotide cycle and the glutamate dehydrogenase reaction towards deamination were much higher than the observed ammonia-production rates. The anaplerotic role of amino acid catabolism in the myocardium is discussed.

Takala, T; Hiltunen, J K; Hassinen, I E

1980-01-01

333

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

334

Construction materials for reaction unit in the liquid-phase synthesis of propylene oxide  

SciTech Connect

The main components of the reaction medium in equipment for the synthesis of propylene oxide by liquid-phase oxidation of gaseous propylene with peracetic acid are propylene, peracetic acid, ethyl acetate, acetic acid, propylene oxide, carbon dioxide, oxygen, methane, and propylene glycol acetates. The operating conditions of the equipment and content of the main components of the medium are shown. Results are given for the investigation of the corrosion behavior of 12Kh18N10T, 10Kh17N13M2T, 08Kh22N6T, and 08Kh21N6M2T steels, AD0 and AD1 aluminum, and VT1-0 titanium. VSt3 carbon steel was tested for comparison.

Zaritskii, V.I.D.

1987-09-01

335

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

336

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

337

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

SciTech Connect

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

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

1989-08-18

338

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

339

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.

340

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

341

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

342

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

343

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

2009-05-13

344

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

345

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

346

Synthesis of phosphorus-doped graphene and its multifunctional applications for oxygen reduction reaction and lithium ion batteries.  

PubMed

We develop a simple and economical thermal annealing method for the synthesis of phosphorus-doped graphene, which exhibits remarkable electrocatalytic activity towards the oxygen reduction reaction and enhances the electrochemical performance as an anode material for lithium ion batteries. The experimental results suggest the significant role of phosphorus atoms in graphene. PMID:23864555

Zhang, Chenzhen; Mahmood, Nasir; Yin, Han; Liu, Fei; Hou, Yanglong

2013-07-17

347

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

348

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

349

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

350

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

351

Gold(III) Salen complex-catalyzed synthesis of propargylamines via a three-component coupling reaction.  

PubMed

[reaction: see text] Propargylamines have been synthesized by a gold(III) salen complex-catalyzed three-component coupling reaction of aldehydes, amines, and alkynes in water in excellent yields at 40 degrees C. With chiral prolinol derivatives as the amine component, excellent diastereoselectivities (up to 99:1) have been attained. This coupling reaction has been applied to the synthesis of propargylamine-modified artemisinin derivatives with the delicate endoperoxide moieties remaining intact. Cytotoxicities with IC(50) values up to 1.1 microM against a human hepatocellular carcinoma cell line (HepG2) were exhibited by these artemisinin derivatives. PMID:16597102

Lo, Vanessa Kar-Yan; Liu, Yungen; Wong, Man-Kin; Che, Chi-Ming

2006-04-13

352

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

353

Ammonia and manganese increase arginine uptake in cultured astrocytes.  

PubMed

Recent work has suggested a possible role for nitric oxide (NO) in the development of hepatic encephalopathy (HE). In this study, we examined the effect of ammonia and manganese, factors implicated in the pathogenesis of HE, on the transport of arginine (a precursor of NO) into primary cultures of astrocytes. Treatment with 5 mM ammonia for 1-4 days produced a maximal (53%) increase in L-arginine uptake at 3 days when compared to untreated cells. Kinetic analysis following 4-day treatment with 5 mM ammonia revealed an 82% increase in the Vmax and a 61% increase in the Km value. Similar analysis with 100 microM manganese showed a 101% increase in Vmax and a 131% increase in the Km value. These results suggest that both manganese and ammonia alter L-arginine uptake by modifying the transporter for arginine. A decrease of 32% in the non-saturable component of L-arginine transport was also observed following treatment with ammonia. When cultures were treated separately with 5 mM ammonia and 100 microM manganese for 2 days, the uptake of L-arginine increased by 41% and 57%, respectively. Combined exposure led to no further increase in uptake. Our results suggest that ammonia and manganese may contribute to the pathogenesis of HE by influencing arginine transport and thus possibly NO synthesis in astrocytes. PMID:9572676

Hazell, A S; Norenberg, M D

1998-06-01

354

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

2012-10-26

355

3-(Dimethylboryl)pyridine: synthesis, structure, and remarkable steric effects in scrambling reactions.  

PubMed

A facile method for the synthesis of 3-(dimethylboryl)pyridine (1a) is described. Compound 1a assembles into a rigid cyclic tetramer stabilized via intermolecular boron-nitrogen coordination bonds both in the crystalline state and in solution. The outstanding structural feature of 1a, as compared with previously reported 3-(diethylboryl)pyridine (2a) (which adopts a cone conformation), is that the tetramer of 1a adopts a 1,2-alternate conformation. To investigate the effect of substituents at the boron atom on the stabilities of the oligomers, scrambling experiments of the component molecules using 1, 2, and 3-(di-n-butylboryl)pyridines 3 were carried out. Although heating at 80-90 degrees C for 20 h was required to attain the equilibrium of the scrambling reactions when the component molecules of the tetramers were 2 or 3, the scrambling in 1 proceeded under relatively mild conditions (60 degrees C, 3 h). This difference in reaction conditions required for 1, as compared to conditions required for 2 or 3, could not be explained solely by the stabilities based on bond lengths or THC. It appears that whereas only an S(N)1-type pathway may be involved in the scrambling of 2 or 3, both S(N)1- and S(N)2-type mechanisms operate simultaneously during scrambling reactions of 1 or an intermediate mechanism between S(N)1 and S(N)2 operates, which was supported by kinetic studies and calculations using model compounds. PMID:18052387

Wakabayashi, Shigeharu; Imamura, Saori; Sugihara, Yoshikazu; Shimizu, Makoto; Kitagawa, Toshikazu; Ohki, Yasuhiro; Tatsumi, Kazuyuki

2007-12-06

356

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

Microsoft Academic Search

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

K. Lovegrove; A. Luzzi

1996-01-01

357

Experimental Ammonia Battery.  

National Technical Information Service (NTIS)

An engineering investigation was performed to design and develop a 10 watt, 24/32 volt, low temperature primary reserve liquid ammonia battery with minimum requirements for a prototype of 20 milliamperes output, 36 hours life, 5 pounds over-all weight, 55...

B. Sykes

1966-01-01

358

Ring-chain tautomerism in organic synthesis: synthesis of heterocyclic enamines from a novel and practical formal ring transformation reaction of lactones.  

PubMed

A novel approach to heterocyclic enamines has been developed from the formal ring transformation reaction of lactones. The synthesis comprises consecutive Reformatsky reaction of lactones and mesylation of the resulting mixture of ring-chain tautomers in a one-pot reaction, followed by cyclocondensation reaction with primary amines. The synthetic application of this method was demonstrated by a straightforward preparation of indolizidine compounds via N-(3-bromopropyl)-substituted enamine intermediates. The use of cheap and readily available materials and reagents under very mild conditions renders this formal ring transformation method practical and applicable in the preparation of various heterocyclic enamines that are the precursors for (poly)hydroxylated alkaloid derivatives. PMID:12688802

Wang, Mei-Xiang; Liu, Yong; Gao, Hong-Yun; Zhang, Yan; Yu, Chu-Yi; Huang, Zhi-Tang; Fleet, George W J

2003-04-18

359

Total synthesis of (+)-achalensolide based on the rh(i)-catalyzed allenic Pauson-Khand-type reaction.  

PubMed

The first total synthesis of (+)-achalensolide was achieved from a commercially available d-(-)-isoascorbic acid. The known epoxide, derived from d-(-)-isoascorbic acid, was converted into the allenyne, the Rh(I)-catalyzed Pauson-Khand-type reaction of which directly provided the bicyclo[5.3.0]decane system, a core framework of the title natural product. The construction of the gamma-lactone moiety and some chemical modifications resulted in the completion of the total synthesis of (+)-achalensolide. PMID:18161987

Hirose, Toshiyuki; Miyakoshi, Naoki; Mukai, Chisato

2007-12-28

360

Fusion by diffusion. II. Synthesis of transfermium elements in cold fusion reactions  

SciTech Connect

We describe a method of estimating cross sections for the synthesis of very heavy nuclei by the fusion of two lighter ones. The cross section is considered to be the product of three factors: the cross section for the projectile to overcome the Coulomb barrier, the probability that the resulting composite nucleus reaches the compound nucleus configuration by a shape fluctuation treated as a diffusion of probability in one dimension, and the probability that the excited compound nucleus survives fission. Semi-empirical formulas for the mean Coulomb barrier height and its distribution around the mean are constructed. After overcoming the Coulomb barrier the system is assumed to be injected into an 'asymmetric fission valley' by a rapid growth of the neck between the target and projectile at approximately frozen asymmetry and elongation. Diffusion in the elongation coordinate in this valley can occasionally bring the system over the saddle separating the injection point from the compound nucleus configuration. This is the stage that accounts for the hindrance to fusion observed for very heavy reacting systems. The competition between deexcitation of the compound nucleus by neutron emission and fission is treated by standard methods, but an interesting insight allows one to predict in an elementary way the location of the maximum in the resulting excitation function. Adjusting one parameter in the theory causes the calculated peak cross sections to agree within about a factor of 2 or so with 12 measured or estimated values for 'cold' one-neutron-out reactions where targets of {sup 208}Pb and {sup 209}Bi are bombarded with projectiles ranging from {sup 48}Ca to {sup 70}Zn. The centroids of the excitation functions agree with theory to within 1 or 2 MeV for the six cases where they have been determined, and their widths are reproduced. 'Hot' fusion reactions, where several neutrons are emitted, are not treated, except that a comparison is made between the hindrance factors in cold and hot reactions to make elements with atomic numbers 112 to 118. The calculated diffusive hindrances in the hot reactions are less unfavorable by 4 to 5 orders of magnitude.

Swiatecki, W.J. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Siwek-Wilczynska, K. [Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Wilczynski, J. [Andrzej Soltan Institute for Nuclear Studies, 05-400 Otwock-Swierk (Poland)

2005-01-01

361

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

PubMed

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

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

2006-12-14

362

Construction of vicinal all-carbon quaternary stereocenters by catalytic asymmetric alkylation reaction of 3-bromooxindoles with 3-substituted indoles: total synthesis of (+)-perophoramidine.  

PubMed

Highly congested vicinal all-carbon quaternary stereocenters were generated via catalytic asymmetric alkylation reaction of 3-bromooxindoles with 3-substituted indoles. These catalytic reactions proceeded in excellent yields with a broad scope on either reaction partner, and with outstanding diastereo- and enantiocontrol. The newly developed method led to the total synthesis of (+)-perophoramidine in a highly efficient manner. PMID:24032694

Zhang, Hailong; Hong, Liang; Kang, Hong; Wang, Rui

2013-09-13

363

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

364

Anhydrous ammonia injuries.  

PubMed

Anhydrous ammonia, a pungent, colorless gas or liquid, is commonly used around the world as a refrigerant and fertilizer in agriculture. It is an alkali causing liquefaction or freeze-dry lesions with skin contact. Initial emergency response involves evacuation, decontamination, first aid and alerting proper authorities. Decontamination must be complete and rescuers must avoid being overcome by fumes. Emergency department care is directed at respiratory, ocular, skin and gastrointestinal treatment. Respiratory and ocular lesions tend to be the most severe and can be used as a triage guide. The need for a multidisciplinary approach to hospital care is stressed. In severe exposures, adult respiratory distress syndrome is a common finding. In children who have ingested aqua ammonia, early endoscopy, aggressive antibiotic therapy and serial dilatations of strictures are recommended. Long-term complications occur predominately to the eyes and respiratory tract. PMID:19785216

Lessenger, James E

2004-01-01

365

Ammonia abundances in comets  

NASA Astrophysics Data System (ADS)

The emission band strengths of the NH2 bands of Comets Halley, Hartley-Good, Thiele, and Borrelly were measured to determine the NH2 column densities for the comets. Production rates obtained using the Haser and vectorial models are in agreement within the observational errors, suggesting that a simple two-step decay model may be used to approximate the NH2 distribution in a comet's coma. Ammonia-to-water abundance ratios from 0.01 to 0.4 percent were found for the four comets. The ratio in Comet Halley is found to be Q(NH3)/Q(H2O) = 0.002 + or - 0.001. No significant difference in the ammonia abundance was found before or after perihelion in Comet Halley.

Wyckoff, S.; Tegler, S.; Engel, L.

366

Reaction mechanisms of silicon carbide fiber synthesis by heat treatment of polycarbosilane fibers cured by radiation. 2: Free radical reaction  

Microsoft Academic Search

Silicon carbide (SiC) fibers were synthesized by the pyrolysis of radiation-cured polycarbosilane (PCS) fibers. The pyrolytic reaction was analyzed through free radicals by electron spin resonance (ESR). Free radicals on Si and C atoms were produced in the pyrolysis, and their yield as a function of reaction temperature depended on the oxygen content in the cured PCS fibers. There were

Masaki Sugimoto; Toshio Shimoo; Kiyohito Okamura; Tadao Seguchi

1995-01-01

367

Ignition phenomena and reaction mechanisms of the self-propagating high-temperature synthesis reaction in the titanium-carbon-aluminum system  

SciTech Connect

The effect of the addition of aluminum on the ignition and self-propagating high-temperature synthesis (SHS) reaction between titanium and carbon was experimentally investigated. Although TiC was the only product compound in the final product, the reaction between titanium and aluminum was believed to occur before the ignition of the reaction between titanium and carbon, as evidenced by a hump that appeared in the temperature profile during heating. The ignition temperature of the reaction between titanium and carbon was significantly decreased by the addition of aluminum. This was explained by the fact that the aluminum provides an easier route for reactant mass transfer, thus significantly increasing the reaction rate of the reaction between titanium and carbon. As the temperature was increased to beyond the melting point of aluminum during heating, aluminum melted and titanium dissolved into it. As the temperature was increased to beyond the melting point of aluminum during heating, aluminum melted and titanium dissolved into it. As the temperature was increased further (>1,050 C), the titanium-containing aluminum spread over the carbon particles. Ignition is believed to have occurred by the reaction of titanium and carbon at the interface by the diffusion of titanium through the aluminum melt to the interface. The rate of heating and the density of the reactant compact also affected the ignition temperature. These were explained by their influence on the extent of the capillary spreading of the titanium-containing aluminum melt on the carbon particles or by the formation of a TiAl{sub x} layer at the interface between the aluminum melt and the titanium particles. Fracture surfaces of the product showed three different types of morphology. A possible reaction mechanism was proposed that describes the ignition process and explains the formation of each type of product.

Lee, W.C.; Chung, S.L. [National Cheng Kung Univ., Tainan (Taiwan, Province of China). Dept. of Chemical Engineering

1997-01-01

368

Synthesis and reaction pathway investigation of chalcopyrite CuInSe2 nanoparticles for one-pot method  

NASA Astrophysics Data System (ADS)

Highly dispersed and near stoichiometric chalcopyrite CuInSe2 nanoparticles were successfully synthesized via a facile and rapid one-pot method. For understanding the reaction pathway, the solid intermediates obtained at different stages of CuInSe2 nanoparticles synthesis process were investigated in detail by powder X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), energy dispersive spectroscopy (EDS) and Raman spectroscopy. The XRD patterns showed that the phase formation sequence was CuSe ? CuInSe2. The XPS results indicated that the valences of Cu and Se in CuSe were +1 and -1, respectively. The chemical composition of the solid intermediates revealed the presence of the solid-state In-Se secondary phases in the synthesis process. However, no XRD signals or Raman signals of the solid-state In-Se secondary phase were observed. Based on the experimental results, the possible reaction pathway was proposed.

Han, Zhaoxia; Zhang, Dawei; Zhang, Daohua; Hong, Ruijin; Chen, Qinmiao; Tao, Chunxian; Huang, Yuanshen; Ni, Zhengji; Zhuang, Songlin

2013-10-01

369

Base-dependent stereodivergent intramolecular aza-Michael reaction: asymmetric synthesis of 1,3-disubstituted isoindolines.  

PubMed

The nucleophilic addition (AN ) / intramolecular aza-Michael reaction (IMAMR) process on Ellman's tert-butylsulfinyl imines, bearing a Michael acceptor in the ortho position, is studied. This reaction affords 1,3-disubstituted isoindolines with a wide range of substituents in good yields and diastereoselectivities. Interestingly, careful choice of the base for the aza-Michael step allows either the cis or the trans diastereoisomers to be exclusively obtained. This stereodivergent cyclization has enabled the synthesis of C2 -symmetric bisacetate-substituted isoindolines. In addition, bisacetate isoindolines bearing two well-differentiated ester moieties are also noteworthy because they may allow for the orthogonal synthesis of ?,?'-dipeptides using a single nitrogen atom as a linchpin. PMID:23852920

Fustero, Santos; Herrera, Lidia; Lázaro, Ruben; Rodríguez, Elsa; Maestro, Miguel A; Mateu, Natalia; Barrio, Pablo

2013-07-12

370

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

371

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

PubMed Central

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

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

2010-01-01

372

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

2013-09-17

373

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 Thomas

2013-05-17

374

Transition Metal-Mediated Higher-Order Cycloaddition Reactions: Application To The Total Synthesis Of Complex Natural Products  

Microsoft Academic Search

\\u000aTRANSITION METAL-MEDIATED HIGHER-ORDER CYCLOADDITION REACTIONS: APPLICATION TO THE TOTAL SYNTHESIS OF COMPLEX NATURAL PRODUCTS\\u000aby\\u000aBILAL ABOU ALEIWI\\u000aOctober 2010\\u000aAdvisor: Dr. James H. Rigby\\u000aMajor: Chemistry (Organic)\\u000aDegree: Doctor of Philosophy\\u000aChromium (0)-mediated [6ð + 2ð] and [6ð + 2ð + 2ð] cycloaddition reactions between cyclic trienes and alkynes is reported. The development, investigation and the application of these

Bilal Abou Aleiwi

2010-01-01

375

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

376

Synthesis of 1,5-benzodiazepine and its derivatives by condensation reaction using H-MCM-22 as catalyst.  

PubMed

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

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

2012-04-11

377

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

NASA Astrophysics Data System (ADS)

A layered titanate, potassium lithium titanate, with the size range from 0.1 to 30 µm was prepared to show the effects of the particle size on the materials performance. The potassium lithium titanate was prepared by solid-state reaction as reported previously, where the reaction temperature was varied. The reported temperature for the titanate preparation was higher than 800 °C, though 600 °C is good enough to obtain single-phase potassium lithium titanate. The lower temperature synthesis is cost effective and the product exhibit better performance as photocatalysts due to surface reactivity.

Ogawa, Makoto; Morita, Masashi; Igarashi, Shota; Sato, Soh

2013-10-01

378

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

379

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

380

Stereoregulated synthesis of unsaturated compounds Communication 9. Stereochemistry of the reactions of aldehydes with ?,?-unsaturated triphenylphosphonium ylides [alkylidenetriphenylphosphoranes  

Microsoft Academic Search

Conclusions 1.A study was made of the effect of the polarity of the medium and the nature of the halide ions on steric orientation in “carbonyl-olefination” with the aid of?,?-unsaturated triphenylphosphonium ylides.2.The conditions were found which made it possible to use the carbonyl-olefination reaction for the stereospecific synthesis of trans-trans and trans-cis dienes.

L. D. Bergel'son; V. D. Solodovik; M. M. Shemyakin

1966-01-01

381

Synthesis of Heterocycles Through Classical Ugi and Passerini Reactions Followed by Secondary Transformations Involving One or Two Additional Functional Groups  

Microsoft Academic Search

\\u000a The combination of classical isocyanide-based multicomponent reactions (Ugi and Passerini) with a variety of post-condensation\\u000a transformations, which take advantage of suitably positioned additional functional groups, allows the straightforward synthesis,\\u000a often in 1–2 synthetic steps, of many diverse nitrogen-containing heterocycles. This review will cover all the applications\\u000a of this strategy reported to date (September 2009).

Luca Banfi; Andrea Basso; Renata Riva

2010-01-01

382

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

2008-05-09

383

Selective Synthesis and Reactions of 6-Substituted- 2-?-galactosyl-1,2,4-triazines of Potential Anticancer Activity  

Microsoft Academic Search

Selective synthesis and reactions of different 6-substituted-2-?-D-galactosyl-3-thioxo-2,3-dihydro-1,2,4-triazin-5(4H)-ones using the developed amino or aryl protecting group strategy were investigated. Primary human anticancer screening of twelve selected compounds (in vitro) resulted in an active compound against both MCF7 (Breast) and SF-268(CNS) cell lines.

Abdel Kader Mansour; Mohga M. Eid; Nasser S. A. M. Khalil

2003-01-01

384

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

Microsoft Academic Search

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

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

2011-01-01

385

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

386

N-Heterocyclic carbene-catalyzed direct cross-aza-benzoin reaction: Efficient synthesis of ?-amino-?-keto esters  

PubMed Central

Summary An efficient catalytic synthesis of ?-amino-?-keto esters has been newly developed. Cross-coupling of various aldehydes with ?-imino ester, catalyzed by N-heterocyclic carbene, leads chemoselectively to ?-amino-?-keto esters in moderate to good yields with high atom efficiency. The reaction mechanism is discussed, and it is proposed that the ?-amino-?-keto esters are formed under thermodynamic control.

Uno, Takuya; Kobayashi, Yusuke

2012-01-01

387

Synthesis of gold-poly (dimethylsiloxane) nanocomposite through a polymer-mediated silver\\/gold galvanic replacement reaction  

Microsoft Academic Search

Silver-poly (dimethylsiloxane) nanocomposite films are prepared by an in-situ synthesis by incubating the polymer film in\\u000a a silver nitrate aqueous solution and using the reducing properties of the polymer’s curing agent. Silver nanoparticles concentrated\\u000a in the surface layer of the silver-poly (dimethylsiloxane) nanocomposite are further replaced by gold through a galvanic replacement\\u000a reaction at the poly (dimethylsiloxane)\\/gold salt solution interface.

Pooja Devi; Simona Badilescu; Muthukumaran Packirisamy; Pethaiyan Jeevanandam

2010-01-01

388

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

389

Ammonia emissions from seabird colonies  

NASA Astrophysics Data System (ADS)

Ammonia emissions were measured from two entire seabird colonies with contrasting species assemblages, to ascertain the ammonia volatilisation potentials among seabird species in relation to their nesting behaviour. Emissions were calculated from downwind plume measurements of ammonia concentration using both inverse dispersion and tracer ratio methods. Measured colony emissions ranged 1-90 kg NH3 hour-1, and equated to 16 and 36% volatilization of excreted nitrogen for colonies dominated by ground/burrow nesting and bare rock nesting birds, respectively. The results were applied in a bioenergetics model with a global seabird database. Seabird colonies are found to represent the largest point sources of ammonia globally (up to ~6 Gg NH3 colony-1 year-1). Moreover the largest emissions occur mainly in remote environments with otherwise low NH3 emissions. These ammonia ``hot spots'' explain significant perturbations of the nitrogen cycle in these regions and add ~20% to oceanic ammonia emissions south of latitude 45°S.

Blackall, Trevor D.; Wilson, Linda J.; Theobald, Mark R.; Milford, Celia; Nemitz, Eiko; Bull, Jennifer; Bacon, Philip J.; Hamer, Keith C.; Wanless, Sarah; Sutton, Mark A.

2007-05-01

390

Cobalt-catalyzed oxidative [3 + 2] cycloaddition reactions: an efficient synthesis of pyrrolo- and imidazo-[2,1-a]isoquinolines.  

PubMed

A cobalt-catalyzed oxidative [3 + 2] cycloaddition cascades of dihydroisoquinoline esters with nitroolefins or N-sulfuryl aldimines were developed at room temperature. A multi-component reaction for the synthesis of 5,6-dihydroimidazo[2,1-a]isoquinolines were also realized under almost identical conditions. This method is particularly suitable for the synthesis of tricyclic nitrogen heterocycles due to its simple manipulation, wide scope of the reaction substrates and excellent regioselectivity. PMID:23995231

Feng, Chengtao; Su, Ji-Hu; Yan, Yizhe; Guo, Fengfeng; Wang, Zhiyong

2013-08-30

391

A phosgene-free process for the synthesis of methyl N-phenyl carbamate by the reaction of aniline with methyl carbamate  

Microsoft Academic Search

A phosgene-free route for the synthesis of methyl N-phenyl carbamate (MPC) by the reaction of aniline with methyl carbamate in the presence of methanol was studied. Effects of catalysts, reaction temperature, reaction time, and catalyst content, the molar ratio of reactants and the content of water on the reaction were investigated. The results demonstrated that an aniline conversion of 90.1%

Qi-Feng Li; Jun-Wei Wang; Wen-Sheng Dong; Mao-Qing Kang; Xin-Kui Wang; Shao-Yi Peng

2004-01-01

392

Highly Chemoselective Rauhut-Currier Reaction between Maleimides and Enones and Dual Phosphine-Mediated One-Pot Synthesis of Bicyclic and Polycyclic Skeletons.  

PubMed

A highly chemoselective phosphine-catalyzed Rauhut-Currier reaction between maleimides and enones has been realized under very mild conditions, affording the corresponding cross-coupling products in moderate to excellent yields. On the basis of this reaction, an efficient dual phosphine-mediated one-pot synthesis of bicyclic and polycyclic compounds containing a cyclopenta[c]pyrrole skeleton has been accordingly developed, which features a tandem sequence of intermolecular Rauhut-Currier reaction and intramolecular Wittig reaction. PMID:24087883

Zhou, Rong; Wang, Jianfang; Yu, Jia; He, Zhengjie

2013-10-14

393

Equilibria of the marine multiphase ammonia system  

Microsoft Academic Search

A lack of empirical data has made it difficult to ascertain whether ammonia is in equilibrium between the oceanic, atmospheric gas and atmospheric particle phases in the remote marine environment. Reported here are simultaneous measurements of the saturation concentration of ammonia relative to ammonia concentrations in ocean surface waters; total seawater ammonia; atmospheric gas phase ammonia; and atmospheric particulate-phase ammonium,

P. K. Quinn; W. E. Asher; R. J. Charlson

1992-01-01

394

The Synthesis of Carboxylic Acids via an Aldol-Grob Reaction Sequence  

Microsoft Academic Search

Ketones react with aromatic aldehydes via a tandem Aldol-Grob reaction sequence. The reaction, initiated by boron trifluoride, produces a carboxylic acid fragment and can serve as an alternative to the Baeyer-Villiger reaction.

G. W. Kabalka; N.-S. Li; D. Tejedor; R. R. Malladi; X. Gao; S. Trotman

1999-01-01

395

Stereoselective synthesis of unsaturated and functionalized L-NHBoc amino acids, using Wittig reaction under mild phase-transfer conditions.  

PubMed

The stereoselective synthesis of a new amino acid phosphonium salt was described by quaternization of melting triphenylphosphine with the ?-iodo NHBoc-amino ester, derived from L-aspartic acid. The deprotection of the carboxylic acid function to afford the phosphonium salt with a free carboxylic acid group was achieved by a palladium-catalyzed desallylation reaction. This phosphonium salt was used in the Wittig reaction with aromatic or aliphatic aldehydes and trifluoroacetophenone, under solid-liquid phase-transfer conditions in chlorobenzene and in the presence of K(3)PO(4) as weak base, to afford the corresponding unsaturated amino acids without racemization. Thus, the reaction with substituted aldehydes allows to graft various functionalized groups on the lateral chain of the amino acid, such as trifluoromethyl, cyano, nitro, ferrocenyl, boronato, or azido. In addition, the reaction of the amino acid Wittig reagent with ?,?-unsaturated aldehydes leads to amino acids bearing a diene on the lateral chain. Finally, this amino acid phosphonium salt appears to be a new powerful tool for the preparation of unsaturated and non-proteinogenic ?-amino acids, directly usable for the synthesis of customized peptides. PMID:22870957

Rémond, Emmanuelle; Bayardon, Jérôme; Ondel-Eymin, Marie-Joëlle; Jugé, Sylvain

2012-08-23

396

Purification of tetraethyllead by treatment with aqueous ammonia solution  

SciTech Connect

The purpose of this work was to study the exhaustive removal of trace amounts of metals from tetraethyllead using aqueous ammonia solution. To assess the possibilities of the method, the authors studied the behavior of trace amounts of diethylzinc and ferric chloride during treatment of TEL with aqueous ammonia. Radioactive compounds of WVZn and VZFe were used in the investigations. (The radioactive tracer method can be used in the region of trace concentrations and greatly simplifies monitoring of the impurity contents in the original substances and reaction products.) Radioactive iron-59 was used directly in the form of ferric chloride; labeled diethylzinc was obtained from metallic zinc-65 by reaction.

Zorin, A.D.; Feshchenko, I.A.; Leonov, M.R.; Ronina, O.V.; Tainov, A.V.; Tsinovoi, Y.N.; Veryulina, L.N.

1985-05-10

397

Organometallics in organic synthesis. Applications of a new diorganozinc reaction to the synthesis of C-glycosyl compounds with evidence for an oxonium-ion mechanism.  

PubMed

The mechanistic and stereochemical features of a new organozinc-based substitution process [heteroatom-C-(R1,R2)-SPh + R3(2)Zn----heteroatom-C-(R1,R2,R3)], first discovered during a total synthesis of the alkaloid mycotoxin alpha-cyclopiazonic acid, are described. Phenyl thioglycosides were valuable substrates in studying the nature of this reaction process. Since these sulfur compounds are converted into C-glycosyl compounds with some degree of stereoselectivity, the organozinc chemistry does provide a new entry to these biologically active substances. PMID:3442773

Kozikowski, A P; Konoike, T; Ritter, A

1987-12-31

398

Metabolic fates of ammonia-N in ruminal epithelial and duodenal mucosal cells isolated from growing sheep.  

PubMed

The objective of this experiment was to determine the capability of ruminant gut tissues to detoxify ammonia-N using short-term incubations of isolated cells in vitro. Ruminal epithelial cells (REC) and duodenal mucosal cells (DMC) were isolated from growing Texel-Polypay ram lambs (n = 4) fed a pelleted forage:concentrate-based diet. Immediately after isolation, primary cells were incubated for 60 min with glucose (1mM), glutamate (1mM), [15N]ammonium chloride (5, 10, 20, or 40 mM), and 1 of 4 combinations of substrates (1 mM each) that could support urea synthesis [control, N-carbamoylglutamate (NCG); NCG + ornithine (ONCG); and ONCG + aspartate (AONCG)]. Treatments were arranged in a 4 x 4 factorial design. Incorporation of ammonia-15N into alanine, citrulline, arginine, and urea was determined by gas chromatography-mass spectrometry. For both cell types, ammonia-N transfer to alanine was lower when incubation medium contained NCG compared with control, whereas use of ammonia-N for net alanine synthesis increased quadratically with ammonia concentration regardless of substrate treatment. For REC, ammonia-N was not incorporated into citrulline, arginine, or urea, nor into arginine or urea by DMC. Ammonia-N use for net citrulline synthesis exhibited an inverse relationship with ammonia concentration, decreasing linearly as media ammonia concentration increased. Thus, ala-nine synthesis may be a significant metabolic pathway for ruminant gut tissues to detoxify ammonia-N when it is presented luminally at high concentrations as compared with detoxification by the ornithine-urea cycle. Furthermore, DMC do exhibit a metabolic capability to incorporate ammonia-N into citrulline, but low or absent activity of downstream enzymes of the ornithine-urea cycle appears to limit ammonia-N transfers to urea. PMID:16230702

Oba, M; Baldwin, R L; Owens, S L; Bequette, B J

2005-11-01

399

Synthesis of Unsymmetrical Diaryl Ureas via Pd-Catalyzed C-N Cross-Coupling Reactions  

PubMed Central

A facile synthesis of unsymmetrical N,N?-diaryl ureas is described. The utilization of the Pd-catalyzed arylation of ureas enables the synthesis of an array of diaryl ureas in good to excellent yields from benzylurea via a one-pot arylation-deprotection protocol, followed by a second arylation.

Breitler, Simon; Oldenhuis, Nathan J.; Fors, Brett P.; Buchwald, Stephen L.

2011-01-01

400

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

401

46 CFR 154.1760 - Liquid ammonia.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 2012-10-01 false Liquid ammonia. 154.1760 Section 154...Operating Requirements § 154.1760 Liquid ammonia. The master shall ensure that no person sprays liquid ammonia into a cargo tank containing...

2012-10-01

402

46 CFR 154.1760 - Liquid ammonia.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 2011-10-01 false Liquid ammonia. 154.1760 Section 154...Operating Requirements § 154.1760 Liquid ammonia. The master shall ensure that no person sprays liquid ammonia into a cargo tank containing...

2011-10-01

403

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

Microsoft Academic Search

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

Abraham Langlet; Ulf Wellmar; Ulf Bemm

1998-01-01

404

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

2013-02-06

405

The formation and removal characteristics of aerosols in ammonia-based wet flue gas desulfurization  

Microsoft Academic Search

The characteristics of aerosol generation were studied experimentally in an ammonia-based wet flue gas desulfurization process. Particle size distributions and concentrations, morphologies and compositions before and after desulfurization were measured using an electrical low pressure impactor and scanning electron microscopy, respectively. The results show that aerosols can be generated between ammonia and sulfur dioxide resulting in gas-phase reaction and the

Jinpei Yan; Jingjing Bao; Linjun Yang; Fengxian Fan; Xianglin Shen

2011-01-01

406

Pd-catalyzed copper-free carbonylative Sonogashira reaction of aryl iodides with alkynes for the synthesis of alkynyl ketones and flavones by using water as a solvent.  

PubMed

The Pd-catalyzed copper-free carbonylative Sonogashira coupling reaction to synthesize alkynyl ketones from terminal alkynes and aryl iodides was achieved by using water as a solvent. The reaction was carried out at room temperature under balloon pressure of CO with Et(3)N as a base. The developed method was successfully applied to the synthesis of flavones. PMID:16018709

Liang, Bo; Huang, Mengwei; You, Zejin; Xiong, Zhengchang; Lu, Kui; Fathi, Reza; Chen, Jiahua; Yang, Zhen

2005-07-22

407

Three-component reactions of isocyanides, dialkyl acetylenedicarboxylates, and trans-cinnamoyl chlorides for the synthesis of highly functionalized 2-vinyl furans.  

PubMed

In this study, we present a convenient and efficient method for the synthesis of novel, highly substituted 2-vinyl furans using a three-component reaction. The zwitterions generated from the reaction of isocyanides and dialkyl acetylenedicarboxylates are reacted with trans-cinnamoyl chlorides to produce the desired products in good yields. PMID:22173695

Esmaeili, Abbas Ali; Zangouei, Mahdieh; Hosseinabadi, Rahele; Fakhari, Ali Reza

2011-12-16

408

PEG-mediated catalyst-free expeditious synthesis of polysubstituted anilines and benzenes via the reaction of malononitrile and ?-ketoester derivatives in the presence of activated acetylenes.  

PubMed

Poly(ethylene glycol) (PEG) has been used as a sustainable, non-volatile, and environmentally friendly reaction solvent for synthesis of functionalized anilines and benzenes via the reaction of malononitrile and ?-ketoester derivatives in the presence of activated acetylenes at 80° C. No additional solvent and catalyst are required. PMID:22292778

Piltan, Mohammad; Moradi, Loghman; Salimi, Hiwa; Zargoosh, Kiomars; Zarei, Seyed Amir

2012-08-01

409

An efficient electrochemical synthesis of diamino-o-benzoquinone: mechanistic and kinetic evaluation of the reaction of azide ion with o-benzoquinone.  

PubMed

An efficient method for the synthesis of diamino-o-benzoquinone based on the Michael reaction of electrochemically generated o-benzoquinone with azide ion is described, as well as an estimation of the homogeneous rate constant (k(obs)) of the reaction of o-benzoquinone with azide ion by the digital-simulation method. PMID:17180233

Nematollahi, Davood; Afkhami, Abbas; Tammari, Esmail; Shariatmanesh, Tahere; Hesari, Mahdi; Shojaeifard, Maryam

2006-10-25

410

Visible light-mediated oxidative quenching reaction to electron-rich epoxides: highly regioselective synthesis of ?-bromo (di)ketones and mechanism study.  

PubMed

A novel and simple procedure was developed for the regioselective synthesis of ?-bromo (di)ketones from electron-rich epoxides via visible light photoredox catalysis. Through optimization of solvent and light source, the reaction can be rapidly achieved under mild conditions. Moreover, the possible reaction mechanism was proposed and further supported by control experiments. PMID:23903874

Guo, Lin; Yang, Chao; Zheng, Lewei; Xia, Wujiong

2013-08-14

411

Practical synthesis of 1,3-oleoyl 2-docosahexaenoylglycerol by lipase-catalyzed reactions: An evaluation of different reaction routes  

Microsoft Academic Search

Three new synthetic routes were critically evaluated for the lipase-catalyzed production of 1,3-oleoyl-2 docosahexaenoylglycerol (ODO) in relatively large-scale (approximately 200g). First, the production of 1,3-diolein by the reaction of glycerol and oleic acid followed by incorporation of docosahexaenoic (DHA) ethyl ester at the sn-2 position was studied. 1,3-Diolein was produced in 68.3% and 84.6% yield when stoichiometric amounts of the

H. Zhang; G. Önal; C. Wijesundera; X. Xu

2009-01-01

412

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

SciTech Connect

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

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

2009-11-15

413

Simulation of Reaction Dynamics for Synthesis of Energetic Materials and Resistant Coatings.  

National Technical Information Service (NTIS)

The objective of this research was the development of theoretical and computational methods to guide the efficient synthesis of HEDM (High Energy Density Matter) for use in advanced propellants and POSS (polyhedral oligomeric silsesquioxanes) for use in c...

S. Hammes-Schiffer

2004-01-01

414

Sulfamic Acid Catalyzed One-Pot Synthesis of Polyhydroquinolines via the Hantzsch Four Component Condensation Reaction  

Microsoft Academic Search

The synthesis of polyhydroquinoline derivatives has been achieved using catalytic amounts of green, inexpensive and environmentally benign sulfamic acid. The process is operationally simple and has good to excellent yields.

Naser Foroughifar; Akbar Mobinikhaledi; Mohammad Ali Bodaghi Fard; Hassan Moghanian; Sattar Ebrahimi

2009-01-01

415

Design and synthesis of fluconazole\\/bile acid conjugate using click reaction  

Microsoft Academic Search

Novel fluconazole\\/bile acid conjugates were designed and their regioselective synthesis was achieved in very high yield via Cu(I) catalyzed intermolecular 1,3-dipolar cycloaddition. These new molecules showed good antifungal activity against Candida species.

Vandana S. Pore; Nilkanth G. Aher; Manish Kumar; Praveen K. Shukla

2006-01-01

416

Stereoselective synthesis of unsymmetrical ?,?-diarylacrylates by a Heck-Matsuda reaction: versatile building blocks for asymmetric synthesis of ?,?-diphenylpropanoates, 3-aryl-indole, and 4-aryl-3,4-dihydro-quinolin-2-one and formal synthesis of (-)-indatraline.  

PubMed

?,?-Disubstituted ?,?-unsaturated esters may serve as valuable derivatives for the preparation of other highly functionalized systems found in many natural products and marketed drugs. The stereoselective synthesis of unsymmetrical ?,?-diarylacrylate compounds possessing two similar aromatic groups remains a substantial challenge. A simple and convenient stereoselective protocol for the preparation of ?,?-disubstituted acrylates via a Heck-Matsuda reaction is reported. Good to high yields were accomplished by a "ligand-free" Pd-catalyzed arylation reaction of cinnamate esters with arenediazonium tetrafluoroborates. Both electron-deficient and electron-rich arenediazonium salts could be employed as arylating reagents, and cinnamate esters were generally more reactive when substituted with an electron-donating group. The overall methodology is highly stereoselective, and this attribute was taken advantage of in the asymmetric Cu-catalyzed 1,4 reduction reaction to provide ?,?-diarylpropanoates in high enantioselectivities. The synthesis of a 3-aryl indole and a chiral 4-aryl-2-quinolone from ?,?-diarylacrylates was achieved by cyclization in the presence of a diphosphine ligated CuH catalyst. A convenient route for the asymmetric formal synthesis of the psychoactive compound (-)-Indatraline is also presented. PMID:21241065

Taylor, Jason G; Correia, Carlos Roque D

2011-01-11

417

DABCO-catalyzed [2+2] cycloaddition reactions of allenoates and trifluoromethylketones: synthesis of 2-alkyleneoxetanes  

Microsoft Academic Search

DABCO was found to be an efficient catalyst for the formal [2+2] cycloaddition reaction of allenoates and trifluoromethylketones (Paterno–Buchi reaction) to give the corresponding 2-alkyleneoxetanes in good yields with good diastereoselectivities.

Tong Wang; Xiang-Yu Chen; Song Ye

2011-01-01

418

Dipeptide vinyl sultams: synthesis via the Wittig-Horner reaction and activity against papain, falcipain-2 and Plasmodium falciparum.  

PubMed

The synthesis of phosphonate derivatives of N-phenyl- and N-benzyl-gamma- and delta-sultams, and their application in the Wittig-Horner reaction with N-Boc-L-phenylalanine aldehyde to afford E- and Z-isomers, are described. These compounds were further processed to provide five dipeptide vinyl sultams, which were found to be inactive against papain at concentrations up to 50 microM. In contrast, vinyl sultams demonstrated weak activity against recombinant falcipain-2 and Plasmodium falciparum W2. PMID:16697641

Valente, Cláudia; Guedes, Rita C; Moreira, Rui; Iley, Jim; Gut, Jiri; Rosenthal, Philip J

2006-05-12

419

Studies on the synthesis of hydroxyl-terminated isophthalate-based oligoesters via transesterification reaction  

Microsoft Academic Search

A series of isophthalate-based oligoesters was synthesized via the transesterification reaction of dimethyl isophthalate (DI) with various aliphatic diols under different diol(s)\\/diester molar ratios. The effect of a series of reaction parameters, such as the diols\\/diester molar ratio, the molar ratio of the diols in the reaction mixture, the species of the diol, the reaction time, the heating procedure, and

C. D Diakoumakos; F. N Jones

2001-01-01

420

Reaction of oxiranes and oxetanes with carbonyl compounds. Synthesis of 1,3-dioxacycloalkanes (review)  

Microsoft Academic Search

Data on the reaction of oxiranes and oxetanes with carbonyl compounds are correlated. The effect of the nature of the catalyst and the structure of the starting reagents on the selectivity of the reaction and the kinetics, stereochemistry, and mechanism of the reaction are discussed.

D. L. Rakhmankulov; O. B. Chalova; T. K. Kiladze; E. A. Kantor

1984-01-01

421

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

ERIC Educational Resources Information Center

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

Martin, Eric; Kellen-Yuen, Cynthia

2007-01-01

422

Cu-catalyzed synthesis of diaryl thioethers and S-cycles by reaction of aryl iodides with carbon disulfide in the presence of DBU.  

PubMed

Diaryl thioethers and S-cycles were obtained on the basis of the copper-catalyzed reaction of carbon disulfide and aryl iodides in the presence of DBU. This reaction enables the one-pot synthesis of diaryl thioethers by employing cheap, available, and easy-to-handle carbon disulfide with aryl iodides. The reaction was successfully employed in the construction of sulfur-containing cyclic molecules. PMID:23611365

Zhao, Peng; Yin, Hang; Gao, Hongxin; Xi, Chanjuan

2013-05-02

423

The formation of TiC\\/Al2O3 microstructures by a self-propagating high-temperature synthesis reaction  

Microsoft Academic Search

The effect of processing variables on reaction rate and ceramic microstructure are examined for the self-propagating high-temperature synthesis reaction 3TiO2+4Al+3C ? 3TiC+2Al2O3. Reaction controlling methods used are reactant particle size, the use of diluents (to lower the combustion temperature) and the use of reactant preheating (to increase the combustion temperature). The ceramic microstructure has an unusual laminar structure which is

C. R. Bowen; B. Derby

1996-01-01

424

Abiotic synthesis of purines and other heterocyclic compounds by the action of electrical discharges  

Microsoft Academic Search

Summary The synthesis of purines and pyrimidines using Oparin-Urey-type primitive Earth atmospheres has been demonstrated by reacting methane, ethane, and ammonia in electrical discharges. Adenine, guanine, 4-aminoimidazole-5-carboxamide (AICA), and isocytosine have been identified by UV spectrometry and paper chromatography as the products of the reaction. The total yields of the identified heterocyclic compounds are 0.0023%. It is concluded that adenine

S. Yuasa; D. Flory; B. Basile; J. Oró

1984-01-01

425

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

2013-07-31

426

Hydrothermal oxidation of ammonia/organic waste mixtures  

SciTech Connect

Hydrothermal oxidation is a promising new technology for the treatment of radioactive contaminated hazardous organic wastes. Los Alamos National Laboratory is currently evaluating this technology for the U. S. Department of Energy. In this paper, we present experimental results from the study of the hydrothermal oxidation of an ammonia/alcohol/uranium waste mixture. The use of a co-oxidant system consisting of hydrogen peroxide combined with nitrate is discussed. Experiments demonstrate near complete destruction of ammonia and organic compounds at 500{degrees} C, 38 MPa, and 50 seconds reaction time. The ammonia and total organic carbon (TOC) concentrations in a waste simulant is reduced from 8,500 mg/L of ammonia and 12,500 mg/L TOC to 30 mg/L ammonia and less than 10 mg/L TOC. The major reaction products are CO{sub 2}, N{sub 2}, and a small amount of N{sub 2}O. Comparison experiments with nitrate and hydrogen peroxide used individually show the advantage of the co-oxidant system.

Luan, Li; Proesmans, P.I.; Buelow, S.J.

1997-05-01

427

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

PubMed

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

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

2010-03-09

428

Acid-Promoted Cyclization Reactions of Tetrahydroindolinones. Model Studies for Possible Application in a Synthesis of Selaginoidine  

PubMed Central

The synthesis of various substituted bicyclic lactams by an acid-induced Pictet-Spengler reaction of tetrahydroindolinones bearing tethered heteroaromatic rings is presented. The outcome of the cyclization depends on the position of the furan tether, tether length, nature of the tethered heteroaromatic ring and the substituent group present on the 5-position of the tethered heteroaryl group. A one-pot procedure was developed to efficiently prepare tetrahydroindolinones containing tethered furan rings. In a typical example, the reaction of furanyl azide 26 with n-Bu3P delivered iminophosphorane 27, which was allowed to react with a 1 -alkyl-(2-oxocyclohexyl)acetic acid to provide the desired furanyl substituted tetrahydroindolinone system 29. Treatment of 29 with trifluoroacetic acid afforded the tetracyclic lactam skeleton 30 found in the alkaloid (±)-selaginoidine.

Rose, Mickea D.; Cassidy, Michael P.; Rashatasakhon, Paitoon

2008-01-01

429

Synthesis of ?-azido-?-ureido ketones and their transformation into functionalized pyrrolines and pyrroles via Staudinger/aza-Wittig reaction.  

PubMed

A simple two-step procedure yielding ?-azido-?-ureido ketones or/and their cyclic isomers, 6-(1-azidoalkyl)-4-hydroxyhexahydropyrimidin-2-ones, has been developed. The synthesis includes three-component condensation of acetals of 2-azidoaldehydes with urea or methylurea and p-toluenesulfinic acid in aqueous formic acid followed by reaction of the obtained N-[(2-azido-1-tosyl)alkyl]ureas with sodium enolates of ?-functionalized ketones. The azido ketones or their cyclic isomers are transformed into ureido-substituted ?(1)- or/and ?(2)-pyrrolines via Staudinger/aza-Wittig reaction promoted by PPh(3). The obtained pyrrolines are converted into 3-functionalized 1H-pyrroles via elimination of urea under acidic conditions. Convenient one-pot syntheses of 1H-pyrroles starting from N-[(2-azido-1-tosyl)alkyl]ureas or ?-azido-?-ureido ketones have been also developed. PMID:23256785

Fesenko, Anastasia A; Shutalev, Anatoly D

2013-01-10

430

Ammonia Emissions from Dairy Production Systems in Wisconsin  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

431

Combustion hazard of mixing ammonia with nitric oxide  

Microsoft Academic Search

Premixed ammonia\\/nitric oxide flame was simulated using the Lindstedt 1994 and Miller–Bowman 1989 reaction mechanisms in CHEMKIN. The predicted laminar burning velocities compared well with limited measured values in the literature. The effects of unburnt mixture temperature and pressure on laminar burning velocity, flammability limits, adiabatic flame temperature and species profiles were studied. The unburnt mixture temperature had a positive

Rui Liu; David S.-K. Ting; M. David Checkel

2003-01-01

432

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

PubMed

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

Auyoong, Yow Loo; Yap, Pei Lay; Huang, Xing; Abd Hamid, Sharifah Bee

2013-04-10

433

AQUEOUS AMMONIA EQUILIBRIUM - TABULATION OF PERCENT UN-IONIZED AMMONIA  

EPA Science Inventory

The percent of un-ionized ammonia as a function of pH and temperature in aqueous ammonia solutions of zero salinity is presented in tabular form over the following ranges: temperature 0.0 to 40.0 C in increments of 0.2 degree, and pH 5.00 to 12.00 in increments of 0.01 pH unit....

434

Synthesis of different-sized silver nanoparticles by simply varying reaction conditions with leaf extracts of Bauhinia variegata L.  

PubMed

Green synthesis of nanoparticles is one of the crucial requirements in today's climate change scenario all over the world. In view of this, leaf extract (LE) of Bauhinia variegata L. possessing strong antidiabetic and antibacterial properties has been used to synthesise silver nanoparticles (SNP) in a controlled manner. Various-sized SNP (20-120?nm) were synthesised by varying incubation temperature, silver nitrate and LE concentrations. The rate of SNP synthesis and their size increased with increase in AgNO(3) concentration up to 4?mM. With increase in LE concentration, size and aggregation of SNP was increased. The size and aggregation of SNP were also increased at temperatures above and below 40°C. This has suggested that size and dispersion of SNP can be controlled by varying reaction components and conditions. Polarity-based fractionation of B. variegata LE has suggested that only water-soluble fraction is responsible for SNP synthesis. Fourier transform infrared spectroscopy analysis revealed the attachment of polyphenolic and carbohydrate moieties to SNP. The synthesised SNPs were found stable in double distilled water, BSA and phosphate buffer (pH 7.4). On the contrary, incubation of SNP with NaCl induced aggregation. This suggests the safe use of SNP for various in vivo applications. PMID:22423864

Kumar, V; Yadav, S K

2012-03-01

435

ENGINEERING DESIGN CONFIGURATIONS FOR BIOLOGICAL AMMONIA REMOVAL  

EPA Science Inventory

Many regions in the United States have excessive levels of nutrients including ammonia in their source waters. For example, farming and agricultural sources of ammonia in the Midwest contribute to relatively high levels of ammonia in many ground waters. Although ammonia in water ...

436

Breath Ammonia Analysis: Clinical Application and Measurement  

Microsoft Academic Search

This review covers in detail the complexity of human breath, how the body metabolizes ammonia, clinical conditions which are directly related to the regulation of ammonia concentration, and analysis of current techniques that are capable of detecting breath ammonia. Focusing on these areas provides the information needed to develop a breath ammonia sensor for monitoring dysfunction of the human body.

Troy Hibbard; Anthony J. Killard

2011-01-01

437

Ammonia distribution and excretion in fish  

Microsoft Academic Search

This paper reviews the literature concerning ammonia production, storage and excretion in fish. Ammonia is the end product of protein catabolism and is stored in the body of fish in high concentrations relative to basal excretion rates. Ammonia, if allowed to accumulate, is toxic and is converted to less toxic compounds or excreted. Like other weak acids and bases, ammonia

David J. Randall; Patricia A. Wright

1987-01-01

438

Two Types of Rearrangement of Benzhydryltrimethyl Ammonium Ion by Sodium Amide in Liquid Ammonia.  

National Technical Information Service (NTIS)

Previously, the product from the reaction of the benzhydryltrimethylammonium ion with sodium amide in liquid ammonia was thought to consist exclusively of the tertiary amine, which arose through the ortho-substitution rearrangement. It is now found that o...

K. P. Klein C. R. Hauser

1966-01-01

439

Ammonia-Based Hydrogen Generation Apparatus and Method for Using Same.  

National Technical Information Service (NTIS)

The present disclosure provides teachings relating to ammonia-based hydrogen generation apparatus and associated methods of use. Exemplary methods and apparatus comprise a thermocatalytic hydrogen generation reactor which includes a reaction chamber conta...

A. Chellappa M. R. Powell

2005-01-01

440

The Exposure of Ammonia to the Photodissociated Hemoglobin of the Marine Bloodworm, 'Glycera dibranchiata'.  

National Technical Information Service (NTIS)

Ammonia was injected into an anaerobic reaction chamber containing non-liganded hemoglobin (from the bloodworm, Glycera dibranchiata) obtained by employing a photolytic technique to dissociate carbon monoxide from the hemoglobin molecule. No major alterat...

R. J. Sousa T. L. Meade G. T. Felbeck

1976-01-01

441

Electrolytic decomposition of ammonia to nitrogen in a multi-cell-stacked electrolyzer with a self-pH-adjustment function  

Microsoft Academic Search

This paper describes a study of continuous decomposition characteristics of ammonia to nitrogen in a multi-cell-stacked electrolyzer with an anion exchange membrane. The pH change of ammonia solution in both the anodic and cathodic chambers of a divided cell due to the water splitting reactions was studied together with the electrolytic decomposition of ammonia. The electrolytic decomposition efficiency of ammonia

Kwang-Wook Kim; In-Tae Kim; Geun-Il Park; Eil-Hee Lee

2006-01-01

442

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

443

Enantioselective synthesis of anti- and syn-homopropargyl alcohols via chiral Brønsted acid catalyzed asymmetric allenylboration reactions.  

PubMed

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 highly diastereoselective syntheses of a variety of anti, anti-stereotriads, the direct synthesis of which has constituted a significant challenge using previous generations of aldol and crotylmetal reagents. PMID:22731887

Chen, Ming; Roush, William R

2012-06-25

444

Synthesis and Polymerization of Renewable 1,3-Cyclohexadiene Using Metathesis, Isomerization, and Cascade Reactions with Late-metal Catalysts.  

PubMed

Synthesis and subsequent polymerization of renewable 1,3-cyclohexadiene (1,3-CHD) from plant oils is reported via metathesis and isomerization reactions. The metathesis reaction required no plant oil purification, minimal catalyst loading, no organic solvents, and simple product recovery by distillation. After treating soybean oil with a ruthenium metathesis catalyst, the resulting 1,4-cyclohexadiene (1,4-CHD) was isomerized with RuHCl(CO)(PPh(3) )(3) . The isomerization reaction was conducted for 1?h in neat 1,4-CHD with [1,4-CHD]/[RuHCl(CO)(PPh(3) )(3) ] ratios as high as 5 000. The isomerization and subsequent polymerization of the renewable 1,3-CHD was examined as a two-step sequence and as a one-step cascade reaction. The polymerization was catalyzed with nickel(II)acetylacetonate/methaluminoxane in neat monomer, hydrogenated d-limonene, and toluene. The resulting polymers were characterized by FTIR, DSC, and TGA. PMID:21648003

Mathers, Robert T; Shreve, Michael J; Meyler, Etan; Damodaran, Krishnan; Iwig, David F; Kelley, Diana J

2011-06-01

445

Mass Spectroscopy of Chemical Reaction of 3d Metal Clusters Involved in Chemical Vapor Deposition Synthesis of Carbon Nanotubes  

NASA Astrophysics Data System (ADS)

The chemical reactions of transition metal clusters in the gas phase have aroused considerable scientific interest and are also of critical scientific importance. For example, these reactions are involved in the synthesis of single-walled carbon nanotubes, which are considered ideal materials because of their outstanding properties. Alcohol catalytic chemical vapor deposition (ACCVD) is one of the best synthetic processes for carbon nanotubes (CNTs); however, even the initial growth mechanism is still unclear, unlike those of other synthetic processes. In this study, we used a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer to determine the initial reactions of transition metal cluster ions (iron, cobalt, and nickel) that are typically adopted in the alcohol CVD process. Metal clusters with approximately 10-25 atoms each, generated by a pulsed laser ablation system in a supersonic-expansion cluster beam source, were directly carried into the FT-ICR cell. Subsequently, ethanol was introduced into the ICR cell. We observed two different results: one was simple chemisorption observed in the iron cluster and the other was dehydrogenated chemisorption observed in the nickel cluster; however, cobalt clusters exhibited both patterns, and a sequential reaction was observed. Furthermore, the dehydrogenation of ethanol on the cobalt cluster is fully described from isotope-labeled experiments.

Inoue, Shuhei; Maruyama, Shigeo

2008-04-01

446

Ammonia transport by terrestrial and aquatic insects.  

PubMed

Ammonia, an end product from amino acid and nucleic acid metabolism, is highly toxic for most animals. This review will provide an update on nitrogen metabolism in terrestrial and aquatic insects with emphasis on ammonia generation and transport. Aspects that will be discussed include metabolic pathways of nitrogenous compounds, the origin of ammonia and other nitrogenous waste products, ammonia toxicity, putative ammonia transporters as well as ammonia transport processes known in insects. Ammonia transport mechanisms in the mosquito Aedes aegypti, the tobacco hornworm Manduca sexta and the locust Schistocerca gregaria will be discussed in detail while providing additional, novel data. PMID:22100291

Weihrauch, Dirk; Donini, Andrew; O'Donnell, Michael J

2011-11-10

447

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

448

Facile synthesis of functionalized spiro[indoline-3,2'-oxiran]-2-ones by Darzens reaction  

PubMed Central

Summary A series of functionalized spiro[indoline-3,2'-oxiran]-2-ones was efficiently synthesized by Darzens reaction of phenacyl bromides with isatins both with N-alkyl groups and without N-substituent in the presence of potassium carbonate as a base catalyst. When two equivalents phenacyl bromides were used in the reaction, the N-substitution reaction of isatin also finished with the formation of spiro-oxirane-oxindoles.

Fu, Qin

2013-01-01

449

Synthesis of [2]rotaxanes by the copper-mediated threading reactions of aryl iodides with alkynes.  

PubMed

The catalytic activity of the macrocyclic phenanthroline-copper(I) complex is utilized for the Sonogashira-type reaction to synthesize [2]rotaxanes. Thus, [2]rotaxanes were prepared by reactions between terminal alkynes and aryl iodides in the presence of the macrocyclic copper complex. Bulky substituents were introduced to the substrates to stabilize the rotaxane. The bond-forming reaction proceeded selectively inside the macrocyclic complex so that the rotaxanes could be synthesized. PMID:23668333

Ugajin, Kenta; Takahashi, Eiko; Yamasaki, Ryu; Mutoh, Yuichiro; Kasama, Takeshi; Saito, Shinichi

2013-05-13

450

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