Search results for "AMMONIA"
showing 10 items of 233 documents
Substituent effect on ammonia–borane donor–acceptor complexes: a G2(MP2) molecular orbital study
1998
Abstract H3BNHnMe3−n and Me3−nHnBNH3 (n=0–3) donor–acceptor complexes have been studied using the G2(MP2) method. Predicted equilibrium structures and dissociation energies have been correlated to the degree of substitution on the donor and the acceptor separately. It is found that successive methyl substitutions on boron reduce the dissociation energies of the complexes, contrary to the successive substitutions on nitrogen. The NBO partitioning scheme suggests that there is no correlation between the charge transfer and the dissociation energies. These results are interpreted in terms of the changes in the HOMO−LUMO gap, the type of acceptor and donor involved, and distortion of the accept…
Effect of Temperature on N2O and NO Emission in a Partial Nitrification SBR Treating Reject Wastewater
2017
Temperature is a very important parameter during nitritation, having a direct effect on ammonia oxidation rate (AOR) and enzymatic activities which relate to both N2O and NO emission. This study aims at investigating the effect of temperature on AOR, N2O and NO production in an enriched ammonia oxidizing bacteria (AOB) sequencing batch reactor (SBR) performing partial nitrification (PN) of synthetic reject wastewater. To achieve that, a SBR was subject to several shifts in temperature (in the range of 30 to 15 °C, 5 °C for each decrease). Cycle studies, which contain two aeration phases, were conducted under each temperature. The results showed that AOR specific exponentially correlates wit…
Ammonia Synthesis: State of the Bellwether Reaction
2013
Catalytic ammonia synthesis has been judged to be one of mankind's greatest scientific achievements during the twentieth century. The socioeconomic implications of producing ammonia industrially have been a strong driving force, and this development has spurred a range of new discoveries within physics, chemistry, and chemical engineering. In this chapter, we describe how it has been possible in recent years to provide a full understanding of the catalytic ammonia synthesis reaction at the atomic level through the combined use of experiments and quantum mechanical electronic structure calculations, thus clearly showing many of the reasons why ammonia synthesis has been, and still is, the be…
Reduction of Dinitrogen to Ammonia in Irradiated Heterogeneous Systems
1988
The recent developments of the research in the field of dinitrogen reduction to ammonia at mild conditions of pressure and temperature are reported. After a brief historical recapitulation of the traditional thermal process, the new routes for NH3 synthesis (biological photosynthesis, direct electrochemical reduction, and photocatalytic reduction) are presented and critically discussed. A particular attention is devoted to heterogeneous photocatalytic reduction performed by irradiating pure, mixed, and doped semiconducting catalysts in gas-solid and liquid-solid systems. The fixation of dinitrogen in aqueous solutions containing complexes and photoactive particulate systems is also reported…
Imidazolsynthesen, 8. Mitt.: N-Substituierte Imidazole nach Weidenhagen
1976
Die Weidenhagen-Synthese N-unsubstituierter Imidazole aus α-substituierten Carbonylverbindungen 1, Aldehyden 3, wasrigem Ammoniak (4) und Kupfer(II)-salzen als Oxidationsmittel ist in Gegenwart primarer Amine 5 auch zur Darstellung N-substituierter Imidazole 6 geeignet. Weidenhagen Synthesis of N-Substituted Imidazoles The Weidenhagen synthesis of N-unsubstituted imidazoles from α-substituted carbonyl compounds 1, aldehydes 3, and aqueous ammonia (4) with copper (II) salts as oxidizing agents is also usable for the synthesis of N-substituted imidazoles 6 through the addition of primary amines 5.
Contribution of Bacteria to Initial Input and Cycling of Nitrogen in Soils
2005
Nitrogen was discovered by the Scottish chemist and physician Daniel Rutherford in 1772 by removing oxygen and carbon dioxide from air. At the same time, the French chemist, Antoine Laurent Lavoisier, isolated what we would call nitrogen and named it azote, meaning without life since it did not support life or combustion. However, nitrogen is the fourth most common element in many biomolecules, which are essential for life, being outrankedonly by carbon, hydrogen andoxygen. Thus, nitrogen is found in amino acids that form proteins and in the nucleoside phosphates of nucleic acids. The cycle of nitrogen in soil has been studied more extensively than any other nutrient cycle. Nevertheless, de…
ChemInform Abstract: Fluoro Heterocycles. A Photochemical Methodology for the Synthesis of 3-Amino- and 3-(N-Alkylamino)-5-perfluoroalkyl-1,2,4-oxadi…
2000
Abstract A photochemical methodology for the synthesis of perfluoroalkyl-1,2,4-oxadiazoles has been described. 3-Amino- and 3-( N -alkylamino)-5-perfluoroalkyl-1,2,4-oxadiazoles have been prepared by irradiation of 3-perfluoroalkanoylamino-4-phenyl-1,2,5-oxadiazoles (furazans) at λ =313 nm in methanol and in the presence of ammonia or primary aliphatic amines.
Imidazolsynthesen, 10. Mitt. Zur selektiven Synthese N-substituierter Imidazol-4-äthanole
1977
Die Synthese N-substituierter Methoxyathylimidazole 5, 6 aus Aldehyden 1, 1-Hydroxy-4-methoxy-2-butanon (2), primaren Aminen 3 und Ammoniak (4) nach Weidenhagen liefert Gemische, in denen im GC die 1,4-Isomere 5 in der Regel deutlich uberwiegen. Aus diesen lassen sich durch Atherspaltung mit HJ die N-substituierten Imidazol-4-athanole 8 erhalten. Selective Synthesis of N-Substituted Imidazole-4-ethanols The synthesis of N-substituted methoxyethylimidazoles 5, 6 from aldehydes 1, 1-hydroxy-4-methoxy-2-butanone (2), primary amines 3, and ammonia (4), using the Weidenhagen cyclisation, yields mixtures in which, according to gc analysis, the 1,4-isomers 5 prevail. Ether cleavage with HI gives t…
ChemInform Abstract: Photoinduced Molecular Rearrangements. The Photochemistry of Some 1,2, 4-Oxadiazoles in the Presence of Nitrogen Nucleophiles. F…
2010
The photochemistry of some 3,5-disubstituted 1,2,4-oxadiazoles in the presence of nitrogen nucleophiles [external, such as added amines or hydrazines, or internal, such as an o-aminophenyl moiety at C(3) of the oxadiazole ring] has been investigated. In the irradiation of 5-amino-(or 5-N-substituted amino) 3-phenyl-1,2,4-oxadiazoles in the presence of aliphatic primary amines (or ammonia), photolytic species arising from heterolytic cleavage of the ring O−N bond capture the nucleophilic reagent to give open-chain intermediates, which develop into 1,2,4-triazolin-5-ones. Similarly, irradiations of 3,5-diphenyl-, 3-methoxy-5-phenyl-, and 5-methyl-3-phenyl-1,2,4-oxadiazoles gave 1,2,4-triazole…
ChemInform Abstract: New Developments in Nitrogen Fixation.
2010
The production of ammonia from atmospheric dinitrogen at room temperature and ambient pressure in analogy to nature is a long-term goal for coordination chemists. Novel reactions of N2 -containing transition metal complexes with H2 , the first side-on N2 -bridged structure of an actinide complex, and an interesting variation of synthetic N2 fixation are the key points addressed in this contribution. The results are related to the known chemistry of N2 complexes, and their significance is discussed with respect to enzymatic N2 fixation.