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Intermediate Formation (intermediate + formation)
Selected AbstractsFacile Preparation of 3-Amino-4-(arylamino)-1H -isochromen-1-ones by a New Multicomponent ReactionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2005Till Opatz Abstract Reactions between 2-formylbenzoic acid, various anilines and HCN result in the formation of 3-amino-4-(arylamino)-1H -isochromen-1-ones in high yield. The mechanism of this three-component condensation involves the intermediate formation of an ,-aminonitrile and subsequent cyclization through nucleophilic attack of the ortho -carboxylate at the nitrile carbon. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Kinetics and mechanism of the oxidation of carbon by NO2 in the presence of water vaporINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2009M. Jeguirim The kinetics and mechanism of the oxidation of carbon by NO2 in absence and presence of water vapor were studied in a fixed bed reactor. The rate of carbon oxidation by NO2 is enhanced in the presence of water vapor in the range of temperature 300,400°C. The benefit effect of water is attributed to the intermediate formation of traces of nitric and nitrous acids, which enhance the rate of the carbon oxidation without modifying the global mechanism reaction. Therefore, water acts as a catalyst for the carbon oxidation by NO2. A kinetic mechanism derived from this parametric study shows a decrease in the activation energy of carbon oxidation by NO2 in the presence of water vapor. This result is in agreement with the experimental observation. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 236,244, 2009 [source] One-Pot Synthesis of Quinoline Derivatives Directly from Terminal Alkynes via Sequential Ruthenium(II) and Acid CatalysisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Min Zhang Abstract A convenient one-pot synthesis of 2,3-disubstituted, 2,3,6-trisubstituted, and 2,3,6,7-tetrasubstituted quinoline analogues from terminal alkynes via sequential ruthenium(II) and para -toluenesulfonic acid (p -TSA) co-catalyzed reactions is described. The catalytic process is shown to take place first via intermediate formation of an allyl ketone and then addition of an aniline derivative to the allyl ketone. The p -TSA is a catalyst for both allyl ketone and quinoline synthetic steps. The method allowed us to synthesize a wide range of quinoline derivatives and introduce different substituents by employing various simple starting materials. The reaction allows the synthesis of halogen-containing products. [source] Ketonization of 1,5-Cyclooctadiene by Nitrous OxideADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Dmitry Abstract The kinetics and mechanism of the liquid phase ketonization of 1,5-cyclooctadiene (COD) by nitrous oxide have been studied. The reaction proceeds without catalyst in the temperature range 473,553,K with the activation energy 113,kJ,mol,1 and is first order with respect to the initial reactants. The mechanism includes consecutive ketonization of two CC bonds in the COD molecule, with the intermediate formation of an unsaturated monoketone (MK). Further ketonization of MK leads to two isomeric diketones (DK): 1,4- and 1,5-cyclooctanedione. The 1,5-DK is a stable final product while the 1,4-DK undergoes further intramolecular aldol transformation leading to two bicyclic compounds, that retain the same number of carbon atoms. The distribution of mono- and diketones in the course of reaction is described by theoretical dependences pointing to identical reactivities of the CC double bonds residing in COD and MK molecules. The ketonization of COD by nitrous oxide exemplifies a prospective way for the preparation of valuable organic products in perfect harmony with the strategy of green chemistry. [source] Preparation of halogenated derivatives of thiazolo[5,4- d]thiazole via direct electrophilic aromatic substitutionJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 3 2008Vladimir Benin Chlorination and bromination reactions of thiazolo[5,4- d]thiazole led to the generation of its mono- and dihalogenated derivatives. These are the first instances of successful direct electrophilic aromatic substitution in the thiazolo[5,4- d]thiazole ring system. X-ray analysis demonstrates that both 2-bromothiazolo[5,4- d]-thiazole and 2,5-dibromothiazolo[5,4- d]thiazole are planar structures, with strongly manifested ,-stacking in the solid state. Theoretical analysis of the pyridine-catalyzed halogenation (MP2/6-31+G(d) and B3LYP/6-31+G(d) calculations) reveals that introduction of one halogen actually leads to a slightly enhanced reactivity towards further halogenation. Several halogenation mechanisms have been investigated: 1) The direct C-halogenation with N-halopyridine as electrophile; 2) C-halogenation via intermediate N-halogenation, and 3) C-halogenation following an addition - elimination pathway, with intermediate formation of a cyclic halonium ion. The theoretical studies suggest that the direct C-halogenation is the favored mechanism. [source] Solid-solid reactions in series: A modeling and experimental studyAICHE JOURNAL, Issue 9 2009A. K. Suresh Abstract Reactions among particulate solid phases are important and abundant in many materials, chemical, and metallurgical process industries. Many of these are reaction networks, and not single-step reactions as normally assumed. There is no theoretical framework available for the analysis of such systems, and single-reaction models derived from the gas,solid literature continue to be used. Formation of cement clinker in the rotary cement kiln is a prime example of the genre, in which mechanistic aspects play an important role in determining energy efficiency and the composition and nature of the phases that form. In the present study, we formulate a model within the ambit of the "shrinking core" class of models, for reactions in series among solid phases. The model shows the presence of one or two moving fronts in the reacting particle, depending on the relative rates of the processes involved. A single Thiele-type parameter controls the model behavior, at once describing the relative rates of the intermediate formation and consumption processes, and the diffusion-reaction competition for the product formation step. The model has been shown to reduce to the well known single reaction models at the limits of low and high values of the Thiele parameter. Experimental data have been obtained on the calcia-alumina system, an important one in cement manufacture, in the temperature range 1150,1250°C. The model has been fitted to these data and the kinetic parameters determined. The comparison bears out the salient features of the theory, and shows that a degree of diffusion limitation exists for the intermediate conversion step under these conditions. The diffusivity values estimated are in the range of 10,19 to 10,18 m2/s and agree with values found in the literature for similar systems. The rate constant for the intermediate conversion step is of the order of 10,6 s,1. This being among the first such determinations, this value awaits confirmation from other studies. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Synthesis of the First Chiral Bidendate Bis(trifluoromethyl)phosphane Ligand through Stabilization of the Bis(trifluoromethyl)phosphanide Anion in the Presence of AcetoneCHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2006Berthold Hoge Priv.-Doz. Abstract Lewis acid/Lewis base adduct formation of the P(CF3)2, ion and acetone leads to a reduced negative hyperconjugation and, therefore, limits the CF bond activation. The resulting increased thermal stability of the P(CF3)2, ion in the presence of acetone allows selective substitutions and enables the synthesis of the first example of a chiral, bidentate bis(trifluoromethyl)phosphane ligand: a DIOP derivative, [(2,2-dimethyl-1,3-dioxolane-4,5-diyl)bis(methylene)]bis(diphenylphosphane), in which the phenyl groups at the phosphorus atoms are replaced by strong electron-withdrawing trifluoromethyl groups. The resulting high electron-acceptor strength of the synthesized bidentate (CF3)2P ligand is demonstrated by a structural and vibrational study of the corresponding tetracarbonyl,molybdenum complex. The stabilization of the P(CF3)2, ion in the presence of acetone is based on the formation of a dynamic Lewis acid/Lewis base couple, (CF3)2PC(CH3)2O,. Although there is no spectroscopic evidence for the formation of the formulated alcoholate ion, the intermediate formation of (CF3)2PC(CH3)2O, could be proved through the reaction with (CF3)2PP(CF3)2, which yields the novel phosphane,phosphinite ligand (CF3)2PC(CH3)2OP(CF3)2. This ligand readily forms square-planar Pt(II) complexes upon treatment with solid PtCl2. [source] Spatial near-infrared imaging of hydroxyl band coverage on ceria-based catalystsAICHE JOURNAL, Issue 4 2006Farid Aiouache Abstract High-throughput near-infrared imaging was used to distinguish catalyst activity for low-temperature methane steam-reforming. Geminal hydroxyls of reduced ceria were depicted during methane reforming at 673 K. The changes in absorbance maps under various water partial pressures showed evidence of formate intermediate formations without redox exchanges. Higher resolution was observed in absorbance change images than that of thermal images obtained from catalyst surface self-emissions. The experimental results illustrated higher activity of pure rhodium catalyst than that of bimetallic ones, likely because of the high dispersion of rhodium on the catalyst support. Moreover, the reaction was accelerated when high surface area silica was added because more reduced sites were exposed. Our filter bandwidths limited our interest in band-shift distribution of geminal hydroxyl band during the reduction process. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source] | ||||||||||