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Reaction Shows (reaction + shows)
Selected AbstractsKinetics and Mechanism of Oxidation of Fe2+ by the Tris(biguanide)manganese(IV) Ion in Aqueous Acid MediaEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2004Basab Bijayi Dhar Abstract Tris(biguanide)manganese(IV), [Mn(LH2)3]4+ (LH2 = biguanide, C2N5H7), quantitatively oxidises Fe2+ to Fe3+ and is itself reduced to Mn2+ with almost quantitative (> 95%) release of biguanide. The reaction rate strongly depends on added Fe3+; in the presence of externally added Fe3+, the reaction shows a clear first-order dependence in [MnIV], whereas in the absence of any added Fe3+, an initial quick loss of MnIV is associated with a subsequent very sluggish decay. Two consecutive one-electron transfer inner-sphere steps are proposed for the entire redox process where [Mn(LH2)3]3+, the initial one-electron-reduced product of MnIV, is believed to be a steady-state intermediate. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Carbothermal synthesis of vanadium nitride: Kinetics and mechanismINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2006A. Ortega Constant rate thermal analysis (CRTA) has been used for the first time to study the kinetics of the carbothermal reduction of V2O5 in nitrogen to obtain vanadium nitride. It is noteworthy to point out that CRTA method allows both a good control of pressure in the sample surroundings and the use of reaction rates low enough to keep temperatures gradients at a negligible level to avoid any heat or mass transfer phenomena. This method allows one to control the texture and the structure of many materials through kinetic control of the thermal treatment of the precursors. The precise control of the external parameters of the reaction shows that CRTA is an attractive method for kinetic studies and leads to more reliable kinetic data. It has been shown that the carbothermal synthesis of vanadium nitride is best described by a three-dimensional diffusion kinetic model (the Jander equation) with an activation energy which falls in the range of 520,540 kJ/mol. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 369,375, 2006 [source] Kinetics and mechanism of the oxidation of 4-methyl-3-thiosemicarbazide by acidic bromate,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2002Sreekantha B. Jonnalagadda The oxidation of 4-methyl-3-thiosemicarbazide (MTSC) by bromate and bromine was studied in acidic medium. The stoichiometry of the reaction is extremely complex, and is dependent on the ratio of the initial concentrations of the oxidant to reductant. In excess MTSC and after prolonged standing, the stoichiometry was determined to be H3CN(H)CSN(H)NH2 + 3BrO3, , 2CO2 + NH4+ + SO42, + N2 + 3Br, + H+ (A). An interim stoichiometry is also obtained in which one of the CO2 molecules is replaced by HCOOH with an overall stoichiometry of 3H3CN(H)CSN(H)NH2 + 8BrO3, , CO2 + NH4+ + SO42, + HCOOH + N2 + 3Br, + 3H+ (B). Stoichiometry A and B are not very different, and so mixtures of the two were obtained. Compared to other oxidations of thiourea-based compounds, this reaction is moderately fast and is first order in both bromate and substrate. It is autocatalytic in HOBr. The reaction is characterized by an autocatalytic sigmoidal decay in the consumption of MTSC, while in excess bromate conditions the reaction shows an induction period before autocatalytic formation of bromine. In both cases, oxybromine chemistry, which involves the initial formation of the reactive species HOBr and Br2, is dominant. The reactions of MTSC with both HOBr and Br2 are fast, and so the overall rate of oxidation is dependent upon the rates of formation of these reactive species from bromate. Our proposed mechanism involves the initial cleavage of the CN bond on the azo-side of the molecule to release nitrogen and an activated sulfur species that quickly and rapidly rearranges to give a series of thiourea acids. These thiourea acids are then oxidized to the sulfonic acid before cleavage of the CS bond to give SO42,, CO2, and NH4+. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 237,247, 2002 [source] Reaction mechanism of methanol decomposition on Pt-based model catalysts: A theoretical studyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2010Cui-Yu Niu Abstract The decomposition mechanisms of methanol on five different Pt surfaces, the flat surface of Pt(111), Pt-defect, Pt-step, Pt(110)(1 × 1), and Pt(110)(2 × 1), have been studied with the DFT-GGA method using the repeated slab model. The adsorption energies under the most stable configuration of the possible species and the activation energy barriers of the possible elementary reactions involved are obtained in this work. Through systematic calculations for the reaction mechanism of methanol decomposition on these surfaces, we found that such a reaction shows the same reaction mechanism on these Pt-based model catalysts, that is, the final products are all H (Hads) and CO (COads) via OH bond breaking in methanol and CH bond scission in methoxy. These results are in general agreement with the previous experimental observations. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010. [source] The [2+2]-Cycloaddition Reaction of Bisallenes: A Dramatic Substituent Effect,CHINESE JOURNAL OF CHEMISTRY, Issue 9 2010Ping Lu Abstract The bisallenes 1 possessing a phenylsulfonyl or n -butyl substituent at the internal position of allene moieties could be smoothly transformed to the bicyclo[5.2.0] or bicyclo[6.2.0] derivatives 2 in moderate to excellent yields with good regioselectivity upon refluxing in toluene. This [2+2]-cycloaddition reaction shows an interesting substituent effect as unveiled by comparing with the results of unsubstituted substrates. However, further attention should be paid to the control of the regioselectivity of the [2+2]-cycloaddition involving different CC bonds. [source] | ||||||||||