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Initial Rate Method (initial + rate_method)
Selected AbstractsKinetic study of triphenylphosphine addition to para -benzoquinoneINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2004Davood Nori-Shargh Kinetics of the addition reaction of triphenylphosphine to para -benzoquinone in 1,2-dichloroethane as solvent was studied. Initial rate method was used to determine the order of the reaction with respect to the reactants. Pseudo-first-order method was also used to calculate the rate constant. This reaction was monitored by UV-vis spectrophotometry at 520 nm by variable time method. On the basis of the obtained results, the Arrhenius equation of this reaction was obtained: The activation parameters, Ea, ,H#, ,G#, and ,S# at 300 K were 5.701, 6.294, 19.958 kcal mol,1 and ,45.853 cal mol,1 K,1, respectively. This reaction is first and second order with respect to triphenylphosphine and para -benzoquinone, respectively. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:472,479, 2004 [source] Kinetics of (Porphyrin)manganese(III)-Catalyzed Olefin Epoxidation with a Soluble Iodosylbenzene DerivativeEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2006James P. Collman Abstract We examined the kinetics of a well-behaved system for homogeneous porphyrin-catalyzed olefin epoxidation with a soluble iodosylbenzene derivative 1 as the terminal oxidant and Mn(TPFPP)Cl (2) as the catalyst. The epoxidation rates were measured by using the initial rate method, and the epoxidation products were determined by gas chromatography. The epoxidation rate was found to be first order with respect to the porphyrin catalyst and zero order on the terminal oxidant. In addition, we found the rate law to be sensitive to the nature and concentration of olefin substrates. Saturation kinetics were observed with all olefin substrates at high olefin concentrations, and the kinetic data are consistent with a Michaelis,Menten kinetic model. According to the observed saturation kinetic results, we propose that there is a complexation between the active oxidant and the substrate, and the rate-determining step is thought to be the breakdown of this putative substrate,oxidant complex that generates the epoxidation products and the resting state porphyrin catalyst. Competitive epoxidations further indicate a reversible complexation of the active oxidant and the olefin substrate. The activation parameters ,H, and ,S, for the oxygen-transfer process (k2) in the cis -cyclooctene epoxidation were determined to be 12.3,±,0.9 kcal,mol,1 and,15.6,±,3.2 cal,mol,1,K,1, respectively. In addition, the Hammett constant ,+ was measured for the epoxidation of para -substituted styrenes, and the value of ,0.27,±,0.04 is too low to be consistent with the involvement of a discrete carbocation in the transition state. We also prepared a (porphyrin)manganese catalyst immobilized on silica support, and found the epoxidation of cis -cyclooctene catalyzed by this heterogeneous catalyst proceeds at virtually the same turnover frequency as by the homogeneous porphyrin catalyst. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Kinetic study of the nitrosation of 1,3-dialkylureas in aqueous-perchloric acid mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2004Guillermo González-Alatorre The kinetics of the nitrosation of 1,3-dimethyl (DMU), 1,3-diethyl (DEU), 1,3-dipropylurea (DPU), 1,3-dibuthyl (DBU), and 1,3-diallylurea (DAU) were studied in a conventional UV/vis spectrophotometer in aqueous-perchloric acid media. The kinetic study was carried out using the initial rate method. The reaction rate observed was where Ka is the acidity constant of nitrous acid. The diureas exhibited the reactivity order DMU , DEU > DPU > DAU, which can be interpreted as a function of the steric impediment generated by the R alkyl group in the rate controlling step. A probable relationship between both the chemical reactivity and structure of the nitrosable substrate with the biological activity of the N-nitroso compounds generated is proposed. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 273,279, 2004 [source] Advanced oxidation of cork-processing wastewater using Fenton's reagent: kinetics and stoichiometryJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2004Jesús Beltrán de Heredia Abstract This work evaluates Fenton oxidation for the removal of organic matter (COD) from cork-processing wastewater. The experimental variables studied were the dosages of iron salts and hydrogen peroxide. The COD removal ranged from 17% to 79%, depending on the reagent dose, and the stoichiometric reaction coefficient varied from 0.08 to 0.43 g COD (g H2O2),1 (which implies an efficiency in the use of hydrogen peroxide varying from 17% to 92%). In a study of the process kinetics, based on the initial rates method, the COD elimination rate was maximum when the molar ratio [H2O2]o:[Fe2+]o was equal to 10. Under these experimental conditions, the initial oxidation rate was 50.5 mg COD dm,3 s,1 with a rate of consumption of hydrogen peroxide of 140 mg H2O2 dm,3 s,1, implying an efficiency in the use of the hydrogen peroxide at the initial time of 77%. The total amount of organic matter removed by Fenton oxidation was increased by spreading the H2O2 and ferrous salt reagent over several fractions by 15% for two-fractions and by 21% for three-fractions. Copyright © 2004 Society of Chemical Industry [source] | ||||||||||