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First-order Dependence (first-order + dependence)
Selected AbstractsKinetic and Thermodynamic Studies of the Disproportionation of Hydrogen Peroxide by Dimanganese(ii,ii) and -(ii,iii) Complexes of a Bridging Phenolate LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2005Lionel Dubois Abstract The dimanganese(ii,ii) complexes [Mn2(L)(OAc)2(CH3OH)]-(ClO4) (1a) and [Mn2(L)(OBz)2(H2O)](ClO4) (1b) as well as the dimanganese(ii,iii) complex [Mn2(L)(OAc)2(CH3OH)]-(ClO4)2 (2a), where HL is the asymmetric phenol ligand2-[bis(2-pyridylmethyl)aminomethyl]-6-{[(benzyl)(2-pyridyl-methyl)amino]methyl}-4-methylphenol, react with hydrogen peroxide in acetonitrile solution. The initial reaction rates and their temperature and acid/base dependencies were investigated by monitoring the dioxygen evolution. These studies revealed a first-order dependence on both the catalyst and H2O2 and a strong influence of the carboxylate. Electrospray ionisation mass spectrometry as well as EPR and UV/Vis spectroscopy were used to monitor the reaction catalysed by 2a. The same bis(,-oxo)dimanganese(III,IV) and (,-oxo)dimanganese(ii,iii) active species as found for 1a were detected in the catalytic medium. The EPR spectra recorded during the catalase-like reaction revealed the accumulation of the magnetically uncoupled dimanganese(ii,iii) precursor of the active bis(,-oxo)dimanganese(III,IV) species which dominates the spectra in the case of 1a. This difference can be attributed to the different pH conditions generated by the reaction and reflects differences in the initiation phases for the two catalysts. Overall, the kinetic and thermodynamic studies of H2O2 disproportionation by these dimanganese complexes are fully consistent with the mechanism deduced from our previous extensive spectroscopic studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Kinetics 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] Kinetics and mechanism of the dehydration reaction of sarcosine to a bislactame through diacyclperoxide intermediate in strong acidic mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2009Homayoon Bahrami The influence of substitution on the amine functional group of glycine in the permanganic oxidation of such an ,-amino acid in moderately concentrated sulfuric acid medium has been investigated. Reaction products analysis has revealed that contrary to the usual ,-amino acid oxidation product, which is an aldehyde species, a valuable compound, namely 1,4-dimethylpiperazine-2,5-dione, has been obtained as the main product via a cheap, simple, efficient, and novel method. Sarcosine has been chosen as a substituted derivative of glycine, and the kinetics and mechanism of its permanganic oxidation have been investigated using a spectrophotometric technique. Conclusive evidence has proven delayed autocatalytic activity for Mn(II) in this reaction, analogous to some ,-amino acids. It has been revealed that such activity can show up when a certain concentration ratio of Mn(II) to sarcosine is built up in the medium, which we call the "critical ratio." The magnitude of the latter ratio depends on the sulfuric acid concentration. Considering the "delayed autocatalytic behavior" of Mn(II) ions, rate equations satisfying observations for both catalytic and noncatalytic routes have been presented. The reaction shows first-order dependence on permanganate ions and sarcosine concentrations in both catalytic and noncatalytic pathways, and apparent first-order dependence on Mn2+ ions in catalytic pathways. The correspondence of pseudo-order rate constants of the catalytic and noncatalytic pathways to Arrhenius and Eyring laws has verified "critical ratio" as well as "delayed autocatalytic behavior" concepts. The activation parameters associated with both pathways have been computed and discussed. Mechanisms for both catalytic and noncatalytic routes involving radical intermediates as well as a product having a diketopiperazine skeleton have been reported for the first time. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 689,703, 2009 [source] Kinetics and mechanism of the oxidative regeneration of carbonyl compounds from oximes by pyridinium bromochromateINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2006Pradeep K. Sharma The oxidative deoximination of several aldo- and keto-oximes by pyridinium bromochromate (PBC), in dimethylsulfoxide, exhibited a first-order dependence on both the reductant (oxime) and the oxidant (PBC). The oxidation of ketoximes is slower than that of aldoximes. The rates of oxidation of aldoximes correlated well in terms of the Pavelich,Taft dual substituent-parameter equation. The low positive value of polar reaction constant indicated a nucleophilic attack by a chromate-oxygen on the carbon. The reaction is subject to steric hindrance by the alkyl groups. The reaction of acetaldoxime has been studied in 19 different organic solvents. The solvent effect has been analyzed by Taft's and Swain's multiparametric equations. A mechanism involving the formation of a cyclic intermediate, in the rate-determining step, has been proposed. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 364,368, 2006 [source] Kinetics and mechanism of esterification of epoxy resin in presence of triphenylphosphineINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2004Neelam Pal The kinetics of esterification of bisphenol-A based epoxy resin with acrylic acid in presence of triphenylphosphine has been studied. The reaction exhibits a first-order rate dependence with respect to [Epoxy] and [Catalyst]. A first-order dependence of rate with respect to [Acid] has been observed during a particular kinetic run. However, a retarding effect of [Acid] on the rate has been observed by increasing the initial concentration of acid. A suitable mechanism consistent with the kinetic data is proposed and discussed. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 280,285, 2004 [source] Kinetics and mechanism of oxidation of 2-mercaptosuccinic acid by bis(,-oxo)- manganese(III,IV)-cyclam complex in aqueous medium: Influence of externally added copper(II)INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2004Nizamuddin Shaikh Kinetic studies on the oxidation of 2-mercaptosuccinic acid by dinuclear [Mn2III/IV(,-O)2(cyclam)2](ClO4)3] (1) (abbreviated as MnIII,MnIV) (cyclam = 1,4,8,11-tetraaza-cyclotetradecane) have been carried out in aqueous medium in the pH range of 4.0,6.0, in the presence of acetate buffer at 30°C by UV,vis spectrophotometry. In the pH region, two species of complex 1 (MnIII,MnIV and MnIII,MnIVH, the later being ,-O protonated form) were found to be kinetically significant. The first-order dependence of the rate of the reactions on [Thiol] both in presence and absence of externally added copper(II) ions, first-order dependence on [Cu2+] and a decrease of rate of the reactions with increase in pH have been rationalized by suitable sequence of reactions. Protonation of ,-O bridge of 1 is evidenced by the perchloric acid catalyzed decomposition of 1 to mononuclear Mn(III) and Mn(IV) complex observed by UV,vis and EPR spectroscopy. The kinetic features have been rationalized considering Cu(RSH) as the reactive intermediate. EPR spectroscopy lends support for this. The formation of a hydrogen bonded outer-sphere adduct between the reductant and the complex in the lower pH range prior to electron transfer reactions is most likely to occur. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 170,177 2004 [source] Uncatalyzed and ruthenium(III)-catalyzed reaction of acidic chlorite with methylene violetINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2003S. B. Jonnalagadda The kinetics and mechanism of the uncatalyzed and Ru(III)-catalyzed oxidation of methylene violet (3-amino-7-diethylamino-5-phenyl phenazinium chloride) (MV+) by acidic chlorite is reported. With excess concentrations of other reactants, both uncatalyzed and catalyzed reactions had pseudo-first-order kinetics with respect to MV+. The uncatalyzed reaction had first-order dependence on chlorite and H+ concentrations, but the catalyzed reaction had first-order dependence on both chlorite and catalyst, and a fractional order with respect to [H+]. The rate coefficient of the uncatalyzed reaction is (5.72 ± 0.19) M,2 s,1, while the catalytic constant for the catalyzed reaction is (22.4 ± 0.3) × 103 M,1 s,1. The basic stoichiometric equation is as follows: 2MV+ + 7ClO2, + 2H+ = 2P + CH3COOH + 4ClO2 + 3Cl,, where P+ = 3-amino-7-ethylamino-5-phenyl phenazinium-10-N-oxide. Stoichiometry is dependent on the initial concentration of chlorite present. Consistent with the experimental results, pertinent mechanisms are proposed. The proposed 15-step mechanism is simulated using literature; experimental and estimated rate coefficients and the simulated plots agreed well with the experimental curves. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 294,303, 2003 [source] A Mechanistic Study on Alcohol Oxidations with Oxygen Catalysed by TPAP-Doped Ormosils in Supercritical Carbon DioxideADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2005Sandro Campestrini Abstract The heterogeneous oxidation of various alcohols with oxygen catalysed by TPAP-doped ormosils in scCO2 at 75,°C and 22.0,MPa has been studied in detail. Sol-gel segregation of TPAP into the inner porosity of an organically modified silica (ormosil) xerogel along with the use of a reaction medium which does not dissolve the catalyst, prevents aggregation of oxidation-inactive ruthenium derivatives without the need of chemical tethering. Thus, at least 140 TONs may be obtained in the oxidation of primary alcohols with the formation of aldehydes as sole reaction products. Investigation of the oxidation mechanism shows that the catalytic process exhibits a first-order dependence on the amount of catalyst, a fractional order on the alcohol concentration and a negative order for oxygen pressures higher than 0.2,bar. Evidence is presented for an associative oxidation mechanism simultaneously involving TPAP, organic substrate and oxygen. [source] Kinetics and mechanism of sodium N -halo- p -toluenesulfonamides oxidation of diclofenac in alkaline mediumAICHE JOURNAL, Issue 12 2009Puttaswamy Abstract Diclofenac belongs to a class of drugs called nonsteroidal antiinflammatory drugs. The kinetics and mechanism of oxidation of diclofenac by sodium N -halo- p -toluenesulfonamides viz., chloramine-T and bromamine-T in NaOH medium have been studied at 293 K. Under comparable experimental conditions, reactions with both the oxidants follow identical kinetics with a first-order dependence on each [oxidant]o and a fractional-order dependence on each [diclofenac]o and [NaOH]. Activation parameters have been computed. N -hydroxyldiclofenac is identified as the oxidation product of diclofenac. Michaelis-Menten type of mechanism has been suggested. The rate of oxidation of diclofenac is about four-fold faster with bromamine-T when compared with chloramine-T. This may be attributed to the difference in electrophilicities of Cl+ and Br+ ions and also the van der Waal's radii of chlorine and bromine. Plausible mechanism and related rate law have been designed for the observed kinetics. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] | ||||||||||