摘要:

AbstractThe kinetics of the reactions of manganese(III) complexes oftrans‐cyclohexane‐1,2‐diamine‐NNN′N′‐tetraacetic acid (H4cydta) and 2,2′‐bipyridyl (bpy) have been investigated in the acid ranges [H+] = 1.00 ×10−5− 3.16 × 10−3M and [H+] = 0.10 − 1.00 M, respectively, at different temperatures and at a constant ionic strength. Both the molecular and mono‐anionic forms of ascorbic acid have been found to be reactive in the experimental acid ranges. The monoanionic species has been found to be more reactive than the molecular form. Attempts have been made to correlate the kinetic results in terms of the Marcus relationship for outer‐sphere electron transfer reaction. Differences between the calculated rates (k0.8) and experimental rates (k) by approximately four and seven orders of magnitude (k0.8≪k) suggest an innersphere pathway for the reaction of Mn(cydta)(H2O)−. Inner‐sphere reaction is also believed to be operative for the other reaction. The activation parameters have been evaluated and

ISSN:0538-8066    

DOI:10.1002/kin.550230202

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe kinetics and mechanism of the oxidation of 3,3′‐dimethoxybenzidine (oda,o‐dianisidine) by potassium bromate in aqueous acidic medium were studied by monitoring the formation rate of the reaction product, 3,3′‐dimethoxy 4,4′‐diphenoquinone at 447 nm. The reaction is, first order with respect to both the substrate and oxidant, and second order with respect to H+. The oda: bromate stoichiometric ratio is 1:1. Plausible mechanism and rate laws are proposed accounting the experimental findings. Computer simulations were done using the propo

ISSN:0538-8066    

DOI:10.1002/kin.550230203

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractKinetics of oxidation of cinnamaldehyde (Cinn) by chloramine‐T (CAT) has been studied in solutions containing HCl and H2SO4at 313 K. The respective experimental rate laws obtained in HCl and H2SO4media are as follows:andHere the value ofxvaries from 0.9 to zero while the values ofyandzare 0.83 and 0.72, respectively. Effects, on the reaction rate, of ionic strength, reaction product (p‐toluenesulfonamide), dielectric constant of the solvent medium, and the anions, Cl−and SO42−, have been investigated. Activation parameters have been computed, based on the rate constants determined at different temperatures. Mechanisms proposed and the rate laws derived are consistent with the observed kinetic data represented by the experimental ra

ISSN:0538-8066    

DOI:10.1002/kin.550230204

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractIn the stirred batch experiment, the Mn(II)‐catalyzed bromate‐saccharide reaction in aqueous H2SO4or HClO4solution exhibits damped oscillations in the concentrations of bromide and Mn(II) ions. Peculiar multiple oscillations are observed in the system with arabinose or ribose. The apparent second‐order rate constants of the Mn(III)‐saccharide reactions at 25°C are (0.659, 1.03, 1.76, 2.32, and 6.95) M−1s−1in 1.00 M H2SO4and (4.69, 7.51, 10.2, 13.5, and 36.2) M−1s−1in (2.00–4.00) M HClO4for (glucose, galactose, xylose, arabinose, and ribose), respectively. At 25°C, the observed pseudo‐first‐order rate constant of the Mn(III)‐Br−reaction iskobs= (0.2 ± 0.1) [Br−] + (130 ± 5)[Br−]2+ (2.6 ± 0.1) × 103[Br−]3+ (1.2 ± 0.2) × 104[Br−]4s−1and the rate constant of the Br2Mn(II) reaction is less than 1 × 10−4M−1s−1. The second‐order rate constants of the Br2‐saccharide reactions are (3.65 ± 0.15, 11.0 ± 0.5, 4.05, 12.5 ± 0.7, and 2.62) × 10−4M−1s−1at 25°C

ISSN:0538-8066    

DOI:10.1002/kin.550230205

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe rate constants for the reaction of CN with N2O and CO2have been measured by the laser dissociation/laser‐induced fluorescence (two‐laser pump‐probe) technique at temperatures between 300 and 740 K. The rate of CN + N2O was measurable above 500 K, with a least‐squares averaged rate constant,k= 10−11.8±0.4exp(−3560 ± 181/T) cm3/s. The rate of CN + CO2, however, was not measurable even at the highest temperature reached in the present work, 743 K, with [CO2] ⩽ 1.9 × 1018molecules/cm3.In order to rationalize the observed kinetics, quantum mechanical calculations based on the BAC‐MP4 method were performed. The results of these calculations reveal that the CN + N2O reaction takes place via a stable adduct NCNNO with a small barrier of 1.1 kcal/mol. The adduct, which is more stable than the reactants by 13 kcal/mol, decomposes into the NCN + NO products with an activation energy of 20.0 kcal/mol. This latter process is thus the rate‐controlling step in the CN + N2O reaction. The CN + CO2reaction, on the other hand, occurs with a large barrier of 27.4 kcal/mol, producing an unstable adduct NCOCO which fragments into NCO + CO with a small barrier of 4.5 kcal/mol. The large overall activation energy for this process explains the negligibly low reactivity of the CN radical toward CO2below 1000 K.Least‐squares analyses of the computed rate constants for these two CN reactions, which fit well with experimental data, give rise to\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{{\rm N}_{\rm 2} {\rm O}} \, = \,6.4 \times 10^{- 21} {\rm T}^{{\rm 2}{\rm .6}} \exp (- 1860/{\rm T)cm}^{\rm 3} /{\rm s} $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{{\rm C} {\rm O}_{\rm 2}} \, = \,6.1 \times 10^{- 18} {\rm T}^{{\rm 2}{\rm .2}} \exp (- 13530/{\rm T)cm}^{\rm 3} /{\rm s} $$\end{document}for the temper

ISSN:0538-8066    

DOI:10.1002/kin.550230206

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractRates of solvolysis of complex ions [Co(3Rpy)4Cl2]+with R = Me and Et have been determined in mixtures of water with the hydrophobic co‐solvent propan‐;2‐ol for a range of temperatures. The variations of the enthalpies and entropies of activation with the solvent composition have been correlated with the physical properties of the solvent and it has been shown that the linear plot found for ΔH* against ΔS* in water + propan‐2‐ol is coincident with that found for water + methanol mixtures. A free energy cycle has been applied to the dissociative‐type process of initial state (Cn+) going to the transition state (M(n+1)+…‥ Cl−) using values for the free energy of transfer of the chloride ion from water into the mixture, ΔG t∘(Cl−), derived from the solvent sorting technique or from the TATB/TPTB method. Irrespective of the source of ΔG t∘(Cl−), it is found that ΔG t∘(Co(3Rpy)4Cl2+*) ca. ΔG t∘(Co(3Rpy)4Cl2+) (where * indicates a species in the transition state) for mol fractions of propan‐2‐olx2≳ 0.04–0.05 with ΔG t∘(Co(3Rpy)4Cl2+*) becoming increasingly more negative than ΔG t∘(Co(3Rpy)4Cl2+) asx2increases above 0.05. These variations are compared with those for the solvolysis of the same ions in water + methanol mixtures and of a range of other ions in water + propan‐2‐ol mixtures. It is concluded that, using values for ΔG t∘(Cl−) from either source, the stabilizing influence of changes in solvent structure is greater on the cation in the transition state than on the cation in the initi

ISSN:0538-8066    

DOI:10.1002/kin.550230207

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe reactions of NH(X3Σ−) with NO, O2, and O have been studied in reflected and incident shock wave experiments. The source of NH in all the experiments was the thermal dissociation of isocyanic acid, HNCO. Time‐histories of the NH(X3Σ) and OH(X2Π) radicals were measured behind the shock waves using cw, narrow‐linewidth laser absorption at 336 nm and 307 nm, respectively. The second‐order rate coefficients of the reactions:were determined to be:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{\rm 3} \, = \,1.7 \times 10^{14} \exp (- 6400/{\rm T,K)}\,\,\,\,\,\,{\rm (}f\, = \,0.65,{\rm F}\,{\rm =}\,{\rm 1}{\rm .5)}\,\,\,\,\,\,{\rm T}\,{\rm =}\,{\rm 2220 - 3350\, K,} $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{\rm 4} \, = \,3.5 \times 10^{13} \exp (- 6800/{\rm T,K)}\,\,\,\,\,\,{\rm (}f\, = \,0.65,{\rm F}\,{\rm =}\,{\rm 1}{\rm .5)}\,\,\,\,\,\,{\rm T}\,{\rm =}\,{\rm 2220 - 3370\, K,} $$\end{document}and\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{\rm 5} \, = \,9.2 \times 10^{13} \,\,\,\,\,\,\,\,\,\,\,\,{\rm (}f\, = \,0.60,{\rm F}\,{\rm =}\,{\rm 1}{\rm .6)}\,\,\,\,\,\,{\rm T}\,{\rm =}\,{\rm 2730 - 3380\, K,} $$\end{document}cm3mol−1s−1, where ƒ and F define the lower and upper uncertainty limits, respectively.The branching fraction of channeldefined ask3b/k3total, was determined to be 0.19 ± 0.10 over the temperature range of

ISSN:0538-8066    

DOI:10.1002/kin.550230208

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550230201

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY