摘要:

AbstractCF3radicals were generated by the photolysis of perfluoroacetic anhydride. In the presence of pentafluorobenzene, the CF3radicals react according to the following mechanism:It was found that the addition reaction (3) becomes reversible above ca. 453 K. The addition rate parameters have been revised and they satisfactorily agree with those reported previously.At temperatures higher than 593 K, only true H‐abstraction occurs. The rate constantkHfor reaction (5) is given by:\documentclass{article}\pagestyle{empty}\begin{document}$$ \log [(k_{\rm H} /k_c^{1/2}){\rm mol}^{- 1/2} \,{\rm cm}^{{\rm 3/2}} \,{\rm s}^{{\rm - 1/2}}]\, = \,(4.34\, \pm \,0.43)\, - \,(59,00\, \pm \,2.62)/\theta $$\end{document}where θ = 2.303RTkJmol−1andkcis the rate constant for combination of CF3radicals. The reactions of CF3with benzene and pentafluorobenzene are comp

ISSN:0538-8066    

DOI:10.1002/kin.550230502

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractVibrationally excited 1,1‐difluorocyclopropane, generated by addition of singlet methylene to 1,1‐difluoroethene, reacts according to four reaction channels by isomerization as well as by elimination of difluoromethylene. Identification of the products leads to a critical view on an early study dealing with this reaction system. The pressure dependence of the reaction is investigated. The apparent rate‐constants of the reaction paths were deter

ISSN:0538-8066    

DOI:10.1002/kin.550230503

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe stopped‐flow measurements on the disappearance of alkaline osmium(VIII) at 402 nm indicated a first‐order dependence each in [Os(VIII)] and [HCHO]. The pseudo first‐order rate constantkobs([HCHO] ≫ [Os(VIII)]) decreased with increasing [OH−]. The ionic strength, however, had no effect onkobs. The rapid scan spectra of the reaction mixture indicated the formation of an inert complex which absorbs at 319 nm. Therefore the rate determining step is considered to involve the bimolecular collision between OsO4(OH) 22−and hydrated formaldehyde. The values of the rate limiting constantkand the equilibrium constant Khafor the formation of the alkoxide ion from the reaction of hydrated formaldehyde with OH−are evaluated. The equilibrium constant Kha, within the experimental limits, is independent of temperature. The pKavalue, calculated from Kha, is 13.62 ± 0.05 which is in good agreement with the pKavalue 13.27 for formaldehyde. The activation parameters, ΔH‡ = 40 ± 2 kJ mol−1and ΔS‡ = −51 ± 6 JK−1mol−1, for the rate

ISSN:0538-8066    

DOI:10.1002/kin.550230504

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe rate of reaction of (Fe(DTPA)) with H2O2was investigated at various temperatures. The observed rate law is given by the expression.\documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{- {\rm d[H}_{\rm 2} {\rm O}_{\rm 2} {\rm]}}}{{\rm dt}}\, = \,{\rm kK[FeY(H}_{\rm 2} {\rm O)]}^{{\rm 2 -}} [{\rm H}_{\rm 2} {\rm O}_{\rm 2}]\, + \,{\rm k}_3 {\rm K}_{\rm 1} {\rm K}_{\rm 2} \frac{{{\rm [FeY(OH)]}^{{\rm 3 -}} [{\rm OOH}^{\rm -}]}}{{{\rm [H}^{\rm+}]}} $$\end{document}The rate constants and the related thermodynamic parameters are calculated. Substitution controlled mechanisms are suggested to account for the formation of the violet peroxy intermediate. The results are compared with previously data for Fe EDTA complex.

ISSN:0538-8066    

DOI:10.1002/kin.550230505

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractRecent shock tube measurements [1,2] of the reactions of OH radicals with various hydrocarbons provide the incentive for revising an earlier model [3]used to carry out thermochemical transition state theory calculations for the reaction rate coefficients of OH radicals with alkanes. In this article, details of the revised model are presented and calculations are described and compared with experiments. Of particular interest is the question of the reliability of an additive formulation for H atom abstraction rate coefficients; i.e., can we evaluate the total rate coefficient as the sum of site‐specific rate coefficients,ktotal= Σin H iki, where we sum either over primary, secondary, and tertiary H atoms or over some larger number of classes of atoms? It is argued that there are two major reasons for expecting different primary, secondary, or tertiary H atoms to have different rate parameters: (1) activation energies may depend on next‐nearest neighbors and (2) activation entropies can be mass‐dependent. In principle the first factor invalidates the common procedure of treating the total rate coefficient for OH + RH H abstraction processes as the sum of invariant primary, secondary, and tertiary rates multiplied by the respective number of such H atoms in the molecule. The second factor places limits on the accuracy of any additive formulation. A separate question is whether there is sufficient experimental evidence to justify these distinctions, or whether, given experimental and theoretical uncertainties, it is adequate to treat them all as equivalent. It is concluded that (1) mass‐dependent variations are just barely discernible; and (2) there are measurable differences among various primary H atom abstractions, and possibly among secondary atoms, but the data base does not justify distinguishing among tert

ISSN:0538-8066    

DOI:10.1002/kin.550230506

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe oxidation of thiourea by chlorite within the pH range of 2 to 5.5 has been found to produce a single wave of chlorine dioxide in unstirred solutions. The wave has been studied in narrow tubes of varying diameters and in petri dishes. The wave appears after an induction period that depends on the acid concentration, the [ClO2−]/[CS(NH2)2] ratio, the temperature, and the diameter of the tube. The wave starts from the surface in a tube and from the edges in a petri dish. The rate of wave movement is proportional to the ratio and the acid concentration. Barium chloride and starch were used as indicators. The wave could be initiated electrochemically and by addition of a drop of solution containing chlorine dioxide. The chlorine dioxide is produced by the oxidation of chlorite by hypochlorous aci

ISSN:0538-8066    

DOI:10.1002/kin.550230507

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractCross‐disproportionation to combination ratios for CF2H andn‐C3H7radicals have been determined (the hydrogen acceptor radical is given first) to be Δ(n‐C3H7, CF2H) = 0.30 ± 0.01 and Δ(CF2H,n‐C3H7) = 0.0

ISSN:0538-8066    

DOI:10.1002/kin.550230508

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractEthane oxidation in jet‐stirred reactor has recently been investigated at high temperature (800–1200 K) in the pressure range 1–10 atm and molecular species (H2, CO, CO2, CH4, C2H2, C2H4, C2H6) concentration profiles were obtained by probe sampling and GC analysis. Ethane oxidation was modeled using a comprehensive kinetic reaction mechanism including the most recent findings concerning the kinetics of the reactions involved in the oxidation of C1C4hydrocarbons. The proposed mechanism is able to reproduce experimental data obtained in our high‐pressure jet stirred reactor and ignition delay times measured in shock tube in the pressure range 1–13 atm, for temperatures extending from 800 to 2000 K and equivalence ratios of 0.1 to 2. It is also able to reproduce atoms concentrations (H,O) measured in shock tube at ≈2 atm. The same detailed kinetic mechanism can also be used to model the oxidation of methane, ethylene, propyne, and allene in simil

ISSN:0538-8066    

DOI:10.1002/kin.550230509

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550230501

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY