摘要:

AbstractBenzyl chloride and benzyl acetate were photolyzed in 30% methanol–water mixtures (V/V) at 0°C. The photolysis produces benzyl carbocations that react with nucleophiles. The reaction products were analyzed by gas chromatography or liquid chromatography. From the amounts of products the relative values of rate constants of reactions of benzyl carbocation with nucleophiles N and waterk(N)/k(H2O) were calculated. Benzyl carbocation reacts with I−, Br−, Cl−, and Ac−ions with approximately diffusion‐controlled rate. A value of 2.4 × 107dm3mol−1s−1for the rate constantk(H2O) and a lifetime of 0.7 ns were estimated for benzyl carbocation in the

ISSN:0538-8066    

DOI:10.1002/kin.550170902

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractA continuous stirred tank reactor (CSTR) was used to study the gas‐phase reaction between HO⋅ and toluene. HO⋅ was generated by thein situphotolysis of nitrous acid. Flow reactor operation at steady‐state conditions with a residence time of 20 min allowed investigation of primary and very rapid secondary reactions. CSTR and batch reactor experiments were also performed with selected products. Both gas‐phase and aerosol products were identified by chromatography and mass spectroscopy, with total product yields between 55 and 75% of reacted carbon. Toluene reaction products included cresols, nitrocresols, nitrotoluenes, 3,5‐dinitrotouluene, benzaldehyde, benzyl nitrate, nitrophenols, methyl‐p‐benzoquinone, glyoxal, methylglyoxal, formaldehyde, methyl nitrate, PAN, and CO. The fraction of HO⋅ methyl hydrogen abstraction was calculated to be 0.13 ± 0.04. The ratio of reaction rate constants for nitrotoluene versus cresol formation from the HO⋅‐adduct was calculated to be about 3.3 × 104. Also, the ratio of cresol formation versus O2addition to the HO⋅‐adduct was estimated to be ≥0.5 for atmospheric conditions. Comparisons of these measurements with previous values and the implications with respect to photochemical kinetics modeling of

ISSN:0538-8066    

DOI:10.1002/kin.550170903

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractRate constants for the gas‐phase reactions of NO3radicals with a series of cycloalkenes have been determined at 298 ± 2 K, using a relative rate technique. Using an equilibrium constant for the NO2+ NO3⇄ N2O5reactions of 3.4 × 10−11cm3molecule−1, the following rate constants (in units of 10−13cm3molecule−1s−1) were obtained: cyclopentene, 4.52 ± 0.52; cycloheptene, 4.71 ± 0.56; bicyclo[2.2.1]‐2‐heptene, 2.41 ± 0.28; bicyclo[2.2.2]‐2‐octene, 1.41 ± 0.17; bicyclo[2.2.1]‐2,5‐heptadiene, 9.92 ± 1.13; and 1,3,5‐cycloheptatriene, 12.6 ± 2.9. When combined with previous literature rate constants for cyclohexene and 1,4‐cyclohexadiene, these data show that the rate constants for the nonconjugated cycloalkenes studied depend to a first approximation on the number of double bonds and the degree and configuration of substitution per double bond. No obvious effects of ring strain energy on these NO3radical addition rate constants were observed. Our previous a priori predictive techniques for the alkenes and cycloalkenes can now

ISSN:0538-8066    

DOI:10.1002/kin.550170904

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe origin of autocatalysis in the pyrolysis of methane has been investigated by kinetic modeling. A mechanism is presented that provides good agreement with experimental data at 1038 K and 433 torr into the autocatalytic region. The main causes of autocatalysis are secondary initiation by hydrocarbon products larger than C2H6and chain radical methylation sequences.

ISSN:0538-8066    

DOI:10.1002/kin.550170905

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractPulsed laser photolysis of N2O5near 290 nm coupled with fluorescence detection (calibrated by NO2photolysis) showed that the O(3P) quantum yield is ≤0.1. A pulsed laser optoacoustic technique in a flow tube (ca. 6 torr of N2) was tested by photolysis of NO2and then applied to N2O5. Nitric oxide was added to react with NO3free radical and the resulting increase in the optoacoustic signal confirmed the presence of NO3free radicals. Based on the relative optoacoustic signals observed for NO2and N2O5, the quantum yield for NO3production is 0.8 ± 0

ISSN:0538-8066    

DOI:10.1002/kin.550170906

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe rate of oxygen exchange betweentrans‐[Re(py)4O2]+and solvent water in pypyH+buffer solution follows simple first‐order kinetics and both oxygens are equivalent. The half‐life for isotopic oxygen exchange is about 12 h at a pH of 5.0, 25°C, and [py] = 0.10 M. The observed rate constant for exchange increases with acidity, in the pH range 4 to 6, decreases with [py], and is nearly independent of ionic strength. A small but significant increase ofkobsoccurs with increasing complex concentration. The rate of exchange follows the rate equationkobs/2 =k0+k1/[py] withk0= 1.4 × 10−5(2) s−1andk1= 4.7 × 10−7(1) M, s−1at 25°C. The activation parameters for the reaction at pH = 7.15 (predominately thek0term) are: ΔH* = +137.(1) kJ/M and ΔS* = +126.(1) J/MK. The pH effect and complex concentration effect are discussed in mechanistic terms. These results are compared to those found for [Re(en)2O2

ISSN:0538-8066    

DOI:10.1002/kin.550170907

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractKinetics of oxidation of fumarate, acrylate, cinnamate, and maleate anions by hexavalent manganese has been studied in aqueous alkaline medium. The order in [oxidant] was unity while that in [substrate]was fractional. The order of reactivity of anions is fumarate → acrylate → cinnamate → maleate. The reactions followed Michaelis–Menten kinetics suggesting the formation of a cyclic intermediate between Mn(VI) and the substrate followed by its disproportionation in a slow step. The equilibrium constant (K) for the preequilibrium step and the rate constant (k) for the slow disproportionation step have been calculated from the intercept and the slope values of the linear plot of 1/kobsversus 1/[substrate]. Activation parameters are also presented and discussed. A convenient iodometric method is reported for the estimation of

ISSN:0538-8066    

DOI:10.1002/kin.550170908

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550170901

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY