摘要:

AbstractFor the solvolysis of Co(4‐t‐Bupy)4Cl2−ions in water + methanol and water + ethanol, log (rate constant) does not vary linearly with the reciprocal of the dielectric constant. The Gibbs free energy, the enthalpy, and the entropy of activation are insensitive to changes in the solvent composition in these mixtures, although a slight broad maximum in ΔH* and ΔS* probably exists at mole fractions of about 0.2 in water + ethanol. This contrasts with the extrema in ΔH* and ΔS* found with more hydrophobic alcohols used as cosolvents. However, the application of a Gibbs energy cycle to the solvolysis in water and in the mixtures shows that there is a differential effect of changes in solvent structure on the emergent solvated CoIIIcation in the transition state and on Co(4‐t‐Bupy)4Cl2+in the initial state. The stability of the former increases relative to that of the latter as the cosolvent content of the mixture rises. © 1995 John W

ISSN:0538-8066    

DOI:10.1002/kin.550270202

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe title amines were pyrolyzed in a stirred‐flow reactor at 380–510°C, pressures of 8–15 torr and residence times of 0.3–2.4 s, using toluene as carrier gas. The substrates with an allyl group yielded propene and iminonitriles as reaction products. HCN is formed by decomposition of the iminonitriles. The first‐order rate coefficients for propene formation fit the Arrhenius equationsAllyl cyanomethyl amine:\documentclass{article} \pagestyle{empty} \begin{document} $$ k({\rm s}^{ - {\rm 1}}) = 10^{13.29 \pm 0.35} {\rm exp(} - {\rm 189} \pm 5{\rm kJ/mol }RT{\rm)} $$ \end{document}Diallyl cyanomethyl amine:\documentclass{article} \pagestyle{empty} \begin{document} $$ k({\rm s}^{ - {\rm 1}}) = 10^{13.00 \pm 0.20} {\rm exp(} - {\rm 183} \pm 3{\rm kJ/mol }RT{\rm)} $$ \end{document}Diethyl cyanomethyl amine gave a 20:1 gas mixture of ehylene and ethane, plus HCN. The liquid product fraction contained mainlyN‐ethyl methanaldimine. The first‐order rate coefficients for ethylene formation followed the Arrhenius equation\documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm s}^{ - {\rm 1}}) = 10^{15.30 \pm 0.24} {\rm exp(} - {\rm 226} \pm 3{\rm kJ/mol }RT{\rm)} $$\end{document}Diethyl propargyl amine decomposed cleanly into allene andN‐ethyl ethanaldimine. The first‐order rate coefficients for allene formation fit the Arrhenius equation\documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm s}^{ - {\rm 1}}) = 10^{12.84 \pm 0.30} {\rm exp(} - {\rm 168} \pm 4{\rm kJ/mol }RT{\rm)} $$\end{document}The results suggest that the above allyl and propargyl amines decompose unimolecularly by mechanisms involving six‐center cyclic transition states. For diethyl cyanomethyl amine, a nonchain free radical mechanism is proposed. © 1995

ISSN:0538-8066    

DOI:10.1002/kin.550270203

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractA kinetic study has been carried out on the oxidation ofN,N,N′,N′,‐tetraethyl‐p‐phenylenediamine (TEPD) by metal ion like Ce4+, oxoanions viz., MnO4−and Cr2O72−; peroxides such as peroxomonosulphate (PMS), peroxodisulphate (PDS), and H2O2; and halogens namely Cl2, Br2, and I2. The fast kinetics of the formation and decay of the radical cation TEPD˙+have been analyzed at 565 nm by the stopped‐flow technique under pseudo‐first‐order conditions. From the kinetic data, it has been inferred that the reactions were found to be of first‐order with respect to [TEPD] and [oxidant]but over all it has been of second‐order. The observed second‐order rate constants in both the formation and decay of TEPD˙+has been correlated with the oxidation potentials of the various oxidants employed in this study. The effect of pH on the oxidation has been investigated in the formation and decay of TEPD˙+as well as reduction studies have also been carried out using dithionite which has been found to regenerate the TEPD from the TEPD˙+and the corresponding rate constant has also been determined. Besides these, this article also explains how the TEPD, which forms TEPD˙+acts as a better electron relay than TMPD(N,N,N′,N′‐tetramethyl‐p‐phenylenediamine) which forms TMPD˙+, even though both of them undergo one‐electron oxidation and are used in the chemical routes to solar energy conversions. The observed rate constants for electron transfer were correlated theoretically using Marcus theory. The observed and calculated rate constants have go

ISSN:0538-8066    

DOI:10.1002/kin.550270204

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractA series of laboratory and modelling experiments on the oxidation of propene in the gas phase has been undertaken to determine conditions which give high yields of propene oxide. The conditions under which the experiments were conducted were 505–549 K and up to 4 bar pressure. It is proposed that propene oxide is formed from propene by reaction with several peroxy radicals including HO2and CH3CO3. However, one of the more important radicals is hydroxypropylperoxy. Its reaction with propene, under these conditionsis more important than concerted decomposition to formaldehyde and acetaldehyde. © 1995 John Wiley&Sons, I

ISSN:0538-8066    

DOI:10.1002/kin.550270205

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe kinetics and mechanism of ozone reactions with aliphatic ethers in CCl4solution have been investigated with a set of six symmetrical ethers: ethyl, chloroethyl,iso‐propyl,n‐butyl,iso‐amyl, andn‐amyl. The corresponding kinetic constants at ambient temperature are 3.1, 0.035, 5.4, 6.3, 6.8, and 7.8 1/(mol s). Upon ozonation ofn‐butylether the main products are butylalcohol, butylaldehyde (butyric acid), and butylbutyrate. A common precursor of these products is the α‐hydrotrioxybutylether. Experimental values of the preexponential factors are compared with those calculated according to the activation complex theory with linear or cyclic form of the activated complex. The cyclic form of the activated complexes is unfavorable because of the kinetic factor. Abstraction of hydrogen atom or the far less probable hydride ion abstraction from α‐position in the ether molecules is the rate‐determining step of ozonation. The rate‐determining factors are the electron density and geometry of the reaction center and the energy of the α‐CH bonds. ©

ISSN:0538-8066    

DOI:10.1002/kin.550270206

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractAbsolute rate constants and their temperature dependencies were determined for the addition of hydroxymethyl radicals (CH2OH) to 20 mono‐ or 1,1‐disubstituted alkenes (CH2= CXY) in methanol by time‐resolved electron spin resonance spectroscopy. With the alkene substituents the rate constants at 298 K (k298) vary from 180 M−1s−1(ethyl vinylether) to 2.1 middot; 106M−1s−1(acrolein). The frequency factors obey logA/M−1s−1= 8.1 ± 0.1, whereas the activation energies (Ea) range from 11.6 kJ/mol (methacrylonitrile) to 35.7 kJ/mol (ethyl vinylether). As shown by good correlations with the alkene electron affinities (EA), logk298/M−1s−1= 5.57 + 1.53 · EA/eV (R2= 0.820) andEa= 15.86 − 7.38 · EA/eV (R2= 0.773), hydroxymethyl is a nucleophilic radical, and its addition rates are strongly influenced by polar effects. No apparent correlation was found betweenEaor logk298with the overall reaction enthalpy.

ISSN:0538-8066    

DOI:10.1002/kin.550270207

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractLaser flash photolysis (at 248 or 308 nm) or aryl iodides in water or water/methanol solutions produces iodine atoms and phenyl radicals. Iodine atoms react rapidly with added I−to form I2−but do not react rapidly with O2(k⩽ 107L mol−1s−1). Iodine atoms oxidize phenols to phenoxyl radicals, with rate constants that vary from 1.6 × 107L mol−1s−1for phenol to about 6 × 109L mol−1s−1for 4‐methoxyphenol and hydroquinone. Ascorbate and a Vitamin E analogue are also oxidized very rapidly.N‐Methylindole is oxidized by I atoms to its radical cation with a diffusion‐controlled rate constant, 1.9 × 1010L mol−1s−1. Iodine atoms also oxidize sulfite and ferrocyanide ions rapidly but do not add to double bonds. The phenyl radicals, produced along with the I atoms, react with O2to give phenylperoxyl radicals, which react with phenols much more slowly than I atom

ISSN:0538-8066    

DOI:10.1002/kin.550270208

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractUsing a relative rate technique the reactions of fluorine and chlorine atoms with CF3COOH have been determined to proceed with rate constants of (5.6 ± 0.7) × 10−11and<1 × 10−17cm3molecule−1s−1, respectively. Quoted errors for the F atom rate constant reflect statistical uncertainty (two standard deviations). Systematic errors could add an additional 20% uncertainty. Experiments were performed at 295 ± 2 K and 700 torr total pressure of nitrogen diluent. The reactions of Cl and F atoms with CF3COOH are of no atmospheric importance. Rainout is believed to be the dominant mechanism by which CF3COOH is removed from the atmosphere. The results from this study are discussed with respect to the design and interpretation of laboratory studies of the atmospheric chemistry of CFC replacements. © 1995 John Wil

ISSN:0538-8066    

DOI:10.1002/kin.550270209

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe author pointed out that hydrolysis of acetonitrile, trace impurity of someorganic solvents, and insolubility of benzene can make great effects on B‐Z or B‐R oscillators in aqueous‐organic mixed media. And surfactant is better than organic solvent in the design of chemical oscillators with insoluble substance as substrate. © 1995 John Wiley&Son

ISSN:0538-8066    

DOI:10.1002/kin.550270210

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550270211

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY