Rate constants for reduction of substituted methylperoxyl radicals by ascorbate ions and N,N,N',N'-tetramethyl-p-phenylenediamine
作者:P. Neta、R. E. Huie、S. Mosseri、L. V. Shastri、J. P. Mittal、P. Maruthamuthu、S. Steenken
DOI:10.1021/j100347a045
日期:1989.5
Perfluorobutylperoxyl radical as an oxidant in various solvents
作者:G. S. Nahor、P. Neta、Z. B. Alfassi
DOI:10.1021/j100164a047
日期:1991.5
Perfluorobutylperoxyl radicals were produced by pulse radiolysis of aerated solutions of perfluorobutyl iodide. The rate constants for reaction of this radical with several organic reductants, chlorpromazine, trolox, hydroquinone, and several other phenols, were determined in various solvents and were found to be in the range of 10(5)-10(9) M-1 s-1. By comparison with other haloalkylperoxyl radicals, C4F9OO. was found to be a much more powerful oxidant, whose reactions took place more rapidly and were less sensitive to solvent and substituent effects. The rate constants (k) for oxidation of a series of para-substituted phenols by C4F9OO. gave a good linear correlation between log k and the electrophilic substituent constant sigma+, with a slope of rho+ = -2.3, indicating formation of a positively charged transition state. Parallel experiments with CCl3OO. were limited to the most reactive phenols and gave a higher slope, rho+ = -3.3. The rates of reaction of C4F9OO. with trolox and chlorpromazine were found to depend on solvent viscosity, but much less on solvent polarity and acid-base properties, probably because they were closer to the diffusion-controlled limit. The longer chain C10F21OO. was somewhat less reactive than C4F9OO. because of geometric factors.
Temperature dependence of the rate constants for oxidation of organic compounds by peroxyl radicals in aqueous alcohol solutions
作者:Z. B. Alfassi、R. E. Huie、M. Kumar、P. Neta
DOI:10.1021/j100181a045
日期:1992.1
Rate constants for reactions of chlorinated methylperoxyl radicals with chlorpromazinc (2-chloro-10-[3-(dimethylamino)-propyl]phenothiazine), trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxy?? lic acid), and ascorbate in aqueous alcohol solutions have been measured by pulse radiolysis as a function of temperature, generally between 5 and 75-degrees-C. The rate constants varied between 10(6) and 10(9) M-1 s-1, the calculated Arrhenius activation energies ranged from 1 to 30 kJ mol-1, and the preexponential factors also varied considerably, with log A ranging from 7 to 14. In general, room temperature rate constants increase with an increase in the number of chlorine atoms on the radical (increasing its electron affinity and thus the driving force for the reaction) and with an increase in the solvent polarity. The Arrhenius preexponential factor and the activation energy both increased as the proportion of water in the solvent mixture increased; i.e., the increase in rate constant with solvent polarity is a result of two compensating effects. Electron transfer from the organic reductants to the chlorinated methylperoxyl radicals is suggested to take place via an inner-sphere mechanism involving a transient adduct of the peroxyl radical to the reductant.
Reactivities of chlorine atoms and peroxyl radicals formed in the radiolysis of dichloromethane
作者:Z. B. Alfassi、S. Mosseri、P. Neta
DOI:10.1021/j100341a040
日期:1989.2
Preparation of 1-chloroalkyl hydroperoxides by the addition of hydrogen chloride to carbonyl oxides