FORMATION AND REACTIVITY OF PHENYLPEROXYL RADICALS IN AQUEOUS-SOLUTIONS

The reaction of phenyl radicals with oxygen, to produce phenylperoxyl radicals, and the reactions of several phenylperoxyl radicals with a n umber of organic compounds in aqueous solutions have been studied by p ulse radiolysis. Phenyl radicals were produced by reduction of aryl ha lides with hydrated electrons. The rate constant for the reaction of 4 -carboxyphenyl with O-2 was determined from the rate of buildup of the peroxyl radical absorption at 520 nm as a function of [O-2] and found to be 1.6 x 10(9) L mol(-1) s(-1). Phenyl radicals react with 2-PrOH by H abstraction; a rate constants of 4 x 10(6) L mol(-1) s(-1) was de termined for 4-carboxyphenyl by competition with the reaction of this radical with O-2. Phenylperoxyl radicals react with 4-methoxyphenolate ions, trolox C (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic aci d), ascorbate ions, chlorpromazine, and ABTS [2,2'-azinobis(3-ethylben zothiazoline-6-sulfonate ion)] by one-electron oxidation. The rate con stants for such reactions, determined from the rate of formation of th e one-electron oxidation product as a function of substrate concentrat ion, were found to be near 10(8)-10(9) L mol(-1) s(-1). The reaction w ith neutral phenols, however, was much slower and could not be observe d under the pulse radiolysis conditions. Phenylperoxyl radicals are fo und to be much more reactive than methylperoxyl and more reactive than most substituted methylperoxyls, except for the halogen-substituted r adicals. Electron-withdrawing substituents at the 4-position of phenyl peroxyl increase the fate constant and electron-donating groups decrea se the rate constant for oxidation by this radical, in accordance with the Hammett substituent constants.