FORMATION AND REACTIONS OF HALOGENATED PHENYLPEROXYL RADICALS IN AQUEOUS ALCOHOL-SOLUTIONS

Halogenated phenylperoxyl radicals were produced in irradiated aqueous alcohol solutions by reductive dehalogenation of dihalo- and polyhalobenzenes with solvated electrons and subsequent reaction of the halophenyl radicals with oxygen. Phenylperoxyl radicals oxidize 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate ion) (ABTS(2-)) with rate constants between 3 x 10(7) and 3 x 10(9) L mol(-1) s(-1), depending on the structure of the peroxyl radical and the alcohol concentration. For monohalogenated phenylperoxyl radicals, the reactivity changed in the order F < Cl < Br and p < m < o. The reactivity increased on going from the (monohalophenyl)- to the (dihalophenyl)- and (trihalophenyl)peroxyl radicals. The rate constants were correlated with the substituent constants and with the pK(a) values of similarly halogenated phenols. The reduction potential for PhOO(.)/PhOO(-) was estimated to be near 0.7 V vs NHE; that for the trichloro derivative, near 0.9 V. The rate constants in various solvent mixtures were correlated with the cohesive pressure of the medium.