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 × 10⁷ and 3 × 10⁹ 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.