On the reaction of methyl and phenyl radicals with p-benzoquinone in aqueous solution

Abstract

˙CH₃ and ˙ C₆H₅ radicals (from the reaction of ·OH with dimethyl and diphenyl sulphoxide) react with p-benzoquinone with k(4.5 ± 1.0)× 10⁷ and (1.2 ± 0.2)× 10⁹ dm³ mol^–1 s^–1, respectively. In both cases an immediate formation of a transient is observed which could be identified as the unsubstituted semiquinone radical. The reaction mechanism is considered to proceed via addition of the ˙CH₃ or ˙C₆H₅ radicals to one p-benzoquinone molecule and immediate subsequent reaction of these radical adducts with a second p-benzoquinone molecule. The latter process is likely to be an electron transfer. The pulse radiolysis results are supported by steady-state irradiation product analysis.