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

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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.