Preparation of unstable quinones in aqueous solution via pulse radiolytic one-electron oxidation of dihydroxybenzenes

Abstract

The stoichiometry of the reactions of semiquinones resulting from the one-electron oxidation of various dihydroxybenzenes is examined. It is verified that the semiquinones of hydroquinone and catechol disproportionate completely to give p-benzoquinone and o-benzoquinone, respectively. With resorcinol, however, the corresponding semioxidised radical reaction is different, giving unstable dimers which subsequently rearrange to tetrahydroxybiphenyls. The usefulness of catechol one-electron oxidation followed by o-semiquinone disproportionation as a means of preparing biologically important unstable o-quinones is exemplified by three new examples: (1) The o-quinone of oestradiol which may have melanocytotoxic properties; (2) the o-quinone of salsolinol whose oxidative metabolites may be responsible for neuronal damage in alcoholism and (3)o-quinone of tetrahydropapaveroline whose oxidative metabolism may play a role in both alcohol addiction and Parkinson's disease.