Homolytic aromatic substitution. Part XXXIV. Major products from the reaction of benzoyl peroxide with p-disubstituted benzenes

Abstract

The reaction of benzoyl peroxide with para-disubstituted benzenes (excluding those with sulphur-containing substituents) can lead to substitution by phenyl and/or benzoyloxy-radicals. Product formation is dependent upon the nature of the substituent groups and may be correlated with Hammett σp values. In para-substituted toluenes, the formation of bibenzyls is reduced with increase in the σp value of the para-substituent. Neither phenylation nor benzoyloxylation of the aromatic ring is observed in the reactions of benzoyl peroxide with methyl phenyl sulphide, methyl p-tolyl sulphide, or methyl p-tolyl sulphoxide. The major reaction is oxidation at the sulphur atom, which leads to the formation of, in addition to benzoic anhydride, arylthiomethyl and arylsulphinylmethyl benzoates from the aryl sulphides and sulphoxides respectively. There is no evidence that free radicals are involved in the reaction of benzoyl peroxide with these sulphur-containing compounds.