Aryloxy-radicals. Part VII. The electron spin resonance spectra of the secondary radicals formed during the heterogeneous oxidation of some substituted phenols

Abstract

The heterogeneous oxidation of some substituted phenols has been studied by means of electron spin resonance. The strong signals observed during the oxidation of the phenols having a free para-position were due to secondary radicals derived from C(4)–O linked dimeric and polymeric phenols and not to substituted 4,4′-diphenosemiquinones. Special attention was given to the oxidation of 2,6-dimethylphenol, which yields a radical with non-equivalent methyl groups. The e.s.r. spectra of the secondary radicals from some 4-substituted 2,6-dimethylphenols were identical with each other and with that from 2,6-dimethylphenol itself. This indicates that in these radicals the para-substituent had been displaced by an aryloxy-group. The ease of this displacement could be determined by use of the flow technique. The bromine atom in 4-bromo-2,6-dimethylphenol can be displaced more easily than the 4-hydrogen atom in 2,6-dimethylphenol.