An e.s.r. investigation of radical reactions of some sulphur-containing phenolic antioxidants

Abstract

E.s.r. spectroscopy has been employed to detect radicals formed by the oxidation of some alkyl-substituted bis-(4-hydroxyphenyl) sulphides under a variety of conditions. Spectra described include those of the cation-radicals of the parent compounds (obtained by oxidation with Lewis acids) and those of sulphur-substituted phenoxyl radicals (from reaction of the parent compounds with Ce^IV or Pb^IV) and semiquinones (from reaction with Fe^III in basic solution). Secondary radicals detected in some instances include stable semiquinones and hydroxylated semiquinones formed in basic solution in the presence of oxygen. The mechanisms of their formation are discussed. Results of molecular orbital calculations on some of the sulphur-containing radicals are reported.