ANTIOXIDANT ACTIVITIES OF PHENOTHIAZINES AND RELATED-COMPOUNDS - CORRELATION BETWEEN THE ANTIOXIDANT ACTIVITIES AND DISSOCIATION-ENERGIES OF O-H OR N-H BONDS

The antioxidant activities of phenothiazines, carbazoles, and related diphenylamines were evaluated in the oxidation of tetralin at 60 degre es C and linoleic acid micelles in aqueous dispersion at 37 degrees C induced by an azo initiator. Phenothiazines were highly antioxidant in both systems. Although diphenylamine and carbazole were not good anti oxidants, those having a hydroxy group as a substituent at the ortho o r para position to the amino group were potently antioxidant. The anti oxidant activity of o-hydroxydiphenylamine was much greater than that of other compounds in both systems due to a stabilization of the pheno xyl radical by delocalization of the unpaired electron to the p-type l one pair of the amino group. A semiempirical MNDO-AM1 calculation was applied to study hydrogen abstractions of antioxidants in the chain pr ocess of autoxidation. These results indicated that the rates of oxida tion during the induction period correlated with the dissociation ener gies of the O-H or N-H bonds.