Antioxidant activities of phenothiazines and related compounds: Correlation between the antioxidant activities and dissociation energies of O-H or N-H bonds

Article abstract of DOI:10.1246/bcsj.70.413

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