Substituted thiobisphenols as antioxidants: Correlation between antioxidant activities and13C chemical shifts

The antioxidant activities of ten thiobisphenols were evaluated by an oxygen-absorption method at 60°C in tetralin and determination of peroxide values at 160°C in paraffin. For the 4,4′-thiobisphenols, alkyl groupsortho to the phenolic hydroxyl groups increased the induction period compared to that of other thiobisphenols for both oxidation of tetralin and paraffin. The data on electrochemical oxidation potentials that were determined by linear-sweep voltammetry and the13C nuclear magnetic resonance chemical shifts (δ) of these compounds were associated with antioxidant activities. In particular, the activities exhibited during the induction period closely correlated with the13C chemical shifts of ipso-carbon of the OH substituent.