Mechanism of the antioxidant action of dialkyl sulfoxides II. Aspects of the antioxidant and pro‐oxidant actions of sulfoxides

This paper analyses several complicating factors which can play a role in the inhibition of autoxidation by dialkyl sulfoxides, the uncomplicated case having been dealt with in the first paper1. It was found that in those cases where the autoxidation proceeds via tertiary peroxy radicals, sulfoxides yielding tertiary (or, possibly, also secondary) alkylsulfenic acids show poor antioxidant activity. This is attributed to the generation of radicals from the sulfinic acid perester formed by the reaction of peroxy radicals with the sulfinic radicals produced in the inhibition reaction. A type of inhibition of autoxidation which does not involve radical scavenging arises from the ionic decomposition of hydroperoxides by strong acids formed from sulfoxides; this type of inhibition is most effective with those sulfoxides which are also active as inhibitors via the formation of sulfenic acid. Sulfoxides also display a pro‐oxidant action, which is explained as a catalysis of the radical decomposition of hydroperoxides via the formation of a compound or complex from hydroperoxide and sulfoxide.