Mechanism of antioxidant action in the stabilization of hydrocarbon systems

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Abstract
Four antioxidant classifications, based on differences in the method by which they exert their effect, are noted. The mechanism of the chain‐stopping action is discussed in terms of four different reactions which have been proposed. The participation of the antioxidant in the mechanism of inhibited thermal oxidation is reviewed. The hydrogen donation mechanism as the first step in the chain‐stopping mechanism has been investigated by observing the effect of replacing the active hydrogen of the antioxidant by deuterium. Contrary to the findings of some prior workers, a kinetic isotope effect has been demonstrated with a secondary aryl amine antioxidant as well as with phenols. These results, together with other supporting evidences reported in the literature, indicate that abstraction of a hydrogen from the antioxidant is the initial step in the usual mechanism by which antioxidants serve as chain stoppers in the oxidation of hydrocarbon systems.