The importance of hydrogen abstraction by peroxy radicals as a mechanism of antioxidant action in rubber has been studied by investigation of a deuterium isotope effect with amine and phenolic inhibitors in the oxidation of butadiene‐styrene rubber. Deuterium was substituted for the active hydrogen of N‐phenyl‐2‐naphthylamine and 2,6‐di‐tert‐butyl‐4‐methylphenol by reacting the antioxidants with methylmagnesium iodide and then with deuterium oxide. The oxidation rates of butadiene–styrene polymer inhibited with 3 parts per hundred of these compounds were measured and compared with the oxidation rates using normal antioxidants. A kinetic isotope effect in the rate of oxidation was observed with both the phenolic inhibitor (kD/kH = 1.3 with not less than 77% substitution) and the amine inhibitor (kD/kH = 1.8 with not less than 60% substitution). The existence of an isotope effect leads to the conclusion that hydrogen donation to a peroxy radical is a controlling step in the mechanism by which these antioxidants function to retard the oxidation of rubber.
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