Amine autoxidation in aqueous solution

Abstract

The uncatalysed autoxidation of aqueous solutions of tertiary aliphatic amines has been studied in order to obtain information concerning the mechanism of oxidation of Sirotherm resins. Oxidation occurs most rapidly in the free base, and the general correlation of rate with pK, or ionization potential suggests that electron transfer to form an aminium radical cation is rate-determining. The reaction is not initiated by free radical initiators, nor inhibited by radical traps. It is significantly catalysed by strong electron acceptors and by light and is moderately inhibited by the electron donor N-phenylanthranilic acid. Pyrrolidines and hexahydroazepines are oxidized faster than piperidines, and hydroxyl groups on β-carbons increase the rate of oxidation, while those on γ-carbons decrease it. The major products of autoxidation of alkyl pyrrolidines in water were found to be N-oxides. Various pyrrolidinones were isolated in smaller yield.