Formation of radicals in the amine inhibited decomposition of t-butyl hydroperoxide

Abstract

The radicals formed in the amine inhibited, α,α′-azo-bis-isobutyronitrile initiated, decomposition of t-butyl hydroperoxide at 65° have been examined by electron spin resonance. In the absence of amine a strong peroxy radical signal is obtained. Amines with structures that do not correspond to those of conventional antioxidants (i.e. primary and secondary aliphatic amines and tertiary amines) generally have little or no effect on this signal. Nitroxide radicals are generated from secondary aromatic (diaryl and alkaryl) amines. The rate of conversion of these amines to nitroxides reached a maximum of 50–60% of the rate of chain initiation for some diphenylamines. A maximum concentration of nitroxide of about half the initial amine concentration was obtained with 4,4′-dimethyldiphenylamine.N,N,N′,N′-Tetramethyl-p-phenylenediamine is very rapidly oxidized by t-butyl hydroperoxide to give Wurster's Blue cation and, presumably, a t-butoxy radical. This amine is therefore an initiator of oxidation rather than an inhibitor as has commonly been supposed.Primary aromatic amines do not appear to form simple aryl nitroxides. It is proposed that arylamino radicals [Formula: see text] are directly oxidized to nitroso compounds by peroxy radicals.