The inhibition of autoxidation by aromatic amines

Recent work on the inhibition of autoxidation by aromatic amines is reviewed. The rate controlling step for the inhibition process is abstraction of the amino hydrogen by a peroxy radical. The rate of this reaction is increased by electron donating substituents attached to the aromatic ring. Nitroxide radicals may be produced in the reaction of peroxy radicals with secondary amino radicals. The efficiency of nitroxide formation is greater for tertiary than for secondary peroxy radicals because, in the latter case, the caged nitroxide and alkoxy radical may disproportionate to give a hydroxylamine and a carbonyl compound. Primary aromatic amines do not give nitroxides, presumably because the peroxy radical‐amino radical reaction gives an alcohol and a nitroso aromatic. The tertiary amine, N,N,N′,N′‐tetramethyl‐p‐phenylenediamine is shown to be a catalyst of autoxidation rather than an inhibitor, as has been previously reported. The products of the N‐phenyl‐2‐naphthylamine‐peroxy radical reaction have been identified.