Mechanism of the catalytic inhibition of hydrocarbon autoxidation by secondary amines and nitroxides

Abstract

Abstract A study has been made of the mechanism of the catalytic inhibition of autoxidation of hydrocarbons at 130°C by secondary amines and derivatives thereof (hydroxylamines and nitroxides). From the effect of hydrocarbon structure on the inhibition and from the various reactions of possible intermediates of the catalytic cycle, it is concluded that alkyl and alkylperoxyl radicals are scavenged alternately. Reaction of an alkyl radical with a nitroxide produces an O ‐alkylated hydroxylamine. In the case of tertiary alkyl radicals this hydroxylamine decomposes thermally ‐ via transfer of the β‐hydrogen from the alkyl group to the nitroxide moiety ‐ into olefin and hydroxylamine. The hydroxylamine is subsequently oxidized back to the nitroxide by alkylperoxyl radicals. Kinetic data on the individual steps of the cycle are in accord with the observed inhibiting effect.