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 0-alkylated hydroxylamine. In the case of tertiary alkyl radicals this hydroxylamine decomposes thermally ~ via transfer of the P-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.

Inhibition of hydrocarbon autoxidation by nitroxide-catalyzed cross-dismutation of hydroperoxyl and alkylperoxyl radicals

“…It must be emphasized that this is not the only evidence that diarylamines and/or diarylnitroxides catalytically trap radicals via an alternative to the Korcek cycle. For example, an oft-overlooked result of the seminal work of Bolsman et al 65 is that 4′,4-dinitrodiphenylnitroxide is a catalytic inhibitor of paraffin autoxidation at 130 °C, while the corresponding amine is completely ineffective. This could not be explained by the Korcek mechanism, and lead the authors to argue that the amines themselves are not involved in the catalytic cycle of diarylamine antioxidants, but need to be ‘activated’ to the catalytic radical-trapping antioxidant: the nitroxide.…”

Chemo-Mechanical Model for Predicting the Lifetime of Epdm Rubbers

“…42,43 In addition, .NO radicals would be regenerated according to a two-step reaction: .NOP would decompose into hydroxyl amine (.NOH) that would then react with PO 2 radicals to give a .NO radical and a POOH. 44,45 This two-step reaction is usually written in the form of a balance reaction. The action mechanism of hindered amines is summarized by Scheme 8.…”

Labile alkoxyamines: past, present, and future

“…This chemistry did not arouse too much interest 12,13 for one decade, except for a few articles related to the degradation of polymers. [14][15][16][17] In fact, the kinetics underlying this amazing result were unveiled 24 years later by Fischer et al 18 Indeed, the apparent high stability of alkoxyamines is governed by the so-called ''Persistent Radical Effect''. [19][20][21] ‡ Using alkoxyamine 1 (Fig.…”