The antioxidant activity of 3,5‐di‐tert‐butyl‐4‐hydroxybenzyl derivatives

Abstract

AbstractVarious electron donating groups such as alkoxyl, alkylthio, and alkylamino groups were used to replace a hydrogen atom of the para‐methyl group of 2,6‐di‐tert‐butyl‐4‐methylphenol, BHT. The antioxidant activity of these 3,5‐di‐tert‐butyl‐4‐hydroxybenzyl derivatives in stripped corn oil at 79.5°±1.0C was measured on the basis of the length of the induction period. A modified peroxide determination was devised and used in the present study. The overall average of the per cent accuracy, based on the standard error, was 2.5%.The results indicated that the tertiary methyl and ethylamine derivatives had the strongest potency among all compounds tested. Both amine derivatives were able to prolong the induction period of the corn oil twice as much as BHT. The alkoxyl derivatives were as effective as BHT. The alkylthio derivatives showed stronger activity than either BHT or the alkoxyl derivatives. The secondary alkylamine derivatives, except the n‐hexadecylamine derivative, demonstrated nearly the same degree of potency as BHT. However, the n‐hexadecylamine derivative exhibited far stronger activity than either the three lower alkylamine derivatives or BHT. In all three homologous series, the methyl derivatives showed significantly lower activity than the ethyl or n‐propyl derivatives. Differences between the ethyl and n‐propyl derivatives were not significant. 3,5‐Di‐tert‐butyl‐4‐hydroxybenzylpyridinium bromide acted as a prooxidant. An attempt has been made to explain the variation in activity of these derivatives in terms of the inductive effect exerted by the nucleophilic substituents and/or in terms of the structural features of the derivatives.