Mechanisms of antioxidant action: Auto-synergistic behaviour of sulphur-containing phenols

The powerful antioxidant activity of 3,5-di-tert-butyl-4-hydroxybenzyl sulphides has been shown to be due to the generation of a Lewis acid catalyst which may destroy > 3 × 10⁵ moles of hydroperoxide per mole of sulphur compound. The same catalytic species formed from a variety of benzylic sulphides and is believed to be an inorganic sulphur acid (probably S0₃). Dibenzyl monosulphide itself is not initially an antioxidant and one function of the hindered phenolic group in the auto-synergists is believed to be the removal of free radicals formed during the early stages of the reaction.