[Behavior of alpha-tocopherol during the autoxidation of linoleic acid in aqueous solution]

Addition of great quantity of alpha-tocopherol to an aqueous solution containing linoleic acid dispersed with twen 20 conduce to an important augmentation of the rate of formation of linoleic hydroperoxides. In these particular conditions, alpha-tocopherol have a prooxidant effect. In the same time, alpha-tocopherol is rapidly transformed into tocopherylquinone and a dimer of alpha-tocopherol. Transitorily there is formation of a dihydroxydimer of alpha-tocopherol. Comparison of these compounds behaviour on the oxydation rate of linoleic acid in the same conditions show a near relation between a prooxidant effect and chemical structure of these compounds as well as alpha-tocopherol. So, alpha-tocopherol and its dihydroxydimer are both prooxidant and both have a free hydroxyl on carbon 6. Dimer of alpha-tocopherol and tocopherylquinone are both antioxidant and they have neither free hydroxyl on carbon 6. alpha-tocopherol acetate in the same conditions have an antioxidant comportment. This confirms the importance of free hydroxyl on carbon 6 to obtain a prooxidant effect.