Kinetic study of the reaction between vitamin E radical and alkyl hydroperoxides in solution

Kinetic study of the reaction between vitamin E radical and alkyl hydroperoxides has been performed, as a model for the reactions of lipid hydroperoxides with vitamin E radical in biological systems. The rates of reaction of hydroperoxides (n-butyl hydroperoxide 1, sec-butyl hydroperoxide 2, and tert-butyl hydroperoxide 3) with vitamin E radical (5,7-diisopropyl-tocopheroxyl 4) in benzene solution have been determined spectrophotometrically. The second-order rate constants, k-1, obtained are 1.34 x 10(-1) M-1s-1 for 1, 2.42 x 10(-1) M-1s-1 for 2, and 3.65 x 10(-1) M-1s-1 for 3 at 25.0 degrees C. The result indicates that the rate constants increase as the total electron donating capacity of the alkyl substituents at alpha-carbon atom of hydroperoxides increases. The above rates, k-1, are about seven order of magnitude lower than those, k1, for the reaction of vitamin E with peroxyl radical.