Optical absorption studies of the kinetics of UV- and self-initiated autoxidation of linoleate micelles.

Autoxidation of linoleate micelles in aqueous alkaline solutions was studied by absorption spectroscopy. Autoxidation was initiated in either a UV-induced or a spontaneous decomposition (self-initiation) of hydroperoxides, initially present as trace impurity. In both cases, the hydroperoxides, the primary oxidation products, increased quadratically with time. In the presence of vitamin E, UV irradiation initially caused an exponential photodecomposition of hydroperoxides, with a rate constant of 2.6 center dot 10(-3) s-1, towards a stationary level. The period of inhibition of autoxidation by vitamin E was in proportion to the amount of vitamin E added to the solution. In the course of autoxidation, when the concentration of hydroperoxides exceeded a certain critical level, the micelles collapsed, which was monitored by light scattering. A model for the consumption of vitamin E, in the case of UV initiation, was developed and from which an initiation rate of 4.05 center dot 10(-7) M center dot s-1 was derived. From the initiation rate and the coefficient of the second-order dependence of hydroperoxides with time, an oxidizibility of 1.28 (M center dot s)-1/2 was derived.