Kinetics of the chain oxidation of methyl linoleate in aqueous micellar solutions of sodium dodecyl sulfate

The kinetics of absorption of O-2 upon the chain oxidation of methyl linoleate (ML) in aqueous-micellar solutions of sodium dodecyl sulfate (SDS) in the presence of a water-soluble initiator, azo-bis-(4-carboxyisovaleronitrile) (ACVN), was studied at 40 degrees C at various concentrations of ML, SDS, and ACVN over the range of pH from 4.5 to 9.8 using the Clarke electrode. The initiation rate constant was shown to increase with an increase in [SDS] and a decrease in pH, which is caused by an increase in the probability of penetration of radicals of the initiator inside micelles. The oxidation rate in micellar solutions calculated per the full volume of the reaction mixture is considerably higher (in some runs, more than by an order of magnitude) than in homogeneous solutions. The dependence of the oxidation rate (w) on the initiation rate (w(i)) is described by the function w similar to w(i)(m), where m changes from 0.7 to 0.9. This fact suggests a considerable contribution of the linear termination. The dependence of the chain length on [ML] has an S-like shape. At a given concentration of ML, the chain length shortens as [SDS] increases. It is likely that these dependences are related to the change in the ratio between two channels of the chain propagation as the [ML]/[SDS] ratio changes. These two channels are a comparatively slow intermicellar channel (the reactants, the peroxide radical, and the substrate of oxidation ML are in different micelles) and a faster intramicellar one (the reactants are localized in the same micelle).