Micellar kinetics of acyl transfer from n-nonanoyloxybenzenesulfonate and phenyl nonanoate bleach activators to hydrogen peroxide and pernonanoic acid: effect of charge on the surfactant and activator

Abstract

The effect of surfactants on the kinetics of the title reactions is analysed using a combined multiple micellar pseudophase model and transition state pseudoequilibrium constant approach which leads to the micellar association constants of the reactants and the apparent (virtual) micellar association constants of the transition states. These association constants reflect the stabilisation of the reactants and transition states, respectively, by the micelle compared with their stability in the bulk aqueous phase. For the reaction of n-nonanoyloxybenzenesulfonate with pernonanoate in the presence of sodium dodecyl sulfate (SDS) the apparent micellar association constant of the transition state is larger than the micellar association constant of the activator; this is consistent with micellar catalysis, whilst micellar inhibition occurs with the anion of hydrogen peroxide. The micellar association constant of phenyl nonanoate with SDS is four orders of magnitude greater than that of n-nonanoyloxybenzenesulfonate due to the absence of the negatively charged sulfonate group, whilst the apparent micellar association constant of the transition state for its reaction with pernonanoate is more than an order of magnitude less. In the non-ionic surfactant Brij-35, the micellar association constant of n-nonanoyloxybenzenesulfonate and the corresponding apparent quantity for the transition state for the reaction with the hydroperoxide anion are, respectively, about one and two orders of magnitude greater than in SDS.