Micellar effects on reaction rates and acid-base equilibria

The effects of ionic surfactant micelles on reaction rates in solution on acid-base equilibria often conform quite well to a theory known as the pseudophase ion-exchange model (PPIEM). Despite its success the theory suffers from several limitations. These are outlined and an alternative approach which overcomes them is forwarded. This new theory is based on the equilibrium formulation of transition-state theory. The philosophy underlying it is similar to that used in the treatment of salt effects on the kinetics of reactions involving ions. Attention is focused on the partition coefficients of reactants and activated complexes between micellar and aqueous environments. The author's previous work on the equilibrium thermodynamics of micellar solutions is used to describe the dependence of these coefficients on the concentrations of surfactants and supporting electrolyte. However, the approach is not restricted to any particular equilibrium theory. The conceptual basis of the new theory is more sound than that of the PPIEM. It successfully explains experimental data both when the PPIEM succeeds and when it fails. Hence it explains why the PPIEM often works in practice. It is equally convenient to use and is applicable to all types of micelle. Its only limitations are those of the theoriesmore » on which it is based.« less