Ion reactivity in reversed-micellar systems. Kinetics of reaction between micelles containing hydrated nickel(II) and murexide-containing micelles in the system aerosol–OT + water + heptane

Abstract

A stopped-flow kinetic study has been made of a metal–ligand substitution process taking place in Aerosol–OT stabilised water pools in n-heptane. In a typical stopped-flow experiment, reversed micelles containing solubilised metal ion are mixed with micelles containing ligand such that the total concentration of micelles is unchanged on mixing. Micelle sizes are dependent on the water: surfactant mole ratio “R”(where R=[H₂O]/AOT]) and the system has been characterised by ultracentrifugation methods over the range R= 0.26–16.9. The kinetic results for complexation in the reversed micellar system support a mechanism involving rapid exchange of reactants between aqueous pools followed by rate-limiting loss of a solvated water molecule from the metal-ion in a water pool. Rate constants for ligand release and water-exchange in the water pools are close to the bulk water values and are not very dependent on pool size.