INTERACTION OF THE CHLOROPENTAAMMINECOBALT(III) CATION WITH MIXED MICELLES OF ANIONIC AND NONIONIC SURFACTANTS - A KINETIC-STUDY

Alkaline hydrolysis rates of the chloropentaamminecobalt(III) cation h ave been studied at 25.0-degrees-C and an ionic strength of 0.05 mol d m-3 in aqueous mixed micelles composed of anionic sodium dodecyl sulfa te (SDS) and non-ionic n-dodecylpenta(oxyethylene glycol) monoether (C 12E5) surfactants over a wide range of total surfactant concentration (C(t)) and SDS mole fraction (alpha). The critical micelle concentrati ons (c.m.c.s) of mixtures of the two surfactants over the entire alpha range have also been determined and found to follow the regular solut ion model for non-ideal mixing. The kinetic results have shown that in teractions of the cationic cobalt complex with the mixed micelles caus e a decrease of the reaction rate with increasing C(t) (at constant al pha) and alpha (at constant C(t)). The estimated binding constant of t he complex decreases markedly as alpha decreases as a result of the re duction of the charge density at the mixed micellar surface. The prese nt findings are compared with those obtained previously concerning the effect of urea and its alkyl derivatives upon the rate of the same hy drolysis reaction in SDS micellar solutions.