KINETIC EVIDENCE FOR THE EFFECTS OF UREA ON THE PROPERTIES OF AQUEOUSMICELLAR SOLUTIONS OF SODIUM DODECYL-SULFATE

The kinetics of the alkaline hydrolysis of the chloropentaamminecobalt (III) cation have been studied at 25.0-degrees-C in water and in aqueo us micellar solutions of sodium dodecyl sulfate (SDS) in the presence of varying amounts of urea. The rate of the alkaline hydrolysis with a nd without added urea is strongly retarded by the SDS surfactant above the critical micelle concentration (c.m.c.) as a result of binding of the cobalt complex to the anionic micellar surface. The effects of ad ded urea on the c.m.c. of the surfactant have been demonstrated kineti cally. Moreover, urea addition causes an enhancement of the overall hy drolysis rate both in water and, to a larger extent, in the aqueous mi cellar solutions, and a decrease in the estimated binding constant of the cobalt complex. The observed effects of urea on the hydrolysis rat e and on the other parameters derived kinetically have been discussed and related to changes in the properties of the SDS micellar aggregate s, such as reduction of the micelle surface charge density on urea add ition.