The nature of the micellar Stern region as studied by reaction kinetics

The nature of the rate retarding effects of cationic, anionic and nonionic micelles on the water-catalysed hydrolysis reactions of 1-benzoyl-3-phenyl-1,2,4-triazole (1) and p-methoxyphenyl dichloroacetate (2) has been studied by kinetic methods using UV/VIS Spectroscopy. A comparison was made between medium effects in micellar solutions and in solutions of a model compound, in which the model compound is a small molecule resembling the surfactant headgroup. The rate retarding effect of micelles on the hydrolysis of 1 and 2 was shown to be largely caused by the high concentration of headgroups in the Stern region where 1 and 2 bind to the micelle. Other factors which contribute to the rate inhibition are also briefly discussed.