EFFECT OF CETYLTRIMETHYLAMMONIUM MICELLES WITH BROMIDE, CHLORIDE, ANDHYDROXIDE COUNTERIONS ON THE RATES OF DECOMPOSITION OF PARASUBSTITUTED ARYL-2,2,2-TRICHLOROETHANOLS IN AQUEOUS NAOH

The effect of cetyltrimethylammonium micelles with bromide, chloride, and hydroxide counterions, CTAX, X = Br, Cl, OH, on the decomposition of aryl-2,2,2-trichloroethanols was determined. This reaction follows an (Elcb)R type mechanism, i.e., rapid reversible deprotonation of the alcohol by OH- followed by rate determining loss of trichloromethyl c arbanion to give the benzaldehyde product. In the presence of surfacta nts, despite the 3-5-fold decrease in the rate constant for the unimol ecular decomposition of the alkoxide ion in the micellar phase, k(m), the dependence of k(m) on substituents effects (values of rho of -0.49 , -0.46, and -0.45 were obtained from the corresponding Hammett plots for CTABr, CTACl, and CTAOH) is similar to that observed in water (rho = -0.5). The observed inhibition can be rationalized in terms of char ge stabilization of the ground state, i.e., quaternary ammonium ions i nteract more strongly with alkoxy anions than with trichloromethyl car banions.