EFFECT OF HEXADECYLTRIMETHYLAMMONIUM BROMIDE MICELLES ON THE HYDROLYSIS OF SUBSTITUTED BENZOATE ESTERS

The alkaline hydrolysis of nine para-substituted phenyl esters of para-substituted benzoates was studied in the presence and absence of hexadecyltrimethylammonium bromide (CTAB) micelles. The second-order rate constant for alkaline hydrolysis in CTAB micelles (k2m) was calculated using a pseudo-phase ion-exchange model. The substituent effect on the second-order rate constant in the aqueous phase (k2w) and on k2m was analysed using Hammett's sigma-rho plots. The calculated rho values in micelles were 0.8 unit larger than those in water. The effective low dielectric constant in the micellar surface may be responsible for the general effect of increasing the sensitivity of reactions to the electronic effect of substituents in micelles.