Effects of organic salts on the rate of intramolecular general base-catalyzed piperidinolysis of ionized phenyl salicylate in the presence of cationic micelles

Abstract

Pseudo-first-order rate constants (k_obs), obtained for the cleavage of ionized phenyl salicylate (PS⁻) at constant [NaOH], [MeCN], [CTABr]_T (total concentration of cetyltrimethylammonium bromide), [Pip]_T (total concentration of piperidine) and varying concentrations of sodium o-, m- and p-toluate ([MX]), follow the relationship: k_obs = (k₀ + θK[MX])/(1 + K[MX]), where θ and K are empirical parameters. The values of θ are almost independent of [CTABr]_T, while the K values decrease with increasing [CTABr]_T within its range 0.005–0.020 mol dm⁻³. The values of θ and K are explained in terms of a pseudophase model of the micelle coupled with an empirical relationship: K_S = K_S⁰/(1 + k_X/S[MX]), where K_S is the CTABr micellar binding constant of PS⁻ in the presence of MX. The value of K_X/S, for the o-toluate ion is nearly 2.5-fold smaller than those for the m- and p-toluate ions. The values of θ/(kⁿ_W[Pip]_T) {where kⁿ_W[Pip]_T = k_obs at [CTABr]_T = [MX] = 0} vary from nearly 0.5 to 0.6 within the [CTABr]_T range 0.005–0.020 mol dm⁻³.