An empirical approach to study the anion selectivity at aqueous cationic micellar surface: Effects of inorganic salts on kinetically determined cationic micellar binding constant of ionized phenyl salicylate

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Pseudo-first-order rate constants for methanolysis and hydrolysis of ionized phenyl salicylate (PS −), obtained at different [CTABr] T in the presence of a constant [NaOH] and [MX] (MX = Na 2SO 4 or NaBr), obey the pseudophase model of micelles which enables to determine the CTABr micellar binding constant (K S) of PS − at different [MX]. The values of K S at different [MX] follow the empirical relationship: K S = K S 0 / (1 + K X/S [MX]) where the magnitude of the empirical constant, K X/S, is the measure of the ability of X − to expel S − (= PS −) from micellar pseudophase to the aqueous pseudophase. The values of K X/S vary in the order K X/S (sulfate ion) < K X/S (bromide ion) and the ratio K SO4/PS / K Br/PS ( = 0.4) is shown to be equal to K SO4 Br, the ion-exchange constant for ion-exchange SO 4 2− / Br − i.e. K SO4 Br = ([SO 4M][Br W]) / (SO 4W][Br M]).