Micellar effects on the hydrolysis and aminolysis of 2,4-dinitrophenyl sulphate

Abstract

Effects of micellar hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulphate (NaLS), polyoxyethylene(20) nonylphenol (lgepal CO-850), 3-(dimethyldodecylammonio)-propane-1-sulphonate (DDAPS) and that of their co-micellar mixtures have been investigated on the nucleophilic reactivity of primary, secondary, and tertiary amines toward 2,4-dinitrophenyl sulphate. Observed second-order rate constants, k_2,obs have been separated into those due to hydrolysis, K_2,hyd, and to nucleophilic attack, K_2,nuc. Micellar CTAB, DDAPS, and lgepal CO-850 enhance k_2,hyd for the different amines from 4 to 33 fold, while micellar NaLS has no appreciable effect. A more dramatic result is the complete suppression of K_2,nuc by micellar CTAB, DDAPS, and mixtures of CTAB and lgepal CO-850 for reactions of hydrazine and morpholine. Sensitivities of hydrolysis to amine basicity (Brønsted β-values) are greater in micellar CTAB, DDAPS, and lgepal CO-850 than in pure water.