The modifying effects of a cationic surfactant on the rates of base catalysed hydrolysis of esters of different structures

Abstract

Abstract The effect of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), on the hydrolysis rates of four esters of different structure has been investigated. The esters used were ethyl p-aminobenzoate (EPAB), p-nitrophenyl acetate (PNPA), ethyl p-nitrobenzoate (EPNB) and p-aminophenyl acetate (PAPA). Association between the esters and the CTAB occurs so that above its cmc the surfactant modifies the rates of hydrolysis, increasing those of EPNB and PNPA and decreasing those of EPAB and PAPA. It thus appears that the type of group on the p-position of the aromatic ring plays a major role in determining the kind of effect brought about by the CTAB. Possible reasons to explain the two different effects that CTAB has on ester hydrolysis are put forward.