Micellar effects upon the hydrolysis of bis-2,4-dinitrophenyl phosphate

Abstract

Micellar effects upon the reaction between hydroxide ion and bis-2,4-dinitrophenyl phosphate to give 2,4-dinitrophenyl phosphate have been examined. The reaction is catalyzed up to 30-fold by cationic micelles of cetyltrimethylammonium bromide, CTABr, unaffected by anionic micelles of sodium lauryl sulfate, NaLS, and inhibited by uncharged micelles of a polyether. Added salts, particularly those with large, low charge density anions effectively inhibit catalysis by CTABr. Turbidity measurements show that the substrate and CTABr form submicellar aggregates, but that added salts reduce their formation. The ability of salts to inhibit formation of these submicellar aggregates increases with decreasing charge density of the anion, e.g., tosylates are more effective than chlorides. The micellar effects upon the second stage of the reaction, hydrolysis of 2,4-dinitrophenyl phosphate, follow the usual pattern of catalysis by CTABr and no effect of an anionic or uncharged detergent and only a a slight rate enhancement by hydroxide ion. The catalysis of the hydrolysis of 2,4-dinitrophenyl phosphate by CTABr and CTACl is not sensitive to large changes in detergent concentration which lead to a change in micellar shapes.