MICELLAR EFFECTS UPON REACTION OF P-NITROPHENYL DIPHENYL PHOSPHATE WITH HYDROXIDE AND FLUORIDE IONS

The reactions between p-nitrophenyl diphenyl phosphate and hydroxide or fluorideions in water at 25° are catalyzed strongly by cationic micelles of cetyltrimethylammonium bromide, with the rate increasing to a maximum at ca. 3 × 10-3 M detergent. The detergent increases the activation enthalpy, but makes the activation entropy less negative. Added salts inhibit the catalysis, and the inhibition is largest with anions of low charge density. Anionic micelles of sodium lauryl sulfate strongly inhibit the reaction, as does the uncharged detergent Igepal, but here there is marked inhibition at submicellar concentrations. The inhibition can be related to the extent of incorporation of the substrate into the micelles, or its association with the detergent. © 1969, American Chemical Society. All rights reserved.