HYDROLYSIS OF 2,4-DINITROPHENYL PHOSPHATE IN NORMAL AND REVERSE MICELLES

The rate of spontaneous hydrolysis of the 2,4-dinitrophenyl phosphate dianion (DNPP2-) is strongly increased by aqueous cationic micelles of cetyltrialkylammonium bromides (alkyl = Me, Pr, Bu) and tetradecylqui nuclidinium bromide. First order rate constants reach limiting values in dilute surfactant where DNPP2- is fully micellar bound. Rate enhanc ements increase with increasing bulk of the head group and are associa ted with decreases in activation enthalpies. Betaine sulfonate micelle s (C14H29N+ R(2)[CH2]3SO3-, R = Me, Et, Pr, Bu) also speed hydrolysis, but first order rate constants continue to increase even up to 0.2 mo l dm(-3) surfactant, because DNPP2- is not strongly bound. Reverse mic elles of cetyltrialkylammonium bromide(alkyl = Me, Bu) in dichlorometh ane give rapid hydrolysis, but rate constants decrease on addition of water approximately to the value observed with aqueous cationic micell es as 'water pool' reverse micelles of CTABr are formed. N,N-Dimethylh ydroxylamine increases the rate of hydrolysis in water, but not in rev erse micelles, and a (hypothetical) phosphoramidate is not trapped by F-.