Hydrolyses of dianionic 2,4-dinitrophenyl phosphate, substituted at position 5 by Me, OMe, n-OC14H29 (DNMePP2-, DNMeOPP2-, and DNTDOPP2- respectively) are accelerated by cationic micelles of cetyl trialkylammonium bromide (CTABr, CTPABr, and CTBABr, with alkyl = Me, n-Pr, and n-Bu, respectively). There are well-defined rate maxima in dilute surfactant, below the critical micelle concentration, for reaction of DNTDOPP2- in the sequence CTBABr > CTPABr > CTABr, because of acceleration by premicelles which is not observed with the methoxy and unsubstituted derivatives. The rate maxima disappear as these species "dissolve" in micelles at higher surfactant concentrations.