Rate constants of reactions of OH- with thiol and thione phosphorus (V) esters are increased by cationic surfactants, cetyltrimethylammonium bromide, and mesylate (CTAX, X = Br, OMs) and there are double rate maxima at [CTAX] almost-equal-to the critical micelle concentration (cmc). The esters are R2' PO . SR, 1a, R'= OEt; R = Ph, 1b R'= R = Ph; 1c, R'= Ph, R = OEt and Parathion, (EtO)2 PS . OC6H4NO2 (4). In CTAOMs maximum rate enhancements are by factors of ca. 20 in 0.01 M OH-and are slightly lower in CTABr and at higher [OH-]. Changes in H-1 chemical shifts of CTAOMs on addition of 1b show that complexes form below the cmc. Reaction of OH with 1b is speeded by tri-n-octyl methylammonium mesylate. These results show that submicellar complexes of substrate and hydrophobic ammonium ions are more reactive towards OH- than free substrate. (C) 1994 Academic Press, Inc.