Enhancements provided by micellized cetyltrimethylammonium bromide (ctab), to the rates of reaction between 2-iodosyl-5-octyloxybenzoic acid and 4-nitrophenyl diphenyl phosphate (3), 4-nitrophenyl acetate (4), 1-methylethyl methylphosphonofluoridate (5), 1, 2, 2-trimethylpropyl methylphosphonofluoridate (6) and ethyl N, N-dimethylphosphoramidocyanidate (7) are determined over a range of ctab concentrations. The maximum enhancements observed for substrates (5)-(7) are greater than predicted by the phase-separation model.1 The suitability of the model to describe these reactions is considered. © 1990 ASEG.