NUCLEOPHILICALLY ASSISTED DEACYLATION IN SODIUM DODECANOATE AND DODECYL-SULFATE MICELLES - QUANTITATIVE EVIDENCE ON PREMICELLAR COMPLEXES

Hydrolyses of 2,4-dinitrophenyl acetate and octanoate (DNPA and DNPO, respectively) and benzoic anhydride (Bz(2)O) in the pH range 8.9-10.2 are inhibited by anionic micelles of sodium dodecyl sulfate (SDS), and reactions of fully micellar-bound substrates are very slow. The effect of micellized sodium dodecanoate, SDOD, depends on pH. At high pH reactions of DNPA and Bz(2)O involve OH- and are inhibited by SDOD, but there are significant rates at high [SDOD]. At low-pH reactions of DNPA and Bz(2)O are inhibited at low [SDOD] and assisted at high [SDOD]. The inhibition is due to formation of kinetically ineffective premicellar complexes and rate-surfactant profiles can be fitted quantitatively in terms of this. model. When the substrates are fully micellar-bound rate constants in mixtures of SDOD and SDS follow the mole fraction of SDOD and second-order rate constants of nucleophilic attack by the dodecanoate ion at micellar surfaces are similar to those for the reactions of OAc- in water.