Reactions of p-Nitrophenyl Diphenyl Phosphinate with Fluoride and Hydroxide Ion in Nonionic Micelles: Kinetic Salt Effects

Reactions of p-nitrophenyl diphenyl phosphinate (p-NPDP) with OH- and F- are inhibited by micelles of dodecyl polyoxyethylene ethers C12E10 and C12E23. Rate constants decrease sharply in very dilute surfactant and become approximately constant as p-NPDP becomes fully micellar bound, with inhibition by approximately an order of magnitude. The first-formed fluoridate is detected by NMR spectroscopy in reaction with F- in DMSO-d6:D2O 85:15 v/v, but not in other conditions. Kinetic salt effects on the micellar reactions are ion specific. Bulky anions, ClO-4 and naphthalene-2-sulfonate ion (ONs-), inhibit reactions much more than small ions, and (C7H15)4N+ accelerates reaction of F-. Micellar incorporation of ONs- in the micelles is demonstrated by changes in 1H-NMR spectra of the surfactants. Comparison of rate constants of reaction of F- in PEG (MW 10(4)) and in nonionic micelles shows that the micellar inhibition is due largely to lower ionic concentrations in the micelles than in water. Copyright 1999 Academic Press.