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- ar e inhibited by micelles of dodecyl polyoxyethylene ethers C12E10 and C12E23 . Rate constants decrease sharply in very dilute surfactant and become appr oximately constant as p-NPDP becomes fully micellar bound, with inhibition by approximately an order of magnitude. The first-formed fluoridate is dete cted by NMR spectroscopy in reaction with F- in DMSO-d(6): D2O 85:15 v/v, b ut not in other conditions. Kinetic salt effects on the micellar reactions are ion specific. Bulky anions, ClO4- and naphthalene-2-sulfonate ion (ONs( -)), inhibit reactions much more than small ions, and (C7H15)(4)N+ accelera tes reaction of F-. Micellar incorporation of ONs(-) in the micelles is dem onstrated by changes in H-1-NMR spectra of the surfactants. Comparison of r ate 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 concentrat ions in the micelles than in water. (C) 1999 Academic Press.