ABSTRACT
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.
ABSTRACT
The SN2 reaction of Br- with methylnaphthalene-2-sulfonate (MeONs) in water is accelerated by micelles of tetradecyldialkyl amine oxide (alkyl = methyl, n-propyl) and rates increase sharply in HBr due to increased binding of Br- to the protonated amine oxide. Second-order rate constants at the micellar surface are similar to those at surfaces of trialkylammonium and sulfobetaine micelles. The reaction of OH- with MeONs is weakly inhibited by amine oxide micelles, showing that dispersive, as well as coulombic and charge-dipole, forces play a major role in the association of ions with surfaces of micellar aggregates. Copyright 1999 Academic Press.
