SN2 reactions of a sulfonate ester in mixed cationic/phosphine oxide micelles

Abstract

Addition of the nonionic surfactant, dodecyl(dimethyl)phosphine oxide (C12PO) to aqueous cetyltrimethylammonium bromide (CTABr) inhibits the micellar-mediated reaction of Br– with fully bound methyl naphthalene-2-sulfonate (MeONs). Reaction in the micellar pseudophase depends on the concentration of Br– in the interfacial surface region, which is decreased on addition of C12PO by increases in both the fractional micellar ionization, α, and the volume of the micellar pseudophase. The inhibition of the reaction is partially offset by an increase in the second-order rate constant in the micellar pseudophase on addition of C12PO which appears to be related to a solvent-like effect at the micelle–water interface. Interactions of CTABr and C12PO in the mixed micelles were explored by using 1H and 31P NMR spectroscopy.