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.