Quantitative treatment of micellar effects upon nucleophilic substitution

Abstract

Cationic micelles of cetyltrimethylammonium surfactants [CTA(X), X = Cl, Br, OMs] increase first-order rate constants for the basic hydrolysis of tent-butyl perbenzoate and 2-naphthyl benzoate. Dealkylation of both butyl 4-nitrobenzenesulfonate and butyl 4-bromobenzenesulfonate by halide ions in micelles of CTACl, CTABr and CTAOMs, and by azide ion in micelles of cetyltrimethylammonium mesylate (CTAOMs) have been examined. The nucleophilic aromatic substitutions of 2-chloro-3,5-dinitropyridine by OH^– and N₃^– ions in the presence of CTABr, CTACl and CTAOMs micelles have also been examined. The rate enhancements have been treated in terms of concentration of both substrates and nucleophilic anions at the micellar surface. The anionic concentrations depend upon specific and non-specific coulombic interactions, which were calculated by solving the Poisson–Boltzmann equation (PBE). The same parameters were used in fitting data for reactions of N₃^–, Br^– or Cl^– as nucleophiles and for systems with Cl^–, Br^– and OMs^– as inert counter-anions in CTACl, CTABr and CTAOMs, respectively.