Effects of alcohol-modified micelles on deacylation and nucleophilic aromatic substitution by azide ion

Abstract

Alcohol-modified micelles and oil–water microemulsions have similar rate effects upon aromatic nucleophilic substitution by N₃^–. Relative values of k₂^m/k_w for aromatic nucleophilic substitution and deacylation show that enhancements of the rate of deacylation can be ascribed wholly to increased reactant concentrations in the micelles, but that there is an additional catalytic effect upon nucleophilic aromatic substitution.

Reactions of azide ion with 1-chloro-2,4-dinitronaphthalene and p-nitrophenyl benzoate in water containing dilute t-pentyl alcohol are accelerated by cationic micelles, but the rate enhancements are lower than in aqueous micelles. At constant [N₃^–], first-order rate constants for reaction of 1-chloro-2,4-dinitronaphthalene go through maxima with increasing concentration of cetyltrimethylammonium chloride or bromide (CTACl or CTABr). Similar behaviour was found with p-nitrophenyl benzoate in CTACl. Rate constants of reaction of the naphthalene substrate in cetyltrimethylammonium azide increase with increasing [surfactant]. Estimated rate constants of deacylation at the micellar surface are slightly lower than in the absence of surfactant, but are higher for reaction of 1-chloro-2,4-dinitronaphthalene.