Tautomerization of 2-acetylcyclohexanone in assemblies of cationic surfactants

Abstract

The kinetic study of the keto-enol interconversion of 2-acetylcyclohexanone (ACHE) has been performed in organic solvents such as dimethylsulfoxide, 1-propanol, 2-propanol, methanol, dioxane, tetrahydrofuran and acetonitrile, as well as in aqueous micellar solutions of the cationic surfactants tetradecyltrimethylammonium chloride and tetradecyltrimethylammonium bromide at 25 °C. Either the solvent-assisted or H⁺-catalyzed reaction rates of tautomerization are reduced in both organic solvents and in micellar medium. In 70% v/v solvent–water or at fixed concentration of any cationic surfactant, the observed rate constant moderately increases with [H⁺]. The nitrosation of the enol has also been studied in micellar solutions of both cationic and anionic surfactants. Under experimental conditions of first-order dependence on [H⁺], [nitrite], and [X⁻] (X = Cl or Br), the presence of cationic micelles reduces strongly the rate of nitrosation, whereas in the presence of anionic micelles, the first-order rate constant, k_o, goes through a maximum on increasing the surfactant concentration.