Tautomerization of 2-acetylcyclohexanone in assemblies of cationic surfactants. Nitrosation of the enol.

Abstract

The kinetic study of the keto-enol interconversion of 2-acetylcyclohexanone (ACHE) has been performed in organic solvents such as dimethylsulfoxide (DMSO), 1-propanol (1-PrOH), 2-propanol (2-PrOH), methanol (MeOH), dioxane, tetrahydrofuran (THF), and acetonitrile (MeCN) and in aqueous micellar solutions of the cationic surfactants tetradecyltrimethylammonium chloride (TTACl) and tetradecyltrimethylammonium bromide (TTABr) at 25 ºC. Either the solvent-assisted or H+-catalysed reaction rates of tautomerization are strongly 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, ko, goes through maxima on increasing the surfactant concentration.