Tautomerization of 2-acetylcyclohexanone. 1. Characterization of keto-enol/enolate equilibria and reaction rates in water.

The keto-enol tautomerism of 2-acetylcyclohexanone (ACHE) was studied in water under different experimental conditions. By contrast with other previously studied beta-diketones, the keto-enol interconversion in the ACHE system is a slow process. Under equilibrium conditions, the analysis of the absorbance readings of ACHE aqueous solutions yielded more than 40% of enol content at 25 degrees C; nevertheless, in aprotic solvents such as dioxane, ACHE is almost completely enolized. In alkaline medium, the enolate ion is the only existing species; the study of the effect of pH on the UV-absorption spectrum of ACHE yielded a value of 9.85 for the overall pK(a) of ACHE. Under nonequilibrium conditions, the keto-enol tautomerization was studied in water. Several factors affecting the reaction have been investigated, which include H(+)-catalysis, ionic strength effect, buffer catalysis, deuterium isotope effects, temperature effect, or solvent effects.