Optical studies on the effect of pressure IV : the effects of pressure on the keto-enol equilibria of ethyl acetoacetate and acetylacetone

Abstract

The effects of pressure on the keto-enol equilibria of ethyl acetoacetate and acetylacetone in the solvents of methanol, ethanol, iso-propanol, n-hexane and n-heptane have been studied from the measurement of the ultraviolet spectra at high pressure. Comparing the molal volume of the keto form with that of the enol form, which are conjectured from their parachors, it is expected that the enol form is favorable with increasing pressure. However, the effect of pressure on the keto-enol equilibria of ethyl acetoacetate and acetylacetone is small. The keto-enol equilibria of ethyl acetoacetate and acetylacetone shift to the keto form in the polar solvents, and to the enol form in the non-polar solvents at high pressure. From these results, it is expected that the variation of the dielectric constant of the solvent with pressure would have influence upon the keto-enol equilibria at high pressure. That is, it may be necessary to consider the following factors for the purpose of studying the effects of pressure on the keto-enol equilibria. I The volume change of tautomers. II The increment of the dielectric constant of the solvent with increasing pressure.