Role of Keto-Enol Tautomerism in the Polarographical Reduction of Some Carbonyl Compounds

Abstract

DURING some polarographical investigations of certain α-aminoketones¹ and on the elimination of Mannich bases² experimental data were gathered, which can be explained by the occurrence of keto-enol transformation. Though considerable attention has been paid to the mechanism of polarographical reduction of carbonyl compounds³, no experimental evidence has been adduced for the participation of the keto-enol tautomerism in the reduction of the carbon–oxygen bond. This follows from the fact that, in most cases examined, the keto form is the predominating form, and in buffered solutions used, establishment of keto-enol tautomeric equilibrium is fast. However, the decrease of the limiting current of some keto acids has recently been interpreted⁴ as being influenced by the keto-enol equilibrium in addition to hydration. Experimental evidence for the role of enolization in the behaviour of substances like acetyl and acetonyl acetone⁵ is unconvincing. On the other hand, it has been discovered that the enolate form participates when anodic waves occur, corresponding to the formation of mercury salts, in alkaline solutions of enolizable ketones (Heyrovský, M., private communication). Keto-enol equilibria were involved also in the complicated and, in some ways, questionable scheme derived⁶ for the reduction of thenoyl trifluoroacetone.