The Enol of Mandelic Acid, Detection, Acidity in Aqueous Solution, and Estimation of the Keto‐Enol Equilibrium Constant and Carbon Acidity of Mandelic Acid

Abstract

An acidity constant pK of 6.62 and a constant pKE of 15.4 were determined for the keto–enol equilibrium of 2, the enol of mandelic acid, in water. Compound 2 is accessible from 1 and 3 by photoelimination. The values confirm the assumption that simple carboxylic acids contain a much lower amount of the enol form than simple aldehydes and ketones, since their keto form is stabilized by interaction of carbonyl and hydroxyl groups