Characterization of the indan-1-one keto–enol system

Abstract

3-Hydroxyindene was generated by Norrish type II photoelimination of 2-Methoxyindan-1-one, and its subsequent rate of ketonization was measured in dilute aqueous perhloric acid, sodium hydroxide, acetic acid buffer and ammonia beffer solutions. These data, when combined with acid-catalysed rates of enolization of indan-1-one determined by both bromine and iodine scavenging, give pK_E= 7.48 for the keto–enol equilibrium constant, pK_a^E= 9.48 for the acidity constant of the enol ionizing as an oxygen acid, and pK_a^K= 16.96 for the acidity constant of the ketone ionzing as a carbon acid. These results are compared with corresponding values for the acetophenone keto–enol system, using the redetermined acetophenone enol acidity constant, pK_a^E= 10.40, obtained here from rates of ketonization of the enol in sodium hydroxide and ammonia buffer solutions. All present equilibrium constantss refer to wholly aqueous solution at 25 °C and ionic strength = 0.10 mol dm^–3.