The Equilibrium between an Areneselenic Acid and Its Anhydride

Article abstract of DOI:10.1021/jo00216a032

The equilibrium constants (K_eq = ²/) associated with the equilibrium (eq 1) between o-nitro- and o-benzoylbenzeneselenenic anhydrides (2a and 2b) and the corresponding selenenic acids (1a and 1b) have been determined in dioxane containing 0.25-1.5percent water.For the 2b-1b equilibrium, K_eq = 0.16 (25 deg C) and ΔH⁰ = +0.6 kcal/mol.The equilibrium constant for the 2a-1a system is ca. 10 times larger.That ΔH⁰ for the hydrolysis of 2b is slightly endothermic contrasts sharply with the exothermic nature of the hydrolysis of most common acid anhydrides.The values of K_eq for both 2b and 2a are such that conditions can easily be encountered in media of low water content, where a significant fraction of the selenenic anhydride will remain unhydrolyzed at equilibrium, a situation without precedent in the chemistry of typical acid anhydrides.