Acidic dissociation constants of malonic acid in 50 mass percent ethylene carbonate + water from 20 to 55°C

Abstract

The first and second acidic dissociation constants of malonic acid in 50 mass % ethylene carbonate + water solvent have been determined at eight temperatures from 20 to 55°C by e.m.f. measurements of cells without transference. The results have been used to derive the standard changes of enthalpy, entropy and heat capacity for the two dissociation processes in the mixed solvent. It was found that K₁/K₂ is ∼2700 in the mixed solvent, compared with ∼700 in water. There is evidence that the addition of the aprotic component to the solvent stabilizes the internal hydrogen bond in the primary anion.