Hydration and ion pairing of maleinates, malonates, and substituted malonates in aqueous solution

Abstract

Association constants and enthalpies of association for salts of maleic acid, malonic acid and substituted malonic acids with alkali metals and alkaline earth metals were measured colorimetrically in aqueous solution. Agreement with previous determinations by other methods was obtained. Calorimetric and colorimetric determinations of enthalpy of association led to consistent results. Interpreted by means of Bjerrum's theory of ion association in conjuction with a simple model for hydrated ions, the experimental findings show that the extent of hydration increases with the size of the hydrocarbon residue on the anion. The observation is discussed in the light of other measurements on aqueous carboxylate solutions.