Thermodynamics of dissociation of DL-malic, maleic and fumaric acids in water and water + dioxan mixtures

Abstract

Electromotive force measurements on cells without a liquid junction have been used to determine the pK₁ and pK₂ values, at different temperatures, of DL-malic, maleic and fumaric acids in water and water + 10, + 20, + 30 and + 40 mass percent dioxan. From the temperature coefficients, the thermodynamic quantities ΔG°, ΔH°, ΔS° and ΔC°_p of the dissociation processes have been calculated. The results have been discussed with respect to preferential solvation. The distances between the carboxylic groups have been calculated from the ratio of the successive dissociation constants in these media.