Thermodynamic functions of succinic acid in acetone–water binary mixtures based on computation of KI & KII constants

Abstract

Succinic acid is commonly used in various chemical, pharmaceutical, environmental and industrial activities and its reactivity is principally determined by the pK(I & II) values. Therefore, the dissociation constants of succinic acid have been determined in this study on the basis of emf measurements in both different acetone mole fractions and temperature range. The pK(I or II) values of the studied acids in acetone aqueous media were found higher than those obtained in other organic aqueous media with the same conditions (temperature and mole fraction of solvent). Moreover, (KI/KII) in 40 wt% acetone–water mixture was identified to follow succinic acid < malic acid < malonic acid < maleic acid owing to the stabilization of intramolecular hydrogen bonding. The free energy of transfer (ΔG0I or II) for succinic acid was increased with the increasing of pKI or pKII values due to the decrease in relative permittivity (εr) via increment of the acetone fraction in the aqueous medium. The trend of ΔS°I value among the studied acids were found to follow maleic < malic < succinic < malonic. ΔS°II values were characterized lower than ΔS°I due to possible solvent interactions with the acid anion (L2-). Therefore, ΔH°II values of the second dissociation process were identified lower than ΔH°I to favor an exothermic reaction.