Thermodynamic Studies of Dissociation Reactions of Some Dicarboxylic Acids in 20% (w/w) Acetonitrile - Water Mixture

Abstract

pK 1 and pK 2 values at zero ionic strength of some dicarboxylic acids (succinic, tartaric, malonic, malic and maleic) in 20% (w/w) acetonitrile-water at temperatures ranging from 30°C to 60°C have been determined using a precise EMF method. The thermodynamic parameters H°, G°and S°of the first and the second dissociation reactions are calculated from well known equations and discussed in terms of solute-solvent interactions. An extrathermodynamic analysis of the obtained results has been performed and indicates that these dissociation reactions are entropycontrolled reactions where solute-solvent interaction plays an important role.

Kinetics of Ion-Pair Effect of Aquation of Bromopentaammine Cobalt(III) Complex in Different Dicarboxylate Media

“…Furthermore, the electrostatic action transmitted through solvent molecules (field effect) also governs these solute-solvent interactions and their thermodynamics results. The charged anions (HL -, L 2-) of these acids impose order on the surrounding solvent molecules, which interferes with the internal rotation of the alkyl chain of the acid [13] for the different dicarboxylates is probably related to ion solvation, where the controlled factor is the reorientation of the hydration shell for position taken by every dicarboxylate buffer in the above linear correlations depends on its reactivity toward the ion-pair formation which differs from one dicarboxylate to another primarily because of the electrostatic action on the dicarboxylate groups transmitted through (-CH 2 -) groups and the hydroxyl groups. From the above discussions, the order imposed on the solvent about mono-succinate anion should restrict internal rotation in an -CH 2 -CH 2 -COOH group more than in the -CH 2 -COOH group in the case of mono-malonate anion [14].…”