Thermodynamic studies of dissociation reactions of some dicarboxylic acids in 20% (w/w) acetonitrile – water mixture

摘要

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 ΔH°,ΔG° and ΔS° 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.