Correlation of Solubility and Solution Thermodynamics of DL-Malic Acid in Organic Solvents at Different Temperatures

The solubility of DL-malic acid in methanol, ethanol, propanol, butanol, ethyl acetate and acetonitrile in the temperature range 283–318 K was measured by acid–base titration method. The solubility of DL-malic acid increased with elevating temperature. The solubility data were correlated by the modified Apelblat, Buchowski–Książczak, Van’t Hoff, Wilson, and non-random two-liquid equations. The calculation results showed that these equations provide good prediction with the acceptable ARD values and RMSD values among all the satisfactory fitting results given by each equation. The mixing Gibbs energy, enthalpy and entropy of real solution were derived based on the Wilson equation and the measured solubility data.