Measurement and prediction of phase diagrams of the enantiomeric 3-chloromandelic acid system

The identification of racemic species of enantiomeric 3-chloromandelic acid (3-ClMA) as well as ternary solubility measurement in a mixture of water and isopropanol (IPA) was studied in this paper. Thermal analyses were carried out for mixtures of the two enantiomers with different compositions. The binary fusion diagram suggested the presence of a racemic compound for racemate 3-ClMA. It was verified with the ternary solubility phase diagram by dissolving various mixtures into the H₂O/IPA solution. Ternary phase diagram revealed a strong temperature dependency of solubility for the 3-ClMA system. In order to shorten the experimental time in the solubility measurement, a semi-empirical thermodynamic model (UNIQUAC) was used to predict the solubility of various compositions of enantiomers at different temperatures. Results indicate that UNIQUAC model can provide good predictions in the solubility of racemate, eutectic and (R)-3-ClMA in both pure water and H₂O/IPA (9/1 weight ratio) system. In addition, structures of racemate and pure (R)-3-ClMA were also studied using a powder X-ray diffractometer. Thermodynamic prediction, thermal analysis, and structural study are in excellent agreement for identifying the enantiomeric 3-ClMA system as a racemic compound forming system.