Solubility correlation and thermodynamic analysis of two forms of Metaxalone in different pure solvents

The solubility data of two forms of MTX in ethanol, isopropanol, ethyl acetate and toluene was measured over the temperature range from 283.15 K to 323.15 K using shake flask method under atmospheric pressure. The experimental results indicated that the solubility of both forms of MTX increased as the temperature increased. And it was clear that the solubility of form B was lower than the solubility of form A at the same state. The experimental data was correlated by the modified Apelblat equation, the polynomial equation and the Buchowski–Ksiazczak λh equation. All these thermodynamic models gave satisfactory correlation results, with the polynomial equation showing better fitting degree than the other two equations. The results of thermodynamic parameters (△Hd > 0, △Sd > 0, △Gd > 0) indicated an endothermic, entropy driven and nonspontaneous dissolution process of MTX in selected pure solvents.