Solubility and Thermodynamic Stability of the Enantiotropic Polymorphs of 2,3,5-Trimethyl-1,4-diacetoxybenzene

The solubility data of two polymorphs of 2,3,5-trimethyl-1,4-diacetoxybenzene (TMHQ-DA) in ethanol, 1-propanol, 2-propanol, and 1-butanol at various temperatures were experimentally measured using gravimetrical method and correlated by the modified Apelblat model and the van't Hoff equation, respectively. Differential scanning calorimetry (DSC) and thermogravimetry (TG) analyses were performed to investigate the thermodynamic stability and the transition of the two forms of TMHQ-DA. An enantiotropic relationship was found between TMHQ-DA Form A and TMHQ-DA Form B, and the transition point between them was experimentally determined to be 314.50 +/- 1 K. A thermodynamic model for estimation of the transition point was also derived, and the estimated results are satisfactorily consistent with the experimental values. Finally, the accuracy of the transition point obtained in this research was validated by the polymorphic transformation experiments monitored using Raman spectroscopy.