Measurement, correlation of solubility and thermodynamic properties analysis of 2,4,6-trinitroresorcinol hydrate in pure and binary solvents

The solubility of 2,4,6-trinitroresorcinol hydrate (TNR∙2/3H2O) in the pure solvents (methanol, ethanol, isopropanol and water) and the binary mixed solvents (methanol-water, ethanol-water and isopropanol-water) was measured by the laser dynamic method from 298.15 K to 323.15 K under the atmospheric pressure. The TNR∙2/3H2O do not change before and after the solubility measurement in the selected solvents. The solubility increases with the increase of the temperature, and methanol is more suitable for the cooling crystallization of TNR∙2/3H2O. In the pure solvents, the solubility order at the same temperature is: methanol > ethanol > isopropanol > water, which may be affected by the properties (such as hydrogen bond, polarity, dielectric constant, cohesive energy density etc.) of the alcohol solvents, self-association of water molecules, the hydrophobic wing of the TNR∙2/3H2O and so on. In the mixed solvents, the solubility has different sensitivity to the content of organic components (x2) in the solvent. The possible reason is that: the interaction between solvent and solvent plays an important role (the formation of azeotropic mixtures of alcohols and water, the interaction between water and alcohol solvents, the properties of the solvents etc.). The solubility data of TNR∙2/3H2O were compared with that of 2,4,6-trinitrophenol (TNP) that have been reported. It can be found that the solubility of TNP is always greater than that of TNR∙2/3H2O with the same solvent and temperature, and x2 = 0.63–0.69 (ethanol-water) and x2 ≈ 0.73 (isopropanol-water) are more suitable as the solvents for solution crystallization to separate TNR∙2/3H2O from the mixture of TNP and TNR∙2/3H2O. The experimental mole fraction solubility data (xexp) of TNR∙2/3H2O were correlated by the modified Apelblat, Van't Hoff, CNIBS R-K, and Jouyban-Acree-modified Apelblat model. All of these models give satisfactory results, and the Van't Hoff model has better correlation and helps to expand the solubility data of TNR∙2/3H2O. The thermodynamic properties during the dissolution process were analyzed based on the Van't Hoff. And the dissolution of TNR∙2/3H2O in the solvents used is considered to be an “endothermic, non-spontaneous and entropy-driven” process and the enthalpy is the main contributor to the Gibbs free energy in the process of dissolution.