Solubility, Correlation, Dissolution Properties, and Molecular Simulations of an Explosive Intermediate in Twelve Pure Solvents

The solubility and thermodynamic properties of N-nitropyrazole (N-NP) in different pure solvents are crucial for crystallization, purification, and further theoretical research. The solid-liquid equilibrium solubility of N-NP in the range of 293.15- 323.15 K was determined in 12 pure solvents of water, mesitylene, n-hexane, cyclohexane, ethanol, chlorobenzene, benzonitrile, propylene glycol, anisole, dimethyl sulfoxide, N,N-dimethylformamide, and o-dichlorobenzene by the laser dynamic method at an atmospheric pressure of 0.1 MPa. In the temperature range of 293.15-323.15 K, the solubility of N-NP in water, mesitylene, n-hexane, cyclohexane, ethanol, chlorobenzene, benzonitrile, propylene glycol, anisole, dimethyl sulfoxide, N,N-dimethylformamide, and o-dichlorobenzene displayed the mole fraction solubility of 0.001271-0.003540, 0.033858-0.139782, 0.001966-0.009268, 0.002621-0.013898, 0.013601-0.058669, 0.097849-0.310726, 0.170722-0.387823, 0.017647-0.065427, 0.069507-0.379656, 0.225911-0.457260, 0.210072-0.415353, and 0.017651-0.172345, respectively. The measured solubility data of N-NP had a good correlation with the modified Apelblat equation, the NRTL equation, the Wilson equation, as well as the lambda h equation. Through the comparison of the minor average of the root-mean-square deviation (103RMSD) and the coefficient of determination (R2), the Wilson equation yielded a more satisfactory correlation result. Thermodynamic parameters of mixing enthalpy (Delta mixH), mixing entropy (Delta mixS), and mixing Gibbs energy (Delta mixG) were calculated and analyzed based on the experimental data. The positive Delta mixH and Delta mixS implied that the dissolution process of N-NP in the selected solvents was endothermic and entropy-driven. The relative contributions of enthalpy and entropy demonstrated that enthalpy was the main contributor to the Gibbs free energy in the dissolution process. In addition, the solute-solvent interaction was calculated to elaborate the solubility of N-NP in selected solvents deeply. In addition, the solid-liquid surface tension and the surface entropy factor of N-NP were discussed on the basis of the experimental solubility data.