Determination and thermodynamic modelling for 4-nitropyrazole solubility in (methanol + water), (ethanol + water) and (acetonitrile + water) binary solvent mixtures from T = (278.15 to 318.15) K

• 4-Nitropyrazole solubility in three binary mixed solvents was determined.
• The determined solubility were correlated and calculated by six co-solvent models.
• Standard dissolution enthalpy for 4-nitropyrazole in mixed solvents were calculated.

The solubility of 4-nitropyrazole in mixed solvents of (methanol + water), (ethanol + water) and (acetonitrile + water) was determined experimentally by using the isothermal dissolution equilibrium method within the temperature range from (278.15 to 318.15) K under atmosphere pressure (101.3 kPa). The solubility of 4-nitropyrazole increased with increasing temperature and mass fraction of methanol for the (methanol + water) system. For the systems of (acetonitrile + water) and (ethanol + water), at a certain composition of acetonitrile or ethanol, the solubility of 4-nitropyrazole increased with the increase in temperature; nevertheless at the same temperature, they increased at first and then decreased with the increase in the mass fraction of acetonitrile or ethanol. At the same temperature and mass fraction of methanol, ethanol or acetonitrile, the solubility of 4-nitropyrazole in (acetonitrile + water) was greater than those in the other mixed solvents. The solubility values obtained were correlated with the Jouyban–Acree model, van’t Hoff–Jouyban–Acree model, modified Apelblat–Jouyban–Acree model, Ma model, Sun model and CNIBS/R-K model. For the first five models, the maximum of the relative average deviation (RAD) and the root-mean-square deviations (RMSD) were 4.51 × 10−2 and 3.37 × 10−3, respectively. The Ma model was proven to provide good representation of the experimental solubility results. On the basis of the measured solubility, the standard dissolution enthalpy of the dissolution process was calculated. Dissolution of 4-nitropyrazole in these mixed solvents is an endothermic process. The experimental solubility and the models in this study could be helpful in purifying the crude 4-nitropyrazole.

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