Measurement, Solvent Effect, and Thermodynamic Modeling of the Solubility of Benzohydrazide and 2-Hydroxybenzohydrazide in Six Pure Solvents

Benzohydrazide (BH) and 2-hydroxybenzohydrazide (HBH) have gained attention due to their diverse characteristics and wide applications in pharmacy and organic synthesis. In this study, a gravimetric technique was used to measure the ability of BH and HBH to dissolve in six monosolvents [water, methanol (MeOH), ethanol (EtOH), propan-1-ol (1-PrOH), propan-2-ol (2-PrOH), and butan-1-ol (1-BuOH)] at an atmospheric pressure of 0.1 MPa. The solubility of BH and HBH was measured in the temperature range of 288.15–328.15 at 5 K intervals. It is revealed that the ability of BH and HBH to dissolve in the monosolvents is based on temperature, and the solubility rises with an increase in temperature. BH dissolves from high to low in the monosolvents in the following order: water < 1-BuOH < 2-PrOH < 1-PrOH < EtOH < MeOH, while for HBH, it is in the following order: water > MeOH > EtOH > 1-PrOH > 2-PrOH > 1-BuOH. The solvent effects, which account for the connections between solvent and solvent and solvent and solute, were studied using the linear solvation energy relationship. The solubilities were successfully correlated using the modified Apelblat equation, van’t Hoff equation, NRTL, Wilson models, and λh equation. The values calculated from these models aligned with the experimental solubility. The highest values of relative average deviation and root-mean-square deviation were 21.30 × 10–4 and 4.04% for BH (λh equation) and 11.62 × 10–4 and 6.09% for HBH (NRTL model), respectively. Also, the Wilson model and experimental solubility data were utilized to evaluate the mixing thermodynamic properties of HBH and BH, including excess Gibbs free energy and excess enthalpy.