Equilibrium solubility of dinitolmide in several neat solvents and binary aqueous co-solvent mixtures: Experimental determination and thermodynamic analysis

Abstract

The dinitolmide solubility in twelve pure solvents such as methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol (EG), ethyl acetate, dimethyl sulfoxide (DMSO), acetonitrile, cyclohexane, 1,4-dioxane and water and co-solvent mixtures of ethanol (1) + water (2), isopropanol (1) + water (2) and EG (1) + water (2) was studied by using a saturation shake-flask method over the temperatures from 283.15 K to 328.15 K under local atmospheric pressure p = 101.2 kPa. It was highest in solvent DMSO and lowest in solvent water. The achieved solubility data in monosolvents was mathematically described through the modified Apelblat equation; and in the binary mixtures, the Jouyban-Acree model. For the monosolvents, the maximum values of root-mean-square deviation and relative average deviation were 2.71 × 10−4 and 1.27%, respectively; and for the binary solvent mixtures, 0.276 × 10−4 and 1.46%. The solubility was correlated to KAT parameters and cavity term based on linear solvation energy relationships concept to investigate on the solvent effect. Results showed that the solubility in monosolvents depended significantly upon the Hildebrand parameter and nonspecific dipolarity/polarizability interactions. Quantitative values for the local mole fraction of ethanol (isopropanol or EG) and water around the dinitolmide were computed by using the Inverse Kirkwood–Buff integrals method. Dinitolmide was preferentially solvated by water in water-rich compositions; while in the intermediate and co-solvent-rich compositions for the aqueous mixtures of ethanol (isopropanol or EG), dinitolmide is preferentially solvated by the co-solvent. The preferential solvation magnitude of dinitolmide was higher in isopropanol mixtures than that in the other two solvent mixtures. Furthermore, transfer Gibbs free energy (ΔtrGo), enthalpy (ΔtrHo), and entropy (ΔtrSo) were deduced, demonstrating that the solubilization capacity was more favorable in the intermediate concentration of ethanol (isopropanol or EG).