Solubility modelling and thermodynamic aspect of 2,3-dihydro-6-propyl-2-thioxo-4(1H)-pyrimidinone in binary aqueous solutions of several alcohols

Abstract

The equilibrium solubility of 2,3-dihydro-6-propyl-2-thioxo-4(1H)-pyrimidinone in four neat solvents namely methanol, ethanol, n-propanol and isopropanol and co-solvent mixtures of methanol (1) + water (2), ethanol + water (2), n-propanol (1) + water (2) and isopropanol (1) + water (2) at temperature range from (278.15 to 333.15) K was reported. The experiment was carried out by the saturation shake-flask technique under atmosphere pressure (101.1 kPa). At the same composition of methanol, ethanol, n-propanol or isopropanol and temperature, the mole fraction solubility of 2,3-dihydro-6-propyl-2-thioxo-4(1H)-pyrimidinone was highest in methanol (1) + water (2) mixtures, and lowest in isopropanol (1) + water (2) mixtures. By using the Jouyban-Acree model, van’t Hoff-Jouyban-Acree model and Apelblat-Jouyban-Acree model, 2,3-dihydro-6-propyl-2-thioxo-4(1H)-pyrimidinone solubility was well correlated obtaining RAD lower than 2.65% and RMSD lower than 1.85 × 10−4. The transfer Gibbs free energy (ΔtrG°), enthalpy (ΔtrH°), and entropy (ΔtrS°) were calculated, demonstrating that the solubilization capacity was more favorable with the increase in the alcohol concentration. Furthermore, quantitative values for the local mole fraction of methanol (ethanol, n-propanol or isopropanol) and water around the 2,3-dihydro-6-propyl-2-thioxo-4(1H)-pyrimidinone were computed by using the Inverse Kirkwood–Buff integrals method applied to the determined solubility data. 2,3-Dihydro-6-propyl-2-thioxo-4(1H)-pyrimidinone was preferentially solvated by water for the four solvent mixtures in water-rich compositions; while in intermediate and co-solvent-rich composition for alcohol (1) + water (2) mixtures, 2,3-dihydro-6-propyl-2-thioxo-4(1H)-pyrimidinone is preferentially solvated by the alcohol. The preferential solvation magnitude of 2,3-dihydro-6-propyl-2-thioxo-4(1H)-pyrimidinone was highest in isopropanol mixtures than in the other three co-solvent mixtures.