Positive values of the apparent dissolution enthalpy illustrated that the dissolution process of dapsone in these mixed solvents was endothermic. The obtained solubility was mathematically represented by using the Jouyban-Acree model, van't Hoff-Jouyban-Acree model and Apelblat-Jouyban-Acree model obtaining average relative deviations lower than 4.88% and root-mean-square deviation lower than 5.86 × 10⁻⁴ for correlative studies. The type and extent of solvent effect was analyzed by KAT-LSER approach. At the same temperature and mass fraction of the organic solvent, the solubility of dapsone was greater in (1,4-dioxane + water) than in the other two cosolvent mixtures. The mole fraction solubility of dapsone increased with increasing temperature and mass fraction of cosolvent in each binary system. The equilibrium solubility of 1,1′-sulfonylbis(4-aminobenzene) (dapsone) in neat solvents of n-propanol, isopropanol 1,4-dioxane and water and in cosolvent mixtures of n-propanol + water, isopropanol + water and 1,4-dioxane + water were determined experimentally by the saturation shake-flask method within the temperature range from 278.15 K to 323.15 K under atmospheric pressure of 101.0 kPa.
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