Correlation of solubility of hexamethylene-1,6-bisthiosulphate disodium salt dihydrate versus dielectric constants of water + ethanol mixtures

The solubilities of hexamethylene-1,6-bisthiosulphate disodium salt dihydrate (HTS) in ethanol + water mixtures were obtained using the laser detection technique at temperatures from 278.45 K to 327.55 K. The solubility data were well correlated by the modified Apelblat equation and the overall root-mean-square deviation of the correlation was 2.61 × 105. Thermodynamic parameters for HTS dissolution were determined from van’t Hoff plots. The positive values of ΔHd and ΔSd indicate that the dissolving process of HTS is endothermic and the dissolution entropy is increased during the process. On the basis of experimental data, it was revealed that the solubility of HTS was a function of the dielectric constant of the binary solvent, and the model outwardly like the Arrhenius equation was employed to exhibit the relationship quantitatively, expounding the effect of solvent polarity on the solubility of HTS.