ESTIMATION OF THE MOLAR FREE-ENERGY OF MELTING OF CRYSTALS FROM SOLUBILITY DATA ACCORDING TO THE THEORY OF THE MOBILE DISORDER

The ''ideal'' solubility of a crystalline substance at a given temperature is only ruled by its molar free energy of melting DELTAG(m). In absence of H-bonds the actual solubility differs from the ideal one by two correction factors, the first of which originates from the difference in molar volume between solute and solvent and can be quantitatively calculated from the theory of the mobile disorder, and the second one takes into account the differences between solvent-solute, solvent-solvent and solute-solute interactions in the liquid phase and can be described quantitatively by means of adapted solubility parameters. A method is presented which allows to estimate DELTAG(m) and the solubility parameter of the solute delta(B)' from the experimental solubilities of the substance in a series of solvents without hydrogen bonds. The results agree within 5 % with the experimental results obtained for DELTAG(m) by differential scanning calorimetry.