Dielectric Constant Correlations with Solubility and Solubility Parameters

Correlations and lack of correlations of dielectric constants (DEC's) with solubility and solubility parameters are discussed. By restricting various solvent systems to solvents exhibiting similar bonding characteristics, such as by using members of homologous chemical series or by using solvent blends, essentially linear relationships were obtained for plots of log mole fraction of solute versus the DEC of the solvent or solvent system. Relationships of this type were demonstrated for (a) a nonpolar liquid in a series of polar polyethylene glycols, (b) a nonpolar liquid in a series of semipolar polypropylene glycols, (c) nonpolar liquids in blends of polar and semipolar solvents, (d) polar liquids in blends of nonpolar and semipolar solvents, and (e) a solid organic solute in blends of polar solvents. A ternary phase diagram for the system methyl salicylate/isopropanol/water is presented and resolved into a straight line by this procedure. This approach is presented as a means for the quantitative evaluation of solubility in homologous solvent series and solvent blends.