Are solubility parameters relevant for the solubility of liquid organic solutes in room temperature ionic liquids?

A database for the solubilities of (volatile) liquid organic solutes in (non-volatile) room temperature ionic liquids at 298 K (or thereabouts) was constructed in terms of the infinite dilution activity coefficients, lnγ_i^∞, from data in the literature. In most cases the fit of these data by the Hildebrand solubility parameter expression (V_i/RT)(δ_Hi - δ_Hs)² alone is unsuccessful, and in particular this expression cannot account for negative values of lnγ_i^∞. An (negative) entropic correction term related to the relative sizes of the solute and solvent that was suggested is generally inadequate to cause a better fit. The prediction of the solubilities of organic solutes in RTILs remains a challenge.