Polarity of Some [NR1R2R3R4]~+[Tf2N]~- Ionic Liquids in Ethanol: Preferential Solvation versus Solvent-Solvent Interactions

摘要

The polarity of the ionic liquids [N_(4111)][Tf2N], [N_(4441)][Tf2N], and [choline] [Tf2N], as well as their binary mixtures with ethanol has been investigated using solvatochromic dyes and expressed in terms of the Reichardt parameter, E_T~N, and the Kamlet-Taft parameters (π*, α, and β), at 298.15 K. The synergetic behavior revealed essentially by the ethanol + [N_(4441)] [Tf2N] system for the acidity of the solvent shows the potential importance of this solvent media for some chemical applications. Even though the preferential solvation model of Bosch and co-workers has been applied with some statistical success to the whole composition range of EtOH + [N_(4111)]-[Tf2N] and EtOH + [N_(4441)] [Tf2N] binary mixtures, the interpretation of the results is somehow difficult due to the competition of molecular interactions in the evaluation of transition energies for the pairs: dye-solvent (dye-cation and/or dye-anion, dye-EtOH, dye-complex entity) and cation-anion, depending on the composition range. Different patterns of solvent polarity behavior are shown along the entire ionic liquid (IL) composition.