Solvent strength of ionic liquid/CO2 mixtures

Abstract

Previously we have shown that organic solutes can be extracted from ionic liquids (ILs) with supercritical CO₂ and that ILs can be induced to separate from organic and aqueous mixtures by applying gaseous CO₂ pressure. Thus, we are interested in the solvent strength of IL/CO₂ mixtures. Here we use 4-nitroaniline, N,N-diethyl-4-nitroaniline and Reichardt's dye 33 to determine the Kamlet–Taft parameters for four different imidazolium based ILs and their mixtures with CO₂ at 25 and 40 °C. The effect of temperature and carbon dioxide concentration on these parameters was determined. The polarizability parameter depends weakly on the CO₂ concentration. However, the hydrogen bond donating ability and the hydrogen bond accepting ability are virtually independent of CO₂ pressure. The results indicate that the strong interactions between ILs and probe molecules are not influenced by CO₂.