Ionic Liquids and Carbon Dioxide as Combined Solvents for Reactions and Separations: The Miscibility Switch

Ionic liquids (ILs) and carbon dioxide (CO2) are emerging as candidates to replace volatile organic solvents in synthesis and extraction processes. ILs are a relatively new class of substances composed only of ions and liquid at temperatures below 100oC. As a major attractive characteristic, they have negligible vapor pressure - reducing solvent loss by evaporation and environmental pollution. When used simultaneously with carbon dioxide for reactions and extractions, the process will be based on non-toxic, non-flammable solvents and will be applicable for a wide variety of compounds. It has been recently shown that carbon dioxide can be used to split phases in homogenous one-phase systems with ILs. This miscibility switch allows reactions to be carried out in one phase, and by simply changing CO2 pressure, extractions can be carried out more efficiently under heterogeneous conditions. This chapter presents an overview on ionic liquids and carbon dioxide, together with an explanation on the phenomenon of miscibility switch.