A Novel and Environmentally Benign Approach to Combine Reactions and Separations Using Ionic Liquids and Supercritical Carbon Dioxide

A novel and environmentally benign approach is described to combine reactions and separations, using simultaneously ionic liquids (ILs) and supercritical carbon dioxide (SCCO2). The novel approach is based on the phenomenon that two (partially) immiscible liquid phases upon pressurization with CO2 is able to force to form one homogeneous fluid phase. The homogeneous phase allows reactions to be carried out at high rates without the need for an additional co-solvent to enhance solubility. However, pressure reduction will restore the presence of two liquid phases. This behavior is called “miscibility switch”. Since the light liquid phase is free of IL, SC-CO2 is used to extract the product from the reaction mixture, i.e., contamination of the product by the IL is not possible. To investigate the applicability of the miscibility switch, the asymmetric hydrogenation of methyl-(Z)-α-acetamido cinnamate (MAC), yielding methyl-(Z)-α-acetamido hydrocinnamate (MAHC), catalysed by a Rhcatalyst, is chosen as a model reaction. It is possible to bring the IL, the reactant and the product into a homogeneous phase by applying CO2 pressure.