Hydroformylation in Room Temperature Ionic Liquids (RTILs): Catalyst and Process Developments

摘要

Over the last few years, ionic liquids have successfully been applied as alternative solvents for homogeneous biphasic catalysis.1-5 Many transition metal complexes dissolve readily in ionic liquids, which enables their use as solvents for transition metal catalysis. Sufficient solubility for a wide range of catalyst complexes is an obvious, but not trivial, prerequisite for a versatile solvent for homogeneous catalysis. Obviously, there are many other good reasons to apply ionic liquids as alternative solvents in transition metal-catalyzed reactions. Besides their very low vapor pressure and their good thermal stability, an important advantage is the possibility to tune their solubility and acidity/coordination properties by varying the nature of the anions and cations systematically.6 The possibility of adjusting solubility properties is of particular importance for liquid-liquid biphasic catalysis. Liquid-liquid catalysis can be realized when one liquid is able to dissolve the catalyst and displays a partial solubility with the substrates and a poor solubility with the reaction products. Under these conditions, the product phase, containing also the unconverted reactants, is removed by simple phase decantation and the liquid con-taining the catalyst can be recycled. In hydroformylation, this concept has been successfully applied for reactions of short alkenes in the Ruhrchemie/Rh?ne-Poulenc Process (RCH/RP).7-9