Continuous flow homogeneous catalysis using ionic liquid/supercritical fluid biphasic systems

Abstract

Ionic liquid/scCO₂ biphasic systems have been studied as a possible solution to the main problems concerning homogeneous catalysis reactions such as, the product/catalyst separation, the catalyst retention in the reaction medium and the use of organic solvents. The hydroformylation of long chain alkenes (1-octene) has been carried out as a continuous flow reaction using [OctMIM]Tf₂N (OctMIM = 1-octyl-3-methylimidazolium, Tf = CF₃SO₂) as the reaction solvent and scCO₂as the mobile phase to extract the products. The performance of the rhodium complexes formed with the ionic ligands [PentMIM][TPPTS] (1-pentyl-3- methylimidazolium tri(m-sulfonyl)triphenylphosphine) and [OctMIM][TPPTS] (1-octyl-3- methylimidazolium tri(m-sulfonyl)triphenylphosphine) is described under different sets of experimental conditions. Continuous flow hydroformylation of 1-octene was also carried out using a SILP (Supported Ionic Liquid Phase) catalyst formed with the TPPTS-based ionic ligands named above. The SILP system described in this work has the peculiarity of introducing the “without gases” approach: syn gas was synthesised in situ by the decomposition of formaldehyde. The performance of both systems is compared in the end. The extension of the continuous flow ionic liquid/scCO₂ biphasic system is shown with the optimisation of the silver-catalysed heterocyclisation of furans. A comparison is carried out with a previously developed and optimised continuous flow heterogeneous system.