Exploiting Phase Behavior for Coupling Homogeneous Reactions with Heterogeneous Separations in Sustainable Production of Pharmaceuticals

Abstract

John Prausnitz was never content to measure new data solely because the data were new. He always had an application in mind—a separation or even a process that required the data for implementation. We present here an advance in using designed changes in phase equilibria to enable the facile recovery and recycle of homogeneous catalysts. We show a new application of organic-aqueous tunable solvents (OATS) to run homogeneous reactions (fast rates and high selectivities) followed by facile and efficient heterogeneous separations and the recycle of the homogeneous catalysts. This is done by using CO2 to manipulate the phase behavior of monophasic organic−water mixtures to form heterogeneous organic-rich and aqueous-rich phases. The example shown is the hydroformylation of hydrophobic p-methylstyrene catalyzed by rhodium catalyst to which is attached a hydrophilic phosphorus ligand. The OATS method increases the conversion rate of styrene to the aldehyde products by an order of magnitude compared to heterogeneously reported reactions. Also, the selectivity toward the branched aldehyde (the desired product) increases by 30 %. The hydrophobic product partitions into the organic-rich phase with more than 99 % removal efficiency, and the hydrophilic catalyst is retained in the aqueous-rich phase with 99.9 % efficiency. In addition, we recycle the catalyst for five consecutive reactions without significant loss of catalytic activity.