Combining Homogeneous Reactions with Heterogeneous Separations for the Hydroformylation of Styrene Using Tunable Solvents

Organic Aqueous Tunable Solvents combine the benefits of homogeneous and heterogeneous catalysis while overcoming the limitations of both. We are using the hydroformylation of hydrophobic p-methylstyrene as a model chiral reaction, which mimics the active pharmaceutical ingredient in ibuprofen production. The homogeneous hydroformylation reaction is carried out in organic-water mixtures using Rh/TPPMS catalytic complex under 3 MPa of syngas. Reaction rates are improved by an order of magnitude and the yield is increased by 20% when compared to reported heterogeneously catalyzed reactions. After the reaction, moderate pressures of carbon dioxide (around 3 MPa) are used to induce a phase split, as the gas is almost insoluble in water but completely miscible with most organic solvents. The hydrophobic product partitions into the organic-rich phase, which is decanted and then depressurized to yield a facile separation of >99% recovery. The aqueous-rich phase, which contains 99.9% of the hydrophilic catalyst, is recycled for the next reaction cycle. We show five recycles of the catalyst without significant loss of activity.