Asymmetric Hydroformylation of Styrene in Supercritical Carbon Dioxide

Hydroformylation reactions in supercritical carbon dioxide can provide an environmentally conscious method of producing aldehydes for fine-chemical and pharmaceutical products. Asymmetric ligands, such as (R)-BINAP, can be used to provide an enantioselective product. When these reactions are performed in environmentally benign solvents, such as supercritical carbon dioxide (scCO2), additional environmental benefits are derived, such as ease of recycling of the solvent and unconverted reactants and elimination of the need for organic solvents. Rhodium-based catalysts have been prepared through the solid-phase reaction of catalyst precursors in supercritical carbon dioxide and evaluated for the hydroformylation of styrene to produce 2-phenylpropionaldehyde. Triphenylphosphine and (R)-BINAP were tested as ligands, and their effects on the reaction were examined. The catalyst, formed in situ in supercritical carbon dioxide (scCO2), was found to promote the hydroformylation of styrene with enantiomeric selectivity when (R)-BINAP ligands were used.