Hydroformylation of 1-hexene using polymer-supported rhodium catalysts in supercritical carbon dioxide

Hydroformylation of 1-hexene was carried out in supercritical CO2 (scCO(2)) and in organic solvents (toluene and ethyl acetate) using polymer-supported rhodium catalysts, which were prepared from polystyrene bound triphenylphosphine (TPP) and dicarbonylacetylecetonato rhodium. Preparation variables such as TPP/Rh ratio, time of rhodium precursor fixation on the support and time of syngas pretreatment do not produce significant effects on the reaction. The product distribution slightly changes with CO2 pressure. The conversion increases appreciably as H-2 pressure is raised in scCO(2) but CO retards the reaction. The influence of H-2 pressure in scCO(2) is slightly different from that in toluene. Changes of the structure of rhodium complexes on the polymer during the catalyst preparation and the reaction were investigated by diffuse reflectance FT-IR. It should be noted that the catalyst is recyclable for the reaction in scCO(2) and that the reaction rate and selectivity of the hydroformylation are much higher than those in the organic solvents. (c) 2006 Elsevier B.V. All rights reserved.