Rhodium-catalyzed hydrocarbonylation of acetic acid into higher acids

Abstract

The hydrocarbonylation of acetic acid into higher homologues catalyzed by rhodium/iodide systems has been investigated at 20 MPa and 220°C. In homogeneous catalysis the most convenient precursor proved to be [RhI 2(CO) 2] − prepared from [RhCl(CO) 2] 2 in the presence of LiI; mean turnover frequencies of 67 h −1 and selectivities as high as 80% in propionic acid were obtained. In addition, in heterogeneous catalysis, rhodium supported upon activated carbon was observed to be an efficient system for the conversion of acetic acid into propionic acid (80% selectivity) in a fixed bed reactor. The reaction mechanism is thought to be an iodoacetyl rather than an ethanol pathway in the homogeneous system, while the two seem likely to be in operation in the heterogeneous system.