Expanded Scope of Supported Aqueous Phase Catalysis: Efficient Rhodium-Catalyzed Hydroformylation of α,β-Unsaturated Esters

Abstract

The use of supported aqueous-phase (SAP) catalysts for the rhodium-based hydroformylation of methyl acrylate leads under optimal conditions to much higher activities than those observed under comparable homogeneous and biphasic conditions. The results obtained with a series of acrylic esters are found to be dependent on the water content of the solid support and on the solubility of the functionalized olefin in water. For soluble organic reactants, like methyl acrylate, optimal activities are obtained for fully filled pore volume materials. For less soluble organic reactants, like butyl acrylate, hydroformylations are best achieved with a lower degree of pore filling, strictly dependent on the nature of the functionalized olefin. It is assumed that the reaction of hydrophilic olefins occurs mainly in the homogeneous water film dispersed over the solid support, whilst that of lipophilic olefins takes place at the interface between the organic phase and the aqueous film. The effects of temperature and the nature of the solid support are reported. Experiments are described that indicate that the surface area and the chemical nature of the solid play a major role on the activity of the SAP catalyst, whilst the pore diameter has almost no influence. However, a decrease in the activity of methyl acrylate hydroformylation was observed upon recycling of the SAPC materials, which was attributed to the leaching of rhodium into the organic phase and the gradual dehydration of silica.