Rhodium supported aqueous-phase conditions

The thermal instability of rhodium-based hydroformylation catalysts has already been overcome commercially in the Ruhrchemie/Rhone-Poulenc process for propene hydroformylation in which the sodium salt of a sulfonated triphe-nylphosphine ligand (TPPTS, la) is used to solubilize the catalyst in the aqueous phase. In this process, the second phase is toluene and the reaction is carried out as a batch process with rapid stirring to intimately mix the two immiscible phases. After reaction, the system is allowed to separate and the organic phase is simply decanted from the aqueous catalyst phase. Both water-soluble polymers and PAMAM dendrimers have been reported as supports for rhodium-catalyzed hydroformylation under aqueous biphase conditions, but reactivities and regioselec-tivities were only comparable to or worse than those obtained with the reference TPPTS ligand. The aqueous biphase approach has found limited application for the hydroformylation of longer-chain alkenes, because of their very low solubility in water leading to prohibitively slow reaction rates, but there have been a variety of approaches directed at the solution of this problem. 

Hydroformylation of 1-octene under aqueous two-phase conditions was studied using an n N-heterocyclic carbene rhodium catalyst immobilized to an amphiphilic, water-soluble block copolymer support. The catalyst showed high activity up to 2360h turnover frequency at 100°C and 50bar CO H2 = 1 1 pressure in four consecutive cycles [103]. 

In classical liquid-liquid systems, the rate of hydroformylation decreases in the order l-hejKne > 1-octene > 1-decene however, these olefins can react at virtually the same reaction rate with SAPC, because the solubility of the olefin in the aqueous phase is no longer the rate-determining factor [12]. SAPC highly depends on the intrinsic properties of the support such as particle size and surface area. Hanson has reported the preparation of SAPCs [38, 43]. Kalck et al. demonstrated that the hydration of the support is important for the hydroformylation of long-chain l-aUcenes [44]. Horvath found that the SAPC did not leach active rhodium species under hydroformylation conditions. 

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