Hydrogenation and hydroformylation reactions

Hydroformylation of alkenes (Fig. 5.8) is an important commercial process for the production of aldehydes and alcohols from alkenes and is one of the most important examples of homogeneous catalysis in industry with a production capacity of more than 8 million tons/year [38]. Initial work by Manassen on aqueous biphasic catalysis [39] 

In a series of studies performed by different groups hydroformylation of higher alkenes in microemulsions resulted in high turn-over frequencies (TOFs) of up to 5000 per hour for 1 -octene [46] and 1000 per hour for 1-decene [44]. Cationic surfactants such as cetyltrimethyl ammoniumbromide (CTAB) were used in the first studies of hydroformylation of various alkenes with the Rh-TPPTS catalyst. Both high activity and selectivity were observed in the hydroformylation of 1-octene and 1-decene using a sulphonated bisphosphine modified rhodium complex in the presence of ionic surfactants or methanol. 

Homogeneous asymmetric hydrogenation reactions have been studied intensively with amino acid precursors in aqueous micellar solutions. In early work only stabilising effects of added amphiphiles were observed [53, 54]. However, for the hydrogenation of Z-a-acetamidocinnamic acid methyl ester (Fig. 5.10) with an optically active rhodium-phosphane complex (Fig. 5.11) in the presence of micelles a significant increase in activity and enantioselectivity was found in comparison to reaction in pure water [55]. 

This effect was observed by Oehme and co-workers for a variety of ionic and non-ionic surfactants. The surfactants were always added at a concentration of about twice the cmc but in substoichiometric ratio to the substrate. This significant effect of the amphiphiles above the cmc manifests the simultaneous solubilising effect of the micelles for the catalyst and the substrate. In kinetic studies of hydrogenation of MAC in micellar solutions of the anionic surfactant SDS and the non-ionic surfactant octa(ethylene glycol)monotridecyl ether (Ci3E8) micellar solutions the dissociation constant of the catalyst substrate complex was found to be considerably smaller than in methanol as solvent [56]. This indicates 

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In 1996, consumption in the western world was 14.2 tonnes of rhodium and 3.8 tonnes of iridium. Unquestionably the main uses of rhodium (over 90%) are now catalytic, e.g. for the control of exhaust emissions in the car (automobile) industry and, in the form of phosphine complexes, in hydrogenation and hydroformylation reactions where it is frequently more efficient than the more commonly used cobalt catalysts. Iridium is used in the coating of anodes in chloralkali plant and as a catalyst in the production of acetic acid. It also finds small-scale applications in specialist hard alloys. 

When irradiated in the presence of norbornadiene and high-pressure synthesis gas, rhodium chloride is converted to a catalyst which is active for a variety of reactions. /2A/. The salt is probably converted photochemically to the rhodium norbornadiene complex 9. This dimer may undergo a consecutive photoreaction to give the monomeric hydrido complex 10, which is the actual catalyst for polymerisation, hydrogenation, and hydroformylation reactions. 

There are many different homogeneous catalysts available that can be used for hydrogenation and hydroformylation reactions. The most widely used metals that are present in these catalysts are the transition metals, especially Co, Ni, Ru, Rh and Ir [1],... 

The use of alternative solvents in hydrogenation and hydroformylation reactions has developed at an incredible rate over the last few years. Many elegant systems have been designed which offer cleaner alternatives to those carried out in conventional organic solvents. Apart from the attractiveness of the separation process, catalyst lifetimes can be extended which represents another major advantage. In some cases, conventional organic solvents are completely removed from the system. 

Scheme 2.15 Supported metal catalysts for hydrogenation and hydroformylation reactions.

The use of ionic liquids with SCCO2 has recently been reviewed.More information on ionic liquids can be found in Chapter 6. However, their use in biphasic catalysis with SCCO2 is discussed here. They have been used most extensively for hydrogenation and hydroformylation reactions. 

Dimethylamino-l,3-diphenyl-l,3,2-diazaphospholane (102) reacts with primary and secondary alcohols to give crystalline derivatives (103) useful for characterization purposes more interesting is their use to convert alcohols to alkyl halides. Several new ligands for catalysts in asymmetric redox reactions have been prepared. These include (104) and (105), the Rh complexes of which have been used successfully in asymmetric hydrogenations, and (106), which however was inferior to diop in hydrogenation and hydroformylation reactions. ... 

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