Hydroformylation, rhodium

All metals in the neighborhood of rhodium on the periodic table are known to be active in hydroformylation. Rhodium is by far the most active metal being used in concentrations of 10-100 mg/kg, usually at temperatures below 140 °C. Typical concentrations of cobalt-based catalysts are in the range of 1 -10 g/kg at temperatures up to 190 °C to get sufficient space-time yield. Apart from some specialized applications, other metals are only of scientific interest because of their low activity. A proper comparison of metal activity is difficult because of the different requirements on the reaction conditions. A generally accepted rough order of activity is given in Table 1. 

Hydroformylation. Rhodium catalysts are generally preferred to cobalt catalysts by industry for hydroformylation of alkenes to give the homologous aldehydes because of the former s greater activity and higher regioselectivity. ... 

Hydroformylation Rhodium complexes Insight II DIs- Extended containing BINAPHOS cover cff91... 

As in the case of hydroformylation, rhodium catalysts allow the process to be carried out at low temperatures and pressures (ca. 180 °C, 35 bar, Monsanto process). At the beginning of the reaction, iodide promoters convert the hard substrate methanol to the soft methyl iodide (Eq. 2-91). 

There have been relatively few studies of conventional hydroformylation. Rhodium complexes of some of the chiral phosphines hitherto used in hydrogenation give asymmetric hydroformylation. " A comparison of cobalt and rhodium from the point of view of concurrent isomerization has been made/ " ... 

To improve the productivity, several basic approaches are utilized. The most straightforward solution is to add a cosolvent like lower alcohols (MeOH, EtOH) miscible with water, thus improving the solubility of olefins in the aqueous phase. A certain additional effect may be obtained by varying the nature of the catalyst precursors, though, under the conditions used for hydroformylation, rhodium complexes are rapidly transformed into [HRh(CO)L3] thus masking the differences [128,129]. 

Hydroformylation Rhodium complex/ High activity for homoge- 70 of long chain al- homogeneous and neous catalyst kenes immobilized... 

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