Rhodium catalyst for hydroformylation

Anchoring the catalyst to polymeric materials has some advantages in easy product separation and catalyst recovery for recycling. The first example of a polymer-supported rhodium catalyst for hydroformylation was reported in 1975. Since then, many reports have been published on polymer-supported catalysts here, we focus on examples of normal-sc QcxiY or enantioselective hydroformylation. 

Rhodium Catalysts for Hydroformylation Containing Triarylphosphine Uganda... 

Some rhodium catalysts for hydroformylation of epoxides have been claimed by Union Carbide and Shell (Scheme 6.106) [17]. By the use of phosphites (e.g., Alkanox 240, BIPHEPHOS) or phosphine-modified rhodium catalysts, the selectivity was enhanced and the reaction temperature could be lowered. Noteworthy, occasionally a higher partial pressure of Hg in the syngas mixture with a total pressure of 90 bar was employed. 

Scheme 6.14.7 Rhodium catalyst for hydroformylation linked to a silica surface via an alkyl-triethoxylsilane modified diphenylphosphine ligand. Adapted from Bryant (2006).

Conventional triorganophosphite ligands, such as triphenylphosphite, form highly active hydroformylation catalysts (95—99) however, they suffer from poor durabiUty because of decomposition. Diorganophosphite-modified rhodium catalysts (94,100,101), have overcome this stabiUty deficiency and provide a low pressure, rhodium catalyzed process for the hydroformylation of low reactivity olefins, thus making lower cost amyl alcohols from butenes readily accessible. The new diorganophosphite-modified rhodium catalysts increase hydroformylation rates by more than 100 times and provide selectivities not available with standard phosphine catalysts. For example, hydroformylation of 2-butene with l,l -biphenyl-2,2 -diyl... 

Hydroformylation is an important industrial process carried out using rhodium phosphine or cobalt carbonyl catalysts. The major industrial process using the rhodium catalyst is hydroformylation of propene with synthesis gas (potentially obtainable from a renewable resource, see Chapter 6). The product, butyraldehyde, is formed as a mixture of n- and iso- isomers the n-isomer is the most desired product, being used for conversion to butanol via hydrogenation) and 2-ethylhexanol via aldol condensation and hydrogenation). Butanol is a valuable solvent in many surface coating formulations whilst 2-ethylhexanol is widely used in the production of phthalate plasticizers. 

Cobalt carbonyls are the oldest catalysts for hydroformylation and they have been used in industry for many years. They are used either as unmodified carbonyls, or modified with alkylphosphines (Shell process). For propene hydroformylation, they have been replaced by rhodium (Union Carbide, Mitsubishi, Ruhrchemie-Rhone Poulenc). For higher alkenes, cobalt is still the catalyst of choice. Internal alkenes can be used as the substrate as cobalt has a propensity for causing isomerization under a pressure of CO and high preference for the formation of linear aldehydes. Recently a new process was introduced for the hydroformylation of ethene oxide using a cobalt catalyst modified with a diphosphine. In the following we will focus on relevant complexes that have been identified and recently reported reactions of interest. 

Mitsubishi has patented a triphenylphosphine oxide-modified rhodium catalyst for the hydroformylation of higher alkenes with both alkyl branches and internal bonds. [19] Reaction conditions are 50-300 kg/cm2 of CO/H2 and 100-150 degrees C. The high CO/H2 partial pressures provide stabilization for rhodium in the reactor, but rhodium stability in the vaporizer separation system is a different matter. Mitsubishi adds triphenylphosphine to stabilize rhodium in the vaporizer. After separation, triphenylphosphine is converted to its oxide before the catalyst is returned to the reactor. 

The first report of rhodium catalysts for aldehyde reduction came from Marko who reported the use of RhCl3 3H20 under hydroformylation conditions [9]. It was suggested that the active species were rhodium carbonyls, and the catalyst system was successfully utilized in the hydrogenation of ethanal, propanal, and benzalde-... 

In Chapter 8 we will discuss the hydroformylation of propene using rhodium catalysts. Rhodium is most suited for the hydroformylation of terminal alkenes, as we shall discuss later. In older plants cobalt is still used for the hydroformylation of propene, but the most economic route for propene hydroformylation is the Ruhrchemie/Rhone-Poulenc process using two-phase catalysis with rhodium catalysts. For higher alkenes, cobalt is still the preferred catalyst, although recently major improvements on rhodium (see Chapter 8) and palladium catalysts have been reported [3],... 

Slaugh and Mullineaux (1) disclosed a low pressure hydroformylation process using trialkylphosphines in combination with rhodium catalysts for the preparation of aldehydes as early as 1966. Trialkylphosphines have seen much use in industrial hydroformylation processes but they typically produce a limited range of products and frequently are very oxygen sensitive. 

Rhodium catalysts for the hydroformylation of n-tetradecene-1 were synthesized that are soluble in methanol as well as in water. After reaction took place in methanol solution, the product mixture was separated by the addition of water the aqueous phase contained the catalyst (71). Several runs with the same catalyst showed that the conversion decreased, indicating losses of rhodium. 

Mercier, C. and Chabardes, P. (1995) Organometallic chemistry in industrial vitamin A and vitamin E synthesis. Chem. Ind. (Dekker) Catal. Org. React., 62, 213. Fremy, G., Castanet, Y., Grzybek, R., Monflier, E., Mortreux, A., Trzedak, A.M. and Ziolkowski, J.J. (1995) A new, highly selective, water-soluble rhodium catalyst for methyl acrylate hydroformylation. /. Organomet. Chem., 505, 11. 

Muilwijk KF, Kamer PCJ, van Leeuwen PWNM (1997) A bulky phosphite-modified rhodium catalyst for the hydroformylation of unsaturated fatty acid esters. J Am Oil Chem Soc 74 223-228... 

The catalyst for hydroformylation is a rhodium(I) hydride species, which is clearly distinct from the species that are active for hydrogenation. The hydrogenation catalysts are cationic Rh(I)+ or neutral Rh(I)Cl species. Carbonylation of alcohols also requires an ionic Rh(I) species, e.g. [Rl CO y-- Often rhodium(I) salts are used as the precursor for hydroformylation catalysts. Under the reaction conditions (H2, CO, ligands, temperature >50°C) these salts are converted to a rhodium hydride complex, although there are several papers that seem to invoke cationic rhodium species as the catalysts. Chlorides have a particularly deleterious effect on the activity (i.e. they are not converted into hydrides under mild conditions) and it has been reported that the addition of bases such as amines has a strong promoting effect on such systems ... 

An interesting variation of hydroformylation with a great potential for the industrial preparation of primary amines is hydroaminomethylation. In this process two catalytic reactions are combined, a hydroformylation and a reductive amination of the resulting aldehyde. Although first described more than 60 years ago a really successful procedure was only published recently [78]. To ensure the success of this sequence a rhodium catalyst for the hydroformylation was combined with an iridium catalyst for the imine reduction in a two-phase system, similar to the Ruhrchemie/Rhone-Poulenc process for the hydroformylation. It was demonstrated that less polar solvents such as toluene in combina-... 

Hydr/formyUttion. Swiss chemists recommend rhodium(lII) oxide as catalyst for hydroformylation of olefins. Thus they have prepared cyclohexanecarboxaldchyde (2) in 95% yield from cyclohexene (1). Lower yields were obtained using cobalt catalysts. 

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