Hydroformylation, catalysis

Thermodynamically, hydroformylation requires low temperature and elevated pressure. For the aldehyde formation, the iso-isomer is thermodynamically favored and in a broader sense the hydrogenation of propene to propane is the preferred reaction. 

Thus the catalyst has to favor first of all CO insertion over pure hydrogenation. This selectivity issue is mainly addressed by the choice of central transition metal for the hydroformylation catalysis. Obviously, all metals active in hydroformylation show a pronounced tendency to form metal carbonyl complexes. However, only Rh and Co complexes show sufficiently high hydroformylation activity for commercial applications, with rhodium being 1000-10000-fold more active, but also about 1000-fold more expensive, than cobalt (Moulijn, Makkee, and van Diepen, 2001). 

The hydroformylation catalyst cycle is initiated by a catalyst precursor (P) that is a ligand stabilized form of the active catalyst. In presence of syngas, the active catalyst 

The competing side reactions, olefin hydrogenation, olefin isomerization (in case of higher olefins than propylene), and aldehyde hydrogenation to the corresponding alcohol, can also be explained based on this mechanism  

In the case of dejin hydrogenation the oxidative addition of hydrogen happens directly to the Rh-alkyl complexes n-II or iso-II. Hydrogen transfer and reductive ehmination results in the same saturated alkane product from both regioisomers of the catalyst. Thus, olefin hydrogenation is a favored side reaction for all catalyst complexes that favor the kinetics of oxidative hydrogen addition over CO association and insertion. Olefin hydrogenation is, for example, much more relevant for Co hydroformylation catalysts compared to their Rh counterparts. 

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To estimate costs for the liquid-liquid biphasic hydroformylation using ionic liquids, a process was designed for the production of 100,000 tons per year of nonanal. The use of ionic liquids in hydroformylation catalysis is a fairly new technology and exact kinetic data are scarce, thus the TOFs reported for the Rh-sulfoxantphos system [80] have been used to determine catalyst inventory and reactor dimensions. In a similar way the plant design for the SILP process for a production capacity of 100,000 tons per year of butanal has been derived based on preliminary literature results [68]. The process flow sheets for both process variations are shown in Figures 7.12 and 7.13. 

These assembly ligands will be tested in suitable catalytic reactions that leave the assemblies intact. Salt-forming reactions are not attractive as the salts might interact with the assembly, nor is the use of catalytic metals that compete with the assembly metal for the salen type positions in the ditopic ligand ideally, all potential problems can be avoided if the same metal could be used. Rhodium-catalyzed hydroformylation of 1-octene is a suitable reaction, with the only disadvantage that high pressures are needed, but hydrogen or CO do not interfere with our assemblies. Metal salts do not interfere with the rhodium hydrides involved in the hydroformylation catalysis, as for instance the most effective industrial process today for propene hydroformylation... 

Thus transition metal complexes capable of effecting cyanation reactions on aromatic nuclei under mild conditions have been discovered Cassar et al. describe such a catalytic system. The past few years have also seen the discovery of asymmetric catalysis. Asymmetric catalysts contain optically active ligands and, like enzymes, can promote catalytic reactions during which substantial levels of optical activity are introduced into the products. This volume contains examples of asymmetric hydrogenation and asymmetric hydroformylation catalysis in the papers, respectively, by Knowles et al. and Pino et al. 

Applying P-31 NMR to the field of hydroformylation catalysis by triphenylphosphine rhodium complex-based systems is the subject of this chapter. These hydroformylation catalyst systems are of high academic and technological interest. They are effective for hydroformylat-ing 1-olefins at low pressure and temperature and exhibit a high selectivity to n-aldehydes ... 

The supramolecular binding motifs described here were also used to attach catalysts to solid (silica) supports (128). The active metal complex could be switched from palladium to rhodium by using a polar solvent that breaks up the binding of the supramolecular motif. Allylic alkylation and hydroformylation catalysis could be carried out by using the same support "receptor" material and different "guest" ligands for the two metals a... 

The production of carboxylic acids via carbonylation catalysis is the second most important industrial homogeneous group of processes. Reppe developed most of the basic carbonylation chemistry in the 1930s and 1940s. The first commercial carbonylation process was the stoichiometric Ni(CO)4-based hydroxycarbonylation of acetylene to give acrylic acid (see Section 3.5 for details). This discovery has since evolved into a trae Ni-catalyzed process, used mainly by BASF. The introduction of rhodium catalysts in the 1970s revolutionized carboxylic acid production, particularly for acetic acid, much in the same way that Rh/PPhs catalysts changed the importance of hydroformylation catalysis. 

Another route to carboxylic acids from aldehyde products (once again, generally produced via hydroformylation catalysis) was discovered by Wakamatsu and coworkers. They reported the carbonylation of aldehydes and primary organic amides to produce A-acylamino acids (equation 16). The reaction is efficiently catalyzed by HCo(CO)4 at 100 °C and 140 bar of 3 2 H2/CO (hydrogen is needed to help stabilize HCo(CO)4). Yields of over 90% of the appropriate... 

Figure 2.13 Examples of three concepts of catalysis in supported ionic liquids (a) hydroformylation catalysis [121] (b) methanol carbonylation [122] (c) supported ionic liquid phase catalysis combined with SCCO2 [127].

G. G. Stanley, Bimetallic Hydroformylation Catalysis The Uses of Homobimetallic Co-operativity in Organic Synthesis , in M. G. Scaros, M. L. Prunier (editors). Catalysis of Organic Reactions, Marcel Dekker, New York, 1995, p. 363. 

Figure 7 Representative ligand systems used in hydroformylation catalysis.

The comparisons just cited indicate that under conditions where reaction chemistry controls the rates (namely, at temperatures near 80 °C), supercritical CO2 does not alter the measured parameters much from those obtained for a typical hydroformylation-type medium. Thus, one can anticipate that at higher temperatures, where mass transport across the liquid-gas interface normally controls the rates, the supercritical medium would achieve higher rates than expected for any liquid solvent. Perhaps of greater importance than reaction rate in hydroformylation catalysis is the selectivity to linear versus branched aldehyde product. The ratio of n-butyraldehyde to isobutyraldehyde products in supercritical CO2 solution, obtained by integration of the aforementioned proton NMR signals, is 7.2. This value is appreciably higher than has previously been achieved with conventional solvents measured values [57,58] for these vary from 3.8 to 4.6. 

The cluster [MoCoNi( 3-CMe)Cp2(CO)s] (11) was found to isomerize 1-pentene, a competition reaction observed during hydroformylation catalysis, and hydrogenate 2-pentene and styrenesj ° ° Hydroformylation of styrene was also inves-... 

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