Hydroformylation, cobalt catalysed

In the following sections a few typical processes will be described. An example of a cobalt catalysed hydroformylation reaction for higher alkenes is the Kuhlmann process (now Exxon process), for which the flow-scheme -a liquid/liquid separation- is shown in Figure 7.4. In this process the hydroformylation is done in one, organic phase consisting of alkene and aldehyde. The reactor is often a loop reactor or a reactor with an external loop to facilitate heat transfer. 

Thermal cracking of wax. From thermal cracking a thermodynamic mixture might have been expected, but the wax-cracker product contains a high proportion of 1-alkenes, the kinetically controlled product. Still, the mixture contains some internal alkenes as well. For several applications this mixture is not suitable. In polymerisation reactions only the 1-alkenes react and in most cases the internal alkenes are inert and remain unreacted. For the cobalt catalysed hydroformylation the nature of the alkene mixture is not relevant, but for other derivatisations the isomer composition is pivotal to the quality of the product. 

HP IR measurements have recently been reported by workers at Sasol for cobalt-catalysed 1-dodecene hydroformylation reactions using bicyclic phosphines (4) derived from (R)-(+)-limonene [68]. Using Fourier deconvolution to separate absorptions due to [HCo(CO)4] and [Co2(CO)7(phosphine)], it was possible to estimate the ratio of modified [HCo(CO)3(phosphine)] to un-modified [HCo(CO)4] in the catalytic mixture, using peak areas. Values of this ratio ranged from ca. 2-20, depend-... 

The hydroformylation of olefins is the most widely used homogeneous catalytic process using CO gas. It involves the addition of one molecule of CO and H2 to an olefin in the presence of a transition metal catalyst, most frequently based on cobalt or rhodium, resulting in the formation of an aldehyde. Generally, it is believed that the activation of H2 in cobalt-catalysed hydroformylation occurs on the unsaturated species Co2(CO)7 or Co(acylXCO)3 formed by the following reactions ... 

Unligated rhodium has the ability to hydroformylate a wide range of different olefins, both branched internal forms as well as linear. Virtually no water is used or created in the process (unlike a cobalt-catalysed system which needs water for catalyst recovery). Other key advantages of a rhodium (I) system are ... 

Any discussion of mechanisms should take into account the early work on cobalt-catalysed hydroformylation. A monometal mechanism was proposed that has become the generally accepted pathway for both cobalt and rhodium catalysts. A more speculative mechanism was also suggested involving an inter-molecular hydride transfer from [CoH(CO)4] to [Co(acyl)(CO)4.]. Elimination... 

One of the earliest indications that the heterobimetallic [iW]cBER+UNi catalytic mechanism may exist came from the work on the addition of lanthanide complexes to unmodified cobalt-catalysed alkene hydroformylation [73]. Upon addition of the lanthanide complexes, a dramatic rate increase was observed. Lanthanides are known to readily generate highly reactive hydrides, and this would support the supposition that lanthanide hydrides are attacking the acyl cobalt complex RCOCo (CO)3/RCOCo(CO)4. In situ spectroscopic analysis was not available/reported. 

A series of phosphine ligands with different electronic and steric properties has been evaluated by Bungu and Otto at fully modified conditions in cobalt-catalysed hydroformylation of 1-octene. Their electron donating ability has been evaluated on the basis of the /pse couplings determined from the corresponding phosphine selenides the range of the couplings covered 672-752 Hz. 

There are several problems with cobalt catalysed hydroformylation. The pressures required are high, leading to high capital costs. The selectivity (n iso) is rather low and there are side reactions. Catalyst losses arise through its volatility and also by decomposition to metallic cobalt. The metal has to be removed with acids from time to time, causing corrosion. Fortunately, cobalt is cheap. As better processes are now available it is unlikely that new plants of this type will be built. It is economic, however, to keep plants running which are already in operation. This is still the major industrial route to butanal. 

R 49 L. Damoense, M. Datt, M. Green and C. Steenkamp, Recent Advances in High-Pressure Infrared and NMR Techniques for the Determination of Catalytically Active Species in Rhodium- and Cobalt-Catalysed Hydroformylation Reactions , p. 2393... 

The hydroformylation of alkenes was accidentally discovered by Roelen while he was studying the Fischer-Tropsch reaction (syn-gas conversion to liquid fuels) with a heterogeneous cobalt catalyst in the late thirties. In a mechanistic experiment Roelen studied whether alkenes were intermediates in the "Aufbau" process of syn-gas (from coal, Germany 1938) to fuel. He found that alkenes were converted to aldehydes or alcohols containing one more carbon atom. It took more than a decade before the reaction was taken further, but now it was the conversion of petrochemical hydrocarbons into oxygenates that was desired. It was discovered that the reaction was not catalysed by the supported cobalt but in fact by HCo(CO)4 which was formed in the liquid state. 

Na5[Co+(CO)3(19)2]5 was used as catalyst for the hydroformylation of 1-hexene and 1-octene in a two phase system without leaching of cobalt into the organic phase.122 The products obtained were almost exclusively aldehydes (4-38%) and very little (0.4-3%) or no alcohol formation122 in contrast with cobalt/phosphine catalysed hydroformylation in organic solvents which give alcohols. The n/i ratios of the aldehydes were low (1.1-2.5),122 however, and never approached that expected for a phosphine modified cobalt catalyst in non-aqueous media324,325,393 (see Table 8). 

Use of chirally modified salicylimines is reported in early examples of cobalt complex catalysed asymmetric hydroformylation of styrene. A prominent example is (Aj-A -a-methyl-benzylsalicylaldimine [(+ )-A -SalH, 1] prepared from (5)-l-phenylethylamine and salicyl-aldehyde21-131-134. ( + )-(S)-3-5ec-Butylpyridine (2)164 is one of the few further examples of nonphosphorus-containing chiral ligands used in asymmetric hydroformylation23. 

Hydroformylation (or the Oxo-process) is the conversion of alkenes to aldehydes (reaction 26.17). It is catalysed by cobalt and rhodium carbonyl complexes and has been exploited as a manufacturing process since World War II. 

Chalk, A. J., and J. F. Harrod, Adv. Organometallic Chem., 1968, 6, 119 (catalyses by cobalt carbonyls hydrogenation, hydroformylation, carboxylation, hydrosilylation, etc.). 

Cobalt. Solvent effects on hydroformylation of propene and of pent-l-ene catalysed by CoH(CO)4 have been investigated by product distribution analysis. Effects of temperature and pressures of hydrogen and carbon monoxide on the mechanism of hydroformylation of propene in the presence of Co2(CO)8(PBu8)a have similarly been probed by product analysis. The reaction of (36) with methanol or ethanol (R OH) produces CHR(COaRi)2. ... 

---