Cobalt carbonyl catalyst

The partial pressures of hydrogen and carbon monoxide are critical in maintaining the concentration of the active species, cobalt hydridotetracarbonyl and 

The usually accepted reaction mechanism with cobalt octacaibonyl can be simplified as follows  

The reaction steps are reversible and isomerization of the olefin, alkyl, or acyl species can take place to allow the formation of isoaldehydes. The typical 4 1 prodnct distribntion of normal and isoaldehydes mnst be separated if the mixture cannot be nsed commercially. Efforts were therefore made to increase the proportion of nseful normal aldehydes during operation. Partial success was achieved by operating at lower temperatures with higher carbon monoxide partial presstrres, althongh this decreased conversion to aldehydes. A major problem with the cobalt catalyst was the tendency to decompose at high temperatrrre and to deposit metal onto the reactor walls. This led to loss of activity and low catalyst recovery. 

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An early attempt to hydroformylate butenediol using a cobalt carbonyl catalyst gave tetrahydro-2-furanmethanol (95), presumably by aHybc rearrangement to 3-butene-l,2-diol before hydroformylation. Later, hydroformylation of butenediol diacetate with a rhodium complex as catalyst gave the acetate of 3-formyl-3-buten-l-ol (96). Hydrogenation in such a system gave 2-methyl-1,4-butanediol (97). 

CO, and methanol react in the first step in the presence of cobalt carbonyl catalyst and pyridine [110-86-1] to produce methyl pentenoates. A similar second step, but at lower pressure and higher temperature with rhodium catalyst, produces dimethyl adipate [627-93-0]. This is then hydrolyzed to give adipic acid and methanol (135), which is recovered for recycle. Many variations to this basic process exist. Examples are ARCO s palladium/copper-catalyzed oxycarbonylation process (136—138), and Monsanto s palladium and quinone [106-51-4] process, which uses oxygen to reoxidize the by-product... 

Ligand-Modified Cobalt Process. The ligand-modified cobalt process, commercialized in the early 1960s by Shell, may employ a trialkylphosphine-substituted cobalt carbonyl catalyst, HCo(CO)2P( -C4H2)3 [20161 -43-7] to give a significantly improved selectivity to straight-chain... 

The first CO route to make adipic acid is a BASF process employing CO and methanol in a two-step process producing dimethyl adipate [627-93-0] which is then hydroly2ed to the acid (43—46). Cobalt carbonyl catalysts such as Co2(CO)g are used. Palladium catalysts can be used to effect the same reactions at lower pressures (47—49). 

A simplified reaction scheme is shown in Fig. 26.5 Again, the ability of rhodium to change its coordination number and oxidation state is crucial, and this catalyst has the great advantage over the conventional cobalt carbonyl catalyst that it operates efficiently at much lower temperatures and pressures and produces straight-chain as opposed to branched-chain products. 

The formation of isomeric aldehydes is caused by cobalt organic intermediates, which are formed by the reaction of the olefin with the cobalt carbonyl catalyst. These cobalt organic compounds isomerize rapidly into a mixture of isomer position cobalt organic compounds. The primary cobalt organic compound, carrying a terminal fixed metal atom, is thermodynamically more stable than the isomeric internal secondary cobalt organic compounds. Due to the less steric hindrance of the terminal isomers their further reaction in the catalytic cycle is favored. Therefore in the hydroformylation of an olefin the unbranched aldehyde is the main reaction product, independent of the position of the double bond in the olefinic educt ( contrathermodynamic olefin isomerization) [49]. 

A particularly useful phosphine ligand for the cobalt carbonyl catalyst is a bicyclic tertiary phosphine available from 1,5-cyclooctadiene, phosphine, and an a-olefin ... 

FIG. 4 Hydroformylation of higher molecular weight olefins with a cobalt carbonyl catalyst (Kuhlmann process). 

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. 

Maeda and Yoshida (74) found that acrolein cyclic acetals (17-19) could be hydroformylated with cobalt carbonyl catalyst in benzene at 110°C and 200 atm of hydrogen and carbon monoxide. 

The behaviour of the ruthenium catalysts is quite different from that previously reported for cobalt carbonyl catalysts, which give a mixture of aldehydes and their acetals by formylation of the alkyl group of the orthoformate (19). The activity of rhodium catalysts, with and without iodide promoters,is limited to the first step of the hydrogenation to diethoxymethane and to a simple carbonylation or formylation of the ethyl groups to propionates and propionaldehyde derivatives (20). 

Fig. 4. Stability of cobalt carbonyl catalyst [Co2(CO)8 and HCo(CO)4] as a function of CO partial pressure and reaction temperature (57, 58). (Reproduced with permission of Ernest Benn Ltd. and Springer-Verlag.)...

T,he hydroformylation reaction or oxo synthesis has been used on an industrial scale for 30 years, and during this time it has developed into one of the most important homogeneously-catalyzed technical processes (I). A variety of technical processes have been developed to prepare the real catalyst cobalt tetracarbonyl hydride from its inactive precursors, e.g., a cobalt salt or metallic cobalt, to separate the dissolved cobalt carbonyl catalyst from the reaction products (decobaltation) and to recycle it to the oxo reactor. The efficiency of each step is of great economical importance to the total process. Therefore many patents and papers have been published concerning the problem of making the catalyst cycle as simple as possible. Another important problem in the oxo synthesis is the formation of undesired branched isomers. Many efforts have been made to keep the yield of these by-products at a minimum. 

Step 1 Formation of the Active Cobalt Carbonyl Catalyst. Many efforts have been made (2, 3, 4) to prepare carbonyl catalyst by treating metallic cobalt or cobalt compounds at high temperatures (150°-200°C) and pressures with carbon monoxide and hydrogen (Reactions 1 and 2). 

The catalyst is always fed as the true active cobalt carbonyl catalyst to the reactor, and its concentration in the reactor may be varied within a wide range. 

T T ydroformylation of olefins to aldehydes over cobalt carbonyl catalysts is the first step in the industrial synthesis of oxo alcohols (1, 2). Reaction conditions require temperatures above 150 °C and pressures up to 3000 psig. Subsequent aldehyde hydrogenation occurs over supported cobalt or molybdenum disulfide catalysts. 

The base (B) used was dicyclohexylethylamine. At the higher temperatures the isomeric products that one would expect from an isomerization of the acylcobalt carbonyls were formed (see Section II, A). Amines were also used in place of alcohols to give amides. Thus benzyl chloride reacted with carbon monoxide and aniline in tetrahydrofuran solution at 35° C in the presence of sodium cobalt carbonylate catalyst to give a 47% yield of phenylacetanilide. 

With the conventional cobalt carbonyl catalyst, the ratio of n- to isobutyraldehyde produced is between 3 and 4 1. This low ratio represents a significant loss of propylene and synthesis gas (20-25%) to the lower valued or unwanted isobutyraldehyde. In lieu of having large and expensive storage facilities, isobutyraldehyde or isobutanol is frequently burned for fuel value. An alternative to burning is the expensive catalytic cracking of isobutyraldehyde to form synthesis gas and propylene for recycle and consumption in the hydroformylation step (2). 

In the case of the unpromoted cobalt carbonylation catalyst, a relatively clear picture as to the nature of the transformations is available. The original proposal of Wender et al. that the first step in the mechanism is the protonation of methanol by the strongly acidic HCo(CO)4 (48) has stood the test of time and is now generally accepted for this mechanism (Scheme 5). Subsequent migratory insertion yields the corresponding acyl derivative, which, when followed by hydrolysis by solvent water or alcohol, leads to the... 

Oxo process The commercial hydroformylation of an alkene by treatment with CO and H2 over, usually, a cobalt carbonyl catalyst. 

Note that tetracobalt dodecacarbonyl is a catalyst precursor for reaction at 150 and 10 atm CO. Only 0.01 equiv of the cobalt cluster is required. Actually catalytic amount of Co2(CO)g of high purity is sufficient to complete the intramolecular P-K reaction, also the hexacarbonyldicobalt complex of 2-methyl-3-butyn-2-ol can be decomposed with triethylsilane to generate an active cobalt carbonyl catalyst. ... 

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