Hydroformylation with cobalt

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. 

Another route to the diol monomer is provided by hydroformylation of allyl alcohol or allyl acetate. Allyl acetate can be produced easily by the palladium-catalyzed oxidation of propylene in the presence of acetic acid in a process similar to commercial vinyl acetate production. Both cobalt-and rhodium-catalyzed hydroformylations have received much attention in recent patent literature (83-86). Hydroformylation with cobalt carbonyl at 140°C and 180-200 atm H2/CO (83) gave a mixture of three aldehydes in 85-99% total yield. 

The alternative processes include cobalt-catalyzed hydroformylation and similar rhodium-based processes. Hydroformylation with cobalt requires much higher temperatures (140-170°C) and pressures (70-200 bar). The activity ratio of rhodium and cobalt may be of the order of 1000 but the costs of the metals... 

Practical examples include nitration of aromatics, olefin hydroformylation with cobalt hydrocarbonyls and phosphine-substituted hydrocarbonyls as catalysts, and ethyne dimerization. 

Example 12.2. Potential mass transfer-induced instability in olefin hydroformylation [14]. The rate of olefin hydroformylation with cobalt hydrocarbonyl catalysts in a liquid phase obeys in good approximation the Martin equation... 

One might say, a mass-transfer limitation under normal conditions acts as a gentle brake on the reaction, slowing it down at worst to the rate that mass transfer to the reacting phase can sustain, whereas in hydroformylation with cobalt hydrocarbonyl catalysts, mass transfer imposes an upper limit on the amount of catalyst the system will tolerate. Assume a small amount of catalyst is used mass transfer then has no trouble supplying as much CO as the reaction consumes (note conversion is first order in catalyst). However, if now the amount of catalyst and thereby the conversion rate are increased, the point may be reached where mass transfer can no longer keep up with CO consumption. The self-accelerating conversion then depletes the liquid of CO to the extent that the catalyst added beyond the limit of mass-transfer stability decomposes. 

The anomalous heat- and mass-transfer problems are illustrated with examples from olefin hydroformylation with cobalt hydrocarbonyl catalysts. 

The regioselectivities and rates of hydroformylation with cobalt catalysts were improved significantly by the addition of phosphines to HCo(CO) (Equation 17.6). This hydroformylation catalyzed by HCo(CO)3(PRj) complexes was developed by Slaugh and Mullineaux at... 

Noteworthy, the hydroformylation with cobalt catalysts can draw benefit from the addition of ruthenium [9]. For example, the initial rate of the reaction with cyclohexene was 19 times faster with Co2(CO)g/Ru3(CO)j2 in comparison to the monometallic Co system [10]. By combining the superior hydroformylation properties of a rhodium catalyst with the excellent hydrogenation activity of... 

Hydroformylation, also known as the oxoprocess, was first discovered in 1938 when it was found that in the presence of a cobalt catalyst, ethylene could be converted into propanal when treated under high pressures of CO and H2. Since then, many transition metal complexes have been found to catalyze hydroformylation, with cobalt, platinum, and rhodium catalysts being the most commonly used. However, cobalt catalysts have not featured prominently in asymmetric syntheses and are not discussed here, whereas platinum catalysts have been superseded in recent years. 

Often the aldehyde is hydrogenated to the corresponding alcohol. In general, addition of carbon monoxide to a substrate is referred to as carbonylation, but when the substrate is an olefin it is also known as hydroformylation. The eady work on the 0x0 synthesis was done with cobalt hydrocarbonyl complexes, but in 1976 a low pressure rhodium-cataly2ed process was commerciali2ed that gave greater selectivity to linear aldehydes and fewer coproducts. 

The switch from the conventional cobalt complex catalyst to a new rhodium-based catalyst represents a technical advance for producing aldehydes by olefin hydroformylation with CO, ie, by the oxo process (qv) (82). A 200 t/yr CSTR pilot plant provided scale-up data for the first industrial,... 

One of the most selective hydroformylation catalysts was obtained when cobalt acetate was irradiated in the presence of an excess of a phosphine, with synthesis gas at 80 atm, in methanol as the solvent. Propylene was hydroformylated with this catalyst to give butyraldehyde with an n/i ratio of more than 99/1 /10/. In the absence of phosphine, the cobalt acetate forms a more active catalyst which is, however, less selective for straight chain products /23/. 

With cobalt catalysts, hydroformylation of ethyl cinnamate gave 91% of the hydrogenation product ethyl hydrocinnamate (15) and only 8% of the expected lactone, 16 (72). However, rhodium catalysis was effective in directing the reaction in favor of hydroformylation (70). The comparative results obtained with cobalt and rhodium are outlined in Table XXV. 

Allen (106) also studied cobalt hydroformylation with a polymer-bound catalyst. The polymer was formed from diphenyl-p-styrylphosphine cross-linked with divinylbenzene. 2-Hexene was the substrate, and reaction conditions were 175°C and 1500-3000 psi of 1/1 H2/CO. The product aldehyde was 55% linear, and the effluent product solution contained 20-50 ppm cobalt. 

In 1975 Kuntz has described that the complexes formed from various rhodium-containing precursors and the sulfonated phosphines, TPPDS (2) or TPPTS (3) were active catalysts of hydroformylafion of propene and 1-hexene [15,33] in aqueous/organic biphasic systems with virtually complete retention of rhodium in the aqueous phase. The development of this fundamental discovery into a large scale industrial operation, known these days as the Ruhrchemie-Rhone Poulenc (RCH-RP) process for hydroformylation of propene, demanded intensive research efforts [21,28]. Tire final result of these is characterized by the data in Table 4.2 in comparison with cobalt- or rhodium-catalyzed processes taking place in homogeneous organic phases. 

Investigations of cobalt stability as a function of catalyst concentration, temperature, and CO partial pressure have been carried out in connection with cobalt-catalyzed hydroformylation (5658). The stability of Co2(CO)g in heptane is shown by Fig. 4, which relates to the equilibrium... 

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). 

The overall stereochemistry of the hydroformylation reaction exhibits syn addition of the hydride and the formyl groups, both with cobalt and rhodium catalysts. Thus in the hydroformylation of 1-methylcy-clohexene, where ( )/(Z)-isomerization cannot occur, the predominate product is franj-2-methylcyclo-hexanecarbaldehyde (equation 7) resulting from the delivery of the aldehyde and the formyl groups from the same face of the alkene.18 Similarly the hydroformylation of (Z)-3-methyl-2-pentene gives mainly the erythro-aldehyde (equation 8).19... 

The hydroformylation of ally and vinyl acetals yields some useful intermediates. Allyl acetate undergoes partial double bond migration prior to hydroformylation with a cobalt catalyst in the absence of phosphine (equation 20).2-5 Rhodium catalysts containing chelating phosphines are more selective to the linear aldehyde.31... 

The above results were reviewed in 1974 (5). Since then the main advances in the field have been the achievement of asymmetric hydro-carbalkoxylation (see Scheme I, X = -OR) using palladium catalysts in the presence of (-)DIOP (6), the use of other diphosphines as asymmetric ligands in hydroformylation by rhodium (7), and the achievement of the platinum-catalyzed asymmetric hydroformylation (8, 9). Further work in the field of asymmetric hydroformylation with rhodium catalysts has been directed mainly towards improving optical yields using different asymmetric ligands (10), while only very few efforts were devoted to asymmetric hydroformylation catalyzed by cobalt or other metals (11, 12) and it will be discussed in a modified form in this chapter. 

Asymmetric hydroformylations of all the above types have been achieved with rhodium catalysts enantioface- and enantiomer-discriminating hydroformylations also occur with cobalt and platinum catalysts whereas with ruthenium or iridium complexes only enantioface-discriminating synthesis has been reported up to now (see Sect. 2.1.4.). 

The stoichiometric hydroformylation of olefins with cobalt hydrocarbonyl is also inhibited by an atmosphere of carbon monoxide (62, 73) (Section II, A) and this has been shown to involve a CO inhibition of alkylcobalt carbonyl formation (Eq. (18)). 

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