Cobalt hydrocarbonyl catalyst

Table 5.2. Hydroformylation of propene in 2-ethylhexanol with phosphine-substituted cobalt hydrocarbonyl catalyst, HCo(CO)3Ph (Ph = organic phosphine) and synthesis gas of 2 1 H2-to-CO ratio at 50 atm and 130° C in semi-batch reactor.

Example 5.3. Hydroformylation of 1-pentene with phosphine-substituted cobalt hydrocarbonyl catalyst [2], Results of hydroformylation of 1-pentene in a semi-batch reactor are shown in Table 5.5. 

An application to a considerably more complex reaction is shown in the next example, that of hydroformylation of olefins with a cobalt hydrocarbonyl catalyst. 

Example 6.5. Olefin hydroformylation with phosphine-substituted cobalt hydrocarbonyl catalyst [30], The pathway 6.9 of olefin hydroformylation with the "oxo" catalyst, HCo(CO)4, has been shown in Example 6.2 in Section 6.3. For phosphine-substituted catalysts, HCo(CO)3Ph (Ph = organic phosphine), the pathway olefin — aldehyde is essentially the same. However, these catalysts also promote hydrogenation of aldehyde to alcohol (Examples 7.3 and 7.4) and of olefin to paraffin (Example 7.5). Moreover, straight-chain primary aldehydes under the conditions of the reaction undergo to some extent condensation to aldol, which is subsequently dehydrated and hydrogenated to yield an alcohol of twice the carbon number (e.g., 2-ethyl hexanol from n-butanal see Section 11.2). The entire reaction system is... 

Example 7.6. Olefin hydroformylation with phosphine-substituted cobalt hydrocarbonyl catalyst [7], The overall reaction system of olefin hydroformylation with a phosphine-substituted cobalt hydrocarbonyl catalyst to produce alcohol, paraffin, and a heavy alcohol has been shown in Example 6.5 (Section 6.5) ... 

Synthesis of intermediates. An excellent technique for confirming or refuting a postulated pathway is to synthesize intermediates and use them as starting materials. Often, a key intermediate that is reactive enough to remain at trace level under reaction conditions is stable at very low temperatures (e.g., that of liquid nitrogen) and can be synthesized. If the reaction starting with the postulated intermediate yields the same products in the same ratios, this can be taken as evidence in favor of the presumed pathway. For example, the essential features of the Heck-Breslow mechanism of hydroformylation (see Example 6.2 in Section 6.3) with cobalt hydrocarbonyl catalysts have been verified in this way by synthesis and use of the alkyl-and acyl-cobalt species [42]. 

Example 8.11. Hydrcformylation with phosphine-substituted cobalt hydrocarbonyl catalyst. The phosphine-substituted cobalt hydrocarbonyl catalyst used for hydro-formylation of olefins has been described in Section 8.2 (see network 8.13). The principal reaction... 

Example 11.1. Hydroformylation of cyclohexene with phosphine-substituted cobalt hydrocarbonyl catalyst. The most probable network of cyclohexene hydroformylation catalyzed by a phosphine-substituted cobalt hydrocarbonyl is shown on the facing page. HCo(CO)3Ph (cat) is in equilibrium with the CO-deficient HCo(CO)2Ph (cat ) and CO. For greater generality, quasi-equilibrium of these species with the 7r-complex, X, is not assumed. Actual hydroformylation olefin — aldehyde proceeds via a Heck-Breslow pathway (cycle 6.9 that includes the trihydride, X2) but without... 

Example 11.2. Streamlined network for hydroformylation of n-heptene catalyzed by phosphine-substituted cobalt hydrocarbonyl. In hydroformylation of straight-chain olefins with a phosphine-substituted cobalt hydrocarbonyl catalyst, the model must account for three complications that are absent with cyclohexene isomerization by migration of the double bond along the hydrocarbon chain, formation of isomeric aldehydes and alcohols, and condensation of the straight-chain aldehyde to "heavy ends (chiefly an alcohol of twice the carbon number, such as 2-ethylhexanol from propene via n-butanal and a C8 aldol). A streamlined network for n-heptene is ... 

Example 12.1. Hydroformylation of long-chain 1-olefins with phosphine-substituted cobalt hydrocarbonyl catalysts. Hydroformylation of long-chain 1-olefins with phosphine-substituted cobalt hydrocarbonyl catalysts provides a striking example of coupled parallel steps and the potential of an uncommon heat-transfer problem. The network is of the type 12.5 below, with the A, as the olefin isomers and the P, as the isomeric alcohol products (arrows represent multistep pathways see also Example 5.3, Figure 5.9, and network 5.43 in Section 5.3 and network 7.40 in Section 7.4). 

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. 

Mass transfer can also affect the selectivity of a single, multistep reaction by altering the reactant ratios. An example is homogeneous liquid-phase hydro-formylation with phosphine-substituted cobalt hydrocarbonyl catalysts. Alcohol and paraffin byproduct are formed from olefin, H2, and CO. Mass transfer of CO is slower than that of H2, so that the H2 CO ratio in the liquid phase shifts in favor of H2. This causes more paraffin to be formed (see Example 7.5 in Section 7.3.2). 

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