Cobalt-catalyzed carbonylations competing reactions

To achieve, then, high acetic acid selectivity directly from synthesis gas (eq. 1) it is necessary to balance the rates of the two consecutive steps of this preparation - ruthenium-carbonyl catalyzed methanol formation (10) (Figures 2 and 5) and cobalt-carbonyl catalyzed carbonylation to acetic acid (Figure 6) - such that the instantaneous concentration of methanol does not build to the level where competing secondary reactions, particularly methanol homologation (7, H), ester homologation (12, 13), and acid esterification (1 ), become important. 

Not only changing the ligand sphere but also the addition of a co-catalyst can dramatically increase catalyst-efficiency. In an interesting exanq>le is the cobalt-catalyzed amido-carbonylation. In a perfectly atom economic way N-acylamino acids can be produced fi om simple amides, aldehydes and carbon monoxide. Although amidocarbonylation reactions which were originally developed by Wakamatsu in the early seventies cannot compete commercially against cheap natural sources or fermentation, for non-natural amino acids this salt fi ee process must be considered as a viable alternative to the conventional Strecker reaction. 

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