Cativa acetic acid syntheses

The conversion of MeOH to MeCOjH (eq. 25.15) is carried out on a huge industrial scale, and 60% of the world s acetyls are manufactured using the Monsanto and Cativa processes. Currently, 7 Mt per year of acetic acid are consumed worldwide, with the formation of vinyl acetate (25.15) being the most important commercial end use. Vinyl acetate is the precursor to polyvinylacetate (PVA, 25.16). 

Before 1970, acetic acid was manufactured by the BASF process utilizing cobalt-based catalysts, and high temperatures and pressures. Replacement of this procedure by the Monsanto process brought advantages of milder conditions and greater selectivity (Table 25.3). The Monsanto process uses a rhodium-based catalyst, and involves two interrelated 

The yields of products in any industrial manufacturing process must be optimized. One difficulty in the Monsanto process is the oxidation of cis-[Rh(CO)2l2] by HI (eq. 25.16). The product easily loses CO, precipitating Rhl3 thereby removing the catalyst from the system (eq. 25.17). Operating under a pressure of CO prevents this last detrimental step and, as eq. 25.18 shows, reverses the effects of reaction 25.16. Adding small amounts of H2 prevents oxidation of Rh(I) to Rh(III). 

Between 1995 and 2000, BP Chemicals commercialized and began to operate the Cativa process for the production of acetic acid. The catalyst is cz5-[Ir(CO)2l2] in the presence of a ruthenium-based promoter (e.g. Ru(CO)4l2) or an iodide promoter (a molecular iodide, e.g. Inl3). Catalyst 

On going from Rh to Ir, metal-ligand bonding becomes stronger. Explain how the following data provide evidence for this. 

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Detailed mechanistic and theoretical analysis of the key mechanistic steps of the Cativa process, for the Cativa process See Ref 257,257a that is, the iridium-based catalytic carbonylation of methanol to acetic acid, have allowed several groups, " particularly Haynes and co-workers, to unravel the mechanism of the catalytic process. Ir(l) complexes [Ir(CO)(L-L)I] (LL = dppms, dppe, dppmo) provided important mechanistic information about the influence of stereoelectronic ligand effects on the organometallic reactivity of modified metal centers with Mel. The carbonylation of methanol promoted by iridium and rhodium complexes which is at the basis of both Cativa and Monsanto processes for the synthesis of acetic acid will be described in detail in a different chapter of this volume. 

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