Rhodium carbonyls syngas

Eastman-Halcon A process for making acetic anhydride from syngas. The basic process is the carbonylation of methyl acetate. Methanol is made directly from the carbon monoxide and hydrogen of syngas. Acetic acid is a byproduct of the cellulose acetate manufacture for which the acetic anhydride is needed. The carbonylation is catalyzed by rhodium chloride and chromium hexacarbonyl. 

The mechanism proposed in the original paper, [2] however, proved to be inconsistent with further mechanistic studies by Stanley et al. The original catalytic cycle was based on neutral dinuclear rhodium intermediates, the first of which, the neutral hydrido-carbonyl complex rac-[Rh2(CO)2( / 7 -L)], was believed to form from the dicationic rac-1 under syngas (CO/H2) conditions with liberation of and norbomadiene. In order to model the intermediacy of this neutral species, Stanley et al. designed the neutral allyl (C3H5) analogue rac-[Rh2(7/ -C3H5)2( / / -L)] (rac-... 

Morimoto [20] extended the scope of the formaldehyde-based hydro-formylation to alkynes as substrates, where in a double carbonylation step, a,P-butenolides were formed in up to 98% yield finally (Scheme 3.8). The reaction mediated by the water-soluble TPPTS (trisodium salt of 3,3, 3"-phosphinidynetris(benzenesulfonic acid)) rhodium catalyst was conducted in water. For increasing the solubility, a surfactant was added. Noteworthy, the use of dppp (l,3-bis(diphenylphosphino)propane) instead of TPPTS resulted in a serious decrease in the yield. Formalin gave higher yields than paraformaldehyde or syngas (CO/H2 = 1 1,1 atm). 

The methyl acetate carbonylation process was successfully started and operated in the early 1980s as part of a coal-to-syngas-to-acetic anhydride complex. This new process introduction resulted in a major improvement in acetic anhydride production economics. In this process, methyl acetate, itself the product of a one-step esterification of acetic acid and methanol, is reacted with carbon monoxide in the presence of a promoted rhodium-iodide catalyst. Figure 22.20 illustrates this process... 

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