Syngas reactions *1IX. Acetic acid from synthesis gas

Acetic acid has been generated directly from synthesis gas (COH2) in up to 95 wt% selectivity and 97% carbon efficiency using a RuCoIBu4PBr “melt” catalyst combination. The critical roles of each of the ruthenium, cobalt and iodide catalyst components in achieving maximum selectivity to HOAc have been identified. C1-oxygenate formation is only observed in the presence of ruthenium carbonyls; [Ru(CO)3I3]− is here the dominant species. Controlled quantities of iodide ensure that initially formed MeOH is rapidly converted to the more reactive methyl iodide. Subsequent cobalt-catalyzed carbonylation to acetic acid may be preparatively attractive (>80% selectivity) relative to competing syntheses where the [Co(CO)4]− concentration is maximized; that is, where the Co/Ru ratio is > 1, the syngas feedstock is rich in CO and the initial iodide/cobalt ratios are close to unity. Formation of cobalt-iodide species in significant concentrations appears to be an inhibiting step in this synthesis.