Oxygenates Synthesis – Homogeneous

AbstractThe current status of direct (from CO/H2) and indirect (via methanol, formaldehyde, or methyl acetate) homogeneously catalyzed C1chemistry based routes for the selective production of the oxygenates methanol, ethanol, and ethylene glycol (including higher alcohols, diols, and acetate esters); acetic and propionic acid; ethyl and vinyl acetate; acetic anhydride; and methyl formate is described. While none of the direct synthesis gas based routes have been commercialized, largely because of low catalytic activities and extreme operating pressure requirements, indirect routes including the Co‐, Rh‐, and Ir‐catalyzed carbonylation of methanol to acetic acid and the Rh‐catalyzed carbonylation of methyl acetate to acetic anhydride, together with the coproduction of both, are well‐established commercial processes. The majority of these transformations are uniquely homogeneously catalyzed. Although mechanistic pathways associated with the carbonylation of methanol to acetic acid are well‐established, uncertainty surrounds the mechanism of the initial step in the reduction of CO, to a purported formyl intermediate, during its direct conversion to oxygenates. A characteristic mechanistic feature of the latter chemistry is the operation of kinetic reaction control that is manifest in the absence of the thermodynamically favored products, hydrocarbons (particularly methane); with the exception of catalysts for methanol manufacture, this behavior is in sharp contrast to that of typical heterogeneous catalysts for synthesis gas reactions.