Rhodium-Catalyzed Carbonylation of Methyl Acetate

In principle, the rhodium-catalyzed carbonylation of methyl acetate involves the types of transformations found in the conversion of methanol to acetic acid, namely the activation of a normally unreactive methyl group, insertion of carbon monoxide, and recombination with the initial leaving group. However, several significant differences become apparent upon switching from the well-documented aqueous methanol carbonylation to the anhydrous methyl acetate carbonylation to acetic anhydride. A mechanism based primarily upon high-pressure kinetic and infrared data is proposed. The operational and mechanistic similarities and differences involved in the carbonylation of methanol to acetic acid and the carbonylation of methyl acetate to acetic anhydride will be discussed, as well as the historical development of the process.