Monsanto process

The Monsanto process is an industrial method for the manufacture of acetic acid by catalytic carbonylation of methanol.

This process operates at a pressure of 30–60 atm and a temperature of 150–200 °C and gives a selectivity greater than 99%.

[2] The catalytically active species is the anion cis-[Rh(CO)2I2]− (top of scheme).

This anion rapidly transforms, via the migration of a methyl group to an adjacent carbonyl ligand, affording the pentacoordinate acetyl complex [(CH3CO)Rh(CO)I3]−.

Hence the oxidative addition of methyl iodide is proposed as the rate-determining step.

The catalytic cycle of the Monsanto process
The catalytic cycle of the Monsanto process