Eastman Chemical Company recently disclosed a process for the Rh catalyzed carbonylation of MeOH to AcOH in ionic liquids which operates in the absence of any added MeI co-catalyst. Kinetic measurements using Rh in methylpyridinium iodide (MePyI) as catalyst revealed the rate law followed the equation: d[acetate]/dt = kobs[Rh][MePyI]2[CO]-1 with an Eact of 21.5 kcal/mol. Based on the kinetics, we believe the key steps are dissociation of MePyI to MeI and pyridine and subsequent generation of Rh(py)(CO)I2-  from  Rh(CO)2I2-  by ligand exchange.  Since Rh(py)(CO)I2- is much more nucleophilic than Rh(CO)2I2-, the oxidative addition of MeI is much faster. The higher nucleophilicity of Rh(py)(CO)I2- likely compensates for what must be very low levels MeI, given that the dissociation of MePyI is highly disfavored. In this presentation, we will review some prior work in the carbonylation of methanol in ionic liquids and discuss our mechanistic conclusions regarding this unique process.

Carbonylation in ionic liquids: Process and mechanism for the carbonylation of methanol using methyl pyridinium iodide and rhodium in the absence of added methyl iodide

243rd National Meeting (2012)

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