On the mechanism of carbonylation in acetic acid and higher acid synthesis from methanol and syngas mixtures on supported rhodium catalysts.

In high pressure gas phase conditions, methanol and syngas mixtures can be converted to acetic and higher carboxylic (C-3-C-5) acids on supported rhodium catalysts in presence of methyl iodide. Chemical trapping and FTIR spectroscopic studies show that two mechanisms are involved in the carboxylic acid formation. One is the conventional carbon monoxide insertion model on the rhodium part of the catalyst. The second proceeds through the isomerization of methyl formate on the support. On the support alone the chain growth stops at the C-2-intermediate since no rhodium is present to convert acetic acid or methyl acetate to ethanol or ethoxy species.