Carbonylation of Methanol Using Nickel Complex Catalyst: A Kinetic-Study

The carbonylation of alcohols to give carboxylic acids is of commercial importance, as evidenced by the Monsanto process for the manufacture of acetic acid. Several transition metal complexes consisting of Co, Rh, Ir, Ru, and Ni are known to catalyze the carbonylation of alcohols, but Rh was found to be the most active and selective catalyst. Recent reports described Ni catalyzed carbonylation of methanol at lower temperatures and pressures giving high activity and selectivity. This development is particularly important as it will provide a cheaper and alternative catalyst to rhodium. For NiI{sub 2}-PPh{sub 3} and Ni(PPh{sub 3}){sup 2}(CO){sub 2}-PPh{sub 3} catalysts with methyl iodide as a promoter, methanol conversion of 98% with a selectivity of 75 to 90% has been reported. Further, Kelkar et al. have reported that Ni(isoq){sub 4}Cl{sub 2} as a catalyst is highly active with 99% conversion and 90-98% selectivity for carbonylation of methanol as well as higher alcohols. Rizkalla has also investigated the influence of catalyst, methyl iodide, methanol, and water concentrations and partial pressure of CO and hydrogen on the rate of reaction for NiI{sub 2}-PPh{sub 3} system; however, this study was limited to only one temperature (453 K) and no rate equation has been proposed. The present work was undertaken to study the intrinsic kinetics of the reaction using the Ni-isoquinoline catalyst system to develop a rate equation. 14 refs., 8 figs., 1 tab.