Further Study of Methanol Carbonylation Catalyzed by Cobalt, Rhodium, and Iridium Catalysts

Abstract The effect of iodide ion was examined in methanol carbonylation with use of Co-, Rh-, and Ir-catalysts. Sodium iodide gives no noticeable effect on carbonylation catalyzed by Rh-catalyst to give acetic acid, and retards that catalyzed by Ir-catalyst. Methyl iodide is effective for methanol carbonylation with Co-catalyst in the presence of hydrogen to give mainly acetaldehyde, which is readily hydrogenated to ethanol during the course of carbonylation on addition of a catalytic amount of Ru3(CO)12. Sodium iodide is also effective for acetaldehyde formation, although it strongly retards the hydrogenation of acetaldehyde with Ru-catalyst. The different effect of iodide ion on methanol carbonylation catalyzed by Co-, Rh-, or Ir-catalyst is discussed in terms of neucleophilicity of the active catalyst species.