A fundamental investigation of the ruthenium-catalyzed homologation of methyl esters with synthesis gas

The homologation of methyl esters with synthesis gas in the presence of iodine-promoted ruthenium catalysts has been examined. This investigation, which uses a gas-purged liquid-sampling autoclave, shows that there are four major reactions occurring simultaneously. These are homologation of the methyl ester to form an ethyl ester, carbonylation of the methyl ester to generate acetic acid, reduction of the acyl moiety, and hydrogenolysis of the methyl ester to yield methane. When LiI was used as the iodine promoter at an I/Ru ratio of 15/1, the predominant pathways was homologation. When methyl iodide was used as the promoter in place of LiI, a selectivity change resulted. The predominant pathway with methyl iodide was acyl reduction. The relative contribution of each pathway was affected by the partial pressures of carbon monoxide and hydrogen, and by the level of iodine present. A deuterium-labeling experiment was also performed and established the integrity of the processes described above and excluded the hydrogenation of carbon monoxide to methanol as a potential pathway to products.