Ruthenium catalysts methanol homologation

Table II. Methanol homologation with ruthenium catalysts...

Besides cobalt, other catalyst metals haw also been examined for the methanol homologation reaction [26], More detailed studies have been reported for iron [85]. ruthenium [86], and rhodium [87]. whereas little is known about nickel [88]. osmium, iridium, and palladium [5]. 

Methanol homologation catalyzed by ruthenium has been studied by Braca etal. [86, 89, 90]. Catalyst systems such as Ru(acac)3/Nal and Ru(C0)4lj/NaI have been shown to be active. In contrast to cobalt catalysts, no reaction occurs in the absence of 1" and a proton supplier is needed. As can be taken from Table XI, the reaction is higidy selective to C -products and no higlter products are formed. Due to the high hydrogenation activity of ruthenium, however, methane and ethane arc formed as side products in considerable amounts as well as dimethyl ether. Thus, the overall yield of ethanol is limited. The same catalyst systems have also been shown to be active in the homologation/carbonylation of ethers and esters. 

The synergistic effect of ruthenium and rhodium in methanol homologation was observed at 100 atm synthesis gas pressure, whereas ruthenium or rhodium chloride alone is inactive for ethanol synthesis.No enhancement of ethanol production was observed with the mixed-metal compounds [HRuRh3(CO)i2], [HRuRh3(CO)io(PPh3)2], [H2Ru2Rh2(CO),2], and [PPN][RuRh5(CO),6] as catalyst precursors. This is consistent with the cluster decomposition found to occur in all the experiments. ... 

Alcohol Homologation Solvent and promoter effects on the cobalt carbonyl catalysed methanol homologation have been studied under synthesis gas pressure.The main product in a methanol/hydrocarbon two-phase system is 1,1-dimethoxyethane (ca. 70 selectivity).Using similar iodide promoted cobalt catalysts, R2C 0Me)2 and dimethylcarbonate are converted to acetaldehyde with up to 87 selectivity.Ruthenium in the presence of Co, 12 and dppe improves the ethanol selectivity in the homologation of dimethylether. Best results are achieved in inert solvents with high dielectric constants, e.g. sulfolane (e = 44), and with BF3 as activator. 

Homologation is the one-carbon extension reaction of organic compounds such as alcohols and carboxylic esters, and is very important. Cobalt, rhodium, and ruthenium complexes are known to be efficient catalysts. Methanol and methyl ester can be converted to ethanol and ethyl ester, respectively, using Ru/F [28] and Ru/Co [29] catalysts (Eq. 11.9). 

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