Iodide catalyst methanol homologation

AJthaugh various propiisals for the ni chani m of methanol homologation exist, the course of the reaction is still not fully understood. This is especially true for the activation of methanol with a concomitant C-0 bond scission. Also, the folc of the iodine promoter and of ligands remains unclear. This situation is controversial to the closely-related carbonylation of methanol to acetic acid with rhodium catalysts, where the oxidative addition of the intermediate methyl iodide to a rhodium (1) is a generally-accepted reaction path [SR]. 

Salts of [FeCo3(CO)i2]- - or [Et4N][Fe3Co(CO)i3] " promoted with methyl iodide have proven to be catalysts for methanol homologation when the reaction was performed at relatively high pressures and moderate temperatures. It was possible to obtain acetaldehyde in 80% selectivity with methanol conversions... 

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 of methanol catalysed by 1 and 2 in presence of iodide promoter hydroiodic acid (entry Nos. 1 and 3), gave dimethyl ether selectively and while in the presence of water along with hydroiodic acid ( entry Nos. 2 and 4), both catalyst systems favoured the formation of acetic acid and dimethyl ether as the products. Catalyst 2 also gave methyl acetate a product of esterfication of acetic acid by methanol. Homogeneous catalyst 1 is at least two times more reactive than 2 in presence of water, however, catalyst 2 is more selective towards the formation of acetic acid (80%). 

Carbonylation and decarbonylation reactions of alkyl complexes in catalytic cycles have been reviewed . A full account of the carbonylation and homologation of formic and other carboxylic acid esters catalysed by Ru/CO/I systems at 200 C and 150-200 atm CO/H2 has appeared. In a novel reaction, cyclobutanones are converted to disiloxycyclopentenes with hydrosilane and CO in the presence of cobalt carbonyl (reaction 4) . The oxidative addition of Mel to [Rh(CO)2l2] in aprotic solvents (MeOH, CHCI3, THF, MeOAc), the rate determining step in carbonylation of methyl acetate and methyl halides, is promoted by iodides, such as Bu jN+I", and bases (eg 1-methylimidazole) . A further kinetic study of rhodium catalysed methanol carbonylation has appeared . The carbonylation of methanol by catalysts prepared by deposition of Rh complexes on silica alumina or zeolites is comparable with the homogeneous analogue . 

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