Methanol homologation using

Methanol homologation using carbon dioxide catalyzed by ruthenium-cobalt bimetallic complex system... 

Hydrogenation of the acyl complex [Co(COMe)(CO)3PPh2Me] gave a product distribution very similar to that obtained when [Co(CO)3PPh2Me] was used as a catalyst for methanol homologation.402 This was regarded as further evidence for the presence of an acyl intermediate in the catalytic reaction. 

Another unsolved problem is catalyst recycling, especially when bimetallic cobalt systems are used. In summary, it must be Slated that the known processes for methanol homologation still lack sufficient conversion rates and ethanol/ acetaldehyde selectivittes. 0 far. no ethanol yields exceeding 40% have been reported under acceptable catalyst concentrations and reaction conditions. 

There are few reports on the use of rhodium for methanol homologation, although this metal is best suited for the related methanol carbonylation. The extreme selectivity of rhodium for carbonylation is noteworthy and even when a 1 1 H]/CO mixture Ls applied, selective formation of acetic acid occurs and virtually no hydrogenated by products, such as ethanol or acetaldehyde, arc detected [68],... 

In the transformation of methanol to ethanol, which is called methanol homologation, synthesis-gas (CO/H2) is usually used as the carhon source (eq. 1). 

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. 

Methanol homologation to hi er alcohols, in which the carbon being added to the alcohols comes from methanol, has been claimed in a noncatalytic reaction with metal acetylides [100]. For example, the reaction of methanol and CeC2 at 400°C and 0.1 MPa yielded alcohols up to pentanols, with a maximum selectivity for 2-methyl-1-propanol of 77%. The product distribution included a mixture of alcohols, CO, H2, and CH4. Depending on the contact time in the laboratory-scale test reactor, ethanol selectivities ran d from 1.3% (C atom) to 12.5% and 2-methyl-1-propanol selectivities ranged from 58 to 86%. Methanol conversion was <2%. Using 13C-labeled methanol. Fox et al [101] showed that methanol rather than the metal acetylide was the source of carbon in the higher alcohols. A formaldehyde condensation reaction mechanism has been invoked to e q)lain the 13C distribution in the product. 

Esters of the homologous acids are prepared by adding silver oxide in portions rather than in one lot to a hot solution or suspension of the diazo ketone in an anhydrous alcohol (methyl, ethyl or n-propyl alcohol) methanol is generally used and the silver oxide is reduced to metallic silver, which usually deposits as a mirror on the sides of the flask. The production of the ester may frequently be carried out in a homogeneous medium by treating a solution of the diazo ketone in the alcohol with a solution of silver benzoate in triethylamlne. 

Nelson and Scliut investigated the reaction of 5a-cholestanone (lb) with diazomethane in a search for a direct, one-step preparation of A-homo ketones. Using a large excess of diazomethane generated in situ from A-methyl-nitrosourea with potassium hydroxide in ether-methanol at 0°, 5a-cholestanone (lb) is converted into the 7-membered ring homolog (3b) as the predominant product. Both theoretically possible A-homo ketones can be expected with an unsymmetrically-substituted cyclohexanone such as 5a-cholestanone (lb). 

Detectability may be a significant problem with homologous series of unsaturated compounds, particularly //-alkanes. For these compounds, refractive index detection or evaporative light-scattering, both of which are described elsewhere in the book, may be of use. Indirect photometry is a useful detection scheme for compounds that do not absorb in the UV. Acetone, methylethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, and acetophenone are added to an acetonitrile/water mobile phase, generating a negative vacancy peak when the nonchro-mophoric analyte emerges and a positive peak if the ketone is adsorbed and displaced.70 Dodecyl, tetradecyl, cetyl, and stearyl alcohols also have been derivatized with 2-(4-carboxyphenyl)-5,6-dimethylbenzimidazole and the derivatives separated on Zorbax ODS in a mobile phase of methanol and 2-propanol.71... 

Fio. 26. Methylene group selectivity, ocn,i of several hydroorganic mobile phases when octadecyl silica stationary phase is used. The selectivity is the ratio of the retention factor of a member of a homologous series to that of another member which differs in having one less methylene group. The solvents shown here are (A) acetone, (B) acetonitrile, and (C) methanol. The dau were taken at ambient temperature and the selectivity values are plotted on a logarithmic scale. Reprinted with permission ftom Kaiger et al. (/4S).. ... 

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