Ruthenium acetic acid homologation

The principal competing reactions to ruthenium-catalyzed acetic acid homologation appear to be water-gas shift to C02, hydrocarbon formation (primarily ethane and propane in this case) plus smaller amounts of esterification and the formation of ethyl acetate (see Experimental Section). Unreacted methyl iodide is rarely detected in these crude liquid products. The propionic acid plus higher acid product fractions may be isolated from the used ruthenium catalyst and unreacted acetic acid by distillation in vacuo. 

Effect of Operating Conditions. Yield data, summarized in Figures 1 and 2, point to acetic acid homologation activity being sensitive to at least four operating variables, viz. ruthenium and methyl iodide concentrations, syngas composition and operating pressure. 

For catalyst combinations containing initial I/Ru ratios 5, the product solutions also show strong new bands at 1999 and 2036 cm characteristic (6) of ruthenium pentacarbonyl. Where acetic acid homologation is run at [RuJ > 0.2 M, then another ruthenium iodocarbonyl, Ru(C0)3I2, may be isolated from the product mix as a yellow crystalline solid. A typical spectrum of this material is illustrated in Figure 3b. 

Deuteration studies with acetic acid-d4 (99.5% atom D) as the carboxylic acid building block, ruthenium(IV) oxide plus methyl iodide-d3 as catalyst couple and 1/1 (C0/H2) syngas, were less definitive (see Table III). Typical samples of propionic and butyric acid products, isolated by distillation in vacuo and glc trapping, and analyzed by NMR, indicated considerable scrambling had occurred within the time frame of the acid homologation reaction. 

Syngas Homologation of Acetic Acid. To a N2-flushed liquid mix of acetic acid (50.0 gm) and methyl iodide (5.67 gm, 40 mmole), set in a glass liner is added 0.763 gm of ruthenium(IV) oxide, hydrate (4.0 mmole). The mixture is stirred to partially dissolve the ruthenium and the glass liner plus contents charged to a 450 ml rocking autoclave. The reactor is sealed, flushed... 

To achieve, then, high acetic acid selectivity directly from synthesis gas (eq. 1) it is necessary to balance the rates of the two consecutive steps of this preparation - ruthenium-carbonyl catalyzed methanol formation (10) (Figures 2 and 5) and cobalt-carbonyl catalyzed carbonylation to acetic acid (Figure 6) - such that the instantaneous concentration of methanol does not build to the level where competing secondary reactions, particularly methanol homologation (7, H), ester homologation (12, 13), and acid esterification (1 ), become important. 

There are two possible pathways to homologate methanol with carbon dioxide the CO2 insertion path and CO insertion path (Scheme 2). As for the former, Fukuoka et al. reported that the cobalt-ruthenium or nickel bimetallic complex catalyzed acetic acid formation from methyl iodide, carbon dioxide and hydrogen, in which carbon dioxide inserted into the carbon-metal bond to form acetate complex [7]. However, the contribution of this path is rather small because no acetic acid or its derivatives are detected in this reaction. Besides, the time course... 

In 1981, Texaco announced the ruthenium/H2/CO-catalyzed homologation of carboxylic acids. Homologation refers to a chain-extension reaction that increases the carbon number of the carboxylic acid see Homologation Reaction. The particular reaction that was initially studied was the conversion of acetic acid to propionic acid. The proposed mechanism shown in Scheme 22 is based on a Ru VRtf cycle, similar to that suggested by Knifton and coworkers at Texaco. 

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