Ruthenium catalysts acid production

Catalytic Isomerisation of Linoleic Acid over Supported Ruthenium Catalysts for Production of Anticarcinogenic Food Constituents, Ind Eng. Chem. Res. 42 718-727... 

Treatment of tetrahydroberberine (26) with sodium benzenethiolate (48) or -selenolate (49) in the presence of ruthenium catalyst afforded the C-14—N bond cleavage products 51 or 52 with a phenylthio or phenylseleno group at C-14 (Scheme 12). The latter was converted to the 10-membered amino olefin 53 on treatment with m-chloroperbenzoic acid. 

When we first contemplated thermochemical products available from Glu, a search of the literature revealed no studies expressly directed at hydrogenation to a specific product. Indeed, the major role that Glu plays in hydrogenation reactions is to act as an enantioselectivity enhancer (17,18). Glu (or a number of other optically active amino acids) is added to solutions containing Raney nickel, supported nickel, palladium, or ruthenium catalysts and forms stereoselective complexes on the catalyst surface, leading to enantioselective hydrogenation of keto-groups to optically active alcohols. Under the reaction conditions used, no hydrogenation of Glu takes place. 

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. 

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. 

About the same time, we published our own results on the cross-metathesis of the amino acid homoallylglycine using the Grubbs ruthenium catalyst 17 [42]. Both styrene and oct-l-ene were successfully cross-metathesised with protected homoallylglycine to give the desired products in moderate to good yields (Eq. 24). 

Mitsubishi have reported several processes based on Ru-catalyzed hydrogenation of anhydrides and acids. Succinic anhydride can be converted into mixtures of 1,4-butane-diol and y-butyrolactone using [Ru(acac)3]/trioctylphosphine and an activator (often a phosphonic acid) [97]. Relatively high temperatures are required ( 200°C) for this reaction. The lactone can be prepared selectively under the appropriate reaction conditions, and a process has been developed for isolating the products and recycling the ruthenium catalyst [98-100]. 

Extensive investigations in our laboratories on the deactivation of rhodium and iridium catalysts has shown there to be a number of different mechanisms involved. Both, rhodium and iridium catalysts are generally less stable at higher temperatures, and have more labile ligands than their ruthenium counterparts. All of the catalysts are affected by pH, but the ruthenium catalysts seem to be more readily deactivated by acid. Indeed, these reactions are often quenched with acetic acid, whilst stronger acids are used to quench the rhodium reactions. Each of the catalysts can be deactivated by product inhibition, the ruthenium catalyst with aromatic substrates such as phenylethanol, and the rhodium and iridium ones by bidentate chelating products. 

Figure 2 illustrates the effect of incremental changes in ruthenium catalyst content upon the production of acetic acid and its C1--C2 alkyl acetate esters. Acetic acid production is maximized at Ru/Co ratios of ca. 1.0 1.5 however, the data in Figure 2 do show an approximate first order dependence of lOAc (acetic acid plus acetate esters) upon initial ruthenium content—at least up to the 2/1, Ru/Co stoichiometry under the chosen conditions. Selectivity to acetic acid in the liquid product peaks at 92 wt % (carbon efficiency 95 mol %) for a catalyst combination with initially low Ru/Co ratios (e.g. 1 4). The formation of C1-C2 alkanols and their acetate esters rapidly exceeds acetic acid productivity when the Ru/Co atomic ratio is raised above 1.5, although two-carbon oxygenates continue to be the predominant fraction. Smaller quantities of glycol may also be in evidence. 

Reactions of ruthenium catalyst precursors in carboxylic acid solvents with various salt promoters have also been described (170-172, 197) (Table XV, Expt. 7). For example, in acetic acid solvent containing acetate salts of quaternary phosphonium or cesium cations, ruthenium catalysts are reported to produce methyl acetate and smaller quantities of ethyl acetate and glycol acetates (170-172). Most of these reactions also include halide ions the ruthenium catalyst precursor is almost invariably RuC13 H20. The carboxylic acid is not a necessary component in these salt-promoted reactions as shown above, nonreactive solvents containing salt promoters also allow production of ethylene glycol with similar or better rates and selectivities. The addition of a rhodium cocatalyst to salt-promoted ruthenium catalyst solutions in carboxylic acid solvents has been reported to increase the selectivity to the ethylene glycol product (198). 

Very similar reactions using a ruthenium catalyst, carboxylic acid solvent, and a slightly different promoter system have been reported (197) to give increased amounts of ethyl ester product (Table XVI, Expts. 4 and 5). Most examples show the use of Ru02 H20 as the catalyst precursor in a carboxylic... 

The homogeneous catalytic asymmetric hydrogenations of 2-arylacrylic acids have been studied. Both rhodium and ruthenium catalysts have been examined. The reaction temperatures and hydrogen pressures have profound effects on the optical yields of the the products. The presence of a tertiary amine such as triethylamine also significantly increases the product enantiomer excess. Commercially feasible processes for the production of naproxen and S-ibuprofen have been developed based on these reactions. 

The usefulness of rhodium catalysts is also seen in the hydrogenation of pyrogallol (eq. 11.19)101 and gallic acid (eq. 11.20)102 over 5% Rh-Al203 in ethanol. The all-m products were also obtained in higher yields than with supported palladium, platinum, or ruthenium catalysts. 

An efficient synthesis of the fungal germination inhibitor Aitemaric Acid required an ester which survived the ruthenium catalyst used in the formation of 103.1 [Scheme 6.103. 232 Since the product 103w2 was also acid-sensitive, an ester... 

Simple a-substituted styrenes are reduced in the presence of RuCl2(DuPhos)(DMF) . The reactivity of the ruthenium catalyst is enhanced by the addition of potassium te/t-butoxide, which may facilitate generation of a ruthenium hydride. The products are obtained under low hydrogen pressures and selectivities obtained are up to 89% ee (eq 8). Neutral Rh-DuPhos complexes catalyze the hydrogenation of a,3-unsaturated acids such as tiglic acid (eq 9). The product is obtained in quantitative yield and good enantioselectivity. ... 

The carbonylation of allylic compounds by transition metal complexes is a versatile method for synthesizing unsaturated carboxylic acid derivatives (Eq. 11.22) [64]. Usually, palladium complexes are used for the carbonylation of allylic compounds [65], whereas ruthenium complexes show characteristic catalytic activity in allylic carbonylation reactions. Cinnamyl methyl carbonate reacts with CO in the presence of a Ru3(CO)i2/l,10-phenanthroline catalyst in dimethylformamide (DMF) to give methyl 4-phenyl-3-butenoate in excellent yield (Eq. 11.23) [66]. The regioselectivity is the same as in the palladium complex-catalyzed reaction. However, when ( )-2-butenyl methyl carbonate is used as a substrate, methyl ( )-2-methyl-2-butenoate is the major product, with the more sterically hindered carbon atom of the allylic group being carbo-nylated (Eq. 11.24). This regioselectivity is characteristic of the ruthenium catalyst [66]. 

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