Carbon on rhodium

Rhodium-on-carbon has also been found to bring about the formation of 2,2 -biquinoline from quinoline, the yield and the percentage conversion being similar to that obtained with palladium-on-carbon. On the other hand, rhodium-on-carbon failed to produce 2,2 -bipyridine from pyridine, and it has not yet been tried with other bases. Experiments with carbon-supported catalysts prepared from ruthenium, osmium, iridium, and platinum have shown that none of these metals is capable of bringing about the formation of 2,2 -biquinoline from quinoline under the conditions used with palladium and rhodium. ... 

Catalysts show remarkable product variation in hydrogenation of simple nitriles. Propionitrile, in neutral, nonreactive media, gives on hydrogenation over rhodium-on-carbon high yields of dipropylamine, whereas high yields of tripropylamine arise from palladium or platinum-catalyzed reductions (71). Parallel results were later found for butyronitrile (2S) and valeronitrile (74) but not for long-chain nitriles. Good yields of primary aliphatic amines can be obtained by use of cobalt, nickel, nickel boride, rhodium, or ruthenium in the presence of ammonia (4J 1,67,68,69). 

Two hydrogen-transfer systems have been developed that also give good yields of hydroxylamines. One uses 5% palladium-on-carbon in aqueous tetrahydrofuran with phosphinic acid or its sodium salt as hydrogen donor the other uses 5% rhodium-on-carbon in aqueous tetrahydrofuran and hydrazine as donor. These systems are complementary and which is the better may depend on the substrate (36). The reductions cannot be followed by pressure drop, and both require analysis of the product to determine when the reduction should be terminated. 

Hydrogen was introduced into a standard hydrogenation vessel containing 10 grams 6-deoxy-6-demethyl-6-methylene-5-oxytetracycline hydrochloride (methacycline), 150 ml methanol and 5 grams 5% rhodium on carbon. The pressure was maintained at 50 psi while agitating at room temperature for 24 hours. The catalyst was then filtered off, the cake washed with methanol and the combined filtrates were evaporated to dryness. The dry solids were slurried in ether, filtered and the cake dried. The resulting solids exhibited a bioactivity of 1,345 units per mg versus K. pneumoniae. 

To hydrogenate an aromatic ring, it s necessary either to use a platinum catalyst with hydrogen gas at several hundred atmospheres pressure or to use a more effective catalyst such as rhodium on carbon. Under these conditions, aromatic rings are converted into cyclohexanes. For example, o-xylene yields 1,2-dimethylcvclohexane, and 4-terf-butylphenol gives 4-terf-butyl-cyclohexanol. 

More recently Hartog and Zwietering (103) used a bromometric technique to measure the small concentrations of olefins formed in the hydrogenation of aromatic hydrocarbons on several catalysts in the liquid phase. The maximum concentration of olefin is a function of both the catalyst and the substrate for example, at 25° o-xylene yields 0.04, 1.4, and 3.4 mole % of 1,2-dimethylcyclohexene on Raney nickel, 5% rhodium on carbon, and 5% ruthenium on carbon, respectively, and benzene yields 0.2 mole % of cyclohexene on ruthenium black. Although the cyclohexene derivatives could not be detected by this method in reactions catalyzed by platinum or palladium, a sensitive gas chromatographic technique permitted Siegel et al. (104) to observe 1,4-dimethyl-cyclohexene (0.002 mole %) from p-xylene and the same concentrations of 1,3- and 2,4-dimethylcyclohexene from wi-xylene in reductions catalyzed by reduced platinum oxide. 

In a detailed study of the reduction of the xylenes in the liquid phase on a 5% rhodium on carbon catalyst, Siegel and Ku (105) showed that both 1,2- and 2,3-dimethylcyclohexenes are formed from orlAo-xylene (Fig. 19). The initial (extrapolated) ratio, l,2-/2,3-, lies between 0.5 and 1 but rises as the reaction proceeds. If the initial distribution of cyclo-alkenes was random as previously postulated (97) the ratio should be 0.5. 

Ferber and Bruckner reduced />-aminobenzoic acid using Adams catalyst (Pt02) at atmospheric pressure, and Schneider and Dillman reduced p-aminobenzoic acid using 10% rhodium on carbon at 140 atm. and 70°. 3-Isoquinuclidone has been prepared, by the previously mentioned investigators, by heating the dry 4-aminocyclohexane carboxylic acid at elevated temperatures. 

Catalytic hydrogenation of 2-alkyl-2,5-dihydro-l//-pyrrole with 5% rhodium on carbon gave 2-substituted pyrrolidines in 95-96% ee (Pirkle analysis42) without attendant racemization. 

To a 0.02 M soln of 2-alkyl-2,5-dihydro-l //-pyrrole (85-90% pure) in methanol is added with stirring 5% rhodium on carbon (catalyst/substrate 1 20). The mixture is pressurized (4.6 x 107 Torr) with hydrogen and is stirred at 25 °C for a minimum of 5 h. The catalyst is removed by vacuum filtration, the solution is concentrated under reduced pressure and the residue is purified by bulb-to-bulb distillation to give the product in 95% purity. 

Dibutylamine, piperidine, N-ethylcyclohexylamine, N-ethyldicyclohexylamine, and the ketones were reagent grade chemicals. The 5% palladium on carbon, 5% platinum on carbon, sulfided 5% platinum on carbon and sulfided 5% rhodium on carbon catalysts were obtained from Engelhard Industries. The 20% molybdenum sulfide on alumina (Girdler T-318) was obtained from the Chemetron Corp. Palladium chloride was obtained from Matheson, Coleman and Bell. Ruthenium trichloride was obtained from Ventron. 

DAB (3) through efficient hydrogenation over rhodium on carbon.38 Similar paclitaxel and docetaxel analogues containing cyclohexyl groups were independently reported by Georg and coworkers.56... 

Quinaldic acid N-Ethylmorpholine Rhodium on carbon Citric acid... 

A large excess of ammonia suppresses formation of di- and trialkylamines. With a rhodium-on-carbon catalyst in process conditions of 75°C and 50 psig plus continuous removal of ammonia, the reduction of propionitrile with hydrogen proceeds with greater than 85% selectivity for di-n-propylamine, with 2 to 5% mono-n-propylamine coproduct. Several companies produce amines in the C 2 to Ci8 range from fatty nitriles by this route116. 

Partial reduction of phenols affords mixtures of allylic and vinylic alcohols. From the generality derived for aliphatic systems, the most hydrogenolysis of this mixture is expected with platinum, palladium, and iridium catalysts, and much less with rhodium and ruthenium, an expectation substantiated in practice. For example, hydrogenation of resorcinol in neutral medium affords 20, 19, and 70% cyclohexanediol over palladium-, platinum-, and rhodium-on-carbon, respectively (29). Many examples attest to the value of rhodium and ruthenium at elevated pressure in avoiding hydrogenolysis. 

Rhodium on carbon, Rh/C Acts as a hydrogenation catalyst in the reduction of benzene rings to yield cyclohexanes (Section 16.10). 

Norbornadiene (463 g., 5.03 moles), distilled from calcium hydride, and 5% rhodium on carbon (2.S-4.5 g., 0.001-0.002 g.-atom of Rh, Engelhard Industries) are added and the mixture is stirred and refluxed for 1 day, and the rhodium on carbon is filtered. The filtrate is distilled at atmospheric pressure, yielding recovered norbornadiene and a distillation residue containing the reaction product. The procedure is repealed using the recovered norbornadiene, and the repetitions are continued until norbornadiene is consumed. 

The initial treatments probably remove a catalyst poison from the norbornadiene. Thus while after the first or second reflux about 95 % of the norbornadiene is recovered, on a fifth reflux 120 g. of norbornadiene was completely oligomerized by 2.5 g. of 5% rhodium on carbon in 10 hr. Norbornadiene that has been refluxed with Norit gives a higher yield than norbornadiene that has not, but the simplest procedure for effecting the oligomerization is to reflux norbornadiene with rhodium on carbon until the yield is high. Five such treatments using a total of 20 g. of 5°/ rhodium on carbon may be required. 

HYDROGENATION CATALYSTS Bis-(pyridine)dimethylformamidcdichlororbo-dium borohydride. Iron pentacarbonyl. Lindlar catalyst. Nickel boride. Palladium-on-calcium carbonate. Rhodium-on-alumina. Rhodium-on-carbon. Ruthenium trichloride hydrate. Triton dodecacar-bonyL Tris(tiiplienylpho ine)chloto-... 

The preparation of N-phenylhydroxylamine in high yields from nitrobenzene under catalytic transfer hydrogenation conditions is also possible utilizing wet 5% rhodium on carbon and hydrazine hydrate. Unfortunately, the transition metal catalysts tend to be expensive and the high temperatures required can be detrimental, particularly when the resulting hydroxylamines are explosive in nature. ... 

A. N-Phenylhydroxylamine. Het, 5% rhodium on carbon (1.1 g) (Note 1), tetrahydrofuran (200 nt) (Note 2) and nitrobenzene (41.0 g) (Note 3) are Introduced Into a 500-mL, three-necked, round-bottomed flask fitted with a mechanical stirrer, thermometer and condenser. The mixture Is cooled to 15°C and hydrazine hydrate (17.0 g) (Note 4) is introduced Into the reaction mixture from a pressure-equalized addition funnel over 30 min. The temperature of the mixture 1s maintained at 25-30°C throughout the addition by means of an ice-water bath. After the mixture is stirred for a further 2 hr at 25-30 C, the reaction is complete (Note 5), The mixture Is filtered and the catalyst washed with a little tetrahydrofuran. The solution Is used immediately In the acylation step (Note 6). 

The 5% rhodium on carbon used was purchased dry from Engelhard Industries Ltd. The checkers purchased it from Aldrich Chemical Company, Inc. The catalyst is used wet (40-50% water) to reduce the risk of fire when the solvent is added. 

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