Rhodium on alumina

Pyrrole can be reduced catalyticaHy to pyrroHdine over a variety of metal catalysts, ie, Pt, Pd, Rh, and Ni. Of these, rhodium on alumina is one of the most active. Less active reducing agents have been used to produce the intermediate 3-pyrroline (36). The 2-pyrrolines are ordinarily obtained by ring-closure reactions. Nonaromatic pyrrolines can be reduced easily with to pyrroHdines. 

Oxidations of pyridopyrimidines are rare, but the covalent hydrates of the parent compounds undergo oxidation with hydrogen peroxide to yield the corresponding pyridopyrimidin-4(3 T)-ones. Dehydrogenation of dihydropyrido[2,3-(i]pyrimidines by means of palladized charcoal, rhodium on alumina, or 2,3-diehloro-5,6-dicyano-p-benzo-quinone (DDQ) to yield the aromatic derivatives have been reported. Thus, 7-amino-5,6-dihydro-1,3-diethylpyrido[2,3-d]-pyri-midine-2,4(lif,3f/)-dione (177) is aromatized (178) when treated with palladized charcoal in refluxing toluene for 24 hours. 

Hydrogenation of quinoxaline, or 1,2,3,4-tetrahydroquinoxaline, over a 5% rhodium-on-alumina catalyst at 100°C and 136 atm, or over... 

A solution of resorcinol (11 g) in sodium hydroxide solution (4.8 g of sodium hydroxide in 20 ml of water) is hydrogenated in the presence of 1.1 g of 5 % rhodium on alumina for 16-18 hours at 50 psi initial pressure in a Parr apparatus. The reduction stops after the absorption of 1 equivalent of hydrogen. The catalyst is removed by filtration through celite, and the aqueous solution is carefully acidified with concentrated hydrochloric acid at 0°. The crude product is collected by filtration, dried in air, and recrystallized from benzene to give 1,3-cyclohexanedione, mp 105-107. ... 

A solution of hydroquinone (11.0 g) in 50 ml of acetic acid containing 1.1 g of 5 % rhodium on alumina is hydrogenated at 50 psi in a Parr apparatus. Three equivalents of hydrogen are rapidly absorbed. The catalyst is removed by filtration through celite. 

A solution of 76 g (S)-( + )-mandelic acid in 400 ml methanol and 5 ml acetic acid was reduced over 5% rhodium-on-alumina under 100 psig for 10 h. The catalyst was removed by filtration through Celite, and the methanol was removed in a rotary evaporator. The white, solid residue was dissolved in I 1 of hot diethyl ether and filtered while hot. After reduction of the volume to 400 ml, 250 ml cyclohexane was added. The remainder of the ether was removed, and the cyclohexane solution was stored for several hours in a refrigerator. The white crystals were filtered and dried in vacuo at 40 C the yield of (S)-( + )-hexahydromandelic acid was 71%. 

A rhodium-on-alumina catalyst deactivated in bis-(4-aminophenyl)-methane saturation (I IS C, 100 psig) was regenerated by two washings with aqueous ammonia at 65°C, followed by drying at 90°C(I6) or by washing with acetic acid. 

In a study on the influence of supports on rhodium, the amount of dicyclohexylamine was found to decrease in the order carbon > barium carbonate > alumina > barium sulfate > calcium carbonate. Plain carbon added to rhodium-on-alumina-catalyzed reactions was found to cause an increase in the amount of dicyclohexylamine, suggesting that carbon catalyzes the formation of the intermediate addition product (59). 

When benzene, in the gas phase, was adsorbed onto a surface of 10% rhodium-on-alumina, the reverse reaction took place, and acetylene was formed. 

Granger, P., Delannoy, L., Lecomte, J.J. et al. (2002) Kinetics of the CO + NO Reaction over Bimetallic Platinum-Rhodium on Alumina Effect of Ceria Incorporation into Noble Metals, J. Catal., 207, 202. 

A complex naturally occurring amino acid 5-hydroxypiperazic acid (5HyPip) 100 was prepared by a multistep procedure that included Diels-Alder addition of 2,4-pentadienoic acid to phthalazinedione 83a as a first step (Scheme 24). Adduct 97 was esterified and oxidized with mercuric acetate to 98, which on hydrogenation over rhodium on alumina and subsequent hydrolysis provided a mixture of enantiomers from which the required enantiomer 99 was obtained by resolution with quinine. Its hydrazinolysis provided 100 [71JCS(C)514 77H119],... 

The azatriquinane 36a which may be regarded as an annulated bis-pyrrolizine readily undergoes stereoselective hydrogenation in presence of rhodium on alumina, leading to the fully saturated tricyclic compound with a trans relative orientation between the benzyl group and the two hydrogen atoms located on the two other junctions carbon atoms <2005JA1352>. 

Rhodium-on-alumina, catalyzed reduction of aromatic nuclei, 51, 105... 

High yields of secondary amines are obtained when solutions of nitriles in acetic acid are hydrogenated at room temperature and pressure over a 5% rhodium-on-alumina catalyst (equation 4) hydroxy, ethoxycarbonyl and tosylamino substituents are not affected23. 

Catalytic reduction of cytidine in water over rhodium on alumina yields the tetrahydro derivative [l-(/3-D-ribofuranosyl)-4-aminotetrahydropyrimidin-2(l//)-one] and l-( 3-D-ribofuranosyl)tetrahydropyrimidin-2(l/0-one as the major products [680]. The former hydrolyses readily to give tetrahydrouridine,which is a potent inhibitor of human liver deaminase. The latter compound is also formed by sodium borohydride reduction of 5,6-dihydrouridine. 

In the absence of potassium hydroxide hydrogenation of vinylic and allylic chlorides to the saturated chlorides (with only partial or no hydrogenolysis of chlorine) is accomplished over 5% platinum, 5% palladium and, best of all, 5% rhodium on alumina [40]. 

Ketals of acetone and cyclohexanone with methyl, butyl, isopropyl and cyclohexyl alcohols are hydrogenolyzed to ethers and alcohols by catalytic hydrogenation. While platinum and ruthenium are inactive and palladium only partly active, 5% rhodium on alumina proves to be the best catalyst which, in the presence of a mineral acid, converts the ketals to ethers and alcohols in yields of 70-100% [933]. 

Excellent yields of primary amines were obtained by hydrogenation of nitriles over 5% rhodium on alumina in the presence of ammonia. The reaction was carried out at room temperature and at a pressure of 2-3 atm and was finished in 2 hours, giving 63-92.5% yields of primary amines. Under such conditions no hydrogenolysis of benzyl residues was noticed [1157]. Hydrogenation over Raney nickel at room temperature and atmospheric [1158] or slightly elevated pressures [45] also gave high yields of primary amines, especially in the presence of ammonia [7/55]. Comparable results... 

Intramolecular cycloadditions of alkenyl-substituted nitrile oxides produce bicyclic isoxazolines. When monocyclic olehns are used, tricyclic structures are obtained. This approach was pioneered by both Kozikowski s and Curran s groups. A typical case involves the cycloaddition of nitro compound 191 [mixture of diastereomers derived from pentenose pyranoside 190], which produced a diaster-eomeric mixture of isoxazolines that contain cis-fused rings (i.e., 192) in near quantitative yield (326) (Scheme 6.85). Further elaboration of this mixture led to epoxycyclopentano-isoxazoline 193, which was then converted to the aldol product in the usual manner. The hydrogenation proceeded well only when rhodium on alumina was used as the catalyst, giving the required p-hydroxyketone 194. This... 

Hydrogenation of uridine 5 -(a-D-glucopyranosyl pyrophosphate) over rhodium on alumina resulted in the 5,6-dihydrouridine derivative229,324 (75). Several modifications in the heterocyclic base of adenosine 5 -(a-D-glucopyranosyl pyrophosphate) have been described. 

A method for the preparation of 1-hydroxypyrrolizidine was published by Adams et al.7i Cyclization of 1 -(/ -cyanoethyl)pyrrole under the conditions of the Houben-Hoesch reaction gave rise to l-oxo-3/f-l,2-dihydropyrrolo(l,2-a)pyrrole (123) (cf. refe. 48 and 73), which can be converted into 1-hydroxypyrrolizidine by either direct hydrogenation over rhodium on alumina or hydrogenation of the corresponding hydroxy derivative 124. This route has some interest as a potential... 

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