Hydrogenation catalysts Adams catalyst

Cyanohydrin (52b 5 g mp 160-164°) is dissolved in acetic acid (200 ml) and placed in a 2-liter hydrogenation flask. Adams catalyst (0.75 g) is added (for 100 g cyanohydrin use 7.5 gof catalyst) and the mixture is hydrogenated until the theoretical amount of hydrogen is taken up (477 ml). The catalyst is removed by filtration, the filtrate is transferred to a 600 ml beaker provided with a stirrer and thermometer, treated with water (20 ml) and cooled to 0° (ice-salt). A solution of sodium nitrite (10 g) in water (30 ml) is added dropwise with stirring at 0°. The reaction mixture is then stirred for additional 2 hr at room temperature, treated with water (100 ml) and, after standing overnight, the precipitate is collected by filtration. The product is dissolved in ether (50 ml), the ether solution is washed sequentially... 

Hydrogenation with Adams catalyst took place only with the 6-alkyl derivatives. Dioxohexahydrotriazine itself acted as a catalyst poison (in common with 1,3,5-triazine and cyanuric acid ). Dioxo-tetrahydrotriazine as well as its A-alkyl and 6-alkyl derivatives can be readily hydrogenated by using Raney nickel. ... 

Anhydro-bases derived from quaternary )S-carbolinium salts are reduced to p /r-A-substituted-l,2,3,4-tetrahydro-j8-carboline derivatives on hydrogenation over Adams catalyst in methanol solution made alkaline to ensure the presence of anhydro-base. ... 

Other methods of reducing the nitroso compound include the use of ammonium sulfide4 and hydrogenation utilizing Adams catalyst.5... 

Carbon reacts also with other sulfur-containing compounds with resulting fixation of sulfur. Reaction of various forms of carbon with hydrogen sulfide was reported by Baraniecky, Riley, and Streeter (126) and by Polansky, Knapp, and Kinney (128). The reaction of carbon blacks with hydrogen sulfide and with sulfur was studied extensively by Studebaker (86). At 150°, the increase in sulfur content was proportional to the quinone content as measured by catalytic hydrogenation using Adams catalyst (see page 203). 

Conversion of the keto ketoxime 1 to the exo-exo-amino alcohol 2 has been accomplished by hydrogenation over Adams catalyst and by reduction with lithium aluminum hydride. Amino alcohol 2 has also been prepared from 1 by a two-stage process in which selective reduction of the ketone is carried out with sodium borohydride, and the resultant hydroxy oxime is reduced with lithium aluminum hydride or by hydrogenation over Adams catalyst. ... 

Nitraramine and A-hydroxynitraramine were isolated from Nitraria schoberi (194,195). There are active hydrogen absorption bands in the IR spectrum of nitraramine at 3280 and 3530 cm- and a low intensity band at 1660 cm" (double bond). Acetylation of nitraramine (171) gave A-acetyl and A,0-diacetyl derivatives. Hydrogenation over Adams catalyst in acetic acid gave di-hydronitraramine (172) and dihydrodesoxynitraramine (173) (Scheme 30). The presence of peaks typical for quinolizidine alkaloids in the mass spectra of 171-... 

An important advance was made when it was observed that photolysis of the (3-enamido ketone 165, which was readily available from the indoline 163 by Birch reduction followed by N-aryloylation, delivered the lactam 168 as the only photoproduct (Scheme 17) (125). Reduction of 168 with LiAlH4 gave ( )-a-anhydrodihydrocaranine (143), which was then converted to ( )--y-lycorane (93) on hydrogenation over Adams catalyst in acetic acid. In a similar fashion, irradiation of the bromo or iodo enaminones 166 (Z = Br, I), which were obtained by alkylation of the intermediate imino ether formed on Birch reduction of 163, afforded a mixture (approximately 3 2) of the lactam 168 together with the photoreduction product 167 (126). 

The main problem here is removing the phenyl ester groups from the phosphonic moiety.We have found that convenient routes for deblocking are hydrogenation on Adams catalyst and transesterification methods followed by hydrogen bromide in glacial acetic acid treatment. The best results ewre obtained if transesterification was carried out using potassium fluoride-crown ether-methanol system. 

Quaternary phenanthridinium compounds are reduced to the corresponding A-alkyldihydrophenanthridines by hydrogenation over Adams catalyst. The reaction forms part of the modified Emde sequence284 shown below. 

Diazomethane reacts with the salts of enamines to yield aziridinium salts.327 327a ThusiV-cyclohexylidenepyrrolidinium perchlorate yields 2,2 -pentamethylene-1,1 -tetramet hyleneaziridinium perchlorate (101). Hydrogenation over Adams catalyst cleaves the bond between the quaternary nitrogen atom and the methylene group to form A-(l-methylcyclohexyl)pyrrolidinium perchlorate (102). 

Interestingly, 5-azaindole resists atmospheric-pressure hydrogenation with Adams catalyst in acidic medium. Also, 7-azaindole and its 1-ethoxycarbonyl derivatives are recovered from treatment with lithium aluminum hydride. This reagent readily reduced the dihydropyridine ring of 6,7-dihydro-4-methyl-7-azaindole to the corresponding 4,5,6,7-tetrahydro compound in 83% yield. ... 

The aromaticity of the imidazole nucleus ensures stability towards reduction, and when benzimidazole (27) is hydrogenated over Adams catalyst in acetic acid the carbocyclic ring is reduced first to give the tetrahydrobenzimidazole (28). However, if the solvent is changed to acetic anhydride, A(-acylation promotes the reduction of the heterocycle and the 1,3-diacetylbenzimidazoline (29) is then formed (Scheme 1). Imidazole (30) under these conditions gives 1,3-diacetylimidazoline (31). Imidazolium salts (32) are easily reduced and treatment with excess sodium borohydride in 95% aqueous ethanol culminates in the formation of 1,2-diamines, (33) or (34). Either N—C bond may cleave, although if the substituent R is benzyl the major products are benzylamines (33 R = Bn). ... 

Various ketones have been converted to optically active alcohols with high optical purity and in high yield using alcohol dehydrogenases. In addition, successful reductions have been performed by catalytic hydrogenation, over Adams catalyst, " Raney nickel, and palladium on carbon, and lithium in tcrf-butyl alcohol/ammonia, and in one case even with lithium dibutylcuprate. ... 

Hydrogenation of the tricyclic diene 1 over palladium on carbon yields the product of 1,4-addition with a tetrasubstituted double bond 2, which is extremely resistant to further hydrogenation. In contrast, hydrogenation with Adams catalyst affords 9-pupukeanone (3)5. Iridium black as catalyst gives the latter product with excellent diastereoselectivity (yield not reported d.r. >98 2)6. 

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