Adams catalyst solvents

For more selective hydrogenations, supported 5—10 wt % palladium on activated carbon is preferred for reductions in which ring hydrogenation is not wanted. Mild conditions, a neutral solvent, and a stoichiometric amount of hydrogen are used to avoid ring hydrogenation. There are also appHcations for 35—40 wt % cobalt on kieselguhr, copper chromite (nonpromoted or promoted with barium), 5—10 wt % platinum on activated carbon, platinum (IV) oxide (Adams catalyst), and rhenium heptasulfide. Alcohol yields can sometimes be increased by the use of nonpolar (nonacidic) solvents and small amounts of bases, such as tertiary amines, which act as catalyst inhibitors. 

Reflux 6.9 g triphenylphosphine and 6.6 g lauryl bromide (or equimolar amount of homolog) in 40 ml xylene for 60 hours. Remove solvent and wash residue with 5X20 ml ether (by decanting) to get 11 g lauryl triphenylphosphonium bromide (I). To a stirred suspension of 5.6 g (0.011M)(I) in 50 ml ether add 0.01M butyllithium solution (see Organic Reactions 8,258(1954) for preparation). Stir Vz hour at room temperature and slowly add 1.66 g 3,5-dimethoxybenzaldehyde (preparation given elsewhere here) in 10 ml ether over Vi hour. After 15 hours, filter, wash filtrate with water and dry, evaporate in vacuum. Dilute residue with pentane, filter and remove solvent. Dissolve the residual oil in 25 ml ethyl acetate and hydrogenate over O.lg Adams catalyst at one atmosphere and room temperature for 2 hours. Filter and evaporate in vacuum to get the 5-alkylresorcinol dimethyl ether which can be reciystallized from pentane and demethylated as described elsewhere here. 

The bulk of the l-(2,5-dimethoxyphenyl)-2-(t-butylamino)propiophenone was dissolved in methanol and hydrogenated over platinum (Adams catalyst). After removal of the catalyst, the solvent was removed in vacuo and the residual solid was dissolved in water and the solution was washed with ether. 

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). ... 

Catalytic hydrogenation of fluoro- and difluOTO-m- and tran -butenedioic acids and their esters frequently affords products only of hydrogenolysis, especially when platinum oxide (Adams catalyst) is used. Hydrogenolysis is favored in polar solvents, and is found to be more effective when rhodium or nickel rather than palladium are used as the catalysts (Table 2). Hydrogenolysis takes place prior to the saturation of the double bonds fluoro- and 2,3-difluoro-succinic acids do not suffer any loss of fluorine under the same reaction conditions. ... 

Quinolinamine 53 A suspension of 5-nitroquinoline (34.8 g) in anhydrous ethanol (200ml) is shaken with hydrogen in the presence of Adams catalyst (platinum dioxide) (0.4 g). The reaction is complete in about 2 h, there being a marked rise in temperature. The solution is clarified with charcoal, the solvent is removed in a vacuum, and the residue is distilled, giving a product (27 g, 95%) having b.p. 180-181°/7 mm and m.p. 100-107°. Recrystallization from ether gives material (23.5 g, 82%) of m.p. 108-110°. 

Reactions catalysed by Adams catalyst can be carried out in alcoholic solution which is sometimes enhanced by the presence of HCl a variety of other organic solvents have been used which include EtOAc, EtOAc+15% AcOH, EtOAc+8%EtOH, and glacial AcOH and neat CF3CO2H is a particirlarly good solvent for the reduction of C=N in heterocyclic compounds. 

To tetrahydrohumulone (1 g 2.73 x 10r mol) in methanol (20 ml) are added 5% platinum(IV) oxide (Adams catalyst) and 2% platinum as dihydrogen hexachloroplatinate. After complete hydrogenation (5 mols H2) the solvent is removeo and the residue is separated by chromatography on silica gei with benzene as eluent. Recrystallization from iso-octane yields white crystalline 4-(3-methyibutanoyl)-2,6-bis(3-methylbutyl)-resorcinol (35-40%). 

Humulinic acid (2 g 7.52 x 10 mol) is dissolved in acetic add (10 g 1.7 x 10 mol), to which 5% Adams catalyst (platinum(IV) oxide) is added. The temperature of the hydrogenation vessel is adjusted to 55°C. After hydrogenation during 6-8 h the catalyst is filtered off and the solvent is removed. Trans dihydrodeoxohumulinic add... 

In 1961, the catal5dic reduction of 3.5-diphenyl-, 3-phenyl-5-methyl and 3-methyl-S-phenyl oxadiazole has been reported by Palazzo [61b) who studied the influence of various reaction conditions such as the temperature, the solvent and the nature of the catalyst Pd on C, Adams-Pt and Raney-Ni. The opening of the N—O linkage occurs in each experiment. In the reduction of diphenyloxadiazole with Pd on C under 3 atm. one equivalent of hydrogen is absorbed and benzamidine benzoate is isolated in high yield. A small amount of benzoyl benzamidine is also formed ... 

The practical difficulty with carrying out a crystalhzation DTR process is the need to operate under conditions that allow selective crystalhzation of the least soluble diastereomer while permitting the racemization to take place. Amine racemization catalysts, such as SCRAM , Shvo, Pd/C, and Adam s, are more active at higher temperatures, which runs counter to the conditions required for crystaUization. A solution to this problem is to separate the diastereomeric resolution and racemization steps but couple them with a flow engineering design. In this way each reaction can be operated under optimal conditions for example, temperature, concentration and solvent, via an intermediary solvent exchange unit Since the racemization catalyst itself may affect the crystalhzation (or indeed the crystalhzation may affect the catalyst), it is preferred to keep them separate. This can be achieved by having the catalyst or product either permanently or temporarily in a different phase by immobilization, extraction, precipitation, distil-... 

Adams platinum oxide catalyst is readily prepared from chloroplatinio acid or from ammonium chloroplatinate, and is employed for catalytio hydrogenation at pressures of one atmosphere to several atmospheres and from room temperature to about 90°. Reduction is usually carried out with rectified spirit or absolute alcohol as solvents. In some cases (e.g., the reduction of benzene, toluene, xylene, mesitylene, cymene and diphenyl ), the addition to the absolute alcohol solution of 2-5 per cent, of the volume of rectified spirit which has been saturated with hydrogen chloride increases the effectiveness of the catalyst under these conditions chlorobenzene, bromobenzene, o-, m- and p-bromotoluenes, p-dichloro- and p-dibromo-benzene are reduced completely but the halogens are simultaneously eliminated. Other solvents which are occasionally employed include glacial acetic acid, ethyl acetate, ethyl acetate with 17 per cent, acetic acid or 8 per cent, of alcohol. In the actual hydrogenation the platinum oxide Pt02,H20 is first reduced to an active form of finely-divided platinum, which is the real catalyst allowance must be made for the consumption of hydrogen in the process. 

Voorhees and Adams141 obtained an active platinum black from the platinum oxide prepared by fusing a mixture of chloroplatinic acid and sodium nitrate at 500-550°C. The platinum oxide is readily reduced to an active black with hydrogen in a solvent in the presence or absence of substrate. The platinum oxide-platinum black thus prepared has been shown to be very active in the hydrogenation of various organic compounds and is now widely used as Adams platinum oxide catalyst. Frampton et al. obtained a platinum oxide catalyst of reproducible activity by adding a dry powder of a mixture of 1 g of chloroplatinic acid and 9 g of sodium nitrate in its entirety to 100... 

---