Platinum in hydrogenation

Cadmium.—By heating platinum in hydrogen laden with cadmium vapour obtained from boiling metal, a white, crystalline, and very brittle compound, of formula PtCd2, is obtained.4... 

Boreskov, G.K., Slin ko, M.G., Filippova, A.G., 1953. Catalytic activity of nickel, palladium, and platinum in hydrogen oxidation. Dokl. Akad. Nauk SSSR 92, 353-355. 

Frotts, S. D., Gervasio, D., Zeller, R. L., and Savinell, R. R, 1991, Investigation of gas transport in recast Nafion films coated on platinum in hydrogen saturated 85% phosphoric acid, J. Electrochem. Soc. 138 3345-3349. 

This electrode, shown diagrammatically in Figure 4.4, is assigned zero potential when hydrogen gas at one atmosphere bubbles over platinised platinum in a solution of hydrogen ions of concentration 1 mol 1 (strictly, at unit activity). 

Production is by the acetylation of 4-aminophenol. This can be achieved with acetic acid and acetic anhydride at 80°C (191), with acetic acid anhydride in pyridine at 100°C (192), with acetyl chloride and pyridine in toluene at 60°C (193), or by the action of ketene in alcohoHc suspension. 4-Hydroxyacetanihde also may be synthesized directiy from 4-nitrophenol The available reduction—acetylation systems include tin with acetic acid, hydrogenation over Pd—C in acetic anhydride, and hydrogenation over platinum in acetic acid (194,195). Other routes include rearrangement of 4-hydroxyacetophenone hydrazone with sodium nitrite in sulfuric acid and the electrolytic hydroxylation of acetanilide [103-84-4] (196). 

Isoquinoline can be reduced quantitatively over platinum in acidic media to a mixture of i j -decahydroisoquinoline [2744-08-3] and /n j -decahydroisoquinoline [2744-09-4] (32). Hydrogenation with platinum oxide in strong acid, but under mild conditions, selectively reduces the benzene ring and leads to a 90% yield of 5,6,7,8-tetrahydroisoquinoline [36556-06-6] (32,33). Sodium hydride, in dipolar aprotic solvents like hexamethylphosphoric triamide, reduces isoquinoline in quantitative yield to the sodium adduct [81045-34-3] (25) (152). The adduct reacts with acid chlorides or anhydrides to give N-acyl derivatives which are converted to 4-substituted 1,2-dihydroisoquinolines. Sodium borohydride and carboxylic acids combine to provide a one-step reduction—alkylation (35). Sodium cyanoborohydride reduces isoquinoline under similar conditions without N-alkylation to give... 

Vinyl chloride can be hydrogenated over a 0.5% platinum [7440-06-4], Pt, on alumina catalyst to ethyl chloride and ethane [74-84-0]. This reaction is 2ero order in vinyl chloride and first order in hydrogen. 

Hydrogenation. Hydrogenation is one of the oldest and most widely used appHcations for supported catalysts, and much has been written in this field (55—57). Metals useflil in hydrogenation include cobalt, copper, nickel, palladium, platinum, rhenium, rhodium, mthenium, and silver, and there are numerous catalysts available for various specific appHcations. Most hydrogenation catalysts rely on extremely fine dispersions of the active metal on activated carbon, alumina, siHca-alumina, 2eoHtes, kieselguhr, or inert salts, such as barium sulfate. 

Metals and alloys, the principal industrial metalhc catalysts, are found in periodic group TII, which are transition elements with almost-completed 3d, 4d, and 5d electronic orbits. According to theory, electrons from adsorbed molecules can fill the vacancies in the incomplete shells and thus make a chemical bond. What happens subsequently depends on the operating conditions. Platinum, palladium, and nickel form both hydrides and oxides they are effective in hydrogenation (vegetable oils) and oxidation (ammonia or sulfur dioxide). Alloys do not always have catalytic properties intermediate between those of the component metals, since the surface condition may be different from the bulk and catalysis is a function of the surface condition. Addition of some rhenium to Pt/AlgO permits the use of lower temperatures and slows the deactivation rate. The mechanism of catalysis by alloys is still controversial in many instances. 

An interesting field of application is the protection of tantalum against hydrogen embrittlement by electrical connection to platinum metals. The reduction in hydrogen overvoltage and the shift of the free corrosion potential to more positive values apparently leads to a reduced coverage by adsorbed hydrogen and thereby lower absorption [43] (see Sections 2.1 and 2.3.4). 

Because of the presence of alkali in Raney nickel, ketones are hydrogenated over this catalyst to yield the more stable, equatorial alcohol e.g. 59) as the predominant product, Similar results can be expected with platinum in basic media or with platinum oxide in an alcoholic solvent since this catalyst also contains basic impurities. 

The earliest attempts to prepare deuterated steroids were carried out by exchange reactions of aliphatic hydrogens with deuterium in the presence of a surface catalyst. Cholesterol, for example, has been treated with platinum in a mixture of deuterium oxide and acetic acid-OD, and was found to yield... 

Tetrahydro derivatives are formed when either quinoxaline or 6-chloroquinoxaline is reduced with lithium aluminum hydride in ethereal solution. Similar reduction of 2,3-dimethylquinoxaline gives the meso-(cts)-1,2,3,4-tetrahydro derivative. This is shown to be a stereospecific reduction since lithium aluminum hydride does not isomerize the dl-(trans)-compound. Low temperature, platinum catalyzed, hydrogenation of 2,3-dimethylquinoxaline in benzene also gives meso (cis) -l,2,3,4-tetrahydro-2,3-dimethylquinoxaline. ... 

In general, hydrogenolysis of vinylic compounds is favored by platinum and hydrogenation by ruthenium and rhodium 31,55,59,72,106). In the reduction of 4-methyl-1-cyclohexenyl ether, the order of decreasing hydrogenolysis to give methylcyclohexane was established as Pt Ir > Rh > Os Ru = Pd (52). 

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). 

Catalysts dilTer widely in their ability to elTect dehydrohalogenation. Palladium is usually the catalyst of choice. Platinum and rhodium are relatively inelTective and are often used in hydrogenations when halogen is to be preserved. A sequential use of platinum and palladium is illustrated in... 

The product (12.1 mg) obtained in the above step was dissoived in 0.3 mi of water, to which was then added a catalytic quantity (about 5 mg) of platinum oxide. Hydrogenation was made with hydrogen gas at a pressure of 35 kg/cm for 1.5 hours. The reaction solution was filtered to remove the catalyst, and the filtrate was concentrated to dryness, giving the desired product 3, 4 -dideoxykanamycin B in the form of its monocarbonate. The yield was 11.5 mg (95%). -f 110° (c 1, water). The overall yield of 3, 4 -dideoxykanamycin B... 

The flask of a Parr hydrogenation apparatus was charged with 10,5 g of 3,3-diphenylpropyl-amine, 7.7 g of cyclohexylacetone, 50 ml methanol and 150 mg of platinum dioxide. Hydrogen at a pressure of 3 atmospheres was introduced and the mixture stirred. Upon absorption of the theoretical amount of hydrogen, stirring is discontinued, the catalyst is filtered off and the solution is evaporated to dryness. The residue is taken up with ether and the hydrochloride is precipitated with HCI in alcoholic solution. The product, as collected on a filter and washed with ether, is recrystallized from isopropanol. Yield 17 g (92.5% of theory). 

ID) Obtaining Ethyl [3-l6-Methoxy-2-Naphthyl)J2,2-Dimethyl Pentanoate by Hydrogenation of the Previous Ethylene Ester 3.5 g of the previous ethylene ester, purified by chromatography, are hydrogenated in the presence of 3.6 g of platinum in 30 cc of ether. The quantity of hydrogen fixed corresponds to the theoretical quantity calculated. After filtering, the ether is evaporated, 3.45 g of ester are thus obtained in the form of an oil which quickly solidifies. Purification is effected by chromatography. 

The method is more useful with titanium, and the effect of alloying titanium with a small amount of palladium is described in Section 5.4. The use of platinum in the prevention of hydrogen embrittlement in tantalum. 

Whereas reduction of dimethyl 1,2,7-trimethyl-l T/-azepine-3,6-dicarboxylate (5) with platinum and hydrogen in cyclohexane yields the hexahydroazepine 6, hydrogenation in methanol solution results in loss of methylamine and formation of dimethyl 2,3-dimethylbenzene-1,4-dicar-boxylate (52% mp 66-67 C).239... 

Dimethyl 2,7-dimethyI-4//-azepine-3,6-dicarboxylate (7) with platinum and hydrogen in cyclohexane solution at atmospheric pressure undergoes rapid partial reduction to the 4,5-dihydro-l//-azepine 8.29... 

Complete reduction to dimethyl 2,7-dimethylhexahydroazepine-3,6-diearboxylate (bp 92-94 C/0.05 Torr) is achieved on prolonged treatment with platinum and hydrogen in ethanol solution. 

Decomposition of platinum hexafluoro-2,4-pentadionate, Pt(CF3COCHCOCF3)2 or tetrakis-trifluorophosphine, Pt(PF3)4 at 200-300°C in hydrogen. 

Eq. (77)] 114). The reaction of (Me3Si)2Pt(diphos) with hydrogen in benzene at atmospheric pressure affords Me3SiPtH(diphos) at 40° C and (diphos)jPt4 at 80° C (77). Kinetic studies showed that the reaction is first order in hydrogen and in the platinum complex (Aj = 6.0 x 10 ... 

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