Preparation of platinum oxide

Platinum oxide catalyst prepared by the method of K. Adams has recently come into use because it is very convenient to prepare and handle and at the same time has very high activity. When in use it is first reduced by hydrogen in the hydrogenation bulb to very finely divided platinum. 

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This procedure is particularly time-saving when scrap platinum or spent catalyst is used for the preparation of platinum oxide, for after conversion to chloroplatinic acid a purification is conveniently effected by precipitating the ammonium salt, and the direct fusion of this with sodium nitrate eliminates the tedious process of reconversion to chloroplatinic acid. Furthermore ammonium chloroplatinate is not hygroscopic and can he accurately weighed. The amount of catalyst obtained is almost exactly half the weight of the ammonium salt employed. 

Bruce uses ammonium chloroplatinate for preparation of platinum oxide.143 According to Shriner and Adams144 palladium oxide is prepared in the same way as the platinum catalyst, but as it peptizes readily it must be washed only with 1% sodium carbonate or sodium nitrate solution. 

Salts of neodecanoic acid have been used in the preparation of supported catalysts, such as silver neodecanoate for the preparation of ethylene oxide catalysts (119), and the nickel soap in the preparation of a hydrogenation catalyst (120). Metal neodecanoates, such as magnesium, lead, calcium, and zinc, are used to improve the adherence of plasticized poly(vinyl butyral) sheet to safety glass in car windshields (121). Platinum complexes using neodecanoic acid have been studied for antitumor activity (122). Neodecanoic acid and its esters are used in cosmetics as emoUients, emulsifiers, and solubilizers (77,123,124). Zinc or copper salts of neoacids are used as preservatives for wood (125). 

The requisite intermediate, ethyl 4-dimethylaminocyclohexylcarboxylate is prepared as follows 33 g of ethyl p-aminobenzoate dissolved in 300 cc of absolute ethanol containing 16.B cc of concentrated hydrochloric acid is hydrogenated at 50 pounds hydrogen pressure in the presence of 2 g of platinum oxide. The theoretical quantity of hydrogen is absorbed in several hours, the catalyst removed by filtration and the filtrate concentrated to dryness in vacuo. The residue Is dissolved in water, made alkaline with ammonium hydroxide and extracted with chloroform. After removal of the solvent, the residual oil is distilled to yield ethyl 4-aminocyclohexylcarboxylate, boiling point 114°C to 117°C/10 mm. 

If a considerable quantity of platinum oxide is desired it is more satisfactory to prepare several runs of the size indicated than one large run, since spattering and the evolution of gases make large amounts inconvenient to handle. The activity of the catalyst appeared in certain cases to decrease after standing for several weeks and therefore the oxide should preferably be prepared as required. 

An alternative procedure for the protection of L-sorbose (25), followed by oxidation at C-l and cyclization of the product to L-ascorbic acid, was developed by Hinkley and Hoinowski.257 L-Sorbose (25) was converted into methyl a-L-sorbopyranoside (37) by treatment with methanol and hydrogen chloride.258 Glycoside 37 was then oxidized with air in the presence of a suspension of platinum oxide in aqueous sodium hydrogencarbonate solution at 60°, to afford methyl ot-L-xylo-2-hexulopyranosidonic acid (38), which, when heated in hydrochloric acid, was converted into L-ascorbic acid (1), presumably by way of L-xy/o-2-hexulosonic acid (see Scheme 5). Acid 38 has also been prepared by oxidation of 37 with nitrogen tetraoxide.259,280 Yields were not reported for this reaction sequence, and it appears to offer no potential... 

Preparation of metal oxide thin film by means of stepwise absorption of metal alkoxide has been carried out in the past for the activation of heterogeneous catalysts [13]. For example, Asakura et al. prepared one-atomic layer of niobium oxide by repeating chemisorption of Nb(OEt)5 on silica beads. The catalyst obtained by immobilizing platinum particles on a niobum oxide layer showed improved reactivity for hydrogenation of ethylene in comparison with... 

Freifelder obtained an 82% yield of benzylhydrazine by hydrogenating a freshly prepared hydrazone over Pd-C in ethanol at 0.3 MPa H2 in less than 30 min.83 However, when the hydrazone was allowed to stand for several days to a week, the yield dropped to 45-48%. In the hydrogenation of phenylacetone hydrazone, Biel et al. observed that the formation of large amounts of jV,iV -bis(l -phenyl-2-propylidene)hydrazine took place when hydrogenation proceeded slowly and incompletely with such catalysts as Pd-C, rhodium, ruthenium, and platinum oxide, and with solvents such as alcohol, water, ethyl acetate, tetrahydrofuran, and dioxane. The A(A%disubstituted hydrazine was obtained when the hydrogenation proceeded slowly to completion, as over platinum oxide in aqueous acetic acid. With Raney Ni in ethanol, the azine and l-pheny-2-propylamine were formed almost exclusively. 1-Phenyl-2-propylhy-drazine was obtained in acceptable yields of 55-70% by use of platinum oxide or supported platinum in alcoholic acetic acid at a pressure of 13.8 MPa H2. The products obtained over platinum oxide in various conditions are summarized in eq. 8.40.78... 

One of the major reasons why this reaction is not more widely used is that the catalyst is usually deactivated before the oxidation is completed. This deactivation is thought to be caused by either the oxidation of the metal or the blocking of the metal surface by the strong adsorption of reaction by-products. A number of procedures have been employed to minimize this deactivation. Most of the early work in this area used a large amount of platinum, prepared by the hydrogenation of platinum oxide (Adam s catalyst), as the catalyst.52 These larger metal particles are more resistant to oxidation than the smaller particles present on supported platinum catalysts.63 In addition, the large quantity of catalyst ensures that some active species will still be available toward the end of the reaction. 

K.-I. Machida, A. Fukuoka, M. Ichikawa, M. Enyo, Preparation of platinum cluster-derived electrodes from metal carbonyl complexes and their electrocatalytic properties for anodic oxidation of methanol. J. Electrochem. Soc. 1991, 138(7) 1958-1965. 

Hydroxyisoquinoline was readily converted to the corresponding 1,2,3,4-tetrahydro derivatives under low pressure conditions by means of platinum oxide (176a). When an attempt was made to prepare the corresponding decahydro compound by carrying out the reduction in alcohol in the presence of an active nickel catalyst (11) at 125° and 200 atm only 2-ethyl-5-hydroxydecahydroisoquinoline was obtained. It was necessary first to acetylate the tetrahydro compound and then subject it to further hydrogenation with the same nickel catalyst in order to avoid N-alkylation. 

The ephedrine synthesis described by Manske and Johnson (74) and by Skita and Keil (77) in 1929 is founded on a different reaction. If a mixture of o -phenylpropane-a,/S-dione and methylamine, in absolute alcohol is hydrogenated catalytically in the presence of platinum oxide (Manske) or colloidal platinum (Skita), dl-ephedrine, with a little dJr -ephedrine is obtained. The reaction has been further elaborated by Coles, Manske, and Johnson (76), by Skita, Keil and coworkers (78, 79, 262, 263) and by Couturier (265). Manske and Johnson (75) synthesized some ephedrine homologs and resolved racemic ephedrine by means of d-and f-mandelic acid. The pure I form of this acid is prepared easily with the aid of natural ephedrine, as confirmed by Jarowski and Hartung (268). 

Maehida K, Fukuoka A, lehikawa M, Enyio M. Preparation of platinum eluster-derived eleetrodes from metal earbonyl eomplexes and their eleetrocatalytie properties for anodie oxidation of methanol. J Eleetrochem Soc 1991 138 1958. 

Maillard F, Gloaguen F, Leger JM. Preparation of methanol oxidation electrocatalysts ruthenium deposition on carbon-supported platinum nanoparticles. J Appl Electrochem 2003 33 1-8. 

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