Platinum oxides colloidal

Method 1. From ammonium chloroplatinate. Place 3 0 g. of ammonium chloroplatinate and 30 g. of A.R. sodium nitrate (1) in Pyrex beaker or porcelain casserole and heat gently at first until the rapid evolution of gas slackens, and then more strongly until a temperature of about 300° is reached. This operation occupies about 15 minutes, and there is no spattering. Maintain the fluid mass at 500-530° for 30 minutes, and allow the mixture to cool. Treat the sohd mass with 50 ml. of water. The brown precipitate of platinum oxide (PtOj.HjO) settles to the bottom. Wash it once or twice by decantation, filter througha hardened filter paper on a Gooch crucible, and wash on the filter until practically free from nitrates. Stop the washing process immediately the precipitate tends to become colloidal (2) traces of sodium nitrate do not affect the efficiency of the catalyst. Dry the oxide in a desiccator, and weigh out portions of the dried material as required. 

Reactions. w-Hydroxybenzoic acid affords a variety of products, depending on the catalyst and conditions employed. Catalytic reduction over platinum black or platinum oxide in alkaline solution gives 3-hydroxycyclohexanecarboxylic acid [22267-35-2]. Reduction of a warm aqueous solution over platinum oxide or over colloidal platinum yields cyclohexanecarboxylic acid. w-Hydroxybenzaldehyde can be prepared by reducing ///-hydroxybenzoic acid with sodium amalgam. Finally, reduction over Raney nickel gives cydohexanol. 

Adams Platinum Oxide (by Adams et a/.).148 In a porcelain casserole is prepared a solution of 3.5 g of chloroplatinic acid in 10 ml of water, and to this is added 35 g of sodium nitrate.The mixture is evaporated to dryness while stirring with a glass rod. The temperature is then raised to 350-370°C within 10 min. Fusion takes place, brown oxides of nitrogen are evolved, and a precipitate of brown platinum oxide gradually separates. After 15 min, when the temperature has reached about 400°C, the evolution of gas has gently decreased. After 20 min the temperature should be 500-550°C. The temperature is held until about 30 min have elapsed, when the fusion should be complete. The mass is allowed to cool and is then treated with 50 ml of water.The brown precipitate settles to the bottom and can be washed by decantation once or twice, then filtered, and washed until practically free from nitrates. If the precipitate becomes colloidal, it is better to stop washing immediately at that stage. The oxide is either used directly or dried in a desiccator. The yield is 1.57-1.65 g (95-100% of the theoretical amount). 

Over ruthenium dioxide quinoline was hydrogenated to tetrahydroquinoline in 97.5% yield at 80°C and 8.2 MPa H2 and to decahydroquinoline in 98% yield at 120°C and 9.3 MPa H2.3 Quinoline was also hydrogenated to tetrahydroquinoline over colloidal platinum in neutral solution or as the hydrochloride over platinum oxide in absolute ethanol.30 Hydrogenation to decahydroquinoline was performed with platinum black (Willstatter) or colloidal platinum (Skita) in acetic acid.73,74 Hiickel and Stepf hydrogenated quinoline under almost the same conditions as used by Skita and Meyer, and obtained the decahydroquinoline consisting of approximately 80% of trans and 20% of cis isomers (eq. 12.46). 

Acetylbenzofuran or 2-(l-hydroxyethyl)benzofuran was hydrogenated to 2-(l-hy-droxyethyl)-2,3-dihydrobenzofuran in high yields over Raney Ni in ethanol at room temperature and 0.2-0.3 MPa H2 (eq. 12.1 ll).215 The selective transformation of 2-acetylbenzofuran to 2-(l-hydroxyethyl)benzofuran was successful over platinum oxide in ethanol (eq. 12.111), while the hydrogenation over a colloidal platinum on Norit catalyst from chloroplatinic acid and platinum oxide gave a mixture of 2-(l-hy-droxyethyl)benzofuran, 2-ethylbenzofuran, and their 2,3-dihydro derivatives. 

The most common catalyst for low- and medium-pressure hydrogenation is platinum. Platinum oxide is available from a number of suppliers and is converted to colloidal platinum in situ by hydrogenation. Palladium is another commonly used catalyst and is usually prepared on some inert support such as charcoal, barium sulfate, or calcium carbonate. The procedure for the preparation of these catalysts is given in Organic Syntheses. - A rhodium catalyst appears to be particularly effective in reducing aromatic compounds at low pressure and is available on an alumina support. ... 

An a-dihydrodesoxycodeine , amorphous, alkali-insoluble, and poorly characterized, was reported by Freund [4] to result from the reduction of a-chlorocodide using a colloidal palladium catalyst. A reinvestigation of this reduction, however, showed that under the conditions prescribed by Freund the product consists of 95 per cent. dihydrodesoxycodeine-D with palladized barium sulphate the results are substantially the same, but an amorphous product is obtained in 40 per cent, yield if the amount of catalyst used is large, and this can bo increased to 96-100 per cent, using palladized calcium carbonate and 100 per cent, using platinum oxide as catalyst [29]. The product appears to bo bis- 6 0 -dihydrodosoxycodeino-D [xlvj] and is probably formed... 

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). 

Dendrimer-protected colloids are capable of adsorbing carbon monoxide while suspended in solution, but upon removal from solution and support on a high surface area metal oxide, CO adsorption was nil presumably due to the collapse of the dendrimer [25]. It is proposed that a similar phenomena occurs on PVP-protected Pt colloids because removal of solvent molecules from the void space in between polymer chains most likely causes them to collapse on each other. Titration of the exposed surface area of colloid solution PVP-protected platinum nanoparticles demonstrated 50% of the total metal surface area was available for reaction, and this exposed area was present as... 

Ru(bipy)3 formed in this reaction is reduced by the sacrificial electron donor sodium ethylenediaminetetra-acetic acid, EDTA. Cat is the colloidal catalyst. With platinum, the quantum yield of hydrogenation was 9.9 x 10 . The yield for C H hydrogenation was much lower. However, it could substantially be improv l by using a Pt colloid which was covered by palladium This example demonstrates that complex colloidal metal catalysts may have specific actions. Bimetalic alloys of high specific area often can prepared by radiolytic reduction of metal ions 3.44) Reactions of oxidizing radicals with colloidal metals have been investigated less thoroughly. OH radicals react with colloidal platinum to form a thin oxide layer which increases the optical absorbance in the UV and protects the colloid from further radical attack. Complexed halide atoms, such as Cl , Br, and I, also react... 

Balthis and Bailar6 obtained tris (ethylenediamine) chromium-(III) complexes by the oxidation of chromium(II) solutions, using a procedure somewhat similar to that used for the synthesis of cobalt (III) com plexes. Mori7 described the preparation of hexaamminechromium(III) salts from the oxidation of chromium (II) salts in the presence of ammonia. The results obtained in both syntheses have been erratic.8,9 Berman noted that the foregoing syntheses are rendered dependable by the use of a catalyst of activated platinum on asbestos. Schaeffer,100 in a subsequent study, independently used colloidal platinum as a catalyst but reported some difficulty in separating it from the product.106 The procedures recommended and described here are based on the use of platinized asbestos as the catalyst. 

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