Platinum-charcoal

X-Ray studies confirm that platinum crystallites exist on carbon supports at least down to a metal content of about 0.03% (2). On the other hand, it has been claimed that nickel crystallites do not exist in nickel/carbon catalysts (50). This requires verification, but it does draw attention to the fact that carbon is not inert toward many metals which can form carbides or intercalation compounds with graphite. In general, it is only with the noble group VIII metals that one can feel reasonably confident that a substantial amount of the metal will be retained on the carbon surface in its elemental form. Judging from Moss s (35) electron micrographs of a reduced 5% platinum charcoal catalyst, the platinum crystallites appear to be at least as finely dispersed on charcoal as on silica or alumina, or possibly more so, but both platinum and palladium (51) supported on carbon appear to be very sensitive to sintering. 

More than three decades ago, skeletal rearrangement processes using alkane or cycloalkane reactants were observed on platinum/charcoal catalysts (105) inasmuch as the charcoal support is inert, this can be taken as probably the first demonstration of the activity of metallic platinum as a catalyst for this type of reaction. At about the same time, similar types of catalytic conversions over chromium oxide catalysts were discovered (106, 107). Distinct from these reactions was the use of various types of acidic catalysts (including the well-known silica-alumina) for effecting skeletal reactions via carbonium ion mechanisms, and these led... 

The functionalized dichlorosilane monomers are synthesized generally by radical addition of dichloro-methylsilane to an unsaturated carboxylic acid ester or an unsaturated nitrile. Catalysts used for this purpose are platinum/charcoal (Jl 0,J 1 ), or organic peroxides (T2), but for laboratory syntheses hexachloroplati-nic acid (13,14) proved to be most convenient (scheme 1 a). ... 

The metal-catalysed hydrogenation of the higher olefins exhibit general features which are similar to those observed with the n-butenes. Thus, for example, the hydrogenation of hex-1-ene over Adams platinum catalyst [144] is accompanied by very low amounts of double-bond migration the relative rates of isomerisation and hydrogenation are in the ratio 0.03 1. Similarly, in the liquid phase hydrogenation of the n-pentenes over platinum—charcoal and iridium—charcoal [145], little or no isomerisation... 

If a catalyst mass contains only one type of catalytic site we shall call it a monofunctional catalyst. By one type is meant that every catalytic site or surface exhibits the same qualitative catalytic property as to what reaction or reaction steps it can catalyze. We shall concern ourselves only, of course, with reaction steps which are thought to be relevant to the reaction examined. For example, we normally assume that platinum/charcoal is a monofunctional catalyst in the hydrogenation of olefins. (For the present purpose we need not be concerned about the quantitative equivalence of every Pt-surface site, i.e., whether or not there is uniformity or a spectrum of catalytic effectiveness for the same reaction among different platinum sites.)... 

A palladium-platinum-charcoal catalyst appears to be particularly effective for the dehydrogenative coupling of two benzene rings with formation of a third such ring, as in the conversion of o-terphenyl (8) to triphenylene (9), and of 1,1 -dinaphthyl (10) to perylene (II). The catalyst is prepared by adding 400 g. of granular... 

The first examples of skeletal rearrangements on metals were reported by the Soviet school of catalysis. A major step in hydrocarbon chemistry was the finding that platinum, unlike palladium and nickel, selectively catalyzes the hydrogenolysis of cyclopentane hydrocarbons. At about 300°C, on the classical Zelinskii platinum-charcoal catalyst, cyclopentane yields -pentane as sole reaction product (3, 4), while palladized charcoal is completely inactive (J) and nickel-alumina produces all the possible acyclic hydrocarbons, from methane to pentane (5-7). 

Dehydrocyclization of straight-chain or branched acyclic alkanes—the reverse of the hydrogenolysis of cyclopentanes—takes place on the same platinum-charcoal catalyst under similar conditions. This reaction is often accompanied by aromatization (20-27) (Scheme 4). 

As developed in the introduction, a number of important features in hydrogenolysis of cycloalkanes on platinum-charcoal catalysts emerges from the work of the Soviet school of catalysis. In a different approach, the hydrogenolysis of methyl- and 1,3-dimethylcyclopentanes was investigated on a series of platinum-alumina catalysts with various metal loadings (0.2-20%) (84, 85). It was found that the product distribution changed substantially with the percentage of platinum on the carrier. An almost selective... 

Similarly slow rates of isomerization have been observed in the hydrogenation of the w-pentenes in the liquid phase over platinum-charcoal (58) and of 1-hexene in the liquid phase over Adams platinum (14) (see Fig. 15). In the latter reaction, which was also studied using deuterium, the relative rates of addition, olefin exchange and double-bond migration were 1 0.3 0.03. The deuterohexane distribution was therefore slightly conversion-dependent (see Table XV). 

Catalytic hydrogenation of nitrosamines to A, A-di substituted hydrazines is effected in water or aqueous alcohol with 10% palladium-charcoal, 10% platinum-charcoal, or 5% rhodium-charcoal as catalyst,132 in the presence of a salt (e.g., calcium chloride, ammonium acetate, or lithium chloride) at temperatures between 25° and 60° for example, 0.2 mole of 4-nitrosomorpholine in a solution of 30 g of calcium chloride in 150 ml of water is stirred with 2 g of 10% palladium-charcoal under a hydrogen pressure of 3-4 atm for 22 hours at 60°, thereby affording an 82.7% yield of 4-aminomorpholine. 

Dehydration of cyclopentanemethanol over aluminum oxide at 320° tgave an olefin mixture whence hydrogenation afforded a mixture (94%) of [14C]methylcyclopentane with about 34% of [14C]cyclohexane. The mixed cycloalkanes were transformed into [14C]cyclo-hexane by Nenitzescu and Cantuniari s method,154 and dehydrogenation on a platinum-charcoal catalyst at 360° then yielded [14C1]benzene. 

The products of catalytic reduction of chromone-2-carboxylic acids or esters depend partly on the catalyst used, the amount of hydrogen present and the conditions of reaction. Ethyl chromone-2-carboxylate is reduced (in 86 per cent yield) to the corresponding chromanone in the presence of Raney nickel and hydrogen at a pressure of 50 Ib/in [184]. The 5-hydroxy analogue is similarly reduced at 80°C and 30 Ib/in in 44 per cent yield [8]. A nitro group on the benzene ring is more readily hydrogenated than the pyrone double bond (10 atmospheres, platinum-charcoal or palladium-charcoal catalyst) [24,40]. 

Preparation of 30 per cent, palladium or platinum catalysts (charcoal or asbestos carrier). 

Method A. Cool a solution of the nitrate-free dichloride, prepared from or equivalent to 5 0 g. of palladium or platinum, in 50 ml. of water and 5 ml. of concentrated hydrochloric acid in a freezing mixture, and treat it with 50 ml. of formahn (40 per cent, formaldehyde) and 11 g. of the carrier (charcoal or asbestos). Stir the mixture mechanically and add a solution of 50 g. of potassium hydroxide in 50 ml. of water, keeping the temperature below 5°. When the addition is complete, raise the temperature to 60° for 15 minutes. Wash the catalyst thoroughly by decantation with water and finally with dilute acetic acid, collect on a suction filter, and wash with hot water until free from chloride or alkali. Dry at 100° and store in a desiccator. 

Broadly speaking, the differences in effectiveness of palladium and platinum catalysts are very small the choice will generally be made on the basis of availability and current price of the two metals. Charcoal is a somewhat more efficient carrier than asbestos. 

Reaction with Hydrogen and Metals. Bromine combines directiy with hydrogen at elevated temperatures and this is the basis for the commercial production of hydrogen bromide [10036-10-6]. Heated charcoal and finely divided platinum metals are catalysts for the reaction (17). 

Nitropyridazines are reduced catalytically either over platinum, Raney nickel or palladium-charcoal catalyst. When an N-oxide function is present, palladium-charcoal in neutral solution is used in order to obtain the corresponding amino N-oxide. On the other hand, when hydrogenation is carried out in aqueous or alcoholic hydrochloric acid and palladium-charcoal or Raney nickel are used for the reduction of the nitro group, deoxygenation of the N- oxide takes place simultaneously. Halonitropyridazines and their N- oxides are reduced, dehalogenated and deoxygenated to aminopyridazines or to aminopyridazine N- oxides under analogous conditions. 

Benzoic acid [65-85-0] M 122.1, m 122.6-123.1, pK 4.12. For use as a volumetric standard, analytical reagent grade benzoic acid should be carefully fused to ca 130 (to dry it) in a platinum crucible, and then powdered in an agate mortar. Benzoic acid has been crystd from boiling water (charcoal), aq acetic acid, glacial acetic acid, C6H6, aq EtOH, pet ether (b 60-80 ), and from EtOH soln by adding water. It is readily purified by fractional crystn from its melt and by sublimation in a vacuum at 80. ... 

The most commonly used catalysts are palladized charcoal or calcium carbonate and platinum oxide. For better isotopic purity, the use of platinum oxide may be preferred for certain olefins since the substrate undergoes fewer side reactions while being chemisorbed on the platinum surface as compared to palladium.Suitable solvents are cyclohexane, ethyl acetate, tetrahydrofuran, dioxane or acetic acid-OD with platinum oxide. 

Catalytic reduction of quinazolines unsubstituted in position 4 using palladium-charcoal, palladium on calcium carbonate, Raney nickel, or Adam s platinum has been used for preparing 3,4-dihydro-... 

Simple l,2,3,4-tetrahydro-)3-carbolines have been aromatized in this manner. Palladium black at 160-170° or at higher temperature, palladium-maleic acid in aqueous solution, and platinum/oxygen have been used for the purpose. Palladium-on-charcoal in a high-boiling solvent has been used also to aromatize 5,6,7,8-tetrahydro-j3-carbohnes and 6,7,8,9-tetrahydro-3-carbo-hne. ... 

Platinum and palladium are the most common catalysts for alkene hydrogenations. Palladium is normally used as a very fine powder supported" on an inert material such as charcoal (Pd/C) to maximize surface area. Platinum is normally used as PtC, a reagent called Adams catalyst after its discoverer, Roger Adams. 

Reductions of 5//-dibenz[/j,/]azepines to their 10,11-dihydro derivatives have been accomplished in high yield with sodium in ethanol,29 133 with copper(II) chromite (2CuO Cr203) and barium carbonate,224 with 5 % palladium on charcoal29 or platinum(IV) oxide30 in ethanol, and with magnesium in methanol.225 4//-Thieno[3,2-/)][1]benzazepine is reduced similarly with hydrogen and palladium on charcoal in ethanol.137... 

Platinum catalysts were prepared by ion-exchange of activated charcoal. A powdered support was used for batch experiments (CECA SOS) and a granular form (Norit Rox 0.8) was employed in the continuous reactor. Oxidised sites on the surface of the support were created by treatment with aqueous sodium hypochlorite (3%) and ion-exchange of the associated protons with Pt(NH3)42+ ions was performed as described previously [13,14]. The palladium catalyst mentioned in section 3.1 was prepared by impregnation, as described in [8]. Bimetallic PtBi/C catalysts were prepared by two methods (1) bismuth was deposited onto a platinum catalyst, previously prepared by the exchange method outlined above, using the surface redox reaction ... 

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