Platinum dioxide, hydrogenation catalyst

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). 

Because of the possibility of racemization during the transesterification reaction (strong basic conditions) alternative methods are reported. These include transesterification in the presence of the KF/18-crown-6 ether 461 or the use of titanium tetraalkoxides. 471 The methods are efficient and represent a route to any required dialkyl ester using diphenyl esters as starting materials. Diphenyl groups can also be removed by hydrogenation in the presence of platinum dioxide (Adams catalyst) to provide the free phosphonic acid moiety directly)46 ... 

Platinum in a finely divided form is obtained by the in situ reduction of hydrated platinum dioxide (Adams catalyst) finely divided platinum may also be used supported on an inert carrier such as decolourising carbon. Finely divided palladium prepared by reduction of the chloride is usually referred to as palladium black. More active catalysts are obtained however when the palladium is deposited on decolourising carbon, barium or calcium carbonate, or barium sulphate. Finely divided ruthenium and rhodium, usually supported on decolourising carbon or alumina, may with advantage be used in place of platinum or palladium for some hydrogenation reactions. 

Cyclopropane rings are opened hydrogenolytically, e.g., over platinum on platinum dioxide (Adam s catalyst) in acetic acid at 2 - 4 bars hydrogen pressure. The bond, which is best accessible to the catalyst and most activated by conjugated substituents, is cleaved selectively (W.J. Irwin, 1968 R.L. Augustine, 1976). Synthetically this reaction is useful as a means to hydromethylate C—C double bonds via carbenoid addition (see p. 74f. Z. Majerski, 1968 C.W. Woodworth, 1968). 

The hydrogenation of pyrazolylacetylenes shows no peculiarities. Ethynylpyra-zoles are hydrogenated in high yields to the corresponding ethane derivatives on Raney nickel catalyst, platinum dioxide, or palladium catalyst at room temperature in alcohol solution. 

To 20 g of the above compound dissolved in 300 ml 95% ethanol In a Parr reaction vessel is added 1.5 g Adams catalyst, platinum dioxide, and the mixture shaken under hydrogen at 50 psi for 1 hour at ambient temperature. The mixture Is then filtered and the ethanol removed on a standard rotary evaporator. The resulting oil is dissolved in 200 ml ether and slowly added to 1,200 ml ether with continuous stirring. The product separates as crystals which are removed after 15 to 30 minutes by filtration. The compound melts at 148°C to 147°C and needs no further purification. 

Some catalysts used in gasoline manufacture consist of finely divided platinum supported on an inert solid. Suppose that the platinum is formed by the high temperature reaction between platinum dioxide, PtOj, and hydrogen gas to form platinum metal and water. 

Poisoning of platinum fuel cell catalysts by CO is undoubtedly one of the most severe problems in fuel cell anode catalysis. As shown in Fig. 6.1, CO is a strongly bonded intermediate in methanol (and ethanol) oxidation. It is also a side product in the reformation of hydrocarbons to hydrogen and carbon dioxide, and as such blocks platinum sites for hydrogen oxidation. Not surprisingly, CO electrooxidation is one of the most intensively smdied electrocatalytic reactions, and there is a continued search for CO-tolerant anode materials that are able to either bind CO weakly but still oxidize hydrogen, or that oxidize CO at significantly reduced overpotential. 

Platinum (IV) oxide (Pt" + 20 —> Pt O ) is also known as platinum dioxide. It is a dark-brown to black powder known as Adams catalyst that is used as a hydrogenation catalyst. 

Unsaturated amines are hydrogenated at the multiple bonds by catalytic hydrogenation over any catalyst. The double bond in indole was saturated in catalytic hydrogenation over platinum dioxide in ethanol containing fluoro-boric acid and indoline was obtained in greater than 85% yield [456. AUylic amines such as allylpiperidine are also reduced by sodium in liquid ammonia in the presence of methanol (yield 75%) [709. ... 

Platinum dioxide, also known as Adams catalyst, is used commercially in many hydrogenation reactions at ordinary temperatures, such as reduction of olefinic and acetylenic unsaturation, aromatics, nitro, and carbonyl groups. 

Carnahan et al. obtained good yields of alcohols and glycols by hydrogenation of lower mono- and dicarboxylic acids over ruthenium dioxide or Ru-C at 135-225°C and 34-69 MPa H2 (eqs. 10.1 and 10.2).8 In general, the optimum temperature was about 150°C. The chief side reaction was hydrogenolysis of the alcohols, as exemplified in the formation of ethanol from oxalic acid and of butanol and propanol from succinic acid (see eq. 10.2). Platinum and palladium catalysts were ineffective under similar or even more severe conditions. 

PLATINUM (7440-06-4) Pt Powdered form is highly reactive catalyst, and may cause fire and explosions on contact with many substances including oxidizers, acetone, strong acids, finely divided aluminum, dioxygen difluoride, ethyl alcohol, hydrazine, hydrogen peroxide, lithium, methyl hydroperoxide, nitrosyl chloride, ozonides, peroxymonosulfliric acid, red phosp] oms. Incompatible with ammonia, arsenic, chlorine dioxide, hydrogen, methyl hydroperoxide, selenium, tellurium, vanadium dichloride. 

D, L-Lysine dihydrochloride 23 Diethyl a-(acetylamino)-a-(3-cyanopropyl)malonate (15 g) is dissolved in freshly distilled acetic anhydride (100 ml), platinum dioxide (0.5 g) is added, and hydrogenation carried out at an initial pressure of 3 atm. Absorption is complete in 3 h. The catalyst is removed, and the acetic anhydride is hydrolysed by cautious addition of water (25 ml). The A,A-diacetyllysine is then cleaved by boiling it for 18 h in acetic acid solution containing concentrated hydrochloric acid (d 1.19 100 ml). Evaporation then affords d,l-lysine dihydrochloride (9g, 77%), m.p. 175-180°, which, after dissolution in anhydrous ethanol and precipitation by ether, melts at 187-188°. 

A silk catalyst of especial efficiency has been developed for hydrogenation of aromatic nitro compounds.51 Boiling silk fibroin fibres with an aqueous solution of potassium tetrachloroplatinate affords a brown, hair-like silk-platinum chelate from which the actual black silk catalyst is obtained by hydrogenation at 9 atm in the presence of 1 % acetic acid. Its activity, calculated on platinum content, for hydrogenation of nitrobenzene to aniline, is 250 times that of platinum dioxide. 

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°. 

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