Platinum dioxide, reaction

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). 

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. 

For example, the reaction of nitronates (123) with a zinc copper pair in ethanol followed by treatment of the intermediate with aqueous ammonium chloride a to give an equilibrium mixture of ketoximes (124) and their cyclic esters 125. Heating of this mixture b affords pyocoles (126). Successive treatment of nitronates (123) with boron trifluoride etherate and water c affords 1,4-diketones (127). Catalytic hydrogenation of acyl nitronates (123) over platinum dioxide d or 5% rhodium on aluminum oxide e gives a-hydroxypyrrolidines (128) or pyrrolidines 129, respectively. Finally, smooth dehydration of a-hydroxypyrrolidines (128) into pyrrolines (130f) can be performed. 

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. 

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 ... 

In fact, the sole product is 29, because in this case p-hydride elimination occurs more slowly than the competing second carbo-palladination Vinylpalladium species 29 is converted via 30 into product 31 through a cross-coupling reaction with dimethyl/inc. Subsequent hydrogenation of the terminal double bound of 31 with platinum dioxide in acetic acid ethyl acetate in a second reaction results in product 11... 

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. 

The reaction of a molten mixture of 3,4-dihydro-2//-pyrido[ 1,2-a] pyrimidin-2-one 675 and phosphorous acid with phosphorus trichloride, followed by treatment of the reaction mixture with 2 N aqueous hydrochloric acid, afforded 3,4-dihydropyridopyrimidine-2,2-diphosphoric acid 676 in 38% yield (91GEP3930130). Catalytic reduction of diphosphonic acid 676 in water over platinum dioxide gave hexahydropyrido[l,2-a]pyrimi-dine-2,2-diphosphonic acid 677. 

Later it was described the synthesis of the donepezil HCI from 5,6-dimethoxy-2-(pyridin-4-yl)methylene-indan-l-one by the reaction with H2 over platinum dioxide at room temperature in acetic acid-methanol mixture to give 4-[(5,6-dimethoxy-l-indanon)-2-yl]methylpiperidine. The last one yielded donepesyl HCI by refluxing with benzyl bromide and triethylamine for 4 hours with the following addition of methanolic HCI (10%). 

Reaction of Platinum Dioxide with Some Metal Oxides... 

The structure of platinum dioxide and its reactions with some di, tri, and tetravalent metal oxides have been investigated. Ternary platinum oxides were synthesized at high pressure (40 kUobars) and temperature (to 1600°C). Properties of the systems were studied by x-ray, thermal analysis, and infrared methods. Complete miscibility is observed in most PtO2-rutile-type oxide systems, but no miscibility or compound formation is found with fluorite dioxides. Lead dioxide reacts with Pt02 to form cubic Pb2Pt207. Several corundum-type sesquioxides exhibit measurable solubility in PtOz. Two series of compounds are formed with metal monoxides M2PtOh (where M is Mg, Zn, Cd) and MPt306 (where M is Mg, Co, Ni, Cu, Zn, Cd, and Hg). 

The reaction of platinum dioxide with other metal dioxides can be separated into three groups—i.e., compounds with metal-oxygen coordination numbers of 4 2, 6 3, and 8 4. We have investigated only a single... 

Taking advantage of the slow hydrogenation of carbon-carbon double bonds at room temperature in the presence of platinum dioxide, it was possible to perform the ruthenium-catalyzed cross coupling reaction of electron-deficient olefins such as conjugated enones and acrylic derivatives with allyl silanes in the presence of Pt(>2 under hydrogen (Scheme 46) [99]. Prolonged... 

Several high-temperature procedures have been described in the literature for the preparation of the transition-metal dioxides. Direct oxidation of the metals, lower oxides, chlorides, or nitrate precursors provides a convenient route to the dioxides of several metals Ti, Mn, Ru, Rh, Os, Ir, and Pt.1,3-5 (Syntheses of the rutile forms of rhodium and platinum dioxides by direct oxidation requires application of high pressures.5) Reduction of higher oxides is the most common method of synthesis for these dioxides V02, Nb02, Mo02, W02, and /3-Re02.4,6-8 Stoichiometry in these reactions is most readily controlled by use of the respective metal or a lower oxide as reductant. Chromium dioxide is normally synthesized by hydrothermal reduction of the trioxide.9... 

The conversion of primary alcohols into carboxylic acids is not a difficult task. Often, the same oxidant that has been used to oxidize alcohols to aldehydes is applicable to the oxidation to acids when used in appropriate amounts, in different solvents, at higher temperatures, or at longer reaction times. An example is the oxidation of primary alcohols with air or oxygen with platinum-on-charcoal or, better still, platinum dioxide as catalyst (equation 228) [56]. 

Industry uses mainly combinations of catalysts laboratory processes employ mainly Raney nickel, platinum, platinum dioxide, or palladium, the last of these often on a carrier such as charcoal or barium sulfate. Since it is only the reduced surface of a. platinum dioxide catalyst that is active and reduction of the oxide to the metal is checked by adsorption of nitro compounds (particularly if aromatic), it is advisable to reduce this catalyst in a preliminary operation. When platinum dioxide is used in solvents of differing acidities, the rate of reaction increases in the following order neutral > alkaline > acid solution > glacial acetic acid. 

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°. 

Carbon monoxide (CO) and oxygen (Og) combine to form carbon dioxide (CO2). Carrying out the reaction ne a clean platinum surface greatly speeds up the reaction at ordinary temperatures and pressures. Students of the platinum-catalyzed reaction, notably Bodenstein and Fink in 1907, had shown the rate of the reaction to be directly proportional to the oxygen concentration, and inversely proportional to the carbon monoxide concentration. This contrasts with the uncatalyzed reaction. Its rate is directly proportional to both O2 and CO concentrations.(4)... 

---