Platinum effect

Palladium on charcoal (Pd/C) is commonly used in the catalytic hydrogenation of pyrimidines in acidic media to form 1,2,4,5-tetrahydro derivatives which are stabilized as amidinium salts (62JOC2170, 65JCS1406). Platinum effects hydrogenation of the 5,6-double bond of uracils, for example, in the addition of deuterium to produce [5,6-2H2]5,6-dihydrouracil. The use of rhodium-on-charcoal and Raney nickel also gives good results. The addition of hydrogen to the 5,6-bond of thymidine and other 5-substituted uridines is stereospecific with rhodium-on-alumina as catalyst. 

At 1600° C. platinum effects the reduction of both ferric oxide and ferrosoferric oxide in air, oxygen being evolved and a solid solution of iron in platinum remaining as residue. The same reaction obtains at lower temperatures, namely, at 1200° C., if the oxygen pressure is very small. This explains why platinum crucibles sometimes increase in weight when used to heat oxides of iron at high temperatures.2... 

Bond energy contributions and total Bond energy (eV) of CO adsorbed to (111) face of platinum. Effect of alkali coadsorptiont. ... 

Lead reacts with metals such as rhodium, palladium, and platinum, effectively covering these metals and ehminating their catalytic activity. 

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. 

Ruthenium is a hard, white metal and has four crystal modifications. It does not tarnish at room temperatures, but oxidizes explosively. It is attacked by halogens, hydroxides, etc. Ruthenium can be plated by electrodeposition or by thermal decomposition methods. The metal is one of the most effective hardeners for platinum and palladium, and is alloyed with these metals to make electrical contacts for severe wear resistance. A ruthenium-molybdenum alloy is said to be... 

The uncatalyzed addition of hydrogen to an alkene although exothermic is very slow The rate of hydrogenation increases dramatically however m the presence of cer tain finely divided metal catalysts Platinum is the hydrogenation catalyst most often used although palladium nickel and rhodium are also effective Metal catalyzed addi tion of hydrogen is normally rapid at room temperature and the alkane is produced m high yield usually as the only product... 

The most obvious way to reduce an aldehyde or a ketone to an alcohol is by hydro genation of the carbon-oxygen double bond Like the hydrogenation of alkenes the reac tion IS exothermic but exceedingly slow m the absence of a catalyst Finely divided metals such as platinum palladium nickel and ruthenium are effective catalysts for the hydrogenation of aldehydes and ketones Aldehydes yield primary alcohols... 

In this pyrolysis, sub atmospheric partial pressures are achieved by employing a diluent such as steam. Because of the corrosive nature of the acids (HE and HCl) formed, the reactor design should include a platinum-lined tubular reactor made of nickel to allow atmospheric pressure reactions to be mn in the presence of a diluent. Because the pyrolysate contains numerous by-products that adversely affect polymerization, the TFE must be purified. Refinement of TFE is an extremely complex process, which contributes to the high cost of the monomer. Inhibitors are added to the purified monomer to avoid polymerization during storage terpenes such as t7-limonene and terpene B are effective (10). 

The main cause of anode wear is electrochemical oxidation or sulfur attack of anodic surfaces. As copper is not sufficiently resistant to this type of attack, thin caps of oxidation and sulfur-resistant material, such as platinum, are bra2ed to the surface, as shown in Eigure 15a. The thick platinum reinforcement at the upstream corner protects against excessive erosion where Hall effect-induced current concentrations occur, and the interelectrode cap protects the upstream edge from anodic corrosion caused by interelectrode current leakage. The tungsten undedayment protects the copper substrate in case the platinum cladding fails. 

Impurities in cmde metal can occur as other metals or nonmetals, either dissolved or in some occluded form. Normally, impurities are detrimental, making the metal less useful and less valuable. Sometimes, as in the case of copper, extremely small impurity concentrations, eg, arsenic, can impart a harmful effect on a given physical property, eg, electrical conductivity. On the other hand, impurities may have commercial value. For example, gold, silver, platinum, and palladium, associated with copper, each has value. In the latter situation, the purity of the metal is usually improved by some refining technique, thereby achieving some value-added and by-product credit. 

Platinum compounds are the most active catalysts for hydrosilylation. Compounds such as and PtCl2(CH2CHCOCH2)2 are effective. In the... 

Oxidation. Carbon monoxide can be oxidized without a catalyst or at a controlled rate with a catalyst (eq. 4) (26). Carbon monoxide oxidation proceeds explosively if the gases are mixed stoichiometticaHy and then ignited. Surface burning will continue at temperatures above 1173 K, but the reaction is slow below 923 K without a catalyst. HopcaUte, a mixture of manganese and copper oxides, catalyzes carbon monoxide oxidation at room temperature it was used in gas masks during World War I to destroy low levels of carbon monoxide. Catalysts prepared from platinum and palladium are particularly effective for carbon monoxide oxidation at 323 K and at space velocities of 50 to 10, 000 h . Such catalysts are used in catalytic converters on automobiles (27) (see Exhaust CONTHOL, automotive). 

Cumulative organ toxicity also presents a significant obstacle for effective chemotherapy. In many cases, the severity of the toxicity impedes the broader use of an agent. Other specific toxicities are associated with specific agents, for example cardiotoxicity with adriamycin (32), renal toxicity with i7j -platinum (28), and neurotoxicity with vincristine (49). 

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