Platinum black

Aqueous solutions of hydrogen peroxide decompose slowly the decomposition is catalysed by alkalis, by light and by heterogeneous catalysts, for example dust, platinum black and manganese... 

The second reaction is favoured by sunlight and by catalysts such as platinum black or metallic oxides (cf. the decomposition of... 

It is advisable to test a small portion of the filtrate for platinum by acidifying with hydrochloric acid and adding a few drops of stannous chloride solution a yellow or brown colour develops according to the quantity of platinum pVesent. The yellow colour is soluble in ether, thus rendering the t t more sensitive. If platinum is found, treat the filtrate with excess of formaldehyde and sodium iQrdroxide solution and heat,- platinum black septarates on standing and may be filtered and worked up with other platinum residues (see Method 3). 

Heating metallic lithium in a stream of gaseous ammonia gives lithium amide [7782-89-0] LiNH2, which may also be prepared from Hquid ammonia and lithium in the presence of platinum black. Amides of the alkaH metals can be prepared by double-decomposition reactions in Hquid ammonia. For example... 

Reduction of vanillin by means of platinum black in the presence of ferric chloride gives vanillin alcohol in excellent yields. In 1875, Tiemann reported the reduction of vanillin to vanillin alcohol by using sodium amalgam in water. The yields were poor, however, and there were a number of by-products. High yields of vanillin alcohol have been obtained by electrolytic reduction. 

The packaging approach utilized for tliis battery is similar to that for nickel—hydrogen single cylindrical cells as shown in Figure 23. The sdv er electrode is typically the sintered type used in rechargeable sdv er—zinc cells. The hydrogen electrode is a Teflon-bonded platinum black gas difhision electrode. 

Dihydrocholesterol has been prepared by the reduction of cholestenone with sodium and amyl alcohoP and by the hydrogenation of cholesterol. In the presence of platinum black or platinum oxide, yields varying from 6.5 per cent to 40 per cent have been obtained in ether, acetone, ethyl acetate, and acetic acid. ... 

Platinum Catalyst for Reductions (Coll. Vol. i, 452) Preparation from platinum black by heating with oxygen underpressure. Laffiteand Grandadam, Compt. rend. 200, 456 (193s). 

A mixture of A,A-dimethylcyclohexylmethylamine (49.4 g, 0.35 mole. Chapter 2, Section I), 30% hydrogen peroxide (39.5 g, 0.35 mole) and 45 ml of methanol is placed in a 500-ml Erlenmeyer flask, covered with a watch glass, and allowed to stand at room temperature. After 2 hours, and again after an additional 3 hours, 30% hydrogen peroxide (39.5-g portions each time) is added with swirling. The solution is allowed to stand at room temperature for an additional 30 hours, whereupon excess peroxide is destroyed by the cautious addition (swirling) of a small amount of platinum black. Cessation of oxygen evolution indicates complete decomposition of the excess peroxide. 

Sabinene appears to be fairly closely related to thujene (tanacetene), since both a-thujene and /3-thujene yield the same body, thujane CjjHjg, as does sabinene when reduced by hydrogen in the presence of platinum black. 

Its low specific gravity indicates that it is an open-chain compound, and from its easy reduction by sodium and alcohol, into dihydroaplotaxene, and by hydrogen and platinum black into normal heptadecane OjjHj,., it is evident that aplotaxene is a tetraolefinic normal chain hydrocarbon. 

G. Vavon has examined the hydrogenation of carvone, in presenc of platinum black as a catalyst, and shown that it takes place in three entirely distinct phases. Carvone fixes successively three molecules of hydrogen, giving dextro-carvotanacetone, then tetrahydrocarvone, and finally carvomenthol. 

A solution of 20 g of 1 -isonicotinyl-2-isopropy lidene hydrazine in 1 50 cc of methanol was reduced with hydrogen at room temperature and 50 psi using 300 mg of platinum black as a catalyst. 

This procedure may be varied in certain cases where it seems advantageous to reduce the platinum oxide to platinum black in the presence of the solvent alone (see Note 12, p. 98). 

The platinum black by reduction of the oxide may sometimes be used a second, third or even more times in the reduction of certain compounds merely by reactivating (Note 8) with air or oxygen. A spent catalyst must be reworked (Note 9)... 

The products prepared at temperatures below 450° and above 600 0 have a lower activity and require a greater length of time for reduction to platinum black than those prepared at temperatures between 450° and 6oo°. 

The brown oxide is a heavy granular powder which settles to the bottom of the solution in the bottle in which the reduction is carried out (p. 10). It must be reduced to platinum black before it becomes a catalyst for the reduction. When the hydrogen is admitted and the bottle shaken the brown oxide becomes black and whips up into a fine suspension. The time necessary for the change of the oxide to platinum black is called the lag. The time of lag varies usually from several seconds to two or three minutes, depending upon the conditions under which... 

In certain reductions it is an advantage to reduce the platinum oxide to platinum black by shaking with hydrogen in the presence of solvent only, before the substance to be reduced is added to the mixture. More often the catalyst is reduced in the presence of the substance to be reduced with aldehydes for example the platinum black is usually more finely divided and generally more active if prepared in presence of the aldehyde. 

Platinic oxide has been prepared previously by the interaction of platinic chloride and excess sodium hydroxide.4 Since the catalyst itself is platinum black, the other methods for its preparation are given below. 

Platinum black has been prepared chiefly by the reduction of chloroplatinic acid with formaldehyde 5 the details have been improved by Willstatter and Hatt 6 Willstatter and Waldschmidt-Leitz,7 and by Feulgen.8... 

Recently it was demonstrated that a platinum black-PTFE electrode, originally designed for a fuel cell, is excellent for the chlorination of double bonds and, depending on the other electrolysis conditions, it was possible to isolate the dichlorocompound or the chlorohydrin (Danger and Yurchak, 1970). Moreover, if a chlorine cathode is used, the overall process occurs with a net output of energy, i.e. the cell may do external work and the procedure has been named electrogenerative chlorination . 

Investigations at Siemens in Erlangen, Germany, have used unsupported platinum-ruthenium anodes (4 mg/cm ) and platinum black cathodes (4 mg/cm ). Their best performances were 0.52 V at 400 mA/cml At Los Alamos National Laboratory in New MexicoJ the electrocatalyst was unsupported R-RuOx at the anode and unsupported R black at the cathode (R loading about 2 mg/cm ). In a subsequent study, the thinner Nafion 112 membrane was used to reduce the ohmic drop. Under pressure at 400 mA/cm cell potentials of 0.57 V with Oj and 0.52... 

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