Ruthenium Finely divided

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... 

Ruthenium and Os are stable to atmospheric attack though if Os is very finely divided it gives off the characteristic smell of OSO4. By contrast, iron is subject to corrosion in the form of rusting which, because of its great economic importance, has received much attention (see Panel above). 

The goal of Haber s research was to find a catalyst to synthesize ammonia at a reasonable rate without going to very high temperatures. These days two different catalysts are used. One consists of a mixture of iron, potassium oxide. K20, and aluminum oxide. Al203. The other, which uses finely divided ruthenium, Ru. metal on a graphite surface, is less susceptible to poisoning by impurities. Reaction takes place at 450°C and a pressure of 200 to 600 atm. The ammonia... 

Dissolution of a zinc-ruthenium alloy in hydrochloric acid leaves an explosive residue of finely divided ruthenium [1], More probably this is the hydride, which may decompose on slight stimulus, the evolved hydrogen probably igniting because of the catalytic activity of the metal. Ruthenium prepared from its compounds by borohydride reduction is especially dangerous in this respect [2],... 

The most commonly used catalysts for hydrogenation (finely divided platinum, nickel, palladium, rhodium, and ruthenium) apparently serve to adsorb hydrogen molecules on their surface. 

When recovered from the mineral osmiridium, the mineral is fused with zinc to convert it into a zinc alloy. The alloy is then treated with hydrochloric acid to dissolve the zinc away leaving a finely divided material. This finely divided sohd then is fused with sodium peroxide and caustic soda to convert osmium and ruthenium into their water-soluble sodium salts, sodium osmate and sodium iridate, respectively. While osmium is fully converted to osmate salt, most ruthemium and a small part of iridium are converted to ruthenate and iridate, respectively. The fused mass is leached with water to separate metals from sohd residues. 

When finely-divided Ru metal is heated with carbon monoxide under 200 atm pressure, ruthenium converts to pentacarbonyl, Ru(CO)5, a colorless liquid that decomposes on heating to diruthenium nonacarbonyl, Ru2(CO)g, a... 

The most active catalyst is platinum applied in finely divided form, for example platinised asbestos. Certain elements, especially arsenic and mercury, have a powerful effect in reducing the activity of the platinum, a quantity of arsenic equal to 0-2 per cent, of the weight of the platinum reducing the activity by 50 per cent.5 These poisons, as they are termed, also include less harmful substances such as antimony, lead, bismuth, etc. The presence of small quantities of rhodium, iridium or osmium in the platinum also causes diminished yields of trioxide, but the presence of palladium or ruthenium has the opposite effect.6... 

The finely divided metal is soluble in hypohalites if an excess of alkali is present. At red heat, the metal combines with C z to form the dichlondc. Ruthenium(VIIl) oxide is formed when an alkaline ruthenium solution is treated with a strong oxidant, such as chlorine, or bromate ion when the Ru is in acid solution,... 

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. 

Finely divided ruthenium acts as a catalyser, inducing, for example, the oxidation of alcohol to aldehyde and acetic acid in the presence of air. 

Explosive Ruthenium is obtained by dissolving an alloy of the metal with excess of zinc in hydrochloric acid. The zinc passes into solution, leaving metallic ruthenium as a finely divided, explosive residue. Unlike rhodium and iridium, ruthenium is explosive even when prepared in the entire absence of air. It seems hardly possible, therefore, that the same explanation for the explosivity can apply as for the first two metals (see pp. 156, 239). Perhaps Bunsen s original explanation is the correct one, namely, that an unstable modification or allotrope is first formed, and that this is converted into the stable variety with considerable heat evolution.7... 

Ruthenium Fluoride, RuFa, results as a volatile substance when the finely divided metal is heated to redness in fluorine. It occurs under these conditions as a dense, coloured vapour.3... 

Ruthenium tetroxide dissolves to a slight extent in water. It is also soluble in caustic alkali, from which solutions a black precipitate of finely divided ruthenium is obtained on addition of alcohol.2 Both the aqueous solution and the pure substance itself possess an odour resembling that of ozone. Its vapour, however, is not poisonous like that of the corresponding tetroxide of osmium. In contact with alcohol the solid tetroxide is reduced with explosive violence.3-4 When covered with water, to which a concentrated solution of caesium chloride is subsequently added and a little hydrochloric acid, ruthenium tetroxide is gradually converted into the oxy-salt, Cs2Ru02CI4. The corresponding rubidium salt has likewise been prepared.3... 

Ruthenium tetroxide is permanent when kept in sealed tubes in the dry state and protected from light. Exposed to light it assumes a brown colour, but the brown product is soluble in alkali, yielding a ruthenate. Presumably the coloration is due to partial reduction. Owing to its ready reduction by organic substances whereby a black precipitate of finely divided ruthenium is obtained, potassium per-ruthenate has been found useful for histological microscopy. ... 

Ruthenium Silicide, RuSi, results on heating a mixture of finely divided ruthenium and crystallised silicon in the electric furnace.3 The product is crushed and treated successively with alkali and a mixture of hydrofluoric and nitric acids. The silicide together with carborundum remains behind. The two may be separated with methylene iodide on account of the high density of ruthenium silicide, namely, 5-4. 

Detection.—Metallic Iridium, like rhodium, is insoluble in all acids, save that in a very finely divided condition it is slowly attacked by aqua regia. Fusion with potassium hydrogen sulphate oxidises the metal but does not effect its solution (contrast ruthenium and rhodium). When fused with a mixture of potassium nitrate and hydroxide an insoluble residue containing the sesquioxide, lr203, with alkali is obtained. 

Analysis of Osmiridium.2—Osmiridmm, in a finely divided condition, is intimately mixed with four times its weight of sodium peroxide and added to fused sodium hydroxide in a nickel crucible. On treating the product with water and washing the residue with sodium hypochlorite solution, a solution is obtained which holds all the osmium and ruthenium as alkali osmate and ruthenate respectively, and some of the iridium as iridate. 

Many normal oxides are formed on burning the element in air or oxygen. This is true not only of the non-metals boron, carbon, sulphur and phosphorus, but also for the volatile zinc, cadmium, indium and thallium, the transition metals cobalt and iron, in finely divided condition, and the noble metals osmium, ruthenium and rhodium. With some elements, limiting the supply of oxygen produces the lower oxide (e,g, P40g in place of P4O40 (p. 332)). 

Haber and his co-worlccrs have made numerous experiments on the most suitable catalysts to use as contact substances, describing the results of experiments with cerium and allied metals, manganese, tungsten, uranium, ruthenium, and osmium. The best caialyst proved to be finely divided osmium, but as this substance is limited in quantities and very expensive, it was found that uranium (pieces the size of a pin s head) also acted efficiently. 

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