Metals dissolved, reduction with

Rhodium was discovered in 1803 by the eminent Norfolk scientist W.H. Wollaston he dissolved platinum metal concentrates in aqua regia and found that on removing platinum and palladium he was left with a red solution. From this he obtained the salt Na3RhCl6, which yielded the metal on reduction with hydrogen. The rose-red colour (Greek rhodon) of many rhodium salts gave the element its name. 

The reduction of zirconium tetrachloride in a carrier salt with sodium as a reducing agent may be examined next. Again, as described before, complete deoxidation of the bath before reduction is the essential condition for success, if ductile metal is wanted. Zirconium tetrachloride is soluble in sodium chloride or potassium chloride (48) and a salt with about 25% zirconium tetrachloride can be melted without excessive zirconium chloride losses. Such a bath can even be obtained from powdery commercial zirconium silicide and iron dichloride, which react when heated and deliver a stream of zirconium tetrachloride, contaminated with some titanium tetrachloride and silicon tetrachloride. The gas so produced can be condensed in a fused salt bath such as potassium chloride-sodium chloride, in which only the zirconium tetrachloride dissolves (47), To obtain a low oxide metal after reduction with sodium, the conditions for fluo salt deoxidation must be observed. This process of zirconium production has no special interest, except for obtaining powder for getter purposes. A carrier salt, which might introduce oxide, is not wanted, as the reaction itself liberates sodium chloride. 

Cobalt has an odd number of electrons, and does not form a simple carbonyl in oxidation state 0. However, carbonyls of formulae Co2(CO)g, Co4(CO)i2 and CoJCO),6 are known reduction of these by an alkali metal dissolved in liquid ammonia (p. 126) gives the ion [Co(CO)4] ". Both Co2(CO)g and [Co(CO)4]" are important as catalysts for organic syntheses. In the so-called oxo reaction, where an alkene reacts with carbon monoxide and hydrogen, under pressure, to give an aldehyde, dicobalt octacarbonyl is used as catalyst ... 

Bina Selenides. Most biaary selenides are formed by beating selenium ia the presence of the element, reduction of selenites or selenates with carbon or hydrogen, and double decomposition of heavy-metal salts ia aqueous solution or suspension with a soluble selenide salt, eg, Na2Se or (NH 2S [66455-76-3]. Atmospheric oxygen oxidizes the selenides more rapidly than the corresponding sulfides and more slowly than the teUurides. Selenides of the alkah, alkaline-earth metals, and lanthanum elements are water soluble and readily hydrolyzed. Heavy-metal selenides are iasoluble ia water. Polyselenides form when selenium reacts with alkah metals dissolved ia hquid ammonia. Metal (M) hydrogen selenides of the M HSe type are known. Some heavy-metal selenides show important and useful electric, photoelectric, photo-optical, and semiconductor properties. Ferroselenium and nickel selenide are made by sintering a mixture of selenium and metal powder. 

Only two processes of tantalum metal production are of worldwide commercial significance. These are the electrolysis of fluoride-chloride melts containing potassium heptafluorotantalate, K TaF , and tantalum oxide, Ta20s, and the reduction with sodium of K-salt or K—salt that is dissolved in potassium fluoride-chloride melts. 

The reaction of magnesium metal with aqueous strong acid, which appears in Figure 4-12. illustrates the fundamental principles of oxidation-reduction. When a piece of magnesium is dropped into a solution of hydrochloric acid, a reaction starts almost Immediately. The metal dissolves, and gas bubbles from the solution. The gas is H2, and analysis of the solution reveals the presence of ions. A list of chemical species before and after the reaction... 

The first and very simple solid contact polymeric sensors were proposed in the early 1970s by Cattrall and Freiser and comprised of a metal wire coated with an ion-selective polymeric membrane [94], These coated wire electrodes (CWEs) had similar sensitivity and selectivity and even somewhat better DLs than conventional ISEs, but suffered from severe potential drifts, resulting in poor reproducibility. The origin of the CWE potential instabilities is now believed to be the formation of a thin aqueous layer between membrane and metal [95], The dominating redox process in the layer is likely the reduction of dissolved oxygen, and the potential drift is mainly caused by pH and p02 changes in a sample. Additionally, the ionic composition of this layer may vary as a function of the sample composition, leading to additional potential instabilities. 

Double bonds conjugated with benzene rings are reduced electrolytically [344] (p. 23). Where applicable, stereochemistry can be influenced by using either catalytic hydrogenation or dissolving metal reduction [401] (p. 24). Indene was converted to indane by sodium in liquid ammonia in 85% yield [402] and acenaphthylene to acenaphthene in 85% yield by reduction with lithium aluminum hydride in carbitol at 100° [403], Since the benzene ring is not inert toward alkali metals, nuclear reduction may accompany reduction of the double bond. Styrene treated with lithium in methylamine afforded 25% of 1-ethylcyclohexene and 18% of ethylcyclohexane [404]. 

Various processes separate rare earths from other metal salts. These processes also separate rare earths into specific subgroups. The methods are based on fractional precipitation, selective extraction by nonaqueous solvents, or selective ion exchange. Separation of individual rare earths is the most important step in recovery. Separation may be achieved by ion exchange and solvent extraction techniques. Also, ytterbium may be separated from a mixture of heavy rare earths by reduction with sodium amalgam. In this method, a buffered acidic solution of trivalent heavy rare earths is treated with molten sodium mercury alloy. Ybs+ is reduced and dissolved in the molten alloy. The alloy is treated with hydrochloric acid, after which ytterbium is extracted into the solution. The metal is precipitated as oxalate from solution. 

Ac, actinium, was initially identified in 1899 by Andr6-Louis Debierne, a French chemist, who separated it from pitchblende. He dissolved the mineral in acid, then added NH4OH, and found that a radioactive species was carried down with the rare earth hydroxides. He named the element actinium after the Greek aktinos which means ray. Because of its low abundance in U, the element is usually not obtained by isolation from U. It can be obtained in mlligram amounts by irradiation of Ra-226 in a nuclear reactor. The preparation of Ac metal involves reduction of AcFs by Li at high temperature. 

The electron transfer to the acetylenic bond forms the frans-sodiovinyl radical 20 that, after protonation, produces tram radical 21. At low temperature (—33°C) in the presence of excess sodium, the conversion of the trans radical to sodiovinyl intermediate 22 is slightly more rapid than the conversion of the tram radical to the cis radical 23 (21 —> 22 > 22 —> 23). As a result, protonation yields predominantly the trans alkene. However, low sodium concentration and increased temperature lead to increasing proportion of the cis alkene. Although other dissolving-metal reductions are less thoroughly studied, a similar mechanism is believed to be operative.34 Another synthetically useful method for conversion of alkynes to trans alkenes in excellent yields is the reduction with CrS04 in aqueous dimethylforma-mide.198... 

Purification of TiCI4. The chlorides that are solid at room temperature and the entrained dust can be separated from the TiCl4 by simply evaporating (distilling) this off (j). Dissolved chlorine can be removed by heating or reduction with metal powders (Fe, Cu, or Sn). 

The Ncrnst equation was given before (Eq. 10.115), and in this chapter the effect of pH on the reduction potential of the hydrogen ion has been mentioned, but the effect in general should be emphasized. There are several types of reactions in which concentrations of the reactants and products affect the stability of various oxidation states. This can be understood through application of the Nemst equation. The reduction potential of hydrogen will vary with the concentration of the hydrogen ion hence the commonly known fact that many reasonably active metals dissolve in acid but rot in base. 

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