Pentachloride reduced oxides

Several methods are described for the production of tantalum and niobium metal. Metals can be obtained by reduction of pentachlorides with magnesium, sodium, hydrogen or by thermal decomposition in vacuum [24,28]. Oxides can be reduced using carbon, aluminum, calcium, magnesium [28, 537, 538] or alkali and rare earth metals [539]. 

Tantalum Trichloride, TaCls, is prepared by reducing the pentachloride with aluminium in the presence of aluminium chloride and heating the product to between 350° and 400° C. It is a dark green substance which yields intensely green aqueous solutions without evolution of hydrogen. These solutions are fairly stable, and oxidise only slowly on being exposed to air the rate of oxidation is accelerated by the presence of alkali and checked by the addition of acids. 

Phosphorus pentachloride also reacts to yield arsenic trichloride.7 Arsenious oxide in aqueous solution is reduced by hypophosphorous acid, especially on boiling, when phosphine is liberated and brown arsenic precipitated.8 The reduction is readily brought about by calcium hypophosphite dissolved in 10 parts of hydrochloric acid (dens. 1-126), this salt being preferable in use to the sodium salt and providing an extremely sensitive reagent, although in the presence of slight traces of arsenic the brown colour may appear only after the lapse of 20 to 30 minutes.9 Arsenious oxide dissolves in arsenic trichloride to form an oxychloride.10... 

Typical oxidising dopants used include iodine, arsenic pentachloride, iron(III) chloride and NOPF6. A typical reductive dopant is sodium naphthalide. The main criteria is its ability to oxidise or reduce the polymer without lowering its stability or whether or not they are capable of initiating side reactions that inhibit the polymers ability to conduct electricity. An example of the latter is the doping of a conjugated polymer with bromine. Bromine it too powerful an oxidant and adds across the double bonds to form sp3 carbons. The same reaction may occur with NOPF, but at a lower rate. 

The pentachloride is a little unstable in air when heated to about 1380° C. or less it leaves a residue of molybdenum when heated in hydrogen at 250° C. it is reduced to amorphous molybdenum trichloride. Its aqueous solution is unstable in air, especially on warming, when hydrogen chloride is more rapidly evolved and the blue oxide (p. 131) remains. Decomposition of its solution in hydrochloric acid also readily takes place. In alcohol and ether it dissolves to a green solution in sulphuric acid its solution is bluish green and in nitric acid colourless alkalies dissolve it with production of the hydrated dioxide and a molybdate. ... 

The trioxide remains unchanged when heated in a current of nitric oxide it is reduced to lower oxides by ethylene or acetylene at red heat, by methane at a higher temperature, and by phosphine at 125° to 150° C. Heated with phosphorus pentachloride in an atmosphere of carbon dioxide it yields a red-brown product which consists of a mixture of tungsten chlorides and oxychlorides. ... 

The full report of the preparation and properties of two octacyanoniobates has appeared (Vol. 4, p. 75). Impure K5[Nb(CN)8] can be obtained from the reaction of an excess of aqueous potassium cyanide with an electrolytically reduced solution of niobium pentachloride in methanol. Oxidation of the product by air or H2O2 gives orange K4[Nb(CN)8],2H20 (see p. 73). Solutions of this salt are stable in the dark but disproportionate photolytically to the Nb complex, Nb20s, and HCN. M5[Nb-... 

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