Vanadium trichloride reduction

Fig. 6.17. Vanadium trichloride reduction (Foley, E., Ward, M. and Hock,...

Commercial production from petroleum ash holds promise as an important source of the element. High-purity ductile vanadium can be obtained by reduction of vanadium trichloride with magnesium or with magnesium-sodium mixtures. 

The conversion of a higher chloride to a lower chloride by hydrogen reduction has been mentioned earlier in connection with the formation of the relatively less volatile ferrous chloride from ferric chloride. This type of reaction is more general and is widely used. Vanadium trichloride can be reduced to the dichloride by hydrogen at temperatures higher than 500 °C ... 

Some samples of vanadium prepared by magnesium reduction of vanadium dichloride or vanadium trichloride are pyrophoric. 

The dropwise addition of sodium naphthalenide to THF containing vanadium trichloride and l,2-bis(dimethylphosphino)ethane (dmpe) causes changes of colours suggesting a stepwise reduction from +2 to 0. Brown [V(dmpe)3] was isolated41 (fieff = 2.10BM) and IR data suggest octahedral coordination. The same complex was synthesized by a metal vapour technique.42 The ESR was that expected and the unit cell is cubic with a = 11.041(3) A. 

Vandenberg (77) has found that vinylethers are polymerized by combinations of vanadium tetrachloride and triethylaluminum. Vandenberg believed that the intermediate vanadium trichloride, produced by reduction of the vanadium tetrachloride, reacted with the triisobutyl-aluminum-tetrahydrofuran complex to produce the modified Friedel-Crafts catalysts that converted the vinylether to isotactic polymer. 

The pure vanadium trichloride product is a purple solid which decomposes at about 500°C and is best stored in absence of air to prevent oxidation to the oxytrichloride. As made by the above method, the principal metal chloride impurities, those of magnesium and iron, are both reduced to about 0-02 per cent and the trichloride is satisfactory for reduction to metal with magnesium by a Kroll type process. 

Vanadium trichloride is a purple solid, made by thermal decomposition or reduction of the tetrachloride, the latter, in turn, being produced by chlorination of ferrovanadium as described in Chapter 2. Before use, the trichloride can be freed from the oxytrichloride, and other low boiling impurities, by simple distillation. The solid is then cooled, crushed and screened ready for use. 

The magnesium is then melted and the temperature raised to between 750°C and 800°C. Vanadium trichloride is next fed to the molten magnesium, under controlled condition, at such a rate as to maintain the temperature between 750 C and 850°C without the use of further external heat. Additional blocks of magnesium are added towards the end of the reaction, to provide an adequate excess for reasonably complete utilization of the vanadium. Reductions require about 7 hr for completion. 

Chemical deoxygenation of sulfoxides to sulfides was carried out by refluxing in aqueous-alcoholic solutions with stannous chloride (yields 62-93%) [186 Procedure 36, p. 214), with titanium trichloride (yields 68-91%) [203], by treatment at room temperature with molybdenum trichloride (prepared by reduction of molybdenyl chloride M0OCI3 with zinc dust in tetrahydrofuran) (yields 78-91%) [216], by heating with vanadium dichloride in aqueous tetrahydrofuran at 100° (yields 74-88%) [216], and by refluxing in aqueous methanol with chromium dichloride (yield 24%) [190], A very impressive method is the conversion of dialkyl and diaryl sulfoxides to sulfides by treatment in acetone solutions for a few minutes with 2.4 equivalents of sodium iodide and 1.2-2.6 equivalents of trifluoroacetic anhydride (isolated yields 90-98%) [655]. 

Vanadium metal is prepared from pentoxide, V2O5, by reduction with calcium at elevated temperatures. Presence of iodine lowers calcium reduction temperature to 425°C because of heat of formation of calcium iodide. Pentoxide also may be converted to the trichloride, VCI3, and the trichloride reduced with magnesium metal or magnesium-sodium mixture at high temperatures to form high purity ductile metal. Alternatively, a fused mixture of vanadium chloride, sodium chloride, and hthium chloride may be electrolyzed to produce the metal in high purity. 

The method adopted for the preparation of vanadium (II) chloride is the reduction of the trichloride by hydrogen at temperatures not exceeding 675°. 

TiCU is produced by the reduction of the tetrachloride with hydrogen or a metal like silver or mercury. When heated in the air it breaks up, giving the volatile tetrachloride and the solid dichloride. TiCl is deli quescent, forms a reddish violet solution with water, and violet crystals, TiCU 6 H20, from a hydrochloric acid solution. An unstable green hydrate of the same composition is formed when an aqueous solution of the trichloride is covered with ether and saturated at 0° with HC1. From the violet form all the chlorine may be removed by AgNO , but this is probably not true of the green modification. The trichlorides of chromium and vanadium likewise are known in two forms. TiCla forms double salts with the chlorides of rubidium and caesium. It is a more powerful reducing agent than stannous chloride and on this account finds extensive application in both qualitative and quantitative analysis. 

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