Vanadium dichloride reduction

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

Aqueous solutions of vanadous chloride (vanadium dichloride) are prepared by reduction of vanadium pentoxide with amalgamated zinc in hydrochloric acid [213], Reductions are carried out in solution in tetrahydrofuran at room temperature or under reflux. Vanadiiun dichloride reduces a-halo ketones to ketones [214], a-diketones to acyloins [215], quinones to hydroquinones [215], sulfoxides to sulfides [216] and azides to amines [217] (Procedure 40, p. 215). 

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]. 

When he began his researches on vanadium, its compounds were listed at .35 per ounce, and the metal itself was unknown. After all attempts at direct reduction of the oxides had failed, Roscoe attempted to reduce vanadium dichloride, VC12, with hydrogen. Rigorous exclusion of oxygen and moisture was necessary, and, since vanadium metal reacts violently with glass and porcelain, the chloride was placed in platinum boats inside a porcelain tube. The tube itself could not be made of platinum because of the porosity of that metal at red heat. 

Hypovanadous Chloride, vanadium dichloride, VC12.—Solutions of vanadium dichloride can be prepared by electrolytic reduction of higher chlorides,3 or by the addition of amalgamated zinc to a hydrochloric acid solution of vanadium pentoxide.4 The solution undergoes very rapid oxidation, hence the isolation of vanadium diehloride cannot... 

Metallurgy. — Metallic vanadium may be prepared in a number of ways. (1) By reduction of vanadium dichloride by pure hydrogen. This method is difficult to use because at red heat vanadium unites readily with oxygen and water, so both must be carefully excluded. (2) By making a plastic mass of vanadium pentoxide with carbon and paraffin, shaping into rods and passing the electric current through them in a vacuum. 

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 ... 

Vanadium(II) chloride is formed when a mixture of vanadium (IV) chloride and hydrogen is passed through a hot tube1 and by the reduction of vanadium(III) chloride with hydrogen.2 It is also produced by the thermal disproportionation of vanadium(III) chloride3,4 into the nonvolatile dichloride and the volatile tetrachloride. 

The uncharged compound V (05115)2 was first prepared from vanadium tetrachloride and an excess of cyclopentadienyl magnesium bromide in the absence of air (51) it was later obtained by reduction of the dichloride by lithium aluminum hydride (209). It forms readily volatile violet-black crystals of mp 167-168°. It is very soluble in benzene, ether, and petroleum ether, and is stable in the absence of air. 

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. 

No allyl complexes of titanium or vanadium have yet been reported. We have prepared allyl-bis(cyclopentadienyl)-titanium [I] by various methods, of which the following is the most convenient one. Red bis(cyclopentadienyl)-titanium dichloride [II] in tetrahydrofuran solution was reduced to the green monochloride by means of zinc powder (1). When the reduction was completed, one equivalent of allylmagnesium chloride was added to the solution, the col r of which changed to violet. The reaction mixture was evaporated in vacuo, and the residue exuacted with pentane. When the violet pentane solution was concentrated to saturation and cooled to -80 , purple crystals of [I] precipitated. After two recrystallizations from pentane pure [I] was obtained in 36%yield. Analysis found 21,8%Ti 70,89%C 7,01%H calc, for (CgHg TifC Hg) 21,86%Ti 71,24%C 6,89%H. Melting point . 118 C (decomp.). Reaction of [I] with octanol gave propene in 80% of the theoretical yield. 

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