Hypovanadates

Hypovanadic Oxide, V02, is amphoteric, and dissolves both in alkalis and acids. In passing from trivalent to tetravalent vanadium, however, the basic character of the oxide becomes less pronounced and... 

In some cases, however, the modus operandi is modified. In the oxidation of hydriodic acid with chromic acid, the data indicate that while liberation of iodine takes place, the vanadous or hypovanadic salt employed as the catalyst also undergoes oxidation to vanadate.2 The vanadium compound here belongs to the class of catalysts known as inductors, and the reaction is comparable to the oxidation in aqueous solution of sodium sulphite with sodium arsenite, whereby both sodium sulphate and sodium arsenate are produced. 

Hypovanadous Fluoride, vanadium difluoride, VFS, has not been isolated, but a reddish-violet solution containing it is obtained by the action of excess of hydrofluoric acid on vanadium aluminium silieide,2 VsAl2Si]3, in the absence of air. In the presence of air the solution becomes green, with evolution of hydrogen ... 

Vanadium Tetrafluoride, hypovanadic fluoride, VF4, is produced by the action of anhydrous hydrogen fluoride on the corresponding chlorine compound, VC14, at temperatures from —28° to 0° C. It is an extremely deliquescent brown powder which readily undergoes hydrolysis with water, so that it does not give rise to double salts as in the case of the trifluoride. Its density at 23° C. is 2 9749. It decomposes above 325° C., yielding a mixture of the pentafluoride and the trifluoride 1... 

Vanadyl Difluoride, VOF2, is prepared by the action of anhydrous hydrogen fluoride on vanadyl dibromide, VOBr2. It is a yellow substance. Density at 19° C., 3-3956.s A hydrated vanadyl difluoride, V0F2.a, H20, is obtained as microscopic blue crystals when hypovanadic oxide, V02, is dissolved in excess of hydrofluoric acid and the solution concentrated slowly over sulphuric acid.1 The following double salts have been prepared, all of which are crystalline and fairly stable —5... 

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... 

Hypovanadic Chloride, vanadium tetrachloride, VC14, can be prepared synthetically from the lower chloride, VC13, by heating in a stream of chlorine at 600° C. Another convenient method consists in passing dry chlorine over ferrovanadium contained in a hard glass tube heated in a combustion furnace. The reaction is expressed ... 

Hypovanadic Bromide, vanadium tetrabromide, VBr4, has not hitherto been isolated, but it is of interest to note that a double salt of composition VBr4.SbBr3.7HaO has been obtained by dissolving antimony tribromide and vanadium pentoxide in hydrobromic acid and adding bromine. ... 

Vanadyl Dibromide, VOBr2, is obtained by passing bromine vapour or, preferably, a mixture of sulphur bromide, SaBra, and bromine over a mixture of vanadium pentoxide and sulphur at a red heat the product is heated in vacuo at 240° C., whereupon the vanadyl dibromide is obtained as a yellow powder.8 An alternative method of preparation consists in heating vanadium oxytribromide, VOBr3, to 180° C.9 Vanadyl dibromide is no doubt present in the blue solution which results when hypovanadic oxide, VOa, is dissolved in hydrobromic acid. 

An oxybromide of possible constitution V02Br3.5H20 is known, but the constitution of this compound is a matter of doubt. It is obtained by dissolving hypovanadic oxide, V02, in dilute aqueous hydrobromic acid. Hydrochloric acid under similar conditions yields the compound VOaCl 2.8H20.s... 

Hypovanadous oxide resembles the metal in many of its properties. It is insoluble in water, but dissolves in acids without evolution of hydrogen to yield the lavender-coloured solutions which are characteristic of solutions of hypovanadous salts. These salts are, however, most conveniently prepared in solution by electrolytic reduction in an inert atmosphere of solutions of vanadium pentoxide in the various acids.7 Hypovanadous salts are isomorphous with salts of divalent iron, chromium, and manganese. On being treated with caustic alkalis, a brown precipitate of hypovanadous hydroxide, V(OH)a, is obtained, which rapidly oxidises to the greyish-green vanadous hydroxide, V(OH)s. 

Hypovanadic oxide is most conveniently obtained by heating any of the foregoing hydrates in the absence of air. It is also formed (a) from vanadium pentoxide by heating in admixture with the trioxide, carbon, or oxalic acid,6 and (b) from vanadous oxide by prolonged exposure to air.7... 

The red, amorphous form of vanadium pentoxide is the form most frequently met with in the laboratory. Its preparation has been described above. It melts at 658°10 or 675° C.u to a dark red liquid, but is not volatile even at high temperatures it can be vaporised only in the electric furnace.18 The fused solid conducts electricity, with formation of hypovanadic oxide, V02 18 the electrical conductivity has been measured.14 The oxide absorbs water on exposure to the air, the... 

With hydrobromic acid and hydriodic acid reduction may proceed to the trivalent state,9 and it has been shown that in the presence of acetic acid, hydrazine also produces vanadous oxide, V203, instead of hypovanadic oxide, V02 10... 

Reduction of add solutions of vanadium pentoxide to the tetravalent state also takes place with bismuth amalgam 5 magnesium gives the trivalent salts of vanadium, while by using zinc, zinc coated with cadmium, electrolytically deposited cadmium, or sodium amalgam in the absence of air, divalent vanadium salts are obtained in solution.7 Vanadous salts and hypovanadous salts are, however, much more conveniently prepared by electrolytic reduction of acid solutions of vanadium pentoxide in an atmosphere of carbon dioxide.8... 

Vanadium pentoxide becomes markedly photo-sensitive when immersed in glycerol, benzaldehyde, cinnamic aldehyde, cuminol, or aqueous mannitol solution, and exposed to light. It blackens and undergoes reduction, giving rise, initially, to hypovanadic oxide, VOg. With aqueous solutions of citric acid or tartaric acid carbon dioxide is evolved during the change.9... 

Vanadyl Sulphates.—By treating hypovanadic oxide, V02, with sulphuric acid at about 200° C., or by reducing a sulphuric acid solution... 

Vanadyl Selenite, V02.Se02.2H20, is obtained in blue, microscopic crystals when the hydrate of hypovanadic oxide, V02.2Ha0, is dissolved in an aqueous solution of selenous acid and the solution evaporated.3 Efforts to prepare normal selenates and selenate alums of trivalent vanadium were unsuccessful, but several hydrated aceto-selenates of trivalent vanadium have been isolated.4... 

Alkali Vanadyl Nitrites.—By dissolving hypovanadic oxide, V02, in aqueous solutions of vanadyl nitrites the following alkali vanadyl nitrites have been prepared —... 

Vanadium Nitrates.—No nitrates of vanadium have been isolated. When hypovanadic oxide is dissolved in nitric acid the blue solution which results probably contains vanadyl nitrate, V0(N03)2, but on evaporation oxidation ensues and hydrated vanadium pentoxide is obtained. Blue solutions of vanadyl nitrate arc more conveniently obtained by precipitating vanadyl chloride with silver nitrate or vanadyl sulphate with barium nitrate. Addition of nitric acid to hexammino-vanadium trichloride yields hexammino-vanadium nitrate,10 [V (NH3)6](N03)3. 

Vanadyl Phosphates, V02.P205.3H20 and 2VO2.3P2O5.10H2O, are prepared in blue needles by the action of hypovanadic oxide on phosphoric add.2... 

Vanadyl Arsenates.—Two of these have been prepared by the action of hydrated hypovanadic oxide on solutions of arsenic acid 2V02.2As206.3H20 and 2V02.3As205.6H20. They are both sky-blue, crystalline compounds, and the latter rapidly becomes green on exposure to air.1... 

Vanadyl Cyanide.—Berzelius5 obtained vanadyl cyanide by the action of hydrocyanic acid on hydrated hypovanadic oxide in the absence of air. The product was not, however, analysed. 

Hypovanadic oxide, V02, and vanadium pentoxide, V205, both dissolve in hydrofluosilicic acid to yield a vanadyl fluosilicate and a vanadium fluosilicate, both of doubtful composition.14... 

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