Hypovanadous Chloride, VCl₂

Solutions of vanadium dichloride can be prepared by electrolytic reduction of higher chlorides, or by the addition of amalgamated zinc to a hydrochloric acid solution of vanadium pentoxide. The solution undergoes very rapid oxidation, hence the isolation of vanadium dichloride cannot be effected by a wet method. It is deposited in apple-green hexagonal flakes when the vapour of vanadium tetrachloride mixed with dry hydrogen is passed through a glass tube heated to dull redness.Vanadium trichloride undergoes decomposition to the dichloride and tetrachloride when heated to 900° C. in a stream of nitrogen or carbon dioxide. The tetrachloride produced at the same time distils away at the temperature of the reaction. More recently, vanadium dichloride has been obtained by the action of hydrogen chloride on commercial ferrovanadium. Its density at 18° C. is 3.23. It is a hygroscopic solid which deliquesces with oxidation to a brown liquid. In the presence of mineral acid a violet solution is formed, which, like all other solutions of divalent vanadium salts, acts as an extremely powerful reducing agent; it is, in fact, one of the strongest reducing agents known. It slowly evolves hydrogen from its aqueous or acid solutions, with formation of the trichloride; a vigorous evolution of hydrogen takes place from the acid solution in the presence of platinum foil. It bleaches litmus and indigo, precipitates the metals from solutions of salts of copper, tin, silver, gold and platinum, and has been successfully employed in the isolation of certain organic radicals, as, for example, the triphenylmethyl radical from triphenyl carbinol. At a bright red heat it reduces carbon dioxide to the monoxide:

3VCl₂ + 2CO₂ = 2VOCl + VCl₄ + 2CO;

and with even stronger heating the reaction proceeds further,

4VCl₂ + 3CO₂ = V₂O₃ + 2VCl₄ + 3CO,

pure vanadium sesquioxide being produced.