Hypovanadic Chloride, VCl₄

Hypovanadic Chloride, vanadium tetrachloride, VCl₄, can be prepared synthetically from the lower chloride, VCl₃, 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:

2FeV + 7Cl₂ = 2FeCl₃ + 2VCl₄.

The vanadium tetrachloride distils over and is purified from any ferric chloride present either by distillation or by extraction of the product with carbon tetrachloride, in which only the vanadium halide is soluble. Sulphuryl chloride, thionyl chloride, sulphur monochloride, and phosgene can all be used in the last reaction instead of chlorine, and the ferrovanadium also can be substituted by vanadium carbide, V₄C₃, nitride, VN, subsilicide, V₂Si, disilicide, VSi₂, or pentoxide.

Vanadium tetrachloride is a reddish-brown, viscous liquid, which boils at 153.7° C. at 768 mm. and melts at -109° C. Density at 0° C., 1.8584. The dielectric constant has been investigated. The electrical conductivity is extremely low even near the boiling-point. On being heated to 900° C. in the presence of iron it undergoes reduction to the metal. It decomposes slowly and spontaneously in a dry atmosphere at ordinary temperatures into vanadous chloride, VCl₃, and chlorine. In moist air it undergoes slow hydrolysis with formation of hydrochloric acid, which gives rise to the usual fuming effect; on being thrown into water it is immediately hydrolysed and forms vanadyl dichloride, VOCl₂, which gives a blue solution. The tetrachloride is stable only at temperatures above about 630° C. It is too unstable to form double salts with other chlorides. In benzene solution, however, it reacts with ammonia and its derivatives, e.g. aniline, to yield compounds which consist of one molecule of the tetrachloride in association with from three to six molecules of ammonia or its derivative.