Titanium Dichloride, TiCl₂

Titanium Dichloride, TiCl₂, was first prepared by Friedel and Guerin, who heated the trichloride to a red heat in a current of hydrogen, thus decomposing it into the tetrachloride, which distilled, and the dichloride, which remained behind; von der Pfordten, however, reduced the cold tetrachloride with sodium amalgam or hydrogen sulphide, and distilled off the unchanged tetrachloride in a current of carbon dioxide. Stahler and Bachran have obtained the dichloride nearly pure by heating the trichloride at 660°-700° C. in an atmosphere of hydrogen:

2TiCl₃ ⇔ TiCl₂ + TiCl₄.

The dichloride remains after the volatilisation of the tetrachloride as a deep black powder which begins to sublime at 300° C. in a vacuum.

The properties of the dichloride have been variously described. According to Friedel and Guerin it is a brown powder which decomposes water and alcohol, evolving hydrogen and forming a yellow solution; while, according to von der Pfordten, it dissolves unchanged in these solvents, forming yellow solutions which gradually oxidise in the air. It is insoluble in non-hydroxylic solvents - a fact which suggests its saline character; it burns in the air, evolving titanium tetrachloride vapour and forming titanic oxide; it combines with bromine to form a chlorobromide. A satisfactory test for bivalent titanium is the formation of a violet colour, due to TiCl₃, when it is mixed with a hydrochloric acid solution of titanium tetrachloride.