Titanium Tetrachloride, TiCl₄

Titanium Tetrachloride, TiCl₄. - Titanium and chlorine combine when heated together to 350° C., forming Titanium Tetrachloride, TiCl₄. In place of the pure metal that containing carbon, or the carbide, may be employed. This chloride is also conveniently prepared, like non-metallic chlorides, by passing chlorine over a heated mixture of titanic oxide and carbon, as well as by leading the vapour of carbon tetrachloride or chloroform over the heated dioxide. Ferrotitanium may also be used as a source of the tetrachloride. Most of the iron is first removed by hydrochloric acid, and the residue is heated in a porcelain tube through which chlorine is passed. Ferric chloride condenses in the cooler parts of the tube, and titanic chloride is obtained by further cooling and then fractionated. In another process rutile is reduced by aluminium according to the Goldschmidt reaction, and the product heated in a current of chlorine; the crude titanic chloride thus obtained needs to be separated by fractional distillation from silicon tetrachloride, derived from the silica of the rutile.

Titanium tetrachloride is a colourless, mobile liquid of density 1.7604 at 0° C. and 1.5222 at its boiling-point. It boils at 136.4° C. under 760 mm. pressure (Thorpe), its critical temperature is 358° C., at low temperature it forms a solid mass which melts at -23° C. The vapour density was found by Dumas to be 6.836 (air = 1) or 197.4 (O = 16), theory requiring 190 in the latter case.

Titanium tetrachloride has a penetrating smell, and fumes excessively in moist air. With water it forms a series of oxychlorides: TiCl₃OH, TiCl₂(OH)₂, TiCl(OH)₃; with excess of water Ti(OH)₄ is formed; nevertheless titanium tetrachloride dissolves in water with evolution of considerable heat, the hydrochloric acid formed simultaneously with the titanic hydroxide sufficing to redissolve the voluminous precipitate of Ti(OH)₄ first formed. According to Thomsen the heat evolved by the solution of 1 molecule of TiCl₄ in 1600 molecules of water at 17° C. is 57,870 calories. In its behaviour towards water titanium tetrachloride stands between the tetrachlorides of silicon and tin.

Sodium amalgam at ordinary temperature reduces the tetrachloride to dichloride, hydrogen at red heat reduces it to the trichloride.