Silicochloroform, SiHCl₃

Silicochloroform, SiHCl₃, so named because of its analogy with chloroform, was obtained impure by Buff and Wohler in 1857 by heating silicon in a current of dry hydrogen chloride gas, and was examined later by Friedel and Laden- burg.2 Gattermann 3 showed that it could be obtained in the same way from the crude silicon formed by heating silica with magnesium; it must, hoWever, be freed from the tetrachloride formed at the same time by fractional distillation, and then be 'condensed in a freezing mixture. Ferrosilicon and copper silicide may be employed in place of silicon itself.

Silicochloroform is a colourless, mobile, strongly smelling liquid which boils at 33° C. under 758 mm. pressure and forms a crystalline solid which melts at -134° C. The density of the liquid at 15° C. is 1.3438, and its vapour density 4.64, which corresponds with theory. It may be observed that chloroform, CHCl₃, boils at 61.5° C. It will be noticed in the course of what follows that, apart from polymerisation, silicon compounds are generally more volatile than the corresponding carbon compounds.

When silicochloroform is heated in an indifferent atmosphere it decomposes similarly to silicofluoroform, thus:

4SiHCl₃ = 3SiCl₄ + 2H₂ + Si;

its vapour burns in the air with a green-mantled flame, like that of chloroform, producing clouds of silica, and forms with air a mixture which can be exploded by means of a hot glass rod. Unlike chloroform and carbon tetrachloride, but like silicon tetrachloride, silicochloroform fumes in moist air, and is decomposed by water, with evolution of heat, forming silicic and hydrochloric acids. If, however, the reaction takes place at 0° C. the hydrogen is retained, and silicoformic anhydride is produced as a white, insoluble powder:

2SiHCl₃ + 3H₂O = + 6HCl.

Alcohol reacts normally, producing ethyl orthosilicoformate: SiHCl₃ + 3C₂H₅OH = SiH(OC₂H₅)₃ + 3HCl,

and not ethyl orthosilicate, as with silicofluoroform.