Silicon Tetrachloride

Silicon tetrachloride (SiCl₄) is the most important of silicon's simple halides.

Preparation. It can be prepared by passing dry chlorine gas over a heated intimate mixture of silica and carbon (in a porcelain tube at 1675 K): SiO₂ + 2C + 2Cl₂ → SiCl₄ + 2CO. On a commercial scale, it is made by reacting silicon directly with hydrogen chloride gas above 600 K: Si + 4HCl → SiCl₄ + 2H₂.

Properties. Silicon tetrachloride is a colourless, fuming liquid that freezes at -70 °C. In moist air it hydrolyses readily to silica and hydrochloric acid: SiCl₄ + 2H₂O → SiO₂ + 4HCl. Hydrolysed instead with moist ether, it gives linear perchlorosiloxane chains, [Cl-(SiCl₂O)ₙSiCl₃], where n = 1 to 6. Its chloride ions can be substituted by nucleophiles such as -OH or -OR: reacted with alcohols (alcoholysis), it forms silicic esters, e.g. tetraethoxysilane, SiCl₄ + 4C₂H₅OH → Si(OC₂H₅)₄ + 4HCl; reacted with ammonia (ammonialysis), it gives chlorosilazanes, e.g. 2SiCl₄ + NH₃ →(330 K, ether)→ Cl₃Si-NH-SiCl₃ + 2HCl. …