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Concept
Silicon tetrachloride
Summary
Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl4. It is a colorless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications. It is a part of the chlorosilane family.
Silicon tetrachloride is prepared by the chlorination of various silicon compounds such as ferrosilicon, silicon carbide, or mixtures of silicon dioxide and carbon. The ferrosilicon route is most common.
In the laboratory, can be prepared by treating silicon with chlorine at :
It was first prepared by Jöns Jakob Berzelius in 1823.
Brine can be contaminated with silica when the production of chlorine is a byproduct of a metal refining process from metal chloride ore. In rare occurrences, the silicon dioxide in silica is converted to silicon tetrachloride when the contaminated brine is electrolyzed.
Like other chlorosilanes or silanes, silicon tetrachloride reacts readily with water:
SiCl4 + 2 H2O → SiO2 + 4 HCl
In contrast, carbon tetrachloride does not hydrolyze readily. The reaction can be noticed on exposure of the liquid to air, the vapour produces fumes as it reacts with moisture to give a cloud-like aerosol of hydrochloric acid.
With alcohols it reacts to give orthosilicate esters:
SiCl4 + 4 ROH → Si(OR)4 + 4 HCl
At higher temperatures homologues of silicon tetrachloride can be prepared by the reaction:
Si + 2 SiCl4 → Si3Cl8
In fact, the chlorination of silicon is accompanied by the formation of hexachlorodisilane Si2Cl6. A series of compounds containing up to six silicon atoms in the chain can be separated from the mixture using fractional distillation.
Silicon tetrachloride is a classic electrophile in its reactivity. It forms a variety of organosilicon compounds upon treatment with Grignard reagents and organolithium compounds:
4 RLi + SiCl4 → R4Si + 4 LiCl
Reduction with hydride reagents afford silane.
Silicon tetrachloride is used as an intermediate in the manufacture of polysilicon, a hyper pure form of silicon, since it has a boiling point convenient for purification by repeated fractional distillation.
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