Silicon tetrachloride

Silicon tetrachloride
IUPAC name	Silicon (IV) chloride
Other names	Silicon tetrachloride Tetrachlorosilicane
Identifiers
CAS number	[10026-04-7]
PubChem	24816
EC number	233-054-0
UN number	1818
RTECS number	VW0525000
SMILES	[Si](Cl)(Cl)(Cl)Cl
InChI	1/Cl4Si/c1-5(2,3)4
Properties
Molecular formula	SiCl4
Molar mass	169.90 g/mol
Appearance	Colourless liquid
Density	1.483 g/cm3
Melting point	−68.74 °C
Boiling point	57.65 °C
Solubility in water	decomposes
Solubility	soluble in benzene, toluene, chloroform, ether
Vapor pressure	25.9 kPa at 20 °C
Structure
Crystal structure	Tetrahedral
Coordination geometry	4
Hazards
MSDS	External MSDS
EU Index	014-002-00-4
EU classification	Irritant (Xi)
R-phrases	R14, R36/37/38
S-phrases	(S2), S7/8, S26
NFPA 704	0 3 2 W
Flash point	-18 °C
Related compounds
Other anions	Silicon tetrafluoride Silicon tetrabromide Silicon tetraiodide
Other cations	Carbon tetrachloride Germanium tetrachloride Tin(IV) chloride Lead(IV) chloride
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

Silicon tetrachloride is a non-polar chemical compound with the formula SiCl₄. It was prepared by Jöns Jakob Berzelius in 1823.

Chemistry

This colourless volatile liquid compound is prepared by the treatment of silicon with chlorine:

Si + 2 Cl₂ → SiCl₄

It reacts readily with water, in contrast with carbon tetrachloride. The differing rates of hydrolysis are attributed to the greater atomic radius of the silicon atom, whereas carbon has a smaller atomic radius so the chlorine atoms effectively shield the carbon from attack. In water, the following reaction occurs:

SiCl₄ + 2 H₂O → SiO₂ + 4 HCl

The reaction can be noticed on exposure of the liquid to air at room temperature: the vapour produces fumes as it reacts with moisture in the air.^[1] With methanol and ethanol it reacts to give tetramethyl orthosilicate and tetraethyl orthosilicate:

SiCl₄ + 4 ROH → Si(OR)₄ + 4 HCl

At higher temperatures homologues of silicon tetrachloride can be prepared by the reaction:

Si + SiCl₄ → Si₂Cl₆ + homologues

A series of compounds containing up to six silicon atoms in the chain can be separated from the mixture using fractional distillation.

Uses

Silicon tetrachloride is sometimes used as an intermediate in the manufacture of extremely pure silicon, since it has a boiling point convenient for purification by repeated fractional distillation; it can be reduced to silicon by hydrogen gas, or hydrolysed to SiO₂ as a precursor for extremely pure synthetic fused silica. Very pure silicon derived from silicon tetrachloride is used in large amounts in the semiconductor industry, and also in the production of photovoltaic cells. Reports of silicon tetrachloride pollution in China have been associated with the increased demand for photovoltaic cells that has been stimulated by subsidy programs.^[2]

References