Silicon tetrachloride

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Silicon tetrachloride
Silicon tetrachloride.svgSilicon-tetrachloride-3D-vdW.png
Identifiers
CAS number10026-04-7 YesY
PubChem24816
ChemSpider23201 YesY
EC number233-054-0
UN number1818
RTECS numberVW0525000
Jmol-3D imagesImage 1
Properties
Molecular formulaSiCl4
Molar mass169.90 g/mol
AppearanceColourless liquid
Density1.483 g/cm3
Melting point−68.74 °C (−91.73 °F; 204.41 K)
Boiling point57.65 °C (135.77 °F; 330.80 K)
Solubility in waterReaction
Solubilitysoluble in benzene, toluene, chloroform, ether, hydrochloric acid
Vapor pressure25.9 kPa at 20 °C
Structure
Crystal structureTetrahedral
Coordination
geometry
4
Thermochemistry
Std molar
entropy
So298
240 J·mol−1·K−1[1]
Std enthalpy of
formation
ΔfHo298
−687 kJ·mol−1[1]
Hazards
MSDSExternal MSDS
EU Index014-002-00-4
EU classificationIrritant (Xi)
R-phrasesR14, R36/37/38
S-phrases(S2), S7/8, S26
NFPA 704
Related compounds
Other anionsSilicon tetrafluoride
Silicon tetrabromide
Silicon tetraiodide
Other cationsCarbon tetrachloride
Germanium tetrachloride
Tin(IV) chloride
Titanium tetrachloride
Related chlorosilanesChlorosilane
Dichlorosilane
Trichlorosilane
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral dataUV, IR, NMR, MS
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references
 
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Silicon tetrachloride
Silicon tetrachloride.svgSilicon-tetrachloride-3D-vdW.png
Identifiers
CAS number10026-04-7 YesY
PubChem24816
ChemSpider23201 YesY
EC number233-054-0
UN number1818
RTECS numberVW0525000
Jmol-3D imagesImage 1
Properties
Molecular formulaSiCl4
Molar mass169.90 g/mol
AppearanceColourless liquid
Density1.483 g/cm3
Melting point−68.74 °C (−91.73 °F; 204.41 K)
Boiling point57.65 °C (135.77 °F; 330.80 K)
Solubility in waterReaction
Solubilitysoluble in benzene, toluene, chloroform, ether, hydrochloric acid
Vapor pressure25.9 kPa at 20 °C
Structure
Crystal structureTetrahedral
Coordination
geometry
4
Thermochemistry
Std molar
entropy
So298
240 J·mol−1·K−1[1]
Std enthalpy of
formation
ΔfHo298
−687 kJ·mol−1[1]
Hazards
MSDSExternal MSDS
EU Index014-002-00-4
EU classificationIrritant (Xi)
R-phrasesR14, R36/37/38
S-phrases(S2), S7/8, S26
NFPA 704
Related compounds
Other anionsSilicon tetrafluoride
Silicon tetrabromide
Silicon tetraiodide
Other cationsCarbon tetrachloride
Germanium tetrachloride
Tin(IV) chloride
Titanium tetrachloride
Related chlorosilanesChlorosilane
Dichlorosilane
Trichlorosilane
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral dataUV, IR, NMR, MS
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Silicon tetrachloride is the inorganic compound with the formula SiCl4. It is a colourless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications.

Preparation[edit]

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.[2]

In the laboratory, SiCl4 can prepared by treating silicon with chlorine:

Si + 2 Cl2 → SiCl4

It was first prepared by Jöns Jakob Berzelius in 1823.

Reactions[edit]

Hydrolysis and related reactions[edit]

Like other chlorosilanes, silicon tetrachloride reacts readily with water:

SiCl4 + 2 H2O → SiO2 + 4 HCl

In contrast, carbon tetrachloride does not hydrolyze readily. The differing rates of hydrolysis are attributed to the greater atomic radius of the silicon atom, which allows attack at silicon, and to the weaker nature of the Si-Cl bonds.[citation needed] 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.[3] With methanol and ethanol it reacts to give tetramethyl orthosilicate and tetraethyl orthosilicate:

SiCl4 + 4 ROH → Si(OR)4 + 4 HCl

Polysilicon chlorides[edit]

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 Si2Cl6. A series of compounds containing up to six silicon atoms in the chain can be separated from the mixture using fractional distillation.

Reactions with other nucleophiles[edit]

Silicon tetrachloride is a classic electrophile in its reactivity.[4] 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.

Uses[edit]

Silicon tetrachloride is used as an intermediate in the manufacture of high purity silicon,[2] since it has a boiling point convenient for purification by repeated fractional distillation. It can be reduced to silicon by hydrogen gas. Very pure silicon derived from silicon tetrachloride is used in large amounts in the semiconductor industry, and also in the production of photovoltaic cells. It can also be hydrolysed to fumed silica. High purity silicon tetrachloride is used in the manufacture of optical fibres. This grade should be free of hydrogen containing impurities like trichlorosilane. Optical fibres are made using processes like MCVD and OFD where silicon tetrachloride is oxidized to pure silica in the presence of oxygen.

Safety and environmental issues[edit]

Pollution from the production of silicon tetrachloride has been reported in China associated with the increased demand for photovoltaic cells that has been stimulated by subsidy programs.[5]

See also[edit]

References[edit]

  1. ^ a b Zumdahl, S. S. (2009). Chemical Principles (6th ed.). Houghton Mifflin. p. A22. ISBN 0-618-94690-X. 
  2. ^ a b Simmler, W. (2005), "Silicon Compounds, Inorganic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a24_001 
  3. ^ Clugston, M.; Flemming, R. (2000). Advanced Chemistry. Oxford University Press. p. 342. ISBN 9780199146338. 
  4. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  5. ^ "Solar Energy Firms Leave Waste Behind in China". The Washington Post. 9 March 2008.