Silicon tetrachloride

Silicon tetrachloride or tetrachlorosilane 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.

Silicon tetrachloride
Names
IUPAC name
Silicon (IV) chloride
Other names
Silicon tetrachloride
Tetrachlorosilane
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.037
EC Number
  • 233-054-0
RTECS number
  • VW0525000
UNII
UN number 1818
Properties
SiCl4
Molar mass 169.90 g/mol
Appearance Colourless liquid
Density 1.483 g/cm3
Melting point −68.74 °C (−91.73 °F; 204.41 K)
Boiling point 57.65 °C (135.77 °F; 330.80 K)
Reaction
Solubility soluble in benzene, toluene, chloroform, ether[1]
Vapor pressure 25.9 kPa at 20 °C
−88.3·10−6 cm3/mol
Structure
Tetrahedral
4
Thermochemistry
240 J·mol−1·K−1[2]
Std enthalpy of
formation (ΔfH⦵298)
 −687 kJ·mol−1[2]
Hazards
Safety data sheet See: data page
MSDS
Irritant (Xi)
R-phrases (outdated) R14, R36/37/38
S-phrases (outdated) (S2), S7/8, S26
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
0
3
2
Related compounds
Other anions
 Silicon tetrafluoride
Silicon tetrabromide
Silicon tetraiodide
Other cations
 Carbon tetrachloride
Germanium tetrachloride
Tin(IV) chloride
Titanium tetrachloride
Related chlorosilanes
 Chlorosilane
Dichlorosilane
Trichlorosilane
Supplementary data page
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Preparation

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.[3]

In the laboratory, SiCl4 can be prepared by treating silicon with chlorine:[1]

Si + 2 Cl2 → SiCl4

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.[4]

Reactions

Like other chlorosilanes, 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.[5]

With alcohols and ethanol it reacts to give tetramethyl orthosilicate and tetraethyl orthosilicate:

SiCl4 + 4 ROH → Si(OR)4 + 4 HCl

Polysilicon chlorides

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.[1]

Reactions with other nucleophiles

Silicon tetrachloride is a classic electrophile in its reactivity.[6] 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

Silicon tetrachloride is used as an intermediate in the manufacture of polysilicon, a hyper pure form of silicon,[3] since it has a boiling point convenient for purification by repeated fractional distillation. It is reduced to trichlorosilane (HSiCl3) by hydrogen gas in a hydrogenation reactor, and either directly used in the Siemens process or further reduced to silane (SiH4) and injected into a fluidized bed reactor. Silicon tetrachloride reappears in both these two processes as a by-product and is recycled in the hydrogenation reactor. Vapor phase epitaxy of reducing silicon tetrachloride with hydrogen at approximately 1250oC was done:

SiCl
4(g) + 2 H
2(g) → Si(s) + 4 HCl(g) at 1250oC[7]

The produced polysilicon is used as wafers in large amounts by the photovoltaic industry for conventional solar cells made of crystalline silicon and also by the semiconductor industry.

Silicon tetrachloride 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

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.[8] The MSDS notes that one should "avoid all contact! In all cases consult a doctor! ... inhalation causes sore throat and Burning sensation".[9]

See also

References
  1. P. W. Schenk (1963). "Phosphorus(V) fluoride". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. 1. NY,NY: Academic Press. pp. 282–683.
  2. Zumdahl, S. S. (2009). Chemical Principles (6th ed.). Houghton Mifflin. p. A22. ISBN 978-0-618-94690-7.
  3. Simmler, W. "Silicon Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a24_001.
  4. White, George Clifford (1986). The handbook of chlorination (2nd ed.). New York: Van Nostrand Reinhold. pp. 33–34. ISBN 0-442-29285-6.
  5. Clugston, M.; Flemming, R. (2000). Advanced Chemistry. Oxford University Press. p. 342. ISBN 978-0199146338.
  6. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  7. Morgan, D. V.; Board, K. (1991). An Introduction To Semiconductor Microtechnology (2nd ed.). Chichester, West Sussex, England: John Wiley & Sons. p. 23. ISBN 0471924784.
  8. "Solar Energy Firms Leave Waste Behind in China". The Washington Post. 9 March 2008.
  9. "International Chemical Safety Cards Tetrachlorosilane".
Salts and covalent derivatives of the chloride ion
HCl He
LiCl BeCl2 BCl3
B2Cl4		 CCl4 NCl3
ClN3		 Cl2O
ClO2
Cl2O7		 ClF
ClF3
ClF5		 Ne
NaCl MgCl2 AlCl
AlCl3		 SiCl4 P2Cl4
PCl3
PCl5		 S2Cl2
SCl2
SCl4		 Cl2 Ar
KCl CaCl
CaCl2		 ScCl3 TiCl2
TiCl3
TiCl4		 VCl2
VCl3
VCl4
VCl5		 CrCl2
CrCl3
CrCl4		 MnCl2 FeCl2
FeCl3		 CoCl2
CoCl3		 NiCl2 CuCl
CuCl2		 ZnCl2 GaCl2
GaCl3		 GeCl2
GeCl4		 AsCl3
AsCl5		 Se2Cl2
SeCl4		 BrCl KrCl
RbCl SrCl2 YCl3 ZrCl3
ZrCl4		 NbCl4
NbCl5		 MoCl2
MoCl3
MoCl4
MoCl5
MoCl6		 TcCl4 RuCl3 RhCl3 PdCl2 AgCl CdCl2 InCl
InCl2
InCl3		 SnCl2
SnCl4		 SbCl3
SbCl5		 Te3Cl2
TeCl4		 ICl
ICl3		 XeCl
XeCl2
XeCl4
CsCl BaCl2   HfCl4 TaCl5 WCl2
WCl3
WCl4
WCl5
WCl6		 Re3Cl9
ReCl4
ReCl5
ReCl6		 OsCl4 IrCl2
IrCl3
IrCl4		 PtCl2
PtCl4		 AuCl
AuCl3		 Hg2Cl2,
HgCl2		 TlCl PbCl2,
PbCl4		 BiCl3 PoCl2,
PoCl4		 AtCl RnCl2
FrCl RaCl2   Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
↓
LaCl3 CeCl3 PrCl3 NdCl2,
NdCl3		 PmCl3 SmCl2,
SmCl3		 EuCl2,
EuCl3		 GdCl3 TbCl3 DyCl2,
DyCl3		 HoCl3 ErCl3 TmCl2
TmCl3		 YbCl2
YbCl3		 LuCl3
AcCl3 ThCl4 PaCl5 UCl3
UCl4
UCl5
UCl6		 NpCl4 PuCl3 AmCl2
AmCl3		 CmCl3 BkCl3 CfCl3 EsCl3 Fm Md No LrCl3
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