Silicon tetrachloride

Last updated
Silicon tetrachloride
Silicon tetrachloride.svg
Silicon-tetrachloride-3D-vdW.png
Names
IUPAC name
Tetrachlorosilane
Other names
Silicon tetrachloride
Tetrachlorosilane
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.037 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 233-054-0
PubChem CID
RTECS number
  • VW0525000
UNII
UN number 1818
  • InChI=1S/Cl4Si/c1-5(2,3)4 Yes check.svgY
    Key: FDNAPBUWERUEDA-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/Cl4Si/c1-5(2,3)4
  • [Si](Cl)(Cl)(Cl)Cl
Properties
SiCl4
Molar mass 169.90 g/mol
AppearanceColourless 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
Std molar
entropy
(S298)
240 J·mol−1·K−1 [2]
−687 kJ·mol−1 [2]
Hazards
GHS labelling:
GHS-pictogram-exclam.svg
Warning
H315, H319, H335
P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501
NFPA 704 (fire diamond)
3
0
2
W
Safety data sheet (SDS) MSDS
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
Silicon tetrachloride (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

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. It's part chlorosilane family.

Contents

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 at 600 °C (1,112 °F): [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 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. [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 hexachlorodisilane 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.

Comparison with other SiX4 compounds

SiH4SiF4SiCl4SiBr4SiI4
b.p. (˚C) [7] -111.9-90.356.8155.0290.0
m.p. (˚C) [7] -185-95.0-68.85.0155.0
Si-X bond length (Å)>0.74 [8] 1.552.022.202.43
Si-X bond energy (kJ/mol) [9] 384582391310234

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 1250 °C was done:

SiCl
4
(g) + 2 H
2
(g) → Si(s) + 4 HCl(g) at 1250°C [10]

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.

As a feedstock in production of fused silica.

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. [11] The MSDS notes that one should "avoid all contact! In all cases consult a doctor! ... inhalation causes sore throat and Burning sensation". [12]

See also

Related Research Articles

<span class="mw-page-title-main">Silicon</span> Chemical element, symbol Si and atomic number 14

Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic table: carbon is above it; and germanium, tin, lead, and flerovium are below it. It is relatively unreactive.

Silane is an inorganic compound with chemical formula, SiH4. It is a colourless, pyrophoric, toxic gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. Silane with alkyl groups are effective water repellents for mineral surfaces such as concrete and masonry. Silanes with both organic and inorganic attachments are used as coupling agents.

<span class="mw-page-title-main">Trichlorosilane</span> Chemical compound

Trichlorosilane is an inorganic compound with the formula HCl3Si. It is a colourless, volatile liquid. Purified trichlorosilane is the principal precursor to ultrapure silicon in the semiconductor industry. In water, it rapidly decomposes to produce a siloxane polymer while giving off hydrochloric acid. Because of its reactivity and wide availability, it is frequently used in the synthesis of silicon-containing organic compounds.

<span class="mw-page-title-main">Silanol</span> Si–OH functional group in silicon chemistry

A silanol is a functional group in silicon chemistry with the connectivity Si–O–H. It is related to the hydroxy functional group (C–O–H) found in all alcohols. Silanols are often invoked as intermediates in organosilicon chemistry and silicate mineralogy. If a silanol contains one or more organic residue, it is an organosilanol.

Chlorosilanes are a group of reactive, chlorine-containing chemical compounds, related to silane and used in many chemical processes. Each such chemical has at least one silicon-chlorine bond. Trichlorosilane is produced on the largest scale. The parent chlorosilane is silicon tetrachloride.

<span class="mw-page-title-main">Chloroplatinic acid</span> Chemical compound

Chloroplatinic acid (also known as hexachloroplatinic acid) is an inorganic compound with the formula [H3O]2[PtCl6](H2O)x (0 ≤ x ≤ 6). A red solid, it is an important commercial source of platinum, usually as an aqueous solution. Although often written in shorthand as H2PtCl6, it is the hydronium (H3O+) salt of the hexachloroplatinate anion (PtCl2−
6
). Hexachloroplatinic acid is highly hygroscopic.

<span class="mw-page-title-main">Organosilicon chemistry</span> Organometallic compound containing carbon–silicon bonds

Organosilicon compounds are organometallic compounds containing carbon–silicon bonds. Organosilicon chemistry is the corresponding science of their preparation and properties. Most organosilicon compounds are similar to the ordinary organic compounds, being colourless, flammable, hydrophobic, and stable to air. Silicon carbide is an inorganic compound.

<span class="mw-page-title-main">Binary silicon-hydrogen compounds</span>

Silanes are saturated chemical compounds with the empirical formula SixHy. They are hydrosilanes, a class of compounds that includes compounds with Si-H and other Si-X bonds. All contain tetrahedral silicon and terminal hydrides. They only have Si–H and Si–Si single bonds. The bond lengths are 146.0 pm for a Si–H bond and 233 pm for a Si–Si bond. The structures of the silanes are analogues of the alkanes, starting with silane, SiH
4
, the analogue of methane, continuing with disilane Si
2
H
6
, the analogue of ethane, etc. They are mainly of theoretical or academic interest.

Titanium disilicide (TiSi2) is an inorganic chemical compound of titanium and silicon.

Hydrosilanes are tetravalent silicon compounds containing one or more Si-H bond. The parent hydrosilane is silane (SiH4). Commonly, hydrosilane refers to organosilicon derivatives. Examples include phenylsilane (PhSiH3) and triethoxysilane ((C2H5O)3SiH). Polymers and oligomers terminated with hydrosilanes are resins that are used to make useful materials like caulks.

<span class="mw-page-title-main">Dichlorosilane</span> Chemical compound

Dichlorosilane, or DCS as it is commonly known, is a chemical compound with the formula H2SiCl2. In its major use, it is mixed with ammonia (NH3) in LPCVD chambers to grow silicon nitride in semiconductor processing. A higher concentration of DCS·NH3 (i.e. 16:1), usually results in lower stress nitride films.

<span class="mw-page-title-main">Tetraethyl orthosilicate</span> Chemical compound

Tetraethyl orthosilicate, formally named tetraethoxysilane (TEOS), ethyl silicate is the organic chemical compound with the formula Si(OC2H5)4. TEOS is a colorless liquid. It degrades in water. TEOS is the ethyl ester of orthosilicic acid, Si(OH)4. It is the most prevalent alkoxide of silicon.

Dimethyldichlorosilane is a tetrahedral, organosilicon compound with the formula Si(CH3)2Cl2. At room temperature it is a colorless liquid that readily reacts with water to form both linear and cyclic Si-O chains. Dimethyldichlorosilane is made on an industrial scale as the principal precursor to dimethylsilicone and polysilane compounds.

Polysilicon hydrides are polymers containing only silicon and hydrogen. They have the formula where 0.2 ≤ n ≤ 2.5 and x is the number of monomer units. The polysilicon hydrides are generally colorless or pale-yellow/ocher powders that are easily hydrolyzed and ignite readily in air. The surfaces of silicon prepared by MOCVD using silane (SiH4) consist of a polysilicon hydride.

Polysilicon halides are silicon-backbone polymeric solids. At room temperature, the polysilicon fluorides are colorless to yellow solids while the chlorides, bromides, and iodides are, respectively, yellow, amber, and red-orange. Polysilicon dihalides (perhalo-polysilenes) have the general formula (SiX2)n while the polysilicon monohalides (perhalo-polysilynes) have the formula (SiX)n, where X is F, Cl, Br, or I and n is the number of monomer units in the polymer.

Chlorotrifluorosilane is an inorganic gaseous compound with formula SiClF3 composed of silicon, fluorine and chlorine. It is a silane that substitutes hydrogen with fluorine and chlorine atoms.

Khimprom Novocheboksarsk is a chemicals-producing company based in Novocheboksarsk, Russia. It is part of Orgsintez Group (Renova).

<span class="mw-page-title-main">Organosilanols</span> Organic compounds of the form R3–Si–OH

In organosilicon chemistry, organosilanols are a group of chemical compounds derived from silicon. More specifically, they are carbosilanes derived with a hydroxy group on the silicon atom. Organosilanols are the silicon analogs to alcohols. Silanols are more acidic and more basic than their alcohol counterparts and therefore show a rich structural chemistry characterized by hydrogen bonding networks which are particularly well studied for silanetriols.

<span class="mw-page-title-main">Tris(trimethylsilyl)silane</span> Chemical compound

Tris(trimethylsilyl)silane is the organosilicon compound with the formula (Me3Si)3SiH (where Me = CH3). It is a colorless liquid that is classified as a hydrosilane since it contains an Si-H bond. The compound is notable as having a weak Si-H bond, with a bond dissociation energy estimated at 84 kcal/mol. For comparison, the Si-H bond in trimethylsilane is 94 kcal/mol. With such a weak bond, the compound is used as a reagent to deliver hydrogen atoms. The compound has been described as an environmentally benign analogue of tributyltin hydride.

Silanes refers to diverse organosilicon charge-neutral compounds with the formula SiR
4
. The R substituents can any combination of organic or inorganic groups. Most silanes contain Si-C bonds, and are discussed under organosilicon compounds. Some contain Si-H bonds and are discussed under hydrosilanes.

References

  1. 1 2 3 P. W. Schenk (1963). "Phosphorus(V) fluoride". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 1. NY,NY: Academic Press. pp. 282–683.
  2. 1 2 Zumdahl, S. S. (2009). Chemical Principles (6th ed.). Houghton Mifflin. p. A22. ISBN   978-0-618-94690-7.
  3. 1 2 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. 1 2 Silicon Compounds, Silicon Halides. Collins, W.: Kirk-Othmer Encyclopedia of Chemical Technology; John Wiley & Sons, Inc, 2001.
  8. "What is the bond length of the H-H bond?". Answers.com .
  9. Ebsworth, E. A. V. In Volatile Silicon Compounds; Taube, H.; Maddock, A. G.; Inorganic Chemistry; Pergamon Press Book: New York, NY, 1963; Vol. 4.
  10. Morgan, D. V.; Board, K. (1991). An Introduction To Semiconductor Microtechnology (2nd ed.). Chichester, West Sussex, England: John Wiley & Sons. p. 23. ISBN   0471924784.
  11. "Solar Energy Firms Leave Waste Behind in China". The Washington Post. 9 March 2008.
  12. "International Chemical Safety Cards Tetrachlorosilane".