Tetraethyl orthosilicate

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Tetraethyl orthosilicate
Tetraethyl orthosilicate.svg
Tetraethyl orthosilicate 3D.png
Identifiers
CAS number 78-10-4 YesY
PubChem 6517
ChemSpider 6270 YesY
Jmol-3D images Image 1
Properties
Molecular formula SiC8H20O4
Molar mass 208.33 g mol−1
Appearance colourless liquid
Density 0.933 g/mL at 20°C
Melting point −77 °C (−107 °F; 196 K)
Boiling point 166 to 169 °C (331 to 336 °F; 439 to 442 K)
Solubility in water miscible, but readily decomposes
Hazards
Main hazards Flammable, Harmful by inhalation
Flash point 45 °C (113 °F; 318 K)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Tetraethyl orthosilicate is the chemical compound with the formula Si(OC2H5)4. Often abbreviated TEOS, this molecule consists of four ethyl groups attached to SiO44− ion, which is called orthosilicate. As an ion in solution, orthosilicate is difficult to isolate as it is ephemeral and only occurs in very dilute solutions. Alternatively TEOS can be considered to be the ethyl ester of orthosilicic acid, Si(OH)4. It is a prototypical alkoxide.

TEOS is a tetrahedral molecule. Many analogues exist, and most are prepared by alcoholysis of silicon tetrachloride:

SiCl4 + 4 ROH → Si(OR)4 + 4 HCl

where R = alkyl such as methyl, ethyl, propyl, etc.

Applications[edit]

TEOS is mainly used as a crosslinking agent in silicone polymers and as a precursor to silicon dioxide in the semiconductor industry.[1] TEOS is also used as the silica source for synthesis of zeolites.[2] Other applications include coatings for carpets and other objects. TEOS is used in the production of aerogel. These applications exploit the reactivity of the Si-OR bonds.[3]

Other reactions[edit]

TEOS has the remarkable property of easily converting into silicon dioxide. This reaction occurs upon the addition of water:

Si(OC2H5)4 + 2 H2O → SiO2 + 4 C2H5OH

This hydrolysis reaction is an example of a sol-gel process. The side product is ethanol. The reaction proceeds via a series of condensation reactions that convert the TEOS molecule into a mineral-like solid via the formation of Si-O-Si linkages. Rates of this conversion are sensitive to the presence of acids and bases, both of which serve as catalysts. The Stöber process allows the formation of monodisperse silica particles.

At elevated temperatures (>600 °C), TEOS converts to silicon dioxide:

Si(OC2H5)4 → SiO2 + 2 (C2H5)2O

The volatile coproduct is diethyl ether.

References[edit]

  1. ^ Bulla, D.A.P; Morimoto, N.I (1998). "Deposition of thick TEOS PECVD silicon oxide layers for integrated optical waveguide applications". Thin Solid Films 334: 60. doi:10.1016/S0040-6090(98)01117-1. 
  2. ^ Kulprathipanja, Santi (2010) Zeolites in Industrial Separation and Catalysis, Wiley-VCH Verlag GmbH & Co. KGaA, ISBN 3527629572.
  3. ^ Rösch, Lutz; John, Peter and Reitmeier, Rudolf (2002) "Silicon Compounds, Organic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a24_021.

External links[edit]