Tetraethyl orthosilicate 1
CAS number 78-10-4
Jmol-3D images Image 1
Molecular formula SiC8
Molar mass 208.33 g mol−1
Appearance colourless liquid
Density 0.933 g/mL at 20°C
Melting point −77 °C, 196 K, -107 °F
Boiling point 166-169 °C, 439-442 K, 331-336 °F
Solubility in water miscible, but readily decomposes
Main hazards Flammable, Harmful by inhalation
Flash point 45 °C
(what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Tetraethyl orthosilicate is the chemical compound with the formula Si(OC
. Often abbreviated TEOS, this
molecule consists of four ethyl groups attached to SiO
ion, which is called orthosilicate. As an ion in solution,
Tetraethyl orthosilicate 2
orthosilicate does not exist. Alternatively TEOS can be considered to be the ethyl ester of orthosilicic acid, Si(OH)
It is a prototypical alkoxide.
TEOS is a tetrahedral molecule. Many analogues exist, and most are prepared by alcoholysis of silicon tetrachloride:
+ 4 ROH → Si(OR)
+ 4 HCl
where R = alkyl such as methyl, ethyl, propyl, etc.
TEOS is mainly used as a crosslinking agent in silicone polymers and as a precursor to silicon dioxide in the
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.
TEOS has the remarkable property of easily converting into silicon dioxide. This reaction occurs upon the addition
+ 2 H
O → SiO
+ 4 C
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:
+ 2 (C
The volatile coproduct is diethyl ether.
 D. Bulla, Deposition of thick TEOS PECVD silicon oxide layers for integrated optical waveguide applications. Thin Solid Films. 1998;
334(1-2):60-64. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0040609098011171.
 Lutz Rösch, Peter John, Rudolf Reitmeier "Silicon Compounds, Organic" Ullmann's Encyclopedia of Industrial Chemistry, 2002,
Wiley-VCH, Weinheim. . Article Online Posting Date: June 15, 2000
• NIST Standard Reference Database 69, June 2005 Release: NIST Chemistry WebBook (http://webbook.nist.
• Details of TEOS deposition process (http://timedomaincvd.com/CVD_Fundamentals/films/
• CDC - NIOSH Pocket Guide to Chemical Hazards (http://www.cdc.gov/niosh/npg/npgd0282.html)