|Jmol-3D images||Image 1|
|Molar mass||208.33 g mol−1|
|Density||0.933 g/mL at 20°C|
−77 °C, 196 K, -107 °F
166-169 °C, 439-442 K, 331-336 °F
|Solubility in water||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(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 does not exist. Alternatively TEOS can be considered to be the ethyl ester of orthosilicic acid, Si(OH)4. It is a prototypical alkoxide.
- SiCl4 + 4 ROH → Si(OR)4 + 4 HCl
TEOS is mainly used as a crosslinking agent in silicone polymers and as a precursor to silicon dioxide in the semiconductor industry. 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.
Other reactions 
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.
- 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.doi:10.1016/S0040-6090(98)01117-1
- Lutz Rösch, Peter John, Rudolf Reitmeier "Silicon Compounds, Organic" Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a24_021. Article Online Posting Date: June 15, 2000