tetraethyl orthosilicate; ethyl silicate; silicic acid tetraethyl ester; silicon ethoxide; TEOS
|Molar mass||208.33 g mol−1|
|Density||0.933 g/mL at 20°C|
|Melting point||−77 °C (−107 °F; 196 K)|
|Boiling point||166 °C (331 °F; 439 K)|
|insoluble in water, soluble in ethanol, and 2-propanol|
|Main hazards||Flammable, Harmful by inhalation|
|Flash point||45 °C (113 °F; 318 K)|
|US health exposure limits (NIOSH):|
|TWA 100 ppm (850 mg/m3)|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
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.
- 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. TEOS is also used as the silica source for synthesis of zeolites. 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 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.
- "NIOSH Pocket Guide to Chemical Hazards". National Institute for Occupational Safety and Health (NIOSH). id=0282.
- 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.
- Kulprathipanja, Santi (2010) Zeolites in Industrial Separation and Catalysis, Wiley-VCH Verlag GmbH & Co. KGaA, ISBN 3527629572.
- 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.