Tetraethyl orthosilicate

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Tetraethyl orthosilicate
Tetraethyl orthosilicate.svg
Tetraethyl orthosilicate 3D.png
Names
IUPAC name
tetraethoxysilane
Other names
tetraethyl orthosilicate; ethyl silicate; silicic acid tetraethyl ester; silicon ethoxide; TEOS; tetraethyl silicate
Identifiers
78-10-4 YesY
ChemSpider 6270 YesY
Jmol-3D images Image
PubChem 6517
UNII 42064KRE49 YesY
Properties
SiC8H20O4
Molar mass 208.33 g mol−1
Appearance colourless liquid
Odor sharp, alcohol-like[1]
Density 0.933 g/mL at 20°C
Melting point −77 °C (−107 °F; 196 K)
Boiling point 168 °C (334 °F; 441 K)
reacts with water, soluble in ethanol, and 2-propanol
Vapor pressure 1 mmHg[1]
Hazards
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)[1]
TWA 10 ppm (85 mg/m3)[1]
700 ppm[1]
Except where noted otherwise, data is 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, it is a colorless liquid that degrades in water. TEOS is the ethyl ester of orthosilicic acid, Si(OH)4. It is a prototypical alkoxide.

TEOS is a tetrahedral molecule. Like its many analogues, TEOS is prepared by alcoholysis of silicon tetrachloride:

SiCl4 + 4 EtOH → Si(OEt)4 + 4 HCl

where Et = C2H5

Applications[edit]

TEOS is mainly used as a crosslinking agent in silicone polymers and as a precursor to silicon dioxide in the semiconductor industry.[2] TEOS is also used as the silica source for synthesis of zeolites.[3] 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.[4]

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.

Safety[edit]

Although nontoxic to ingestion, TEOS vapor is highly damaging to eyes since it deposits silica.[5]

References[edit]

  1. ^ a b c d e "NIOSH Pocket Guide to Chemical Hazards #0282". National Institute for Occupational Safety and Health (NIOSH). 
  2. ^ 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. 
  3. ^ Kulprathipanja, Santi (2010) Zeolites in Industrial Separation and Catalysis, Wiley-VCH Verlag GmbH & Co. KGaA, ISBN 3527629572.
  4. ^ 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.
  5. ^ https://www.mathesongas.com/pdfs/msds/MAT09230.pdf

External links[edit]