Tetraethyl orthosilicate

 ( Ethoxy Compounds ) 

Tetraethyl orthosilicate, formally named tetraethoxysilane ( TEOS), ethyl silicate is the organic chemical compound with the chemical formula Si(OC₂H₅)₄. TEOS is a colorless liquid. It degrades in water. TEOS is the of Silicic acid, Si(OH)₄. It is the most prevalent alkoxide of silicon.

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

SiCl₄ + 4 EtOH → Si(OEt)₄ + 4 HCl

where Et is the ethyl group, C₂H₅, and thus EtOH is ethanol.

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Applications 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 some zeolites.Kulprathipanja, Santi (2010) Zeolites in Industrial Separation and Catalysis, Wiley-VCH Verlag GmbH & Co. KGaA, . 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.Rösch, Lutz; John, Peter and Reitmeier, Rudolf "Silicon Compounds, Organic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2002. . TEOS has historically been used as an additive to alcohol based rocket fuels to decrease the heat flux to the chamber wall of regeneratively cooled engines by over 50%.

TEOS is used in steel casting industry as an inorganic binder and stiffener for making silica-based ceramic molding forms (see also sodium silicate). and as an inorganic binder for coatings (passivation) of different materials such as steel, glass, brass, and wood in order to make surfaces resistant to water, oxygen and high temperatures.. Further applications of TEOS include its use as an additive to solid polymers to enhance their adhesion to glass, steel or wood, as a binder for porcelain teeth crowns, and as a precursor to .

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Other reactions TEOS easily converts to silicon dioxide upon the addition of water:

Si(OC₂H₅)₄ + 2 H₂O → SiO₂ + 4 C₂H₅OH

An idealized equation is shown, in reality the silica produced is hydrated. 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 and bases, both of which serve as . The Stöber process allows the formation of monodisperse and mesoporous silica.

(2025). 9781118866955, John Wiley & Sons. ISBN 9781118866955

Guido Kicklebick (2025). 9783527334865, John Wiley & Sons. ISBN 9783527334865

John C. Berg (2025). 9789813100985, World Scientific Publishing. ISBN 9789813100985

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

Si(OC₂H₅)₄ → SiO₂ + 2 (C₂H₅)₂O

The volatile coproduct is diethyl ether.

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Safety Inhalation of TEOS induces eye and nose irritation, and eye contact with the liquid is irritating. High exposure to TEOS can lead to pulmonary edema, but hazards can be reduced by atmospheric humidity and vapor pressure conditions. The mechanism of irritation is similar to that of tetramethyl orthosilicate.

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External links

• NIST Standard Reference Database 69, June 2005 Release: NIST Chemistry WebBook
• CDC – NIOSH Pocket Guide to Chemical Hazards

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