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Tetraethyl orthosilicate

Tetraethyl orthosilicate
IUPAC name tetraethoxysilane
Other names tetraethyl orthosilicate; ethyl silicate; silicic acid, tetraethyl ester; silicon ethoxide; TEOS
CAS number 78-10-4
PubChem 6517
Molecular formula SiC8H20O4
Molar mass 208.32
Appearance colourless liquid
Density 0.94
Melting point

-77 °C

Boiling point

166-169 °C

Solubility in water decomp
Main hazards Toxic
Flash point 45 °C
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Tetraethyl orthosilicate is the major 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.

TEOS is a tetrahedral molecule. Many analogues exist, and most are prepared by alcoholysis of silicon tetrachloride:

SiCl4 + 4 ROH → Si(OR)4 + 4 HCl

where R = alkyl such as methyl, ethyl, propyl, etc.


TEOS has many remarkable properties, but perhaps the most useful is its easy conversion 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.

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

Si(OC2H5)4 → SiO2 + O(C2H5)2

The volatile coproduct is diethylether.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Tetraethyl_orthosilicate". A list of authors is available in Wikipedia.
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