Tetraethyl orthosilicate

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Tetraethyl orthosilicate
Image:Tetraethyl orthosilicate.svg	Image:Tetraethyl orthosilicate 3D.png
IUPAC name	tetraethoxysilane
Other names	tetraethyl orthosilicate; ethyl silicate; silicic acid, tetraethyl ester; silicon ethoxide; TEOS
Identifiers
CAS number	78-10-4
PubChem	6517
Properties
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
Hazards
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 SiO₄^4- 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.

Applications

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.

External links

• WebBook page for SiC8H20O4de:Tetraethylorthosilikat