TETRAETHYL ORTHOSILICATE

'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.

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Applications

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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 SiC8H20O4