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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:
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:
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:
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.|