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Tetraethyl orthosilicate is the 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:
where R = alkyl such as methyl, ethyl, propyl, etc. [edit] ApplicationsTEOS is mainly used as a crosslinking agent in silicone polymers. Other applications include coatings for carpets and other objects. These applications exploit the reactivity of the Si-OR bonds.[1] [edit] Other reactionsTEOS has the remarkable property of easily converting 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. [edit] References
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