| Tetraethyl orthosilicate | |
|---|---|
 |
 |
| 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 | 208.33 |
| 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 |
| (what is this?) (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
|
| Infobox references | |
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:
- SiCl4 + 4 ROH → Si(OR)4 + 4 HCl
where R = alkyl such as methyl, ethyl, propyl, etc.
Applications
TEOS is mainly used as a crosslinking agent in silicone polymers. Other applications include coatings for carpets and other objects. TEOS is used in the production of aerogel. These applications exploit the reactivity of the Si-OR bonds.[1]
Other reactions
TEOS has the remarkable property of easily converting 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 + 2O(C2H5)2
The volatile coproduct is diethylether.
References
- ^ Lutz Rösch, Peter John, Rudolf Reitmeier "Silicon Compounds, Organic" Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a24_021. Article Online Posting Date: June 15, 2000
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