Tetraethyl orthosilicate

Chembox new
ImageFileL1 = Tetraethyl orthosilicate.svg
ImageSizeL1 = 150px
ImageFileR1 = Tetraethyl orthosilicate 3D.png ImageSizeR1 = 150px
IUPACName = tetraethoxysilane
OtherNames = tetraethyl orthosilicate; ethyl silicate; silicic acid, tetraethyl ester; silicon ethoxide; TEOS
Section1 = Chembox Identifiers
CASNo = 78-10-4
PubChem = 6517
SMILES =

Section2 = Chembox Properties
Formula = SiC₈H₂₀O₄
MolarMass = 208.32
Appearance = colourless liquid
Density = 0.94
MeltingPt = -77 °C
BoilingPt = 166-169 °C
Solubility = decomp
Section3 = Chembox Hazards
MainHazards = Toxic
FlashPt = 45 °C
Autoignition =

Tetraethyl orthosilicate is the 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 HClwhere 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. These applications exploit the reactivity of the Si-OR bonds. [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]

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)₂The volatile coproduct is diethylether.

References

* [http://webbook.nist.gov/cgi/cbook.cgi?ID=C78104 NIST Standard Reference Database 69, June 2005 Release: NIST Chemistry WebBook]