Tetraethyl orthosilicate

Tetraethyl orthosilicate
Names
IUPAC name
tetraethoxysilane
Other names
tetraethyl orthosilicate; ethyl silicate; silicic acid tetraethyl ester; silicon ethoxide; TEOS; tetraethyl silicate
Identifiers
78-10-4 YesY
3D model (Jmol) Interactive image
ChemSpider 6270 YesY
ECHA InfoCard 100.000.986
PubChem 6517
UNII 42064KRE49 N
Properties
SiC8H20O4
Molar mass 208.33 g mol−1
Appearance colourless liquid
Odor sharp, alcohol-like[1]
Density 0.933 g/mL at 20 °C
Melting point −77 °C (−107 °F; 196 K)
Boiling point 168 to 169 °C (334 to 336 °F; 441 to 442 K)
reacts with water, soluble in ethanol, and 2-propanol
Vapor pressure 1 mmHg[1]
Hazards
Main hazards Flammable, Harmful by inhalation
Flash point 45 °C (113 °F; 318 K)
Lethal dose or concentration (LD, LC):
6270 mg/kg (rat, oral)[2]
1000 ppm (rat, 4 hr)
700 ppm (guinea pig, 6 hr)
1740 ppm (guinea pig, 15 min)
1170 ppm (guinea pig, 2 hr)[2]
US health exposure limits (NIOSH):
PEL (Permissible)
 TWA 100 ppm (850 mg/m3)[1]
REL (Recommended)
 TWA 10 ppm (85 mg/m3)[1]
IDLH (Immediate danger)
 700 ppm[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Tetraethyl orthosilicate, formally named tetraethoxysilane, is the chemical compound with the formula Si(OC2H5)4. Often abbreviated TEOS, it is a colorless liquid that degrades in water. TEOS is the ethyl ester of orthosilicic acid, Si(OH)4. It is the most prevalent alkoxide of silicon.

TEOS is a tetrahedral molecule. Like its many analogues, it is prepared by alcoholysis of silicon tetrachloride:

SiCl4 + 4 EtOH → Si(OEt)4 + 4 HCl

where Et is the ethyl radical, C2H5, and thus EtOH is ethanol.

Applications

TEOS is mainly used as a crosslinking agent in silicone polymers and as a precursor to silicon dioxide in the semiconductor industry.[3] TEOS is also used as the silica source for synthesis of some zeolites.[4] 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.[5]

Other reactions

TEOS easily converts to silicon dioxide upon the addition of water:

Si(OC2H5)4 + 2 H2O → SiO2 + 4 C2H5OH

An idealized equation is shown, in reality the silica produced is hydrated. 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. The Stöber process allows the formation of monodisperse and mesoporous silica.[6][7][8]

At elevated temperatures (>600 °C), TEOS converts to silicon dioxide:

Si(OC2H5)4 → SiO2 + 2 (C2H5)2O

The volatile coproduct is diethyl ether.

Safety

Although nontoxic to ingestion, TEOS vapor is highly damaging to eyes since it deposits silica.[9]

References

  1. 1 2 3 4 5 "NIOSH Pocket Guide to Chemical Hazards #0282". National Institute for Occupational Safety and Health (NIOSH).
  2. 1 2 "Ethyl silicate". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH).
  3. ↑ Bulla, D.A.P; Morimoto, N.I (1998). "Deposition of thick TEOS PECVD silicon oxide layers for integrated optical waveguide applications". Thin Solid Films. 334: 60. Bibcode:1998TSF...334...60B. doi:10.1016/S0040-6090(98)01117-1.
  4. ↑ Kulprathipanja, Santi (2010) Zeolites in Industrial Separation and Catalysis, Wiley-VCH Verlag GmbH & Co. KGaA, ISBN 3527629572.
  5. ↑ Rösch, Lutz; John, Peter and Reitmeier, Rudolf "Silicon Compounds, Organic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a24_021.
  6. ↑ Boday, Dylan J.; Wertz, Jason T.; Kuczynski, Joseph P. (2015). "Functionalization of Silica Nanoparticles for Corrosion Prevention of Underlying Metal". In Kong, Eric S. W. Nanomaterials, Polymers and Devices: Materials Functionalization and Device Fabrication. John Wiley & Sons. pp. 121–140. ISBN 9781118866955.
  7. ↑ Kicklebick, Guido (2015). "Nanoparticles and Composites". In Levy, David; Zayat, Marcos. The Sol-Gel Handbook: Synthesis, Characterization and Applications. 3. John Wiley & Sons. pp. 227–244. ISBN 9783527334865.
  8. ↑ Berg, John C. (2009). "Colloidal Systems: Phenomenology and Characterization". An Introduction to Interfaces and Colloids: The Bridge to Nanoscience. World Scientific Publishing. pp. 367–368, 452–454. ISBN 9789813100985.
  9. ↑ https://www.mathesongas.com/pdfs/msds/MAT09230.pdf
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