Tetraethylorthosilicate

Tetraethyl orthosilicate

Names
IUPAC name tetraethoxysilane
Other names tetraethyl orthosilicate; ethyl silicate; silicic acid tetraethyl ester; silicon ethoxide; TEOS; tetraethyl silicate
Identifiers
CAS Number	78-10-4 Y
3D model (JSmol)	Interactive image
ChemSpider	6270 Y
ECHA InfoCard	100.000.986
PubChem CID	6517
UNII	42064KRE49 N
InChI InChI=1S/C8H20O4Si/c1-5-9-13(10-6-2,11-7-3)12-8-4/h5-8H2,1-4H3 Y Key: BOTDANWDWHJENH-UHFFFAOYSA-N Y InChI=1/C8H20O4Si/c1-5-9-13(10-6-2,11-7-3)12-8-4/h5-8H2,1-4H3 Key: BOTDANWDWHJENH-UHFFFAOYAS
SMILES CCO[Si](OCC)(OCC)OCC
Properties
Chemical formula	SiC8H20O4
Molar mass	208.33 g mol−1
Appearance	colourless liquid
Odor	sharp, alcohol-like
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)
Solubility in water	reacts with water, soluble in ethanol, and 2-propanol
Vapor pressure	1 mmHg
Hazards
Main hazards	Flammable, Harmful by inhalation
Flash point	45 °C (113 °F; 318 K)
Lethal dose or concentration (LD, LC):
LD50 (median dose)	6270 mg/kg (rat, oral)
LCLo (lowest published)	1000 ppm (rat, 4 hr) 700 ppm (guinea pig, 6 hr) 1740 ppm (guinea pig, 15 min) 1170 ppm (guinea pig, 2 hr)
US health exposure limits (NIOSH):
PEL (Permissible)	TWA 100 ppm (850 mg/m3)
REL (Recommended)	TWA 10 ppm (85 mg/m3)
IDLH (Immediate danger)	700 ppm
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
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:

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

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

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

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.