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Structural formula
Structural formula of tetramethylorthosilicate
Surname Tetramethylorthosilicate
other names
  • Tetramethyl orthosilicate
  • Tetramethyl silicate
  • Methyl silicate
  • TMOS
Molecular formula C 4 H 12 O 4 Si
Brief description

colorless liquid with an ethereal odor

External identifiers / databases
CAS number 681-84-5
EC number 211-656-4
ECHA InfoCard 100.010.598
PubChem 12682
ChemSpider 12161
Wikidata Q377159
Molar mass 152.22 g mol −1
Physical state



1.03 g cm −3

Melting point

−2 ° C

boiling point

122 ° C

Vapor pressure
  • 13 h Pa (20 ° C)
  • 18 hPa (25 ° C)

Decomposes in water

Refractive index

1.3683 (20 ° C)

safety instructions
GHS labeling of hazardous substances
02 - Highly / extremely flammable 06 - Toxic or very toxic 05 - Corrosive


H and P phrases H: 226-315-318-330
P: 210-260-280-304 + 340 + 310-305 + 351 + 338 + 310-370 + 378

Switzerland: 1 ml m −3 or 6 mg m −3

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Tetramethylorthosilicate (also tetramethoxysilane , silicic acid tetramethyl ester or methyl silicate , TMOS for short ) is a colorless liquid.

Extraction and presentation

Tetramethylorthosilicate can be obtained by reacting silicon tetrachloride with methanol .


Tetramethylorthosilicate slowly hydrolyzes with water to form orthosilicic acid and methanol :

TMOS is flammable and toxic.

Tetramethylorthosilicate forms highly flammable vapor-air mixtures. The compound has a flash point of 26 ° C. The explosion range is between 0.88% by volume as the lower explosion limit (LEL) and 23.8% by volume as the upper explosion limit (UEL). The ignition temperature is 245 ° C. The substance therefore falls into temperature class T3.


It is used in sol-gel processes as silica - precursor for the preparation of gels used especially silica aerogels . The compound is sparingly soluble in water; an alcohol is therefore usually used as the reaction medium as a solubilizer.

safety instructions

Contact of tetramethylorthosilicate with the skin causes redness and pain. Contact with the vapors can cause irritation and redness in the eyes. Inhalation causes a burning sensation, a sore throat and cough and can lead to pulmonary edema, kidneys and liver can also be damaged. If swallowed, stomach pain may occur. Risk of blindness through inhalation (releases methanol in the blood).

The vapors of tetramethylorthosilicate can form an explosive mixture with air ( flash point 26 ° C, ignition temperature 240 ° C).

Individual evidence

  1. a b c d e f g h i j k l m Entry on tetramethyl orthosilicate in the GESTIS substance database of the IFA , accessed on August 21, 2019(JavaScript required) .
  2. David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-480.
  3. Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values (search for 681-84-5 or tetramethylorthosilicate ), accessed on November 2, 2015.
  4. Georg Brauer (Ed.), With the collaboration of Marianne Baudler a . a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume I, Ferdinand Enke, Stuttgart 1975, ISBN 3-432-02328-6 , p. 702.