Tetramethyl orthosilicate

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Tetramethyl orthosilicate
Tetramethyl orthosilicate.svg Tetramethyl orthosilicate 3D.png
CAS number 681-84-5 YesY
PubChem 12682
ChemSpider 12161 YesY
Jmol-3D images Image 1
Molecular formula SiC4H12O4
Molar mass 152.25
Appearance colourless liquid
Density 1.032
Melting point 4–5 °C
Boiling point 121–122 °C
Solubility in water organic solvents
Main hazards toxic
Related compounds
Other cations Trimethyl borate
Trimethyl phosphite
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Tetramethyl orthosilicate is the chemical compound with the formula Si(OCH3)4. This molecule consists of four methyl groups attached to the hypothetical anion SiO44-. The basic properties are similar to the more popular tetraethyl orthosilicate, which is usually preferred because the product of hydrolysis, ethanol, is less toxic than methanol.

Tetramethyl orthosilicate hydrolyzes to SiO2:

Si(OCH3)4 + 2 H2O → SiO2 + 4 CH3OH

In organic synthesis, Si(OCH3)4 has been used to convert ketones and aldehydes to the corresponding ketals and acetals, respectively.[1]


The hydrolysis of Si(OCH3)4 produces insoluble SiO2 and CH3OH (methanol). Even at low concentrations inhalation causes lung lesions, and at slightly higher concentrations eye contact with the vapor causes blindness. Worse, at low concentrations (200ppm/15min) the damage is often insidious, with onset of symptoms hours after exposure.[2] The mode of action is the precipitation of silica in the eyes and/or lungs. Contrary to common information, including several erroneous MSDS sheets, the methanol produced is relatively innocuous. The mechanisms of methanol toxicity are well established, methanol causes blindness via conversion to toxic formaldehyde in the liver; methanol splashes to the eye cause only moderate and reversible eye irritation.[3]

Tetraethyl orthosilicate is safer for two reasons. 1) It is considerably less volatile. 2) It is hydrolyzed more slowly by the water in the lungs and on the eyes (due to steric bulk).


  1. ^ Sakurai, H. "Silicon(IV) Methoxide" in Encyclopedia of Reagents for Organic Synthesis 2001 John Wiley & Sons. doi:10.1002/047084289X.rs012
  2. ^ "Tetramethyl silicate". National Library of Medicine - Hazardous Substances Data Bank. National Library of Medicine. Retrieved 11 February 2013. 
  3. ^ "Methanol". Hazardous Substances Data Bank - National Library of Medicine. National Library of Medicine. Retrieved 11 February 2013. 

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