Tetramethyl orthosilicate

Tetramethyl orthosilicate
Names
	IUPAC name Tetramethyl orthosilicate
	Other names tetramethyl orthosilicate; methyl silicate; silicic acid, tetramethyl ester; silicon methoxide; TMOS
Identifiers
CAS Number	681-84-5 ;
3D model (JSmol)	Interactive image;
ChemSpider	12161 ;
ECHA InfoCard	100.010.598
PubChem CID	12682;
UNII	19D35VPL66 ;
CompTox Dashboard (EPA)	DTXSID3027291 ;
	InChI InChI=1S/C4H12O4Si/c1-5-9(6-2,7-3)8-4/h1-4H3 Key: LFQCEHFDDXELDD-UHFFFAOYSA-N ; InChI=1/C4H12O4Si/c1-5-9(6-2,7-3)8-4/h1-4H3 Key: LFQCEHFDDXELDD-UHFFFAOYAT;
	SMILES CO[Si](OC)(OC)OC;
Properties
Chemical formula	SiC4H12O4
Molar mass	152.25
Appearance	colourless liquid
Density	1.032
Melting point	4 to 5 °C (39 to 41 °F; 277 to 278 K)
Boiling point	121 to 122 °C (250 to 252 °F; 394 to 395 K)
Solubility in water	organic solvents
Vapor pressure	12 mmHg (25°C)
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	toxic
Flash point	96 °C; 205 °F; 369 K
	NIOSH (US health exposure limits):
PEL (Permissible)	none
REL (Recommended)	TWA 1 ppm (6 mg/m3)
IDLH (Immediate danger)	N.D.
Related compounds
Other cations	Trimethyl borate; Trimethyl phosphite
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Tetramethyl orthosilicate (TMOS) is the chemical compound with the formula Si(OCH₃)₄. This molecule consists of four methoxy groups bonded to a silicon atom. 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.^[2]

Safety

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^{[citation needed]}. Worse, at low concentrations (200 ppm/15 min) the damage is often insidious, with onset of symptoms hours after exposure.^[3] The mode of action is the precipitation of silica in the eyes and/or lungs^{[citation needed]}. Contrary to common information, including several erroneous MSDS sheets, the methanol produced is only a risk through chronic exposure and is a comparatively small concern. The mechanisms of methanol toxicity are well established, methanol causes blindness via conversion to formaldehyde, then to toxic formic acid in the liver; methanol splashes to the eye cause only moderate and reversible eye irritation.^[4]

References

^ ^a ^b ^c ^d ^e NIOSH Pocket Guide to Chemical Hazards. "#0428". National Institute for Occupational Safety and Health (NIOSH).
^ Sakurai, H. "Silicon(IV) Methoxide" in Encyclopedia of Reagents for Organic Synthesis 2001 John Wiley & Sons. doi:10.1002/047084289X.rs012
^ "Tetramethyl silicate". National Library of Medicine - Hazardous Substances Data Bank. National Library of Medicine. Retrieved 11 February 2013.
^ "Methanol". Hazardous Substances Data Bank - National Library of Medicine. National Library of Medicine. Retrieved 11 February 2013.

External links

[PGCH-1] NIOSH Pocket Guide to Chemical Hazards. "#0428". National Institute for Occupational Safety and Health (NIOSH).

[2] Sakurai, H. "Silicon(IV) Methoxide" in Encyclopedia of Reagents for Organic Synthesis 2001 John Wiley & Sons. doi:10.1002/047084289X.rs012

[HSDB_-_Tetramethyl_silicate-3] "Tetramethyl silicate". National Library of Medicine - Hazardous Substances Data Bank. National Library of Medicine. Retrieved 11 February 2013.

[Methanol_-_HSDB-4] "Methanol". Hazardous Substances Data Bank - National Library of Medicine. National Library of Medicine. Retrieved 11 February 2013.

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