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Tetramethyl orthosilicate
View on Wikipedia| Names | |
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| IUPAC name
Tetramethyl orthosilicate
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Other names
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| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.010.598 |
PubChem CID
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| UNII | |
CompTox Dashboard (EPA)
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| Properties | |
| Si(OCH3)4 | |
| Molar mass | 152.221 g·mol−1 |
| 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) |
| organic solvents | |
| Vapor pressure | 12 mmHg (25°C)[1] |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards
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toxic |
| Flash point | 96 °C; 205 °F; 369 K[1] |
| NIOSH (US health exposure limits): | |
PEL (Permissible)
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none[1] |
REL (Recommended)
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TWA 1 ppm (6 mg/m3)[1] |
IDLH (Immediate danger)
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N.D.[1] |
| Related compounds | |
Other cations
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Tetraethyl orthosilicate Trimethyl borate Trimethyl phosphite |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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. It is the tetramethyl ester of orthosilicic acid. 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:
In organic synthesis, Si(OCH3)4 has been used to convert ketones and aldehydes to the corresponding ketals and acetals, respectively.[2]
Safety
[edit]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]. At low concentrations (200 ppm per 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
[edit]- ^ 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
[edit]Tetramethyl orthosilicate
View on GrokipediaChemical Identity
Formula and Structure
Tetramethyl orthosilicate, also known as tetramethoxysilane, has the molecular formula , which can also be written as . This composition includes one silicon atom and four methoxy groups, resulting in a total of four carbon atoms, twelve hydrogen atoms, and four oxygen atoms, corresponding to the empirical formula . The molecule features a central silicon atom covalently bonded to four methoxy () groups, forming a tetrahedral geometry around the silicon center with bond angles approximately 109.5°. This structure is confirmed by electron diffraction studies in the gas phase, which reveal a roughly tetrahedral arrangement consistent with the sp³ hybridization of the silicon atom. The molecular weight of tetramethyl orthosilicate is 152.22 g/mol, calculated from the atomic masses of its constituent elements. In comparison to analogous orthosilicates, such as tetraethyl orthosilicate (TEOS) with the formula , tetramethyl orthosilicate possesses shorter methyl alkyl chains rather than ethyl groups, which influences its volatility and hydrolysis kinetics while maintaining the same tetrahedral silicon core.Nomenclature
Tetramethoxysilane is the systematic name for the compound, reflecting its structure as a silicon atom bonded to four methoxy groups. The preferred IUPAC name is tetramethyl silicate.[3] Commonly referred to as tetramethyl orthosilicate or TMOS, it is also known as methyl silicate.[3] The abbreviation TMOS is widely used in scientific literature for brevity.[1] The prefix "ortho" in tetramethyl orthosilicate denotes its derivation from orthosilicic acid, Si(OH)4, distinguishing it from partially condensed or dehydrated silicate forms; this nomenclature convention, established in the mid-19th century, signifies the acid with the maximum water content or hydration degree.[4] The CAS Registry Number assigned to the compound is 681-84-5.[3] Additional synonyms documented in chemical databases include silicic acid tetramethyl ester, silicon methoxide, and methyl orthosilicate.[3]Physical Properties
Appearance and Basic Characteristics
Tetramethyl orthosilicate is a colorless, clear liquid at standard conditions.[5] It exhibits a mild, ethereal odor.[6] The compound has a density of 1.032 g/cm³ at 20 °C.[7] Its refractive index ranges from 1.3670 to 1.3700 at 20 °C (589 nm).[8] The flash point is 26 °C (closed cup).[1] Tetramethyl orthosilicate is insoluble in water (hydrolyzes on contact) but it is soluble in organic solvents such as ethanol, acetone, and chloroform.[1][9][10]Thermodynamic Data
Tetramethyl orthosilicate exhibits the following key thermodynamic properties relevant to its handling and storage. Its melting point is -4 °C, indicating it exists as a liquid near room temperature under typical ambient conditions.[1] The boiling point is 121–122 °C at standard atmospheric pressure (760 mmHg), reflecting moderate volatility suitable for distillation processes.[1] Vapor pressure data underscore its potential for evaporation in open systems. At 25 °C, the vapor pressure is 12 mmHg, which facilitates its use in vapor deposition but necessitates controlled environments to prevent unintended losses.[11]| Property | Value | Conditions | Source |
|---|---|---|---|
| Enthalpy of vaporization | 41.4 kJ/mol | Standard conditions | NIST WebBook[12] |
| Specific heat capacity (liquid) | 240.5 J/mol·K | 298.15 K | NIST WebBook[13] |


