Tetramethyl orthosilicate
[CAS# 681-84-5]

Identification

• Classification: Chemical reagent >> Organic reagent >> Silane
• Name: Tetramethyl orthosilicate
• Synonyms: Methyl silicate; Tetramethoxysilane
• Molecular Formula: C₄H₁₂O₄Si
• Molecular Weight: 152.22
• CAS Registry Number: 681-84-5
• EC Number: 211-656-4
• SMILES: CO[Si](OC)(OC)OC

Properties

• Density: 1.0±0.1 g/cm³ Calc.^*, 1.023 g/mL (Expl.)
• Melting point: -4 ºC (Expl.)
• Boiling point: 121.2±8.0 ºC 760 mmHg (Calc.)^*, 121 - 122 ºC (Expl.)
• Flash point: 28.9 ºC (Calc.)^*, 26 ºC (Expl.)
• Solubility: water, hydrolysis (Expl.)
• Index of refraction: 1.382 (Calc.)^*, 1.368 (Expl.)

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS02;GHS05;GHS06;GHS07;GHS08 DangerGHS02
• Hazard Statements: H226-H315-H318-H330-H335-H372
• Precautionary Statements: P210-P233-P240-P241-P242-P243-P260-P261-P264-P264+P265-P270-P271-P280-P284-P302+P352-P303+P361+P353-P304+P340-P305+P354+P338-P316-P317-P319-P320-P321-P332+P317-P362+P364-P370+P378-P403+P233-P403+P235-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Flammable liquids	Flam. Liq.	3	H226
Serious eye damage	Eye Dam.	1	H318
Acute toxicity	Acute Tox.	1	H330
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335
Specific target organ toxicity - repeated exposure	STOT RE	1	H372
Acute toxicity	Acute Tox.	4	H302
Acute toxicity	Acute Tox.	2	H330
Specific target organ toxicity - single exposure	STOT SE	1	H370
Skin corrosion	Skin Corr.	1A	H314
Flammable liquids	Flam. Liq.	2	H225
Flammable liquids	Flam. Liq.	2	H226
Eye irritation	Eye Irrit.	2A	H319
Reproductive toxicity	Repr.	1B	H360
Specific target organ toxicity - single exposure	STOT SE	2	H371

• Transport Information: UN 2606

Discovory and Applicatios

Tetramethyl orthosilicate (TMOS), also known as tetramethoxysilane, is an organosilicon compound with the formula Si(OCH₃)₄. It is a colorless, volatile liquid that serves as a key silicon alkoxide used in the preparation of silica-based materials. TMOS is a structural analogue of tetraethyl orthosilicate (TEOS), differing only by the presence of methyl instead of ethyl substituents, which makes it more volatile and reactive toward hydrolysis. The compound is an essential precursor in sol–gel chemistry, thin-film deposition, and the synthesis of silicate glasses, coatings, and ceramics.

TMOS was first studied in the early 20th century during investigations into organosilicon chemistry and the hydrolysis of silicon esters. It became widely used after the development of the sol–gel process in the 1950s and 1960s, when silicon alkoxides were recognized as efficient precursors for producing high-purity silica materials under mild conditions. TMOS hydrolyzes in the presence of water to form silicic acid (Si(OH)₄), which subsequently undergoes condensation to yield amorphous silica (SiO₂) and methanol as a byproduct. The overall process allows for controlled formation of porous or dense silica structures, depending on reaction parameters such as pH, temperature, and solvent composition.

In materials science, TMOS is employed to synthesize silica gels, aerogels, and thin films with precise control over pore size and morphology. Due to its high reactivity, it is particularly suited for low-temperature sol–gel processes that require fine particle formation or thin coating applications. TMOS-derived silica coatings are used to provide abrasion resistance, thermal insulation, or optical transparency on glass, metal, or polymer substrates. Furthermore, TMOS is utilized as a precursor in chemical vapor deposition (CVD) and plasma-enhanced CVD for producing high-quality silicon oxide layers in microelectronics and optics.

In the field of biotechnology, TMOS has been applied in the encapsulation of enzymes, cells, and biomolecules within silica matrices. The mild hydrolysis and condensation conditions make it possible to entrap biological materials without denaturation, creating stable bioactive composites used for biosensors, biocatalysts, and controlled-release systems. TMOS-based sol–gel matrices are also valued for their tunable porosity and chemical inertness, which enhance the lifetime and functionality of encapsulated biomolecules.

TMOS must be handled with care, as it reacts violently with water and moisture to form methanol and silica, both of which can present health hazards. Exposure to TMOS vapors may lead to irritation of the eyes and respiratory tract, and inhalation can result in the formation of silica particles in the lungs. Therefore, appropriate protective equipment and ventilation are required when handling the compound, and storage must be under dry, inert conditions.

The reactivity and versatility of tetramethyl orthosilicate have made it one of the most important reagents in the field of inorganic and materials chemistry. Its applications extend from advanced coatings and catalysts to optoelectronics and bioencapsulation systems, demonstrating its central role as a molecular bridge between organosilicon chemistry and practical silica materials.

References

Brinker CJ and Scherer GW (1990) Sol–Gel Science: The Physics and Chemistry of Sol–Gel Processing. Academic Press, San Diego. DOI: 10.1016/C2009-0-22386-5

Hench LL and West JK (1990) The sol–gel process. Chemical Reviews 90(1) 33–72. DOI: 10.1021/cr00099a003

Schmidt H (1988) Chemistry of material preparation by the sol–gel process. Journal of Non-Crystalline Solids 100(1–3) 51–64. DOI: 10.1016/0022-3093(88)90006-3