Tetraethyl orthosilicate
[CAS# 78-10-4]

Identification

• Classification: Organic raw materials >> Inorganic acid ester
• Name: Tetraethyl orthosilicate
• Synonyms: Ethyl silicate; Tetraethoxysilane; TEOS
• Molecular Formula: C₈H₂₀O₄Si
• Molecular Weight: 208.33
• CAS Registry Number: 78-10-4
• EC Number: 201-083-8
• SMILES: CCO[Si](OCC)(OCC)OCC

Properties

• Density: 0.9±0.1 g/cm³ Calc.^*, 0.934 g/mL (Expl.)
• Melting point: -85 °C (Expl.)
• Boiling point: 165.5 °C 760 mmHg (Calc.)^*, 168 °C (Expl.)
• Flash point: 46.7 °C (Calc.)^*, 46 °C (Expl.)
• Solubility: water, Hydrolysis (Expl.)
• Index of refraction: 1.409 (Calc.)^*, 1.382 (Expl.)

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

Safety Data

• Hazard Symbols: GHS02;GHS07 Warning
• Risk Statements: H226-H319-H332-H335
• Safety Statements: P210-P233-P240-P241-P242-P243-P261-P264+P265-P271-P280-P303+P361+P353-P304+P340-P305+P351+P338-P317-P319-P337+P317-P370+P378-P403+P233-P403+P235-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Flammable liquids	Flam. Liq.	3	H226
Eye irritation	Eye Irrit.	2	H319
Acute toxicity	Acute Tox.	4	H332
Specific target organ toxicity - single exposure	STOT SE	3	H335
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Specific target organ toxicity - single exposure	STOT SE	3	H370
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	1	H370
Acute toxicity	Acute Tox.	4	H302
Specific target organ toxicity - single exposure	STOT SE	3	H336

• Transport Information: UN 1292

Discovery and Applications

Tetraethyl orthosilicate, commonly abbreviated as TEOS, is an organosilicon compound widely used as a precursor in the production of silicon dioxide (SiO₂) through sol–gel and chemical vapor deposition (CVD) processes. Its molecular formula is Si(OC₂H₅)₄. TEOS is a colorless liquid with a characteristic odor and serves as one of the most important alkoxysilanes in materials chemistry. Hydrolysis and condensation of TEOS yield silica-based materials under mild conditions, making it a central reagent in glass and ceramic synthesis.

The compound was introduced in sol–gel chemistry during the mid-20th century as a convenient molecular precursor of silica. When subjected to controlled hydrolysis in the presence of water and catalysts such as hydrochloric acid or ammonia, TEOS undergoes stepwise substitution of ethoxy groups by hydroxyl groups, forming silanols that condense to Si–O–Si networks. This process allows precise control over the microstructure of the resulting silica gels, films, or monoliths. The sol–gel technique using TEOS has been extensively developed for the preparation of porous glasses, optical coatings, and catalyst supports.

In semiconductor manufacturing, TEOS has become a major source of silicon dioxide films deposited via plasma-enhanced or thermal CVD methods. The thermal decomposition of TEOS in oxygen-containing atmospheres yields conformal SiO₂ layers on silicon wafers, a process that offers uniformity superior to that of traditional oxidation techniques. This has made TEOS indispensable for interlayer dielectric deposition, shallow trench isolation, and passivation layers in integrated circuits.

TEOS also plays a key role in surface modification and nanomaterial synthesis. It serves as the silicon source in the formation of silica shells on nanoparticles, as well as in the synthesis of mesoporous silica materials such as MCM-41 and SBA-15. The controlled hydrolysis of TEOS in micellar systems or under template conditions enables the formation of ordered porous structures with tunable pore size and surface area. These materials are applied in catalysis, adsorption, and drug delivery systems.

In coating technologies, TEOS is used to prepare anti-reflective films and protective layers on metals and glass. Its versatility extends to hybrid organic–inorganic materials through co-condensation with organoalkoxysilanes, allowing the incorporation of organic functional groups into the silica matrix. This property underpins many modern sol–gel derived coatings with tailored mechanical, optical, or chemical resistance properties.

Toxicologically, TEOS exhibits moderate reactivity due to its hydrolysis products—ethanol and silicic acid—and must be handled under dry conditions. Its vapor can cause irritation to the eyes and respiratory tract. Nevertheless, under controlled laboratory or industrial conditions, TEOS remains a relatively safe reagent compared to other silicon alkoxides. It is stable under storage if protected from moisture and is compatible with a range of organic solvents.

The combination of availability, stability, and controllable reactivity has made tetraethyl orthosilicate one of the most extensively studied and applied organosilicon compounds. Its applications span from advanced microelectronics to nanostructured materials and surface engineering. Continuing developments in sol–gel processing and hybrid materials chemistry maintain TEOS as a foundational compound in both academic and industrial materials research.

References

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

Hench LL & 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