Tetraethyl orthosilicate, formally named tetraethoxysilane (TEOS), ethyl silicate is the organic

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

Si(OC₂H₅)₄. TEOS is a colorless liquid. It degrades in water. TEOS is the of orthosilicic acid, Si(OH)₄. It is the most prevalent

alkoxide In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as , where R is the organyl substituent. Alkoxides are strong bases and, whe ...

of silicon. TEOS is a tetrahedral molecule. Like its many analogues, it is prepared by

alcoholysis In chemistry, solvolysis is a type of nucleophilic substitution (S1/S2) or elimination where the nucleophile is a solvent molecule. Characteristic of S1 reactions, solvolysis of a chiral reactant affords the racemate. Sometimes however, the ster ...

silicon tetrachloride Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl4. It is a colorless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications. It is a part of the ...

: :SiCl₄ + 4 EtOH → Si(OEt)₄ + 4 HCl where Et is the

ethyl group In organic chemistry, an ethyl group (abbr. Et) is an alkyl substituent with the formula , derived from ethane (). ''Ethyl'' is used in the International Union of Pure and Applied Chemistry The International Union of Pure and Applied ...

, C₂H₅, and thus EtOH is

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

Applications

TEOS is mainly used as a crosslinking agent in

silicone In Organosilicon chemistry, organosilicon and polymer chemistry, a silicone or polysiloxane is a polymer composed of repeating units of siloxane (, where R = Organyl group, organic group). They are typically colorless oils or elastomer, rubber ...

polymers and as a precursor to

silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...

in the semiconductor industry. TEOS is also used as the silica source for synthesis of some

zeolites Zeolites are a group of several Microporous material, microporous, crystalline aluminosilicate minerals commonly used as commercial adsorption, adsorbents and Catalysis, catalysts. They mainly consist of silicon, aluminium, oxygen, and have the ge ...

. Other applications include coatings for carpets and other objects. TEOS is used in the production of

aerogel Aerogels are a class of manufacturing, synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas, without significant collapse of the gel structure. The result is a solid wit ...

. These applications exploit the reactivity of the Si-OR bonds. TEOS has historically been used as an additive to alcohol based rocket fuels to decrease the heat flux to the chamber wall of regeneratively cooled engines by over 50%. TEOS is used in steel casting industry as an inorganic binder and stiffener for making silica-based

ceramic molding file:Old-Babylonian clay mould for ceramic plaques, from Southern Mesopotamia, Iraq.jpg, alt=whitish mould, Clay mould for ceramic (fired clay) plaques, from Southern Mesopotamia, Iraq Ceramic molding is a versatile and precise manufacturing proces ...

forms (see also

sodium silicate Sodium silicate is a generic name for chemical compounds with the formula or ·, such as sodium metasilicate (), sodium orthosilicate (), and sodium pyrosilicate (). The anions are often polymeric. These compounds are generally colorless tra ...

). and as an inorganic binder for coatings ( passivation) of different materials such as steel, glass, brass, and wood in order to make surfaces resistant to water, oxygen and high temperatures.. Further applications of TEOS include its use as an additive to solid polymers to enhance their adhesion to glass, steel or wood, as a binder for porcelain teeth crowns, and as a precursor to

siloxane In organosilicon chemistry, a siloxane is an organic compound containing a functional group of two silicon atoms bound to an oxygen atom: . The parent siloxanes include the oligomeric and polymeric hydrides with the formulae and . Siloxanes ...

Other reactions

TEOS easily converts to

upon the addition of water: :Si(OC₂H₅)₄ + 2 H₂O → SiO₂ + 4 C₂H₅OH An idealized equation is shown, in reality the silica produced is hydrated. This hydrolysis reaction is an example of a sol-gel process. The side product is ethanol. The reaction proceeds via a series of condensation reactions that convert the TEOS molecule into a mineral-like solid via the formation of Si-O-Si linkages. Rates of this conversion are sensitive to the presence of

acid An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...

s and bases, both of which serve as

catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

s. The Stöber process allows the formation of monodisperse and

mesoporous silica Mesoporous silica is a form of silica that is characterised by its mesoporous structure, that is, having pores that range from 2 nm to 50 nm in diameter. According to IUPAC's terminology, mesoporosity sits between microporous (50 ...

. At elevated temperatures (>600 °C), TEOS converts to

: :Si(OC₂H₅)₄ → SiO₂ + 2 (C₂H₅)₂O The volatile coproduct is

diethyl ether Diethyl ether, or simply ether, is an organic compound with the chemical formula , sometimes abbreviated as . It is a colourless, highly Volatility (chemistry), volatile, sweet-smelling ("ethereal odour"), extremely flammable liquid. It belongs ...

Safety

Inhalation of TEOS induces eye and nose irritation, and eye contact with the liquid is irritating. High exposure to TEOS can lead to

pulmonary edema Pulmonary edema (British English: oedema), also known as pulmonary congestion, is excessive fluid accumulation in the tissue or air spaces (usually alveoli) of the lungs. This leads to impaired gas exchange, most often leading to shortness ...

, but hazards can be reduced by atmospheric humidity and vapor pressure conditions.{{Cite web , last=PubChem , title=Ethyl silicate , url=https://pubchem.ncbi.nlm.nih.gov/source/hsdb/534 , access-date=2024-05-15 , website=pubchem.ncbi.nlm.nih.gov , language=en The mechanism of irritation is similar to that of tetramethyl orthosilicate.

References

External links

NIST Standard Reference Database 69, June 2005 Release: NIST Chemistry WebBook
Ethoxy compounds Silicate esters