Triethyl borate
[CAS# 150-46-9]

Identification

• Classification: Chemical reagent >> Organic reagent >> Borate
• Name: Triethyl borate
• Synonyms: Triethoxyborane
• Molecular Formula: C₆H₁₅BO₃
• Molecular Weight: 145.99
• CAS Registry Number: 150-46-9
• EC Number: 205-760-9
• SMILES: B(OCC)(OCC)OCC

Properties

• Density: 0.9±0.1 g/cm³ Calc.^*, 0.858 g/mL (Expl.)
• Melting point: -85 ºC (Expl.)
• Boiling point: 120.0 ºC 760 mmHg (Calc.)^*, 117 - 118 ºC (Expl.)
• Flash point: 11.1 ºC (Calc.)^*, 11 ºC (Expl.)
• Index of refraction: 1.374 (Calc.)^*, 1.374 (Expl.)

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

Safety Data

• Hazard Symbols: GHS02;GHS07;GHS08 DangerGHS02
• Hazard Statements: H225-H315-H319-H335-H360-H361
• Precautionary Statements: P203-P210-P233-P240-P241-P242-P243-P261-P264-P264+P265-P271-P280-P302+P352-P303+P361+P353-P304+P340-P305+P351+P338-P318-P319-P321-P332+P317-P337+P317-P362+P364-P370+P378-P403+P233-P403+P235-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Flammable liquids	Flam. Liq.	2	H225
Eye irritation	Eye Irrit.	2	H319
Reproductive toxicity	Repr.	1B	H360FD
Specific target organ toxicity - single exposure	STOT SE	3	H335
Skin irritation	Skin Irrit.	2	H315
Reproductive toxicity	Repr.	2	H361
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410

• Transport Information: UN 1176

Discovory and Applicatios

Triethyl borate, also known as boric acid triethyl ester, is an organoboron compound with the molecular formula B(OC₂H₅)₃. It is a clear, colorless liquid that is flammable and possesses a mild, fruity odor. This compound is a member of the trialkyl borate family, in which three ethyl groups are bonded to a central boron atom via oxygen atoms. It is primarily known for its use as a reagent in organic synthesis and as an intermediate in various industrial applications.

The discovery of triethyl borate dates back to the 19th century, with early reports describing the esterification of boric acid with alcohols. Triethyl borate is typically synthesized through the reaction of boric acid or boron trioxide with ethanol under dehydrating conditions. The process involves the removal of water to drive the equilibrium toward ester formation. Sulfuric acid or other acid catalysts are often used to facilitate the esterification reaction. The resulting product is purified through distillation due to its relatively low boiling point.

One of the most notable features of triethyl borate is its ability to burn with a characteristic green flame, which is a consequence of the presence of boron. This property has led to its use in pyrotechnics and flammable tracer compositions. The bright green color is highly visible and has been utilized in signal flares and other visual signaling applications where flame coloration is required.

In the field of organic synthesis, triethyl borate is used as a reagent and a boron source. It serves as a precursor in the preparation of boronic acids, boronate esters, and other organoboron compounds. These derivatives are important intermediates in various coupling reactions, particularly the Suzuki-Miyaura cross-coupling reaction, which is widely employed in pharmaceutical and materials chemistry. The mild Lewis acidity of triethyl borate allows it to participate in condensation and alkylation reactions, often improving yields or selectivity by activating electrophilic sites.

Triethyl borate also finds application in analytical chemistry. It can be used as a reagent in the determination of certain metal ions and has been employed in the formulation of boron-containing calibration standards. In some cases, it has been used as a solvent or additive in chromatographic techniques due to its relatively low viscosity and miscibility with common organic solvents.

In the electronics industry, triethyl borate is used as a dopant source for boron in semiconductor manufacturing processes. It is introduced into the production environment as part of a controlled doping strategy to modify the electrical properties of silicon wafers. The compound’s volatility and boron content make it a suitable candidate for use in chemical vapor deposition and other thin film technologies where precise control of elemental incorporation is necessary.

Safety considerations are important when handling triethyl borate. It is a flammable liquid and should be stored in tightly sealed containers away from heat sources, sparks, or open flames. It may also cause irritation to the eyes, skin, and respiratory tract upon exposure. Proper ventilation and personal protective equipment are required when working with this compound, especially in laboratory or industrial environments where vapor exposure is possible. In the event of combustion, the compound can release toxic fumes, including boron oxides, which necessitate adequate fire suppression and ventilation systems.

Triethyl borate is hydrolytically unstable and can react with water to regenerate ethanol and boric acid. This reaction can be slow under ambient conditions but is accelerated in the presence of acids or bases. Therefore, it is usually handled in dry environments to prevent degradation and to maintain reagent purity. The sensitivity to moisture limits some of its applications but also provides a useful mechanism for controlled release of boric acid in certain formulations.

Overall, triethyl borate is a versatile chemical compound with established uses in synthetic chemistry, pyrotechnics, materials science, and electronics. Its role as a boron-containing reagent and intermediate continues to be important in both academic research and industrial processes, supported by its availability and well-understood reactivity profile.

References

1971. New derivatives of cyclotriborazane-trimeric B-alkoxy-B-fluoro-N-(�-fluoroethyl)borazenes. Chemistry of Heterocyclic Compounds, 7(9).
DOI: 10.1007/bf00481057

2017. Effect of processing parameters on textural and bioactive properties of sol�gel-derived borate glasses. Journal of Materials Science, 52(14).
DOI: 10.1007/s10853-017-0968-y

2024. Enabling superior cathode/sulfide electrolyte interfacial stability by Li3BO3 coating for all solid-state Li battery. Journal of Materials Science, 59(44).
DOI: 10.1007/s10853-024-10409-w