Triethylborane

Triethylborane (TEB), also called triethylborine and triethylboron, is an organoborane (an organometallic compound), a near-colorless to yellowish transparent liquid with pungent ether-like odor. Its chemical formula can be written as C₆H₁₅B, or (CH₃CH₂)₃B, or (C₂H₅)₃B, or Et₃B.

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Triethylborane is strongly pyrophoric, igniting spontaneously in air. It burns intensely with a very hot flame. The color of the flame is apple-green, which is characteristic for boron compounds. Its fire should not be extinguished with water; a carbon dioxide or dry powder extinguisher (eg. Purple K) would be more suitable. Its vapors may cause flash fire.

It is soluble in tetrahydrofuran and hexane, and is not pyrophoric when in solution. However the solution can slowly react with atmospheric moisture. If the TEB solutions are exposed to air for prolonged time, unstable organic peroxides may form, with the presence of cationic initiators leading to polymerization. It is toxic to peripheral nervous system, kidneys and testes. Triethylborane is extremely corrosive. Some sources incorrectly refer to this chemical as tetraethylborane.

Applications

Triethylborane was used to ignite the JP-7 fuel in the Pratt & Whitney J58 turbojet/ramjet engines powering the Lockheed SR-71 Blackbird spy plane, and its predecessor A-12 OXCART. Triethylborane is suitable for this because of its pyrophoric properties, especially the fact that it burns with very high temperature. It was chosen as an ignition method for reliability reasons, because the JP-7 fuel has very low volatility and is difficult to ignite. Classical ignition plugs posed too high risk of a malfunction. It is used in 50 cm³ doses to start up each engine and to light the afterburners.

Industrially, triethylborane is used as an initiator in radical reactions, where it is effective even at low temperatures. As an initiator, it can replace some organotin compounds. It reacts with metal enolates, yielding enoxytriethylborates with use in selective alkylation and aldol reactions. It is also used in reduction bond cleavage with lithium tri-tert-butoxyaluminohydride, in preparation of various boron compounds, deoxygenation of primary and secondary alcohols, rapid determination of -OH groups in organic compounds, dehydration of salt and sugar hydrates, determination of water content in crystalline hydrate compounds, in a variant of Reformatskii reaction, and has a range of other uses in organoborane chemistry.

Triethylborane is used in vapor deposition techniques as a boron source. Examples are the plasma deposition of boron-containing hard carbon films, silicon nitride-boron nitride films, and for doping of diamond film with boron. Other boron precursors used for such applications are eg. trimethylborane, boron trifluoride, diborane, and decaborane.

Sodium tetraethyl borate (NaTEB), a triethylboron derivative, is used as a powerful ethylation agent.

See also

• Organoboranes
• Pentaborane