|Preferred IUPAC name
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||98.00 g/mol|
|Appearance||Colorless to pale yellow liquid|
|Melting point||−93 °C (−135 °F; 180 K)|
|Boiling point||95 °C (203 °F; 368 K)|
|Not applicable; highly reactive|
|Main hazards||Spontaneously flammable in air; causes burns|
|Safety data sheet||External SDS|
|R-phrases (outdated)||R11 R14/15 R17 R19 R34 R35 R36/37|
|S-phrases (outdated)||S6 S7/8 S16 S33 S36/37/39 S43A S45 S29|
|NFPA 704 (fire diamond)|
|Flash point||< −20 °C (−4 °F; 253 K)|
|−20 °C (−4 °F; 253 K)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|(what is ?)|
Triethylborane (TEB), also called triethylboron, is an organoborane (a compound with a B-C bond). It is a colorless pyrophoric liquid. Its chemical formula is (C2H5)3B, abbreviated Et3B. It is soluble in organic solvents tetrahydrofuran and hexane.
The molecule is monomeric, unlike H3B and Et3Al, which tend to dimerize. It has a planar BC3 core.
Triethylborane was used to ignite the JP-7 fuel in the Pratt & Whitney J58 turbojet/ramjet engines powering the Lockheed SR-71 Blackbird and its predecessor, the A-12 OXCART. Triethylborane is suitable for this because of its pyrophoric properties, especially the fact that it burns with a very high temperature. It was chosen as an ignition method for reliability reasons, and in the case of the Blackbird, because JP-7 fuel has very low volatility and is difficult to ignite. Conventional ignition plugs posed a high risk of malfunction. Triethylborane was used to start each engine and to ignite the afterburners.
It reacts with metal enolates, yielding enoxytriethylborates that can be alkylated at the α-carbon atom of the ketone more selectively than in its absence. For example, the enolate from treating cyclohexanone with potassium hydride produces 2-allylcyclohexanone in 90% yield when triethylborane is present. Without it, the product mixture contains 43% of the mono-allylated product, 31% di-allylated cyclohexanones, and 28% unreacted starting material. The choice of base and temperature influences whether the more or less stable enolate is produced, allowing control over the position of substituents. Starting from 2-methylcyclohexanone, reacting with potassium hydride and triethylborane in THF at room temperature leads to the more substituted (and more stable) enolate, whilst reaction at −78 °C with potassium hexamethyldisilazide, KN[Si(CH
2 and triethylborane generates the less substituted (and less stable) enolate. After reaction with methyl iodide the former mixture gives 2,2-dimethylcyclohexanone in 90% yield while the latter produces 2,6-dimethylcyclohexanone in 93% yield.
It is used in the Barton–McCombie deoxygenation reaction for deoxygenation of alcohols. In combination with lithium tri-tert-butoxyaluminum hydride it cleaves ethers. For example, THF is converted, after hydrolysis, to 1-butanol. It also promotes certain variants of the Reformatskii reaction.
Triethylborane reacts with methanol to form diethyl(methoxy)borane, which is used as the chelating agent in the Narasaka–Prasad reduction for the stereoselective generation of syn-1,3-diols from β-hydroxyketones.
Triethylborane is strongly pyrophoric, with an autoignition temperature of −20 °C (−4 °F), burning with an apple-green flame characteristic for boron compounds. Thus, it is typically handled and stored using air-free techniques. Triethylborane is also acutely toxic if swallowed, with an LD50 of 235 mg/kg in rat test subjects.