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.
3D model (JSmol)
|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|R-phrases (outdated)||R11 R14/15 R17 R19 R34 R35 R36/37|
|S-phrases (outdated)||S6 S7/8 S16 S33 S36/37/39 S43A S45 S29|
|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).
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Preparation and structureEdit
- Et3Al + (MeO)3B → Et3B + (MeO)3Al
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, and its predecessor 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 the JP-7 fuel has very low volatility and is difficult to ignite. Conventional ignition plugs posed a high risk of malfunction. It 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.
- MH + Et3B → MBHEt3 (M = Li, Na)
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.
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- Mission Status Center, June 2, 2010, 1905 GMT, SpaceflightNow, accessed 2010-06-02, Quotation: "The flanges will link the rocket with ground storage tanks containing liquid oxygen, kerosene fuel, helium, gaseous nitrogen and the first stage ignitor source called triethylaluminum-triethylborane, better known as TEA-TEB."
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- Fuels and Chemicals - Autoignition Temperatures