Triethylborane

Triethylborane

Names
IUPAC name Triethylborane
Other names triethylborine, triethylboron
Identifiers
CAS Registry Number	97-94-9 Y
ChemSpider	7079 Y
EC number	202-620-9
InChI InChI=1S/C6H15B/c1-4-7(5-2)6-3/h4-6H2,1-3H3 Y Key: LALRXNPLTWZJIJ-UHFFFAOYSA-N Y InChI=1/C6H15B/c1-4-7(5-2)6-3/h4-6H2,1-3H3 Key: LALRXNPLTWZJIJ-UHFFFAOYAU
Jmol-3D images	Image
PubChem	7357
SMILES B(CC)(CC)CC
Properties
Chemical formula	C6H15B
Molar mass	98.00 g/mol
Appearance	Colorless to pale yellow liquid
Density	0.677 g/cm3
Melting point	−93 °C (−135 °F; 180 K)
Boiling point	95 °C (203 °F; 368 K)
Solubility in water	N/A, Highly reactive
Hazards
MSDS	External MSDS
Main hazards	Spontaneously flammable in air; causes burns
R-phrases	R11 R14/15 R17 R19 R34 R35 R36/37
S-phrases	S6 S7/8 S16 S33 S36/37/39 S43A S45 S29
Flash point	< −20 °C (−4 °F; 253 K)
Autoignition temperature	−20 °C (−4 °F; 253 K)
Related compounds
Related compounds	Tetraethyllead Diborane Sodium tetraethylborate trimethylborane
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

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.

Preparation and structure

Triethylborane is prepared by the reaction of trimethyl borate with triethylaluminium:^[1]

Et₃Al + (MeO)₃B → Et₃B + (MeO)₃Al

The molecule is monomeric, unlike H₃B and Et₃Al, which tend to dimerize. It has a planar BC₃ core.^[1]

Applications

Turbojet engine

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,^[2] 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, 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 too high risk of a malfunction. It was used to start up each engine and to light the afterburners.^[3]

Rocket

Mixed with 10-15% triethylaluminium, it was used before lift-off to ignite the F-1 Engines on the Saturn V Rocket.^[4]

The SpaceX Falcon 9 heavy-lift rocket also uses a triethylaluminium-triethylborane mixture as a first-stage ignitor.^[5]

Organic chemistry

Industrially, triethylborane is used as an initiator in radical reactions, where it is effective even at low temperatures.^[1] As an initiator, it can replace some organotin compounds.

It reacts with metal enolates, yielding enoxytriethylborates that can be C-alkylated more selectively than in its absence. 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 butanol. It also promotes certain variants of the Reformatskii reaction.^[6]

It is the precursor to the reducing agent Superhydride:

LiH + Et₃B → LiBHEt₃

Safety

Triethylborane is strongly pyrophoric, igniting spontaneously in air, burning with an apple-green flame characteristic for boron compounds. Thus, it must be handled and stored in nitrogen or argon.

See also

• Organoboranes
• Pentaborane

References