Formula C6H15B Molar mass 98 g/mol Autoignition temperature −20 °C (−4 °F; 253 K) | Density 677 kg/m³ Melting point -93 °C | |
 | ||
Appearance Colorless to pale yellow liquid Related compounds Main hazards Spontaneously flammable in air; causes burns R-phrases R11 R14/15 R17 R19 R34 R35 R36/37 | ||
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.
Contents
Preparation and structure
Triethylborane is prepared by the reaction of trimethyl borate with triethylaluminium:
Et3Al + (MeO)3B → Et3B + (MeO)3AlThe molecule is monomeric, unlike H3B and Et3Al, which tend to dimerize. It has a planar BC3 core.
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, 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.
Rocket
Mixed with 10-15% triethylaluminium, it was used before lift-off to ignite the F-1 engines on the Saturn V rocket.
The SpaceX Falcon 9 rocket also uses a triethylaluminium-triethylborane mixture as a first and second stage ignitor.
Organic chemistry
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 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.
Triethylborane is the precursor to the reducing agents lithium triethylborohydride ("Superhydride") and sodium triethylborohydride.
MH + Et3B → MBHEt3 (M = Li, Na)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.