Triethylborane

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Triethylborane
Triethylborane Ball-and-stick model of triethylborane
Identifiers
CAS number 97-94-9 YesY
PubChem 7357
ChemSpider 7079 YesY
EC number 202-620-9
Jmol-3D images Image 1
Properties
Molecular 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
R-phrases R11 R14/15 R17 R19 R34 R35 R36/37
S-phrases S6 S7/8 S16 S33 S36/37/39 S43A S45 S29
Main hazards Spontaneously flammable in air; causes burns
Flash point < -20 °C
Autoignition temperature -20 °C
Related compounds
Related compounds Tetraethyllead
Diborane
Sodium tetraethylborate
trimethylborane
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
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[edit]

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[edit]

Turbojet engine[edit]

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[edit]

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[edit]

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[edit]

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[edit]

References[edit]

  1. ^ a b c Robert J. Brotherton, C. Joseph Weber, Clarence R. Guibert, John L. Little "Boron Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2000, Wiley-VCH. doi:10.1002/14356007.a04_309
  2. ^ "Lockheed SR-71 Blackbird". March Field Air Museum. Retrieved 2009-05-05. 
  3. ^ "Lockheed SR-71 Blackbird Flight Manual". www.sr-71.org. Retrieved 2011-01-26. 
  4. ^ A. Young (2008). The Saturn V F-1 Engine: Powering Apollo Into History. Springer. p. 86. ISBN 0-387-09629-9. 
  5. ^ 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-TAB."
  6. ^ Yoshinori Yamamoto, Takehiko Yoshimitsu, John L. Wood, Laura Nicole Schacherer "Triethylborane" Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rt219.pub3