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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.

Triethylborane
Triethylborane
Ball-and-stick model of triethylborane
Names
IUPAC name
Triethylborane
Other names
Triethylborine, triethylboron
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.002.383
EC Number 202-620-9
Properties
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)
Not applicable; highly reactive
Hazards
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R-phrases (outdated) R11 R14/15 R17 R19 R34 R35 R36/37
S-phrases (outdated) S6 S7/8 S16 S33 S36/37/39 S43A S45 S29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
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g., propaneHealth code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gasReactivity code 4: Readily capable of detonation or explosive decomposition at normal temperatures and pressures. E.g., nitroglycerinSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
4
3
4
Flash point < −20 °C (−4 °F; 253 K)
−20 °C (−4 °F; 253 K)
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Contents

Preparation and structureEdit

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]

ApplicationsEdit

Turbojet engineEdit

Triethylborane was used to ignite the JP-7 fuel in the Pratt & Whitney J58 turbojet/ramjet engines powering the Lockheed SR-71,[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 a high risk of malfunction. It was used to start each engine and to ignite the afterburners.[3]

RocketEdit

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 rocket also uses a triethylaluminium-triethylborane mixture as a first and second stage ignitor.[5]

Organic chemistryEdit

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.[6] 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.[7]

Triethylborane is the precursor to the reducing agents lithium triethylborohydride ("Superhydride") and sodium triethylborohydride.[8]

MH + Et3B → MBHEt3 (M = Li, Na)

SafetyEdit

Triethylborane is strongly pyrophoric, with an autoignition temperature of −20 °C (−4 °F),[9] burning with an apple-green flame characteristic for boron compounds. Thus, it is typically handled and stored using air-free techniques.

See alsoEdit

ReferencesEdit

  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. Archived from the original on 2000-03-04. 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-TEB."
  6. ^ Crich, David (2013-05-30). Handbook of Reagents for Organic Synthesis, Reagents for Radical and Radical Ion Chemistry. John Wiley & Sons. ISBN 1118634896.
  7. ^ Yoshinori Yamamoto, Takehiko Yoshimitsu, John L. Wood, Laura Nicole Schacherer "Triethylborane" Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rt219.pub3
  8. ^ Binger, P.; Köster, R., "Sodium triethylhydroborate, sodium tetraethylborate, and sodium triethyl-1-propynylborate", Inorg. Synth. 1974, 15, 136-141. doi:10.1002/9780470132463.ch31
  9. ^ Fuels and Chemicals - Autoignition Temperatures