Triethylborane

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Not to be confused with triethyl borate.
Triethylborane
Triethylborane
Triethylborane
Ball-and-stick model of triethylborane
Ball-and-stick model of triethylborane
Names
Preferred IUPAC name
Triethylborane
Other names
Triethylborine, triethylboron
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.002.383 Edit this at Wikidata
EC Number
  • 202-620-9
UNII
  • InChI=1S/C6H15B/c1-4-7(5-2)6-3/h4-6H2,1-3H3 checkY
    Key: LALRXNPLTWZJIJ-UHFFFAOYSA-N checkY
  • InChI=1/C6H15B/c1-4-7(5-2)6-3/h4-6H2,1-3H3
    Key: LALRXNPLTWZJIJ-UHFFFAOYAU
  • B(CC)(CC)CC
Properties
(CH3CH2)3B
Molar mass 98.00 g/mol
Appearance Colorless 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
Occupational safety and health (OHS/OSH):
Main hazards
 Spontaneously flammable in air; causes burns
GHS labelling:
GHS02: FlammableGHS05: CorrosiveGHS06: ToxicGHS08: Health hazard
Danger
H225, H250, H301, H314, H330, H360
P201, P202, P210, P222, P233, P240, P241, P242, P243, P260, P264, P270, P271, P280, P281, P284, P301+P310, P301+P330+P331, P302+P334, P303+P361+P353, P304+P340, P305+P351+P338, P308+P313, P310, P320, P321, P330, P363, P370+P378, P403+P233, P403+P235, P405, P422, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 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. propaneInstability 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. sodium, sulfuric acid
3
4
4
W
Flash point < −20 °C (−4 °F; 253 K)
−20 °C (−4 °F; 253 K)
Safety data sheet (SDS) External SDS
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

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 (CH3CH2)3B or (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 engines

[edit]

Triethylborane was used to ignite the JP-7 fuel in the Pratt & Whitney J58 turbojet/ramjet engines powering the Lockheed SR-71 Blackbird[2] and its predecessor, the A-12 OXCART. Triethylborane is suitable because it ignites readily upon exposure to oxygen. It was chosen as an ignition method for reliability reasons, and in the case of the Blackbird, because JP-7 fuel has very low volatility and is difficult to ignite. Conventional ignition plugs posed a high risk of malfunction. Triethylborane was used to start each engine and to ignite the afterburners.[3]

Rocketry

[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 Merlin engines that power the SpaceX Falcon 9 rocket use a triethylaluminium-triethylborane mixture (TEA-TEB) as a first- and second-stage ignitor.[5]

The Firefly Aerospace Alpha launch vehicle's Reaver engines are also ignited by a triethylaluminium-triethylborane mixture.[6]

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 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.[7] 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
3)
3]
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.[7][8] The Et stands for ethyl group CH3CH2−.

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.[9]

Triethylborane is the precursor to the reducing agents lithium triethylborohydride ("Superhydride") and sodium triethylborohydride.[10]

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.[11][12]

Safety

[edit]

Triethylborane is strongly pyrophoric, with an autoignition temperature of −20 °C (−4 °F),[13] burning with an apple-green flame characteristic for boron compounds. Thus, it is typically handled and stored using air-free techniques. Triethylborane is also acutely toxic if swallowed, with an LD50 of 235 mg/kg in rat test subjects.[14]

See also

[edit]

References

[edit]
  1. ^ a b c Brotherton, Robert J.; Weber, C. Joseph; Guibert, Clarence R.; Little, John L. (15 June 2000). "Boron Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH. doi:10.1002/14356007.a04_309. ISBN 3-527-30673-0.
  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. Archived from the original on 2011-02-02. Retrieved 2011-01-26.
  4. ^ A. Young (2008). The Saturn V F-1 Engine: Powering Apollo Into History. Springer. p. 86. ISBN 978-0-387-09629-2.
  5. ^ Mission Status Center, June 2, 2010, 1905 GMT Archived May 30, 2010, at the Wayback Machine, 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. ^ "Firefly_Space/status/1090319933534334977". Twitter. Retrieved 2023-02-05.
  7. ^ a b Crich, David, ed. (2008). "Enoxytriethylborates and Enoxydiethylboranes". Reagents for Radical and Radical Ion Chemistry. Handbook of Reagents for Organic Synthesis. Vol. 11. John Wiley & Sons. ISBN 978-0-470-06536-5. Archived from the original on 2022-02-19. Retrieved 2019-01-27.
  8. ^ Negishi, Ei-ichi; Chatterjee, Sugata (1983). "Highly regioselective generation of "thermodynamic" enolates and their direct characterization by NMR". Tetrahedron Letters. 24 (13): 1341–1344. doi:10.1016/S0040-4039(00)81651-2.
  9. ^ Yamamoto, Yoshinori; Yoshimitsu, Takehiko; Wood, John L.; Schacherer, Laura Nicole (15 March 2007). "Triethylborane". Encyclopedia of Reagents for Organic Synthesis. Wiley. doi:10.1002/047084289X.rt219.pub3. ISBN 978-0-471-93623-7.
  10. ^ Binger, P.; Köster, R. (1974). "Sodium Triethylhydroborate, Sodium Tetraethylborate, and Sodium Triethyl-1-Propynylborate". Inorganic Syntheses. Inorganic Syntheses. Vol. 15. pp. 136–141. doi:10.1002/9780470132463.ch31. ISBN 978-0-470-13246-3.
  11. ^ Chen, Kau-Ming; Gunderson, Karl G.; Hardtmann, Goetz E.; Prasad, Kapa; Repic, Oljan; Shapiro, Michael J. (1987). "A Novel Method for the In situ Generation of Alkoxydialkylboranes and Their Use in the Selective Preparation of 1,3-syn Diols". Chemistry Letters. 16 (10): 1923–1926. doi:10.1246/cl.1987.1923.
  12. ^ Yang, Jaemoon (2008). "Diastereoselective Syn-Reduction of β-Hydroxy Ketones". Six-Membered Transition States in Organic Synthesis. John Wiley & Sons. pp. 151–155. ISBN 978-0-470-19904-6. Archived from the original on 2022-02-19. Retrieved 2019-01-27.
  13. ^ "Fuels and Chemicals - Autoignition Temperatures". Archived from the original on 2015-05-04. Retrieved 2017-08-26.
  14. ^ "Archived copy". Archived from the original on 2022-02-19. Retrieved 2020-09-26.{{cite web}}: CS1 maint: archived copy as title (link)