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| Names | |||
|---|---|---|---|
| Preferred IUPAC name Triethylborane | |||
| Other names Triethylborine, triethylboron | |||
| Identifiers | |||
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3D model (JSmol) | |||
| ChemSpider |
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| ECHA InfoCard | 100.002.383 | ||
| EC Number |
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| UNII | |||
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| 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: | |||
    | |||
| 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) | |||
| 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 theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Triethylborane (TEB), also calledtriethylboron, is anorganoborane (a compound with a B–C bond). It is a colorlesspyrophoric liquid. Its chemical formula is(CH3CH2)3B or(C2H5)3B, abbreviatedEt3B. It is soluble in organic solventstetrahydrofuran andhexane.
Triethylborane is prepared by the reaction oftrimethyl borate withtriethylaluminium:[1]
The molecule is monomeric, unlike H3B and Et3Al, which tend to dimerize. It has a planar BC3 core.[1]
Triethylborane was used to ignite theJP-7 fuel in thePratt & Whitney J58turbojet/ramjet engines powering theLockheed SR-71 Blackbird[2] and its predecessor, theA-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 theafterburners.[3]
Mixed with 10–15%triethylaluminium, it was used before lift-off to ignite theF-1 engines on theSaturn V rocket.[4]
TheMerlin engines that power theSpaceXFalcon 9 rocket use atriethylaluminium-triethylborane mixture (TEA-TEB) as a first- and second-stage ignitor.[5]
TheFirefly AerospaceAlpha launch vehicle's Reaver engines are also ignited by a triethylaluminium-triethylborane mixture.[6]
Industrially, triethylborane is used as aninitiator inradical reactions, where it is effective even at low temperatures.[1] As an initiator, it can replace someorganotin compounds.
It reacts with metalenolates, 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 withpotassium 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 withpotassium hexamethyldisilazide,KN[Si(CH
3)
3]
2 and triethylborane generates the less substituted (and less stable) enolate. After reaction withmethyl 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 forethyl groupCH3CH2−.
It is used in theBarton–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, to1-butanol. It also promotes certain variants of theReformatskii reaction.[9]
Triethylborane is the precursor to the reducing agents lithium triethylborohydride ("Superhydride") andsodium triethylborohydride.[10]
Triethylborane reacts withmethanol to form diethyl(methoxy)borane, which is used as the chelating agent in theNarasaka–Prasad reduction for the stereoselective generation ofsyn-1,3-diols from β-hydroxyketones.[11][12]
Triethylborane is stronglypyrophoric, with anautoignition temperature of −20 °C (−4 °F),[13] burning with an apple-green flame characteristic for boron compounds. Thus, it is typically handled and stored usingair-free techniques. Triethylborane is also acutely toxic if swallowed, with anLD50 of 235 mg/kg in rat test subjects.[14]
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