sec-Butyllithium is an organometallic compound with the formula CH3CHLiCH2CH3, abbreviated sec-BuLi or s-BuLi. This chiral organolithium reagent is used as a source of sec-butyl carbanion in organic synthesis.[1]
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IUPAC name
sec-Butyllithium
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Systematic IUPAC name
Butan-2-yllithium | |
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3D model (JSmol)
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3587206 | |
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ECHA InfoCard | 100.009.026 |
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Properties | |
C4H9Li | |
Molar mass | 64.06 g·mol−1 |
Acidity (pKa) | 51 |
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Safety data sheet (SDS) | Fisher MSDS |
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
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sec-BuLi can be prepared by the reaction of sec-butyl halides with lithium metal:[2]
sec-Butyllithium is a colorless viscous liquid.[1][3] Using mass spectrometry, it was determined that the pure compound has a tetrameric structure.[4] It also exists as tetramers when dissolved in organic solvents such as benzene, cyclohexane or cyclopentane.[3] The cyclopentane solution has been detected with 6Li-NMR spectroscopy to have a hexameric structure at temperatures below −41 °C.[5] In electron-donating solvents such as tetrahydrofuran, there exists an equilibrium between monomeric and dimeric forms.[6]
The carbon-lithium bond is highly polar, rendering the carbon basic, as in other organolithium reagents. Sec-butyllithium is more basic than the primary organolithium reagent, n-butyllithium. It is also more sterically hindered. sec-BuLi is employed for deprotonations of particularly weak carbon acids where the more conventional reagent n-BuLi is unsatisfactory. It is, however, so basic that its use requires greater care than for n-BuLi. For example diethyl ether is attacked by sec-BuLi at room temperature in minutes, whereas ether solutions of n-BuLi are stable.[1]
The compound decomposes slowly at room temperature and more rapidly at higher temperatures, giving lithium hydride and a mixture of butenes.[7][8]
Many transformations involving sec-butyllithium are similar to those involving other organolithium reagents.
In combination with sparteine as a chiral auxiliary, sec-butyllithium is useful in enantioselective deprototonations.[9] It is also effective for lithiation of arenes.[10]