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Concept
Tert-Butyllithium
Résumé
tert-Butyllithium is a chemical compound with the formula (CH3)3CLi. As an organolithium compound, it has applications in organic synthesis since it is a strong base, capable of deprotonating many carbon molecules, including benzene. tert-Butyllithium is available commercially as hydrocarbon solutions; it is not usually prepared in the laboratory.
tert-Butyllithium is produced commercially by treating tert-butyl chloride with lithium metal. Its synthesis was first reported by R. B. Woodward in 1941.
Like other organolithium compounds, tert-butyllithium is a cluster compound. Whereas n-butyllithium exists both as a hexamer and a tetramer, tert-butyllithium exists exclusively as a tetramer with a cubane structure. Bonding in organolithium clusters involves sigma delocalization and significant Li−Li bonding. Despite its complicated structure, tert-butyllithium is usually depicted in equations as a monomer.
The lithium–carbon bond in tert-butyllithium is highly polarized, having about 40 percent ionic character. The molecule reacts like a carbanion, as is represented by these two resonance structures.
tert-Butyllithium is renowned for deprotonation of carbon acids (C-H bonds). One example is the double deprotonation of allyl alcohol. Other examples are the deprotonation of vinyl ethers.
In combination with n-butyllithiium, tert-butylllithium monolithiates ferrocene. tert-Butyllithium deprotonates dichloromethane:
Similar to n-butyllithium, tert-butyllithium can be used for lithium-halogen exchange reactions.
To minimize degradation by solvents, reactions involving tert-butyllithium are often conducted at very low temperatures in special solvents, such as the Trapp solvent mixture.
More so than other alkyllithium compounds, tert-butyllithium reacts with ethers. In diethyl ether, the half-life of tert-butyllithium is about 60 minutes at 0 °C. It is even more reactive toward tetrahydrofuran (THF), the half-life in THF solutions is about 40 minutes at −20 °C.
Source officielle
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