N-Butyllithium

  • N-butyllithium
  • BuLi
  • N-BuLi
  • Lithiumbutyl

Colorless liquid, commercially available n- butyllithium is often yellowish

Liquid

  • Reacts violently with water
  • Soluble in many alkanes and cycloalkanes

Risk

Based on 2.5 M solution in n-hexane

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With butyllithium refers generally n-butyllithium ( n-BuLi ), an organometallic compound of the element lithium ( organolithium compound ). There are also the isomeric forms of sec -butyllithium and tert -butyllithium. Butyllithium is used as a reagent in the preparation of a similar nature rubber ( cis 1,4 content) of isoprene. About 600 tons of butyllithium were already for this purpose in 1985 needed.

Production and representation

The synthesis is carried out analogously to the preparation of Grignard compounds by reaction of 1-chlorobutane with elemental lithium in diethyl ether:

Properties

Physical Properties

N- butyl lithium is a very strong base. The basicity of the isomeric Butyllithiumverbindungen increases in the order of n-butyllithium < sec -butyl < tert- butyllithium to. Due to the large electronegativity difference between carbon (2.55 ) and lithium ( 0.98) is the bond between C and Li strongly polarized. From the reactions of n -BuLi could assume that n- BuLi composed of the Butylanion and the lithium cation is, it has an ionic bond. However, this assumption is wrong, because n- BuLi is not ionic. As a solid solution exists, and even as n-BuLi, like most organolithium compounds as molecular groups with covalent bonds between lithium and carbon. For the pure substance a hexamer was detected by mass spectrometry. In nonpolar solvents such as cyclohexane, n- BuLi is hexamerisch, in ether it is arranged tetramerisch.

Chemical Properties

Pure n- butyllithium is a pyrophoric colorless liquid that is ignited in the presence of oxygen itself It is therefore in the trade as a (usually light yellow ) solution available, which must also be kept under an inert gas, with concentrations from 1.6 to 11 mol / l in n-hexane are typical.

As the solvent used ethers such as THF or diethyl ether are suitable as a storage solvent, n- BuLi, since they would decompose slowly. The half-life of n- BuLi in THF at 0 ° C with Deaggregierungsadditiv TMEDA ( tetramethylethylenediamine ) is only 38 minutes. n- butyl lithium also reacts exothermically with carbon dioxide and violently with water. The heat of hydrolysis is -240 kJ · mol -1

Reactions

Lithium -halogen exchange: The halogen in a compound can be replaced with lithium. This results in reagents with nucleophilic carbon centers, which can be used for the preparation of numerous compounds. The exchange is taken usually in ether at -78 ° C before ( Ar is an aromatic radical ):

As a strong base ( the conjugate acid is butane! ) Can deprotonate amines n-BuLi and CH -acidic compounds:

N-BuLi can be used for the preparation of certain aldehydes and ketones from disubstituted amides:

Upon heating of n-BuLi a β -elimination takes place. This results primarily butene and lithium hydride. Butyllithium in turn reacts with the resulting butene, with over butadiene polymeric products formed. The decay follows a first order rate law. The half -lives at 130 ° C 315 min, at 140 ° C and 115.5 min at 150 ° C 49.5 min.

On storage of n- BuLi or t -BuLi longer time than ethereal solution, eg in tetrahydrofuran to a decay of the solvent takes place:

Use

N- BuLi has gained great importance as a very strong base or as Lithiierungsreagenz in modern synthetic organic chemistry. For example, the base B of lithium diisopropylamide (LDA) is prepared in common to the control in situ by deprotonation of diisopropylamine with n- BuLi in THF.

Content determination

Since butyllithium is limited only stable and also is sensitive to water and oxygen must be the content of a solution before use can be determined. To determine the content, an aliquot of the solution is mixed with water and titrated against a dilute solution of hydrochloric acid. However, the aggregate base salary is determined. However, to lithium hydride, lithium hydroxide and alkoxides deduct from the total base is reacted with a large excess of benzyl chloride, an aliquot of the solution in THF. Here, benzyl chloride reacts in a Wurtz - wing reaction to the 1,2- diphenyl ethane and there is lithium chloride. After hydrolysis, the residual base is also titrated against hydrochloric acid. The difference between both values ​​is now supplying the amount of butyllithium.

Safety

As previously mentioned, pure n -BuLi is extremely pyrophoric. But the solutions, especially if they are highly concentrated, can ignite spontaneously. They also react violently with water to form lithium hydroxide and n -butane. Prolonged standing can therefore form in the solutions a precipitate, which is caused by moisture penetration. It can however also be lithium hydride, since n -BuLi very slowly decomposes into butene and lithium hydride.

Pictures of N-Butyllithium

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