Butyllithium

Structural formula
General
Surname	Butyllithium
other names	n -butyllithium BuLi n -BuLi Lithium butyl
Molecular formula	C 4 H 9 Li
Brief description	colorless liquid, commercially available n -butyllithium is often yellowish
External identifiers / databases
CAS number 109-72-8 EC number 203-698-7 ECHA InfoCard 100.003.363 PubChem 61028 ChemSpider 10254339 Wikidata Q410875
properties
Molar mass	64.05 g · mol -1
Physical state	liquid
Melting point	−34 ° C (hexamer)
solubility	reacts violently with water soluble in many alkanes and cycloalkanes
safety instructions
GHS labeling of hazardous substances for the 2.5 M solution in n -hexane danger H and P phrases H: 225-250-260-304-314-336-361f-373-411 EUH: 014 P: 201-231 + 232-280-305 + 351 + 338-370 + 378-422
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Under butyllithium is meant typically n -butyllithium ( n -BuLi), an organometallic compound of the element lithium ( organolithium compound ). There are also the isomeric forms sec -butyllithium and tert -butyllithium . Butyllithium is used as a reagent in the production of a natural rubber (cis 1.4 content) from isoprene. As early as 1985, around 600 tons of butyllithium were required for this purpose.

Extraction and presentation

The synthesis is analogous to the production of Grignard compounds by reacting 1-chlorobutane with elemental lithium in diethyl ether:

${\displaystyle \mathrm {2\ Li+C_{4}H_{9}Cl\longrightarrow LiC_{4}H_{9}+LiCl} }$

properties

Physical Properties

Tetramer of the n -BuLis

n -Butyllithium is a very strong base . The basicity of the isomeric butyllithium compounds increases in the series n -butyllithium < sec -butyllithium < tert -butyllithium. Due to the large electronegativity difference between carbon (2.55) and lithium (0.98), the bond between C and Li is strongly polarized. Based on the reactions of n -BuLi, one could assume that n -BuLi is composed of the butyl anion and the lithium cation , i.e. has an ionic bond . However, this assumption is wrong because n -BuLi is not ionic. As a solid and even as a solution , n -BuLi, like most organolithium compounds, exists as molecular groups with covalent bonds between lithium and carbon . A hexamer structure was demonstrated for the pure substance by mass spectrometry . In non-polar solvents such as cyclohexane , n -BuLi is hexameric, in ether it is tetrameric.

Chemical properties

Pure n -butyllithium is a pyrophoric colorless liquid, so it ignites itself in the presence of oxygen . It is therefore commercially available as a (usually slightly yellow) solution, which must also be stored under an inert gas , with concentrations of 1.6 to 11 mol / l are common in n -hexane .

Ethers used as solvents such as THF or diethyl ether are unsuitable as storage solvents for n -BuLi because they would slowly decompose. The half-life of n -BuLi in THF at 0 ° C with the deaggregation additive TMEDA ( tetramethylethylenediamine ) is only 38 minutes. n -Butyllithium also reacts exothermically with carbon dioxide and oxygen , as well as with water. The heat of hydrolysis is −240 kJ mol ^−1. The thermal decomposition of n-butyllithium leads to lithium hydride and 1-butene .

Reactions

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

${\displaystyle \mathrm {LiC_{4}H_{9}+ArI\longrightarrow LiAr+C_{4}H_{9}I} }$

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

${\displaystyle \mathrm {LiC_{4}H_{9}+R{-}H\rightleftharpoons C_{4}H_{10}+R{-}Li} }$

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

${\displaystyle \mathrm {LiC_{4}H_{9}+RCONMe_{2}\longrightarrow LiNMe_{2}+RCOC_{4}H_{9}} }$

When n -BuLi is heated, β- elimination takes place. This primarily produces butene and lithium hydride . Butyllithium in turn reacts with the butene that is formed, and polymeric products can also be formed via butadiene . The decay proceeds according to a time law of the first order . The half-lives are 315 min at 130 ° C, 115.5 min at 140 ° C and 49.5 min at 150 ° C.

${\displaystyle \mathrm {LiC_{4}H_{9}\longrightarrow LiH+CH_{2}{=}CHCH_{2}CH_{3}} }$

If you store n -BuLi or t -BuLi as an ethereal solution, e.g. B. in tetrahydrofuran , the solvent decomposes:

${\displaystyle \mathrm {LiC_{4}H_{9}+THF\longrightarrow LiO{-}CH{=}CH_{2}+CH_{2}{=}CH_{2}+C_{4}H_{10}} }$

use

In modern synthetic organic chemistry, n -BuLi has gained great importance as a very strong base or as a lithiation reagent. So z. B. the frequently used base lithium diisopropylamide (LDA) is usually produced in situ by deprotonating diisopropylamine with n -BuLi in THF.

Determination of salary

Since butyllithium has only limited stability and is also sensitive to water and oxygen, the content of a solution must be determined before use. To determine the content, an aliquot of the solution is mixed with water and titrated against a dilute solution of hydrochloric acid. The total base content is determined. However, in order to be able to subtract lithium hydride, lithium hydroxide and alcoholates from the total base, an aliquot of the solution in THF is reacted with a large excess of benzyl chloride. Benzyl chloride reacts in a Wurtz-Fittig reaction to form 1,2-diphenylethane and lithium chloride is formed . After hydrolysis, the residual base is also titrated against a hydrochloric acid. The difference between the two values ​​now gives the proportion of butyllithium.

safety instructions

As already mentioned, pure n -BuLi is extremely pyrophoric . But the solutions , especially if they are more concentrated, can ignite spontaneously. They also react violently with water to form lithium hydroxide and n -butane . If the solution is left standing for a long period of time, a precipitate may form due to the ingress of moisture . However, it can also be lithium hydride , since n -BuLi decomposes very slowly into butene and lithium hydride.

Individual evidence

1. ↑ ^{a b c d} Entry on butyllithium in the GESTIS substance database of the IFA , accessed on July 23, 2016(JavaScript required) .
2. ↑ ^{a b} Ullmann’s Encyclopedia of Industrial Chemistry. 6th edition. 2002.
3. ↑ T. Kottke, D. Stalke: Structures of the classical synthesis reagents (nBuLi) ₆ and (tBuLi) ₄ as well as of the metastable (tBuLi · Et ₂ O) ₂ . In: Angew. Chem. 105, 1993, pp. 619-621, doi: 10.1002 / anie.19931050433 .
4. ↑ Entry on butyllithium. In: Römpp Online . Georg Thieme Verlag, accessed on May 5, 2014.
5. ↑ Parts of the labeling of hazardous substances relate to the hazards caused by the solvent.
6. ↑ K. Ziegler, H. Colonius: Investigations on alkali-organic compounds. V. A Convenient Synthesis of Simple Lithium Alkyls. In: Justus Liebigs Ann. Chem. 479, 1930, pp. 135-149, doi: 10.1002 / jlac.19304790111 .
7. ↑ D. Plavsic, D. Srzic, L. Klasinc: Mass spectrometric investigations of alkyllithium compounds in the gas phase. In: J. Phys. Chem. 90, 1986, pp. 2075-2080, doi: 10.1021 / j100401a020 .
8. ↑ P. Stanetty, H. Koller, M. Mihovilovic: Directed ortho lithiation of phenylcarbamic acid 1,1-dimethylethyl ester (N-BOC-aniline). Revision and improvements. In: J. Org. Chem. 57, 1992, pp. 6833-6837, doi: 10.1021 / jo00051a030 .
9. ↑ ^{a b} T. L. Rathman, JA Schwindeman: Preparation, Properties, and Safe Handling of Commercial Organolithiums: Alkyllithiums, Lithium sec-Organoamides, and Lithium Alkoxides. In: Org. Process Res. Dev. 18, 2014, pp. 1192-1210, doi: 10.1021 / op500161b .
10. ^ PA Fowell, CT Mortimer: Heats of Formation and Bond Energies. Part V. n-Butyllithium. In: J. Chem. Soc. 1961, pp. 3793-3796, doi: 10.1039 / JR9610003793 .
11. ^ RA Finnegan, HW Kutta: Organometallic Chemistry. X1I. The Thermal Decomposition of n-Butyllithium, a Kinetic Study. In: J. Org. Chem. 30, 1965, pp. 4138-4144, doi: 10.1021 / jo01023a038 .
12. ^ J. Clayden, SA Yasin: Pathways for decomposition of THF by organolithiums: the role of HMPA. In: New J. Chem. 26, 2002, pp. 191-192, doi: 10.1039 / b109604d .
13. ^ Chemetall, in-house communication, lithium division 1995, 1-8.

literature

• Author collective: Organikum. 21st edition. Wiley-VCH, Weinheim 2001, ISBN 3-527-29985-8 .
• Christoph Elschenbroich : Organometallic chemistry. 5th edition. Teubner, Wiesbaden 2005, ISBN 3-519-53501-7 .