tert -butyllithium

Structural formula
General
Surname	tert -butyllithium
other names	t -butyllithium t -BuLi
Molecular formula	C 4 H 9 Li
Brief description	colorless, pyrophoric solid
External identifiers / databases
CAS number 594-19-4 EC number 209-831-5 ECHA InfoCard 100.008.939 PubChem 638178 ChemSpider 10254347 Wikidata Q287745
properties
Molar mass	64.05 g mol −1
Physical state	firmly
Melting point	140 ° C (decomposition)
solubility	soluble in pentane
safety instructions
GHS labeling of hazardous substances H and P phrases H: 250-252-260-314-318-336-304-411 EUH: 014 P: 223-301 + 310-303 + 361 + 353-305 + 351 + 338-405-422-501
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

tert -Butyllithium ( t -BuLi) is a tertiary organometallic compound of the element lithium ( organolithium compound ). There are also the isomeric forms n -butyllithium and sec -butyllithium . The basicity increases in the series n -Butyllithium < sec -Butyllithium < tert -Butyllithium. t -BuLi is thus the strongest base in this series. t -BuLi breaks down into lithium hydride and isobutene at room temperature. The isobutene formed isdeprotonatedby further t -BuLi in the allyl position, which leads to a further reduction in the concentration of t -BuLi.

presentation

The synthesis can be carried out by reacting t -butyl bromide with lithium (powder).

${\displaystyle \mathrm {2\ Li+C_{4}H_{9}Br\longrightarrow LiC_{4}H_{9}+LiBr} }$

properties

It is only available commercially as a solution in alkanes (mostly in pentane or heptane), a concentration of 1.7  mol / l being common. Ethers such as THF or diethyl ether are unsuitable as solvents for storage because they decompose quickly. t -BuLi is extremely pyrophoric even in solution and burns in the air with a typical red flame .

Reactions

The lithium-carbon bond in the tert- butyllithium molecule is strongly polarized . The carbon atom carries a negative and the lithium atom a positive partial charge. Tert -Butyllithium therefore behaves chemically similar to a corresponding carbanion . This behavior can be illustrated by formulating a mesomeric boundary structure :

Similar to n -Butyllithium , t -BuLi can also be used for lithium - halogen exchange and for the deprotonation of amines and activated CH compounds. t -BuLi can also attack the alpha position of the ethers .

This is shown by the example of tetrahydrofuran , which is decomposed within minutes at room temperature :

This method is used, for example, when deprotonated acetaldehyde is required.

use

In modern synthetic organic chemistry, t -BuLi has achieved importance as an ultra-strong base or as a lithiation reagent. Since it is much more pyrophoric than n -BuLi , it is used less often. In some cases it is used because of the higher basicity or for steric reasons (the t -butyl radical is spatially relatively large).

safety instructions

t -BuLi is extremely pyrophoric even in solution . Handling and storage must therefore always take place under protective gas. t -BuLi also reacts violently with water to form lithium hydroxide and isobutane . With longer storage, a sediment is formed from lithium hydride, which is also pyrophoric (from self-decomposition) and lithium hydroxide (penetrated moisture).

swell

1. ↑ Entry on butyllithium. In: Römpp Online . Georg Thieme Verlag, accessed on May 24, 2014.
2. ↑ ^{a b} Ulrich Wietelmann, Richard Bauer: lithium and lithium compounds. In: Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, Weinheim 2005, doi : 10.1002 / 14356007.a15_393 .
3. ↑ ^{a b} Data sheet tert-butyllithium, nominally 1.5M in n-pentane, packaged under argon in resealable ChemSeal bottles from AlfaAesar, accessed on September 27, 2018 ( PDF )(JavaScript required) .
4. ↑ KPC Vollhardt, NE Schore: Organic Chemistry . 3. Edition. Wiley-VCH, 2005, ISBN 978-3-527-29819-8 .