Preparation
The standard preparation for n-BuLi is reaction of 1-bromobutane or 1-chlorobutane with Li metal:
- 2 Li + C4H9X → C4H9Li + LiX
- where X = Cl, Br
If the lithium used for this reaction contains 1–3% sodium, the reaction proceeds more quickly than if pure lithium is used. Solvents used for this preparation include benzene, cyclohexane, and diethyl ether. When BuBr is the precursor, the product is a homogeneous solution, consisting of a mixed cluster containing both LiBr and BuLi, together with a small amount of octane. BuLi forms a weaker complex with LiCl, so that the reaction of BuCl with Li produces a precipitate of LiCl.
The concentration of butyllithium in commercially available solutions tends to decrease over time as the BuLi reacts with air. Subsequently, butyllithium is often titrated prior to use to ascertain its true concentration. The BuLi is added to a known amount of a weakly acidic compound, such as an alcohol. Because butyllithium is a strong base, it quickly and quantitatively reacts with weak acids to give the corresponding lithium salts and butane. An indicator, such as 1,10-phenanthroline or 2,2'-bipyridine, is commonly used to signal the endpoint of the titration. Both compounds form colored complexes with butyllithium once the titrand is consumed.
Read more about this topic: N-Butyllithium
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