n-Бутиллитий: қасиеттері, қолданылуы және химиялық ерекшеліктері

Chemical compound

n Butyllithium C4H9Li (abbreviated n BuLi) is an organolithium reagent. It is widely used as a polymerization initiator in the production of elastomers such as polybutadiene or styrene butadiene styrene (SBS). Also, it is broadly employed as a strong base (superbase) in the synthesis of organic compounds as in the pharmaceutical industry. Butyllithium is commercially available as solutions (15%, 25%, 1.5 M, 2 M, 2.5 M, 10 M, etc.) in alkanes such as pentane, hexanes, and heptanes. Solutions in diethyl ether and THF can be prepared, but are not stable enough for storage. Annual worldwide production and consumption of butyllithium and other organolithium compounds is estimated at 2000 to 3000 tonnes. Although butyllithium is colorless, n butyllithium is usually encountered as a pale yellow solution in alkanes. Such solutions are stable indefinitely if properly stored, but in practice, they degrade upon aging. Fine white precipitate (lithium hydride) is deposited and the color changes to orange.

n BuLi exists as a cluster both in the solid state and in a solution. The tendency to aggregate is common for organolithium compounds. The aggregates are held together by delocalized covalent bonds between lithium and the terminal carbon of the butyl chain. In the case of n BuLi, the clusters are tetrameric (in ether) or hexameric (in cyclohexane). The cluster is a distorted cubane type cluster with Li and CH2R groups at alternating vertices. An equivalent description describes the tetramer as a Li4 tetrahedron interpenetrated with a tetrahedron [CH2R]4. Bonding within the cluster is related to that used to describe diborane, but more complex since eight atoms are involved. Reflecting its electron rich character, n butyllithium is highly reactive toward Lewis acids. Due to the large difference between the electronegativities of carbon (2.55) and lithium (0.98), the C−Li bond is highly polarized. The charge separation has been estimated to be 55–95%. For practical purposes, n BuLi can often be considered to react as the butyl anion, n Bu−, and a lithium cation, Li+.

Butyllithium is a strong base (pKb ≈  36), but it is also a powerful nucleophile and reductant, depending on the other reactants. Furthermore, in addition to being a strong nucleophile, n BuLi binds to aprotic Lewis bases, such as ethers and tertiary amines, which partially disaggregate the clusters by binding to the lithium centers. Its use as a strong base is referred to as metalation. Reactions are typically conducted in tetrahydrofuran and diethyl ether, which are good solvents for the resulting organolithium derivatives (see below).