- Butyllithium (BuLi) is a highly reactive organolithium compound with the general formula C₄H₉Li, where “butyl” refers to a four-carbon alkyl group.
- It exists in several isomeric forms, the most common being n-butyllithium (n-BuLi), which has a straight-chain structure. Other isomers include sec-butyllithium (sec-BuLi), iso-butyllithium (i-BuLi), and tert-butyllithium (t-BuLi), each varying in the structure of the butyl group and their corresponding reactivity.
- Butyllithium is typically used as a strong base and nucleophile in organic synthesis, especially in lithiation reactions, polymerizations, and metalation processes.
- Commercially, butyllithium is most often supplied as a solution in hexanes or other hydrocarbon solvents, since it is pyrophoric—it ignites spontaneously upon exposure to air or moisture. This extreme reactivity necessitates that it be handled under inert atmospheres, such as nitrogen or argon, and with strict safety protocols. In solution, butyllithium exists as aggregates, such as tetramers or hexamers, depending on the solvent and concentration. These aggregated structures influence its chemical behavior and reactivity in solution.
- Chemically, butyllithium serves as one of the strongest organometallic bases, with its basicity significantly exceeding that of traditional bases like sodium hydroxide or potassium tert-butoxide. It is frequently used to deprotonate weakly acidic protons, particularly in aromatic and heterocyclic compounds, leading to the formation of carbanions that can undergo further functionalization. This makes it a crucial reagent in the formation of carbon–carbon bonds, a foundational process in constructing complex organic molecules, pharmaceuticals, and advanced materials.
- In industrial settings, butyllithium is widely employed in anionic polymerization, such as the synthesis of styrene–butadiene rubber (SBR) and other elastomers. These materials are important in tire manufacturing, adhesives, and sealants. Additionally, BuLi is a key reagent in producing intermediates for agrochemicals, pharmaceuticals, and electronic materials. Its high reactivity and strong nucleophilic character make it indispensable for precise synthetic routes that require controlled generation of reactive intermediates.
- Despite its utility, butyllithium poses significant safety hazards due to its high flammability and reactivity with water, which releases flammable hydrogen gas and heat. Accidental exposure to air can lead to fires or explosions, making its storage, transportation, and handling a serious concern. Laboratories and industrial plants using BuLi must implement strict air-free techniques (e.g., gloveboxes or Schlenk lines) and have emergency protocols in place.
