n-Butyllithium

Description

n-BuLi is a strong base (pKa ~ 50) and is typically sold as a solution in hexanes (1.6M or 2.5M). It reacts violently with water and needs to be stored under an inert atmosphere to prevent its reacting with moisture in the air.

Chemical properties

n-Butyllithium is a colorless crystalline solid or clear yellow solution. Due to its high reactivity and extreme solubility, even in its impurities, it is commonly thought to be a viscous liquid.

The Uses of n-Butyllithium

n-Butyllithium is used as a polymerization initiator in the production of elastomers like polybutadiene and styrene- butadiene- styrene. As a strong base, it is utilized in the synthesis of organic compounds. It undergoes thermal decomposition to prepare 1-butene.

The Uses of n-Butyllithium

To a solution of the SM (5.56 g, 19.6 mmol) in THF (20 mL) was added LDA (2M in THF/heptane/ethylbenzene, 19.6 mL, 39.2 mmol) dropwise at -78 C. The reaction was stirred at -78 C for 1 h, after which time was added dropwise a solution of Iodine (9.94 g, 39.2 mmol) in THF (10 mL). After 30 min, the dry ice bath was removed and the reaction was warmed to RT. The mixture was quenched by the addition of sat aq Na2S2O3, then extracted with EtOAc. The combined organics were washed with H2O, brine, dried (MgSO4), and concentrated. The resulting material was purified by silica gel chromatography (0-20% EtOAc/hexane) to provide the product as a white solid. [2.65 g, 33%]

The Uses of n-Butyllithium

n-Butyllithium is a strong nucleophile in the synthetic organic chemistry. It is also used as an initiator in the polymerization process.

Preparation

Industrially, n-butyllithium is produced by the reaction of n-butyl chloride with lithium metal dispersion in various hydrocarbon solvents. Hexane is the most commonly used solvent. Up to one-half of the lithium is replaced with sodium in order to lower the cost of the butyllithium and increase the reactivity of the dispersion. The reaction is carried out below the boiling point of the solvent.
The laboratory procedure is essentially the same except that pentane and diethyl ether are two of the more popular solvents. The preparation runs smoothly in ether at lower temperatures but the product must either be used immediately or kept refrigerated due to the rapid cleavage of ether by n-butyllithium.

Definition

ChEBI: Butyllithium is an alkyllithium compound.

Flammability and Explosibility

The risk of fire or explosion on exposure of butyllithium solutions to the atmosphere depends on the identity of the organolithium compound, the nature of the solvent, the concentration of the solution, and the humidity. t-Butyllithium solutions are the most pyrophoric and may ignite spontaneously on exposure to air. Dilute solutions (1.6 M, 15% or less) of n-butyllithium in hydrocarbon solvents, although highly flammable, have a low degree of pyrophoricity and do not spontaneously ignite. Under normal laboratory conditions (25 °C, relative humidity of 70% or less), solutions of -20% concentration will usually not ignite spontaneously on exposure to air. More concentrated solutions of n-butyllithium (50 to 80%) are most dangerous and will immediately ignite on exposure to air. Contact with water or moist materials can lead to fires and explosions, and the butyllithiums also react violently with oxygen.

storage

In particular, butyllithium should be stored and handled in areas free of ignition sources, and containers of butyllithium should be stored under an inert atmosphere. Work with butyllithium should be conducted in a fume hood under an inert gas such as nitrogen or argon. Safety glasses, impermeable gloves, and a fire-retardant laboratory coat are required.

Incompatibilities

The butyllithiums are extremely reactive organometallic compounds. Violent explosions occur on contact with water with ignition of the solvent and of the butane produced. t-Butyllithium will ignite spontaneously in air. The butyllithiums ignite on contact with water, carbon dioxide, and halogenated hydrocarbons. The butyllithiums are incompatible with acids, halogenated hydrocarbons, alcohols, and many other classes of organic compounds.

Waste Disposal

Excess butyllithium solution can be destroyed by dilution with hydrocarbon solvent to a concentration of approximately 5 wt %, followed by gradual addition to water with vigorous stirring under an inert atmosphere. Alternatively, the butyllithium solution can be slowly poured (transfer by cannula for s- or tbutyllithium) into a plastic tub or other container of powdered dry ice.
The residues from the above procedures and excess butyllithium should be placed in an appropriate container, clearly labeled, and handled according to your institution's waste disposal guidelines.