SEC-BUTYLLITHIUM

Description

s-Butyllithium (s-BuLi) is a strong base that is useful for deprotonating weak carbon acids, especially when weaker organolithium bases such as n-BuLi don't work well.

Description

sec-Butyllithium. [598-30-1], sec-C4H9Li, Mr 64.06, is a spontaneously flammable, colorless, viscous liquid that forms tetramers in hydrocarbon solvents. It is commercially available only as 12 % solution in cyclohexane and methylcyclohexane. sec-Butyllithium is more nucleophilic and decomposes more readily than n-butyllithium. A 12 % solutionin cyclohexane at 20 ℃ undergoesthermal decomposition to the extent of 1.4 % of the active material per month. The thermal decomposition yields butene gas and LiH; the latter is insoluble and responsible for the increasing turbidity of secbutyllithium solutions on prolonged storage. Therefore solutions of sec-butyllithium must be kept cool during storage and transportation.

Chemical properties

sec-Butyllithium is a colorless crystalline solid or clear yellowish solution. It is more reactive than n-butyllithium. Its solutions are unstable and decompose about 10 to 15 times as fast as n-butyllithium under the same conditions.

The Uses of SEC-BUTYLLITHIUM

sec-Butyllithium is used almost exclusively as a polymerization catalyst. It is more expensive than n-butyllithium and is used mainly because of its greater reactivity and faster polymerization initiation.

Preparation

sec-Butyllithium is produced by the reaction of sec-butyl chloride with lithium metal dispersion in hydrocarbon solvents. The lithium metal should contain catalytic amounts of up to 2 % sodium metal to attain a rapid reaction with the chloride and to minimize coupling. Massive substitution of sodium metal for lithium metal as is done in the preparation of n-butyllithium results in lower yields. Isopentane, hexane and cyclohexahe are typical solvents. Industrial and laboratory preparations are similar.