Methyllithium

UsesThere are no significant industrial uses of methyllithium, but it is widely used in the laboratory in Grignard type reactions. Methyllithium is an organolithium reagent mainly used for deprotonation and as a source of methyl anion. It is a strong base and a strong nucleophile.

UsesMethyllithium lithium bromide complex solution (MeLi.LiBr) can be used as a methylating agent for the α-methylation of alkoxyaryl ketones.

PreparationMethyllithium is produced industrially by the reaction of methyl chloride or methyl bromide with lithium metal dispersion in diethyl ether. The reaction with methyl chloride yields a solution of methyllithium and a precipitate of lithium chloride which may be readily separated. When methyl bromide is used, the lithium bromide byproduct remains in solution and complexes with the methyllithium. This reduces the reactivity of the methyllithium and, in certain cases, affects its usefulness. On the other hand, the less reactive complex is more stable in diethyl ether. Methyllithium produced from methyl chloride contains only about 0.3 % lithium chloride in a 5 % solution in diethyl ether. It is more reactive than the lithium bromide complex, but decomposes at the rate of 1 % of the contained methyllithium per year (that is 5.00 % solution goes to 4.95 %) at room temperature. The decomposition by ether cleavage results in methane and ethylene formation which increases the pressure in the container on long storage. Methyllithium can be prepared easily in tetrahydrofuran but it has a half-life of only about 2 days at room temperature due to solvent cleavage.