Methyllithium

Methyllithium is an organolithium reagent represented by the chemical formula CH₃Li. It is a highly reactive compound used extensively in organic synthesis for the formation of carbon-carbon bonds, among other applications. Methyllithium exists as a tetramer in the solid state and as a highly polar solvate in solution. It is one of the most basic and nucleophilic reagents known in organic chemistry, making it a valuable tool for synthetic chemists.

Properties

Methyllithium is colorless in its pure form but is usually encountered as a solution in various solvents such as diethyl ether or tetrahydrofuran (THF), where it appears as a clear to slightly yellowish liquid. It is extremely reactive towards water, air, and moisture, necessitating its handling under an inert atmosphere in a dry solvent. The reactivity of methyllithium is attributed to the high polarity of the carbon-lithium bond, with the carbon being negatively charged (carbanion) and lithium being positively charged.

Synthesis

Methyllithium is typically synthesized by the reaction of methyl chloride (CH₃Cl) with lithium metal. This process involves the direct exchange of lithium for chlorine, resulting in the formation of methyllithium and lithium chloride (LiCl) as a byproduct. The reaction is highly exothermic and must be controlled carefully to prevent accidents.

Applications

Methyllithium finds widespread use in organic synthesis. Its applications include:

• The formation of carbon-carbon bonds through nucleophilic addition to carbonyl compounds, including aldehydes, ketones, and esters.
• The deprotonation of acids to form carbanions, which can then be further reacted with electrophiles.
• The preparation of other organolithium compounds through transmetalation reactions.
• Use as a strong base in the removal of certain protecting groups.

Safety

Due to its high reactivity, especially with water and air, methyllithium must be handled with extreme caution. Protective gear, including gloves and eye protection, is mandatory. The use of a fume hood and an inert atmosphere (such as nitrogen or argon) is also recommended to prevent exposure to air. Accidental exposure to methyllithium can result in chemical burns and the release of flammable hydrogen gas upon contact with moisture.

See Also

• Organolithium reagent
• Organic synthesis
• Nucleophilic addition
• Carbon-carbon bond formation