Definition
ChEBI: An alkynyllithium compound resulting from the replacement of one of the hydrogens of acetylene by lithium.
Application
Lithium Acetylide is a reagent for adding Acetylene to ketones, opening epoxides, and ethynylation of alkyl halides.
Synthesis
Monolithium lithium acetylide is prepared by treating a THF solution of Acetylene with n-Butyllithium at 78 °C (eq 1). It is critical to keep the temperature at -78 °C. The concentration should be 0.5 M or less. At higher concentrations and temperatures, a white precipitate forms (presumably Dilithium Acetylide), and yields of additional product fall appreciably. Properly formed lithium acetylide in THF should be a clear, colorless solution.
Precautions
Lithium acetylide/THF solution must be used immediately after preparation. It decomposes above -78 °C. A saturated solution of THF/acetylene should not be used during the preparation of lithium acetylide since this may lead to an acetylene atmosphere above the THF. n-Butyllithium dropping through the acetylene atmosphere may react violently. Lithium acetylide is air and moisture sensitive.
