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.
