LiC2H

LiC2H, commonly called lithium acetylide, is an organolithium compound comprising a lithium cation paired with the ethynide anion derived from acetylene (HC≡CH). It is a strong base and a potent nucleophile widely used in organic synthesis to form carbon–carbon bonds, particularly through nucleophilic addition to carbonyl compounds and subsequent workup to give propargyl alcohols or related alkynyl products.

Structure and properties

LiC2H is typically encountered as a solvated salt in dry ether or THF, where lithium centers exist as aggregates. The compound is highly moisture- and air-sensitive, requiring handling under inert atmosphere. In solution, lithium acetylide behaves as a nucleophile and base, capable of adding to electrophiles and promoting alkynyl substitutions.

Preparation

LiC2H is commonly prepared by deprotonation of acetylene with a strong base, such as n-butyllithium or lithium metal, in a dry, aprotic solvent (e.g., diethyl ether or THF) at low temperature. The resulting solution or solid is used directly in subsequent reactions.

Reactions and applications

A key use is the carbonyl addition of lithium acetylide to aldehydes and ketones, yielding propargyl alcohols after acidic workup. It also participates in alkynylations with primary alkyl halides to form substituted alkynes and can engage epoxides to give homoallenyl alcohol derivatives under basic conditions. LiC2H thus enables the introduction of the alkynyl fragment into a wide range of targets, providing a versatile route to alkynes and propargyl motifs.

Safety and handling

As a highly reactive, air- and moisture-sensitive reagent, LiC2H is handled under inert gas in dry solvents. It reacts with water and carbon dioxide to release acetylene gas and generate inorganic bases, so strict dry conditions are essential.