Acetylides

Acetylides are salts or esters of the acetylide anion, C2H−, derived from the deprotonation of terminal alkynes (HC≡CH). They can exist as metal salts such as sodium acetylide and lithium or potassium acetylide, or as calcium carbide, CaC2, which serves as a practical industrial source of acetylene. The term also covers organic acetylides, where the acetylide group is bonded to an organic moiety (R–C≡C−).

Formation and structure: terminal alkynes are converted to acetylide salts by strong bases such as sodium amide, lithium diisopropylamide, or n‑butyllithium, typically in liquid ammonia or suitable aprotic solvents. These species are highly reactive, acting as strong bases and powerful nucleophiles.

Reactivity: acetylides participate in carbon–carbon bond-forming reactions. They can be alkylated by primary alkyl halides to extend the carbon chain and form alkynes after workup, or add to carbonyl compounds to yield propargyl alcohols. Reaction with carbon dioxide followed by acid workup gives propargylic carboxylates. They also serve as precursors to a variety of alkynyl-containing compounds used in organic synthesis.

Applications and safety: metal acetylides are important in organic synthesis for introducing the alkynyl group and in industrial contexts for generating acetylene from calcium carbide. Many acetylides are moisture- and air-sensitive; exposure to water or alcohols liberates acetylene gas. Some metal acetylides, particularly certain copper or transition-metal derivatives, can be shock-sensitive explosives and require careful handling.