Acetylide

Acetylide refers to chemical species that contain the acetylide unit derived from acetylene. In inorganic and organometallic chemistry, acetylides most often denote salts or complexes containing the acetylide dianion C2^2−, or, less commonly, the singly deprotonated form C2H− (ethynide). The term emphasizes the two-carbon, carbon–carbon triple bond that connects to metals or substituents.

Inorganic acetylides are typically salts of the C2^2− unit with metal cations. Common examples include calcium carbide (CaC2), sodium acetylide (Na2C2), and potassium acetylide (K2C2). In these compounds, the C2 unit behaves as a dianion, balancing the charge of the metal cations. These solids are important precursors in synthesis and, upon hydrolysis, release acetylene gas. Many acetylides are moisture- and air-sensitive.

Preparation and properties: Calcium carbide is produced industrially from lime and coke at high temperature and electric furnace conditions. CaC2 readily hydrolyzes with water to give calcium hydroxide and acetylene: CaC2 + 2 H2O → Ca(OH)2 + C2H2. Sodium and potassium acetylides can be prepared by direct reaction of the corresponding alkali metal with acetylene or via carbide routes. Acetylide compounds are strong bases and good nucleophiles, and they react vigorously with water and oxygen, releasing acetylene gas.

Reactions and uses: Acetylide ions act as nucleophiles in alkylation reactions, forming alkynes by reaction with primary and secondary alkyl halides. They also serve as ligands in organometallic chemistry, supporting various coupling and synthetic transformations. The term acetylide may also describe ethynide-type ligands attached to metals in complexes.

Safety: Acetylides are typically air- and moisture-sensitive; contact with water liberates flammable acetylene and can pose explosion risks in concentrated forms. Handle under appropriate inert or dry conditions with proper precautions.