acetilides

Acetilides are compounds containing the acetylide anion, which has the formula RC≡C⁻. This anion is characterized by a carbon-carbon triple bond and a negative charge on one of the sp-hybridized carbon atoms. Acetilides are typically formed from terminal alkynes, which have a weakly acidic acetylenic hydrogen atom. This hydrogen can be abstracted by strong bases, such as organometallic reagents (e.g., Grignard reagents or organolithium compounds) or alkali metals, to generate the corresponding acetylide.

The reactivity of acetilides stems from the nucleophilic nature of the carbanionic center. They are potent nucleophiles and are widely used in organic synthesis to form new carbon-carbon bonds. A classic reaction involving acetilides is their addition to carbonyl compounds (aldehydes and ketones) to form propargyl alcohols. They can also undergo alkylation reactions with primary alkyl halides, although secondary and tertiary alkyl halides tend to undergo elimination due to the strong basicity of the acetilide. Additionally, acetilides can react with epoxides, opening the ring to form new alcohols.

Metal acetylides, where the counterion is a metal cation, are also an important class of compounds. For example, copper(I) acetylide and silver(I) acetylide are known to be explosive, especially when dry. Calcium carbide, CaC₂, is a historically significant compound that reacts with water to produce acetylene gas, which was used for lighting. The stability of metal acetylides varies significantly depending on the metal.

Due to their high reactivity and potential hazards with certain metal derivatives, acetilides require careful handling in the laboratory. Their utility in constructing complex organic molecules, however, makes them indispensable reagents in synthetic chemistry.