Question

Starting from chloroform how would you prepare acetylene?

Answer 1

Acetylene is prepared from chloroform by a dehydrohalogenation reaction using silver metal or a strong base like potassium hydroxide. The reaction with silver involves heating chloroform with silver powder, where the silver removes chlorine atoms, forming acetylene (C₂H₂) and silver chloride (AgCl).

1. Using Silver Metal: Chloroform (CHCl₃) and silver (Ag) powder. Treat chloroform with silver powder and heat the mixture. Acetylene (C₂H₂) and silver chloride (AgCl).
\[\ce{2CHCl3 + 6Ag -> C2H2 + 6AgCl}\]
Each chloroform molecule loses its three chlorine atoms to the silver, and the remaining CH-CH parts from two chloroform molecules combine to form one acetylene molecule.

2. Using a Strong Base (e.g., Potassium Hydroxide): Chloroform (CHCl₃) and a strong base, such as potassium hydroxide (KOH) or sodium hydroxide (NaOH). The strong base facilitates the elimination of hydrogen chloride (HCl). This process can generate dichlorocarbene (CCl₂). Dichlorocarbene undergoes further reactions and eliminations to produce acetylene.
\[\ce{CHCl3 + 3KOH ->[heat][] C2H2 + 3HCl + 3H2O}\]