Answer:
Acetylene and hydrogen cyanide is passed through a red hot tube 2:1 to form benzene.
Reaction
Acetylene on passing through a red-hot iron tube at 873K undergoes cyclic polymerization. Three molecules of acetylene undergo polymerization to produce benzene (C6H6).
\((C_{2}H_{6})_{3}\overset{Red\, hot\, tube}{\rightarrow}C_{6}H_{6}\)
This is the famous Diels Alder reaction.
The Diels-Alder reaction is a conjugate addition reaction of a conjugated diene to an alkene or alkyne (the dienophile) to produce cyclohexane.
