Cyclic Polymerization

Trimerization of Ethyne to Benzene:

$$3\text{HC}\equiv\text{CH} \xrightarrow{\text{Red-hot Fe tube}, \, 873\text{ K}} \text{C}_6\text{H}_6 \quad (\text{Benzene})$$

Concept: Cyclic addition of three ethyne molecules through a red-hot iron or quartz tube at $$873\text{ K}$$ yields benzene.

Trimerization of Propyne to Mesitylene:

$$\begin{aligned}3\text{CH}_3\text{--C}\equiv\text{CH} \xrightarrow{\text{Red-hot Fe tube}, \, 873\text{ K}} 1,3,5\text{-Trimethylbenzene} (\text{Mesitylene})\end{aligned}$$

Concept: Regioselective trimerization of propyne yields symmetrical $$1,3,5\text{-trimethylbenzene}$$.