Question

Convert ethene to benzene.

Answer 1

Hint: Organic compounds can be used to prepare other organic compounds on reaction with suitable reagents and under preferred reaction conditions. Alkynes undergo polymerization reactions.

Complete step by step solution:
We need to prepare benzene. Benzene has alternate double and single bonds.
Alkynes contain a $ - C \equiv C - $triple bond and the carbons have a $sp$ hybridisation. The carbon atom is highly electronegative due to high s- character and the hydrogen atom is acidic. If we consider the polymerization of alkynes, it would involve the breaking of one out of the three bonds thus forming alternate double and single bonds. Alkynes can undergo both linear and cyclic polymerization. Thus, they are very useful in the polymer industry as it can be used to prepare a variety of polymers.
Polymerization of ethyne can be used to make benzene. Thus, first we convert ethene to ethyne. For converting ethene to ethyne we first treat ethene with bromine water to produce vicinal dibromides on dehydrohalogenation of the dibromide by using alcoholic potassium hydroxide to prepare ethyne.
Three moles of ethyne in a red hot iron tube at a high temperature of around $873{\text{K}}$ undergo cyclic polymerization and form benzene.
${C_2}{H_4}\xrightarrow[{CC{l_4}}]{{B{r_2}}}C{H_2}\left( {Br} \right) - C{H_2}Br\xrightarrow[\Delta ]{{alc.KOH}}CH \equiv CH$
$3HC \equiv CH\xrightarrow[{873K}]{{{\text{red hot Fe tube}}}}{C_6}{H_6}$

Note:
Hydrocarbons can be classified widely into three categories which are alkanes, alkenes and alkynes.
Alkanes are saturated organic compounds and contain only single bonds between the carbon atoms. However, alkenes and alkynes are unsaturated compounds and have double and triple bonds between the carbon atoms, respectively, in addition to single bonds. This difference in the bonding gives them different physical as well as chemical properties.