Question

Arenes on treatment with chlorine in presence of ferric chloride as a catalyst undergo what type of reaction ?

• A. Electrophilic substitution
• B. Nucleophilic substitution
• C. Electrophilic addition
• D. Nucleophilic addition

Answer 1

Answer: (A)

Arenes on treatment with chlorine in presence of Lewis acid catalyst, ferric chloride or aluminium chloride and in the absence of light undergoes halogenation. It involves electrophilic substitution reaction



Mechanism of electrophilic substitution is as follows:

Step I Generation of an electrophile

$Cl—Cl+AlC{l}_3\to C{l}^{+}+C{l}^{5+}\dots A{l}^{5-}—C{l}_3$

$\to C{l}^{+}+[AlC{l}_4{]}^{-}$ Chloronium ion

Step II Formation of carbocation (arenium ion)



The arenium ion gets stabilised by resonance



Step III Removal of proton