Question
Discuss the mechanism of chlorination of benzene.
Solution
Mechanism of chlorination of benzene: Benzene on treatment with chlorine in the presence of halogen carrier (Fe or FeCl3) forms chlorobenzene.
Different steps involved in the mechanism are:
(i) Generation of an electrophile (Cl+): The catalyst Lewis acid (FeCl3) helps in the generation of an electrophile (Cl+) by causing polarisation of the chlorine molecule.
(ii) Formation of the carbocation: The electrophile (Cl+) attacks the benzene ring to form an intermediate carbocation which is resonance stabilised. It is a slow step.
Resonance hybrid of the above resonating structures can be represented as,
(iii) Proton transfer from the carbocation to form chlorobenzene.
Different steps involved in the mechanism are:
(i) Generation of an electrophile (Cl+): The catalyst Lewis acid (FeCl3) helps in the generation of an electrophile (Cl+) by causing polarisation of the chlorine molecule.
(ii) Formation of the carbocation: The electrophile (Cl+) attacks the benzene ring to form an intermediate carbocation which is resonance stabilised. It is a slow step.
Resonance hybrid of the above resonating structures can be represented as,
(iii) Proton transfer from the carbocation to form chlorobenzene.
