Question

Discuss the mechanism of halogenation of benzene

Answer 1

Benzene reacts with chlorine or bromine in an electrophilic substitution reaction, but only in the presence of a catalyst. The catalyst is either aluminium chloride or aluminium bromide if you are reacting benzene with bromine or iron.
Strictly speaking iron isn't a catalyst , because it gets permanently changed during the reaction. It reacts with some of the chlorine or the bromine to form iron(III)chloride FeCl3, or iron(III)Bromide FeBr3

2Fe + 3Cl2 --------> 2FeCl3
2Fe + 3Br2 --------> 2FeBr3

These compounds at like catalyst and behave exactly like aluminium chloride in these reactions.

The reaction with Chlorine -
The reaction between benzene and chlorine in the presence of either aluminium chloride or iron gives chlorobenzene.

C6H6 + Cl2 --------> C6H5Cl + HCl

The reaction with Bromine -
The reaction between Benzene and Bromine in the presence of either aluminium bromide or iron gives bromobenzene. Iron is usually used because it is cheaper and more readily available.

C6H6 + Br2 ---------> C6H5 + HBr
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