Question

What is the role of ${\mathrm{FeCl}}_3$ in halogenation of benzene?

Answer 1

Halogenation of benzene:

1. An electrophilic aromatic substitution occurs when benzene is attacked by an electrophile and is substituted by hydrogen, since halogens are not sufficiently electrophile to break the aromatic benzene so a catalyst is needed to break the benzene ring.
2. Chlorobenzene reacts with chlorine gas and forms dichlorobenzene at the ortho and para positions by initiating the chromium ion.
3. There is a deactivation of chlorine ion but the ortho and para are directing.
4. The general equation of halogenation of benzene is shown below:

The importance of ${\mathrm{FeCl}}_3$ in halogenation of benzene:

1. Arenes react with the halogens in the presence of ${\mathrm{FeCl}}_3$ (Lewis acid) to form haloarenes.
2. When ${\mathrm{FeCl}}_3$ acts as Lewis acid in the reaction then there is a replacement of the chlorine atom in the place of a hydrogen atom from the benzene ring.
3. Chlorine polarizes in the substitution reaction by introducing a positive charge on the chlorine tom due to the ${\mathrm{FeCl}}_3$ as Lewis base in the reaction.