A necessary condition for halogenation in benzene is the presence of a halogen carrier.
Halogenation of Benzene
Halogenation is an example of electrophilic aromatic substitution. The benzene is attacked by an electrophile which results in the substitution of hydrogens. The electrophilic bromination of benzenes is an exothermic reaction.
- Benzene reacts with bromine or chlorine in an electrophilic substitution reaction only in the presence of a catalyst which is either chloride or iron.
- Iron is not a catalyst because it changes permanently during the reaction. It reacts with some bromine to form iron 3 chloride, FeCl3 or iron 3 bromides, FeBr3.
- The reaction between bromine and benzene gives bromobenzene in the presence of either iron or aluminium bromide. Iron is used normally because it is readily available and cheaper.