Here’s a explanation of the halogenation of benzene:
What Halogenation Is
- Halogenation is the process in which a halogen atom (like chlorine or bromine) replaces a hydrogen atom on the benzene ring.
- It is a type of electrophilic aromatic substitution.
Step 1: Formation of the Electrophile
- Halogens themselves are not reactive enough to attack benzene directly.
- A Lewis acid catalyst (like FeCl₃ or FeBr₃) is used to activate the halogen.
- This forms a positively charged halogen species (electrophile) that can react with benzene.
Step 2: Attack on the Benzene Ring
- Benzene has a cloud of π-electrons that attacks the halogen electrophile.
- This creates a temporary sigma complex (arenium ion) where the ring loses its aromaticity temporarily.
Step 3: Restoration of Aromaticity
- A hydrogen atom is removed from the carbon that bonded to the halogen.
- This restores the aromatic character of the benzene ring.
- The final product is a halobenzene (like chlorobenzene or bromobenzene).
Key Points
- Halogenation requires a catalyst to generate the reactive halogen species.
- The reaction is substitution, not addition, to preserve aromaticity.
- Halogens are slightly deactivating, so the reaction is slower than benzene nitration.