**Reaction of Benzene with Br-Cl in the Presence of FeCl3**

The reaction of benzene with Br-Cl in the presence of FeCl3 is known as bromination and chlorination of benzene. This reaction is a substitution reaction in which one or more hydrogen atoms of benzene are replaced by bromine and chlorine atoms.

**Mechanism of the Reaction:**

The reaction proceeds through an electrophilic aromatic substitution (EAS) mechanism. The FeCl3 acts as a Lewis acid catalyst, which helps in generating the electrophile and facilitates the reaction.

1. **Generation of Electrophile:**
- FeCl3 reacts with Br-Cl to form a complex, FeCl4- and Br+.
- This complex then reacts with benzene, leading to the formation of a highly reactive electrophile, bromonium ion (Br+).
- The bromonium ion is formed by the attack of the Br+ on the benzene ring, resulting in the formation of a cyclic intermediate.

2. **Attack of Benzene:**
- The benzene ring, being a nucleophile, attacks the bromonium ion at any of the carbon atoms, resulting in the formation of a sigma complex.
- The bromonium ion is opened up, and the bromine atom is attached to one of the carbon atoms of the benzene ring.

3. **Rearrangement:**
- The sigma complex undergoes a rearrangement to stabilize the intermediate carbocation.
- The hydrogen atom is shifted from the adjacent carbon atom to the carbon atom bearing the positive charge, resulting in the formation of a more stable carbocation.

4. **Attack by Chlorine:**
- The carbocation acts as an electrophile, attracting the chlorine ion (Cl-) towards it.
- The chlorine ion then attacks the carbocation, leading to the formation of the final product, chlorobenzene.

**Overall Reaction:**

The overall reaction can be represented as follows:

Benzene + Br-Cl + FeCl3 → Bromobenzene + FeCl4- + HCl

**Conclusion:**

In conclusion, when benzene is treated with Br-Cl in the presence of FeCl3, the bromine and chlorine atoms are substituted for hydrogen atoms of benzene. This reaction occurs through an electrophilic aromatic substitution mechanism, involving the generation of a reactive electrophile, attack of benzene, rearrangement, and attack by chlorine. The FeCl3 catalyst helps in the generation of the electrophile and facilitates the reaction.

Simple addition of Br+ will take place and Bromobenzene will form.
as FeCl3 is a Lewis acid therefore it will take cl and only Br+ (an electrophile ) will remain there.
as partial negative charge appear on benzene electrophilic addition will take place.