Question

What happens when : Chlorobenzene is treated with $CH_{3}Cl$ in the presence of anhydrous $AlCl_{3}$ ?

Hint:

Halogens are deactivating but ortho/para directing. The bulky chlorine atom makes the para position the preferred site of attack.

Answer 1

Step 1: Concept
Friedel-Crafts alkylation of haloarenes via electrophilic aromatic substitution.

Step 2: Meaning
Anhydrous $AlCl_{3}$ acts as a Lewis acid catalyst to generate a methyl carbocation electrophile ($CH_{3}^{+}$) from methyl chloride.

Step 3: Analysis
Chlorobenzene is ortho/para directing because the resonance effect (+R) of the halogen's lone pairs increases electron density at the ortho and para positions. The $CH_{3}^{+}$ electrophile attacks the ring, yielding a mixture of ortho and para substituted products. Due to steric hindrance at the ortho position, the para isomer is the major product.

Final Answer: Friedel-Crafts alkylation occurs, forming a mixture of 1-chloro-2-methylbenzene (minor product) and 1-chloro-4-methylbenzene (major product).