AlCl3 promotes the chlorination ofaromatic molecules such as benzene, when chlorine (Cl2) is added. The AlCl3 is regenerated, and HCl is a byproduct. The Friedel-Crafts reaction is also promoted by AlCl3. In Friedel-Crafts acylation, the product is an aromatic ketone, and the byproduct is HCl.

Importance of Anhy. AlCl3 in Chlorination of Benzene Ring
Chlorination of a benzene ring is a common chemical reaction used to introduce chlorine atoms onto the benzene ring. Anhydrous aluminum chloride (AlCl3) plays a crucial role in this process due to its Lewis acidity and its ability to act as a catalyst in the reaction.

Formation of the Friedel-Crafts Complex
Anhydrous AlCl3 acts as a Lewis acid catalyst in the chlorination of benzene by forming a complex with the chlorine molecule. This complex, known as the Friedel-Crafts complex, helps in activating the chlorine molecule and facilitating its electrophilic attack on the benzene ring.

Enhanced Electrophilicity of Chlorine
The Friedel-Crafts complex formed with anhydrous AlCl3 increases the electrophilicity of the chlorine molecule, making it more reactive towards the benzene ring. This enhanced reactivity allows for the substitution of a hydrogen atom on the benzene ring with a chlorine atom.

Controlled and Efficient Chlorination
Anhydrous AlCl3 also helps in controlling the chlorination process by ensuring that the reaction proceeds in a regioselective manner, leading to the desired mono-substituted chlorobenzene product. This control over the reaction helps in achieving high yields of the desired chlorinated product.
In conclusion, anhydrous aluminum chloride is essential in the chlorination of a benzene ring as it acts as a catalyst, enhances the electrophilicity of chlorine, and ensures a controlled and efficient chlorination process.