The reaction of benzene with CH₃COCl (acetyl chloride) in the presence of AlCl₃ is a classic example of Friedel-Crafts acylation. Here's what happens:

1. Formation of the Electrophile:

* AlCl₃ is a Lewis acid and acts as a catalyst. It reacts with CH₃COCl to form an electrophilic acylium ion (CH₃CO⁺). This is the key step, as the acylium ion is the species that will attack the benzene ring.

2. Electrophilic Attack:

* The acylium ion is a strong electrophile. It attacks the electron-rich benzene ring, forming a carbocation intermediate. This step is the rate-determining step of the reaction.

3. Rearrangement and Deprotonation:

* The carbocation intermediate undergoes a resonance-stabilized rearrangement.

* A proton (H⁺) is removed from the ring, regenerating the aromatic system.

4. Regeneration of the Catalyst:

* AlCl₃ is regenerated and can continue to catalyze the reaction.

Overall Reaction:

```

Benzene + CH<sub>3</sub>COCl (AlCl<sub>3</sub>) --> Acetophenone + HCl

```

Product:

The final product of this reaction is acetophenone, a ketone with a phenyl group attached to the carbonyl group.

Important Notes:

* The reaction requires anhydrous conditions. Water will deactivate the catalyst (AlCl₃) and prevent the reaction from proceeding.

* The reaction is exothermic and can be violent if not carefully controlled.

* Friedel-Crafts acylation is a versatile reaction that can be used to introduce a variety of acyl groups onto aromatic rings.

Let me know if you have any more questions!