Question

What does acylation mean?

Answer 1

Explanation of Acylation

1. Acylation is the process of adding an acyl group to a compound.
2. Acylation is also known as alkanoylation, and the acyl group provided by the compound is the so-called acyl reagent.
3. When they react with metal catalysts they form strong electrophiles, therefore the acyl halides are used as a reagent.

Example of the Acylation reaction: Friedel craft acylation reaction

1. In Friedel craft acylation the reaction occurs between arene and acyl chloride or anhydrides in the presence of a catalyst.
2. The catalyst used is a strong Lewis catalyst.
3. In such a reaction Acetyl chloride$\left({\mathrm{CH}}_3\mathrm{COCl}\right)$ is used as a reagent and Aluminium chloride$\left({\mathrm{AlCl}}_3\right)$ works as a catalyst.
4. When this reagent and catalyst are treated with Benzene$\left(C_6{H}_6\right)$ we get Acetophenone $\left(C_6{H}_5{\mathrm{COCH}}_3\right)$ as their major product.
5. This reaction is represented as:
   

Mechanism:

Step 1: Reaction between Aluminium chloride and acyl halide

• When we react Lewis acid catalyst with acyl halide then acylinium complex ion is formed, which is further stabilized by resonance.
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Step 2: Electrophilic reaction

• The acylinium ion shows an electrophilic attack on the aromatic ring, therefore the aromaticity of the compound is temporarily lost from the complex.
• This can be represented as:
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Step 3:

• The deprotonation of the intermediate complex restores the aromaticity of the ring.
• The proton is attached itself to Chloride ion and thus forming Hydrochloric acid.
• Atlast the Aluminium chloride is regenerated.
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