Question

How to convert benzene to benzophenone?

Answer 1

Freidel-Crafts Acylation:-

• Friedel-Crafts acylation reaction is a type of reaction where an acyl group is added to an aromatic ring.
• Ths reaction occurs under the presence of an acid chloride $\mathrm{R}-(\mathrm{C}=\mathrm{O})-\mathrm{Cl}$ and a Lewis acid catalyst like Aluminium chloride ${\mathrm{AlCl}}_3$.
• Friedel-Crafts acylation reaction, changes the aromatic ring into a aromatic ketone.

Mechanism:-

Step 1: Formation of Acylium ion

• A reaction between the catalyst Aluminium chloride ${\mathrm{AlCl}}_3$ and the Acyl halide occurs
• The Acyl halide loses a halide ion forming an Acylium ion which is stabilized due to resonance.

Step 2: Attack on the Aromatic ring

• The acylium ion $(\mathrm{R}-{\mathrm{CO}}^{+})$executes an electrophilic attack on the Aromatic ring.
• Due to this Aromaticity of the ring is lost temporarily and a complex is formed.

Step 3: Formation of Ketone

• The aromaticity of the ring is restored, due to the deprotonation of the complex ion.
• The proton from the complex Lewis acid attaches itself to a chloride ion thus forming $\mathrm{HCl}$.
• Also the Aluminium chloride${\mathrm{AlCl}}_3$ catalyst is regained.

Conversion of Benzene to Benzophenone:-

Step 1: Formation of Benzophenone

• The Benzene is treated with Benzoyl chloride in presence of anhydrous Aluminium chloride$\left({\mathrm{AlCl}}_3\right)$ to form Benzophenone.
• This reaction is called Freidel-Crafts Acylation.

This conversion of Benzene to benzophenone is a 1 step reaction.

Therefore, Benzene upon treatment with Benzoyl chloride and anhydrous Aluminium chloride$\left({\mathrm{AlCl}}_3\right)$produces Benzophenone.