How is sodium benzoate converted into acetophenone?

Sodium benzoate is converted into acetophenone through a Friedel–Crafts acylation reaction followed by a reduction step. Here’s the process:

1. Acylation: Sodium benzoate is first treated with thionyl chloride (SOCl₂) to convert it into benzoyl chloride (a more reactive acyl chloride). $$\mathrm{C}{}_6\mathrm{H}{}_5\mathrm{COONa}+\mathrm{SOCl}{}_2\to \mathrm{C}{}_6\mathrm{H}{}_5\mathrm{COCl}+\mathrm{NaCl}+\mathrm{SO}{}_2$$ Benzoyl chloride then reacts with benzene in the presence of AlCl₃ (Lewis acid catalyst) to form acetophenone via electrophilic substitution:

C₆H₅COONa+SOCl₂heatC₆H₅COCl+NaCl+SO₂

2. Mechanism: The carbonyl carbon of benzoyl chloride acts as an electrophile, attacking benzene to form a benzoyl-substituted intermediate, which tautomerizes to yield acetophenone.

3. Key Notes:

   • AlCl₃ is essential for generating the electrophile.
   • The reaction is carried out under anhydrous conditions to prevent hydrolysis of the acyl chloride.
   • Acetophenone is purified by distillation.

This sequence is a classic example of Friedel–Crafts acylation followed by in-situ formation of the ketone.