Which method does not give benzene?

Several chemical methods are used to prepare benzene from different organic compounds. Understanding which reactions yield benzene and which do not is crucial in organic chemistry.

1. 
   

   Sodium benzoate + soda lime:
   When sodium benzoate is heated with soda lime (a mixture of NaOH and CaO), it undergoes decarboxylation to produce benzene and sodium carbonate.
   Reaction:
   C₆H₅COONa + NaOH → C₆H₆ + Na₂CO₃
   This is a reliable and well-known laboratory method for preparing benzene.

   
   


2. 
   

   Phenol + Zn dust:
   When phenol is heated with zinc dust, the hydroxyl group is removed, and benzene is formed.
   Reaction:
   C₆H₅OH + Zn → C₆H₆ + ZnO
   This reaction reduces the phenolic group to hydrogen, producing benzene.

   
   


3. 
   

   Chlorobenzene + NaOH (360°C, 150 atm):
   This reaction does not produce benzene. Instead, under these conditions, chlorobenzene reacts with sodium hydroxide to yield phenol via nucleophilic substitution.
   Reaction:
   C₆H₅Cl + NaOH → C₆H₅OH + NaCl
   The harsh conditions are necessary because the aromatic ring resists nucleophilic attack due to its electron delocalization.

   
   


4. 
   

   Benzene sulfonic acid + steam:
   When benzene sulfonic acid is hydrolyzed with superheated steam, benzene is regenerated.
   Reaction:
   C₆H₅SO₃H + H₂O → C₆H₆ + H₂SO₄
   This is a reversible reaction commonly used to purify benzene.

   
   

Hence, the reaction of chlorobenzene with NaOH at 360°C and 150 atm does not yield benzene, making option C the correct answer. This process forms phenol instead due to substitution of chlorine by the hydroxyl group