Reaction of benzene sulfonic acid with base
Reaction of chlorobenzene with base
Acidic oxidation of cumene
Hydrolysis of diazonium salts

Note: The first three methods are primarily industrial methods while the hydrolysis of diazonium salts is the most important laboratory method.

Reaction of Benzene Sulfonic Acid with Hydroxide

Summary

• This is a useful industrial method for the synthesis of phenol.
• Reagents : Usually NaOH, 300-350 ^oC followed by an acidic work-up to neutralize the phenoxide.
• This represents the oldest method for the industrial preparation of phenol.
• The reaction occurs via the addition-elimination mechanism with SO₃^2- functioning as the leaving group.

Question:
Can you remember how to prepare benzene sulfonic acid ?  

Base Hydrolysis of Chlorobenzene

Summary

• This is a useful industrial method for the synthesis of phenol.
• Reagents : Usually NaOH, 350 ^oC followed by an acidic work-up to neutralize the phenoxide.
• The reaction occurs via the elimination-addition mechanism via a benzyne intermediate.
• Elimination of HCl creates the benzyne that then undergoes addition of H₂O to produce the phenol.

Question:
Can you recall how you make chlorobenzene ?  

Acidic Oxidation of Cumene

Summary

• This industrial method is the primary source of phenol.
• Oxidation at the benzylic position gives the hydroperoxide which cleaves to give phenol and acetone.
• Cheap reagents and important products make the process attractive.

Question:
Can you remember how to make isopropyl benzene ?  

Preparation of Phenols from Aryl Diazonium Salts
(review of Chapter 22)

• Aryl diazonium salts can be converted into phenols using H₂O / H₂SO₄ / heat
• Aryl diazonium salts are prepared by reaction of aryl amines with nitrous acid, HNO₂

Question:
How do you prepare aryl amines ?  

Related Reactions

• Transformations of Aryl Diazonium Ions