Preparations of Phenol

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.

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.
  
  

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.

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

Comment and Rate