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Explain the preparation of phenols.

The methods used for the preparation of phenols are given below:
    
From aryl sulphonic acids

Aryl sulphonic acids on fusion with NaOH at 573 K followed by acidification yield phenols.

1616_Phenol preparation.png 

From aryl halides (Dow's process)

Phenol is obtained on a large scale by heating chlorobenzene with 10% NaOH solution at about 623 K and under a pressure of 300 atmospheres in the presence of copper catalyst.

1327_Phenol preparation1.png 

From diazonium salts

In the laboratory phenols are prepared hydrolysis of diazonium salts with water or dilute acids.

994_Phenol preparation2.png 
    
By decarboxylation of sodium salt of saclicyclic acid

Phenol can also be obtained by the decarboxylation of sodium salicyclate with soda lime (an equimolar mixture of NaOH and CaO).
                           
289_Phenol preparation3.png 
    
From Grignard's reagent

when oxygen is bubbled through the solution of phenylmagnesium bromide in ether, it forms an addition product which on acidification with dilute acid gives phenol.

1498_Phenol preparation4.png

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