Methods of Preparation of Phenols: Phenol was initially obtained by fractional distillation of coal tar.
General Methods of Preparation of Phenols:
(a) Dows process: When chlorobenzene is heated with caustic soda at 300°C at 300 atm. pressure, sodium phenoxide is formed. It, upon acidification, gets converted to phenol.
![Methods of Preparation of Phenols](https://pharmacyscope.com/wp-content/uploads/2022/07/Methods-of-Preparation-of-Phenols-1024x241.png)
(b) From diazonium salt: A diazonium salt when warmed in presence of water, produces phenol.
![diazonium salt](https://pharmacyscope.com/wp-content/uploads/2022/07/diazonium-salt-1024x264.png)
(c) From benzene sulphonate: When benzene sulphonate is heated with caustic soda at 300°C, sodium phenoxide is formed which upon acidification gives phenol.
![benzene sulphonate](https://pharmacyscope.com/wp-content/uploads/2022/07/benzene-sulphonate-1024x384.png)
(d) From salicylic acid: Sodium salicylate when heated with soda lime undergoes decarboxylation to give sodium phenoxide which on acidification gives phenol.
![Methods of Preparation of Phenols](https://pharmacyscope.com/wp-content/uploads/2022/07/salicylic-acid-1024x225.png)
(e) Acidic oxidation of cumene: Cumene is oxidized in presence of air to give cumene hydroperoxide. The formation of cumene hydroperoxide proceeds by a free radical chain reaction.
![Acidic oxidation of cumene](https://pharmacyscope.com/wp-content/uploads/2022/07/Acidic-oxidation-of-cumene-1024x273.png)
The creation of the tertiary free radical is the initial step in the reaction.
![tertiary free radical](https://pharmacyscope.com/wp-content/uploads/2022/07/tertiary-free-radical-1024x203.png)
In the next step, the free radical is attached to the O2 molecule. Finally, the hydroperoxide free radical abstracts a hydrogen-free radical from a second molecule of cumene to form cumene hydroperoxide and a new tertiary free radical.
The degradation of cumene hydroperoxide proceeds via a carbocation mechanism.
![carbocation mechanism](https://pharmacyscope.com/wp-content/uploads/2022/07/carbocation-mechanism.png)
(f) From benzene (Rachig’s method):
![benzene (Rachig's method)](https://pharmacyscope.com/wp-content/uploads/2022/07/Screenshot-2022-07-31-181101-1024x184.png)
This method involves heating benzene, HCl, and air over a catalyst (mixture of CuCl2 and FeCl3) at high pressure of 500 K to give chlorobenzene which is then heated with superheated steam at high pressure of 750 K to give phenol.
In yet another method, benzene and air are passed over V₂Os at 600 K. Benzene is thus oxidized to give phenol.
![benzene (Rachig's method)](https://pharmacyscope.com/wp-content/uploads/2022/07/Screenshot-2022-07-31-181112.png)
Make sure you also check our other amazing Article on : Diazo Coupling Reaction