How is carbolic acid prepared from chlorobenzene?
1. Dow’s process:
i. When chlorobenzene is heated with excess of aqueous sodium hydroxide (NaOH) at 613 K under a pressure of 300 atmosphere, sodium phenoxide is formed.
ii. Sodium phenoxide when hydrolysed using dilute hydrochloric acid (HCl), phenol is obtained.
Phenol can also be obtained by passing CO2 (carbon dioxide) gas, through aqueous solution of sodium phenoxide.
2. Raschig process (Industrial method):
i. When chlorobenzene is treated with steam (H2O) at 698 K in the presence of Ca3(PO4)2 or SiO2 as a catalyst, phenol is obtained.
ii. The hydrolysis can also be carried out by using water in the presence of copper catalyst at 673 K and under pressure.
(Any one method)