Question

How to prepare phenol from aniline?

Answer 1

Synthesis of Phenol from Aniline

1. Aniline is treated with Nitrous acid (${\mathrm{NaNO}}_2,\mathrm{HCl}$) in ice-cold conditions.
2. On treatment with Nitrous acid, there is the formation of Benzenediazonium chloride( ${\mathrm{C}}_6{\mathrm{H}}_5-{{\mathrm{N}}_2}^{+}{\mathrm{Cl}}^{-}$)
   $\underset{\mathrm{Aniline}}{{\mathrm{C}}_6{\mathrm{H}}_5-{\mathrm{NH}}_2\left(\mathrm{l}\right)}+\underset{\mathrm{Nitrous}\mathrm{acid}}{\underbrace{{\mathrm{HNO}}_2+\mathrm{HCl}}}\to \underset{\mathrm{Benzenediazonium}\mathrm{chloride}}{{\mathrm{C}}_6{\mathrm{H}}_5-{{\mathrm{N}}_2}^{+}{\mathrm{Cl}}^{-}(\mathrm{aq}.)}+2\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}(\mathrm{aq}.)}$
3. Benzenediazonium chloride hydrolyzes into Phenols when heated with water.
   $\underset{\mathrm{Benzenediazonium}\mathrm{chloride}}{{\mathrm{C}}_6{\mathrm{H}}_5-{{\mathrm{N}}_2}^{+}{\mathrm{Cl}}^{-}}(\mathrm{aq}.)+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}}(\mathrm{aq}.)\to \underset{\mathrm{Phenol}}{{\mathrm{C}}_6{\mathrm{H}}_5-\mathrm{OH}}(\mathrm{aq}.)+\underset{\mathrm{Nitrogen}}{{\mathrm{N}}_2}\left(\mathrm{g}\right)\uparrow +\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\mathrm{HCl}}(\mathrm{aq}.)$

Below is the structural representation of the conversion of aniline to phenol

Hence, Aniline can be converted to Phenol by using Nitrous acid which converts Aniline to Benzenediazonium chloride which upon hydrolysis converts to Phenol.