devarshi-dt-logo

Question:

How do you convert the following: (i) Phenol to anisole (ii) Propan-2-ol to 2-methylpropan-2-ol (iii) Aniline to phenol

Solution:

(i) Phenol to anisole:
Phenol can be converted to anisole (methoxybenzene) by methylation. This is typically achieved using dimethyl sulfate (DMS) in the presence of a base like aqueous sodium hydroxide (NaOH).

The reaction proceeds as follows:

      OH            OCH3
       |              |
  C6H5-OH + (CH3)2SO4 + NaOH  -->  C6H5-OCH3 + NaHSO4 + CH3OH

(ii) Propan-2-ol to 2-methylpropan-2-ol:
This conversion involves first converting propan-2-ol to acetone via oxidation, followed by a Grignard reaction with methylmagnesium bromide, and finally acid hydrolysis.

  1. Oxidation: Propan-2-ol is oxidized to acetone using an oxidizing agent like chromic acid (H2CrO4) or Jones reagent.
       CH3               O
       |                ||
CH3-C-OH  --[O]-->  CH3-C-CH3
       |               
       CH3              
  1. Grignard Reaction: Acetone reacts with methylmagnesium bromide (CH3MgBr), a Grignard reagent, to form a tertiary alcoholate.
       O              OH
       ||             |
CH3-C-CH3 + CH3MgBr --> CH3-C-CH3
               |           |
              MgBr        CH3
  1. Acid Hydrolysis: The alcoholate is then hydrolyzed with dilute acid (e.g., H3O+) to yield 2-methylpropan-2-ol.
       OH               OH
       |
CH3-C-CH3   --[H3O+]--> CH3-C-CH3 
       |                 |
      MgBr               CH3

(iii) Aniline to phenol:
Aniline can be converted to phenol through a diazonium salt intermediate. The process involves the following steps:

  1. Diazotization: Aniline is treated with nitrous acid (HNO2) (prepared in situ from NaNO2 and HCl) at low temperature (0-5°C) to form a diazonium salt (benzenediazonium chloride).
       NH2            N2Cl
        |               |
  C6H5-NH2 + HNO2 + HCl -->  C6H5-N=N-Cl + 2H2O
  1. Hydrolysis: The diazonium salt is then heated with water in the presence of an acid catalyst (e.g., H2SO4) to form phenol and nitrogen gas.
       N2Cl            OH
        |               |
  C6H5-N=N-Cl + H2O --[H+]-->  C6H5-OH + N2 + HCl