JEE Class main Answered

Dear Student,

 

Phenol in aqueous medium is partially ionised and deprotonated to certain extent to form phenoxide ion in which the ortho and para positions are even more activated than in phenol itself.

Phenoxide ion is much more reactive than phenol itself towards electrophilic attack. 

 

PhOH + H₂O → PhO⁻+H₃O⁺

 

Moreover, halogen reacts with water forming halogen acid and hypohalous acid. The proton attacks at the OH^- group of hypohalous acid to give H₂O^⊕−X, which acts as a stronger electrophile. 

Therefore, halogenation takes place at all the ortho and para positions.

 

In aqueous medium, phenol is deprotonated to a certain extent, forming the phenoxide ion  

Hence, trisubstitution occurs here.

 

In an organic solvent, phenol is not deprotonated.This is because the ionisation of phenol does not occur in non-aqueous medium. 

If the halogenation is carried out in non-aqueous medium like CS₂ or CCl₄, only mono−substitution takes place. 

 

Similarly aniline also give different products in aqueous and non-aqueous solvents.