Phenol is heated with a solution of mixture of KBr and KBrO3. The major product obtained in the above reaction is :
When phenol is heated with a mixture of KBr and KBrO3, bromination occurs. This mixture generates bromine (Br2) in situ, which acts as the brominating agent. The reaction proceeds via electrophilic aromatic substitution.
KBrO3 reacts with KBr in the presence of acid (often from the phenol or slight acidity) to produce bromine:
This provides a steady supply of Br2.
Phenol has an -OH group that strongly activates the benzene ring towards electrophilic substitution. The -OH group is ortho-para directing due to its electron-donating resonance effect.
Bromine (Br2) acts as an electrophile. The highly activated ring leads to multiple substitutions. Since the mixture provides excess bromine, tribromination occurs.
The -OH group directs incoming electrophiles to the ortho and para positions. With excess bromine, all activated positions (both ortho and the para) are substituted, yielding 2,4,6-tribromophenol.
The major product is 2,4,6-Tribromophenol.
Key Reaction: Phenol + Br2 → 2,4,6-Tribromophenol (white precipitate)
Activation: -OH group is ortho-para directing and strongly activating.
Mechanism: Electrophilic substitution where Br+ attacks the electron-rich ring.
Note: With controlled bromine, monobromination gives mainly para-bromophenol, but with excess Br2 (as here), tribromination is favored.
The major product of the following reaction. :
The major product of the following reaction is:
The major products of the following reaction are :
