1. In the presence of water:
* This reaction results in bromination at the ortho and para positions of the phenol ring.
* The reaction is highly exothermic, and a white precipitate of 2,4,6-tribromophenol is formed.
* This is due to the activating effect of the hydroxyl group (-OH) on the benzene ring, making it highly susceptible to electrophilic attack by bromine.
Reaction Equation:
C6H5OH + 3Br2 → C6H2Br3OH + 3HBr
Mechanism:
The mechanism involves electrophilic aromatic substitution, where the bromine molecule is polarized by the hydroxyl group, forming an electrophile (Br+). This electrophile attacks the aromatic ring, resulting in the substitution of a hydrogen atom with bromine.
2. In the presence of a weak base like sodium bicarbonate (NaHCO3):
* This condition leads to the formation of monobromophenol (2-bromophenol or 4-bromophenol).
* The weak base helps in controlling the reaction and prevents over-bromination.
Reaction Equation:
C6H5OH + Br2 → C6H4BrOH + HBr
Overall, the reaction of phenol with bromine is a significant example of electrophilic aromatic substitution and highlights the activating effect of electron-donating groups on the benzene ring.
