Bromination of Phenols

Phenols are aromatic compounds in which a hydroxyl group (-OH) is directly attached to an aromatic ring. Bromination refers to the reaction of phenols with bromine.
Unlike benzene, phenol is reactive enough to undergo bromination directly without the use of a catalyst. This disparity is due to the increased electron density in the benzene ring provided by the presence of the hydroxyl functional group in phenol, making it more reactive towards electrophiles.
This reaction classifies under electrophilic aromatic substitution. Bromine (Br2), an electrophile, reacts with phenol and substitutes a hydrogen atom from the aromatic ring.
The bromination of phenols happens at room temperature, resulting in the formation of a white precipitate of 2,4,6-tribromophenol.
During this reaction, the bromine adds to the 2, 4, and 6 positions of the benzene ring in phenol. This is an example of substitution at the ortho and para positions and occurs due to the activating effect of the hydroxyl group.
The H-atoms in the -OH group of phenol get partially replaced by Br-atoms of bromine. The reaction is highly exothermic and releases a large amount of heat energy.
This reaction can be halted after the first substitution if desired, creating mono-brominated phenols. To do this, one must control the reaction conditions, such as the concentration of bromine and the temperature.
Further reaction can be induced to form 2,4-dibromophenol, or the reaction can continue until all of the hydrogen atoms on the phenol have been replaced, creating 2,4,6-tribromophenol.
Being able to control the degree of substitution is vital in the bromination reaction because it allows for the preparation of different brominated products.
The bromination of phenols is an important reaction in organic chemistry due to its various applications. The brominated phenols can be used in the preparation of more complex molecules or as intermediates in other chemical reactions.