Question

Name the reagent used for Bromination of phenol to 2,4,6-tribromophenol :

• A. $B{r}_2\text{in}C{S}_2/CHC{l}_3$
• B. $NBS$
• C. $B{r}_2\text{in}{H}_2{O}_2$
• D. $B{r}_2\text{in}{H}_{2}O$

Answer 1

The correct option is D $B{r}_2\text{in}{H}_{2}O$

The reaction of phenol with bromine is known as bromination of phenol.
Solvent has great influence on the reaction. In different solvents, different products are obtained. The action of bromine on phenol can be explained as:
(i) Reaction with bromine in water: Phenol reacts with bromine water to give 2,4,6-tribromophenol.

(ii) Reaction with bromine in $C{S}_2/CHC{l}_3$: Phenol reacts with bromine in a presence of Carbon disulphide to form a mixture of o-bromophenol and p-bromophenol.

In water, ionisation is facilitated. Phenol gets ionised to form phenoxide ion, which is even better ortho, para-directing. Bromine also gets ionised to a larger extent to form a large number of bromonium ions. And Bromine ions are highly stabilized in ionic solvents. So the formation of strong o,p-directing group and stabilization of $B{r}^{+}$ enhances the formation of tribromophenol.