Animated Solution for Chemistry - Organic Chemistry: The given reaction can occur in the presence of (A) bromine water (B) ${\text{Br}}_2$ in ${\text{CS}}_2$, $273\text{ K}$ (C) ${\text{Br}}_2/{\text{FeBr}}_3$ (D) ${\text{Br}}_2$ in ${\text{CHCl}}_3$, $273\text{ K}$ Choose the correct answer from the options given below

We are given a reaction where phenol is converted into para-bromophenol. This is a classic example of an electrophilic aromatic substitution reaction. The goal is to identify which reagents can successfully carry out this specific transformation.

Phenol is a highly reactive molecule. The hydroxyl ($-OH$) group attached to the benzene ring is strongly activating. Through its $+M$ (resonance) effect, it donates electron density into the ring, making the ortho and para positions highly susceptible to electrophilic attack.

If we use bromine water (reagent A), the reaction takes place in a highly polar aqueous medium. In water, phenol ionizes to form the phenoxide ion ($-O^{-}$). The phenoxide ion is even more electron-donating than the hydroxyl group.

This extreme activation causes the ring to undergo polyhalogenation instantly. Instead of stopping at one bromine atom, the reaction yields $2,4,6$-tribromophenol, which appears as a white precipitate. Therefore, bromine water cannot be used to synthesize para-bromophenol.

To achieve monobromination, we must tame the reactivity of the phenol ring. We do this by using non-polar or weakly polar solvents like carbon disulfide ($C{S}_2$) or chloroform ($CHC{l}_3$) at low temperatures ($273K$).

In these solvents, phenol does not ionize into the phenoxide ion. The electrophilic attack is less intense, allowing the reaction to stop after one bromine atom is added. Due to steric hindrance at the ortho position, the para isomer, para-bromophenol, is formed as the major product.

Alternatively, using a Lewis acid catalyst like $FeB{r}_3$ with $B{r}_2$ also facilitates monobromination, yielding the same major product.

Since reagents (B), (C), and (D) all provide the controlled conditions necessary for monobromination, they will successfully yield para-bromophenol. Thus, the correct option is (c).