Halogenation

In Non-Polar Solvent (Monohalogenation):
$$\text{C}_6\text{H}_5\text{OH} + \text{Br}_2 \xrightarrow{\text{CS}_2 \text{ or } \text{CHCl}_3, \; 273\text{ K}} p\text{--}\text{bromophenol (Major)} + o\text{--}\text{bromophenol (Minor)} + \text{HBr}$$

In Aqueous Medium (Polyhalogenation):
$$\text{C}_6\text{H}_5\text{OH} + 3\text{Br}_2\text{(aq)} \xrightarrow{\text{H}_2\text{O}} \text{C}_6\text{H}_2\text{Br}_3\text{OH}\downarrow \quad (2,4,6\text{-Tribromophenol / White Precipitate}) + 3\text{HBr}$$

Concept: The electrophilic bromination of phenol varies significantly depending on the polarity of the solvent used. In low-polarity solvents like carbon disulfide ($$\text{CS}_2$$) or chloroform ($$\text{CHCl}_3$$), ionization of phenol is suppressed, yielding monobrominated phenols. In aqueous medium, phenol ionizes into the phenoxide ion, which strongly activates all ortho and para positions, resulting in complete tribromination without needing a Lewis acid catalyst.