$(A)$ Name the starting material used in the industrial preparation of phenol.
$(B)$ Write the complete reaction for the bromination of phenol in aqueous and non-aqueous medium.
$(C)$ Explain why a Lewis acid is not required in the bromination of phenol.

(N/A) The starting material used in the industrial preparation of phenol is cumene (isopropylbenzene).
$(B)$ Bromination of phenol:
$1$. In aqueous medium (using $Br_2$ water): Phenol reacts with bromine water to give a white precipitate of $2,4,6$-tribromophenol.
$C_6H_5OH + 3Br_2(aq) \rightarrow C_6H_2(OH)Br_3 + 3HBr$
$2$. In non-aqueous medium (using $CS_2$ or $CHCl_3$ at low temperature): Phenol reacts with $Br_2$ to give a mixture of $o$-bromophenol and $p$-bromophenol.
$C_6H_5OH + Br_2 \xrightarrow{CS_2, 298 K} C_6H_4(OH)Br (ortho) + C_6H_4(OH)Br (para)$
$(C)$ $A$ Lewis acid is not required because the $-OH$ group in phenol is a strongly activating group. It increases the electron density in the benzene ring to such an extent that the electrophilic substitution reaction occurs readily even without the presence of a Lewis acid catalyst.