Question

Reaction of bromine water with phenol gives white ppt of:

• A. o - bromophenol
• B. p - bromophenol
• C. 2,4,6 -tribromophenol
• D. m - bromophenol

Answer 1

The correct option is C 2,4,6 -tribromophenol

Phenol when treated with $B{r}_2$ water give polybromoderivative in which all H- atoms at ortho and para positions with respect to $-OH$ group are replace by Cr atoms. It is so because in cequeous medium, phenol iouizes to form pheroxide ion. Due to presence of negative charge, the oxygen of pheroxide ion donates $e^{-}$s to benzene erring to large extent. As a result, the ring gets highly activated and tribubstitution occurs. On the other hand, in non-polar solvents, the ionization of phenol is greatly supressed. As a result, oxygen of $-OH$ group donates $e^{-}$s to benzene ring to a small extent only which results in slight activation of ring and monosubstitution occurs. Furthur, due to steric hindrance at ortho position, para substitution products usually predominates.