Q.(a) Write the reactions for the action of following reagents on phenol:

Reactions of Phenols

Phenol has an –OH bonded directly to a benzene ring, giving it distinctive reactions.

• FeCl$_3$ (ferric chloride) test: phenols give a violet colouration, distinguishing them from alcohols such as cyclohexanol, which do not react.
• Reduction to arenes: heating phenol (or cresols) with zinc dust removes the –OH and gives the arene — phenol $\to$ benzene, p-cresol $\to$ toluene.
• Catalytic hydrogenation: passing phenol vapour with $\text{H}_2$ over nickel at 433 K reduces the ring to give cyclohexanol.
• Electrophilic substitution: the –OH is strongly activating and o/p-directing, so phenol readily nitrates, sulphonates, brominates (giving 2,4,6-tribromophenol with bromine water) and undergoes Reimer–Tiemann and Kolbe reactions. …