Question

Write two reactions of phenol that demonstrate its acidic nature.

Hint:

Show phenol forming a salt with NaOH and releasing \( H_2 \) with sodium metal.

Answer 1

Step 1 (Why phenol is acidic): Phenol can lose the hydrogen of its \( -OH \) group as \( H^{+} \). The resulting phenoxide ion is stabilised by resonance with the benzene ring, so phenol behaves as a weak acid.
Step 2 (Reaction 1 with a strong base): Phenol reacts with sodium hydroxide to form sodium phenoxide and water: \[ C_6H_5OH + NaOH \rightarrow C_6H_5ONa + H_2O \] Neutralising a base is proof of acidic character.
Step 3 (Reaction 2 with an active metal): Phenol reacts with sodium metal, liberating hydrogen gas: \[ 2C_6H_5OH + 2Na \rightarrow 2C_6H_5ONa + H_2\uparrow \] Displacement of hydrogen by a metal again confirms its acidic nature.
Step 4: Both reactions show phenol donating the \( O-H \) proton, which demonstrates its acidic behaviour.