Chemical Reactions of Phenol

Phenol (C₆H₅OH) is an aromatic compound in which a hydroxyl group (–OH) is directly attached to a benzene ring. Due to resonance stabilization, phenol undergoes a wide range of chemical reactions, especially electrophilic substitution reactions.

1. Acidic Nature

Phenol is weakly acidic compared to alcohols but stronger than water because the phenoxide ion formed is resonance stabilized:

C₆H₅OH ⇌ C₆H₅O⁻ + H⁺

2. Reaction with Sodium

Phenol reacts with sodium metal liberating hydrogen gas:

2C₆H₅OH + 2Na → 2C₆H₅ONa + H₂↑

3. Reaction with Sodium Hydroxide

Phenol dissolves in NaOH to form sodium phenoxide:

C₆H₅OH + NaOH → C₆H₅ONa + H₂O

4. Electrophilic Substitution Reactions

Nitration: With dilute HNO₃:
With concentrated HNO₃:
Halogenation: With Br₂ water:

5. Kolbe Reaction

Phenol reacts with CO₂ under pressure in alkaline medium to form salicylic acid:

C₆H₅ONa + CO₂ → o-Hydroxybenzoic acid (Salicylic acid)

6. Reimer–Tiemann Reaction

Phenol reacts with chloroform and NaOH to form salicylaldehyde:

C₆H₅OH + CHCl₃ + 3NaOH → o-Hydroxybenzaldehyde + 3NaCl + 2H₂O

7. Oxidation

Phenol oxidizes to benzoquinone in presence of strong oxidizing agents:

C₆H₅OH + [O] → C₆H₄O₂ (Benzoquinone) + H₂O

8. Reduction with Zinc

On heating with zinc dust, phenol reduces to benzene:

C₆H₅OH + Zn → C₆H₆ + ZnO

Summary Table

Reaction	Reagents	Product
Acidic Reaction	Na / NaOH	Sodium phenoxide + H₂
Nitration	HNO₃ (dil./conc.)	Nitrophenol / Picric acid
Halogenation	Br₂ water	2,4,6-Tribromophenol
Kolbe Reaction	CO₂ + NaOH	Salicylic acid
Reimer–Tiemann	CHCl₃ + NaOH	Salicylaldehyde
Oxidation	Na₂Cr₂O₇ / [O]	Benzoquinone
Reduction	Zn (heat)	Benzene

MCQ Quiz

Phenol is more acidic than alcohol because:
a) Hydrogen bonding
b) Resonance stabilization of phenoxide ion ✅
c) Stronger O–H bond
d) None
The product of Kolbe reaction is:
a) Benzaldehyde
b) Picric acid
c) Salicylic acid ✅
d) Phenyl acetate
Phenol reacts with bromine water to give:
a) Benzaldehyde
b) 2,4,6-Tribromophenol ✅
c) Benzoquinone
d) Benzene

True/False Questions

Phenol reacts with sodium to liberate hydrogen gas. ✅ True
Kolbe reaction produces benzaldehyde. ❌ False (It produces salicylic acid)
Phenol oxidizes to benzoquinone in presence of oxidizing agents. ✅ True