Phenol

Hydroxy derivative of benzene is called phenol.

Phenol
Carbonic acid (monohydroxybenzene)

General preparation of phenol

1) From benzene diazonium chloride

Benzenediazonium chloride when boil with water gives phenol.

2) From chlorobenzene (Dow’s process)

When chlorobenzene fused with NaOH gives sodium phenoxide which on acidification with dil. HCl gives phenol.

3) From sod. salt of salicylic acid (Decarboxylation)

Sodium salt of salicylic acid when react with soda lime (NaOH + CaO) undergoes decarboxylation gives phenol.

4. From Cumene [Industrial preparation]

Benzene when react with phosphoric acid at 250°C temp gives cumene which undergoes oxidation gives cumene hydroperoxide which further react with dil H₂SO₄ gives phenol.

Properties

• Phenol contain 5% water so they are also called carbolic acid.
• Phenol are colourless solid or liquid but slowly change into pink to red due to slow oxidation with atmospheric air.
• Boiling point of phenol is generally high because it produce intermolecular hydrogen bond.

Phenol are partially soluble in water because hydroxy group of phenol is hydrophilic group which tends to make soluble in water but benzene ring is hydrophobic group which tends to make insoluble in water as a result phenol is partially soluble in water.

Among the isomers of nitro-phenol, para-nitrophenol has higher boiling point, solubility and acidic character than ortho-nitrophenol because para-nitrophenol produce inter-molecular H bond but ortho-nitrophenol produce intra-molecular H-bond.

Fig: Resonating structure of phenol

The source page shows a sequence of resonance structures for phenol.

Fig: Resonating structure of phenoxide ion

The source page shows resonance forms of phenoxide ion and a resonance hybrid.

According to the resonating structure phenol contain both positive as well as No negative charge but phenoxide only contain Negative charge therefore phenoxide anion are more reactive than phenol due to which phenol can easily release H⁺ ion to be stable but such phenomenon doesn’t find in alcohol hence phenol are strong acid than alcohol.

1. Acidic character

Action with metal

Phenol react with highly reactive metal gives hydrogen gas.

Action with alkali

Phenol react with strong alkali (NaOH or KOH) gives salt and water.

• Alcohol doesn’t react with alkali it means phenol are strong acid than alcohol.

Action with metallic carbonate and bicarbonate

But carboxylic acid does react with metallic carbonate and bicarbonate it shows that carboxylic acid are stronger acid then phenol.

Acidic character →

2) Alkylation

Replacement of functional group by alkyl group is called alkylation.

3) Acylation

Replacement of functional Hydrogen by acyl group is called acylation.

Benzoylation

The replacement of functional Hydrogen by benzoylchloride is called Benzoylation.

5) Rxn with zinc dust (Reduction rxn)

6. Rxn with ammonia

7) Rxn with FeCl₃ (lab test of phenol)

Phenol react with ferric chloride soln gives water soluble complex of iron hexaphenoxide ion.

This rxn is used to test phenol in lab.

8. Electrophilic substitution rxn

The replacement of ring H₂ by incoming electrophile is called electrophilic substitution rxn.

Phenol is called ortho-para director toward electrophilic substitution rxn.

Reaction with aq. Br₂ — lab test of phenol

Reaction with Br₂ / CS₂

Nitration with dil. HNO₃

Nitration with conc. HNO₃ / conc. H₂SO₄

Reaction with CH₃Cl / AlCl₃

9. Fries rearrangement

Phenylacetate undergoes rearrangement in presence of anhydrous AlCl₃ gives ortho and a para hydroxy aceto-phenone.

10. Kolbe’s rxn

Sodium phenoxide when react with CO₂ gives sodium salt of salicylic acid which on acidification with dil HCl gives salicylic acid.

11) Coupling rxn

Benzenediazoniumchloride react with phenol gives para-hydroxy azobenzene.

12) Rxn with phthalic anhydride

Phenol react with phthalic anhydride gives phenolphthalein which is an indicator.