Alcohols, Phenols and Ethers – Detailed Notes with Name Reactions

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1. Introduction

  • Oxygen-containing organic compounds.

  • Alcohols: –OH attached to alkyl group.

  • Phenols: –OH attached directly to aromatic ring.

  • Ethers: Two alkyl/aryl groups bonded to same oxygen.

2. Classification

Alcohols

  • Monohydric, Dihydric, Trihydric (based on –OH groups).

  • Primary, Secondary, Tertiary (based on C atom attached to –OH).

Phenols

  • Monohydric (phenol), Dihydric (catechol, resorcinol, hydroquinone), Trihydric (phloroglucinol).

Ethers

  • Symmetrical (CH₃–O–CH₃), Unsymmetrical (CH₃–O–C₂H₅), Aromatic (anisole, C₆H₅–O–CH₃).

3. Nomenclature

  • Alcohols: replace –e of alkane with –ol (propan-2-ol).

  • Phenols: derivatives of phenol (o-cresol, m-nitrophenol).

  • Ethers: Alkoxyalkane (methoxyethane, methoxybenzene).

4. Methods of Preparation

Alcohols

  1. Hydration of alkenes (acid-catalysed or hydroboration-oxidation).

  2. Reduction of aldehydes/ketones with NaBH₄ or LiAlH₄.

  3. From alkyl halides (SN1/SN2 with aqueous KOH).

  4. Fermentation of glucose → ethanol.

Phenols

  1. From chlorobenzene (Dow’s process).

  2. From benzene sulphonic acid (fusion with NaOH).

  3. From diazonium salts (hydrolysis).

Ethers

  1. Williamson’s ether synthesis (R–ONa + R′–X → R–O–R′).

  2. Dehydration of alcohols (conc. H₂SO₄, 413 K).

5. Physical Properties

  • Alcohols, Phenols: H-bonding → higher boiling points, soluble in water.

  • Ethers: no H-bonding → lower boiling points, soluble in organic solvents.

6. Chemical Properties & Reactions

A. Alcohols

  1. Acidic nature: R–OH + Na → R–ONa + H₂.

  2. Reaction with HX: R–OH + HCl → R–Cl + H₂O.

  3. Dehydration (conc. H₂SO₄): alcohol → alkene.

  4. Oxidation:

    • 1° alcohol → aldehyde → acid

    • 2° alcohol → ketone

    • 3° alcohol → resistant

B. Phenols

  1. Acidic character (resonance stabilisation of phenoxide ion).

  2. Electrophilic substitution:

    • Halogenation: o- and p-bromophenol.

    • Nitration: o- and p-nitrophenol.

  3. Kolbe’s reaction (Name Reaction):

    • Sodium phenoxide + CO₂ (373 K, 4–7 atm) → o-hydroxybenzoic acid (salicylic acid).


  4. Reimer–Tiemann reaction (Name Reaction):

    • Phenol + CHCl₃ + NaOH → o-hydroxybenzaldehyde (salicylaldehyde).

C. Ethers

  1. Cleavage by HX: R–O–R′ + HI → R–I + R′–OH.

    • Example: Anisole + HI → CH₃I + C₆H₅OH.

  2. Electrophilic substitution in aromatic ethers:

    • Anisole + Br₂ → o- & p-bromoanisole.

7. Important Name Reactions of this Chapter

1. Kolbe’s Reaction

  • Phenol → Salicylic acid

  • Reaction:
    C₆H₅ONa + CO₂ (373 K, 4–7 atm) → o-HOC₆H₄–COONa → (H⁺) → Salicylic acid.

2. Reimer–Tiemann Reaction

  • Phenol → Salicylaldehyde

  • Reaction:
    C₆H₅OH + CHCl₃ + NaOH → o-HOC₆H₄–CHO + HCl.

3. Williamson Ether Synthesis

  • Preparation of ethers

  • Reaction:
    R–ONa + R′–X → R–O–R′ (SN2 mechanism).

  • Example: C₂H₅ONa + CH₃I → CH₃–O–C₂H₅ (Ethoxy methane).

4. Victor Meyer’s Test (to distinguish 1°, 2°, 3° alcohols)

  • Converts alcohol → alkyl iodide → nitro compound → colour test.

    • 1° alcohol → Red colour.

    • 2° alcohol → Blue colour.

    • 3° alcohol → No colour.

5. Lucas Test (for classification of alcohols)

  • Alcohol + HCl (conc., ZnCl₂ catalyst).

    • 3° alcohol → immediate turbidity.

    • 2° alcohol → turbidity in 5–10 minutes.

    • 1° alcohol → no turbidity at room temp.

6. Dow’s Process (Preparation of Phenol from Chlorobenzene)

  • C₆H₅Cl + NaOH (623 K, 300 atm) → C₆H₅ONa → (H⁺) → C₆H₅OH.

7. Fermentation Reaction

  • C₆H₁₂O₆ → (zymase) → 2 C₂H₅OH + 2 CO₂.

8. Uses

  • Alcohols: solvents, fuels, disinfectants, beverages.

  • Phenols: antiseptics, plastics, resins, drugs.

  • Ethers: solvents, anesthetics (diethyl ether).


Location: India

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