Chapter 7: Alcohols, Phenols & Ethers

From Alkenes

• Acid Catalyzed Hydration: Follows Markovnikov's rule. Alkenes react with water in presence of acid to form alcohols.
  CH₃-CH=CH₂ + H₂O (H⁺) → CH₃-CH(OH)-CH₃
• Hydroboration-Oxidation: Follows Anti-Markovnikov's addition of water. Alkene reacts with diborane (B₂H₆) followed by oxidation with H₂O₂/OH⁻.
  CH₃-CH=CH₂ → (B₂H₆, then H₂O₂/OH⁻) → CH₃-CH₂-CH₂-OH (Primary alcohol formed).

From Carbonyl Compounds

• Reduction: Aldehydes yield 1° alcohols, Ketones yield 2° alcohols. Reagents used: NaBH₄, LiAlH₄, or H₂/Pd.
  R-CHO + H₂ (Pd) → R-CH₂OH
• Using Grignard Reagent (R-MgX): Formaldehyde (HCHO) gives 1° alcohol. Other aldehydes give 2° alcohol. Ketones give 3° alcohol.
  HCHO + RMgX → R-CH₂-OMgX (H₂O/H⁺) → R-CH₂OH + Mg(OH)X

From Haloarenes (Dow's Process)

Chlorobenzene is fused with NaOH at very high temp (623K) and pressure (300 atm) to form sodium phenoxide, followed by acidification.

From Cumene (Commercial Method - VERY IMPORTANT)

Isopropylbenzene (Cumene) is oxidized in air to Cumene hydroperoxide. It is then treated with dilute acid to form Phenol and Acetone (a valuable byproduct).

From Benzene Sulphonic Acid & Diazonium Salts

• Benzene → Benzene sulphonic acid (Oleum) → Sodium phenoxide (NaOH melt) → Phenol (H⁺).
• Aniline → Benzene Diazonium Chloride (NaNO₂/HCl, 0-5°C) → Warm with Water → Phenol + N₂ + HCl.

Acidity & Esterification

• Alcohols are weaker acids than water. Acidity order: 1° > 2° > 3° (Due to +I effect of alkyl groups destabilizing the alkoxide ion).
• Esterification: Alcohol + Carboxylic acid (in presence of conc. H₂SO₄) → Ester + Water.

Distinction Test (Lucas Test)

Reagent: Conc. HCl + Anhydrous ZnCl₂.

• 3° Alcohol: Turbidity appears immediately.
• 2° Alcohol: Turbidity appears in 5 minutes.
• 1° Alcohol: No turbidity at room temperature.

Dehydration (Zaitsev's Rule)

Heating with conc. H₂SO₄ at 443 K yields alkenes. Ease of dehydration: 3° > 2° > 1°.

Oxidation

• 1° Alcohol: Mild oxidizing agent (PCC/CrO₃) gives Aldehyde. Strong (KMnO₄) gives Carboxylic Acid.
• 2° Alcohol: Oxidized to Ketones.
• 3° Alcohol: Do not undergo oxidation easily. (With heated Cu at 573K, they undergo dehydration to form alkenes).

Acidity of Phenols

Phenols are much more acidic than alcohols because the phenoxide ion is resonance stabilized. Electron withdrawing groups (like -NO₂) increase acidity, electron donating groups (like -CH₃) decrease acidity.

Electrophilic Aromatic Substitution

• Nitration: Dilute HNO₃ gives ortho & para nitrophenols (separated by steam distillation). Conc. HNO₃ gives 2,4,6-trinitrophenol (Picric Acid).
• Halogenation: Bromine water gives white ppt of 2,4,6-tribromophenol. Br₂ in CS₂ (low polarity solvent) gives mono-substituted o- and p-bromophenol.

Kolbe's Reaction

Sodium phenoxide is heated with CO₂ under pressure, followed by acidification to yield Salicylic acid (2-Hydroxybenzoic acid).

Reimer-Tiemann Reaction

Treatment of phenol with chloroform (CHCl₃) in presence of aqueous NaOH introduces an aldehyde group (-CHO) at the ortho position.

Oxidation

Phenol oxidized by Na₂Cr₂O₇/H₂SO₄ produces a conjugated diketone known as benzoquinone.

Preparation (Williamson Synthesis)

Important laboratory method for symmetrical and unsymmetrical ethers. Follows SN2 mechanism.

Crucial Rule: The alkyl halide (R-X) must be Primary (1°). If 3° alkyl halide is used, elimination dominates and an alkene is formed instead of ether.

Cleavage by HX (Chemical Property)

Ethers are cleaved by concentrated HI or HBr at high temperatures.

• If alkyl groups are primary/secondary, the Halide (I⁻) goes to the smaller alkyl group (SN2 steric reasons).
• If one group is Tertiary (3°), the Halide (I⁻) goes to the tertiary group (SN1 carbocation stability).
• In Alkyl Aryl ethers (Anisole), cleavage always produces Phenol and Alkyl Halide (because Aryl-Oxygen bond has double bond character).