Chapter 7: Alcohols, Phenols & Ethers

From Alkenes

• Acid Catalyzed Hydration: Follows Markovnikov's rule. Alkenes react with water in presence of acid (H₂SO₄) to form alcohols.
  CH₃-CH=CH₂ + H₂O (H⁺) → CH₃-CH(OH)-CH₃ (Propan-2-ol)
• 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 (Propan-1-ol)

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 extremely high temp (623 K) and pressure (300 atm) to form sodium phenoxide, followed by acidification.

From Cumene (Commercial Method - V.V.I)

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

Other Important Methods

• From Oleum: Benzene → Benzene sulphonic acid (using Oleum) → Sodium phenoxide (NaOH melt) → Phenol (H⁺).
• From Diazonium Salts: 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 electron-donating effect of alkyl groups which destabilizes the alkoxide ion).
• Esterification: Alcohol + Carboxylic acid (in presence of conc. H₂SO₄) → Ester + Water. (Sweet-smelling compounds).

Distinction Tests for 1°, 2°, 3° Alcohols

• Lucas Test: Reagent is Conc. HCl + Anhydrous ZnCl₂.
  - 3° Alcohol: Turbidity (cloudiness) appears immediately.
  - 2° Alcohol: Turbidity appears in 5 minutes.
  - 1° Alcohol: No turbidity at room temperature.
• Victor Meyer Test (RBC Rule):
  - 1° Alcohol gives Red color.
  - 2° Alcohol gives Blue color.
  - 3° Alcohol gives Colorless solution.

Dehydration & Oxidation

• Dehydration: Heating with conc. H₂SO₄ at 443 K yields alkenes (follows Zaitsev's Rule). Ease of dehydration: 3° > 2° > 1° because 3° carbocation is most stable.
• Oxidation (with KMnO₄ or K₂Cr₂O₇):
  - 1° Alcohol → Aldehyde → Carboxylic Acid.
  - 2° Alcohol → Ketone.
  - 3° Alcohol → Resistant to oxidation.
• Action of Heated Copper (Cu at 573 K):
  - 1° Alcohol undergoes dehydrogenation to give Aldehyde.
  - 2° Alcohol gives Ketone.
  - Exception: 3° Alcohol undergoes dehydration to give an Alkene.

Acidity of Phenols

Phenols are much more acidic than alcohols because the phenoxide ion is highly resonance stabilized.
- Electron Withdrawing Groups (-NO₂) increase acidity (e.g., 2,4,6-trinitrophenol or Picric Acid is highly acidic).
- Electron Donating Groups (-CH₃) decrease acidity.

Electrophilic Aromatic Substitution

• Halogenation:
  - Bromine in CS₂ (low polarity) at 273 K gives mono-substituted o- and p-bromophenol.
  - Bromine Water (highly polar) gives white ppt of 2,4,6-tribromophenol.
• Nitration: Dilute HNO₃ gives ortho & para nitrophenols (separated by steam distillation, ortho is volatile due to intramolecular H-bonding). Conc. HNO₃ gives Picric Acid.

Name Reactions of Phenol

• Kolbe's Reaction: Sodium phenoxide + CO₂ (pressure) → Acidification → Salicylic acid (2-Hydroxybenzoic acid).
• Reimer-Tiemann Reaction: Phenol + Chloroform (CHCl₃) + aq. NaOH → Intermediate → Salicylaldehyde.
• Reaction with Zinc Dust: Phenol is reduced to Benzene when distilled with Zn dust.
• Oxidation: Oxidized by Na₂Cr₂O₇/H₂SO₄ to a conjugated diketone called Benzoquinone.

Preparation (Williamson Synthesis)

Follows SN2 mechanism. Sodium alkoxide reacts with an alkyl halide.

Crucial Rule: The alkyl halide (R-X) must be Primary (1°). If 3° alkyl halide is used, the alkoxide acts as a strong base, 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 1° or 2°: Reaction follows SN2. The Halide (I⁻) goes to the smaller, less hindered alkyl group.
• If one group is Tertiary (3°): Reaction shifts to SN1 due to stable carbocation. The Halide (I⁻) goes to the tertiary group.
• In Alkyl Aryl ethers (Anisole): Cleavage always produces Phenol and Alkyl Halide because the Aryl-Oxygen bond has partial double bond character and cannot be broken by I⁻.