Hydroxy compounds

🌿 Hydroxy compounds are organic molecules that contain one or more hydroxyl groups (–OH). This chapter focuses on alcohols and phenols, two major classes of hydroxy compounds with very different chemical behavior due to the bonding of the –OH group.

🔹 Alcohols

🔸 Reaction with Acyl Chlorides to Form Esters

• Reaction Overview:
  Alcohols react with acyl chlorides (acid chlorides) to form esters and hydrogen chloride. General reaction: R−OH+R′−COCl→R′−COOR+HCl
• Example – Formation of Ethyl Ethanoate: CH₃CH₂OH+CH₃COCl→CH₃COOCH₂CH₃+HCl
• Mechanism:
  • Nucleophilic attack by the lone pair on the oxygen of the alcohol on the electrophilic carbon of the acyl chloride.
  • Loss of Cl⁻ and formation of HCl as a by-product.
• Conditions:
  • No catalyst required.
  • Carried out at room temperature.
  • Anhydrous conditions are preferred to prevent hydrolysis of acyl chloride.

🔹 Phenol

Phenol (C₆H₅OH) is an aromatic compound where the –OH group is directly attached to the benzene ring. Its chemistry is different from that of alcohols due to resonance stabilization.

🔸 1. Production of Phenol

• From Phenylamine (Aniline):
• Step 1: Diazotisation (below 10 °C) C₆H₅NH₂+HNO₂→C₆H₅N₂+Cl−+2H₂OC₆H₅NH₂ + HNO₂
• Step 2: Hydrolysis of Diazonium Salt (on warming) C₆H₅N₂+Cl−+H₂O→C₆H₅OH+N₂+HCl

🔸 2. Chemistry of Phenol

• (a) Reaction with Bases (e.g., NaOH): C₆H₅OH+NaOH→C₆H₅O−Na⁺+H₂O
• (b) Reaction with Sodium Metal: 2C₆H₅OH+2Na→2C₆H₅ONa+H₂↑
• (c) Coupling with Diazonium Salts (Azo Dye Formation):
  • In alkaline conditions:
  C₆H₅N₂⁺Cl⁻+C₆H₅O−→C₆H₅–N=N–C₆H₄OH
  • Forms colored azo compounds.
• (d) Nitration with Dilute HNO₃ at Room Temperature: C₆H₅OH+HNO₃→2-nitrophenol+4-nitrophenol+H₂OC₆H₅OH + HNO₃
  • Mixture of ortho and para products due to –OH activation.
• (e) Bromination with Br₂(aq): C₆H₅OH+3Br₂→2,4,6-tribromophenol+3HBrC₆H₅OH + 3Br₂
  • White precipitate forms immediately without catalyst.

🔸 3. Acidity of Phenol

• Phenol is more acidic than ethanol but less acidic than carboxylic acids.
• The phenoxide ion is resonance-stabilized: C₆H₅O−↔resonance structuresC₆H₅O⁻
• This stabilization makes deprotonation easier than in alcohols.

🔸 4. Relative Acidities of Water, Phenol, and Ethanol

Order: Phenol > Water > Ethanol

🔸 5. Reagents and Conditions for Electrophilic Substitution

• Phenol vs Benzene:
  • Phenol has an activating –OH group that increases the electron density on the benzene ring (especially at 2-, 4-, 6- positions).
  • Therefore, milder conditions are needed for phenol.

🔸 6. Directing Effects of the –OH Group

• The lone pair on the oxygen of –OH activates the aromatic ring.
• Directs substitution to positions 2, 4, and 6.
  • This is due to resonance donation of electron density into the ring.

🔸 7. Reactions of Other Phenolic Compounds (e.g., Naphthol)

• Compounds like naphthol show similar chemistry:
  • React with bases to form salts.
  • Undergo electrophilic substitution at activated positions.
  • Couple with diazonium salts to form azo dyes.
• Reactivity depends on the position of the –OH group on the ring system.

✅ Summary of Key Concepts

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