Carboxylic acids and derivatives

Carboxylic Acids

1. Preparation of Carboxylic Acids

(a) Oxidation of Primary Alcohols and Aldehydes

• Reagents: Acidified potassium dichromate (K₂Cr₂O₇) or acidified potassium manganate(VII) (KMnO₄)
• Conditions: Reflux
• Type of Reaction: Oxidation
• Equation Examples:
  • Primary alcohol:
    CH₃CH₂OH + [O] → CH₃COOH (Ethanol to ethanoic acid)
  • Aldehyde:
    CH₃CHO + [O] → CH₃COOH (Ethanal to ethanoic acid)

(b) Hydrolysis of Nitriles

• Reagents:
  • Dilute acid (e.g., HCl) or dilute alkali (e.g., NaOH)
• Conditions: Heat under reflux
• Process:
  • Acid hydrolysis: R-CN → R-COOH
    • RCN + 2H₂O + HCl → RCOOH + NH₄Cl
  • Alkaline hydrolysis (followed by acidification):
    • RCN + NaOH + H₂O → RCOO⁻Na⁺ + NH₃, then
      RCOO⁻ + H⁺ → RCOOH

(c) Hydrolysis of Esters

• Reagents: Dilute acid or dilute alkali
• Conditions: Heat under reflux
• Acid Hydrolysis:
  • RCOOR' + H₂O ⇌ RCOOH + R'OH
• Alkaline Hydrolysis (Saponification):
  • RCOOR' + NaOH → RCOO⁻Na⁺ + R'OH
  • Followed by: RCOO⁻ + H⁺ → RCOOH

2. Reactions of Carboxylic Acids

(a) Reaction with Reactive Metals

• Example: Sodium (Na), Magnesium (Mg)
• Type: Redox
• Equation: 2CH₃COOH + 2Na → 2CH₃COONa + H₂↑

(b) Neutralisation with Alkalis

• Alkalis: NaOH, KOH
• Type: Neutralisation
• Equation: CH₃COOH + NaOH → CH₃COONa + H₂O

(c) Reaction with Carbonates

• Carbonates: Na₂CO₃ or NaHCO₃
• Products: Salt, CO₂, and water
• Equation:
  • 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂↑
  • CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂↑

(d) Esterification

• Reagents: Alcohol (e.g., ethanol)
• Catalyst: Concentrated H₂SO₄
• Type: Condensation reaction
• Equation:
  • CH₃COOH + CH₃CH₂OH ⇌ CH₃COOCH₂CH₃ + H₂O

(e) Reduction to Primary Alcohols

• Reagent: Lithium aluminium hydride (LiAlH₄) in dry ether
• Conditions: Anhydrous (no water)
• Equation: RCOOH → RCH₂OH

Esters

1. Preparation of Esters

(a) Condensation Reaction

• Reagents: Alcohol + Carboxylic acid
• Catalyst: Concentrated H₂SO₄
• Type: Reversible condensation
• Example:
  • CH₃COOH + CH₃CH₂OH ⇌ CH₃COOCH₂CH₃ + H₂O (ethyl ethanoate)

2. Hydrolysis of Esters

(a) Acid Hydrolysis

• Reagent: Dilute acid (e.g., HCl)
• Conditions: Heat under reflux
• Type: Reversible reaction
• Equation:
  • CH₃COOCH₂CH₃ + H₂O ⇌ CH₃COOH + CH₃CH₂OH

(b) Alkaline Hydrolysis (Saponification)

• Reagent: Dilute alkali (e.g., NaOH)
• Conditions: Heat under reflux
• Type: Irreversible
• Equation:
  • CH₃COOCH₂CH₃ + NaOH → CH₃COONa + CH₃CH₂OH

Summary Table

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