Carboxylic Acids and Derivatives

Formation of Acyl Chlorides

• Reagents: Carboxylic acids react with sulfur dichloride oxide (SOCl2) to form acyl chlorides, sulfur dioxide, and hydrogen chloride.
  • CH3COOH + SOCl2 → CH3COCl + SO2 + HCl
• Alternative Methods: Use of phosphorus(V) chloride or phosphorus(III) chloride
  • CH3COOH + PCl5 → CH3COCl + POCl3 + HCl
  • 3CH3COOH + PCl3 → 3CH3COCl + H3PO3

Oxidation of Carboxylic Acids

Methanoic Acid

• Reactions: Can be oxidized using Fehling's or Tollens reagent.
  • Fehling's Reagent: Red precipitate observed.
  • Tollens' Reagent: Silver mirror observed.
• Overall Reaction: HCOOH + [O] → H2O + CO2

Ethanedioic Acid

• Reactions: Oxidized using warm acidified potassium manganate(VII).
  • Use: Standardize potassium manganate(VII) solution.
  • Equation
    • 5(COOH)2 + 2MnO4- + 6H+ → 10CO2 + 2Mn2+ + 8H2O

Relative Acidities

• Order of Acidities: Carboxylic acids > phenols > alcohols
  • Carboxylic Acids: Stable due to delocalized pi system in carboxylate ion.
  • Phenols: More acidic than alcohols; phenoxide ion is relatively stable.
  • Alcohols: Least acidic due to positive inductive effect.

Chlorine-Substituted Ethanoic Acids

• Effect of Chlorine: Increases acidity due to electronegativity.
  • Equilibrium Comparison:
    • CH3COOH ⇌ CH3COO- + H+
    • CH2ClCOOH ⇌ CH2ClCOO- + H+
  • Impact: More chlorines = stronger acid.

Esters

Hydrolysis

• Acid Hydrolysis: Requires water and an acid catalyst, reversible.
  • CH3CH2COOCH3 + H2O ⇌ CH3CH2COOH + CH3OH
• Alkali Hydrolysis: Heat under reflux with dilute alkali, irreversible.
  • CH3CH2COOCH3 + NaOH → CH3CH2COONa + CH3OH
  • Conversion: Carboxylate salt to carboxylic acid via excess acid.

Uses

• Commercial Applications: Solvents, perfumes, and flavorings.

Acyl Chlorides

Structure and Nomenclature

• Structure: Similar to carboxylic acids; -OH group replaced by chlorine.
• Suffix: -oyl chloride (e.g., propanoyl chloride).

Hydrolysis

• Reaction: Water reacts with acyl chloride to form carboxylic acid and HCl.
  • CH3COCl + H2O → CH3COOH + HCl

Reactions

• With Alcohols: Produces esters and HCl fumes.
• With Phenols: Produces aromatic esters.
• With Ammonia: Produces amides and ammonium chloride.
  • CH3CH2COCl + 2NH3 → CH3CH2CONH2 + NH4Cl
• With Primary Amines: Produces N-substituted amides.
  • CH3CH2COCl + 2CH3NH2 → CH3CH2CONH2 + CH3NH3Cl

Hydrolysis Comparison

• Ease of Hydrolysis: Acyl chlorides > alkyl chlorides > aryl chlorides
  • Acyl Chlorides: React vigorously with water.
  • Alkyl Chlorides: Minimal reaction with water.
  • Aryl Chlorides: No reaction with water due to strong C-Cl bond in benzene ring.