FAD1018 W11 — Carboxylic Acids & Derivatives

Week 11 lecture covering carboxylic acids and their derivatives. Source file: W11.pdf from lecture notes folders.

Summary

Study of carboxylic acids, acid chlorides, acid anhydrides, esters, and amides including structure, properties, preparation, and interconversions.

Key Concepts

O=CO          formic acid
CC(=O)O       acetic acid
c1ccccc1C(=O)O  benzoic acid
  • Acyl Chlorides — R-COCl (most reactive derivatives)
CC(=O)Cl      acetyl chloride
  • Acid Anhydrides — (RCO)₂O
CC(=O)OC(=O)C      acetic anhydride
  • Esters — R-COOR'
CC(=O)OC       methyl acetate
CC(=O)OCC      ethyl acetate
  • Amides — R-CONH₂
CC(=O)N        acetamide
  • Nucleophilic Acyl Substitution — Characteristic reaction

Lecture Coverage

1. Carboxylic Acids

Structure and Nomenclature

  • -COOH functional group
  • IUPAC naming (-oic acid suffix)
  • Common names (formic, acetic, benzoic)

Physical Properties

  • Hydrogen bonding (dimer formation)
CC(=O)O...O=C(C)O       acetic acid dimer
  • Higher boiling points than comparable alcohols
  • Water solubility (lower members)
  • Acidity (pKa ~4-5)

Acidity Factors

  • Inductive effects
  • Resonance stabilization of carboxylate anion
CC(=O)[O-]      acetate anion (resonance-stabilized)
  • Substituent effects (electron-withdrawing increases acidity)

2. Preparation of Carboxylic Acids

  • Oxidation of primary alcohols
  • Oxidation of aldehydes
  • Hydrolysis of nitriles
CC#N.O>>CC(=O)O.N       nitrile hydrolysis
  • Carboxylation of Grignard reagents
C[Mg]Br.O=C=O>>CC(=O)[O-].[Mg+2].[Br-]  Grignard carboxylation

3. Reactions of Carboxylic Acids

a) Salt Formation

  • Reaction with bases
  • Soap formation
CC(=O)O.[OH-]>>CC(=O)[O-].O           acid + base → salt
CC(=O)[O-].[Na+]                        sodium acetate (soap type)

b) Reduction

  • LiAlH₄ reduction to primary alcohols
CC(=O)O>>CCO              carboxylic acid → primary alcohol
  • Borane (BH₃) reduction

c) Decarboxylation

  • Loss of CO₂
  • β-Keto acids and malonic acid derivatives
CC(=O)CC(=O)O      acetoacetic acid (β-keto acid)
O=C(O)CC(=O)O      malonic acid
CC(=O)CC(=O)O>>CC(C)=O.O=C=O    decarboxylation → acetone + CO₂

4. Carboxylic Acid Derivatives

Reactivity Order:

Acyl Chloride > Acid Anhydride > Ester ~ Carboxylic Acid > Amide

a) Acyl Chlorides (Acid Chlorides)

  • Preparation: Carboxylic acid + SOCl₂, PCl₅, or PCl₃
CC(=O)O.S(Cl)(Cl)=O>>CC(=O)Cl.S(=O)=O.Cl     SOCl₂ preparation
CC(=O)Cl.CCO>>CC(=O)OCC.Cl                    + alcohol → ester
CC(=O)Cl.N>>CC(=O)N.Cl                         + amine → amide
  • Reactions: With alcohols, amines, water, Gilman reagents
  • Most reactive derivative

b) Acid Anhydrides

  • Preparation: Two carboxylic acids + dehydrating agent
  • Reactions: Similar to acyl chlorides but milder
  • Cyclic anhydrides (succinic, maleic, phthalic)
O=C1CCC(=O)O1           succinic anhydride
O=C1C=CC(=O)O1          maleic anhydride
O=C1OC(=O)c2ccccc12     phthalic anhydride

c) Esters

  • Preparation: Fischer esterification (acid + alcohol)
CC(=O)O.CCO>>CC(=O)OCC.O          Fischer esterification
  • Reactions: Hydrolysis (acidic and basic/saponification)
CC(=O)OCC.[OH-]>>CC(=O)[O-].CCO    saponification
  • Transesterification
  • Reduction to alcohols
  • Reaction with Grignard reagents (tertiary alcohols)

d) Amides

  • Preparation: Acyl chloride + ammonia/amine, or ester + ammonia
CC(=O)Cl.N>>CC(=O)N.Cl              acyl chloride + ammonia
CC(=O)OCC.N>>CC(=O)N.CCO            ester + ammonia
  • Reactions: Hydrolysis (acidic and basic)
  • Dehydration to nitriles
CC(=O)N>>CC#N.O                      amide dehydration → nitrile
  • Hofmann rearrangement
CC(=O)N.Br.[OH-]>>CN.O=C=O.Br-      Hofmann → primary amine

5. Interconversion of Derivatives

Carboxylic Acid → Acyl Chloride → Ester → Amide
       ↓              ↓              ↓
   Anhydride    Alcohol/Amine   Hydrolysis

6. Important Named Reactions

  • Fischer Esterification
CC(=O)O.CCO>>CC(=O)OCC.O
  • Saponification
CC(=O)OCC.[OH-]>>CC(=O)[O-].CCO
  • Hofmann Rearrangement
CC(=O)N.Br.[OH-]>>CN.O=C=O.Br-
  • Gabriel Synthesis (from phthalimide)
O=C1NC(=O)c2ccccc12        phthalimide

Related Topics

*C(=O)*OCCO*                polyester repeating unit
*C(=O)*N*N*                 polyamide repeating unit

Study Notes

[!note] Important organic topic Carboxylic Acids & Derivatives have ~5% mark weight. Focus on reactivity order and interconversions.

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