Carboxylic Acids & Derivatives

Organic compounds containing the carboxyl group (-COOH) and their functional group derivatives.

Carboxylic Acids (R-COOH)

Structure

  • Carbonyl (C=O) + Hydroxyl (-OH) on same carbon
  • sp² hybridized carbonyl carbon
  • Resonance stabilization of carboxylate anion

Nomenclature

  • Replace -e with -oic acid
  • Examples: methanoic (formic), ethanoic (acetic), benzoic

Physical Properties

  • Hydrogen bonding: Dimers in non-polar solvents
  • High boiling points: Due to H-bonding
  • Water solubility: Lower members soluble
  • Acidity: pKa ~4-5 (stronger than alcohols/phenols)

Acidity Factors

  • Electron-withdrawing groups increase acidity
  • Resonance stabilization of conjugate base
  • Inductive effects

Preparation Methods

  1. Oxidation of primary alcohols or aldehydes
  2. Hydrolysis of nitriles (R-CN + H₂O/H⁺ → R-COOH)
  3. Grignard carboxylation: RMgX + CO₂ → RCOOMgX → RCOOH (after H₃O⁺ workup)
  4. Carboxylation of phenol (Kolbe-Schmitt reaction: phenol + CO₂/NaOH → salicylic acid)

Reactions

  1. Salt formation (with bases)
  2. Esterification (with alcohols, acid-catalyzed)
  3. Reduction (LiAlH₄ → primary alcohol)
  4. Decarboxylation (loss of CO₂, especially β-keto acids)
  5. Formation of acid derivatives (acyl chlorides, anhydrides, esters, amides)
CC(=O)O

O=C(O)c1ccccc1

O=C(O)c1ccccc1O

Carboxylic Acid Derivatives

Reactivity Order

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

(Most reactive → Least reactive)

1. Acyl Chlorides (R-COCl)

Preparation

  • R-COOH + SOCl₂ → R-COCl + SO₂ + HCl
  • R-COOH + PCl₅ → R-COCl + POCl₃ + HCl
CC(=O)Cl

O=C(Cl)c1ccccc1

Reactions

  • With alcohols → Esters
  • With amines → Amides
  • With water → Carboxylic acids
  • With Gilman reagents → Ketones

2. Acid Anhydrides ((RCO)₂O)

Preparation

  • Two carboxylic acids + dehydrating agent
  • Or: Acyl chloride + carboxylic acid salt
CC(=O)OC(C)=O

O=C1OC(=O)c2ccccc21

O=C1CCC(=O)O1

Reactions

  • Similar to acyl chlorides but milder
  • Cyclic anhydrides from dicarboxylic acids

3. Esters (R-COOR')

Preparation (Fischer Esterification)

R-COOH + R'-OH ⇌ R-COOR' + H₂O (acid catalyst)

CC(=O)OCC

O=C(OC)c1ccccc1

CC(=O)Oc1ccccc1

Reactions

  • Hydrolysis (acidic or basic/saponification)
  • Reduction (LiAlH₄ → two alcohols)
  • Transesterification (reaction with different alcohol)
  • Grignard reaction (excess RMgX → tertiary alcohol)

4. Amides (R-CONH₂, R-CONHR', R-CONR'₂)

Preparation

  • Acyl chloride + amine
  • Ester + ammonia/amine
  • Nitrile hydrolysis (partial)
CC(=O)N

O=C(N)c1ccccc1

CC(=O)N(C)C

Reactions

  • Hydrolysis (acidic or basic)
  • Dehydration (P₂O₅ → nitrile)
  • Hofmann rearrangement (Br₂/NaOH → amine with loss of CO)

Interconversion Chart

                    Carboxylic Acid
                          ↑
     Alcohol ← Ester ← Acyl Chloride → Acid Anhydride
       ↓                    ↓
   Aldehyde              Amide
       ↓
    Ketone

Important Named Reactions

Reaction Transformation
Fischer Esterification Acid + Alcohol → Ester
Saponification Ester + Base → Carboxylate + Alcohol
Hofmann Rearrangement Amide → Amine (loss of CO)
Gabriel Synthesis Phthalimide → Primary amine

Related Topics

Sources