Carboxylic Acids and Esters

• Carboxylic acids


  Organic compounds containing the carboxyl group (-COOH)
• Esters


  Compounds formed by the reaction of a carboxylic acid and an alcohol
• Solubility of carboxylic acids in water

  • Smaller carboxylic acids (up to C4) dissolve in water in all proportions
  • Solubility rapidly reduces after C4
• Hydrogen bonding


  Carboxylic acids can hydrogen bond to water molecules, allowing them to dissolve
• Acidity of carboxylic acids

  • Carboxylic acids are weak acids in water and only slightly dissociate
  • But they are strong enough to displace carbon dioxide from carbonates
• Dissociation of carboxylic acids

  CH3CO2H(aq) ⇌ CH3CO2-(aq) + H+(aq)
• Delocalisation in carboxylic acid salts


  Delocalisation stabilises the dissociated carboxylate ion, making dissociation more likely
• Factors affecting strength of carboxylic acids

  • Increasing chain length makes the carboxylate ion more negative and less stable, decreasing acidity
  • Electron-withdrawing groups like chlorine make the carboxylate ion more stable, increasing acidity
• Propanoic acid vs ethanoic acid

  Propanoic acid is less acidic than ethanoic acid
• Chloroethanoic acid vs ethanoic acid

  Chloroethanoic acid is more acidic than ethanoic acid
• Salt formation reactions of carboxylic acids

  1. Acid + metal → salt + hydrogen

  2. Acid + alkali → salt + water

  3. Acid + carbonate → salt + water + CO2
• Effervescence test for carboxylic acids


  Effervescence with solid Na2CO3 or aqueous NaHCO3 indicates presence of carboxylic acid
• Esterification


  1. Carboxylic acid + alcohol → ester + water

  2. Reaction is reversible, slow, and needs an acid catalyst
• Ester naming


  Ester name has two parts: alcohol-yl + acid-anoate
• Carboxylic acids cannot be oxidised by oxidising agents, except for methanoic acid
• Oxidation of methanoic acid

  Methanoic acid is oxidised to carbonic acid (H2CO3), which decomposes to CO2
• Esterification using acid anhydrides

  1. Acid anhydride + alcohol → ester + carboxylic acid

  2. Reaction is not reversible and gives higher yields
• Hydrolysis of esters


  1. With acid: ester + water → carboxylic acid + alcohol (reversible)

  2. With base: ester + NaOH → carboxylic acid salt + alcohol (irreversible)
• Acyl chlorides


  More reactive than carboxylic acids and esters due to the good leaving group (Cl)
• Formation of acyl chlorides from carboxylic acids

  Carboxylic acid + SOCl2 → acyl chloride + SO2 + HCl
• Reaction of acyl chlorides with water

  Acyl chloride + H2O → carboxylic acid + HCl
• Reaction of acyl chlorides with alcohols

  Acyl chloride + alcohol → ester + HCl
• Reaction of acyl chlorides with ammonia

  Acyl chloride + 2NH3 → primary amide + NH4Cl
• Reaction of acyl chlorides with primary amines

  Acyl chloride + 2CH3NH2 → secondary amide + CH3NH3+Cl-
• Reaction of acyl chlorides with phenols

  Acyl chloride + phenol → phenyl ester + HCl