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

  CH3CO2H(aq) ⇌ CH3CO2-(aq) + H+(aq)
• Carboxylic acid salts


  • Stabilised by delocalisation of the negative charge
  • Equal C-O bond lengths in the delocalised ion
• Increasing chain length of carboxylic acids

  • Pushes electron density onto the COO- ion, making it more negative and less stable
  • This makes the acid less strong
• Electronegative chlorine atoms


  • Withdraw electron density from the COO- ion, making it less negative and more stable
  • This makes the acid more strong
• Propanoic acid is less acidic than 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 with solid Na2CO3 or aqueous NaHCO3 can be used as a functional group test for carboxylic acids
• Esterification


  1. Carboxylic acid + alcohol → ester + water

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


  Two parts: alcohol part (-yl) and acid part (-anoate)
• Methanoic acid can be oxidised, unlike other carboxylic acids
• Oxidation of methanoic acid

  Methanoic acid → carbonic acid → 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 → ester + HCl