CIE A Level Chemistry (9701) 2019-2021

Revision Notes

7.5.1 Reactions of Carobxylic Acids

Reactions of Carboxylic Acids to Produce Acyl Chlorides

  • Acyl chlorides are compounds with the functional group -COCl
  • They look similar in structure to carboxylic acids but have a Cl atom instead of an -OH group attached to the carbonyl (C=O)
  • Acyl chlorides are more reactive than their corresponding carboxylic acids and are therefore often used as starting materials in the production of organic compounds such as esters
  • They can be prepared from the reaction of carboxylic acids with:
    • Solid phosphorus(V) chloride (PCl5)
    • Liquid phosphorus(III) chloride (PCl3) and heat
    • Liquid sulfur dichloride oxide (SOCl2)
  • For example, the acyl chloride ethanoyl chloride can be formed from ethanoic acid in the above reactions

Carboxylic Acids & Derivatives - Production of Acyl Chlorides, downloadable AS & A Level Chemistry revision notes

Production of acyl chlorides from their corresponding carboxylic acids

Further Oxidation of Carboxylic Acids

  • Carboxylic acids can be formed from the oxidation of primary alcohols
  • The primary alcohols are firstly oxidised to aldehydes and then further oxidised to carboxylic acids
  • Some carboxylic acids can get even further oxidised

Methanoic acid

  • Methanoic acid is a strong reducing agent and gets further oxidised to carbon dioxide (CO2)
  • The oxidation of methanoic acid can occur by:
    • Warming methanoic acid with mild oxidising agents such as Fehling’s or Tollens’ reagent
      • In a Fehling’s solution, the Cu2+ ion is reduced to Cu+ ion which precipitates as red Cu2O
      • With Tollens’ reagent, the Ag+ is reduced to Ag
    • Using stronger oxidising agents such as acidified KMnO4 or acidified K2Cr2O7
      • The purple KMnO4 solution turns colourless as Mn7+ ions are reduced to Mn2+ ions
      • The orange K2Cr2O7 solution turns green as the Cr6+ ions are reduced to Cr3+ ions

Ethanedioic acid

  • Another carboxylic acid that can get further oxidised is ethanedioic acid
  • A strong oxidising agent such as warm acidified KMnO4 is required for the oxidation of ethanedioic acid to carbon dioxide


Carboxylic Acids _ Derivatives - Further oxidation of ethanedioic acid, downloadable AS & A Level Chemistry revision notes

Ethanedioic acid is a dicarboxylic acid that can get further oxidised to carbon dioxide

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