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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Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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