Preparation of Carboxylic Acids (Edexcel International A Level Chemistry)

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Carboxylic Acids - Preparation

  • Carboxylic acids are compounds with a -COOH functional group
  • They can be prepared by a series of different reactions

Oxidation of primary alcohols & aldehydes

  • Carboxylic acids can be formed from the oxidation of primary alcohols and aldehydes by either acidified K2Cr2O7 or acidified KMnO4 and reflux
  • The oxidising agents themselves get reduced causing the solutions to change colour
    • In K2Cr2O7 the orange dichromate ions (Cr2O72-) are reduced to green Cr3+ ions
    • In KMnO4  the purple manganate ions (MnO4-) are reduced to colourless Mn2+ ions

 Carboxylic Acids & Derivatives Oxidation of Primary Alcohols and Aldehydes, downloadable AS & A Level Chemistry revision notes

Oxidation of primary alcohols (1) and aldehydes (2) gives carboxylic acids

Hydrolysis of nitriles

  • Carboxylic acids can also be prepared from the hydrolysis of nitriles using either dilute acid or dilute alkali followed by acidification
    • Hydrolysis by dilute acid results in the formation of a carboxylic acid and ammonium salt
    • Hydrolysis by dilute alkali results in the formation of a sodium carboxylate salt and ammonia; Acidification is required to change the carboxylate ion into a carboxylic acid

  • The -CN group at the end of the hydrocarbon chain is converted to a -COOH group

Hydrolysis of nitriles by either dilute acid (1) or dilute alkali and acidification (2) will form a carboxylic acid

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Richard

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Richard has taught Chemistry for over 15 years as well as working as a science tutor, examiner, content creator and author. He wasn’t the greatest at exams and only discovered how to revise in his final year at university. That knowledge made him want to help students learn how to revise, challenge them to think about what they actually know and hopefully succeed; so here he is, happily, at SME.