Edexcel A Level Chemistry:复习笔记7.3.2 Preparation of Carboxylic Acids

• 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

   

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