Producing Benzoic Acid (CIE A Level Chemistry)

• Benzoic acids are the simplest aromatic carboxylic acids with the molecular formula of C₆H₅COOH
• Benzoic acids and their derivatives are often used as reagents in the synthesis of esters
• The compounds can be produced from the oxidation of alkylbenzenes

Oxidation of alkylbenzenes

• The alkyl side-chain in alkylbenzenes, such as methylbenzene, can be oxidised to a carboxylic acid
• The alkylbenzene is heated under reflux with a solution of hot alkaline KMnO₄ (this is the oxidising agent)
  • The purple colour of the Mn⁷⁺ ions disappears as they are reduced to Mn⁴⁺ ions
  • A brown precipitate of MnO₂ is formed
• The mixture is then acidified with dilute acid (such as hydrochloric acid) to protonate the organic product form and produce a benzoic acid

Making benzoic acid from methylbenzene

Alkylbenzenes such as methylbenzene undergo oxidation to form benzoic acid