Ethanoic Acids & Esterification Reactions | Chemistry for Grade 11 (IGCSE) PDF Download

Formation of Ethanoic Acid

• Two methods for synthesizing carboxylic acids are oxidation through fermentation and using oxidizing agents.
• In fermentation, ethanol undergoes microbial oxidation, resulting in a weak solution of vinegar (ethanoic acid). This process occurs naturally when a bottle of wine is exposed to air, as bacteria (acetobacter) in the air oxidize ethanol with atmospheric oxygen:
  C₂H₅OH (aq) + O₂ (g) → CH₃COOH (aq) + H₂O (l)
• The vinegary taste in wine left open for several days is due to the presence of ethanoic acid.
• Alternatively, carboxylic acids can be synthesized using oxidizing agents like potassium manganate(VII). This involves heating ethanol with acidified potassium manganate(VII) in the presence of an acid. The reaction is conducted under reflux, which involves heating the mixture in a vessel equipped with a condenser to prevent the volatile alcohol from escaping:
  CH₃CH₂OH (aq) + 2[O] → CH₃COOH (aq) + H₂O (l)
• During this process, the solution changes from purple to colorless. The oxidizing agent is represented by the symbol for oxygen in square brackets.
• Diagram showing the experimental setup for the oxidation with KMnO₄ using reflux apparatus:
  

Esterification

• Alcohols and carboxylic acids undergo esterification reactions to produce esters. Esters are characterized by the functional group R-COO-R and are commonly sweet-smelling oily liquids employed in food flavorings and perfumes.
• For instance, ethanoic acid reacts with ethanol in the presence of concentrated sulfuric acid (acting as a catalyst) to yield ethyl ethanoate:
  CH₃COOH (aq) + C₂H₅OH (aq) ⇌ CH₃COOC₂H₅ (aq) + H₂O (l)

Naming Esters

• Esters are derived from the reaction between an alcohol and a carboxylic acid. The naming convention for esters involves indicating the length of the carbon chain in both the alcohol and the carboxylic acid.
• The first part of the ester's name signifies the carbon chain length in the alcohol, ending with "-yl." Meanwhile, the second part indicates the carbon chain length in the carboxylic acid, ending with "-oate."
• For example, if pentanol and butanoic acid react, the resulting ester is named pentyl butanoate.