Ethanoic Acid & Esterification Reactions (CIE IGCSE Chemistry)

Extended tier only

• Two methods used to make carboxylic acids are:
  • Oxidation by fermentation
  • Using oxidising agents 
• The microbial oxidation (fermentation) of ethanol will produce a weak solution of vinegar (ethanoic acid)
• This occurs when a bottle of wine is opened as bacteria in the air (acetobacter) will use atmospheric oxygen from air to oxidise the ethanol in the wine

C₂H₅OH (aq) + O₂ (g) → CH₃COOH (aq)+ H₂O (l)

• The acidic, vinegary taste of wine which has been left open for several days is due to the presence of ethanoic acid
• Alternatively, oxidising agent potassium manganate(VII) can be used 
• This involves heating ethanol with acidified potassium manganate(VII) in the presence of an acid 
• The heating is performed under reflux which involves heating the reaction mixture in a vessel with a condenser attached to the top
• The condenser prevents the volatile alcohol from escaping the reaction vessel as alcohols have low boiling points
• The equation for the reaction is:

CH₃CH₂OH (aq) + 2[O]  →  CH₃COOH (aq) + H₂O (l)

• The solution will change from purple to colourless
• The oxidising agent is represented by the symbol for oxygen in square brackets 

Diagram showing the experimental setup for the oxidation with KMnO₄ using reflux apparatus

Ethanol is heated with acidified potassium manganate(VII) in the presence of an acid 

 

Extended tier only

• Alcohols and carboxylic acids react to make esters in esterification reactions
• Esters are compounds with the functional group R-COO-R

• Esters are sweet-smelling oily liquids used in food flavourings and perfumes
• An acid catalyst is required for an esterification reaction
• Ethanoic acid will react with ethanol in the presence of concentrated sulfuric acid (catalyst) to form ethyl ethanoate:

CH₃COOH (aq) + C₂H₅OH (aq)  ⇌  CH₃COOC₂H₅ (aq) + H₂O (l)

Diagram showing the formation of ethyl ethanoate

During this esterification reaction, a molecule of water is also produced

Naming Esters

• An ester is made from an alcohol and carboxylic acid
• The first part of the name indicates the length of the carbon chain in the alcohol, and it ends with the letters ‘- yl’
• The second part of the name indicates the length of the carbon chain in the carboxylic acid, and it ends with the letters ‘- oate’
  • E.g. the ester formed from pentanol and butanoic acid is called pentyl butanoate

Diagram showing the origin of each carbon chain in ester; this ester is ethyl butanoate

Summary table of some esters and the compounds they are formed from

Name of ester	Alcohol and carboxylic acid it is formed from
propyl methanoate	propanol and methanoic acid
methyl butanoate	methanol and butanoic acid
ethyl propanoate	ethanol and propanoic acid