What are Esters? (Edexcel IGCSE Chemistry)

The Esters

Spec point — 8.10C

Esters

Making esters

• 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
• Ethanoic acid will react with ethanol in the presence of concentrated sulfuric acid (catalyst) to form the ester, ethyl ethanoate:

CH₃COOH + C₂H₅OH → CH₃COOC₂H₅+ H₂O

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 pent anol and butanoic acid is called pentyl butanoate

Diagram showing the origin of each carbon chain in ester

• Some examples of common esters:

Examples of Esters Table

Exam Hint You must be able to write the structure and displayed formula for an ester, given the name or formula of the alcohol and carboxylic acid from which it is formed and vice versa.