Propyl methanoate is an ester used as a flavouring in some sweets and fruit drinks. Describe how propyl methanoate could be made in the laboratory, including the names of the reactants, the type of reaction, and the conditions required.

Pearson Edexcel International GCSE Chemistry (4CH1) — 4.7 Esters · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Propyl methanoate has the structural formula HCOOC₃H₇ and is responsible for the artificial rum flavour found in some confectionery products.

Model answer (4 marks)

Propyl methanoate can be prepared by esterification of methanoic acid with propanol. The reaction is a condensation (acid–base) reaction:

CH₃COOH + C₃H₇OH → CH₃COOC₃H₇ + H₂O

An acid catalyst such as concentrated sulphuric acid is added to protonate the carbonyl oxygen and increase the electrophilicity of the carbonyl carbon. The mixture is heated (reflux) to drive off the water and drive the equilibrium toward ester formation.

Examiner tips

  • Mention the two reactants by name (methanoic acid and propanol).
  • State the reaction is a condensation (esterification).
  • Include that an acid catalyst (e.g. conc. H₂SO₄) is required and that the mixture is refluxed to remove water.

Common mistakes

  • Using the wrong acid (e.g. acetic acid) or alcohol (e.g. ethanol).
  • Failing to mention that the reaction is a condensation/esterification.

Mark scheme (4 marks)

  1. Names the correct carboxylic acid reactant: methanoic acid
  2. Names the correct alcohol reactant: propanol
  3. States that the reaction is a condensation reaction
  4. States that an acid catalyst is required (e.g. concentrated sulfuric acid)

Key terms in this question

ester

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