Esters

Esters are one of the most practically important families of organic compounds. They are responsible for the pleasant smells of many fruits and flowers, and they are used industrially as solvents, plasticisers, and in the production of biodiesel. At A-Level, you need to understand how esters are formed, how they are named, their hydrolysis reactions, and their varied applications.

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Formation of Esters

Esters are formed by a condensation reaction between a carboxylic acid and an alcohol, with the loss of a water molecule:

Carboxylic acid + Alcohol ⇌ Ester + Water

For example:

CH₃COOH + CH₃OH ⇌ CH₃COOCH₃ + H₂O (ethanoic acid + methanol ⇌ methyl ethanoate + water)

This reaction requires:

• A concentrated sulfuric acid catalyst (H₂SO₄)
• Heating under reflux to maintain the temperature without losing volatile components

The reaction is reversible and reaches an equilibrium, so yields are typically moderate unless steps are taken to remove the water or use excess of one reactant.

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Naming Esters

Esters are named from the alcohol part first, then the acid part: