Esters

Introduction to Esters

Esters are derivatives of carboxylic acids except that instead of containing the functional group COOH, they contain COOR where R is an alkyl group or benzene ring. Esters are extremely useful and are used in solvents, plasticisers and food additives, (many esters are recognised by their fruity smells, eg bannana, pear and oranges).

Preparation of Esters

Esters can be prepared by a reaction between:

• Acid chloride and alcohol. This reaction produces a high yield of ester since the reaction is irreversible.
• Carboxylic acid and alcohol. This reaction produces a lower yield of ester due to equilibrium of reaction. A catalyst for this reaction is concentrated sulphuric acid. (See Carboxylic acids for the mechanism).

Reactions of Esters

• Ester hydrolysis

  An ester can be converted to a carboxylic acid and alcohols by ester hydrolysis. This reaction is reversible and can be used to form esters under the appropriate conditions (esterification). an example mechanism is shown below for the ester RCOOR':

  
  

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