Organic Chemistry: Esters

Organic Chemistry: Esters

Organic Compounds: Esters

  • Esters are a group of organic compounds that have a distinct, often fruity, odour.
  • They are used in a variety of applications, from providing flavour and fragrance in food and cosmetic products, to acting as solvents in chemical industries.
  • The generic formula for an ester is R-COO-R’, where R and R’ denote hydrocarbon chains.

Formation of Esters

  • Esters are formed in a reaction known as esterification, where a carboxylic acid reacts with an alcohol in the presence of an acid catalyst, typically sulfuric acid.
  • The reaction results in the formation of an ester and by-product water.
  • The general word equation for esterification can be written as: Carboxylic acid + Alcohol → Ester + Water.

Naming Esters

  • The name of an ester is derived from both the alcohol and the carboxylic acid used in its formation.
  • The part of the ester’s name derived from the alcohol comes first, followed by the part derived from the carboxylic acid.
  • The part of the name from the carboxylic acid is modified by replacing the -oic acid suffix with -oate. For example, the ester formed by methanol and ethanoic acid is methyl ethanoate.

Properties of Esters

  • Esters are volatile, which means they tend to evaporate at room temperature, allowing us to detect their distinctive smells.
  • Unlike carboxylic acids and alcohols, esters do not form hydrogen bonds, making them less polar and less soluble in water.
  • They have a relatively low boiling point due to the absence of hydrogen bonds.

Hydrolysis of Esters

  • The process of breaking an ester down into a carboxylic acid and an alcohol, using water or an acid or base, is known as hydrolysis.
  • Catalysed by acids or bases, hydrolysis is the reverse reaction of esterification.
  • The equation for acid hydrolysis is: Ester + Water → Carboxylic acid + Alcohol.

Importance of Esters

  • Their characteristic smells make esters valuable in the food and cosmetics industries, as they are commonly used in artificial flavours and fragrances.
  • In biomedical applications, some types of esters are used in making polymers for sutures and drug delivery systems.
  • Esters are also used as solvents for resins, paints, and varnishes due to their favourable solubility characteristics.