Esters

Naming Esters

Naming Esters. When naming esters, the -oate part of the name comes from the carboxylate component, and the alkyl part of the name comes from the alkyl group in the alcohol.

Synthesis of Esters

Esters can be made in two ways:

1. Fischer Esterification;
   This is the proper name for the equilibruim reaction btween and alcohol and a carboxylic acid to form an ester and water. This is done in the presence of a strong acid catalyst such as sulphuric acid. e.g.
   CH₃COOH + CH₃CH₂OH → CH₃COOCH₂CH₃ + H₂O
2. Acylation using an alcohol:
   This is the reaction seen in the carboxylic acid derivatives page. It is a more effective way of producing esters. It give a higher yeild as there is no equilibrium, and the HCl can be easily be removed by adding a base, to form water. The ester can be distilled off from this as it has the lower boiling point.

Uses

Esters have 3 main uses

1. Solvents;
   Although esters are insoluble in water, the are polar because of the electronegative oxygen atoms. This makes them very good polar solvents for organic molecules. One example is ethyl ethanoate, which is used in some glues and in printing inks.
2. Plasticisers;
   These are molecules that are incorporated into plastics to aid flexibility. They act as a kind of bearing, helping the long polymer chains to slide over each other better, making the plastic more supple.
3. Food Flavourings;
   Esters are very sweet smelling, e.g. ethyl ethanoate smells of pear drops. This means they are often used to artificially flavour food.

Saponification

This is another term for the hydrolysis of esters, using a base. This reaction produces soap, hence the name. The base used is usually sodium hydroxide and a sodium salt is formed at the end f the reaction. e.g:

CH₃COOCH₂CH₃ + NaOH → CH₃COONa + CH₃CH₂OH

It is usually the longer fatty acid chains that are used to make soap, such as stearic acid (16 carbon atoms).

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