CHEMICAL PROPERTIES AND USES OF ESTERS

Chemical properties

Hydrolysis of esters: Alcohol and acid are produced from the hydrolysis of ester, this reaction reverse to ester formation, Hydrolysis may take place by the use of dilute mineral acids as a catalyst and is called acid hydrolysis, Dilute mineral acid (H+) is used to prevent the reversable reaction.

CH3COOC2H+ H2O → CH3COOH + C2H5OH

Hydrolysis of esters may also be carried out by heating with aqueous alkalies, to produce the alcohol and the salt of the acid, this is called alkaline-hydrolysis or saponification, (since soap is the sodium salt of high carboxylic acids), NaOH is added to react with the produced acid converting it to salt and prevent the reversible reaction.

CH3COOC2H+ NaOH → CH3COONa + C2H5OH

C6H5COOC2H5 + NaOH → C6H5COONa + C2H5OH

Hydrolysis of esters is the reaction of the ester with water (in an acidic medium) to form acid and alcohol, saponification is the heating of ester with aqueous alkalis to produce the alcohol and the salt of the acid, Soap is the sodium salt of high fatty carboxylic acids.

The hydrolysis product of ester depends on the reaction medium because in acidic medium, acid and alcohol are formed while in alkali medium, salt of organic acid and alcohol are formed, Ammonolysis is the reaction of esters with ammonia to produce acid amide and the alcohol.

CH3COOC2H+ NH3 → CH3CONH2 + C2H5OH

C6H5COOC2H5 + NH3 → C6H5CONH2 + C2H5OH

The esterification reaction is not a neutralization reaction as it is a reversible reaction “incomplete”, It needs a dehydrating agent, It is a slow reaction because it takes place between molecules, water is formed due to the combination of molecules, H from alcohol and OH from acid.

Acid + alcohol ↔ ester + H2O

The neutralization reaction is irreversible reaction “complete”, It is a fast reaction because it takes place between ions, water is formed due to the combination of ions H+ from acid and OH from alkali.

Acid + base → salt + H2O

Uses of esters

There are various uses of esters.

1. Esters that are have fragrant odours are used as a constituent of perfumes, essential oils, food flavourings, cosmetics, etc
2. Esters are used as an organic solvent
3. Natural esters are found in pheromones
4. Naturally occurring fats and oils are fatty acid esters of glycerol
5. Phospoesters form the backbone of DNA molecules
6. Nitrate esters, such as nitroglycerin, are known for their explosive properties
7. Polyesters are used to make plastics
8. Esters are used to make surfactants E.g. soap, detergents

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