Ester
Definition and meaning of Ester in chemistry.
An ester is an organic compound in which the hydroxyl (-OH) group of a carboxylic acid has been replaced by an -OR group from an alcohol, giving the general structure R-COO-R'.
In more detail
Esters are typically made by Fischer esterification: a carboxylic acid and an alcohol react under acid catalysis (usually with concentrated sulfuric acid), losing a molecule of water to form the ester bond. This condensation reaction is reversible; the reverse reaction, acid or base hydrolysis, breaks the ester back into its acid and alcohol components. Base-catalyzed hydrolysis (saponification) is irreversible and yields a carboxylate salt plus an alcohol. Esters are important in nature and industry: fats and oils are triglycerides (esters of glycerol and fatty acids), and many small esters have characteristic fruity odors used in flavorings and perfumes.
Key facts
| Field | Organic Chemistry |
|---|---|
| General formula | R-COO-R' |
| Functional group | -C(=O)-O- (carbonyl bonded to a second oxygen) |
| Typical synthesis | Fischer esterification (carboxylic acid + alcohol, acid catalyst, -H2O) |
Ethyl acetate (CH3COOC2H5) forms from the condensation of acetic acid and ethanol; it is a common laboratory and industrial solvent with a fruity, sweet odor.
Frequently asked questions
How are esters named?
Ester names have two parts: the alkyl group from the alcohol comes first, followed by the acid-derived name ending in '-oate', for example, ethyl acetate (from ethanol and acetic acid).
What's the difference between acid and base hydrolysis of an ester?
Acid-catalyzed hydrolysis is the reverse of esterification and reaches equilibrium, regenerating the carboxylic acid and alcohol. Base hydrolysis (saponification) is irreversible and produces a carboxylate salt plus an alcohol.