Any of a class of organic compounds that can react with water (&see; hydrolysis) to produce an alcohol and an organic or inorganic acid. They are formed by the reverse process, esterification, in which acid reacts with alcohol to form an ester and water. Esters of carboxylic acids, the most common esters, contain the acid's carbonyl group (&singlehorzbond;C&doublehorzbond;O; &see; functional group); the carbon's fourth bond is with the alcohol's oxygen atom.
Hydrolysis of esters in the presence of an alkali (saponification) is used to make soaps from fats and oils. Carboxylic acid esters of low molecular weight are colourless, volatile liquids with pleasant odours; they give flavour and fragrance to fruits and flowers and are used as synthetic flavours and fragrances. Others, such as ethyl acetate and butyl acetate, are used as solvents for lacquers, paints, and varnishes. Certain polymers are esters, including Lucite (polymethyl methacrylate) and Dacron (polyethylene terephthalate). Esters of alcohols and inorganic acids include nitrate esters (e.g., nitroglycerin), which are explosive; phosphate esters, including such biologically important compounds as nucleic acids; and others that are used as flame retardants, solvents, plasticizers, gasoline and oil additives, and insecticides.
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