In
chemistry, an ester is a
compound derived from an
acid (organic or inorganic) in which the
hydrogen atom (H) of at least one
acidichydroxyl group (−OH) of that acid is replaced by an
organyl group (−R). Analogues derived from
oxygen replaced by other
chalcogens belong to the ester category as well (i.e. esters of acidic −
SH, −
SeH, −
TeH, −
PoH and −
LvH groups). According to some authors, organyl derivatives of acidic hydrogen of other acids are esters as well (e.g.
amides), but not according to the
IUPAC.[1]
An example of an ester formation is the
substitution reaction between a
carboxylic acid (R−C(=O)−OH) and an
alcohol (R'OH), forming an ester (R−C(=O)−O−R'), where R and R′ are organyl groups, or
H in the case of esters of
formic acid.
Glycerides, which are
fatty acid esters of
glycerol, are important esters in biology, being one of the main classes of
lipids, and making up the bulk of animal fats and vegetable oils. Esters of
carboxylic acids with low molecular weight are commonly used as fragrances and found in
essential oils and
pheromones.
Phosphoesters form the backbone of
DNA molecules.
Nitrate esters, such as
nitroglycerin, are known for their explosive properties, while
polyesters are important
plastics, with
monomers linked by ester
moieties. Esters of carboxylic acids usually have a sweet smell and are considered high-quality solvents for a broad array of plastics,
plasticizers,
resins, and
lacquers.[2] They are also one of the largest classes of synthetic lubricants on the commercial market.[3]
Many esters of
carboxylic acid have distinctive fruit-like odors, and many occur naturally in fruits and the essential oils of plants. This has also led to their common use in artificial flavorings and fragrances which aim to mimic those odors.