In chemistry, an ester is a compound derived from an acid (organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (). Analogues derived from oxygen replaced by other chalcogens belong to the ester category as well (i.e. esters of acidic , , , and 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.
An example of an ester formation is the substitution reaction between a carboxylic acid () and an alcohol (R'OH), forming an ester (), 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. They are also one of the largest classes of synthetic lubricants on the commercial market.
By number of R' group carbons (R−C(=O)−O−R')
1 carbon NameStructureMethyl nitrateMethyl formateWerner Reutemann and Heinz Kieczka "Formic Acid" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. Methyl acetateMerck Index, 12th Edition, 6089.Methyl acrylateMethyl propionateMethyl butyrateMethyl pentanoateMethyl benzoateMethyl anthranilateMethyl salicylateMethyl phenylacetateMethyl cinnamate
2 carbons NameStructureEthyl formateEthyl acetateEthyl propionateEthyl lactateEthyl butyrateEthyl pentanoateEthyl isovalerateEthyl hexanoateEthyl heptanoateEthyl benzoateEthyl salicylateEthyl octanoateEthyl cinnamateEthyl decanoate
3 carbons NameStructurePropyl acetatePropyl propanoatePropyl hexanoateAllyl hexanoateIsopropyl acetateIsopropyl salicylateIsopropyl palmitate
4 carbons NameStructureButyl formateButyl acetateIsobutyl formateIsobutyl acetateSec-Butyl formateSec-Butyl acetateTert-Butyl formateTert-Butyl acetateButyl butyrate
5 carbons NameStructurePentyl acetatePentyl butyratePentyl propanoatePentyl hexanoateSec-Amyl acetate
7 carbons NameStructureBenzyl acetate
8 carbons NameStructureOctyl acetate
10 carbons NameStructureGeranyl acetateBornyl acetateLinalyl acetate
By number of R group carbons (R−C(=O)−O−R')
0 carbons NameStructureMethyl nitrate
1 carbon NameStructureMethyl formateEthyl formateIsobutyl formate
2 carbons NameStructureMethyl acetateEthyl acetatePropyl acetateButyl acetateAmyl acetateBenzyl acetateOctyl acetateGeranyl acetateBornyl acetateLinalyl acetate
3 carbons NameStructureMethyl propionateEthyl propionatePropyl propanoatePentyl propanoateEthyl lactate
4 carbons NameStructureMethyl butyrateEthyl butyrateButyl butyratePentyl butyrate
5 carbons NameStructureMethyl pentanoateEthyl pentanoatePentyl pentanoateEthyl isovalerate
6 carbons NameStructureEthyl hexanoatePropyl hexanoateAllyl hexanoatePentyl hexanoate
7 carbons NameStructureEthyl heptanoateMethyl benzoateEthyl benzoateMethyl anthranilateMethyl salicylateEthyl salicylateIsopropyl salicylate
8 carbons NameStructureEthyl octanoateMethyl phenylacetate
9 carbons NameStructureMethyl cinnamateEthyl cinnamate
10 carbons NameStructureEthyl decanoate
16 carbons NameStructureIsopropyl palmitate
List of ester odorants 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.
Ester name Structure Odor or occurrence Allyl hexanoate pineapple Benzyl acetate pear, strawberry, jasmine Bornyl acetate pine Butyl acetate apple, honey Butyl butyrate pineapple Butyl propanoate pear drops Ethyl acetate nail polish remover, model paint, model airplane glue Ethyl benzoate sweet, wintergreen, fruity, medicinal, cherry, grape Ethyl butyrate banana, pineapple, strawberry Ethyl hexanoate pineapple, waxy-green banana Ethyl cinnamate cinnamon Ethyl formate lemon, rum, strawberry Ethyl heptanoate apricot, cherry, grape, raspberry Ethyl isovalerate apple Ethyl lactate butter, cream Ethyl nonanoate grape Ethyl pentanoate apple Geranyl acetate geranium Geranyl butyrate cherry Geranyl pentanoate apple Isobutyl acetate cherry, raspberry, strawberry Isobutyl formate raspberry Isoamyl acetate pear, banana (flavoring in Pear drops) Isopropyl acetate fruity Linalyl acetate lavender, sage Linalyl butyrate peach Linalyl formate apple, peach Methyl acetate glue Methyl anthranilate grape, jasmine Methyl benzoate fruity, ylang ylang, feijoa Methyl butyrate (methyl butanoate) pineapple, apple, strawberry Methyl cinnamate strawberry Methyl pentanoate (methyl valerate) flowery Methyl phenylacetate honey Methyl salicylate (oil of wintergreen) Modern root beer, wintergreen, Germolene and Ralgex ointments (UK) Nonyl caprylate orange Octyl acetate fruity-orange Octyl butyrate parsnip Amyl acetate (pentyl acetate) apple, banana Pentyl butyrate (amyl butyrate) apricot, pear, pineapple Pentyl hexanoate (amyl caproate) apple, pineapple Pentyl pentanoate (amyl valerate) apple Propyl acetate pear Propyl hexanoate blackberry, pineapple, cheese, wine Propyl isobutyrate rum Terpenyl butyrate cherry
Lactones Lactones are a specific class cyclic carboxylic esters that are formed through intramolecular esterification.
Lactone name Structure β-propiolactone γ-butyrolactone (GBL) D-glucono-δ-lactone (E575)ε-caprolactone
References