Ester

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Editor-In-Chief: Henry A. Hoff

Overview

A carboxylic acid ester. R and R' denote any alkyl or aryl group
A phosphoric acid ester

Esters are a class of chemical compounds and functional groups. Esters consist of an inorganic or organic acid in which at least one -OH (hydroxy) group is replaced by an -O-alkyl (alkoxy) group. The most common type of esters are carboxylic acid esters (R1-C(=O)-O-R2), other esters include phosphoric acid, sulfuric acid, nitric acid, and boric acid esters. Volatile esters often have a smell and are found in perfumes, essential oils, and pheromones and give many fruits their scent. Ethyl acetate and methyl acetate are important solvents, fatty acid esters form fat and lipids, and polyesters are important plastics. Cyclic esters are called lactones. The name "ester" is derived from the German Essig-Äther (literally:vinegar ether), an old name for ethyl acetate. Esters can be synthesized in a condensation reaction between an acid and an alcohol in a reaction known as esterification.

An ester is an often fragrant organic or partially organic compound formed by the reaction between an acid (including amino acids) and an alcohol (alkyl, R) or aromatic alcohol (aryl, R') (including a more basic amino acid) with the elimination of water. For examples,

acetic acid + an alcohol <=> acetic ester + water,

CH3COOH + ROH <=> CH3COOR + H2O,

or

CH3COO- + H+ + R+ + OH- <=> CH3COOR + H2O;

with one amino acid acting as a base:

formic acid + L-methionine <=> N-formyl-L-methionine (an amino acid) + H2O,

or

two amino acids:

Cys + Gly <=> Cys-Gly + H2O,

forming a dipeptide. A reaction between an inorganic hydroxide (e.g. sodium hydroxide) and an organic acid (e.g. acetic acid) produces a salt of acetic acid (sodium acetate). A compound is an ester when the hydroxide donor is organic and a salt when the hydroxide donor is inorganic. Hence, a carbonate can be thought of as a salt or an ester of carbonic acid.

Nomenclature

An ester is named according to the two parts that make it up: the part from the alcohol and the part from the acid (in that order), for example ethyl sulfuric acid ester.

Since most esters are derived from carboxylic acids, a specific nomenclature is used for them. For esters derived from the simplest carboxylic acids, the traditional name for the acid constituent is generally retained, e.g. formate, acetate, propionate, butyrate.[1] For esters from more complex carboxylic acids, the systematic name for the acid is used, followed by the suffix -oate. For example, methyl formate is the ester of methanol and methanoic acid (formic acid): the simplest ester. It could also be called methyl methanoate.[2]

Ethylethanoate.png

Esters of aromatic acids are also encountered, including benzoates such as methyl benzoate, and phthalates, with substitution allowed in the name.

The chemical formulas of esters are typically in the format of R-COO-R', in which the alkyl group (R') is mentioned first, and the carboxylate group (R) is mentioned last.[3] For example the ester: butyl ethanoate - derived from butanol (C4H9OH) and ethanoic acid (CH3COOH) would have the formula: CH3COOC4H9. Sometimes the formula may be 'broken up' to show the structure, in this case: CH3COO[CH2]3CH3.

Oligoesters

The acetic ester, N-formyl-L-methionine, and the dipeptide examples above are each monoesters.

The term oligoester refers to any ester polymer containing a small number of component esters. As an example, chemically, fats are generally diesters of glycerol and fatty acids. Most of the mass of a fat/triester is in the 3 fatty acids.

Tetraesters can be found as part of membrane-spanning lipids in bacteria from the order Thermotogales.[4]

Pentaesters have been used as indicators[5] or in isotopic labelling[6] compounds.

Hexaesters such as calix[6]arene have been used in optodes as sensing devices for optical determination of potassium ion concentration in pH-buffer solutions.[7]

Heptaesters have been found in Euphorbia species.[8]

Octaesters can be inclusions of ester moieties within cavitand cavities.[9]

The number of esters can be up to ten as in oligo-(R)-3-hydroxybutyrate[10].

Physical properties

Esters participate in hydrogen bonds as hydrogen-bond acceptors, but cannot act as hydrogen-bond donors, unlike their parent alcohols. This ability to participate in hydrogen bonding makes them more water-soluble than their parent hydrocarbons. However, the limitations on their hydrogen bonding also make them more hydrophobic than either their parent alcohols or parent acids. Their lack of hydrogen-bond-donating ability means that ester molecules cannot hydrogen-bond to each other, which makes esters generally more volatile than a carboxylic acid of similar molecular weight. This property makes them very useful in organic analytical chemistry: unknown organic acids with low volatility can often be esterified into a volatile ester, which can then be analyzed using gas chromatography, gas liquid chromatography, or mass spectrometry. Many esters have distinctive odors, which has led to their use as artificial flavorings and fragrances. For example:

Ester Name Molar Mass
(g/mol)
Structure Odor or Occurrence
Allyl hexanoate 156.22 Allyl hexanoate.png pineapple
Benzyl acetate 150.18 1 1 0 Benzyl acetate.png pear, strawberry, jasmine
Bornyl acetate 196.29 Bornylacetate.svg pine tree flavor
Butyl butyrate 144.21 2 2 0 Butyl butyrate.png pineapple
Ethyl acetate 88.12 1 3 0 Ethyl acetate.png nail polish remover, model paint, model airplane glue
Ethyl butyrate 116.16 Ethyl butyrate.png banana, pineapple, strawberry
Ethyl hexanoate 144.21 Ethyl hexanoate.png strawberry
Ethyl cinnamate 176.21 Ethyl cinnamate.png cinnamon
Ethyl formate 74.08 Ethyl methanoate.png lemon, rum, strawberry
Ethyl heptanoate 158.27 Ethyl heptanoate.png apricot, cherry, grape, raspberry
Ethyl isovalerate 130.18 Ethyl isovalerate.png apple
Ethyl lactate 118.13 1 1 0 Ethyl lactate.png butter, cream
Ethyl nonanoate 186.29 Ethyl nonanoate.png grape
Ethyl pentanoate 130.18 1 3 0 Ethyl valerate.png apple
Geranyl acetate 196.29 0 1 0 Geranyl acetate.png geranium
Geranyl butyrate 224.34 Geranyl butyrate.png cherry
Geranyl pentanoate 238.37 Geranyl pentanoate.png apple
Isobutyl acetate 116.16 1 3 0 Isobutyl acetate.png cherry, raspberry, strawberry
Isobutyl formate 102.13 Isobutyl formate.png raspberries
Isoamyl acetate 130.19 Isoamyl acetate.png pear, banana (flavoring in Pear Drops)
Isopropyl acetate 102.1 1 3 0 Isopropyl acetate.png fruity
Linalyl acetate 196.29 Linalyl acetate.png lavender, sage
Linalyl butyrate 224.34 Linalyl butyrate.png peach
Linalyl formate 182.26 Linalyl formate.png apple, peach
Methyl acetate 74.08 1 3 0 Methyl acetate.png peppermint
Methyl anthranilate 151.165 Methyl anthranilate.png grape, jasmine
Methyl benzoate 136.15 Methyl benzoate.png fruity, ylang ylang, feijoa fruit
Methyl benzyl acetate 164.20 cherry
Methyl butyrate 102.13 Methyl butyrate.png pineapple, apple
Methyl cinnamate 162.185 Methyl cinnamate .png strawberry
Methyl pentanoate 116.16 Methyl pentanoate.png flowery
Methyl phenyl acetate 150.17 Methyl phenylacetate.png honey
Methyl salicylate (oil of wintergreen) 152.1494 Salicylic acid methyl ester chemical structure.png root beer, wintergreen, Germolene™ and Ralgex™ ointments (UK)
Nonyl caprylate Nonyl caprylate.png orange
Octyl acetate 172.27 Ocyl acetate.png fruity-orange
Octyl butyrate 200.32 Octyl butyrate.png parsnip
Amyl acetate (pentyl acetate) 130.19 Amyl acetate.png apple, banana
Pentyl butyrate (amyl butyrate) 158.24 Pentyl butyrate.png apricot, pear, pineapple
Pentyl hexanoate (amyl caproate) 186.29 Pentyl hexanoate.png apple, pineapple
Pentyl pentanoate (amyl valerate) 172.15 Pentyl pentanoate.png apple
Propyl ethanoate 102.13 Propylethanoate.svg pear
Propyl isobutyrate 130.18 Propylisobutyrate.svg rum
Terpenyl butyrate cherry

Ester synthesis

"Esterification" (condensation of an alcohol and an acid) is not the only way to synthesize an ester. Esters can be prepared in the laboratory in a number of other ways:

Ester reactions

Ester saponification (basic hydrolysis)

Esters react in a number of ways:

External links

References

  1. IUPAC parent groups using traditional names
  2. IUPAC naming of esters
  3. http://www.acdlabs.com/iupac/nomenclature/93/r93_511.htm
  4. Damsté JS, Rijpstra WI, Hopmans EC, Schouten S, Balk M, Stams AJ (2007). "Structural characterization of diabolic acid-based tetraester, tetraether and mixed ether/ester, membrane-spanning lipids of bacteria from the order Thermotogales". Arch Microbiol. 188 (6): 629–41. PMID 17643227. doi:10.1007/s00203-007-0284-z. 
  5. Najafi A, Fawcett HD, Hutchison N (1986). "Sarcoplasmic reticulum interacts with the Ca(2+) indicator precursor fura-2-am". Biochem Biophys Res Commun. 138 (3): 1153–62. PMID 3755905. doi:10.1016/S0006-291X(86)80403-X. 
  6. Highsmith S, Bloebaum P, Snowdowne KW (1986). "Comparison of two methods of labeling proteins with 111In". Int J Rad Appl Instrum B. 13 (4): 345–6. PMID 3539883. 
  7. Chan WH, Lee AW, Kwong DW, Tam WL, Wang KM (1996). "Potassium ion-selective optodes based on the calix[6]arene hexaester and application in human serum assay". Analyst. 121 (4): 531–4. PMID 8633794. doi:10.1039/an9962100531. 
  8. Evanics F, Hohmann J, Rédei D, Vasas A, Günther G, Dombi G (2001). "[New diterpene polyesters isolated from Hungarian Euphorbia species] [Article in Hungarian]". Acta Pharm Hung. 71 (3): 289–92. PMID 11961895. 
  9. Dueno EE, Bisht KS (2004). "Intramolecular inclusion in novel octaester cavitands". Chem Commun (Camb). (8): 954–5. PMID 15069491. doi:10.1039/b316498e. 
  10. Xian M, Fuerst MM, Shabalin Y, Reusch RN (2007). "Sorting signal of Escherichia coli OmpA is modified by oligo-(R)-3-hydroxybutyrate". Biochim Biophys Acta. 1768 (11): 2660–6. PMID 17659252. doi:10.1016/j.bbamem.2007.06.019. 
ar:إستر

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