Editing Ester

{{Short description|Compound derived from an acid}}
{{Other uses}}
[[File:Ester-general.svg|130px|thumb|An ester of a [[carboxylic acid]]. R stands for any group (typically [[hydrogen]] or [[organyl]]) and R{{prime}} stands for any organyl group.]]
In [[chemistry]], an '''ester''' is a [[chemical compound|compound]] derived from an [[acid]] (either organic or inorganic) in which the [[hydrogen]] atom (H) of at least one [[acid]]ic [[hydroxyl]] group ({{chem2|\sOH}}) of that acid is replaced by an [[organyl]] group (R{{prime}}).<ref name=iupac /> These compounds contain a [[ Functional group#Groups containing oxygen |distinctive functional group]].  Analogues derived from [[oxygen]] replaced by other [[chalcogen]]s belong to the ester category as well.<ref name=iupac />  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]].<ref name=iupac>{{GoldBookRef|title=esters | file=E02219}}</ref>

[[Glycerides]] are [[fatty acid ester]]s of [[glycerol]]; they are important in biology, being one of the main classes of [[lipid]]s and comprising the bulk of [[animal fat]]s and [[vegetable oil]]s. [[Lactone]]s are cyclic carboxylic esters; naturally occurring lactones are mainly 5- and 6-membered ring lactones. Lactones contribute to the aroma of fruits, butter, cheese, [[vegetables]] like [[celery]] and other foods.

Esters can be formed from [[oxoacid]]s (e.g. esters of [[acetic acid]], [[carbonic acid]], [[sulfuric acid]], [[phosphoric acid]], [[nitric acid]], [[xanthic acid]]), but also from acids that do not contain oxygen (e.g. esters of [[thiocyanic acid]] and [[Trithiocarbonate|trithiocarbonic acid]]). An example of an ester formation is the [[substitution reaction]] between a [[carboxylic acid]] ({{chem2|R\sC(\dO)\sOH}}) and an [[Alcohol (chemistry)|alcohol]] ({{chem2|R'\sOH}}), forming an ester ({{chem2|R\sC(\dO)\sO\sR'}}), where R stands for any group (typically hydrogen or organyl) and R{{prime}} stands for organyl group.

Organyl esters of carboxylic acids typically have a pleasant smell; those of low molecular weight are commonly used as fragrances and are found in [[essential oil]]s and [[pheromone]]s. They perform as high-grade [[solvent]]s for a broad array of [[plastics]], [[plasticizer]]s, [[resin]]s, and [[lacquer]]s,<ref name="Wright1986">{{cite book|author=Cameron Wright|title=A worker's guide to solvent hazards|url=https://books.google.com/books?id=sFRZAAAAYAAJ|year=1986|publisher=The Group|page=48|isbn=9780969054542}}</ref> and are one of the largest classes of synthetic [[lubricants]] on the commercial market.<ref name="Booser1993">{{cite book|author=E. Richard Booser|title=CRC Handbook of Lubrication and Tribology, Volume III: Monitoring, Materials, Synthetic Lubricants, and Applications|url=https://books.google.com/books?id=gnOJoug5R8IC&pg=PA237|date=21 December 1993|publisher=CRC |isbn=978-1-4200-5045-5|page=237}}</ref> [[Polyester]]s are important plastics, with [[monomer]]s linked by ester [[moiety (chemistry)|moieties]]. [[Phosphoester|Esters of phosphoric acid]] form the backbone of [[DNA]] molecules. [[Nitrate ester|Esters of nitric acid]], such as [[nitroglycerin]], are known for their explosive properties.

There are compounds in which an acidic hydrogen of acids mentioned in this article are not replaced by an organyl, but by some other group. According to some authors, those compounds are esters as well, especially when the first carbon atom of the organyl group replacing acidic hydrogen, is replaced by another atom from the [[group 14 elements]] ([[Silicon|Si]], [[Germanium|Ge]], [[Tin|Sn]], [[Lead|Pb]]); for example, according to them, [[trimethylstannyl acetate]] (or trimethyltin acetate) {{chem2|CH3COOSn(CH3)3}} is a [[Organotin|trimethylstannyl]] ester of [[acetic acid]], and [[dibutyltin dilaurate]] {{chem2|(CH3(CH2)10COO)2Sn((CH2)3CH3)2}} is a [[Organotin|dibutylstannylene]] ester of [[lauric acid]], and the [[Phillips catalyst]] {{chem2|CrO2(OSi(OCH3)3)2}} is a trimethoxysilyl ester of [[chromic acid]] ({{chem2|H2CrO4}}).<ref name=pubchem1>{{cite web | url=https://pubchem.ncbi.nlm.nih.gov/compound/Acetoxytrimethyltin#section=Depositor-Supplied-Synonyms | title=Acetoxytrimethyltin}}</ref><ref name=chemspider1>{{cite web | url=http://www.chemspider.com/Chemical-Structure.21270003.html?rid=38b75d84-f570-45bc-be18-63efe88a552b#synonymsTab | title=Trimethyltin acetate {{pipe}} C5H12O2Sn {{pipe}} ChemSpider}}</ref>
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== Nomenclature ==

=== Etymology ===
The word ''ester'' was coined in 1848 by a German chemist [[Leopold Gmelin]],<ref>Leopold Gmelin, ''Handbuch der Chemie'', vol. 4: ''Handbuch der organischen Chemie'' (vol. 1) (Heidelberg, Baden (Germany): Karl Winter, 1848), [https://books.google.com/books?id=4ooMAQAAIAAJ&pg=PA182 page 182].<br />
Original text:<blockquote>{{lang|de|b. Ester oder sauerstoffsäure Aetherarten.<br />Ethers du troisième genre.<br /><br />Viele mineralische und organische Sauerstoffsäuren treten mit einer Alkohol-Art unter Ausscheidung von Wasser zu neutralen flüchtigen ätherischen Verbindungen zusammen, welche man als gepaarte Verbindungen von Alkohol und Säuren-Wasser oder, nach der Radicaltheorie, als Salze betrachten kann, in welchen eine Säure mit einem Aether verbunden ist.}}</blockquote>Translation:<blockquote>b. Ester or oxy-acid ethers.<br />Ethers of the third type.<br /><br />Many mineral and organic acids containing oxygen combine with an alcohol upon elimination of water to [form] neutral, volatile ether compounds, which one can view as coupled compounds of alcohol and acid-water, or, according to the theory of radicals, as salts in which an acid is bonded with an ether. </blockquote></ref> probably as a contraction of the German {{lang|de|Essigäther}}, "[[Ethyl acetate|acetic ether]]".

=== IUPAC nomenclature ===
{{Main|IUPAC nomenclature of organic chemistry#Esters}}
The names of esters that are formed from an alcohol and an acid, are derived from the parent alcohol and the parent acid, where the latter may be organic or inorganic. Esters derived from the simplest [[carboxylic acid]]s are commonly named according to the more traditional, so-called "[[trivial names]]" e.g. as formate, acetate, propionate, and butyrate, as opposed to the IUPAC nomenclature methanoate, ethanoate, propanoate, and butanoate. Esters derived from more complex carboxylic acids are, on the other hand, more frequently named using the systematic IUPAC name, based on the name for the acid followed by the suffix ''-oate''. For example, the ester hexyl octanoate, also known under the trivial name hexyl [[Caprylic acid|caprylate]], has the formula {{chem2|CH3(CH2)6CO2(CH2)5CH3}}.

[[Image:Butyl acetate ester example.png|thumb|[[Butyl acetate]], an ester derived from a residue of [[butanol]] ({{chem2|CH3CH2CH2CH2OH}}) (the butanol residue is [[butyl group]] {{chem2|\sCH2CH2CH2CH3}}) (right side of the picture, blue) and [[acetic acid]] {{chem2|CH3CO2H}} (left side of the picture, orange). The [[acid]]ic [[hydrogen]] atom ({{chem2|\sH}}) from acetic acid [[molecule]] is replaced by the butyl group.]]

The chemical formulas of organic esters formed from carboxylic acids and alcohols usually take the form {{chem2|RCO2R'}} or RCOOR', where R and R' are the [[organyl]] parts of the carboxylic acid and the alcohol, respectively, and R can be a [[hydrogen]] in the case of esters of [[formic acid]]. For example, [[butyl acetate]] (systematically butyl ethanoate), derived from [[n-Butanol|butanol]] and [[acetic acid]] (systematically ethanoic acid) would be written {{chem2|CH3CO2(CH2)3CH3}}. Alternative presentations are common including BuOAc and {{chem2|CH3COO(CH2)3CH3}}.

Cyclic esters are called [[lactone]]s, regardless of whether they are derived from an organic or inorganic acid. One example of an organic lactone is [[gamma-valerolactone|γ-valerolactone]].

=== Orthoesters ===
An uncommon class of esters are the [[orthoester]]s. One of them are the esters of orthocarboxylic acids. Those esters have the formula {{chem2|RC(OR′)3}}, where R stands for any group (organic or inorganic) and R{{prime}} stands for [[organyl]] group. For example, [[triethyl orthoformate]] ({{chem2|HC(OCH2CH3)3}}) is derived, in terms of its name (but not its synthesis) from [[esterification]] of [[orthoformic acid]] ({{chem2|HC(OH)3}}) with [[ethanol]].

===Esters of inorganic acids===
[[Image:Phosphate Group.svg|130px|thumb|A phosphoric acid ester, where R stands for an [[organyl]] group.]]
Esters can also be derived from inorganic acids.
*[[Perchloric acid]] forms [[perchlorate]] esters, e.g., [[methyl perchlorate]] ({{chem2|CH3\sO\sCl(\dO)3}})
*[[Sulfuric acid]] forms [[organosulfate|sulfate ester]]s, e.g., [[dimethyl sulfate]] ({{chem2|(CH3\sO\s)2S(\dO)2}}) and [[methyl bisulfate]] ({{chem2|CH3\sO\sS(\dO)2\sOH}})
*[[Nitric acid]] forms [[organic nitrate|nitrate esters]], e.g. [[methyl nitrate]] ({{chem2|CH3\sO\sNO2}}) and [[nitroglycerin]] ({{chem2|CH(\sO\sNO2)(\sCH2\sO\sNO2)2}})
*[[Phosphoric acid]] forms [[phosphate ester]]s, e.g. [[triphenyl phosphate]] ({{chem2|O\dP(\sO\sC6H5)3}}) and [[methyl dihydrogen phosphate]] ({{chem2|O\dP(\sO\sCH3)(\sOH)2}})
**[[Pyrophosphoric acid|Pyrophosphoric (diphosphoric) acid]] forms [[pyrophosphate]] esters, e.g. [[tetraethyl pyrophosphate]], [[Adenosine diphosphate|ADP]], [[dADP]], [[ADPR]], [[cADPR]], [[Cytidine diphosphate|CDP]], [[dCDP]], [[Guanosine diphosphate|GDP]], [[Deoxyguanosine diphosphate|dGDP]], [[Uridine diphosphate|UDP]], [[dTDP]], [[MEcPP]], [[HMBPP]], [[DMAPP]], [[Isopentenyl pyrophosphate|IPP]], [[Geranyl pyrophosphate|GPP]], [[Farnesyl pyrophosphate|FPP]], [[Geranylgeranyl pyrophosphate|GGPP]], [[ThDP]], [[FAD]], [[Nicotinamide adenine dinucleotide|NAD]], [[NADP]].
**[[Triphosphoric acid]] forms [[triphosphate]] esters, e.g. [[Adenosine triphosphate|ATP]], [[dATP]], [[Cytidine triphosphate|CTP]], [[dCTP]], [[Guanosine triphosphate|GTP]], [[dGTP]], [[Uridine triphosphate|UTP]], [[dTTP]], [[Inosine triphosphate|ITP]], [[Xanthosine triphosphate|XTP]], [[ThTP]], [[AThTP]].
**[[Tetraphosphoric acid]] forms tetraphosphate esters, e.g. [[hexaethyl tetraphosphate]], [[adenosine tetraphosphate]] (ATPP, Ap4), [[Ap4A]].
*[[Carbonic acid]] forms [[carbonate ester]]s, e.g. [[dimethyl carbonate]] ({{chem2|(CH3\sO\s)2C\dO}}) and 5-membered [[cyclic compound|cyclic]] [[ethylene carbonate]] ({{chem2|(\sCH2\sO\s)2C\dO}}) (if one classifies carbonic acid as an inorganic compound)
*[[Thiocarbonic acid|Trithiocarbonic acid]] forms [[thiocarbonate|trithiocarbonate ester]]s, e.g. [[dimethyl trithiocarbonate]] ({{chem2|(CH3\sS\s)2C\dS}}) (if one classifies trithiocarbonic acid as an inorganic compound)
*[[Chloroformic acid]] forms [[chloroformate]] esters, e.g. [[methyl chloroformate]] ({{chem2|Cl\sC(\dO)\sO\sCH3}}) (if one classifies chloroformic acid as an inorganic compound)
*[[Boric acid]] forms [[Borate#Borate esters|borate esters]], e.g. [[trimethyl borate]] ({{chem2|B(\sO\sCH3)3}})
*[[Chromic acid]] forms [[di-tert-butyl chromate|di-''tert''-butyl chromate]] ({{chem2|((CH3)3C\sO\s)2Cr(\dO)2}})

Inorganic acids that exist as [[tautomers]] form two or more types of esters.
*[[Thiosulfuric acid]] forms two types of [[thiosulfate]] esters, e.g. ''O'',''O''-dimethyl thiosulfate ({{chem2|(CH3\sO\s)2S(\dO)(\dS)}}) and ''O'',''S''-dimethyl thiosulfate ({{chem2|(CH3\sO\s)(CH3\sS\s)S(\dO)2}})
*[[Thiocyanic acid]] forms [[thiocyanate]] esters, e.g. [[methyl thiocyanate]] ({{chem2|CH3\sS\sC\tN}}) (if one classifies thiocyanic acid as an inorganic compound), but forms [[isothiocyanate]] "esters" as well, e.g. [[methyl isothiocyanate]] ({{chem2|CH3\sN\dC\dS}}), although [[organyl]] isothiocyanates are not classified as esters by the [[IUPAC]]
*[[Phosphorous acid]] forms two types of esters: [[phosphite ester]]s, e.g. [[triethyl phosphite]] ({{chem2|P(\sO\sCH2CH3)3}}), and [[Phosphonate|phosphonate esters]], e.g. [[diethyl phosphite|diethyl phosphonate]] ({{chem2|H\sP(\dO)(\sO\sCH2CH3)2}})

Some inorganic acids that are unstable or elusive form stable esters.
*[[Sulfurous acid]], which is unstable, forms stable [[dimethyl sulfite]] ({{chem2|(CH3\sO\s)2S\dO}})
*[[Dicarbonic acid]], which is unstable, forms stable [[dimethyl dicarbonate]] ({{chem2|CH3\sO\sC(\dO)\sO\sC(\dO)\sO\sCH3}})

In principle, a part of metal and metalloid [[alkoxide]]s, of which many hundreds are known, could be classified as esters of the corresponding acids (e.g., [[aluminium triethoxide]] ({{chem2|Al(OCH2CH3)3}}) could be classified as an ester of aluminic acid which is [[aluminium hydroxide]], [[tetraethyl orthosilicate]] ({{chem2|Si(OCH2CH3)4}}) could be classified as an ester of [[orthosilicic acid]], and [[titanium ethoxide]] ({{chem2|Ti(OCH2CH3)4}}) could be classified as an ester of [[Titanic acid|orthotitanic acid]]).

== Structure and bonding ==
Esters derived from [[carboxylic acids]] and [[alcohols]] contain a [[carbonyl]] group C=O, which is a [[divalent]] group at [[Carbon|C]] atom, which gives rise to {{not a typo|120°}} C–C–O and O–C–O angles. Unlike [[amide]]s, carboxylic acid esters are structurally flexible functional groups because rotation about the C–O–C bonds has a low barrier. Their flexibility and low polarity is manifested in their physical properties; they tend to be less rigid (lower melting point) and more volatile (lower boiling point) than the corresponding [[amides]].<ref name=March>March, J. ''Advanced Organic Chemistry'' 4th Ed. J. Wiley and Sons, 1992: New York. {{ISBN|0-471-60180-2}}.</ref> The [[acid dissociation constant|p''K''<sub>a</sub>]] of the alpha-hydrogens on esters of carboxylic acids is around 25 (alpha-hydrogen is a hydrogen bound to the carbon adjacent to the [[carbonyl group]] (C=O) of carboxylate esters).<ref>{{cite web| url=http://pharmaxchange.info/press/2011/02/chemistry-of-enolates-and-enols-acidity-of-alpha-hydrogens/| title=Chemistry of Enols and Enolates – Acidity of alpha-hydrogens| date=13 February 2011}}</ref>

Many carboxylic acid esters have the potential for [[conformational isomerism]], but they tend to adopt an ''S''-''cis'' (or ''Z'') conformation rather than the ''S''-''trans'' (or ''E'') alternative, due to a combination of [[Anomeric effect#Dipole Minimization|hyperconjugation and dipole minimization]] effects. The preference for the ''Z'' conformation is influenced by the nature of the substituents and solvent, if present.<ref>{{cite journal | author=Diwakar M. Pawar | author2=Abdelnaser A. Khalil | author3=Denise R. Hooks | author4=Kenneth Collins | author5=Tijuana Elliott | author6=Jefforey Stafford | author7=Lucille Smith | author8=Eric A. Noe | title=''E'' and ''Z'' Conformations of Esters, Thiol Esters, and Amides | journal=[[Journal of the American Chemical Society]] | year=1998 | volume=120 | issue=9 | pages=2108–2112 | doi=10.1021/ja9723848| bibcode=1998JAChS.120.2108P }}</ref><ref>{{cite journal | author=Christophe Dugave | author2=Luc Demange | title=Cis−Trans Isomerization of Organic Molecules and Biomolecules: Implications and Applications | journal=[[Chemical Reviews]] | year=2003 | volume=103 | issue=7 | pages=2475–2932 | doi=10.1021/cr0104375 | pmid=12848578}}</ref> [[Lactone]]s with small rings are restricted to the ''s''-trans (i.e. ''E'') conformation due to their cyclic structure.

[[File:Ester conformers.png|center|300px]]
[[File:PhCO2MeStructure.png|thumb|left|144px|Metrical details for [[methyl benzoate]], distances in picometers.<ref>{{cite journal|author1=A. A. Yakovenko |author2=J. H. Gallegos |author3=M. Yu. Antipin |author4=A. Masunov |author5=T. V. Timofeeva |journal=Crystal Growth & Design |year=2011 |doi=10.1021/cg200547k |volume=11 |title=Crystal Morphology as an Evidence of Supramolecular Organization in Adducts of 1,2-Bis(chloromercurio)tetrafluorobenzene with Organic Esters |issue=9 |pages=3964–3978|bibcode=2011CrGrD..11.3964Y }}</ref>]]

== Physical properties and characterization ==
Esters derived from [[carboxylic acid]]s and alcohols are more polar than [[ethers]] but less polar than alcohols. They participate in [[hydrogen bond]]s as hydrogen-bond acceptors, but cannot act as hydrogen-bond donors, unlike their parent alcohols. This ability to participate in hydrogen bonding confers some water-solubility. Because of their lack of hydrogen-bond-donating ability, esters do not self-associate. Consequently, esters are more volatile than carboxylic acids of similar molecular weight.<ref name=March/>

=== Characterization and analysis ===
Esters are generally identified by gas chromatography, taking advantage of their volatility. [[IR spectroscopy|IR spectra]] for esters feature an intense sharp band in the range 1730–1750&nbsp;cm<sup>−1</sup> assigned to ''ν''<sub>C=O</sub>. This peak changes depending on the functional groups attached to the carbonyl. For example, a benzene ring or double bond in conjunction with the carbonyl will bring the wavenumber down about 30&nbsp;cm<sup>−1</sup>.

== Applications and occurrence ==
Esters are widespread in nature and are widely used in industry. In nature, [[fat]]s are, in general, triesters derived from [[glycerol]] and [[fatty acid]]s.<ref>Isolation of triglyceride from nutmeg: G. D. Beal "Trimyristen" Organic Syntheses, Coll. Vol. 1, p.538 (1941). [http://orgsynth.org/orgsyn/pdfs/CV1P0538.pdf Link]</ref> Esters are responsible for the aroma of many fruits, including [[apple]]s, [[durian]]s, [[pear]]s, [[banana]]s, [[pineapple]]s, and [[strawberry|strawberries]].<ref>McGee, Harold. ''On Food and Cooking''. 2003, Scribner, New York.</ref> Several billion kilograms of [[polyester]]s are produced industrially annually, important products being [[polyethylene terephthalate]], [[acrylate ester]]s, and [[cellulose acetate]].<ref name=Ullmann>{{Ullmann|first1=Wilhelm|last1=Riemenschneider|first2=Hermann M.|last2=Bolt|title=Esters, Organic|doi=10.1002/14356007.a09_565.pub2}}</ref>
:[[File:Triglyceride unsaturated Structural Formulae V2.svg|thumb|450px|right|Representative [[triglyceride]] found in a linseed oil, a triester of [[glycerol|<span style="color:black;">'''glycerol'''</span>]] (center, black) derived of [[linoleic acid|<span style="color:green;">'''linoleic acid'''</span>]] (bottom right, green), [[alpha-linolenic acid|<span style="color:red;">'''alpha-linolenic acid'''</span>]] (left, red), and [[oleic acid|<span style="color:blue;">'''oleic acid'''</span>]] (top right, blue).]]

== Preparation ==
Esterification is the general name for a [[chemical reaction]] in which two reactants (typically an alcohol and an acid) form an ester as the [[product (chemistry)|reaction product]]. Esters are common in organic chemistry and biological materials, and often have a pleasant characteristic, fruity odor. This leads to their extensive use in the [[fragrance]] and [[flavoring|flavor]] industry. Ester bonds are also found in many [[polymer]]s.

===Esterification of carboxylic acids with alcohols===
The classic synthesis is the [[Fischer esterification]], which involves treating a carboxylic acid with an alcohol in the presence of a [[Dehydration reaction|dehydrating]] agent:
:{{chem2|RCO2H + R'OH ⇌ RCO2R' + H2O}}
The equilibrium constant for such reactions is about 5 for typical esters, e.g., ethyl acetate.<ref>{{cite journal | last1=Williams | first1=Roger J. | last2=Gabriel | first2=Alton | last3=Andrews | first3=Roy C. | year=1928 | title=The Relation Between the Hydrolysis Equilibrium Constant of Esters and the Strengths of the Corresponding Acids | journal=Journal of the American Chemical Society | volume=50 | issue=5| pages=1267–1271 | doi=10.1021/ja01392a005| bibcode=1928JAChS..50.1267W }}</ref> The reaction is slow in the absence of a catalyst. [[Sulfuric acid]] is a typical catalyst for this reaction. Many other acids are also used such as [[Dowex|polymeric sulfonic acids]]. Since esterification is highly reversible, the yield of the ester can be improved using [[Le Chatelier's principle]]:
* Using the alcohol in large excess (i.e., as a solvent).
* Using a dehydrating agent: sulfuric acid not only catalyzes the reaction but sequesters water (a reaction product). Other drying agents such as [[molecular sieves]] are also effective.
* Removal of water by physical means such as [[distillation]] as a low-boiling [[azeotrope]] with [[toluene]], in conjunction with a [[Dean-Stark apparatus]].

Reagents are known that drive the dehydration of mixtures of alcohols and carboxylic acids. One example is the [[Steglich esterification]], which is a method of forming esters under mild conditions. The method is popular in [[peptide synthesis]], where the substrates are sensitive to harsh conditions like high heat. DCC ([[dicyclohexylcarbodiimide]]) is used to activate the carboxylic acid to further reaction. [[4-Dimethylaminopyridine]] (DMAP) is used as an acyl-transfer [[catalyst]].<ref>{{OrgSynth | author=B. Neises | author2=W. Steglich |name-list-style=amp | title=Esterification of Carboxylic Acids with Dicyclohexylcarbodiimide/4-Dimethylaminopyridine: ''tert''-Butyl ethyl fumarate | collvol=7 | collvolpages=93 | prep=cv7p0093}}</ref>
:[[File:Steglich-1.svg|300px]]

Another method for the dehydration of mixtures of alcohols and carboxylic acids is the [[Mitsunobu reaction]]:
:{{chem2|RCO2H + R'OH + P(C6H5)3 + R2N2 → RCO2R' + OP(C6H5)3 + R2N2H2}}

Carboxylic acids can be esterified using [[diazomethane]]:
:{{chem2|RCO2H + CH2N2 → RCO2CH3 + N2}}
Using this diazomethane, mixtures of carboxylic acids can be converted to their methyl esters in near quantitative yields, e.g., for analysis by [[gas chromatography]]. The method is useful in specialized organic synthetic operations but is considered too hazardous and expensive for large-scale applications.

===Esterification of carboxylic acids with epoxides===
Carboxylic acids are esterified by treatment with [[epoxides]], giving β-hydroxyesters:
:{{chem2|RCO2H + RCHCH2O → RCO2CH2CH(OH)R}}
This reaction is employed in the production of [[vinyl ester resin]] from [[acrylic acid]].

=== Alcoholysis of acyl chlorides and acid anhydrides ===
Alcohols react with [[acyl chloride]]s and [[acid anhydride]]s to give esters:
:{{chem2|RCOCl + R'OH → RCO2R' + HCl}}
:{{chem2|(RCO)2O + R'OH → RCO2R' + RCO2H}}

The reactions are irreversible simplifying [[work-up (chemistry)|work-up]]. Since acyl chlorides and acid anhydrides also react with water, anhydrous conditions are preferred. The analogous acylations of amines to give [[amide]]s are less sensitive because amines are stronger [[nucleophile]]s and react more rapidly than does water. This method is employed only for laboratory-scale procedures, as it is expensive.

===Alkylation of carboxylic acids and their salts===
[[Trimethyloxonium tetrafluoroborate]] can be used for [[esterification]] of carboxylic acids under conditions where acid-catalyzed reactions are infeasible:<ref>{{cite journal 
|first1=Douglas J.|last1=Raber|first2=Patrick |last2=Gariano, Jr|first3=Albert O. |last3=Brod|first4=Anne L. |last4=Gariano|first5=Wayne C.|last5=Guida|doi=10.15227/orgsyn.056.0059 |title=Esterification of Carboxylic Acids with Trialkyloxonium Salts: Ethyl and Methyl 4-Acetoxybenzoates |journal=Organic Syntheses |date=1977 |volume=56 |page=59}}</ref>
:{{chem2|RCO2H + (CH3)3OBF4 -> RCO2CH3 + (CH3)2O + HBF4}}
Although rarely employed for esterifications, carboxylate salts (often generated ''in situ'') react with [[electrophilic]] [[alkylating agent]]s, such as [[alkyl halide]]s, to give esters.<ref name=Ullmann/><ref>{{Cite journal|last1=Matsumoto|first1=Kouichi|last2=Shimazaki|first2=Hayato|last3=Miyamoto|first3=Yu|last4=Shimada|first4=Kazuaki|last5=Haga|first5=Fumi|last6=Yamada|first6=Yuki|last7=Miyazawa|first7=Hirotsugu|last8=Nishiwaki|first8=Keiji|last9=Kashimura|first9=Shigenori|date=2014|title=Simple and Convenient Synthesis of Esters from Carboxylic Acids and Alkyl Halides Using Tetrabutylammonium Fluoride|url=http://jlc.jst.go.jp/DN/JST.JSTAGE/jos/ess13199?lang=en&from=CrossRef&type=abstract|journal=Journal of Oleo Science|language=en|volume=63|issue=5|pages=539–544|doi=10.5650/jos.ess13199|pmid=24770480|issn=1345-8957|doi-access=free}}</ref> Anion availability can inhibit this reaction, which correspondingly benefits from [[phase transfer catalyst]]s or such highly polar [[aprotic solvent]]s as [[Dimethylformamide|DMF]]. An additional iodide salt may, via the [[Finkelstein reaction]], catalyze the reaction of a recalcitrant alkyl halide. Alternatively, salts of a coordinating metal, such as silver, may improve the reaction rate by easing halide elimination.

===Transesterification===
[[Transesterification]], which involves changing one ester into another one, is widely practiced:
:{{chem2|RCO2R' + CH3OH → RCO2CH3 + R'OH}}
Like the hydrolysation, transesterification is catalysed by acids and bases. The reaction is widely used for degrading [[triglyceride]]s, e.g. in the production of fatty acid esters and alcohols. [[Poly(ethylene terephthalate)]] is produced by the transesterification of [[dimethyl terephthalate]] and ethylene glycol:<ref name=Ullmann/> 
:{{chem2|''n'' (C6H4)(CO2CH3)2 + 2''n'' C2H4(OH)2 → [(C6H4)(CO2)2(C2H4)]_{''n''} + 2''n'' CH3OH}}

A subset of transesterification is the alcoholysis of [[diketene]]. This reaction affords 2-ketoesters.<ref name=Ullmann/>
:{{chem2|(CH2CO)2 + ROH → CH3C(O)CH2CO2R}}

===Carbonylation===
Alkenes undergo [[carboalkoxylation]] in the presence of [[metal carbonyl]] catalysts. Esters of [[propanoic acid]] are produced commercially by this method:
:{{chem2|H2C\dCH2 + ROH + CO → CH3CH2CO2R}}
A preparation of [[methyl propionate]] is one illustrative example. 
:{{chem2|H2C\dCH2 + CO + CH3OH → CH3CH2CO2CH3}}

The carbonylation of [[methanol]] yields [[methyl formate]], which is the main commercial source of [[formic acid]]. The reaction is catalyzed by [[sodium methoxide]]:
:{{chem2|CH3OH + CO → HCO2CH3}}

===Addition of carboxylic acids to alkenes and alkynes===
In [[hydroesterification]], alkenes and alkynes insert into the {{chem2|O\sH}} bond of carboxylic acids. [[Vinyl acetate]] is produced industrially by the addition of acetic acid to [[acetylene]] in the presence of [[zinc acetate]] catalysts:<ref>{{Ullmann|doi=10.1002/14356007.a27_419.pub2|title=Vinyl Esters |year=2019 |last1=Bienewald |first1=Frank |last2=Leibold |first2=Edgar |last3=Tužina |first3=Pavel |last4=Roscher |first4=Günter |pages=1–16 |isbn=9783527303854}}</ref>
:{{chem2|HC\tCH + CH3CO2H → CH3CO2CH\dCH2}}

[[Vinyl acetate]] can also be produced by [[palladium]]-catalyzed reaction of ethylene, [[acetic acid]], and [[oxygen]]:
:{{chem2|2 H2C\dCH2 + 2 CH3CO2H + O2 → 2 CH3CO2CH\dCH2 + 2 H2O}}

[[Silicotungstic acid]] is used to manufacture [[ethyl acetate]] by the [[alkylation]] of [[acetic acid]] by ethylene:
:{{chem2|H2C\dCH2 + CH3CO2H → CH3CO2CH2CH3}}

===From aldehydes===
The [[Tishchenko reaction]] involves [[disproportionation]] of an [[aldehyde]] in the presence of an anhydrous base to give an ester. [[Catalyst]]s are aluminium alkoxides or sodium alkoxides. [[Benzaldehyde]] reacts with sodium benzyloxide (generated from [[sodium]] and [[benzyl alcohol]]) to generate [[benzyl benzoate]].<ref name="kamm">{{OrgSynth | last1=Kamm | first1=O. | last2=Kamm | first2=W. F. | title=Benzyl benzoate | collvol=1 | collvolpages=104 | year=1922 | volume=2 | pages=5 | doi=10.15227/orgsyn.002.0005 | prep=cv1p0104}}</ref> The method is used in the production of [[ethyl acetate]] from [[acetaldehyde]].<ref name=Ullmann/>

=== Other methods ===
* [[Favorskii rearrangement]] of α-haloketones in presence of base
* [[Baeyer–Villiger oxidation]] of ketones with peroxides
* [[Pinner reaction]] of [[nitrile]]s with an alcohol
* [[Nucleophilic abstraction]] of a metal–acyl complex
*Hydrolysis of [[orthoesters]] in aqueous acid
*Cellulolysis via esterification<ref name="Synthesis of glucose esters from cellulose in ionic liquids">{{cite journal|last=Ignatyev|first=Igor|author2=Charlie Van Doorslaer |author3=Pascal G.N. Mertens |author4=Koen Binnemans |author5=Dirk. E. de Vos |journal=Holzforschung|year=2011|volume=66|issue=4|pages=417–425|title=Synthesis of glucose esters from cellulose in ionic liquids|doi=10.1515/hf.2011.161|s2cid=101737591|url=http://www.degruyter.com/view/j/hfsg.2012.66.issue-4/hf.2011.161/hf.2011.161.xml|url-access=subscription}}</ref>
* [[Ozonolysis]] of [[alkene]]s using a [[Work-up (chemistry)|work up]] in the presence of [[hydrochloric acid]] and various [[alcohols]].<ref>{{cite journal|last1=Neumeister|first1=Joachim|last2=Keul|first2=Helmut|last3=Pratap Saxena|first3=Mahendra|last4=Griesbaum|first4=Karl|title=Ozone Cleavage of Olefins with Formation of Ester Fragments|journal=Angewandte Chemie International Edition in English|date=1978|volume=17|issue=12|pages=939–940|doi=10.1002/anie.197809392}}</ref>
* [[Electrosynthesis#Anodic oxidations|Anodic oxidation]] of [[Methyl group|methyl]] [[ketones]] leading to methyl esters.<ref>{{cite journal|last1=Makhova|first1=Irina V.|last2=Elinson|first2=Michail N.|last3=Nikishin|first3=Gennady I.|title=Electrochemical oxidation of ketones in methanol in the presence of alkali metal bromides|journal=Tetrahedron|date=1991|volume=47|issue=4–5|pages=895–905|doi=10.1016/S0040-4020(01)87078-2}}</ref>
* [[Fat interesterification|Interesterification]] exchanges the fatty acid groups of different esters.

== Reactions ==
Esters are less reactive than acid halides and anhydrides. As with more reactive acyl derivatives, they can react with [[ammonia]] and primary and secondary amines to give amides, although this type of reaction is not often used, since acid halides give better yields. 

===Transesterification===
Esters can be converted to other esters in a process known as [[transesterification]]. Transesterification can be either acid- or base-catalyzed, and involves the reaction of an ester with an alcohol. Unfortunately, because the leaving group is also an alcohol, the forward and reverse reactions will often occur at similar rates. Using a large excess of the [[reactant]] alcohol or removing the leaving group alcohol (e.g. via [[distillation]]) will drive the forward reaction towards completion, in accordance with [[Le Chatelier's principle]].<ref name=wade>Wade 2010, pp. 1005–1009.</ref>

===Hydrolysis and saponification===
{{Main|Ester hydrolysis}}
Acid-catalyzed hydrolysis of esters is also an equilibrium process – essentially the reverse of the [[Fischer esterification]] reaction. Because an alcohol (which acts as the leaving group) and water (which acts as the nucleophile) have similar p''K''<sub>a</sub> values, the forward and reverse reactions compete with each other. As in transesterification, using a large excess of reactant (water) or removing one of the products (the alcohol) can promote the forward reaction.

[[File:Fischer esterification-hydrolysis equilibrium.svg|center|The acid-catalyzed hydrolysis of an ester and Fischer esterification correspond to two directions of an equilibrium process.]]

Basic hydrolysis of esters, known as [[saponification]], is not an equilibrium process; a full equivalent of base is consumed in the reaction, which produces one equivalent of alcohol and one equivalent of a carboxylate salt. The saponification of esters of [[fatty acid]]s is an industrially important process, used in the production of soap.<ref name=wade />

Esterification is a reversible reaction. Esters undergo [[hydrolysis]] under acidic and basic conditions. Under acidic conditions, the reaction is the reverse reaction of the [[Fischer esterification]]. Under basic conditions, [[hydroxide]] acts as a nucleophile, while an alkoxide is the leaving group. This reaction, [[saponification]], is the basis of soap making.
:[[Image:Ester hydrolysis.svg|750px|Ester saponification (basic hydrolysis)]]

The alkoxide group may also be displaced by stronger nucleophiles such as [[ammonia]] or primary or secondary [[amine]]s to give [[amide]]s (ammonolysis reaction):
:{{chem2|RCO2R' + NH2R{{''}} → RCONHR{{''}} + R'OH}}
This reaction is not usually reversible. Hydrazines and hydroxylamine can be used in place of amines. Esters can be converted to [[isocyanate]]s through intermediate [[hydroxamic acid]]s in the [[Lossen rearrangement]].

Sources of carbon nucleophiles, e.g., [[Grignard reagent]]s and organolithium compounds, add readily to the carbonyl.

=== Reduction ===
Compared to ketones and aldehydes, esters are [[Carbonyl reduction#Trends in carbonyl reactivity|relatively resistant to reduction]]. The introduction of catalytic hydrogenation in the early part of the 20th century was a breakthrough; esters of fatty acids are hydrogenated to [[fatty alcohol]]s.
:{{chem2|RCO2R' + 2 H2 → RCH2OH + R'OH}}
A typical catalyst is [[copper chromite]]. Prior to the development of [[catalytic hydrogenation]], esters were reduced on a large scale using the [[Bouveault–Blanc reduction]]. This method, which is largely obsolete, uses sodium in the presence of proton sources.

Especially for fine chemical syntheses, [[lithium aluminium hydride]] is used to reduce esters to two primary alcohols. The related reagent [[sodium borohydride]] is slow in this reaction. [[DIBAH]] reduces esters to aldehydes.<ref>{{cite web | author=W. Reusch | title=Carboxyl Derivative Reactivity | url=http://www.cem.msu.edu/~reusch/VirtualText/crbacid2.htm#react2 | work=Virtual Textbook of Organic Chemistry | url-status=dead | archive-url=http://arquivo.pt/wayback/20160516073829/http://www.cem.msu.edu/~reusch/VirtualText/crbacid2.htm#react2 | archive-date=2016-05-16}}</ref>

Direct reduction to give the corresponding [[ether]] is difficult as the intermediate [[hemiacetal]] tends to decompose to give an alcohol and an aldehyde (which is rapidly reduced to give a second alcohol). The reaction can be achieved using [[triethylsilane]] with a variety of Lewis acids.<ref>{{cite journal|last1=Yato|first1=Michihisa|last2=Homma|first2=Koichi|last3=Ishida|first3=Akihiko|title=Reduction of carboxylic esters to ethers with triethyl silane in the combined use of titanium tetrachloride and trimethylsilyl trifluoromethanesulfonate|journal=Tetrahedron|date=June 2001|volume=57|issue=25|pages=5353–5359|doi=10.1016/S0040-4020(01)00420-3}}</ref><ref>{{cite journal|last1=Sakai|first1=Norio|last2=Moriya|first2=Toshimitsu|last3=Konakahara|first3=Takeo|title=An Efficient One-Pot Synthesis of Unsymmetrical Ethers: A Directly Reductive Deoxygenation of Esters Using an InBr3/Et3SiH Catalytic System|journal=The Journal of Organic Chemistry|date=July 2007|volume=72|issue=15|pages=5920–5922|doi=10.1021/jo070814z|pmid=17602594}}</ref>

=== Claisen condensation and related reactions ===
Esters can undergo a variety of reactions with carbon nucleophiles. They react with an excess of a Grignard reagent to give tertiary alcohols. Esters also react readily with [[enolate]]s. In the [[Claisen condensation]], an enolate of one ester ('''1''') will attack the carbonyl group of another ester ('''2''') to give tetrahedral intermediate '''3'''. The intermediate collapses, forcing out an alkoxide (R'O<sup>−</sup>) and producing β-keto ester '''4'''.

[[File:Claisen condensation - general mechanism.svg|center|The Claisen condensation involves the reaction of an ester enolate and an ester to form a beta-keto ester.]]

Crossed Claisen condensations, in which the enolate and nucleophile are different esters, are also possible. An [[Intramolecular reaction|intramolecular]] Claisen condensation is called a [[Dieckmann condensation]] or Dieckmann cyclization, since it can be used to form rings. Esters can also undergo condensations with ketone and aldehyde enolates to give β-dicarbonyl compounds.<ref>Carey 2006, pp. 919–924.</ref> A specific example of this is the [[Baker–Venkataraman rearrangement]], in which an aromatic ''ortho''-acyloxy ketone undergoes an intramolecular nucleophilic acyl substitution and subsequent rearrangement to form an aromatic β-diketone.<ref>Kürti and Czakó 2005, p. 30.</ref> The [[Chan rearrangement]] is another example of a rearrangement resulting from an intramolecular nucleophilic acyl substitution reaction.

===Other ester reactivities===
Esters react with nucleophiles at the carbonyl carbon.<ref>{{March6th|page=1453}}</ref> The carbonyl is weakly electrophilic but is attacked by strong nucleophiles (amines, alkoxides, hydride sources, organolithium compounds, etc.). The C–H bonds adjacent to the carbonyl are weakly acidic but undergo deprotonation with strong bases. This process is the one that usually initiates condensation reactions. The carbonyl oxygen in esters is weakly basic, less so than the carbonyl oxygen in amides due to resonance donation of an electron pair from nitrogen in amides, but forms [[adduct]]s.

As for [[aldehydes]], the hydrogen atoms on the carbon adjacent ("α to") the carboxyl group in esters are sufficiently acidic to undergo deprotonation, which in turn leads to a variety of useful reactions. Deprotonation requires relatively strong bases, such as [[alkoxide]]s. Deprotonation gives a nucleophilic [[enolate]], which can further react, e.g., the [[Claisen condensation]] and its intramolecular equivalent, the [[Dieckmann condensation]]. This conversion is exploited in the [[malonic ester synthesis]], wherein the diester of [[malonic acid]] reacts with an electrophile (e.g., [[alkyl halide]]), and is subsequently decarboxylated. Another variation is the [[Fráter–Seebach alkylation]].

=== Other reactions ===
{{refimprove section|date = September 2024}}
* Esters can be directly converted to [[nitriles]].<ref>{{Cite journal | doi=10.1016/S0040-4039(01)86746-0| title=A direct conversion of esters to nitriles| journal=Tetrahedron Letters| volume=20| issue=51| pages=4907| year=1979| last1=Wood | first1=J. L. | last2=Khatri | first2=N. A. | last3=Weinreb | first3=S. M.}}</ref>{{primary source inline|date = September 2024}}
* Methyl esters are often susceptible to decarboxylation in the [[Krapcho decarboxylation]].
* Phenyl esters react to hydroxyarylketones in the [[Fries rearrangement]].
* Specific esters are functionalized with an α-hydroxyl group in the [[Chan rearrangement]].
* Esters with β-hydrogen atoms can be converted to alkenes in [[ester pyrolysis]].
* Pairs of esters are coupled to give [[Alpha-hydroxy ketone|α-hydroxyketones]] in the [[acyloin condensation]].

=== Protecting groups ===
As a class, esters serve as [[protecting group]]s for [[carboxylic acid]]s. Protecting a carboxylic acid is useful in peptide synthesis, to prevent self-reactions of the bifunctional [[amino acid]]s. Methyl and ethyl esters are commonly available for many amino acids; the ''t''-butyl ester tends to be more expensive. However, ''t''-butyl esters are particularly useful because, under strongly acidic conditions, the ''t''-butyl esters undergo elimination to give the carboxylic acid and [[isobutylene]], simplifying work-up.

== List of ester odorants ==
Many esters have distinctive fruit-like odors, and many occur naturally in the essential oils of plants. This has also led to their common use in artificial flavorings and fragrances which aim to mimic those odors.<ref>{{cite book |doi=10.1002/14356007.t11_t01 |chapter=Flavors and Fragrances, 2. Aliphatic Compounds |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2015 |last1=Panten |first1=Johannes |last2=Surburg |first2=Horst |pages=1–55 |isbn=978-3-527-30673-2 }}</ref>

{|class="wikitable"
|-
!valign="top" align="left"|Acetate ester
!valign="top" align="left"|Structure
!valign="top" align="left"|Odor or occurrence
|-
|[[Methyl acetate]]
|[[File:Methyl-acetate-2D-skeletal.svg|75px]]
|[[glue]]
|-
|[[Ethyl acetate]]
|[[File:Ethyl-acetate-2D-skeletal.svg|75px]]
|[[nail polish remover]], [[scale model|model]] [[paint]], [[model aircraft|model airplane]] [[adhesive|glue]], [[pears]]
|-
|[[Propyl acetate]]
|[[File:Propyl acetate.svg|75px]]
|[[pear]]
|-
|[[Isopropyl acetate]] 
|[[File:Isopropyl acetate.svg|75px]]
|fruity
|-
|[[Butyl acetate]]
|[[File:Butylacetat.svg|75px]]
| [[apple]], [[honey]]
|-
|[[Isobutyl acetate]]
|[[File:Isobutyl-acetate.svg|75px]]
|[[cherry]], [[raspberry]], [[strawberry]]
|-
|[[Amyl acetate]] (pentyl acetate)
|[[File:Amyl acetate.svg|75px]]
|[[apple]], [[banana]]
|-
|[[Isoamyl acetate]]
|[[File:Isoamyl acetate.svg|75px]]
|[[pear]], [[banana]] (main component of banana essence) (flavoring in [[Pear drop]]s)
|-
|[[hexyl acetate]]
|[[File:Octyl acetate.svg|75px]]
| pear-like
|-
|[[2-Hexenyl acetate]]
|
|fruity, both cis and trans are used, sometimes individually
|-
|[[3,5,5-Trimethylhexyl acetate]]
|
| woody
|-
|[[Octyl acetate]]
|[[File:Octyl acetate.svg|75px]]
|fruity-[[orange (fruit)|orange]]
|-
|[[Benzyl acetate]]
|[[File:Benzyl acetate-structure.svg|75px]]
|[[pear]], [[strawberry]], [[jasmine]]
|-
|[[Bornyl acetate]]
|[[File:Bornyl acetate.svg|75px]]
|[[pine]] (see also [[isobornyl acetate]])
|-
|[[Geranyl acetate]]
|[[File:Geranyl-acetate.svg|75px]]
|[[Pelargonium|geranium]]
|-
|[[menthyl acetate]]
|
|peppermint
|-
|[[Linalyl acetate]]
|[[File:Linalyl acetate.svg|75px]]
|[[lavender]], [[Common sage|sage]]
|-
|}
{|class="wikitable"
|-
!valign="top" align="left"|Formate esters
!valign="top" align="left"|Structure
!valign="top" align="left"|Odor or occurrence
|-
|[[Isobutyl formate]]
|[[File:Isobutyl formate.svg|75px]]
|[[raspberry]]
|-
|[[Linalyl formate]]
|[[File:Linalyl formate.svg|75px]]
|[[apple]], [[peach]]
|-
|[[Isoamyl formate]]
|[[File:Isoamyl formate.svg|75px]]
|[[plum]], [[blackcurrant]]
|-
|[[Ethyl formate]]
|[[File:Ethyl formate Structural Formulae.svg|75x75px]]
|[[lemon]], [[rum]], [[strawberry]]
<!-- REF?|-
|[[Ethyl lactate]] 
|[[File:Ethyl lactate.svg|75px]]
|[[butter]], [[cream]]-->
|-
|[[Methyl formate]]
|[[File:Methyl formate.png|75px]]
|pleasant, [[Diethyl ether|ethereal]], [[rum]], sweet
|}
{|class="wikitable"
|-
!valign="top" align="left"|Propionate, butyrate, and isobutyrate esters
!valign="top" align="left"|Structure
!valign="top" align="left"|Odor or occurrence
|-
|[[Butyl propionate]]
|[[File:Butyl propionate.png|75px]]
|[[pear drops]], [[apple]], rare example of a propionate odorant
|-
|[[Methyl butyrate]]
|[[File:Buttersauremethylester.svg|75px]]
|[[pineapple]], [[apple]], [[strawberry]]
|-
|[[Ethyl butyrate]]
|[[File:Ethyl butyrate2.svg|75px]]
|[[banana]], [[pineapple]], [[strawberry]], perfumes
|-
|[[Propyl isobutyrate]]
|[[File:Propyl isobutyrate.svg|75px]]
|[[rum]]
|-
|[[Butyl butyrate]]
|[[File:Butyl butyrate2.svg|75px]]
|[[pineapple]], honey
|-
|[[Isoamy butyrate]]
|
|banana
|-
|[[hexyl butyrate]]
|
|[[fruit]]s
|-
|[[Ethyl isobutyrate]]
|
|blueberries, used in alcoholic drinks
|-
|[[Linalyl butyrate]]
|[[File:Linalyl butyrate.svg|75px]]
|[[peach]]
|-
|[[Geranyl butyrate]]
|[[File:Geranyl butyrate.svg|75px]]
|[[cherry]]
|-
|[[Terpinyl butyrate]]
|[[File:Terpenyl butyrate.svg|75px]]
|[[cherry]]
|}

{|class="wikitable"
|-
!valign="top" align="left"|C5-C9 aliphatic esters
!valign="top" align="left"|Structure
!valign="top" align="left"|Odor or occurrence
|-
|[[Methyl pentanoate]] (methyl valerate)
|[[File:Methyl pentanoate.svg|75px]]
|[[flower]]y
|-
|[[Ethyl isovalerate]]
|[[File:Ethyl isovalerate structure.svg|75px]]
|[[fruity]], used in alcoholic drinks
|-
|[[Geranyl pentanoate]]
|[[File:Geranyl pentanoate.svg|75px]]
|[[apple]]
|-
|[[Pentyl pentanoate]] (amyl valerate)
|[[File:Pentyl pentanoate.svg|75px]]
|[[apple]]
|-
|[[Propyl hexanoate]]
|[[File:Propyl-hexanoate.svg|75px]]
|[[blackberry]], [[pineapple]]
|-
|[[Ethyl heptanoate]]
|[[File:Ethyl-heptanoate.svg|75px]]
|[[apricot]], [[cherry]], [[grape]], [[raspberry]], used in alcoholic drinks
|-
|[[Pentyl hexanoate]] (amyl caproate)
|[[File:Pentyl hexanoate.svg|75px]]
|[[apple]], [[pineapple]]
|-
|[[Allyl hexanoate]] 
|[[File:Prop-2-enyl hexanoate.svg|75px]]
|[[pineapple]]
|-
|[[Ethyl hexanoate]] 
|[[File:Ethyl-hexanoate.svg|75px]]
|[[pineapple]], [[waxy-green banana]]
|-
|[[Ethyl nonanoate]]
|[[File:Ethyl-nonanoate-2D-skeletal.svg|75px]]
|[[grape]]
|-
|[[Nonyl caprylate]]
|[[File:Nonyl caprylate.svg|75px]]
|[[orange (fruit)|orange]]
|-
|}
{|class="wikitable"
|-
!valign="top" align="left"|Esters of aromatic acids
!valign="top" align="left"|Structure
!valign="top" align="left"|Odor or occurrence
|-
|[[Ethyl benzoate]]
|[[File:Ethyl benzoate.svg|75px]]
|[[sweet]], [[wintergreen]], [[fruit]]y, medicinal, [[cherry]], [[grape]]
|-
|[[Ethyl cinnamate]]
|[[File:Ethyl-cinnamate.svg|75px]]
|[[cinnamon]]
|-
|[[Methyl cinnamate]]
|[[File:methyl cinnamate.svg|75px]]
|[[strawberry]]
|-
|[[Methyl phenylacetate]]
|[[File:Methyl phenylacetate.svg|75px]]
|[[honey]]
|-
|[[Methyl salicylate]] (oil of wintergreen)
|[[File:Methyl salicylate.svg|75px]]
|Modern [[root beer]], [[wintergreen]], [[Germolene]] and [[Ralgex]] ointments (UK)
|-
|}

==See also==
{{Too many see alsos|date=April 2025}}
* [[List of esters]]
* [[Amide]]
* [[Thioamide]]
* [[Carboximidate]]
* [[Carbamate]]
* [[Xanthate]]
* [[Amidine]]
* [[Cyanate]]
* [[Thiocyanate]]
* [[Organic selenocyanates|Selenocyanate]]
* [[Polyester]], [[plastics]] made of [[polymer]]ic ester
* [[Oligoester]], a polymeric ester made of small number of ester [[monomer]]s
* [[Polyolester]], an ester that is a [[synthetic oil]] used in refrigeration [[compressors]]
* [[Thioester]]
* [[Transesterification]]
* [[Ether lipid]], an ester that is a [[lipid]] and an [[ether]]
* [[Acylal]] ({{chem2|(R^{1}\sC(\dO)\sO\s)(R^{2}\sC(\dO)\sO\s)CH\sR^{3}|}})
* [[Ortho ester]], an ester of an [[ortho acid]] (e.g. esters of [[Ortho ester|orthocarboxylic acid]]s, [[orthocarbonic acid]], [[orthosilicic acid]], [[orthotelluric acid]], [[orthophosphoric acid]], [[orthoboric acid]], ...)
* [[Depside]], a polymeric ester, a type of [[polyphenol]]ic compound composed of two or more monocyclic [[Aromaticity|aromatic]] units linked by an ester group
* [[Depsipeptide]], a type of ester that is a [[peptide]] in which one or more of its [[amide]] groups ({{chem2|\sC(\dO)\sNH\s}}) are replaced by the corresponding ester groups ({{chem2|\sC(\dO)\sO\s}})<ref name="GoldBookRef">{{GoldBookRef|title=depsipeptides|file=D01604}}</ref>
* [[Glyceride]] ({{chem2|(R^{1}\sC(\dO)\sO\sCH2\s)(R^{2}\sC(\dO)\sO\sCH2\s)(R^{3}\sC(\dO)\sO\s)CH}}), an ester of [[fatty acids]] and [[glycerol]]
* [[Lactone]], a cyclic carboxylic ester
* [[Lactide]], a type of lactone ester
* [[Vitamin C]] (ascorbic acid), a lactone ester, an [[Nutrient#Essential nutrients|essential nutrient]] for humans and other animals
* [[Phthalide]], a type of lactone ester
* [[Coumarin]], a type of lactone ester
* [[Macrolide]], a class of natural esters that consist of a large [[macrocycle|macrocyclic]] lactone ring to which one or more [[deoxy sugar]]s may be attached
* [[Formate]]
* [[Chloroformate]]

== References ==
{{reflist|30em}}

== External links ==
{{wikiquote}}
* [http://www.chemguide.co.uk/organicprops/esters/background.html An introduction to esters]
* [http://www.chm.bris.ac.uk/motm/ethylacetate/ethylh.htm Molecule of the month: Ethyl acetate and other esters]

{{Functional Groups}}
{{Authority control}}

[[Category:Functional groups]]
[[Category:Esters| ]]