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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.
=== Esterificazione semplice ===
===Esterification of carboxylic acids with alcohols===▼
Qui trattiamo tutti i processi che si verificano tra [[alcool|alcooli]] ed acidi o anidridi.
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:
:RCO<sub>2</sub>H + R′OH {{eqm}} RCO<sub>2</sub>R′ + H<sub>2</sub>O
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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.
== Esterificazioni indirette ==
===Transesterificazioni ===
[[Transesterification]], which involves changing one ester into another one, is widely practiced:▼
: RCO<sub>2</sub>R′ + CH<sub>3</sub>OH → RCO<sub>2</sub>CH<sub>3</sub> + 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/> ▼
: (C<sub>6</sub>H<sub>4</sub>)(CO<sub>2</sub>CH<sub>3</sub>)<sub>2</sub> + 2 C<sub>2</sub>H<sub>4</sub>(OH)<sub>2</sub> → {{frac|''n''}} {(C<sub>6</sub>H<sub>4</sub>)(CO<sub>2</sub>)<sub>2</sub>(C<sub>2</sub>H<sub>4</sub>)}<sub>''n''</sub> + 2 CH<sub>3</sub>OH▼
A subset of transesterification is the alcoholysis of [[diketene]]. This reaction affords 2-ketoesters.<ref name=Ullmann/>▼
:(CH<sub>2</sub>CO)<sub>2</sub> + ROH → CH<sub>3</sub>C(O)CH<sub>2</sub>CO<sub>2</sub>R▼
=== Nitrilazioni degli alcooli ===
* [[Pinner reaction]] of [[nitrile]]s with an alcohol▼
=== Epossidazioni degli acidi ===
Carboxylic acids are esterified by treatment with epoxides, giving β-hydroxyesters:
:RCO<sub>2</sub>H + RCHCH<sub>2</sub>O → RCO<sub>2</sub>CH<sub>2</sub>CH(OH)R
This reaction is employed in the production of [[vinyl ester resin]] resins from [[acrylic acid]].
=== Alcoolisi e fenolisi degli acilalogenuri ===
Alcohols react with [[acyl chloride]]s and [[acid anhydride]]s to give esters:
: RCOCl + R′OH → RCO<sub>2</sub>R′ + HCl
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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.
=== Alchilazione dei sali ===
Although not widely employed for esterifications, salts of carboxylate anions can be alkylating agent with [[alkyl halide]]s to give esters.<ref name=Ullmann/> In the case that an [[alkyl chloride]] is used, an iodide salt can catalyze the reaction ([[Finkelstein reaction]]). The carboxylate salt is often generated ''in situ''.<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> In difficult cases, the silver carboxylate may be used, since the silver ion coordinates to the halide aiding its departure and improving the reaction rate. This reaction can suffer from anion availability problems and, therefore, can benefit from the addition of [[phase transfer catalyst]]s or highly polar [[aprotic solvent]]s such as [[Dimethylformamide|DMF]].
▲[[Transesterification]], which involves changing one ester into another one, is widely practiced:
▲: RCO<sub>2</sub>R′ + CH<sub>3</sub>OH → RCO<sub>2</sub>CH<sub>3</sub> + 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/>
▲: (C<sub>6</sub>H<sub>4</sub>)(CO<sub>2</sub>CH<sub>3</sub>)<sub>2</sub> + 2 C<sub>2</sub>H<sub>4</sub>(OH)<sub>2</sub> → {{frac|''n''}} {(C<sub>6</sub>H<sub>4</sub>)(CO<sub>2</sub>)<sub>2</sub>(C<sub>2</sub>H<sub>4</sub>)}<sub>''n''</sub> + 2 CH<sub>3</sub>OH
▲A subset of transesterification is the alcoholysis of [[diketene]]. This reaction affords 2-ketoesters.<ref name=Ullmann/>
▲:(CH<sub>2</sub>CO)<sub>2</sub> + ROH → CH<sub>3</sub>C(O)CH<sub>2</sub>CO<sub>2</sub>R
===Carbonylation===
Alkenes undergo "[[hydroesterification]]" in the presence of [[metal carbonyl]] catalysts. Esters of [[propanoic acid]] are produced commercially by this method:
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:C<sub>2</sub>H<sub>4</sub> + CH<sub>3</sub>CO<sub>2</sub>H → CH<sub>3</sub>CO<sub>2</sub>C<sub>2</sub>H<sub>5</sub>
=== Dismutazioni delle aldeidi ===
The [[Tishchenko reaction]] involve [[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/>
===
* [[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}} </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>
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