ESTERS THEORY

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ESTERS THEORY
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Esters come from condensing acids with alcohols and are named as salts of the acid from which they come. IUPAC nomenclature changes the -oic ending of the acid to -oate , ending with the name of the alkyl group attached to the oxygen.

esters nomenclature 1

 

[1] Methyl methanoate

[2] Methyl ethanoate

[3] Ethyl propanoate

[4] Methyl butanoate

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ESTERS THEORY
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The esters are hydrolyzed in aqueous media, under acid or base catalysis, to yield carboxylic acids and alcohols.

In acidic media, the hydrolysis of esters can be written by the following chemical equation:
 
hidrolisis-acida-esteres

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ESTERS THEORY
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The esters are hydrolyzed in aqueous media, under acid or base catalysis, to yield carboxylic acids and alcohols. Basic hydrolysis is called saponification and transforms esters into carboxylates.

 

hidrolisis-basica-esteres

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ESTERS THEORY
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Lactones are cyclic esters and hydrolyze in a manner analogous to noncyclic esters, forming compounds containing acid and alcohol groups.

Acid hydrolysis of g -butyrolactone
 
hidrolisis-lactonas

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ESTERS THEORY
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Esters react with alcohols in acidic media, replacing their alkoxy group with the corresponding alcohol, as can be seen in the following reaction. This reaction is called transesterification.

transesterificacion-acida

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ESTERS THEORY
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Esters transesterify in the presence of alkoxides, depending on the reaction:

 

transesterificacion-basica
 
Methyl ethanoate [1] reacts with sodium ethoxide to form ethyl ethanoate [2] and sodium methoxide [3]

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ESTERS THEORY
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Two equivalents of magnesium organometallic add to the ester, to form tertiary alcohols in which two substituents are the same. The mechanism consists of the nucleophilic addition of the organometallic to the carbonyl of the ester. After the first addition, a ketone is formed which is attacked again by a second equivalent of magnesium to form the final alcohol.

esteres-organometalicos

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ESTERS THEORY
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The esters are easily reduced with lithium aluminum hydride to form primary alcohols.

reduccion-esteres

The reductant supplies hydride ions to the carbonyl carbon, transforming it into alcohol.

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ESTERS THEORY
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Esters are reduced to aldehydes with diisobutylaluminum hydride (DIBAL) at -78°C. A single equivalent must be used to stop the reaction in the aldehyde, avoiding its reduction to alcohol.

reduccion-dibal

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ESTERS THEORY
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The esters have acidic hydrogens with pKa=25 in their position, which can be subtracted using bases. The conjugate base is an enolate ester, a highly nucleophilic species that attacks a varied number of electrophiles.

 
enolatos-ester

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ESTERS THEORY
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When an ester with hydrogens a is treated with an equivalent of base (alkoxide) it condenses to form a product of the family of 3-ketoesters. This type of reaction is known as a Claisen condensation.

 
condensacion-claisen
 
Ethyl ethanoate [1] condenses in the presence of an equivalent of ethoxide in ethanol followed by an acid stage, to form ethyl 3-oxobutanoate [2] (3-ketoester)