ETHER THEORY

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ETHER THEORY
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Rule 1. Ethers can be named as alkoxy derivatives of alkanes (substitutive IUPAC nomenclature). The longest chain is taken as the main chain and the alkoxide is named as a substituent.

ethers nomenclature 01
 
[1] Methoxyethane
[2] Ethoxyethane
[3] 1-Methoxybutane
[4] 2-Methoxypentane
[5] 1-Ethoxy-3-methylcyclohexane
 

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ETHER THEORY
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Ethers are molecules similar in structure to water and alcohols. The angle between the C-O-C bonds is greater than in water due to steric repulsions between bulky groups.

 
eteres-estructura

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ETHER THEORY
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Ethers have lower boiling points than alcohols, although their solubility in water is similar. Given their significant stability in basic media, they are used as inert solvents in numerous reactions.

ethers physical properties 01
Diethyl ether
Boiling point = 35ºC
Water solubility = 7.5g/100ml

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ETHER THEORY
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1. Ethers from primary alcohols
Symmetrical ethers can be prepared by condensation of alcohols. The reaction is carried out under heating (140°C) and with acid catalysis. Thus, two molecules of ethanol condense to form diethyl ether.
 
eteres-condensacion-alcoholes

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ETHER THEORY
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The reaction between a primary haloalkane and an alkoxide (or alcohol in a basic medium) is the most important method for preparing ethers. This reaction is known as the Williamson synthesis.

 

sintesis-williamson
 
This reaction proceeds through the SN2 mechanism.

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ETHER THEORY
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Ethers can be obtained by reacting haloalkanes with alcohols through the S N 1 mechanism. The haloalkane must be secondary or tertiary to form stable carbocations.

synthesis ethers sn1 01

Mechanism:

synthesis ethers sn1 02

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ETHER THEORY
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Alcohols can be protected by transforming them into ethers. This process is carried out by reacting the alcohol to be protected with tert-butanol in a sulfuric acid medium. The deprotection takes place in an aqueous acid medium. Let's see an example:

ethers protecting groups 01

In this synthesis it is necessary to form a carbon-carbon bond using organometallic reagents, incompatible with alcohol. Thus, the alcohol must be previously protected to avoid the decomposition of the organometallic.

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ETHER THEORY
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Epoxides (oxacyclopropanes) are three-membered cyclic ethers. Its main characteristic is the tension of the ring, which favors its opening in both basic and acidic media.

Opening in basic media: Epoxides open by nucleophile attack on the least substituted carbon (opening is governed by steric hindrances)

epoxy opening 01