Ether
Ether is the general name for a class of chemical compounds which contain an ether
group an
oxygen atom connected to two
alkyl groups. A typical example is the solvent and
anesthetic diethyl ether, commonly referred to simply as "ether", .
Encyclopedia
Ether is the general name for a class of chemical compounds which contain an ether
group — an
oxygen atom connected to two
alkyl groups. A typical example is the solvent and
anesthetic diethyl ether, commonly referred to simply as "ether", .
Physical properties
Ether molecules cannot form
hydrogen bonds among each other, resulting in a relatively low boiling point comparable to that of the analogous
alkanes. Ethers are more hydrophobic than esters or
amides of comparable structure.
Ethers can act as Lewis bases. For instance, diethyl ether forms a complex with
boron compounds, such as
boron trifluoride diethyl etherate .F
3B:O
2. Ethers also coordinate to magnesium in
Grignard reagents.
Nomenclature
In the
IUPAC nomenclature system, ethers are named using the general formula
"alkoxyalkane", for example CH
3-CH
2-O-CH
3 is methoxyethane. If the ether is part of a more complex molecule, it is described as an alkoxy substituent, so -OCH
3 would be considered a
"methoxy-" group. The nomenclature of describing the two alkyl groups and appending
"ether", e.g.
"ethyl methyl ether" in the example above, is a trivial usage.
Similar structures
Ethers are not to be confused with the following classes of compounds with the same general structure R-O-R.
Furan, also known as
furane and
furfuran, is a heterocyclic [i] organic compound [i] ...
where the oxygen is part of the aromatic system.
- Compounds where one of the carbon atoms next to the oxygen is connected to oxygen, nitrogen, or sulfur:
Primary, secondary, and tertiary ethers
The terms
"primary ether",
"secondary ether", and
"tertiary ether" are occasionally used and refer to the carbon atom next to the ether oxygen. In a
primary ether this carbon is connected to only one other carbon as in diethyl ether CH
3-CH
2-O-CH
2-CH
3. An example of a
secondary ether is
diisopropyl ether 2CH-O-CH
2 and that of a
tertiary ether is
di-tert-butyl ether 3C-O-C
3.
Dimethyl ether, a primary, a secondary, and a tertiary ether.
Polyethers
Polyethers are compounds with more than one ether group. While the term generally refers to
polymers like
polyethylene glycol and
polypropylene glycol, low molecular compounds such as the
crown ethers may sometimes be included.
Organic reactions
Synthesis
Ethers can be prepared in the laboratory in several ways.
- R-OH + R-OH ? R-O-R + H2O
- This direct reaction requires drastic conditions and is usually not applicable. Such conditions can destroy the delicate structures of some functional groups. There exist several milder methods to produce ethers.
- R-O- + R-X ? R-O-R + X-
- This reaction is called the Williamson ether synthesis. It involves treatment of a parent alcohol with a strong base to form the alkoxide anion followed by addition of an appropriate aliphatic compound bearing a suitable leaving group . Suitable leaving groups include iodide, bromide, or sulfonates. This method does not work if R is aromatic like in bromobenzene. Likewise, this method only gives the best yields for primary carbons, as secondary carbons will undergo E2 elimination on exposure to the basic alkoxide anion used in the reaction. Aryl ethers can be prepared in the Ullmann condensation.
- R2C=CR2 + R-OH ? R2CH-C-R2
- Acid catalysis is required for this reaction. Tetrahydropyranyl ethers are used as protective groups for alcohols.
Cyclic ethers which are also known as
epoxides can be prepared:
- By the oxidation of alkenes with a peroxyacid such as m-CPBA
...
.
- By the base intramolecular nuclephilic substitution of a halohydrin.
Reactions
Ethers in general are of very low chemical reactivity. Organic reactions are:
- Ethers are hydrolyzed only under drastic conditions like heating with boron tribromide or boiling in hydrobromic acid. Lower mineral acids containing a halogen, such as hydrochloric acid will cleave ethers, but very slowly. Hydrobromic acid and hydroiodic acid are the only two that do so at an appreciable rate. Certain aryl ethers can be cleaved by aluminium chloride.
- Epoxides, or cyclic ethers in three-membered rings, are highly susceptible to nucleophilic attack and are reactive in this fashion.
- Primary and secondary ethers with a CH group next to the ether oxygen easily form highly explosive
...
organic peroxides in the presence of oxygen, light, and metal and
aldehyde impurities. For this reason ethers like diethyl ether and
THF are usually avoided as solvents in industrial processes.
Important ethers
- Dioxane, a cyclic ether and high boiling solvent:
- THF, a cyclic ether, one of the most polar simple ethers that is used as a solvent:
- Anisole , a major constituent of the essential oil of anise seed:
- Crown ethers, cyclic polyethers that are used as phase transfer catalysts:
See also
- Functional group
- Methoxy
- Petroleum ether, not an ether but a low boiling alkane mixture.
- Thioether, analogs of ethers with the oxygen replaced by sulfur.
- Luminiferous ether
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