Ether




Ether is a class of diethyl ether, commonly referred to simply as "ether" (ethoxyethane, CH3-CH2-O-CH2-CH3).

Physical properties

Ether hydrophobic nature of the carbon chain becomes more predominant over the presence of hydrogen bonding.

Ethers are slightly polar as the C - O - C bond angle in the functional group is about 110 degrees, and the C - O dipole does not cancel out. Ethers are more polar than alkenes but not as polar as alcohols, esters or amides of comparable structure. However, the presence of two lone pairs of electrons on the oxygen atoms makes hydrogen bonding with water molecules possible, causing the solubility of alcohols (for instance, butan-1-ol) and ethers (ethoxyethane) to be quite dissimilar.

Cyclic ethers such as tetrahydrofuran and 1,4-dioxane are totally miscible in water because of the more exposed oxygen atom for hydrogen bonding as compared to aliphatic ethers.

Ethers can act as Lewis bases. For instance, diethyl ether forms a complex with Grignard reagents (RMgBr).

Nomenclature

In the 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 where the oxygen is part of the aromatic system.
  • Compounds where one of the carbon atoms next to the oxygen is connected to oxygen, 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 CH3-CH2-O-CH2-CH3. An example of a secondary ether is diisopropyl ether (CH3)2CH-O-CH(CH3)2 and that of a tertiary ether is di-tert-butyl ether (CH3)3C-O-C(CH3)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 crown ethers may sometimes be included.

Organic reactions

Synthesis

Ethers can be prepared in the laboratory in several different ways.

R-OH + R-OH → R-O-R + H2O
This direct reaction requires drastic conditions (heating to 140 degrees Celsius and an acid catalyst, usually concentrated sulfuric acid). Effective for making symmetrical ethers, but not as useful for synthesising asymmetrical ethers because the reaction will yield a mixture of ethers, making it usually not applicable:
3R-OH + 3R'-OH → R-O-R + R'-O-R + R'-O-R' + 3H2O
Conditions must also be controlled to avoid overheating to 170 degrees which will cause intramolecular dehydration,a reaction that yields alkenes. In addition, the alcohol must be in excess.
R-CH2-CH2(OH) → R-CH=CH2 + H2O
Such conditions can destroy the delicate structures of some functional groups. There exist several milder methods to produce ethers.
X-
This reaction is called the Ullmann condensation.
  • Nucleophilic Displacement of Alkyl halides by phenoxides
The R-X cannot be used to react with the alcohol. However, SN2 mechanism.
HO-C6H5 + OH- → O--C6H5
O--C6H5 + R-X → R-O-C6H5
R2C=CR2 + R-OH → R2CH-C(-O-R)-R2
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 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 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 solvents in industrial processes.

Important ethers

Ethylene oxide The smallest cyclic ether.
Dimethyl ether An aerosol spray propellant.
Diethyl ether A common low boiling solvent (b.p. 34.6°C).
Dimethoxyethane (DME) A high boiling solvent (b.p. 85°C):
Dioxane A cyclic ether and high boiling solvent (b.p. 101.1°C).
Tetrahydrofuran (THF) A cyclic ether, one of the most polar simple ethers that is used as a solvent.
Anisole (methoxybenzene) An aryl ether and a major constituent of the essential oil of anise seed.
Crown ethers Cyclic polyethers that are used as phase transfer catalysts.
Polyethylene glycol (PEG) A linear polyether, e.g. used in cosmetics:

See also

References

This article needs additional citations for verification.
Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (December 2007)
  1. ^ International Union of Pure and Applied Chemistry. "ethers". Compendium of Chemical Terminology Internet edition.
v • d • e
Thiol
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Ether". A list of authors is available in Wikipedia.