- This article is about ether as a general class of chemical compounds. For other meanings, see Ether (disambiguation)
Ether is the general name for a class of chemical compounds which contain an ether group — an oxygen atom connected to two (substituted) alkyl groups. A typical example is the solvent diethyl ether (ethoxyethane, CH3-CH2-O-CH2-CH3).
Ethers are not to be confused with the following classes of compounds with the same general structure R-O-R.
Aromatic compounds like furan where the oxygen is part of the aromatic system.
- Compounds where the carbon atom next to the ether 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 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 are polymeric compounds with more than one ether group. Examples are the polymers of ethylene oxide like the crown ethers and polyethylene glycol.
R-OH + R-OH → R-O-R + H2O
- This direct reaction requires drastic conditions and is usually not applicable. There exist several milder methods to produce ethers.
R-O- + R-X → R-O-R + X-
This is called 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 (R-L). Suitable leaving groups (L) include iodide, bromide, or sulfonates. This method does not work if R is aromatic like in bromobenzene.
R2C=CR2 + R-OH → R2CH-C(-O-R)-R2 (under acid catalysis)
Ethers are of very low chemical reactivity. They 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.
Ethers can act as Lewis bases. For instance, diethyl ether forms a complex with boron compounds, such as boron trifluoride diethyl etherate F3B:O(CH2CH3)2.
Primary and secondary ethers with a CH group next to the ether oxygen easily form highly explosive peroxides (e.g. diethyl ether peroxide) 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.
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.
In the IUPAC nomenclature system, ethers are named using the general formula "alkoxyalkane", for example CH3-CH2-O-CH3 is methoxyethane. If the ether is part of a more complex molecule, it is described as an alkoxy substituent, so -OCH3 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.
Ethylene oxide, the smallest cyclic ether:
Dimethyl ether, a propellant in aerosol cans:
Diethyl ether, a common low boiling solvent:
Dimethoxyethane, a high boiling solvent:
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 (methoxybenzene), a major constituent of the essential oil of anise seed:
Crown ethers, cyclic polyethers that are used as phase transfer catalysts :
Polyethylene glycol, a linear polyether, e.g. used in cosmetics: