Diethyl ether - Definition and Overview

For ether as it applies to physics and philosophy, see Aether; for the Mormon prophet Ether, see Book of Ether.

Ether is the trivial name for the compound diethyl ether, CH₃CH₂OCH₂CH₃; the systematic (IUPAC) name of the compound is ethoxyethane. Alchemist Raymundus Lullus is credited with discovering the compound in 1275, although there is no contemporary evidence of this. It was first synthesized in 1540 by Valerius Cordus, who called it "sweet oil of vitriol" (oleum dulci vitrioli), and noted some of its medicinal properties. At about the same time, Theophrastus Bombastus von Hohenheim, better known as Paracelsus, discovered ether's analgesic properties. The name ether was given to the substance in 1730 by W. G. Frobenius.

The American doctor Crawford Williamson Long, M.D., was the first surgeon to use it as an general anesthetic, on March 30, 1842. Its first use is normally associated with the Etherdome in Boston, Massachusetts. Ether is no longer used as an anesthetic when other, safer substances are available; ether is flammable, and is an irritant to some patients.

In more general chemical terminology, an ether is a functional group consisting of an oxygen atom bonded to two carbon atoms that are not bonded. An example of an ether in this sense is methoxymethane (or dimethyl ether), which has the formula CH₃OCH₃. Note that if either carbon bonded to the oxygen bridge is also double-bonded to another oxygen atom (eg CH₃COOCH₃) then the compound is an ester, not an ether.

Primary, secondary, and tertiary ethers

The terms "primary ether", "secondary ether", and "tertiary ether" are occasionally used. When these terms are used, they refer to the R1 carbon that is connected to the oxygen. If that carbon is a primary carbon, then the ether is a primary ether, etc.

Reactions

Synthesis

1. Two alcohols → ether
   • This direct reaction is not suitable in most synthetic pathways. There exist several milder methods to produce ethers.
2. alkoxide + alkyl halide → ether
   • This is called Williamson ether synthesis. It involves treatment of a parent alcohol (R-OH) with a strong base to form the alkoxide ion (R-O-) followed by addition of an appropriate aliphatic compound bearing a suitable leaving group (R-L). Suitable leaving groups (L) include Iodine, Bromine or Sulfonate esters. This method isn't useful when it comes to aromatic ethers from aromatic halides.
3. alkene + alcohol + acid catalyst → ether

Physical properties

Like esters, ethers are limited in their ability to form hydrogen bonds. They tend to be more hydrophobic than other, analogous condensation products (such as esters or amides). They are resistant to hydrolysis.

Ethers which have a CH group next to the oxygen form peroxides (e.g. diethyl ether hydroperoxide), which are highly explosive. Due to this and the low ignition point of diethyl ether, diethyl ether is one of the risk factors in laboratories.

Despite their comparably attenuated reactivity, ethers can act as Lewis bases (see Acid-base reaction theories). For instance, diethyl ether forms a complex with boron compounds, such as boron trifluoride etherate, F₃B:O(CH₂CH₃)₂

Nomenclature

In the IUPAC 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", eg ethyl methyl ether in the example above, is trivial usage.