Ether

Ether is a class of organic compounds that contain an oxygen atom and 2 alkyl or aryl groups. If stored in the presence of air it can form explosive peroxides such as diethyl ether peroxide, which can be accelerated my light and metal catalysts

Important ethers

 * [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/e/ee/Ethylene_oxide_chemical_structure.png/50px-Ethylene_oxide_chemical_structure.png width="50" height="53" caption="Chemical structure of ethylene oxide" link="http://en.wikipedia.org/wiki/File:Ethylene_oxide_chemical_structure.png"]] || Ethylene oxide || The smallest cyclic ether . ||
 * [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/7/7e/Dimethylether_chemical_structure.svg/90px-Dimethylether_chemical_structure.svg.png width="90" height="40" caption="Chemical structure of dimethyl ether" link="http://en.wikipedia.org/wiki/File:Dimethylether_chemical_structure.svg"]] || Dimethyl ether || An aerosol spray propellant . A potential renewable alternative fuel for diesel engines with a cetane rating as high as 56-57. ||
 * [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/2/23/Diethylether_chemical_structure.svg/120px-Diethylether_chemical_structure.svg.png width="120" height="30" caption="Chemical structure of diethyl ether" link="http://en.wikipedia.org/wiki/File:Diethylether_chemical_structure.svg"]] || Diethyl ether || A common low boiling solvent (b.p. 34.6 °C), and an early anaesthetic . Used as starting fluid for diesel engines. ||
 * [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/c/c1/Dimethoxyethane_chemical_structure.png/140px-Dimethoxyethane_chemical_structure.png width="140" height="41" caption="Chemical structure of dimethoxyethane" link="http://en.wikipedia.org/wiki/File:Dimethoxyethane_chemical_structure.png"]] || Dimethoxyethane (DME) || A high boiling solvent (b.p. 85 °C): ||
 * [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/3/37/1-4-Dioxane.svg/50px-1-4-Dioxane.svg.png width="50" height="67" caption="Chemical structure of dioxane" link="http://en.wikipedia.org/wiki/File:1-4-Dioxane.svg"]] || Dioxane || A cyclic ether and high boiling solvent (b.p. 101.1 °C). ||
 * [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/a/af/Tetrahydrofuran.svg/90px-Tetrahydrofuran.svg.png width="90" height="83" caption="Chemical structure of THF" link="http://en.wikipedia.org/wiki/File:Tetrahydrofuran.svg"]] || Tetrahydrofuran (THF) || A cyclic ether, one of the most polar simple ethers that is used as a solvent. ||
 * [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/2/20/Anisole.svg/90px-Anisole.svg.png width="90" height="153" caption="Chemical structure of anisole" link="http://en.wikipedia.org/wiki/File:Anisole.svg"]] || Anisole (methoxybenzene) || An **aryl ether** and a major constituent of the essential oil of anise seed. ||
 * [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/8/89/18-crown-6.svg/150px-18-crown-6.svg.png width="150" height="144" caption="Chemical structure of 18-crown-6" link="http://en.wikipedia.org/wiki/File:18-crown-6.svg"]] || Crown ethers || Cyclic polyethers that are used as phase transfer catalysts . ||
 * [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/a/a7/Polyethylene_glycol_chemical_structure.png/150px-Polyethylene_glycol_chemical_structure.png width="150" height="49" caption="Chemical structure of polyethylene glycol" link="http://en.wikipedia.org/wiki/File:Polyethylene_glycol_chemical_structure.png"]] || Polyethylene glycol (PEG) || A linear polyether, e.g. used in cosmetics and pharmaceuticals . ||

Reactions
Structure of the polymeric diethyl ether peroxide Ethers in general are of low chemical reactivity, but they are more reactive than alkanes ( epoxides , ketals, and acetals are unrepresentative classes of ethers and are discussed in separate articles). Important reactions are listed below.

Ether cleavage
Although ethers resist hydrolysis, they are cleaved by mineral acids such as hydrobromic acid and hydroiodic acid. Hydrogen chloride cleaves ethers only slowly. Methyl ethers typically afford methyl halides: ROCH3 + HBr → CH3Br + ROH These reactions proceed via onium intermediates, i.e. [RO(H)CH3]+Br-. Some ethers rapidly cleave with boron tribromide (even aluminium chloride is used in some cases) to give the alkyl bromide. Depending on the substituents, some ethers can be cleaved with a variety of reagents, e.g. strong base.

Peroxide formation
When stored in the presence of air or oxygen, ethers tend to form explosive [|peroxides], such as diethyl ether peroxide. The reaction is accelerated by light, metal catalysts, and aldehydes. In addition to avoiding storage conditions likely to form peroxides, it is recommended, when an ether is used as a solvent, not to distill it to dryness, as any peroxides that may have formed, being less volatile than the original ether, will become concentrated in the last few drops of liquid.

Lewis bases
Ethers serve as Lewis bases and Bronsted bases. Strong acids protonate the oxygen to give "onium ions." For instance, diethyl ether forms a complex with boron trifluoride, i.e. diethyl etherate (BF3.OEt2). Ethers also coordinate to Mg(II) center in Grignard reagents. Polyethers, including many antibiotics, cryptands , and crown ethers , bind alkali metal cations strongly.

Alpha-halogenation
This reactivity is akin to the tendency of ethers with alpha hydrogen atoms to form peroxides. Chlorine gives alpha-chloroethers.

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

[ [|edit] ] Dehydration of alcohols
The [|Dehydration] of [|alcohols] affords ethers:

2 R-OH → R-O-R + [|H2O] at high temperature This direct reaction requires elevated temperatures (about 125 °C). The reaction is catalyzed by acids, usually sulfuric acid. The method is effective for generating symmetrical ethers, but not unsymmetrical ethers. Diethyl ether is produced from ethanol by this method. Cyclic ethers are readily generated by this approach. Such reactions must compete with dehydration of the alcohol:

R-CH2-CH2(OH) → R-CH=CH2 + H2O The dehydration route often requires conditions incompatible with delicate molecules. Several milder methods exist to produce ethers.

[ [|edit] ] Williamson ether synthesis
[|Nucleophilic displacement] of [|alkyl halides] by [|alkoxides]

R-ONa + R'-X → R-O-R' + Na [|X] This reaction is called the [|Williamson ether synthesis]. It involves treatment of a parent [|alcohol] with a strong [|base] to form the alkoxide, followed by addition of an appropriate aliphatic compound bearing a suitable [|leaving group] (R-X). Suitable leaving groups (X) include [|iodide], [|bromide] , or [|sulfonates]. This method usually does not work well for aryl halides (e.g. [|bromobenzene] (see Ullmann condensation below). Likewise, this method only gives the best yields for primary halides. Secondary and tertiary halides are prone to undergo E2 elimination on exposure to the basic alkoxide anion used in the reaction due to steric hindrance from the large alkyl groups.

In a related reaction, alkyl halides undergo nucleophilic displacement by [|phenoxides]. The R-X cannot be used to react with the alcohol. However, [|phenols] can be used to replace the alcohol, while maintaining the alkyl halide. Since phenols are acidic, they readily react with a strong [|base] like [|sodium hydroxide] to form phenoxide ions. The phenoxide ion will then substitute the -X group in the alkyl halide, forming an ether with an aryl group attached to it in a reaction with an [|SN2] mechanism.

C6H5OH + OH- → C6H5-O- + H2O C6H5-O- + R-X → C6H5OR

[ [|edit] ] Ullmann condensation
The [|Ullmann condensation] is similar to the Williamson method except that the substrate is an aryl halide. Such reactions generally require a catalyst, such as copper.

[ [|edit] ] Electrophilic addition of alcohols to alkenes
Alcohols add to electrophilically activated [|alkenes].

[|R2C=CR2] + R-OH → R2CH-C(-O-R)-R2 [|Acid] [|catalysis] is required for this reaction. Often, mercury trifluoroacetate (Hg(OCOCF3)2) is used as a catalyst for the reaction, geneating an ether with [|Markovnikov] regiochemistry. Using similar reactions, [|tetrahydropyranyl ethers] are used as [|protective groups] for alcohols.

[ [|edit] ] Preparation of epoxides
Main article: [|epoxide] [|Epoxides] are typically prepared by oxidation of alkenes. The most important epoxide in terms of industrial scale is ethylene oxide, which is produced by oxidation of ethylene with oxygen. Other epoxides are produced by one of two routes:


 * By the oxidation of alkenes with a [|peroxyacid] such as [|m-CPBA].
 * By the base intramolecular nucleophilic substitution of a halohydrin.