Ether 9263 220924598 2008-06-22T06:41:08Z OverlordQ 58193 Reverted edits by [[Special:Contributions/12.215.45.198|12.215.45.198]] to last version by JAnDbot (using [[WP:HG|Huggle]]) {{This|a general class of organic compounds|Aether}} [[Image:Ether-(general).png|thumb|150px|The general structure for an ether]] '''Ether''' is a class of [[organic compound]]s which contain an ether [[functional group|group]] — an [[oxygen]] [[atom]] connected to two (substituted) [[alkyl]] or [[aryl]] groups — of general formula '''R–O–R''''.<ref>{{GoldBookRef|title=ethers|file=E02221}}</ref> A typical example is the [[solvent]] and [[anesthetic]] [[diethyl ether]], commonly referred to simply as "ether" (ethoxyethane, CH<sub>3</sub>-CH<sub>2</sub>-O-CH<sub>2</sub>-CH<sub>3</sub>). ==Physical properties== Ether [[molecule]]s cannot form [[hydrogen bond]]s among each other, resulting in a relatively low [[boiling point]] comparable to that of the analogous [[alcohol]]s. However, the differences in the boiling points of the ethers and their isometric alcohols become smaller as the carbon chains become longer, as the [[hydrophobic]] nature of the carbon chain becomes more predominant over the presence of hydrogen bonding. Ethers are slightly polar as the R - C - O - C - Z bond angle in the functional group is about 110 degrees, and the C - O dipole does cancel out. Ethers are more polar than alkenes but not as polar as alcohols, esters or [[amide]]s 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 base]]s. For instance, diethyl ether forms a complex with [[boron]] compounds, such as [[boron trifluoride]] diethyl etherate (BF<sub>3</sub><sup>.</sup>OEt<sub>2</sub>). Ethers also coordinate to magnesium in [[Grignard reagent]]s (RMgBr). ==Nomenclature== In the [[IUPAC nomenclature]] system, ethers are named using the general formula ''"alkoxyalkane"'', for example CH<sub>3</sub>-CH<sub>2</sub>-O-CH<sub>3</sub> is [[methoxyethane]]. If the ether is part of a more complex molecule, it is described as an alkoxy substituent, so -OCH<sub>3</sub> would be considered a ''"[[methoxy]]-"'' group. The simpler [[alkyl]] radical is written in front, so CH<sub>3</sub>-O-CH<sub>2</sub>CH<sub>3</sub> would be given as ''methoxy''(CH<sub>3</sub>O)''ethane''(CH<sub>2</sub>CH<sub>3</sub>). The nomenclature of describing the two alkyl groups and appending ''"ether"'', e.g. ''"ethyl methyl ether"'' in the example above, is a [[trivial name|trivial usage]]. ==Similar structures== [[Image:Structures not ethers.png|frame|Not all compounds of the formula R-O-R are ethers.]] 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 one of the carbon atoms next to the oxygen is connected to oxygen, [[nitrogen]], or [[sulfur]]: ** [[Ester]]s R-C(=O)-O-R ** [[Acetal]]s R-CH(-O-R)-O-R ** [[Aminal]]s R-CH(-NH-R)-O-R ** [[Anhydride]]s R-C(=O)-O-C(=O)-R ==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<sub>3</sub>-CH<sub>2</sub>-O-CH<sub>2</sub>-CH<sub>3</sub>. An example of a ''secondary ether'' is [[diisopropyl ether]] (CH<sub>3</sub>)<sub>2</sub>CH-O-CH(CH<sub>3</sub>)<sub>2</sub> and that of a ''tertiary ether'' is [[di-tert-butyl ether]] (CH<sub>3</sub>)<sub>3</sub>C-O-C(CH<sub>3</sub>)<sub>3</sub>. <center> [[Image:Dimethylether chemical structure.svg|40px|Dimethyl ether]] [[Image:Diethylether chemical structure.svg|72px|A primary ether (diethyl ether)]] [[Image:Diisopropyl ether chemical structure.svg|71px|A secondary ether (diisopropyl ether)]] [[Image:Di-tert-butyl ether chemical structure.svg|72px|A tertiary ether (di-''tert''-butyl ether)]] <br> Dimethyl ether, a ''primary'', a ''secondary'', and a ''tertiary ether''. </center> ==Polyethers== Polyethers are compounds with more than one ether group. While the term generally refers to [[polymer]]s like [[polyethylene glycol]] and [[polypropylene glycol]], low molecular compounds such as the [[crown ether]]s may sometimes be included. ==Organic reactions== ===Synthesis===<!-- This section is linked from [[Organic reaction]] --> Ethers can be prepared in the laboratory in several different ways. * [[dehydration reaction|Intermolecular Dehydration]] of [[alcohol]]s: : [[Alcohol|R-OH]] + R-OH → R-O-R + [[Water (molecule)|H<sub>2</sub>O]] : 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' + 3[[Water (molecule)|H<sub>2</sub>O]] :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-CH<sub>2</sub>-CH<sub>2</sub>(OH) → R-CH=CH<sub>2</sub> + H<sub>2</sub>O : Such conditions can destroy the delicate structures of some [[functional group]]s. There exist several milder methods to produce ethers. * [[Nucleophilic displacement]] of [[alkyl halide]]s by [[alkoxide]]s : [[Alkoxide|R-O<sup>-</sup>]] + [[Alkyl halide|R-X]] → R-O-R + [[Halide|X<sup>-</sup>]] : This reaction is called the [[Williamson ether synthesis]]. It involves treatment of a parent [[alcohol]] with a strong [[Base (chemistry)|base]] to form the alkoxide [[anion]] followed by addition of an appropriate aliphatic compound bearing a suitable [[leaving group]] (R-X). Suitable leaving groups (X) include [[iodide]], [[bromide]], or [[sulfonate]]s. This method does not work if R is aromatic like in [[bromobenzene]] (Br-C<sub>6</sub>H<sub>5</sub>), however, if the leaving group is separated by at least one carbon from the benzene, the reaction should proceed (as in Br-CH<sub>2</sub>-C<sub>6</sub>H<sub>5</sub>). Likewise, this method only gives the best yields for primary carbons, as secondary and tertiary carbons will undergo E2 elimination on exposure to the basic alkoxide anion used in the reaction due to steric hindrance from the large alkyl groups. Aryl ethers can be prepared in the [[Ullmann condensation]]. * Nucleophilic Displacement of Alkyl halides by [[phenoxide]]s : 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 (chemistry)|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. : HO-C<sub>6</sub>H<sub>5</sub> + OH<sup>-</sup> → O<sup>-</sup>-C<sub>6</sub>H<sub>5</sub> : O<sup>-</sup>-C<sub>6</sub>H<sub>5</sub> + R-X → R-O-C<sub>6</sub>H<sub>5</sub> * [[Electrophilic addition]] of alcohols to [[alkene]]s. : [[alkene|R<sub>2</sub>C=CR<sub>2</sub>]] + R-OH → R<sub>2</sub>CH-C(-O-R)-R<sub>2</sub> : [[Acid]] [[catalysis]] is required for this reaction. Often, Mercury trifluoroacetate (Hg(OCOCF<sub>3</sub>)<sub>2</sub> is used as a catalyst for the reaction, creating an ether with [[Markovnikov]] regiochemistry. [[Tetrahydropyranyl ether]]s are used as [[protective group]]s for alcohols. Cyclic ethers which are also known as [[epoxide]]s can be prepared: * By the oxidation of alkenes with a [[peroxyacid]] such as [[Meta-Chloroperoxybenzoic acid|m-CPBA]]. * By the base intramolecular nuclephilic substitution of a halohydrin. ===Reactions===<!-- This section is linked from [[Organic reaction]] --> [[Image:Diethylether peroxide chemical structure.png|frame|Structure of the polymeric diethyl ether peroxide]]Ethers in general are of very low chemical [[reactivity]]. Organic reactions are: * [[Hydrolysis]]. : Ethers are [[Hydrolysis|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]]. * [[Nucleophilic displacement]]. : [[Epoxide]]s, or cyclic ethers in three-membered rings, are highly susceptible to nucleophilic attack and are reactive in this fashion. * [[Peroxide]] formation. : Primary and secondary ethers with a CH group next to the ether oxygen easily form highly [[Explosive material|explosive]] [[organic peroxide]]s (e.g. [[diethyl ether peroxide]]) in the presence of oxygen, light, and metal and [[aldehyde]] impurities. For this reason ethers like diethyl ether and [[Tetrahydrofuran|THF]] are usually avoided as [[solvent]]s in industrial processes ==Important ethers== {| class="wikitable" | [[Image:Ethylene oxide chemical structure.png|50px|Chemical structure of ethylene oxide]] | [[Ethylene oxide]] |The smallest cyclic ether. |- | [[Image:Dimethylether chemical structure.svg|100px|Chemical structure of dimethyl ether]] |[[Dimethyl ether]] |An [[aerosol spray#Propellant|aerosol spray propellant]]. |- |[[Image:Diethylether chemical structure.svg|200px|Chemical structure of diethyl ether]] |[[Diethyl ether]] |A common low boiling solvent (b.p. 34.6°C). |- | [[Image:Dimethoxyethane chemical structure.png|200px|Chemical structure of dimethoxyethane]] | [[Dimethoxyethane]] (DME) | A high boiling solvent (b.p. 85°C): |- | [[Image:1-4-Dioxane.svg|100px|Chemical structure of dioxane]] | [[Dioxane]] | A cyclic ether and high boiling solvent (b.p. 101.1°C). |- | [[Image:Tetrahydrofuran.svg|100px|Chemical structure of THF]] | [[Tetrahydrofuran]] (THF) | A cyclic ether, one of the most polar simple ethers that is used as a solvent. |- | [[Image:Anisole.svg|100px|Chemical structure of anisole]] |[[Anisole]] (methoxybenzene) |An '''aryl ether''' and a major constituent of the [[essential oil]] of [[anise]] seed. |- | [[Image:18-crown-6.svg|150px|Chemical structure of 18-crown-6]] |[[Crown ether]]s |Cyclic polyethers that are used as [[phase transfer catalyst]]s. |- | [[Image:Polyethylene glycol chemical structure.png|150px|Chemical structure of polyethylene glycol]] | [[Polyethylene glycol]] (PEG) | A linear polyether, e.g. used in [[cosmetics]]: |} ==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]] ==References== {{Refimprove|date=December 2007}} <references/> ==External links== * [http://www.ilpi.com/msds/ref/ether.html ILPI] page about ethers. * [http://www.gutenberg.org/etext/12522 An Account of the Extraordinary Medicinal Fluid, called Aether], by M. Turner, circa 1788, from [[Project Gutenberg]] {{Functional Groups}} [[Category:Ethers]] [[Category:Functional groups]] [[ar:إيثر]] [[ca:Èter]] [[cs:Ethery]] [[da:Æter (kemi)]] [[de:Ether]] [[et:Eetrid]] [[es:Éter (química)]] [[eo:Etero (kemio)]] [[fr:Éther-oxyde]] [[ko:에테르 (화학)]] [[it:Eteri]] [[he:אתר (כימיה)]] [[la:Aether (chemica)]] [[lv:Ēteri]] [[hu:Éter (kémia)]] [[mk:Етер]] [[nl:Ether (chemie)]] [[ja:エーテル (化学)]] [[no:Eter (kjemi)]] [[nn:Eterar]] [[pl:Etery]] [[pt:Éter]] [[ro:Eter]] [[ru:Простые эфиры]] [[sl:Eter]] [[sr:Етар (хемија)]] [[fi:Eetteri]] [[sv:Etrar]] [[vi:Ete]] [[uk:Прості ефіри]] [[zh:醚]]