Editing Ether

{{short description|Organic compounds made of alkyl/aryl groups bound to oxygen (R–O–R')}}
{{for-multi|the substance whose common name is ether|Diethyl ether|the digital asset|Ethereum|other uses|Aether (disambiguation)}}
[[File:Ether-(general).svg|thumb|150px|The general structure of an ether. R and R' represent most [[organyl]] [[substituent]]s.]]

In [[organic chemistry]], '''ethers''' are a class of [[organic compound|compound]]s that contain an ether [[functional group|group]], a single [[oxygen]] atom bonded to two separate carbon atoms, each part of an [[organyl]] group (e.g., [[alkyl]] or [[aryl]]). They have the general formula {{chem2|R\sO\sR′}}, where R and R′ represent the organyl groups. Ethers can again be classified into two varieties: if the organyl groups are the same on both sides of the oxygen atom, then it is a simple or symmetrical ether, whereas if they are different, the ethers are called mixed or unsymmetrical ethers.<ref>{{GoldBookRef|title=ethers|file=E02221}}</ref> A typical example of the first group is the [[solvent]] and [[anaesthetic]] [[diethyl ether]], commonly referred to simply as "ether" ({{chem2|CH3\sCH2\sO\sCH2\sCH3}}). Ethers are common in organic chemistry and even more prevalent in [[biochemistry]], as they are common linkages in [[carbohydrate]]s and [[lignin]].<ref>{{cite book|title=The Ether Linkage|year=1967|editor=Saul Patai|isbn= 978-0-470-77107-5|doi=10.1002/9780470771075|publisher=John Wiley & Sons|series=PATAI'S Chemistry of Functional Groups}}</ref>

==Structure and bonding==
Ethers feature bent {{chem2|C\sO\sC}} linkages. In [[dimethyl ether]], the [[Molecular geometry#Bonding|bond angle]] is 111° and C–O distances are 141&nbsp;[[Picometre|pm]].<ref>{{cite journal |doi=10.1039/b405684a|title=Dichlorosilane–Dimethyl Ether Aggregation: A New Motif in Halosilane Adduct Formation|year=2004|last1= Vojinović|first1=Krunoslav|last2=Losehand|first2=Udo|last3=Mitzel|first3=Norbert W.|journal=Dalton Trans.|issue=16|pages=2578–2581|pmid=15303175}}</ref> The barrier to rotation about the C–O bonds is low. The bonding of oxygen in ethers, alcohols, and water is similar. In the language of [[valence bond theory]], the hybridization at oxygen is sp<sup>3</sup>.

Oxygen is more [[Electronegativity|electronegative]] than carbon, thus the alpha hydrogens of ethers are more acidic than those of simple hydrocarbons. They are far less acidic than alpha hydrogens of carbonyl groups (such as in [[ketones]] or [[aldehydes]]), however.

Ethers can be symmetrical of the type ROR or unsymmetrical of the type ROR'. Examples of the former are [[dimethyl ether]], [[diethyl ether]], [[dipropyl ether]] etc. Illustrative unsymmetrical ethers are [[anisole]] (methoxybenzene) and [[dimethoxyethane]].

===Vinyl- and acetylenic ethers===
Vinyl- and acetylenic ethers are far less common than alkyl or aryl ethers. Vinylethers, often called [[enol ether]]s, are important intermediates in [[organic synthesis]]. Acetylenic ethers are especially rare. [[Di-tert-butoxyacetylene]] is the most common example of this rare class of compounds.

==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>).

===Trivial name===
IUPAC rules are often not followed for simple ethers. The trivial names for simple ethers (i.e., those with none or few other functional groups) are a composite of the two substituents followed by "ether". For example, ethyl methyl ether (CH<sub>3</sub>OC<sub>2</sub>H<sub>5</sub>), diphenylether (C<sub>6</sub>H<sub>5</sub>OC<sub>6</sub>H<sub>5</sub>). As for other organic compounds, very common ethers acquired names before rules for nomenclature were formalized. Diethyl ether is simply called ether, but was once called ''sweet oil of vitriol''. Methyl phenyl ether is [[anisole]], because it was originally found in [[aniseed]]. The [[aromatic]] ethers include [[furan]]s. [[Acetal]]s (α-alkoxy ethers R–CH(–OR)–O–R) are another class of ethers with characteristic properties.

===Polyethers===

Polyethers are generally [[polymer]]s containing ether linkages in their main chain. The term [[polyol]] generally refers to polyether polyols with one or more functional [[end-group]]s such as a [[hydroxyl]] group. The term "oxide" or other terms are used for high molar mass polymer when end-groups no longer affect polymer properties.

[[Crown ether]]s are cyclic polyethers. Some toxins produced by [[dinoflagellate]]s such as [[brevetoxin]] and [[ciguatoxin]] are extremely large and are known as ''cyclic'' or ''ladder'' polyethers.

{| class="wikitable"
|+ Aliphatic polyethers
|-
! Name of the polymers with low to medium molar mass !! Name of the polymers with high molar mass !! Preparation !! Repeating unit !! Examples of trade names
|-
| [[Paraformaldehyde]] || [[Polyoxymethylene plastic|Polyoxymethylene]] (POM) or polyacetal or polyformaldehyde || [[Step-growth polymerisation]] of [[formaldehyde]] || –CH<sub>2</sub>O– || Delrin from [[DuPont]]
|-
| [[Polyethylene glycol]] (PEG) || Polyethylene oxide (PEO) or polyoxyethylene (POE) || [[Ring-opening polymerization]] of [[ethylene oxide]]|| –CH<sub>2</sub>CH<sub>2</sub>O– || Carbowax from [[Dow Chemical Company|Dow]]
|-
| [[Polypropylene glycol]] (PPG) || Polypropylene oxide (PPOX) or polyoxypropylene (POP) || anionic ring-opening polymerization of [[propylene oxide]] || –CH<sub>2</sub>CH(CH<sub>3</sub>)O– || Arcol from [[Covestro]]
|-
| Polytetramethylene glycol (PTMG) or Polytetramethylene ether glycol (PTMEG) || [[Polytetrahydrofuran]] (PTHF) || Acid-catalyzed ring-opening polymerization of [[tetrahydrofuran]]|| {{chem2|\sCH2CH2CH2CH2O\s}} || Terathane from [[Invista]] and PolyTHF from [[BASF]]
|}

The phenyl ether polymers are a class of [[aromatic compound|aromatic]] polyethers containing aromatic cycles in their main chain: [[polyphenyl ether]] (PPE) and [[Poly(p-phenylene oxide)|poly(''p''-phenylene oxide)]] (PPO).

===Related compounds===
Many classes of compounds with C–O–C linkages are not considered ethers: [[Ester]]s (R–C(=O)–O–R′), [[hemiacetal]]s (R–CH(–OH)–O–R′), [[carboxylic acid anhydride]]s (RC(=O)–O–C(=O)R′).

There are compounds which, instead of [[carbon|C]] in the {{chem2|C\sO\sC}} linkage, contain heavier [[group 14]] [[chemical elements]] (e.g., [[silicon|Si]], [[germanium|Ge]], [[tin|Sn]], [[lead|Pb]]). Such compounds are considered ethers as well. Examples of such ethers are [[silyl enol ether]]s {{chem2|R3Si\sO\sCR\dCR2}} (containing the {{chem2|Si\sO\sC}} linkage), [[disiloxane]] {{chem2|H3Si\sO\sSiH3}} (the other name of this compound is disilyl ether, containing the {{chem2|Si\sO\sSi}} linkage) and [[stannoxane]]s {{chem2|R3Sn\sO\sSnR3}} (containing the {{chem2|Sn\sO\sSn}} linkage).

==Physical properties==
Ethers have [[boiling point]]s similar to those of the analogous [[alkane]]s. Simple ethers are generally colorless.

{| style="width:100%;" class="wikitable"
|- style="background:#ffdead;"
! colspan="6" | Selected data about some alkyl ethers
|-
! Ether
! Structure
! m.p. (°C)
! b.p. (°C)
! Solubility in 1 liter of H<sub>2</sub>O
! Dipole moment ([[Debye|D]])
|-
| [[Dimethyl ether]]||CH<sub>3</sub>–O–CH<sub>3</sub>||−138.5||−23.0||70&nbsp;g||1.30
|-
| [[Diethyl ether]]||CH<sub>3</sub>CH<sub>2</sub>–O–CH<sub>2</sub>CH<sub>3</sub>||−116.3||34.4||69&nbsp;g||1.14
|-
| [[Tetrahydrofuran]]||O(CH<sub>2</sub>)<sub>4</sub>||−108.4||66.0||[[Miscibility|Miscible]]||1.74
|-
| [[1,4-Dioxane|Dioxane]]||O(C<sub>2</sub>H<sub>4</sub>)<sub>2</sub>O||11.8||101.3||Miscible||0.45
|}

==Reactions== <!-- This section is linked from [[Organic reaction]] -->
[[Image:Diethylether peroxide chemical structure.png|frame|Structure of the polymeric [[diethyl ether peroxide]]]]
The C-O bonds that comprise simple ethers are strong. They are unreactive toward all but the strongest bases. Although generally of low chemical [[reactivity (chemistry)|reactivity]], they are more reactive than [[alkanes]].

Specialized ethers such as [[epoxide]]s, [[ketal]]s, and [[acetal]]s are unrepresentative classes of ethers and are discussed in separate articles. Important reactions are listed below.<ref name=Ullmann>Wilhelm Heitmann, Günther Strehlke, Dieter Mayer "Ethers, Aliphatic" in ''Ullmann's Encyclopedia of Industrial Chemistry'' Wiley-VCH, Weinheim, 2002. {{doi|10.1002/14356007.a10_023}}</ref>

===Cleavage===
{{see also|Ether cleavage}}
Although ethers resist hydrolysis, they are cleaved by hydrobromic acid and [[hydroiodic acid]]. [[Hydrogen chloride]] cleaves ethers only slowly. Methyl ethers typically afford [[methyl halide]]s:
:ROCH<sub>3</sub> + HBr → CH<sub>3</sub>Br + ROH
These reactions proceed via [[onium compounds|onium]] intermediates, i.e. [RO(H)CH<sub>3</sub>]<sup>+</sup>Br<sup>−</sup>.

Some ethers undergo rapid cleavage with [[boron tribromide]] (even [[aluminium chloride]] is used in some cases) to give the alkyl bromide.<ref>{{OrgSynth|author = J. F. W. McOmie and D. E. West|title = 3,3′-Dihydroxylbiphenyl|collvol = 5|collvolpages = 412|year = 1973|prep = CV5P0412}}</ref> Depending on the substituents, some ethers can be cleaved with a variety of reagents, e.g. strong base.

Despite these difficulties the chemical [[pulp (paper)|paper pulping]] processes are based on cleavage of ether bonds in the [[lignin]].

===Peroxide formation===
When stored in the presence of air or oxygen, ethers tend to form [[Explosive material|explosive]] [[organic peroxide|peroxides]], such as [[diethyl ether hydroperoxide]]. The reaction is accelerated by light, metal catalysts, and [[aldehyde]]s. 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. The presence of peroxide in old samples of ethers may be detected by shaking them with freshly prepared solution of a ferrous sulfate followed by addition of KSCN. Appearance of blood red color indicates presence of peroxides. The dangerous properties of ether peroxides are the reason that diethyl ether and other peroxide forming ethers like [[tetrahydrofuran]] (THF) or [[dimethoxyethane|ethylene glycol dimethyl ether]] (1,2-dimethoxyethane) are avoided in industrial processes.

=== Lewis bases ===
[[File:CSD CIF CANZOG10.png|thumb|right|172px|Structure of VCl3([[Tetrahydrofuran|thf]])3.<ref>{{cite journal|journal=Inorg. Chim. Acta |author=F.A.Cotton |author2=S.A.Duraj |author3=G.L.Powell |author4=W.J.Roth |year=1986|volume=113|page=81|title=Comparative Structural Studies of the First Row Early Transition Metal(III) Chloride Tetrahydrofuran Solvates|doi=10.1016/S0020-1693(00)86863-2}}</ref>{{legend|blue|[[Vanadium]], V}}{{legend|darkgreen|[[Chlorine]], Cl}}{{legend|grey|[[Carbon]], C}}{{legend|white|[[Hydrogen]], H}}{{legend|red|[[Nitrogen]], N}}]]

Ethers serve as [[Lewis base]]s. For instance, [[diethyl ether]] forms a [[Coordination complex|complex]] with [[boron trifluoride]], i.e. borane diethyl etherate ({{chem2|BF3*O(CH2CH3)2}}). Ethers also coordinate to the [[magnesium|Mg]] center in [[Grignard reagent]]s. [[Tetrahydrofuran]] is more basic than [[Open-chain compound|acyclic]] ethers. It forms with many [[transition metal ether complex|complex]]es.

===Alpha-halogenation===
This reactivity is similar to the tendency of ethers with [[alpha]] hydrogen atoms to form peroxides. Reaction with chlorine produces alpha-chloroethers.

==Synthesis==<!-- This section is linked from [[Organic reaction]]-->

===Dehydration of alcohols===
The [[dehydration reaction|dehydration]] of [[Alcohol (drug)|alcohol]]s affords ethers:<ref>{{cite book |title=Organic chemistry |last1=Clayden |last2=Greeves |last3=Warren |year=2001 |publisher=Oxford University Press |isbn=978-0-19-850346-0 |page=[https://archive.org/details/organicchemistry00clay_0/page/129 129] |url-access=registration |url=https://archive.org/details/organicchemistry00clay_0/page/129}}</ref>
: 2 R–OH → R–O–R + [[Water|H<sub>2</sub>O]] at high temperature

[[Image:Acid catalysed alchol condensation to produce symmetrical ether.svg|507px|center]]

This direct nucleophilic substitution reaction requires elevated temperatures (about 125&nbsp;°C). The reaction is catalyzed by acids, usually sulfuric acid. The method is effective for generating symmetrical ethers, but not unsymmetrical ethers, since either OH can be protonated, which would give a mixture of products. Diethyl ether is produced from ethanol by this method. Cyclic ethers are readily generated by this approach. Elimination reactions compete with dehydration of the alcohol:
: R–CH<sub>2</sub>–CH<sub>2</sub>(OH) → R–CH=CH<sub>2</sub> + H<sub>2</sub>O

The dehydration route often requires conditions incompatible with delicate molecules. Several milder methods exist to produce ethers.

===Electrophilic addition of alcohols to alkenes===
Alcohols add to electrophilically activated [[alkene]]s.  The method is atom-economical:
: [[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. Commercially important ethers prepared in this way are derived from [[isobutene]] or [[isoamylene]], which protonate to give relatively stable [[carbocation]]s.  Using ethanol and methanol with these two alkenes, four fuel-grade ethers are produced:  [[methyl tert-butyl ether]] (MTBE), [[tert-Amyl methyl ether|methyl tert-amyl ether]] (TAME), [[ethyl tert-butyl ether]] (ETBE), and [[ethyl tert-amyl ether]] (TAEE).<ref name=Ullmann/>

[[Solid acid catalyst]]s are typically used to promote this reaction.

===Epoxides===
{{main|epoxide}}
[[Epoxide]]s 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 [[Meta-Chloroperoxybenzoic acid|''m''-CPBA]].
* By the base intramolecular nucleophilic substitution of a [[halohydrin]].

Many ethers, [[ethoxylate]]s and [[crown ether]]s, are produced from epoxides.

===Williamson and Ullmann ether syntheses===
[[Nucleophilic displacement]] of [[alkyl halide]]s by [[alkoxide]]s
: R–ONa + R′–X → R–O–R′ + Na[[Halide|X]]
This reaction, the [[Williamson ether synthesis]], involves treatment of a parent [[Alcohol (chemistry)|alcohol]] with a strong [[Base (chemistry)|base]] to form the alkoxide, followed by addition of an appropriate [[aliphatic compound]] bearing a suitable [[leaving group]] (R–X). Although popular in textbooks, the method is usually impractical on scale because it cogenerates significant waste.

Suitable leaving groups (X) include [[iodide]], [[bromide]], or [[sulfonate]]s. 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 [[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|S<sub>N</sub>2]] mechanism.

: C<sub>6</sub>H<sub>5</sub>OH + OH<sup>−</sup> → C<sub>6</sub>H<sub>5</sub>–O<sup>−</sup> + H<sub>2</sub>O
: C<sub>6</sub>H<sub>5</sub>–O<sup>−</sup> + R–X → C<sub>6</sub>H<sub>5</sub>OR

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.<ref>{{cite journal |last1=Frlan |first1=Rok |last2=Kikelj |first2=Danijel |title=Recent Progress in Diaryl Ether Synthesis |journal=Synthesis |date=29 June 2006 |volume=2006 |issue=14 |pages=2271–2285 |doi=10.1055/s-2006-942440}}</ref>

==Important ethers==
{| class="wikitable"
|-
| [[File:Ethylene oxide chemical structure.png|50px|Chemical structure of ethylene oxide]]
| [[Ethylene oxide]]
| A cyclic ether. Also the simplest [[epoxide]].
|-
| [[File:Dimethylether chemical structure.svg|90px|Chemical structure of dimethyl ether]]
|[[Dimethyl ether]]
|A colourless gas that is used as an [[aerosol spray#Aerosol propellants|aerosol spray propellant]]. A potential renewable alternative fuel for [[diesel engine]]s with a [[cetane number|cetane rating]] as high as 56–57.
|-
|[[File:Diethyl ether chemical structure.svg|120px|Chemical structure of diethyl ether]]
|[[Diethyl ether]]

|A colourless liquid with sweet odour. A common low boiling [[solvent]] (b.p.&nbsp;34.6&nbsp;°C) and an early [[anaesthetic]]. Used as starting fluid for diesel engines. Also used as a [[refrigerant]] and in the manufacture of [[smokeless gunpowder]], along with use in [[perfumery]].
|-
| [[File:Dimethoxyethane chemical structure.png|140px|Chemical structure of dimethoxyethane]]
| [[Dimethoxyethane]] (DME)
| A water miscible solvent often found in lithium batteries (b.p.&nbsp;85&nbsp;°C):
|-
| [[File:1-4-Dioxane.svg|50px|Chemical structure of dioxane]]
| [[Dioxane]]
| A cyclic ether and high-boiling solvent (b.p.&nbsp;101.1&nbsp;°C).
|-
| [[File:Tetrahydrofuran.svg|90px|Chemical structure of THF]]
| [[Tetrahydrofuran]] (THF)
| A cyclic ether, one of the most polar simple ethers that is used as a solvent.
|-
| [[File:Anisole.svg|90px|Chemical structure of anisole]]
|[[Anisole]] (methoxybenzene)
|An '''aryl ether''' and a major constituent of the [[essential oil]] of [[anise]] seed.
|-
| [[File:18-crown-6.svg|150px|Chemical structure of 18-crown-6]]
|[[Crown ether]]s
|Cyclic polyethers that are used as [[phase transfer catalyst]]s.
|-
| [[File:Poly(ethylene glycol) alternate.svg|150px|Chemical structure of polyethylene glycol]]
| [[Polyethylene glycol]] (PEG)
| A linear polyether, e.g. used in [[cosmetics]] and [[pharmaceuticals]].
|-
|
| [[Polypropylene glycol]]
| A linear polyether, e.g. used in [[polyurethanes]].
|-
| [[File:Platelet-activating_factor.svg]]
| Platelet-activating factor
| An [[ether lipid]], an example with an ether on sn-1, an ester on sn-2, and an inorganic ether on sn-3 of the glyceryl scaffold.
|}

== See also ==
* [[Ester]]
* [[Ether lipid]]
* [[Ether addiction]]
* [[History of general anesthesia]]
* [[Inhalant]]
* Chemical paper pulping processes: [[Kraft process]] (and [[Soda pulping]]), [[Organosolv]] pulping process and the [[Sulfite process]]

==References==
{{reflist}}

{{Functional Groups}}

{{Authority control}}

[[Category:Ethers| ]]
[[Category:Functional groups]]
[[Category:Impression material]]