18-Crown-6
3173552
209578980
2008-05-01T23:39:44Z
Benjah-bmm27
126395
/* Applications */ new [[space-filling model]] added
{{Chembox new
| Name = 18-Crown-6
| ImageFile = 18-crown-6.svg
<!-- | ImageSize = 120px -->
| ImageName = 18-Crown-6
| IUPACName = 1,4,7,10,13,16-hexaoxacyclooctadecane
| Section1 = {{Chembox Identifiers
| CASOther = {{{CAS|17455-13-9}}}
| SMILES = C1OCCOCCOCCOCCOCCOC1
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>12</sub>H<sub>24</sub>O<sub>6</sub>
| MolarMass = 264.122 g/mol
| Density = 1.237 g/cm³
| MeltingPt = 37-40 °C
| BoilingPt = 116 °C (0.2 Torr)
}}
| Section8 = {{Chembox Related
| OtherCpds = [[Dibenzo-18-crown-6]]<br />[[Triglyme]]}}
}}
'''18-Crown-6''' is an [[organic compound]] with the formula [C<sub>2</sub>H<sub>4</sub>O]<sub>6</sub> and the [[IUPAC]] name of 1,4,7,10,13,16-hexaoxacyclooctadecane. The compound is a [[crown ether]]. Crown ethers coordinate some metal ions in their central cavity; 18-crown-6 displays a particular affinity for potassium cations. The synthesis of the crown ethers led to the Nobel Prize in Chemistry to [[Charles J. Pedersen]].
==Applications==
Crown ethers are useful as [[phase transfer catalyst]]s.<ref>Liotta, C. L.; Berknerin, J. "18-Crown-6" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. {{doi|10.1002/047084289X.rc261}}</ref> In the presence of 18-crown-6 [[potassium permanganate]] dissolves in benzene, although this application is eclipsed by the use of [[quaternary ammonium salt|quaternary ammonium]]/phosphonium salts.
:[[Image:18-crown-6-potassium-3D-vdW-A.png|200px|18-crown-6 coordinating a potassium ion]]
Crown ethers can also be used to change the properties of inorganic compounds in organic solution. For example, in the presence of 18-crown-6, [[potassium acetate]] is a more powerful nucleophile in organic solvents than potassium acetate alone.
It can be purified by [[distillation]], where its tendency to supercool becomes evident. Rigorously dry material can be made by dissolving the compound in THF followed by the addition of [[NaK]] to give [K(18-crown-6)]Na, an [[alkalide]]. Other [[ligand]]s for alkali metal cations include [[cryptand]]s and acyclic [[polyether]]s.
==Synthesis==
It can be prepared by a modified [[Williamson ether synthesis]] or the oligomerization of [[ethylene oxide]] in the presence of a template. The more accessible dibenzo crown-18-Crown-6 is prepared in one-pot from [[catechol]] and bis(chloroethyl)ether.<ref>{{OrgSynth | author = Charles J. Pedersen | title = Macrocyclic Polyethers:Dibenzo-18-Crown-6 Polyether and Dicyclohexyl-18-Crown-6 Polyether | collvol = 6 | collvolpages = 395| year = 1988 | prep = CV6P0008}}</ref>
==Related compounds==
A related and generally superior complexant for alkali metal cations is '''dibenzo-18-crown-6'''.
:[[Image:Dibenzo-18-crown-6.png|200px|Dibenzo-18-crown-6]]
==References==
<references/>
==External links==
* [http://www.sigmaaldrich.com/catalog/search/ProductDetail/SIAL/274984 Sigma Aldrich chemical profile]
{{DEFAULTSORT:Crown-6, 18-}}
[[Category:Crown ethers]]
[[Category:Oxygen heterocycles]]
[[Category:Ethers]]
[[Category:chelating agents]]
[[Category:Macrocycles]]
[[nl:Kroonether]]
[[zh:18-冠-6]]