18-Crown-6 is an organic compound with the formula [C2H4O]6 and the IUPAC name of 1,4,7,10,13,16-hexaoxacyclooctadecane. It is a white, hygroscopic crystalline solid with a low melting point.[1] Like other crown ethers, 18-crown-6 functions as a ligand for some metal cations with a particular affinity for potassium cations (binding constant in methanol: 106 M−1). The point group of 18-crown-6 is S6. The dipole moment of 18-crown-6 varies in different solvent and under different temperature. Under 25 °C, the dipole moment of 18-crown-6 is 2.76 ± 0.06 D in cyclohexane and 2.73 ± 0.02 in benzene.[2] The synthesis of the crown ethers led to the awarding of the Nobel Prize in Chemistry to Charles J. Pedersen.
It can be purified by distillation, where its tendency to supercool becomes evident. 18-Crown-6 can also be purified by recrystallisation from hot acetonitrile. It initially forms an insoluble solvate.[3] 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 salt.[4]
Crystallographic analysis reveals a relatively flat molecule but one where the oxygen centres are not oriented in the idealized 6-fold symmetric geometry usually shown.[5] The molecule undergoes significant conformational change upon complexation.
Reactions
The complex of H3O+ with 18-crown-6
18-Crown-6 has a high affinity for the hydronium ion H3O+, as it can fit inside the crown ether. Thus, reaction of 18-crown-6 with strong acids gives the cation . For example, interaction of 18-crown-6 with HCl gas in toluene with a little moisture gives an ionic liquid layer with the composition , from which the solid can be isolated on standing. Reaction of the ionic liquid layer with two molar equivalents of water gives the crystalline product .[1][6][7]
Applications
18-crown-6 complex with potassium ion
18-Crown-6 binds to a variety of small cations, using all six oxygens as donor atoms. Crown ethers can be used in the laboratory as phase transfer catalysts.[8] Salts which are normally insoluble in organic solvents are made soluble by crown ether.[9] For example, potassium permanganate dissolves in benzene in the presence of 18-crown-6, giving the so-called "purple benzene", which can be used to oxidize diverse organic compounds.[1]
Various substitution reactions are also accelerated in the presence of 18-crown-6, which suppresses ion-pairing.[10] The anions thereby become naked nucleophiles. For example, using 18-crown-6, potassium acetate is a more powerful nucleophile in organic solvents:[1]
The first electride salt to be examined with X-ray crystallography, [Cs(18-crown-6)2]+·e−, was synthesized in 1983. This highly air- and moisture-sensitive solid has a sandwich molecular structure, where the electron is trapped within nearly spherical lattice cavities. However, the shortest electron-electron distance is too long (8.68 Å) to make this material a conductor of electricity.[1]
References
^ abcdefSteed, Jonathan W.; Atwood, Jerry L. (2009). Supramolecular Chemistry (2nd ed.). Wiley. ISBN978-0-470-51233-3.
^Caswell, Lyman R.; Savannunt, Diana S. (January 1988). "Temperature and solvent effects on the experimental dipole moments of three crown ethers". J. Heterocyclic Chem. 25 (1): 73–79. doi:10.1002/jhet.5570250111.
^ abGokel, George W.; Cram, Donald J.; Liotta, Charles L.; Harris, Henry P.; Cook, Fred L. (1977). "18-Crown-6". Org. Synth. 57: 30. doi:10.15227/orgsyn.057.0030.
^Jilek, Robert E.; Fischer, Paul J.; Ellis, John E. (2014). Bis(1,2-Bis(Dimethylphosphano)Ethane)Tricarbonyltitanium(0) and Hexacarbonyltitanate(2−). Inorganic Syntheses. Vol. 36. pp. 127–134. doi:10.1002/9781118744994.ch24. ISBN9781118744994.
^Dunitz, J. D.; Seiler, P. (1974). "1,4,7,10,13,16-Hexaoxacyclooctadecane". Acta Crystallogr. B30 (11): 2739. doi:10.1107/S0567740874007928.
^Atwood, Jerry L.; Bott, Simon G.; Coleman, Anthony W.; Robinson, Kerry D.; Whetstone, Stephen B.; Means, C. Mitchell (December 1987). "The oxonium cation in aromatic solvents. Synthesis, structure, and solution behavior of ". Journal of the American Chemical Society. 109 (26): 8100–8101. doi:10.1021/ja00260a033.
^Atwood, Jerry L.; Bott, Simon G.; Means, C. Mitchell; Coleman, Anthony W.; Zhang, Hongming; May, Michael T. (February 1990). "Synthesis of salts of the hydrogen dichloride anion in aromatic solvents. 2. Syntheses and crystal structures of and the related ". Inorganic Chemistry. 29 (3): 467–470. doi:10.1021/ic00328a025.
^Liotta, C. L.; Berknerin, J. (2004). "18-Crown-6". In Paquette, L. (ed.). Encyclopedia of Reagents for Organic Synthesis. New York: J. Wiley & Sons. doi:10.1002/047084289X.rc261. ISBN0471936235.
^Wynn, David; et al. (1984). "The Solubility of Alkali-Metal Fluorides in Non-Aqueous Solvents With and Without Crown Ethers...". Talanta. 31 (11): 1036–1040. doi:10.1016/0039-9140(84)80244-1. PMID 18963717.
^Cook, Fred L.; Bowers, Chauncey W.; Liotta, C. L. (November 1974). "Chemistry of naked anions. III. Reactions of the 18-crown-6 complex of potassium cyanide with organic substrates in aprotic organic solvents". The Journal of Organic Chemistry. 39 (23): 3416–3418. doi:10.1021/jo00937a026.
crown, also, dibenzo, crown, organic, compound, with, formula, c2h4o, iupac, name, hexaoxacyclooctadecane, white, hygroscopic, crystalline, solid, with, melting, point, like, other, crown, ethers, crown, functions, ligand, some, metal, cations, with, particula. See also Dibenzo 18 crown 6 18 Crown 6 is an organic compound with the formula C2H4O 6 and the IUPAC name of 1 4 7 10 13 16 hexaoxacyclooctadecane It is a white hygroscopic crystalline solid with a low melting point 1 Like other crown ethers 18 crown 6 functions as a ligand for some metal cations with a particular affinity for potassium cations binding constant in methanol 106 M 1 The point group of 18 crown 6 is S6 The dipole moment of 18 crown 6 varies in different solvent and under different temperature Under 25 C the dipole moment of 18 crown 6 is 2 76 0 06 D in cyclohexane and 2 73 0 02 in benzene 2 The synthesis of the crown ethers led to the awarding of the Nobel Prize in Chemistry to Charles J Pedersen 18 Crown 6 NamesPreferred IUPAC name 1 4 7 10 13 16 HexaoxacyclooctadecaneIdentifiersCAS Number 17455 13 9 Y3D model JSmol Interactive imageInteractive imageBeilstein Reference 1619616ChEBI CHEBI 32397 YChEMBL ChEMBL155204 YChemSpider 26563 YECHA InfoCard 100 037 687EC Number 241 473 5Gmelin Reference 4535PubChem CID 28557UNII 63J177NC5B YCompTox Dashboard EPA DTXSID7058626InChI InChI 1S C12H24O6 c1 2 14 5 6 16 9 10 18 12 11 17 8 7 15 4 3 13 1 h1 12H2 YKey XEZNGIUYQVAUSS UHFFFAOYSA N YInChI 1 C12H24O6 c1 2 14 5 6 16 9 10 18 12 11 17 8 7 15 4 3 13 1 h1 12H2Key XEZNGIUYQVAUSS UHFFFAOYAPSMILES O1CCOCCOCCOCCOCCOCC1C1COCCOCCOCCOCCOCCO1PropertiesChemical formula C12H24O6Molar mass 264 315 g molDensity 1 237 g cm3Melting point 37 to 40 C 99 to 104 F 310 to 313 K Boiling point 116 C 241 F 389 K 0 2 Torr Solubility in water 75 g LHazardsGHS labelling PictogramsSignal word WarningHazard statements H302 H315 H319 H335Precautionary statements P261 P264 P270 P271 P280 P301 P312 P302 P352 P304 P340 P305 P351 P338 P312 P321 P330 P332 P313 P337 P313 P362 P403 P233 P405 P501Related compoundsRelated compounds Dibenzo 18 crown 6TriglymeHexaaza 18 crown 6Except where otherwise noted data are given for materials in their standard state at 25 C 77 F 100 kPa Y verify what is Y N Infobox references Contents 1 Synthesis 2 Reactions 3 Applications 4 References 5 External linksSynthesis EditThis compound is prepared by a modified Williamson ether synthesis in the presence of a templating cation 3 It can be also prepared by the oligomerization of ethylene oxide 1 CH2OCH2CH2Cl 2 CH2OCH2CH2OH 2 2 KOH CH2CH2O 6 2 KCl 2 H2OIt can be purified by distillation where its tendency to supercool becomes evident 18 Crown 6 can also be purified by recrystallisation from hot acetonitrile It initially forms an insoluble solvate 3 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 salt 4 Crystallographic analysis reveals a relatively flat molecule but one where the oxygen centres are not oriented in the idealized 6 fold symmetric geometry usually shown 5 The molecule undergoes significant conformational change upon complexation Reactions Edit The complex of H3O with 18 crown 6 18 Crown 6 has a high affinity for the hydronium ion H3O as it can fit inside the crown ether Thus reaction of 18 crown 6 with strong acids gives the cation H 3 O 18 crown 6 displaystyle ce H3O 18 crown 6 For example interaction of 18 crown 6 with HCl gas in toluene with a little moisture gives an ionic liquid layer with the composition H 3 O 18 crown 6 HCl 2 3 8 C 6 H 5 Me displaystyle ce H3O 18 crown 6 HCl2 3 8 ce C6H5Me from which the solid H 3 O 18 crown 6 HCl 2 displaystyle ce H3O 18 crown 6 HCl2 can be isolated on standing Reaction of the ionic liquid layer with two molar equivalents of water gives the crystalline product H 5 O 2 H 3 O 18 crown 6 Cl 2 displaystyle ce H5O2 H3O 18 crown 6 Cl2 1 6 7 Applications Edit 18 crown 6 complex with potassium ion 18 Crown 6 binds to a variety of small cations using all six oxygens as donor atoms Crown ethers can be used in the laboratory as phase transfer catalysts 8 Salts which are normally insoluble in organic solvents are made soluble by crown ether 9 For example potassium permanganate dissolves in benzene in the presence of 18 crown 6 giving the so called purple benzene which can be used to oxidize diverse organic compounds 1 Various substitution reactions are also accelerated in the presence of 18 crown 6 which suppresses ion pairing 10 The anions thereby become naked nucleophiles For example using 18 crown 6 potassium acetate is a more powerful nucleophile in organic solvents 1 K 18 crown 6 OAc C6H5CH2Cl C6H5CH2OAc K 18 crown 6 Cl The first electride salt to be examined with X ray crystallography Cs 18 crown 6 2 e was synthesized in 1983 This highly air and moisture sensitive solid has a sandwich molecular structure where the electron is trapped within nearly spherical lattice cavities However the shortest electron electron distance is too long 8 68 A to make this material a conductor of electricity 1 References Edit a b c d e f Steed Jonathan W Atwood Jerry L 2009 Supramolecular Chemistry 2nd ed Wiley ISBN 978 0 470 51233 3 Caswell Lyman R Savannunt Diana S January 1988 Temperature and solvent effects on the experimental dipole moments of three crown ethers J Heterocyclic Chem 25 1 73 79 doi 10 1002 jhet 5570250111 a b Gokel George W Cram Donald J Liotta Charles L Harris Henry P Cook Fred L 1977 18 Crown 6 Org Synth 57 30 doi 10 15227 orgsyn 057 0030 Jilek Robert E Fischer Paul J Ellis John E 2014 Bis 1 2 Bis Dimethylphosphano Ethane Tricarbonyltitanium 0 and Hexacarbonyltitanate 2 Inorganic Syntheses Vol 36 pp 127 134 doi 10 1002 9781118744994 ch24 ISBN 9781118744994 Dunitz J D Seiler P 1974 1 4 7 10 13 16 Hexaoxacyclooctadecane Acta Crystallogr B30 11 2739 doi 10 1107 S0567740874007928 Atwood Jerry L Bott Simon G Coleman Anthony W Robinson Kerry D Whetstone Stephen B Means C Mitchell December 1987 The oxonium cation in aromatic solvents Synthesis structure and solution behavior of H 3 O 18 crown 6 Cl H Cl displaystyle ce H3O 18 crown 6 Cl H Cl Journal of the American Chemical Society 109 26 8100 8101 doi 10 1021 ja00260a033 Atwood Jerry L Bott Simon G Means C Mitchell Coleman Anthony W Zhang Hongming May Michael T February 1990 Synthesis of salts of the hydrogen dichloride anion in aromatic solvents 2 Syntheses and crystal structures of K 18 crown 6 Cl H Cl displaystyle ce K 18 crown 6 Cl H Cl Mg 18 crown 6 Cl H Cl 2 displaystyle ce Mg 18 crown 6 Cl H Cl 2 H 3 O 18 crown 6 Cl H Cl displaystyle ce H3O 18 crown 6 Cl H Cl and the related H 3 O 18 crown 6 Br H Br displaystyle ce H3O 18 crown 6 Br H Br Inorganic Chemistry 29 3 467 470 doi 10 1021 ic00328a025 Liotta C L Berknerin J 2004 18 Crown 6 In Paquette L ed Encyclopedia of Reagents for Organic Synthesis New York J Wiley amp Sons doi 10 1002 047084289X rc261 ISBN 0471936235 Wynn David et al 1984 The Solubility of Alkali Metal Fluorides in Non Aqueous Solvents With and Without Crown Ethers Talanta 31 11 1036 1040 doi 10 1016 0039 9140 84 80244 1 PMID 18963717 Cook Fred L Bowers Chauncey W Liotta C L November 1974 Chemistry of naked anions III Reactions of the 18 crown 6 complex of potassium cyanide with organic substrates in aprotic organic solvents The Journal of Organic Chemistry 39 23 3416 3418 doi 10 1021 jo00937a026 External links EditSigma Aldrich chemical profile dead link Retrieved from https en wikipedia org w index php title 18 Crown 6 amp oldid 1124047496, wikipedia, wiki, book, books, library,
