18-crown-6
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| General | ||||||||||||||||
| Surname | [18] Crown-6 | |||||||||||||||
| other names |
1,4,7,10,13,16-hexaoxacyclooctadecane |
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| Molecular formula | C 12 H 24 O 6 | |||||||||||||||
| Brief description |
odorless white to light yellow solid |
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| properties | ||||||||||||||||
| Molar mass | 264.32 g mol −1 | |||||||||||||||
| Physical state |
firmly |
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| density |
1.175 g cm −3 |
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| Melting point |
42-45 ° C |
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| boiling point |
116 ° C (at 0.2 mmHg) |
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| solubility |
soluble in water |
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | ||||||||||||||||
[18] Crown-6 is a chemical compound from the group of crown ethers .
Extraction and presentation
[18] Crown-6 can be obtained by a modified Williamson ether synthesis in the presence of a template cation:
The preparation by oligomerization of ethylene oxide is also possible . The compound can also be produced in a yield of more than 90% from potassium tert-butoxide and triethylene glycol ditosylate.
properties
[18] Krone-6 is a light yellow solid. In 1967 Charles Pedersen discovered the special property of the compound that, as a host, it can be in a host-guest relationship with a potassium cation . The reason is that the size of the ring of the connection is between 2.3 and 3.2 Å and thus corresponds quite well with the size of the potassium ion (2.66 Å). In the host-guest relationship, ion-dipole interactions bind the positively charged potassium ion inside the macrocycle with the negatively polarized oxygen atoms of the ether . This makes potassium salts soluble in solvents in which they were previously insoluble. In the presence of [18] crown-6, typical inorganic salts such as potassium permanganate are therefore soluble in solvents such as benzene . The anions of the potassium salts are ready for reaction due to the masking of the potassium ion. In this way stable complex compounds are formed . The stability of such complexes is around a factor of 100 greater than those with sodium or rubidium ions .
use
[18] Crown-6 can be used for phase-transfer catalysis . The compound can act as a phase transfer catalyst (like other crown ethers) because it "organically masks" alkali metal ions and extracts them together with their anions into non-polar organic solvents. It shields the positive charge of the cation and thus promotes the dissociation of the ion pair in polar aprotic solvents . In less polar solvents, they favor the formation of loose ion pairs with higher reactivity, separated by solvent molecules.
Related links
Individual evidence
- ↑ a b c d Data sheet 18-Crown-6, 99% at AlfaAesar, accessed on October 20, 2017 ( PDF )(JavaScript required) .
- ↑ a b c d e f g h i data sheet 18-Krone-6, ≥99.0% from Sigma-Aldrich , accessed on October 20, 2017 ( PDF ).
- ↑ George W. Gokel, Donald J. Cram , Charles L. Liotta, Henry P. Harris, and Fred L. Cook: 18-Krone-6 In: Organic Syntheses . 6, 1988, p. 301, doi : 10.15227 / orgsyn.057.0030 ( PDF ).
- ↑ Jonathan W. Steed, Jerry L. Atwood: Supramolecular Chemistry . Wiley, 2009, ISBN 978-0-470-74089-7 .
- ^ Crown ethers - Lexicon of Chemistry. In: Spektrum.de. Retrieved September 14, 2015 .
- ↑ a b The power of the non-covalent - academics. (No longer available online.) In: academics.de. Archived from the original on October 27, 2017 ; accessed on September 14, 2015 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ Helmut Günzler, A. Müfit Bahadir, Klaus Danzer, Werner Engewald, Wilhelm Fresenius, Rudolf Galensa, Walter Huber, Michael Linscheid, Georg Schwedt, Günter Tölg: Analytiker-Taschenbuch . Springer-Verlag, 2013, ISBN 978-3-642-72167-0 ( books.google.com ).
- ↑ Ahmad Zaeni: Synthesis, characterization and crystal structure studies of new organometallic compounds of lanthanides and alkali metals with fluorenyl and substituted fluorenyl ligands . Cuvillier Verlag, 2004, ISBN 978-3-86537-258-1 ( books.google.com ).
- ↑ Brief introduction to phase transfer catalysis. In: uni-bielefeld.de. www.uni-bielefeld.de, accessed on September 14, 2015 .
