Crown ether



  Crown ethers are oxygen. Crown ethers are much broader than the oligomers of ethylene oxide; an important group are derived from catechol.

Crown ethers strongly bind certain cations, forming denticity of the polyether influences the affinity of the crown ether for various cations. For example, 18-crown-6 has high affinity for potassium cation, 15-crown-5 for sodium cation, and 12-crown-4 for lithium cation. The high affinity of 18-crown-6 for potassium ions contributes towards its toxicity.

 

Crown ethers in nature

Crown ethers are not the only macrocyclic ligands that have affinity for the potassium cation. Ionophores such as valinomycin also display a marked preference for the potassium cation over other cations.

History of synthetic crown ethers

In 1967, phase transfer catalysts, and other emerging disciplines benefited from the discovery of crown ethers. Pedersen particularly popularized the dibenzo crown ethers.[4]

Pedersen shared the 1987 Nobel Prize in Chemistry for the discovery of the synthetic routes to and binding properties, of crown ethers.

Affinity for cations

Apart from its high affinity for potassium cations, amine on their side chains. Those protonated amino groups can bind to the cavity of 18-crown-6 and form stable complexes in the gas phase. Hydrogen-bonds are formed between the three hydrogen atoms of protonated amines and three oxygen atoms of 18-crown-6. These hydrogen-bonds make the complex a stable adduct.

Aza-crowns

"cyclen. Mixed amine-ether crowns are also known.[5]

References

  1. ^ C. J. Pedersen, J. Am. Chem. Soc., 1967, 89, 7017.
  2. ^ D. G. Stewart. D. Y. Waddan and E. T. Borrows, British Patent 785,229, Oct. 23, 1957.
  3. ^ J. L. Down, J. Lewis, B. Moore and G. W. Wilkinson, Proc. Chem. Soc., 1959, 209; J. Chem. Soc., 1959, 3767.
  4. ^ Charles J. Pedersen (1988). "Macrocyclic Polyethers: Dibenzo-18-Crown-6 Polyether and Dicyclohexyl-18-Crown-6 Polyether". Org. Synth.; Coll. Vol. 6: 395. 
  5. ^ Vincent J. Gatto, Steven R. Miller, and George W. Gokel (1988). "4,13-Diaza-18-Crown-6". Org. Synth.; Coll. Vol. 8: 152. 
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Crown_ether". A list of authors is available in Wikipedia.