Crown ether - Definition and Overview

Crown ethers are heterocyclic chemical compounds that, in their simplest form, are cyclic oligomers of dioxane. The essential repeating unit of any simple crown ether is ethyleneoxy, i.e., -CH₂CH₂O-, which repeats twice in dioxane and six times in 18-crown-6. The nine-membered ring 1,4,7-trioxonane (9-crown-3) is often called a crown and can interact with cations. Macrocycles of the (-CH₂CH₂O-)_n type in which n ≥ 4 are generally referred to as crown ethers rather than by their systematic names. This is partly because they comprise a special group of heterocycles that bind cations.

In the mid-1960s, Charles Pedersen, who was a chemist working at Dupont, discovered crown ether when he was trying to prepare a complexing agent for divalent cations. His strategy was to link two catechols through one hydroxyl on each molecule. This would give him a compound that could partially envelop the cation and, by ionization of the phenolic hydroxyls, neutralize the bound dication. He was surprised to isolate a byproduct that bound or complexed with potassium cation but had no ionizable hydroxyl group. He realized that the polyethers represented a new class of complexing agents that were capable of binding alkali metal cations. The fields of anionic synthetic reagents, phase-transfer catalysis, biological ion transfer, and other emerging disciplines benefited profoundly from the discovery of crown ether.

The discovery of crown ethers led to a Nobel Prize in 1987 for Charles Pedersen (with Donald Cram and Jean-Marie Lehn for their contribution to supramolecular chemistry).

See Also

Charles Pedersen's Nobel Lecture (http://nobelprize.org/chemistry/laureates/1987/pedersen-lecture.pdf)