Crown ethers are heterocyclic chemical compounds that, in their simplest form, are cyclic oligomers of ethylene oxide. 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 because the molecules formed when this special group of heterocycles binds to cations resemble a crown sitting on a head in structure. Heterocycles are organic chemical structures containing non-carbon elements. ... A chemical compound is a chemical substance formed from two or more elements, with a fixed ratio determining the composition. ... In chemistry, an oligomer consists of a finite number of monomer units (oligo is Greek for a few), in contrast to a polymer which, at least in principle, consists of an infinite number of monomers. ... 1,4-Dioxane, often just called dioxane, is a clear, colorless organic compound which is a liquid at room temperature and pressure. ... An organic compound with the formula C12H24O6 and the IUPAC name of 1,4,7,10,13,16-Hexaoxacyclooctadecane Sigma Aldrich chemical profile ... A cation is an ion with positive charge. ... A macrocycle is, as defined by IUPAC, In the chemical literature, organic chemists may consider any molecule containing a ring of seven, fifteen, or any arbitrarily large number of atoms to be macrocyclic. ... Ether is the general name for a class of chemical compounds which contain an ether group — an oxygen atom connected to two (substituted) alkyl groups. ...

The crown ethers are notable for their ability to strongly solvate cations. The oxygen atoms are ideally situated to coordinate with a cation in the interior of the ring, whereas the exterior of the ring is hydrophobic. The result is that the complexed cation is soluble in nonpolar solvents. The size of the interior of the crown ether determines the size of the cation it can solvate. Therefore, 18-crown-6 has high affinity for potassium cation, 15-crown-5 for sodium cation and 12-crown-4 for lithium cation.

12-crown-4	15-crown-5	18-crown-6

Crown ethers are not the only macrocyclic ligands that have affinity for the potassium cation. Ionophores such as nonactin and valinomycin also display a marked preference for the potassium cation over other cations. Image File history File links 12-crown-4-ether structure. ... Image File history File links 15-crown-5-ether structure. ... Image File history File links 18-crown-6-ether structure. ... Nonactin is a chelate which acts as an antibiotic. ... Valinomycin is a polypeptide, that is it is made of twelve alternating amino acids to form a macrocyclic molecule. ...

Early reports of crown ethers concentrated on synthetic methods for their production; only later were their properties and the fundamental theoretical implications thereof realized.

In 1967, Charles Pedersen, who was a chemist working at DuPont, discovered a simple method of synthesizing a 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 by-product that bound or complexed with potassium cation but had no ionizable hydroxyl group. Citing earlier work on the dissolution of potassium in 16-crown-4, he realized that the cyclic polyethers represented a new class of complexing agents that were capable of binding alkali metal cations. He proceeded to report systematic studies of the synthesis and binding properties of crown ethers in a seminal series of papers. The fields of anionic synthetic reagents, phase transfer catalysts, biological ion transfer, and other emerging disciplines benefited profoundly from the discovery of crown ether. Charles J. Pedersen (October 3, 1904–October 26, 1989) was an American organic chemist best known for describing methods of synthesizing cyclic polyethers. ... Look up chemist on Wiktionary, the free dictionary. ... This article is about the DuPont company. ... Chelation (from Greek, claw like) describes the reversible binding of an organic ligand, the chelator or chelating agent, to a metal ion, forming a metal complex, the chelate. ... Catechol, also benzene-1,2-diol, is a phenol, with formula C6H4(OH)2. ... ... A by-product is a secondary or incidental product deriving from a manufacturing process or chemical reaction, and is not the primary product or service being produced. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ... Ether is the general name for a class of chemical compounds which contain an ether group — an oxygen atom connected to two (substituted) alkyl groups. ... The alkali metals are the series of elements in Group 1 (IUPAC style) of the periodic table, excluding hydrogen: that is, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). ... In chemistry, an anionic species is one that contains a full negative charge. ... Generally, synthetic means pertaining to synthesis, i. ... A phase transfer catalyst or PTC in chemistry is a type of chemical compound, often a quaternary ammonium salt, which facilitates the migration of a particular chemical component in one phase into a other phase in a heterogeneous system. ...

Pedersen received a Nobel Prize in 1987 for the discovery of the synthetic routes to and binding properties of crown ethers (along with Donald Cram and Jean-Marie Lehn for their contribution to supramolecular chemistry). Donald James Cram (April 22, 1919 - June 17, 2001) was an American chemist who shared the 1987 Nobel Prize in Chemistry for “synthesizing three-dimensional molecules that could mimic the functioning of natural molecules. ... Jean-Marie Lehn (born September 30, 1939) is a French chemist. ... Supramolecular chemistry is a relatively new field of chemistry which focuses quite literally on going beyond molecular chemistry. ...

See Also

Charles Pedersen's Nobel Lecture

D. G. Stewart. D. Y. Waddan and E. T. Borrows, British Patent 785,229, Oct. 23, 1957.

J. L. Down, J. Lewis, B. Moore and G. W. Wilkinson, Proc. Chem. Soc., 1959, 209; J. Chem. Soc., 1959, 3767.

C. J. Pedersen, J. Am. Chem. Soc., 1967, 89, 7017.