Crown ether

Crown ether, also known as "crown compound" because of its crown-like shape, is a class of compounds with a special property of complexation which was newly developed after 1970s. It’s a class of macrocyclic polyether composed of [CH2CH2Y] n (n> 2) units, wherein Y is a heteroatom such as O, N, S, or P. Crown ether narrowly refers to macrocyclic polyether in which Y is O, such as 18-crown-6 and dicyclohexyl-18-crown-6. They are named after the order of non-ring substituents, the number of the ring atoms, class name (crown) and the number of the ring hetero atoms according to the customary nomenclature, such as dibenzo-18-crown-6. Saturated crown ether is a colorless viscous liquid or low melt solid while aromatic ring-containing crown ether is a colorless crystal. Aromatic ring-containing crown ethers are insoluble in water, alcohol and common organic solvents at room temperature but more soluble in dichloromethane, chloroform, pyridine and formic acid. Crown ethers containing cyclohexyl have a higher solubility than the corresponding benzo crown ether in water, alcohols and aromatic hydrocarbons, also in petroleum ether.

Crown ether generally has a good thermal stability. However its ether bonds are susceptible to oxidation when melted or at a high temperature. The aromatic ring in the molecule can take part in bromination, nitration, esterification and ozonization, as well as form a polymer with formaldehyde in condensation. Crown ether can form a complex substance called crypate rendering many salts soluble in non-polar organic solvent, so that many of difficult reactions can be easily carried out. The stronger its lipophilic is, the greater catalytic activity it has. Furthermore, the reaction is selective since its fixed space can only accommodate ion of the corresponding size. The stability of formed by crown ethers and positive ions is mainly dependent on the relative size of the polyether ring and positive ions; and the stability constant is generally small for this crypate was formed by electrostatic interactions. What makes the reaction convenient is that the complexing can be easily broken down by adding water, dilute acid or through heat decomposition.

Preparation: Williamson (Williamson) ether synthesis is generally adopted. But in order to prevent a chain polymerization, high dilution method, fractional condensation and template reaction are recommended.

Currently the most widely used also the most readily available crown ethers are 18-crown-6, dibenzo-18-crown-6 and dicyclohexyl-18-crown-6. It is an important characteristic of crown ethers that it forms complexes with metal cations, which is utilized in phase transfer catalysis in organic synthesis.

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Structure Chemical Name CAS MF
1,4,7-Triazacyclononane 1,4,7-Triazacyclononane 4730-54-5 C6H15N3
18-Crown-6 18-Crown-6 17455-13-9 C12H24O6
Cyclen Cyclen 294-90-6 C8H20N4
2,5-DIMETHOXYCINNAMIC ACID 2,5-DIMETHOXYCINNAMIC ACID 161282-95-7 C40H46O8
DOTA DOTA 60239-18-1 C16H28N4O8
1,4,7,10-TETRAAZACYCLODODECANE TETRAHYDROCHLORIDE 1,4,7,10-TETRAAZACYCLODODECANE TETRAHYDROCHLORIDE 10045-25-7 C8H21ClN4
1,4,8,11-TETRAAZACYCLOTETRADECANE 1,4,8,11-TETRAAZACYCLOTETRADECANE 295-37-4 C10H24N4
Dicyclohexano-18-crown-6 Dicyclohexano-18-crown-6 16069-36-6 C20H36O6
Kryptofix 222 Kryptofix 222 23978-09-8 C18H36N2O6
1,4,7-Triazacyclononane trihydrochloride 1,4,7-Triazacyclononane trihydrochloride 58966-93-1 C6H18Cl3N3
4'-Aminobenzo-15-crown-5-ether 4'-Aminobenzo-15-crown-5-ether 60835-71-4 C14H21NO5
1,4,7-TRIMETHYL-1,4,7-TRIAZACYCLONONANE 1,4,7-TRIMETHYL-1,4,7-TRIAZACYCLONONANE 96556-05-7 C9H21N3
1,4,10,13-TETRAOXA-7,16-DIAZACYCLOOCTADECANE 1,4,10,13-TETRAOXA-7,16-DIAZACYCLOOCTADECANE 23978-55-4 C12H26N2O4
1,4,7,10,13,16-HEXAAZACYCLOOCTADECANE 1,4,7,10,13,16-HEXAAZACYCLOOCTADECANE 296-35-5 C12H30N6
4-NITROBENZO-15-CROWN-5 4-NITROBENZO-15-CROWN-5 60835-69-0 C14H19NO7
2,3-(4-METHOXYCARBONYLBENZO)-1,4,7,10,13-PENTAOXACYCLOPENTADEC-2-ENE 2,3-(4-METHOXYCARBONYLBENZO)-1,4,7,10,13-PENTAOXACYCLOPENTADEC-2-ENE 56683-56-8 C16H22O7
4'-ACETYLBENZO-18-CROWN 6-ETHER 4'-ACETYLBENZO-18-CROWN 6-ETHER 41855-35-0 C18H26O7
4'-FORMYLBENZO-18-CROWN 6-ETHER 4'-FORMYLBENZO-18-CROWN 6-ETHER 60835-74-7 C17H24O7
DIBENZO-30-CROWN-10 DIBENZO-30-CROWN-10 17455-25-3 C28H40O10
1,4,8,12-TETRAAZACYCLOPENTADECANE 1,4,8,12-TETRAAZACYCLOPENTADECANE 15439-16-4 C11H26N4
2-HYDROXYMETHYL-15-CROWN-5 2-HYDROXYMETHYL-15-CROWN-5 75507-25-4 C11H22O6
1,3-DIISOPROPOXYCALIX[4!ARENECROWN-6, 97 1,3-DIISOPROPOXYCALIX[4!ARENECROWN-6, 97 161282-96-8 C44H54O8
Aza-15-crown-5 Aza-15-crown-5 66943-05-3 C10H21NO4
1,4,7-TRIOXA-10-AZACYCLODODECANE 1,4,7-TRIOXA-10-AZACYCLODODECANE 41775-76-2 C8H17NO3
1,4,7,10,13,16,19,22-OCTAOXACYCLOTETRACOSANE 1,4,7,10,13,16,19,22-OCTAOXACYCLOTETRACOSANE 33089-37-1 C16H32O8
1,4,8,11-TETRATHIACYCLOTETRADECANE 1,4,8,11-TETRATHIACYCLOTETRADECANE 24194-61-4 C10H20S4
DIBENZO-15-CROWN-5 DIBENZO-15-CROWN-5 14262-60-3 C18H20O5
1,4,7,10,13-PENTAOXACYCLOPENTADECANE-2-METHANAMINE 1,4,7,10,13-PENTAOXACYCLOPENTADECANE-2-METHANAMINE 83585-56-2 C11H23NO5
4-Vinylbenzo-18-crown-6 4-Vinylbenzo-18-crown-6 39557-71-6 C18H26O6
15-CROWN-4 [4-(2,4-DINITROPHENYLAZO)PHENOL] 15-CROWN-4 [4-(2,4-DINITROPHENYLAZO)PHENOL] 81238-57-5 C20H22N4O9
4'-BROMOBENZO-18-CROWN-6 4'-BROMOBENZO-18-CROWN-6 75460-28-5 C16H23BrO6
BIS(1,4-PHENYLENE)-34-CROWN 10-ETHER BIS(1,4-PHENYLENE)-34-CROWN 10-ETHER 53914-95-7 C28H40O10
N,N'-DIBENZYL-1,4,10,13-TETRAOXA-7,16-DIAZACYCLOOCTADECANE N,N'-DIBENZYL-1,4,10,13-TETRAOXA-7,16-DIAZACYCLOOCTADECANE 69703-25-9 C26H38N2O4
4-NITROBENZO-18-CROWN-6 4-NITROBENZO-18-CROWN-6 53408-96-1 C16H23NO8
N-PHENYLAZA-15-CROWN 5-ETHER N-PHENYLAZA-15-CROWN 5-ETHER 66750-10-5 C16H25NO4
Dibenzo-24-crown-8 Dibenzo-24-crown-8 14174-09-5 C24H32O8
BENZO-12-CROWN-4 BENZO-12-CROWN-4 14174-08-4 C12H16O4
2,3-(4-CARBOXYBENZO)-1,4,7,10,13,16-HEXAOXACYCLOOCTADEC-2-ENE 2,3-(4-CARBOXYBENZO)-1,4,7,10,13,16-HEXAOXACYCLOOCTADEC-2-ENE 60835-75-8 C17H24O8
18-CROWN-5 [4-(2,4-DINITROPHENYLAZO)PHENOL] 18-CROWN-5 [4-(2,4-DINITROPHENYLAZO)PHENOL] 81238-58-6 C22H26N4O10
1,4,8,11-TETRAMETHYL-1,4,8,11-TETRAAZACYCLOTETRADECANE 1,4,8,11-TETRAMETHYL-1,4,8,11-TETRAAZACYCLOTETRADECANE 41203-22-9 C14H32N4
Dicyclohexano-24-crown-8 Dicyclohexano-24-crown-8 17455-23-1 C24H44O8
(+)-(18-CROWN-6)-2,3,11,12-TETRACARBOXYLIC ACID (+)-(18-CROWN-6)-2,3,11,12-TETRACARBOXYLIC ACID 61696-54-6 C16H24O14
1,5,9-TRIAZACYCLODODECANE 1,5,9-TRIAZACYCLODODECANE 294-80-4 C9H21N3
1,4,7,10,13,16-hexaazacyclooctadecane hexahydrochloride 1,4,7,10,13,16-hexaazacyclooctadecane hexahydrochloride 58105-91-2 C12H30N6.6HCl
4'-BROMOBENZO-15-CROWN 5-ETHER 4'-BROMOBENZO-15-CROWN 5-ETHER 60835-72-5 C14H19BrO5
2-(HYDROXYMETHYL)-12-CROWN 4-ETHER 2-(HYDROXYMETHYL)-12-CROWN 4-ETHER 75507-26-5 C9H18O5
4'-Aminobenzo-18-crown-6 4'-Aminobenzo-18-crown-6 68941-06-0 C16H25NO6
1,7-DIAZA-12-CROWN-4 1,7-DIAZA-12-CROWN-4 294-92-8 C8H18N2O2
(BENZO-15-CROWN 5-ETHER)-4'-CARBOXYLIC ACID (BENZO-15-CROWN 5-ETHER)-4'-CARBOXYLIC ACID 56683-55-7 C15H20O7
[2,5]-DIBENZO-21-CROWN-7 [2,5]-DIBENZO-21-CROWN-7 14098-41-0 C22H28O7
2-(ALLYLOXYMETHYL)-18-CROWN 6-ETHER 2-(ALLYLOXYMETHYL)-18-CROWN 6-ETHER 84812-04-4 C16H30O7
1,4,7,10,13-PENTAOXA-16-AZACYCLOOCTADECANE 1,4,7,10,13-PENTAOXA-16-AZACYCLOOCTADECANE 33941-15-0 C12H25NO5
1,4,10-TRIOXA-7,13-DIAZACYCLOPENTADECANE 1,4,10-TRIOXA-7,13-DIAZACYCLOPENTADECANE 31249-95-3 C10H22N2O3
4'-ACETYLBENZO-15-CROWN 5-ETHER 4'-ACETYLBENZO-15-CROWN 5-ETHER 41757-95-3 C16H22O6
4-ACRYLAMIDOBENZO-18-CROWN-6, 98 4-ACRYLAMIDOBENZO-18-CROWN-6, 98 68865-32-7 C19H27NO7
4'-NITRO-5'-(PICRYLAMINO)BENZO-18-CROWN-6 4'-NITRO-5'-(PICRYLAMINO)BENZO-18-CROWN-6 74305-50-3 C22H25N5O14
1,3-DIOCTYLOXYCALIX[4!ARENECROWN-6, 97 1,3-DIOCTYLOXYCALIX[4!ARENECROWN-6, 97 161282-97-9 C54H74O8
4-TERT-BUTYLBENZO-15-CROWN-5 4-TERT-BUTYLBENZO-15-CROWN-5 15196-73-3 C18H28O5
2,3-NAPHTHO-15-CROWN-5 2,3-NAPHTHO-15-CROWN-5 17454-47-6 C18H22O5
4-Aminobenzo-15-crown-5 hydrochloride 4-Aminobenzo-15-crown-5 hydrochloride 111076-66-5 C14H21NO5.ClH
CYCLOHEXANO-18-CROWN-6 CYCLOHEXANO-18-CROWN-6 17454-53-4 C16H30O6
4-T-BUTYLCYCLOHEXANO-15-CROWN-5 4-T-BUTYLCYCLOHEXANO-15-CROWN-5 17454-49-8 C18H34O5
4',4''(5'')-DI-TERT-BUTYLDICYCLOHEXANO-18-CROWN-6 4',4''(5'')-DI-TERT-BUTYLDICYCLOHEXANO-18-CROWN-6 28801-57-2 C28H52O6
POLY(DIBENZO-18-CROWN-6) POLY(DIBENZO-18-CROWN-6) 53660-42-7 C21H26O7
4-AMINOBENZO-18-CROWN-6 SESQUIHYDRATE HYDROCHLORIDE, 99 4-AMINOBENZO-18-CROWN-6 SESQUIHYDRATE HYDROCHLORIDE, 99 205504-06-9 C16H25NO6.ClH.H2O
4',4''(5'')-DI-TERT-BUTYLDIBENZO-18-CROWN-6 4',4''(5'')-DI-TERT-BUTYLDIBENZO-18-CROWN-6 29471-17-8 C28H40O6
CYCLOHEXANO-15-CROWN-5 CYCLOHEXANO-15-CROWN-5 17454-48-7 C14H26O5
4'-AMINO-5'-NITROBENZO-15-CROWN-5 4'-AMINO-5'-NITROBENZO-15-CROWN-5 77001-50-4 C14H20N2O7
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