18-Crown-6, also known as 1,4,7,10,13,16-HEXAOXACYCLOOCTADECANE, is a well-known crown ether used as a food additive.
In terms of toxicity, it fares as moderately toxic but can cause sudden irritation in eye and skin if protective agents are not used. Severe respiratory tract infections can also occur, as specified by the European Chemicals Agency (ECHA). The lethal concentration (LD50) of crown ethers, including 18-Crown-6 in mice is about the same as that found for aspirin. Since it is approved for use as a biochemical ingredient, it is an important chemical compound that undergoes regular toxicity tests.Like other crown ethers, 18-crown-6 is used as an intermediate for chemical synthesis of new biopolymers and specialty chemicals. 18-Crown 6 intermediate is an important compound for chemical manufacturing of alkalide salts.
18-Crown-6 weighs 264.32 grams per mole and remains uncharged at standard temperature and pressure. It shows absorbance peaks at 1100 to 1110 cm-1 in FTIR spectra and ATR-IR spectra. It also exhibits Topological Polar Surface Area of 55.4 A?2.
This organic compound has the general formula of [C2H4O]6 and functions as a ligand for some metal cations with a particular affinity for potassium cations. The dipole moment of 18-crown-6 varies in different solvent and under different temperature. Under 25°C, the dipole moment of 18-crown-6 is 2.76 ± 0.06 D in cyclohexane and 2.73 ± 0.02 in benzene. Therefore, it’s soluble in organic solvents such as cyclohexane and benzene and can be applied in the development of new polymers and new bio-separation techniques.
The clusters of research and innovation using 18-Crown-6 are located in Russia, China, Australia, Czech Republic, Spain, Finland and has expanded across the Pacific as well. While these research groups are exploring new chemical derivatives for industrial application in electronic devices, implantable surgery devices, pesticides, etc. the number of chemical vendors and exporters of all crown ethers including 18-Crown-6 is growing as well. The biggest advantage that crown ethers provide is the binding abilities with highly electropositive ions like K+ and Na+. This allows organic compounds to form binding ligands by forming alkalide salts and allowing hydrophobic interactions as well. The number of 18 Crown 6 intermediate manufacturers and suppliers are spread over US, Japan, France, China, Canada and Germany.
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PVC based membrane containing dicyclohexano-18-crown-6 (I) as active material along with sodium tetraphenyl borate (NaTPB) as an anion excluder and dibutyl phthalate as solvent mediator in the ratio 20: 4: 150: 150 (w/w)(I–NaTPB–DBP–PVC) exhibits good properties with a Nernstian response of 29.0±1.0 mV per decade of activity and a working concentration range of 2.1×10?5–1.0×10?1 M.
The technique uses underivatized amino acids in conjunction with an underivatized capillary, which significantly reduces cost and analysis time. It was found that when (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18-C-6-TCA, MW 440) was used as the background electrolyte/complexation reagent during the capillary electrophoresis/electrospray ionization-mass spectrometry (CE/ESI-MS) analysis of underivatized amino acids, stable complexes were formed between the amino acids and the 18-C-6-TCA molecules.
Rotation of the crown-6 molecules within a Cs2(crown-6)3 supramolecule above 220 K was confirmed using X-ray diffraction, NMR, and specific heat measurements. Strong correlations were observed between the magnetic behavior of the [Ni(dmit)2]- ions and molecular rotation.
Abstract: We present an ab initio, quantum mechanical study of 18-crown-6 (18~ 6) and its interaction with the alkali metal cations Li+, Na+, K+, Rb+, and Cs+. Geometries, binding energies, and binding enthalpies are evaluated at the restricted Hartree-Fock (RHF) level using standard basis sets (3-21G and 6-31+G*) and relativistic effective core potentials.
Abstract: We have performed extensive classical molecular dynamics simulations to examine the mechanism and thermodynamics for ion selectivity of 18-crown-6 ether in aqueous solutions. We have computed the free energy profiles or potentials of mean force and the corresponding binding free energies for M+:18-Crown-6 (M+ = K+, Na+, Rb+, Cs+) complexation in water.
Binding within the first coordination sphere of the dioxoactinide ion is observed for the crown ether ligand in the complex ion [NpO2(crown-6)]+1, which is readily formed on adding crown-6 to an aqueous solution of NpO2+ or NpO22+ in dilute HClO4 or CF3SO3H. The structure of the complex was confirmed by the X-ray structure analysis and spectroscopic data of 1[ClO4].
From extraction experiments and ?-activity measurements, the exchange extraction constants corresponding to the general equilibrium M+(aq)+NaL+(nb)?ML+(nb)+Na+(aq) taking place in the two-phase water-nitrobenzene system (M+=Li+, K+, Rb+, Cs+; L=18-crown-6; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. The stability constants of the ML+ complexes in nitrobenzene saturated with water were calculated; they are found to increase in the cation order Cs+Li+Na+Rb+K+.
A conductance study of the interaction between CO2+, Ni2+, Cu2+, Zn2+, Cd2+, Pb2+ and Hg2+ ions with hexathia-18-crown-6-tetraone in dimethyl sulfoxide solution has been carried out at various temperatures. Formation constants of the resulting 1:1 complexes were determined from the molar conductance–mole ratio data and found to vary in the order Hg2+>Pb2+>Cd2+>Cu2+>Ni2+>Co2+>Zn2+. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. All complexes formed were enthalpy stabilized but entropy destabilized.
Equilibrium constant (K), enthalpy change (?H), and entropy change (?S) values were determined for the interactions of a series of chiral pyridino-18-crown-6 type ligands with enantiomers of several primary alkylammonium salts in various solvents. Good enantiomeric recognition in terms of ? logK was observed in many systems with ? logK values greater than 0.4.
Interaction of dibenzo-18-crown-6 (DBC) with H3O+ (HP) in nitrobenzene-d5 and dichloromethane-d2 was studied by using 1H and 13C NMR spectra and relaxations, FTIR spectra, and quantum chemical DFT calculations. NMR shows that the DBC•HP complex is in a dynamic equilibrium with the reactants, the equilibrium constant K being 0.66 × 103, 1.16 × 104, and 1.03 × 104 L·mol?1 in CD2Cl2, nitrobenzene, and acetonitrile, respectively.