Description
Dibenzo-18-crown-6 (DB18C6) is the first crown ether synthesized by Pedersen in 1967 and has the strongest binding affinity to a potassium cation (K+) among alkali metal cations. With the similarity of the sizes between K+ and the cavity of crown ether, it had long been believed that the binding selectivity comes from the size relationship between the metal cation and the cavity. However, it was reported that under identical experimental conditions, K+ bound strongly to all crown ethers (12-crown-4 to 24-crown-8) irrespective of the ring size among other cations such as Na+, Ca2+, and NH4+. Moreover, in the gas phase, 18-crown-6 (18C6) and dibenzo18-crown-6 (DB18C6) form preferential complexation in the order Li+ > Na+ > K+ > Rb+ > Cs+, while in the aqueous solution both of them show highest complexion capacity for K+ rather than Li+[1-2].
Chemical Properties
white to slightly beige fluffy powder
Uses
Crown ether/Dibenzo-18-crown-6 for synthesis. CAS 14187-32-7, molar mass 360.41 g/mol.
Uses
Dibenzo-18-crown-6, is used as an important raw material and intermediate used in organic Synthesis, pharmaceuticals, agrochemicals and dyestuff. It is an important organic intermediate.
Definition
ChEBI: Dibenzo-18-crown-6 is a crown ether that is 18-crown-6 ortho-fused to two benzene rings at positions 8-9 and 17-18. It has a role as a phase-transfer catalyst. It is a member of benzenes and a crown ether.
Synthesis
General procedure: The synthesis was carried out using the general procedure 2 and the product was purified by recrystallization in methanol. Yield analysis showed that the yield was 35% in open vessel in standard temperature control mode and 13% in power/time mode and 54% in closed vessel in standard temperature control mode and 60% in power/time mode. The product obtained was white crystal with a melting point of 148-150°C (literature value [2]: 150-152°C). Infrared spectra (KBr pressed sheet, cm^-1) showed characteristic absorption peaks located at 1040-1120 (-C-O-). NMR hydrogen spectrum (400MHz, CDCl3, ppm): 2.26 (quadruple peak, 4H, J=5.6Hz, -CH2-), 4.24 (triple peak, 8H, J=5.6Hz, -CH2-), 6.89-6.91 (multiple peaks, 8H, aromatic hydrogen). NMR carbon spectra (100 MHz, CDCl3, ppm): 29.28, 67.32, 115.58, 121.72, 149.44. Calculated values for elemental analysis (C18H20O4): C, 71.98; H, 6.71; O, 21.31; measured values: C, 72.39; H, 6.25; O, 21.36. Similarly, the can be synthesized by a two-step microwave-assisted synthesis, but requires the use of a diphenol intermediate instead of catechol as a precursor. Depending on the alkyl dihalides used in the ring-closing reaction, the method allows the preparation of symmetrical or asymmetrical dibenzocrown ethers (2-6).
Purification Methods
Crystallise it from *benzene, n-heptane or toluene and dry it under vacuum at room temperature for several days. [Szezygiel J Phys Chem 91 1252 1987, V.gtle ed. Top Corr Chem (Host Guest Complex Chemistry) 98 1981.]
References
[1] Pooja Sahu, Jayant K. Singh, Sk. M. Ali. “Structural and dynamical properties of Li+-dibenzo-18-crown-6(DB18C6) complex in pure solvents and at the aqueous-organic interface.” Journal of Molecular Modeling 20 9 (2014).
[2] Chang Min Choi, Nam Joon Kim, Jiyoung Heo. “Binding selectivity of dibenzo-18-crown-6 for alkali metal cations in aqueous solution: A density functional theory study using a continuum solvation model.” Chemistry Central Journal 6 1 (2012): 84.
