The macrocyclic ether 1,4,7,10,13,16-hexaoxaoctadecane (18-crown-6) has the remarkable property of being able to transfer the hydronium (H3O+) ion from an aqueous solution to an organic medium. This property has been used to synthetize a 1:1 stoichiometric complex of this ether with hydronium tetrafluoroborate. This complex is very stable (mp 145 °C) and dissolves readily, without decomposition, in solvents such as CHCl3. The presence of the H3O+ and BF4− ions in the complex has been confirmed by chemical analysis, and by 1H nmr, Raman, and ir spectroscopy. The vibrational spectra indicate that a conformational change of the crown ether takes place in the complex over the temperature range −50 °C to −100 °C. The symmetry of the crown ether, which appears to be relatively high at room temperature, is considerably reduced below the transition temperature.
Unusual enantiomeric separation due to residual amines in chiral crown ether stationary phase linked by long alkyl chain
