Competitive Potentiometric Study of Complexation of Some Organoammonium Ions with Selected Crown Ethers in Ethanol Solution Using Ag+ Ion as a Probe

The complexation of NH 4 +, CH 3 NH 3 +, C 2 H 5 NH 3 +, C 6 H 5 NH 3 + (anilinium), and C 5 H 5 NH + (pyridinum) ions with 18-crown-6, dicyclohexyl-18-crown-6, and 15-crown-5 in ethanol solution has been investigated by a competitive potentiometric method using Ag(I) ion an auxiliary ion. The enthalpy and entropy of the complexes studied were determined from the temperature dependence of the stability constants. For all cations used, the stability of the resulting complexes varies in the order dicyclohexyl-18-crown-6 > 18-crown-6 > 15-crown-5, while, for each crown ether studied, the stability order of the resulting organic ammonium ions is NH 4 + > CH 3 NH 3 + > C 2 H 5 NH 3 + > C 6 H 5 NH 3 + > C 5 H 5 NH + . In all cases studied, the complexes are enthalpy-stabilized but entropy-destabilized.