ROLE OF ANIONS IN THE COMPLEX-FORMATION OF CROWN-ETHERS WITH AMMONIUM-IONS CHEMICALLY BONDED ON SILICA-GEL

The complex formation of crown ethers with ammonium ions chemically bo nded on silica gel has been chromatographically investigated. Although the selectivity in the complex formation of crown ethers is basically the same as in solution, a counter anion existing in the diffuse doub le layer of the silica gel also plays an important role, even when a p olar solvent with hydrogen-bond formation ability such as methanol, is used as a medium. The overall complex formation at the silica gel sur face can be divided into three processes: (i) the dissociation of a co unter anion from its ion-pair with the ammonium ion; (ii) complex form ation of a crown ether with the ammonium ion; (iii) formation of an io n-pair between the anion and the ammonium ion complexed by the crown e ther. This mechanism is evaluated from thermodynamic viewpoints includ ing the solvation of anions, the ion-pair formation of anions with amm onium, etc.