Hans-Jürgen Buschmann, Gerhard Wenz, Ernst Cleve and Eckard Schollmeyer
Deutsches Textilforschungszentrum Nord-West e.V., Frankenring 2, D-47798 Krefeld, Germany
The complex formation between the in water nearly insoluble calix[n]arenes (n=4,5,6,8), their p-tert-butyl derivatives and the alkali ions and NH4+ has been studied in aqueous solutions at 25 °C under slight acidic conditions to prevent an ionization of the calixarenes. Due to the complexation the total concentration of the calixarenes in solution increases. This effect can easily be detected using spectrophotometric methods. The stability constants depend on the ring size of these calixarenes. Calixarene forms the most stable complex. No complexation is observed between the p-tert-butylcalix[n]arenes and the monovalent cations. The spectrophotometric methods allow the quantitative determination of the stability constants. The main advantage of this method is that only very small amounts of the ligands are used.