The determination of complex stabilities with nearly insoluble ligands. Complexation of alkali ions by unsubstituted calixarenes in aqueous solutions

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+ ha s been studied in aqueous solutions at 25 degrees C under slight acidic con ditions to prevent an ionization of the calixarenes. Due to the complexatio n the total concentration of the calixarenes in solution increases. This ef fect can easily be detected using spectrophotometric methods. The stability constants depend on the ring size of these calixarenes. Calix[ 6] arene fo rms the most stable complex. No complexation is observed between the p-tert -butylcalix[n]arenes and the monovalent cations. The spectrophotometric met hods allow the quantitative determination of the stability constants. The m ain advantage of this method is that only very small amounts of the ligands are used.