Pyrrole azocrown ethers. Synthesis, complexation, selective lead transport and ion-selective membrane electrode studies

New 21-membered lipophilic crown ethers, each incorporating a pyrrole unit and two azo groups as macrocyclic ring components, have been synthesized. The complexation behavior of these and two further macrocycles has been investigated in acetonitrile. These ligand systems have been employed as ionophores in transport experiments involving the competitive transport behavior of an equimolar mixture of Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Ag+ and Pb2+ across a water (pH 4.9)/chloroform/water (pH 3) bulk membrane system. In each case transport selectivity for lead(II) was obtained. The macrocycles have been incorporated in solvent polymeric membrane electrodes and their behavior towards a selection of metal ions, including those mentioned above, is reported.