Extraction Studies of Heavy Metal Ions Employing Benzothiaoxacrown Compounds

Benzothiaoxacrown compounds with different numbers of sulfur and oxygen donor atoms (between 4 to 7 donors) dissolved in an organic diluent selectively extract the soft metal ions Ag(I) and Hg(II) from a mixture of Co(II), Cu(II), Zn(II), Ag(I) and Hg(II) present in an aqueous phase. Generally, the extraction efficiency depends on the specific structure of the benzothiaoxacrowns, on the organic diluent employed, as well as on the counter ion present in the aqueous phase. High extractions of Ag(I) and Hg(II) were achieved with all ligands from perchlorate and picrate aqueous media into nitrobenzene organic solutions. In the case of Cu(I) the extraction is significant lower; only ligand 5 with the O2S4 donor atom set gives a moderate extractability. The composition of the extracted complexes depends on the crown ring size and ranges from 1:1 to 1:2 (M:L). Polarographic, UV-Vis and ESI mass spectrometric studies provide a further insight into the complex formation behavior.