Sulfonamide-type di-Schiff base ligands as chelate extraction reagents for divalent metal cations Original Research Article

The nature of sulfonamide-type di-Schiff base ligands, such as N,N′-bis[phenyl[o-(p-toluenesulfonamido)phenyl]methylidene]ethylenediamine (H2tsben-Ph2) and its analogs, as chelate extraction reagents for divalent metal cations such as Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+ was investigated including comparison with that of respective phenol-type ones. These sulfonamide-type ligands acted as dianionic-quadridentate ones to form 1:1 complexes with the divalent cations in the system, which were confirmed from numerical analysis of relationship between distribution ratio of the metals and pH or ligand concentration. Furthermore, they showed unique extraction selectivity that extraction performance for Ni2+ was suppressed and that for Zn2+ was enhanced, which is originated mainly from the use of sulfonamide-donors on the complexation. This tendency was remarkable on H2tsben-Ph2 (log Kex=−10.57±0.11 for Zn2+), and may be controlled by structural rigidity of the ligands including spread of π-conjugation system including the sulfonamide-donor.