Chelating Agents

Abstract

Chelating agents or chelants are compounds having two or more donor atoms that can form cyclic coordination complexes or chelates with acceptor metals. The complexation is an equilibrium reaction which often strongly favors the complex. Chelating is used to modify or control the behavior of metals and their compounds by controlling the concentration of the metals in solution or to utilize the special properties of the chelation compounds. The active groups in chelants may be linear chains, eg, ‐N‐C‐C‐N‐, macrocyclic rings, eg [‐O‐C‐C] n , or polycyclic structures, such as the cryptates, eg, X[‐C‐C‐Y‐C‐C) n ] 3 Y where X and Y are bridgehead and donor atoms, respectively. Some pH, stability, solubility, and electrochemical relationships among simultaneous equilibria in chelation are shown. A broad range of applications based on concentration control, the special properties, and medical uses of chelation compounds are given. Metal sequestration, solubilization, and buffering are discussed as are metal extraction, precipitation, and displacement. Economic data for industrial chelating agents are given. Use of chelating agents is essentially benign environmentally and presents little or no hazard to health or safety under normal conditions of use and handling.

Recovery of Homogeneous Platinoid Catalysts from Pharmaceutical Media: Review on the Existing Treatments and the Perspectives of Membrane Processes

“…As a bidentate ligand, ethylenediamine bonds twice. The efficiency of the chelation process is due to the ring formation that is more stable than the previous catalytic complex [ 79 ]. Ethylenediamine is water-soluble and thus, after the chelation process, the catalyst can easily be removed from an organic phase and dragged into an aqueous phase.…”

“…Ethylenediamine is water-soluble and thus, after the chelation process, the catalyst can easily be removed from an organic phase and dragged into an aqueous phase. Several chelating agents are known, the most common being the ethylenediamine derivatives like ethylenediaminetetraacetic acid (EDTA) or hydroxyethylethylenediamine [ 79 ]. However, in addition to a phase change, chelation often inhibits the activity of catalysts and leads to a need for retreatment process.…”