Agents chelating

Ligands of the NTA and EDTA type complexones or sequestering agents, as they are sometimes called) are often able to dissolve deposits of metal oxides, hydroxides, sulfides, and carbonates because they displace solubility equilibria such as reaction 13.13 to the right by reducing the free 

if 01 is large enough, for a given solubility product Agp, and the pH and free EDTA concentration axe appropriate, the solid M(OH)m of reaction 13.13 will pass entirely into solution (see Exercise 13.6). Since the donor atoms in these ligands are hard oxygen, they are particularly effective against hard ions such as Ca or Fe .  

Boiler tubes are often cleaned with EDTA or NTA solutions to remove both CaC03 scale and corrosion products. In pressurized heavy water nuclear power reactors, radioactive corrosion deposits (in effect, magnetite in which some of the Fe has been replaced by radioactive Co ) can be removed from the coolant water circuits with an aqueous mixtiu e of oxalic and citric acids (both good chelators for Fe ) and EDTA. In home laundry operations, bloodstains on clothing can be removed by treatment with oxalic acid, which takes up the iron from the hemoglobin (Section 8.2) as Fe(ox)3 . By the same token, oxalates axe toxic when taken internally, as are many other complexing agents. For example, EDTA is used as a means 

Transition metal ions, even in trace amounts, catalyze many chemical reactions, such as the decomposition of hydrogen peroxide 

The deleterious effects of heavy metal impurities can be eliminated by the inclusion of chelating agents. A chelating agent refers to a compound, which can form a metal ion complex having two or more 

890388-81-5 3,3 -[[6-[(2-Sulfoethyl)amino]-l,3,5-triazine-2,4-diyl]-bis[imino[3-(3-sulfopropoxy)-4,l-phenylene]azo]]bis-benzoic acid 

Thiocarbamoylpyrazolones are new lead structures with a broad spectrum of antifungal activity (Heuer et al., 1996 Sasse et al., 1992). They are not acting as electrophiles, but are probably acting as chelating agents. 

The variation of substituents showed a broad variability in whereas R and R should be hydrogen and R is limited to hydrogen and methyl. 

In styrene-acrylate based emulsion paints they are active down to 0.3%, but their main disadvantage is their leaching from the paint film. Trials to overcome the leaching by increasing the lipophility lead to Thiazolylpyr-azolones (Heuer et al., 1995). The in-vitro activity toward fungi and the structure-activity relationship is similar to Thiocarbamoylpyrazolones. 

In polyvinylacetate as well as styrene-acrylate based emulsion paints, they are active in the range of 0.3% to 0.6%. After a 24h leaching, the activity decreased to 1%. Evaporative aging gave no decrease in activity. 

The ability to form strong coloured complexes with heavy metal led to a stop of the development. 

---

H02CCH2)2N-CH2 CH2-N(CH2C02H)2-An important compound, which owes its use to its sequestering properties. A multidentate chelating agent. Forms complexes with most elements. 

Liquid-liquid extractions using ammonium pyrrolidine dithiocarbamate (APDC) as a metal chelating agent are commonly encountered in the analysis of metal ions in aqueous samples. The sample and APDC are mixed together, and the resulting metal-ligand complexes are extracted into methyl isobutyl ketone before analysis. 

Cupferron is a ligand whose strong affinity for metal ions makes it useful as a chelating agent in liquid-liquid extractions. The following distribution ratios are known for the extraction of Hg +, Pb +, and Zn + from aqueous solutions to an organic solvent. 

Selected Chelating Agents for the Fluorometric Analysis of Inorganic Metal Ions... 

An ion-selective electrode in which a chelating agent is incorporated into a hydrophobic membrane. 

---