Aminopolycarboxylates

The aminopolycarboxylic acids are used principally as chelating agents, and a large proportion is used in water treatment and cleaning formulations. The data of Table 5 include nitnlotriacetic acid (NTA), most of which was exported. 

The formation of a single complex species rather than the stepwise production of such species will clearly simplify complexometric titrations and facilitate the detection of end points. Schwarzenbach2 realised that the acetate ion is able to form acetato complexes of low stability with nearly all polyvalent cations, and that if this property could be reinforced by the chelate effect, then much stronger complexes would be formed by most metal cations. He found that the aminopolycarboxylic acids are excellent complexing agents the most important of these is 1,2-diaminoethanetetra-aceticacid (ethylenediaminetetra-acetic acid). The formula (I) is preferred to (II), since it has been shown from measurements of the dissociation constants that two hydrogen atoms are probably held in the form of zwitterions. The values of pK are respectively pK, = 2.0, pK2 = 2.7,... 

Edta and other aminopolycarboxylic acids as chromogenic agents. F. Bermejo-Martinez, Chelates Anal. Chem., 1976, 5, 1-161 (266). 

The disadvantage of the polyphosphates is that at the temperatures (100 °C or higher) used in many textile processes they can be hydrolysed into simpler phosphates that cannot retain the metal atom in the sequestered form. For example, dicalcium disodium hexametaphosphate hydrolyses on prolonged boiling to yield the insoluble calcium orthophosphate. This is one of the main reasons why polyphosphate sequestrants are used much less extensively than the more versatile and stable aminopolycarboxylates. 

The consumption of these phosphonates in textile processing is small in relation to that of the aminopolycarboxylates they are mainly used in detergent formulations [21,22] as sodium, potassium, ammonium or alkanolamine salts. 

Figure 10.5 Effect of pH on the conditional stability constants at 25 °C of Fe(m) and Fe(n) chelates of aminopolycarboxylic acids [20]...

Another aminopolycarboxylic acid, closely related to IMDA and forming strong complexes with the lanthanide ions, is nitrilotriacetic acid (NTA). The hy-... 

Nowack B. (2002). Environmental chemistry of aminopolycarboxylate chelating agents. Environmental Science and Technology 36 4009-4016. 

Schmidt, C.K. and Brauch, H.-J. (2007) Occurrence of aminopolycarboxylates in the water cycle and their behaviour during drinking water treatment. Proceedings of the CASIAU Conference 11-15 March. 

The existence of a wide variety of zirconium(IV)-aminopolycarboxylate complexes in solution was established by the potentiometric titration studies of Intorre and Martell.675-677 This work and related solution studies have been reviewed by Larsen.5 Zirconium(IV) forms 1 1 and 1 2 complexes with tetradentate aminopolycarboxylates, 1 1 complexes with hexadentate and octadentate aminopolycarboxylates, and mixed ligand complexes with aminopolycarboxylates and various bidentate ligands, for example 1 1 1 Zr-edta-Tiron and 1 1 2 Zr—nta-Tiron complexes (Tiron = l,2-dihydroxybenzene-3,5-disulfonate). The stoichiometries of these complexes are consistent with the tendency of zirconium to achieve a coordination number of eight. 

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