Sequestering Agents Water Softeners

The word chelating comes from the Latin word for claws, chelae, like the claws of a crab. A chelating agent grabs on to another molecule, like a crab s claw, and prevents it from reacting with other molecules. 

Sodium or calcium EDTA binds to metals, such as nickel, copper, and iron, making them unavailable to react with other ingredients in a product, or with compounds in the human body. 

EDTA sequesters calcium and magnesium from hard water, preventing them from forming insoluble soap films (scum) with soaps and detergents. Chelators are sometimes used to sequester metal ions that interfere with dyes and perfumes. 

EDTA also is used to treat lead and mercury poisoning, as it can lock up those metals so they can do no harm in the body. 

Compounds with similar functions are sodium carbonate, pen-tasodium pentetate, sodium citrate, phosphoric acid, tetrasodium etidronate, and tetrasodium pyrophosphate. 

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Similar chelating properties are exhibited by the following agents (see also Ref. 36) scale inhibitors, sequestering agents, water softeners, surfactants, peroxide. stabilizers, soil antiredeposition agents, well-drilling needs,- etc. 

The sequestering agent tetrasodium pyrophosphate (TSPP) removes calcium and magnesium from the saliva, so they can t deposit on teeth as insoluble deposits called tartar (calcified plaque). In this respect it acts as a water-softening agent. However, it won t remove tartar that already exists. 

Scarlet GN, 119. See also FD C Red 4 scopalomine, 178 SD-40, 56, 70, 174 SD alcohol 40-B. See ethanol SDIC. See sodium dichloroisocyanurate seaweed extract. See agar, carrageenan sequestering agents, 19,49-54,242. See also water softeners serine, 123... 

Use Water softening sequestering, peptizing, or de-flocculating agent food additive and texturizer. 

At 370°C, reaction (5.218) takes place with anhydrous sodium formate. Phosphorous acid reacts with formaldehyde and ammonium chloride to give nitrilotrimethylene phosphonic acid (5.219), an efficient sequestering agent for Cu +, Mg + and Fe +. This compound is employed in water softening and in detergent compositions - it is more stable than sodium triphosphate to hydrolysis. Acetodiphosphonic acid is obtained from phosphorous acid (Chapter 6.18). 

The group 2 metal ions are hard acids and are preferentially coordinated by hard bases (see Table 7.9). In this section we consider complexes formed in aqueous solution in which the metal centre is coordinated by O- and A -donor ligands to give cationic species. Two important ligands are [EDTA]" (see eq. 7.75) and [PsOjo] (see Fig. 15.19). Both form water-soluble complexes with Mg and the heavier metal ions, and are sequestering agents used in water-softening to remove Mg + and Ca ions. 

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