Ammonia, Chelating Agent

EDA reacts with formaldehyde and sodium cyanide under the appropriate alkaline conditions to yield the tetrasodium salt of ethylenediaminetetraacetic acid (24). By-product ammonia is removed at elevated temperatures under a partial vacuum. The free acid or its mono-, di-, or trisodium salts can be produced by the appropriate neutrali2ation using a strong mineral acid. This same reaction with other amines is used to produce polyamino acetic acids and their salts. These products are used widely as chelating agents. 

In order to suppress interferences due to the presence of inorganic species and reliably determine the proteinaceous composition of the sample, a clean-up step has often been introduced in the analytical procedure. This step may include the extraction of the proteinaceous matter by an ammonia solution [8], the use of a cation-exchange resin [8,55], a chelating agent [9,41,44], the use of a Cig resin or the use of barium chloride solution to suppress sulfates [10,81,82]. Table 9.1 reports the methods used to overcome such problems. 

It is also observed that chelating agents (polydentate ligands) form more stable complexes than a comparable number of donor atoms in monodentate ligands. Consider the following example of Ni+ complexes with four ammonia molecules (each monodentate) and two ethylenediamine... 

These molecules are flexible because rotation about single bonds is free, so they can wrap themselves around a metal ion to obtain four comfortable donor-atom-to-metal links within five-membered rings. Nitrilotriacetic acid is easily synthesized industrially from ammonia, formaldehyde, and hydrocyanic acid (the Strecker synthesis) and therefore is potentially an inexpensive but effective chelating agent. 

The first enzyme that was demonstrated to contain nickel was urease (urea amidohydrolase) from jack bean. It catalyzes the hydrolysis of urea to ammonia and carbon dioxide. The protein has a multimeric structure with a relative molecular mass of 590,000 Da. Analysis indicated 12 nickel atoms/mol. Binding studies with the inhibitors indicated an equivalent weight per active site of 105,000, corresponding to 2 nickel atoms/active site. During removal of the metal by treatment with EDTA at pH 3.7, the optical absorption and enzymatic activity correlated with nickel content. This, combined with the sensitivity of the enzyme to the chelating agents acetohydroxamic acid and phos-phoramidate, indicates that nickel is essential to the activity of the enzyme (1). 

A multicomponent positive-imaging process using ammonia release has been described by Ricoh.211 The components of the system are (1) a cobalt(III) hexaammine complex, (2) a quinone photoreductant, (3) a chelating agent such as dimethylglyoxime, (4) a leuco dye (triarylmethane type), (5) a photooxidant (biimidazole) and (6) an organic acid (toluenesulfonic acid). 

The most common chelating agents used to extract metals from water samples are ammonia pyrolidine dithiocarbamate (APDC) and 8-hydroxyquinone. Methyl isobutyl ketone (MIBK) is generally used as a solvent. In a typical extraction, 1 mL of APDC is added to 50 to 100 mL of aqueous sample in a volumetric flask. The pH of the aqueous sample is adjusted for maximum extraction of the analyte of interest. Then 10 mL of MIBK is added (the volumetric ratio of sample to MIBK is usually less than 40) and the mixture is vigorously shaken for 30 seconds. The metal chelate partitions into the organic phase, which floats on the water. More water can be added to raise the organic level into the neck of the flask so that it can be... 

Ethylenediamine is used to produce chelating agents and carbamate fungicides. Monoethanolamine (MEA), reacts with ammonia and hydrogen to produce ethylenediamine. The reaction occurs in the gas phase over a catalyst at temperatures < 300 "C (572 F) and pressiues > 250 bar (246.7 atm) [12]. Other details of the process are proprietary. The products are ... 

Chemical stability is an extremely important characteristic of HDV s, but one that has received relatively limited mention in the literature. Most reported studies have dealt with just two sorts of environments The first are those encountered in chemical dealumination processes—strong acids, chelating agents (e.g., EDTA, or soluble silicon sources (e.g., amnionium f luorosilicate). [9,10,11] The second deals with catalytic process environaients—ammonia vapor in hydrocrackers [12,13] or vanadic acid in fluid crackers [14]. Essentially no studies directed towards the specific needs of the catalyst manufacturer are available. 

Ammonia monooxygenase is very unstable when the cells of N. europaea are destroyed the enzyme is mostly inactivated (Suzuki and Kwok, 1970 Suzuki et al., 1981). Therefore, little is known about the properties of the enzyme. The copper atom seems important for the enzyme to function, as the enzyme is inactivated by many cuprous chelating agents (Hooper and Terry, 1973 Wood, 1986), and the enzyme seems to be activated by cuprous ions (Ensign et al., 1993). Moreover, the enzyme purified from the heterotrophic nitrifier Paracoccus denitrificans has been found to be activated by the cuprous ion (Moir et al., 1996). However, the P. denitrificans enzyme may be a little different from the N. europaea enzyme, because it is not inhibited by acetylene (Moir et al., 1996), while the N. europaea enzyme is inhibited by the compound (Hooper and Terry, 1973). Electron paramagnetic resonance (EPR) studies show that iron is also important for the function of the enzyme (Zahn et al., 1996). The amino acid sequence of the N. europaea enzyme is deduced from DNA (Hyman and Wood, 1985 McTavish et al., 1993 Bergmann and Hooper, 1994), although firm evidence has not been obtained that the DNA really encodes the enzyme. 

EDTA is used to prevent pesticides from precipitation in hard-water solutions, to soften water in soap and detergent, and to prevent the catalytic effects of metal ions present in water in the cold rubber SBR process [57]. EDTA attached to iron catalyzes the direct hydroxylation of phenolic compounds [58] it also is the best way to supply iron-deficient citrus trees [59]. Other chelating agents include nitrilotriacetic acid (NTA) made from ammonia and diethylenetriamine pentacetic acid from diethylenetriamine [60]. 

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