Organic chelators

Iron. As with copper, some dozen or more materials are used as fertilizer Hon sources. These include ferrous and ferric oxides and sulfides and ferrous ammonium phosphate [10101 -60-7] ferrous ammonium sulfate [10045-89-3] frits, and chelates. In many instances, organic chelates are more effective than inorganic materials. Recommended appHcation rates range widely according to both type of micronutrient used and crop. Quantities of Fe range from as low as 0.5 kg/hm as chelates for vegetables to as much as a few hundred kg/hm as ferrous sulfate for some grains. 

Synthetic organic chelates and natural organic complexes are sometimes more effective agronomically per unit of micronuttient than inorganic forms, but the organic materials are more expensive. The chelates can be used with both orthophosphate and polyphosphate Hquids and suspensions. 

The Lo-Cat process, Hcensed by US Filter Company, and Dow/Shell s SulFerox process are additional Hquid redox processes. These processes have replaced the vanadium oxidizing agents used in the Stretford process with iron. Organic chelating compounds are used to provide water-soluble organometaHic complexes in the solution. As in the case of Stretford units, the solution is regenerated by contact with air. 

Ceramic-grade beryllium oxide has also been manufactured by a process wherein organic chelating agents (qv) were added to the filtered beryllium sulfate solution. Beryllium hydroxide is then precipitated using ammonium hydroxide, filtered, and carefully calcined to obtain a high purity beryllium oxide powder. 

Structure and specificity of organic chelating agents. E. Bayer, Angew. Chem., Int. Ed. Engl., 1964, 3, 325-332 (36). 

First Concept in Catalyst Design. Shifting Complexation Equilibria for Ion-Exchange by Oxidation of the Organic Chelates... 

A current area of interest is the use of AB cements as devices for the controlled release of biologically active species (Allen et al, 1984). AB cements can be formulated to be degradable and to release bioactive elements when placed in appropriate environments. These elements can be incorporated into the cement matrix as either the cation or the anion cement former. Special copper/cobalt phosphates/selenates have been prepared which, when placed as boluses in the rumens of cattle and sheep, have the ability to decompose and release the essential trace elements copper, cobalt and selenium in a sustained fashion over many months (Chapter 6). Although practical examples are confined to phosphate cements, others are known which are based on a variety of anions polyacrylate (Chapter 5), oxychlorides and oxysulphates (Chapter 7) and a variety of organic chelating anions (Chapter 9). The number of cements available for this purpose is very great. 

Active zinc oxide is capable of forming chelate cements with a number of liquid organic chelates. These include the ) -diketones, ketoacids and ketoesters as well as the 2-methoxy phenols (Nielsen, 1963). 

Iodo (trimethyl) platinum (IV) is a yellow crystalline product which decomposes at 190 to 195°. It is soluble in most nonpolar solvents and essentially insoluble in polar media such as water and acetone. In benzene solution, the iodo derivative is tetrameric.6 X-ray investigations have shown that in chloro-(trimethyl) platinum four platinum atoms describe a tetrahedron as do the four chlorine atoms, and the two tetrahedra are interpenetrating so as to give a cubic array of platinum and chlorine atoms. Each platinum atom is bonded to three chlorine atoms and to three terminal methyl groups. Some of the trimethylplatinum derivatives of organic chelate ligands are dimeric and in these structures the platinum is again six-coordinate.7... 

In seawater, the major chemical species of copper are Cu(OH)Cl and Cu(OH)2 and these account for about 65% of the total copper in seawater (Boyle 1979). The levels of copper hydroxide (Cu(OH)2) increase from about 18% of the total copper at pH 7.0 to 90% at pH 8.6 copper carbonate (CuC03) dropped from 30% at pH 7.0 to less than 0.1% at pH 8.6 (USEPA 1980). The dominant copper species in seawater over the entire ambient pH range are copper hydroxide, copper carbonate, and cupric ion (USEPA 1980). Bioavailability and toxicity of copper in marine ecosystems is promoted by oxine and other lipid soluble synthetic organic chelators (Bryan and Langston 1992). 

If the metallisable dye is insoluble in water, a miscible solvent such as ethanol or ethylene glycol may be added. Polar solvents such as formamide or molten urea have sometimes been preferred. It is likely that such solvents will preferentially displace water molecules and coordinate with the chromium (III) ion as the first step in the reaction. If colourless organic chelates of chromium, such as those derived from oxalic or tartaric acid, are used instead of or in addition to hydrated chromium (III) salts, the difficulty of replacing the strongly coordinated water molecules in the first stage of the reaction is eliminated. In this way the initial reaction can be carried out at high pH without contamination by the precipitation of chromium hydroxide. Use of the complex ammonium chromisalicylate (5.12) in this connection should also be noted (section 5.4-1). 

Class B Type MA, . Neutral coordinatively saturated complexes formed between the metal ion and a lipophihc organic acid. This class contains the large group of metal-organic chelate compounds. For monbasic acids forming bifunctional chelates, z = N/2. They belong to the extraction Type in-B, treated in section 4.8. 

Formation of metal-organic chelate complexes results in stronger complexation (i.e., larger values) compared to interaction with monodentate ligands (Chapter 3). The common types of bidentate ligands are presented in Table 4.9 the chemistry of these complexes has been extensively discussed in the literature [14,47], Chapter 3 presents the most important factors in the formation of such complexes (1) the type of binding atom (2) the chelate ring size (or bite ) ... 

Bio)chemical reactions may take place prior to or after the continuous separation module and are intended to enhance or facilitate mass transfer, detection or both. The earliest and simplest approach to integrated analytical steps in continuous-flow systems involves a combination of chemical reactions and continuous separations [4,5]. Such is the case with the formation of soluble organic chelates of metal ions in liquid-liquid extractions with the ligand initially dissolved in the organic stream [6], the formation and dissolution of precipitates [7], the formation of volatile reaction products in gas difiusion [8] and that of volatile hydrides in atomic absorption spectro-... 

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