Solubility of chelates

For extraction with supercritical carbon dioxide, metals are first chelated with a ligand such as a derivative of dithiocarbamate. It has been found [96] that while the solubility of chelates of metals with sodium diethyl dithio-... 

Table XI. Solubilities of Chelated Lithium Salts in Benzene...

The solubilities of chelates with palladium, rhodium, lead and copper have been measured with static and dynamic spectroscopic methods at different temperatures and different pressures. The influence of different ligands, ligand modifications and of the metal ions coordination sphere on the solubility were studied and compared to the influence of pressure and temperature of the supercritical carbon dioxide (scCOa). In a series of C2, C4, Ce, Cg copper dithiocarbamates a maximum solubility was measured with the butyl substituents. 

Smart, N. G. Carleson, T. Kast, T. Clifford, A. A. Burford, M. D. Wai, C. M. Solubility of Chelating Agents and Metal Containing Compounds in Supercritical Fluid Carbon Dioxide. Talanta, 1997,44, 137-150. 

NG Smart, TE Carleson, T Kast, AA Clifford, MD Burford, CM Wai. Solubility of chelating agents and metal containing compounds in supercritical fluid carbon dioxide—a review. Talanta 44 137-150, 1997. 

TMED, (CH3)2NCH2CH2N(CH3)2. B.p. 122 C a hygroscopic base which forms a hydrocarbon-soluble stable chelate with lithium ions and promotes enhanced reactivity of compounds of lithium, e.g. LiAlH4, UC4H9, due to enhanced kinetic basicity of the chelate. Used in polymerization catalysts, tetramethyl lead, TML 5 lead tetramethyl. 

The product is equal to the equilibrium constant X for the reaction shown in equation 30. It is generally considered that a salt is soluble if > 1. Thus sequestration or solubilization of moderate amounts of metal ion usually becomes practical as X. approaches or exceeds one. For smaller values of X the cost of the requited amount of chelating agent may be prohibitive. However, the dilution effect may allow economical sequestration, or solubilization of small amounts of deposits, at X values considerably less than one. In practical appHcations, calculations based on concentration equihbrium constants can be used as a guide for experimental studies that are usually necessary to determine the actual behavior of particular systems. 

Spectrophotometric methods may often be applied directly to the solvent extract utilising the absorption of the extracted species in the ultraviolet or visible region. A typical example is the extraction and determination of nickel as dimethylglyoximate in chloroform by measuring the absorption of the complex at 366 nm. Direct measurement of absorbance may also be made with appropriate ion association complexes, e.g. the ferroin anionic detergent system, but improved results can sometimes be obtained by developing a chelate complex after extraction. An example is the extraction of uranyl nitrate from nitric acid into tributyl phosphate and the subsequent addition of dibenzoylmethane to the solvent to form a soluble coloured chelate. 

Lower panel One mg of chelator-soluble polyuronides from the indicated stages was size-fractionated on a Sepharose CL4B column, and the uronie acid content of column fractions determined. 0,7 and 20 day old fruit contain no PG, PGl only and PGl and PG2, respectively. Note the similarity of 7 and 20 day profiles despite the large amount of PG2 activity in the latter. 

Thennodynamic inhibitors are complexing and chelating agents, suitable for specific scales. For example, for scale inhibition of barium sulfate, common chemicals are ethylenediaminetetraacetic acid (EDTA) andnitrilotriacetic acid. The solubility of calcium carbonate can be influenced by varying the pH or the partial pressure of carbon dioxide (CO2). The solubility increases with decreasing pH and increasing partial pressure of CO2, and it decreases with temperature. 

These compounds should be dissolvable in a clean-up solution containing a quaternary organic ammonium salt, or simply ammonium chloride [1749]. The solubilities of some selected particulate bridging agents are shown in Table 9-1. A chelating agent such as citric acid or its salts is also included in the clean-up solution. 

In general, chelating agents possess some unique chemical characteristics. The most significant attribute of these chemicals is the high solubility of the free acids in aqueous solutions. Linear core flood tests were used to study the formation of wormholes. Both hydroxyethylethylene diaminetriacetic acid and hydroxyethyliminodiacetic acid produced wormholes in limestone cores when tested at 150° F. However, the efficiency and capacities differ. Because these chemicals have high solubility in the acidic pH range, it was possible to test acidic (pH less than 3.5) formulations [644]. 

Higher phytoextraction coefficients indicate higher metal uptake. The effectiveness of phytoextraction can be limited by the sorption of metals to soil particles and the low solubility of the metals however, metals can be solubilized through the addition of acids or chelating agents and so allow uptake of the contaminant by the plant. Ethylene diamine tetra-acetic acid (EDTA), citric acid, and ammonium nitrate have been reported to help in the solubilization of lead, uranium, and cesium... 

The solubility of most metals is much higher when they exist as organometallic complexes.4445 Naturally occurring chemicals that can partially complex with metal compounds and increase the solubility of the metal include aliphatic acids, aromatic acids, alcohols, aldehydes, ketones, amines, aromatic hydrocarbons, esters, ethers, and phenols. Several complexation processes, including chelation and hydration, can occur in the deep-well environment. 

Soluble Metal Chelate Polymers of Coordination Numbers 6, 7, and 8... 

---