Chemical reaction anion exchange

The decomposition of dioxetanone may involve the chemically initiated electron-exchange luminescence (CIEEL) mechanism (McCapra, 1977 Koo et al., 1978). In the CIEEL mechanism, the singlet excited state amide anion is formed upon charge annihilation of the two radical species that are produced by the decomposition of dioxetanone. According to McCapra (1997), however, the mechanism has various shortfalls if it is applied to bioluminescence reactions. It should also be pointed out that the amide anion of coelenteramide can take various resonance structures involving the N-C-N-C-O linkage, even if it is not specifically mentioned. 

This polymer resin is in a first step chemically functionalized, yielding initial reactive moieties [3]. In a second step, other groups can be introduced by chemical reaction of these moieties, e.g. creating ammonium groups. By ion exchange, reactive anions are bound which serve as reactants for the reactions to be carried out later on [P 56]. 

Figure 15.4(A) shows the effect of the R = Zn2+/Al3+ ratio, which determines the charge density of the LDH layer, on the Freundlich adsorption isotherms. K values are far higher than those measured for smectite or other inorganic matrices. The increase in Kf with the charge density (Kf= 215, 228, 325mg/g, respectively, for R = 4, 3 and 2) is supported by a mechanism of adsorption based on an anion exchange reaction. The desorption isotherms confirm that urease is chemically adsorbed by the LDH surface. The aggregation of the LDH platelets can affect noticeably their adsorption capacity for enzymes and the preparation of LDH adsorbant appears to be a determinant step for the immobilization efficiency. [ZnRAl]-urease hybrid LDH was also prepared by coprecipitation with R = 2, 3 and 4 and Q= urease/ZnRAl from 1 /3 up to 2.5. For Q < 1.0,100 % of the urease is retained by the LDH matrix whatever the R value while for higher Q values an increase in the enzyme/LDH weight ratio leads to a decrease in the percentage of the immobilized amount.

Oilier examples of this type of reaction are file conversion of the antibiotic streptomycin sulfate to its corresponding chloride hy means of anion exchange, the exchange of Na ions in milk for the K ion. and the conversion of NaCKdj to H CiOi by cation exchange The latter process is used extensively in the plaling industry to concentrate ICCrO, Iron rinse waters, with subsequent reuse of a toxic chemical ami reuse of ihe rinse water in what might be termed a closed system. 

After leaching, a concentration/pmification is done to get rid of other materials leached from the ore. This can be done by ion exchange or solvent extraction. In the ion exchange method, three steps are employed (a) the absorption of uranium from the leach liquor onto the resin, (b) the selective elution of uranium from the resin, and (c) the regeneration of the resin. Anion exchange is the preferred method of ion exchange with the relevant chemical reactions for acid leach being... 

An example of chemical destruction of an anionic species is the elution of aurocyanide from an anion-exchange resin with thiourea, a neutral ligand that reacts with gold cyanide in the presence of acid to form a cationic complex. The elution reaction can be described by the following equation ... 

Phase-transfer catalytic (PTC) conditions, which are specific for anionic reactions (and anionic activation) are perfectly well tailored for microwave activation, because after ion exchange between a substrate and catalyst, the resulting nucleophilic ion pair is a highly polar species especially prone to interaction with microwaves [32]. Eventually, the mixture of neat reagents in an open vessel can lead to a reaction under microwave conditions provided that one of the reagents is liquid or a low melting solid that couples well with microwaves. On the other hand, even a small amount of a good microwave absorber (e.g,. H20, DMF for example, see Table 1.3) added to reaction mixtures that consist of substrates that do not absorb microwaves in the solid state can initiate an increase of reaction mixture temperature and then chemical reaction. 

Quantification and Elucidation of Rate-Limiting Steps 109 Chemical Reaction and Diffusion 112 Rates of Ion Exchange on Soils and Soil Constituents 113 Mineralogical Composition 114 Ion Charge and Radius 116 Binary Cation and Anion Exchange Kinetics 117... 

Homogeneous ion-exchange membranes can be prepared by polymerization of monomers that contain a moiety that either is or can be made anionic or cationic, or by polymerization of a monomer that contains an anionic or a cationic moiety, or by introduction of anionic or cationic moieties into a polymer dissolved in a solvent by a chemical reaction, or grafting functional groups into a preformed polymer film [10]. 

The type of the oxidation product on galena is independent of the chemical environment during preparation. Rao152) measured the adsorption heat of K amyl xanthate (KAX) on unactivated and Cu2+-activated pyrrhotite (FeS) and compared his results with heats of the reaction between KAX and Fe2+ or Cu2+ salts. With the unactivated mineral, the interaction involves a chemical reaction of xanthate with Fe2+ salts present at the interface (i.e. not bound to the crystal surface). The adsorption enthalpy is identical with the formation of Fe2+ amyl xanthate FeS04 + 2 KAX —> FeX2 + K2S04, and -AH = 97.45 kJ/mol Fe2+). As revealed from the enthalpy values and the analysis of anions released into the solution, the interaction of xanthate with Cu2+-activated pyrrhotite consists of xanthate adsorption by exchange for sulfate ions (formed by an oxidation of sulfides) at isolated patches (active spots), and by further multilayer formation of xanthate. The adsorption heat of KAX on pyrrhotite at the initial pH 4.5 was - AH (FeS unactivated) = 93.55 kJ/mol Fe2+ and - AH (FeS activated) = 70.03 kJ/mol Cu2+. 

Usanovic acid-base theory — A general theory of acids and bases taking into consideration electron exchange processes (redox reactions) was proposed in 1939 by Usanovic. His definition is a symmetrical one and includes all concepts discussed above, i.e., an acid is defined as a substance which is able to liberate protons or other cations (cation donator) or to take up anions or electrons (anion acceptor, electron acceptor). A base is defined as a substance which is able to release anions or electrons (anion donator, electron donator) or to take up protons or other cations (cation acceptor). According to that theory, all chemical reactions (excluding reactions between radicals resulting in covalent bindings) can be considered as acid-base reactions. 

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