Oximes hydroxyoximes

The second selective extractant route (that of MRR) uses a hydroxy-oxime to remove palladium. The actual compound used has not been specified, but publications refer to both an aliphatic a-hydroxyoxime and an aromatic S-hydroxyoxime. The a-hydroxyoxime LIX63 has the faster extraction kinetics, but suffers from problems with stripping. For the (i-hydroxyoxime, a kinetic accelerator in the form of an amine (Primene JMT ) has been proposed. The precise mode of operation of this accelerator is unknown, but it may be a similar process to that proposed for the sulfide... 

Benzisoxazoles and isoxazoles are also accessible in excellent yields by intramolecular Mitsunobu reaction or related reactions of o-hydroxy- or a-hydroxyoximes ° . Thus, treatment of oxime 208 in the presence of diethyl azodicarboxylate (DEAD) and PPhs in THE leads to benzisoxazoles 209 (equation 91). ... 

Transition metal hydroxyoxime complexes have been reviewed very recently.2507 Their use in both analytical chemistry and extraction metallurgy is well known. The square planar structure of the bis chelate complex NiL (347) with the deprotonated 2-hydroxybenzaldoxime (HL) is typical of this series of nickel complexes.2508 Their bis adducts, NiLJ, with bases such as py, substituted pyridines and cyclomethyleneimines, are six-coordinate.2509 The acyl oxime (H2L) complexes are similar to the aforementioned complexes being either square planar bis chelates Ni(HL)2 (348) or octahedral bis adducts, Ni(HL)2B2.2507 When the acyl oxime acts as a dibasic ligand L, the corresponding (NiL) complexes are insoluble and involve extensive polymerization. 

An interesting property of resins impregnated with oximes or oxines is that the selectivity of, for example, copper over iron(III), approaches that of a pure solvent-extraction process only when an inert solvent is present in the pores of the resin.396 Thus, in a /S-hydroxyoxime SIR, the selectivity for copper over iron(III) improved by a factor of 20 when the solvent perchloroethylene was introduced into the SIR, and by a factor of 700 in a similar resin impregnated with 8-hydroxy-quinoline.396 This is believed to be due to kinetic and thermodynamic restrictions in the extraction of iron(III), but not of copper, at an aqueous—organic boundary.396 397... 

One-step functionalization of aminomethylpolystyrene, type 4, prepared by the Delepine reaction, or by other routes, with various ligands carrying a benzylic halide group i.s shown in Scheme 3. Reaction of polymers of type 4 (4A, Z = H 4B, Z = Br 4C, 2% DVB, gel-type copolymer) with 2-acetyl-4-chloromethylphenol or 4-chloro-methyl-2-formylphenol (2-acyl-4-chlorometh-ylphenoLs are stable at acidic pH [31]) in CHClj, followed by oximation, yields the hydroxyoxime polymers of type.s 5 (66% conversion) and 6 (48% conversion), respectively. 

Extractants are often used with modifiers (e.g., hydrophobic alcohols, alkylphenols, sterically hindered esters of carboxylic acids, and tributyl phosphate). Modifiers are used for two different reasons first, to increase the solubility of extractants and their complexes and to avoid the formation of the third phase, and second, to modify the extraction properties, i.e., the extraction and stripping abilities. The first option is usually exploited in systems that contain various amines. The second option is associated with hydro-xyoximes and the formation of tailored blends, which optimize the extraction-stripping properties and adjust them to the aqueous feed, i.e., to the acidity and concentration of copper(II). Modifiers that form hydrogen bonds with hydroxyoxime molecules decrease their extraction ability but facilitate back-extraction with acids. Weak hydroxyoxime or j -diketone extractants (e.g., 2-hydroxy-5-alkylbenzo-phenone oxime) can also act as modifiers of strong hydroxyoxime extractants (e.g., salicylaldoxime and its alkyl derivatives). 

Although adsorbed molecules of extractants are well oriented at the interface, the interfacial reactions occur more slowly, as recalculated for the same volume, than reactions in the aqueous phase. The extraction of palladium(II) from HCl solutions with dialkyl sulfides is a classic example of a very slow process. Modifying the extractant structure by adding a hydrophilic hydroxyl group and/or a phase transfer catalyst, e.g., trialkylamine or quaternary ammonium salt, increases the rate of extraction. The addition of sulfonic and phosphoric acids to hydroxyoximes may enhance the rate of copper extraction due to the formation of reverse micelles and the development of the microscopic interface. The a-acyloin oximes that form an intermediate complex that has a five-member ring with copper(II) increase the rate of extraction of aromatic hydroxyoximes. The addition of surfactants may cause both retardation and acceleration of extraction. If the interfacial tension is decreased, surfactants cause an increase in the interfacial surface area in dispersed systems. When they adsorb at the interface, they cause an additional... 

The copper-specific extractants used to extract copper from other base metals in acidic sulfate liquors are known as hydroxyoximes, and the interaction is known as chelation. The basic structures of modem oxime extractants are shown in Figure 5.4, where A = H for aldoximes and A = CHj for ketoximes. The R-chain is usually C9H19 (occasionally C12H25). The complexation of copper by these extractants is shown schematically in Equation (5.1). Extraction of each copper ion releases two protons, thereby providing a useful source of acid for further leaching (see Figure 5.2). pH is an important parameter controlling the equilibrium position of this reaction. 

LIX 63, an aliphatic a-hydroxyoxime, was the first commercial reagent developed for copper. Although it was very selective for copper, it operated at pH values of 5 to 8. Since most leach solutions have pH values between 0.7 and 2.2, it was necessary to optimise the pH dependence of the extractants for use under more acidic conditions. The first reagent used in a full-scale plant was LIX 64N, a P-hydroxybenzophe-none oxime developed by General Mills (now Cognis) and comprising a mixture of LIX 63 (2% by mass) and LIX 65N (40%) (Arbiter and Fletcher 1994 House 1985 Dasher and Power 1971). 

Oximes, a-oximinoketones, and a-hydroxyoximes react with phenylacetic acid in the presence of dicyclohexylcarbodiimide to form the oximino ester. At pH 5 and room temperature, H20-soluble carbodiimides convert hydroxamic acids to amines 7, Cyanooldehydes and -ketones are attainable by conversion of olefins to a-dimethylamino oximes and subjecting these to a Beckmann fragmentation ... 

Numerous other oximes and nitroso compounds are also used as reagents for metal ions, including hydroxyoximes such as salicylaldoxime and derivatives ... 

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