Hydroxyoximes

Certain /3-hydroxyoximes, unsubstituted in the ortho position of an adjacent benzene ring, cyclize when treated with phosphoric acid to give styrylbenzoxazole (equation 60). 

Metal extraction with hydroxyoximes. R, J. Whewell and C. Hanson, Ion Exch. Solvent Extr., 1981,... 

Transition metal hydroxyoxime complexes. M. E. Keenery and K. Osseo-Asare, Coord. Chem. Rev., 1984, 59,141-201 (313). 

Szymanowski, I. Hydroxyoximes and Copper Hydrometallurgy. CRC Press Boca Raton, 1993. 

Boronic acid derivatives are able to form ring structures with other molecules having neighboring functional groups consisting of 1,2- or 1,3-diols, 1,2- or 1,3-hydroxy acids, 1,2- or 1,3-hydroxylamines, 1-2- or 1,3-hydroxyamide, 1,2- or 1,3-hydroxyoxime, as well as various... 

There is considerable interest in amino derivatives of chroman and hydrogen bromide has been found to promote a stereoselective hydrogenation of an a-hydroxyoxime enabling the 5,5-aminochromanol 53 to be obtained in over 30% yield from chroman-4-one on a multi-kilo scale (Scheme 31) <00TL8021>. 

It is interesting to observe that alkylammonium salts, alkylarylsnlfonic acids, hydroxyoximes, aUcylphosphoric acids, and alkylhydroxamic acids, as well as nentral extractants such as crown ethers and tributyl phosphate, all form water-organic interfaces saturated with extractant molecules when their bulk organic concentration is larger than 10" M. 

For simple acidic extractants, such as carboxylic or sulfonic acids, the similarity in formation constants does not produce cobalt-nickel separation factors (Sn° 2) sufficiently large for commercial operation (Fig. 11.4). Data for pH versus extraction for some chelating acid extractants does seem to offer the possibility of separation [e.g., for the hydroxyoxime Acorga P50, the pHso for nickel(II) is 3.5 and for cobalt(II) 5.0]. Normally, this pH difference would be suitable for a separation process, but this particular system has hidden complications. The rate of nickel extraction is very slow compared with cobalt and, in addition, although cobalt is initially extracted... 

An alternative circuit for copper extraction involves ammoniacal leaching, and hydroxyoximes have been studied for this application [2]. However, because of their tendency to extract ammonia, these reagents have been superceded by /i-diketones. 

Although S-diketones cannot compete with hydroxyoximes for the extraction of copper from acid media, they do have advantages for extraction from ammoniacal leach solutions because, unlike hydroxyoximes, they do not transfer ammonia. The extraction follows Eq. (11.6), and the extent of extraction depends on the concentration of ammonia and ammonium salts. 

Two commercial flow sheets (Figs. 11.10 and 11.11) use either di- -octyl sulfide or a hydroxyoxime as selective extractants to remove the palladium, followed by tri- -butylphosphate (TBP INCO) and an amine... 

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... 

More advanced semiempirical molecular orbital methods have also been used in this respect in modeling, e.g., the structure of a diphosphonium extractant in the gas phase, and then the percentage extraction of zinc ion-pair complexes was correlated with the calculated energy of association of the ion pairs [29]. Semiempirical SCF calculations, used to study structure, conformational changes and hydration of hydroxyoximes as extractants of copper, appeared helpful in interpreting their interfacial activity and the rate of extraction [30]. Similar (PM3, ZINDO) methods were also used to model the structure of some commercial extractants (pyridine dicarboxylates, pyridyloctanoates, jS-diketones, hydroxyoximes), as well as the effects of their hydration and association with modifiers (alcohols, )S-diketones) on their thermodynamic and interfacial activity [31 33]. In addition, the structure of copper complexes with these extractants was calculated [32]. 

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). ... 

Synthesis of the 1,2-oxazine ring by intramolecnlar cyclization of y-hydroxyoximes using Mitsunobu reaction was described. ... 

Reactions of a-hydroxyoxime 366 with NaH/i-Pr0H/ClC02Et or CS2 afforded 1,5,2-dioxazines 367 and 368 in 79 or 76% yields, respectively (equation 160) . ... 

For hydroxamic acids, it is generally assumed that it is the Af-hydroxyamide/keto form, as opposed to the hydroximic/hydroxyoxime form, that predominates in acid medium, the environment usually required for most precipitates or colors to form . It is in general unknown what is the stoichiometry and structure of most metal hydroxamate complexes in solution. Nevertheless, the reaction of the majority of hydroxamic acids with metal ions can be written schematically as shown in equation 2. 

Usually, the composition of commercial extractants is proprietary information, but a typical example is an cc-hydroxyoxime carried in a hydrocarbon solvent such as kerosene. 

Metal specific ion-exchange resins bearing hydroxyoxime groups have been prepared [10] from substituted phenylacrylates (Fig. 6). 

Several complexes with hydroxyoximes (especially aromatic) have been prepared. Typically, an ethanolic solution of ligand is added to a solution of a vanadyl salt, the pH and temperature... 

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. 

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