Precipitation hydroxamic acids

Hydroxamic acid complexes, 24 769-770 Hydroxide precipitation, in hazardous waste management, 25 821 Hydroxides... 

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. 

Oximes, hydroxamic acids and related species are often used as reagents in inorganic analytical chemistry for precipitation, gravimetric and volumetric determinations as well as for preconcentration, extraction, derivatizations and subsequent determination of analyte using instrumental techniques. A brief review of analytical chemistry in general and of these species in particular follows. 

Another hydroxamic acid polymer, poly(N -methylacryloyl-hydroxamic acid) (P-3) (X) in tdiich the hydroxamic acid units are separated by only three atoms was similarly prepared. Because of the short side chains and closely spaced hydroxamic acid groups, P-3 tends to cross link and precipitate on complexation with iron. In cases such as this, the groups are too closely spaced to give soluble intramolecular complexes with iron. 

Molecular modeling was used to design the ligand isophthal-di-A -(4-methyl-phenyl)hydroxamic acid 73 (H2L ). The reaction of 73 with [Ga(acac)3] led to the white microcrystalline precipitate of [Ga4L (j] 74 (Scheme 10) whereas the dark red complex [Fe4L g] was formed in a similar reaction with [Fe(acac)3] [91]. The... 

Thus the structures of tetrakis(N-isopropyl-3,3-dimethylbutano-and -2,2-dimethylpropano)hydroxamatothorium(IV) have been determined by single crystal X-ray diffraction (77). Keeping the pH as low as possible, these compounds precipitate upon the addition of an aqueous solution of thorium tetrachloride to an aqueous solution of the sodium salt of the hydroxamic acid. The analogous uranium(IV) complexes were prepared similarly under an inert atmosphere using deaerated solvents. In addition to their hydrocarbon solubility, the bulky alkyl substituents impart other interesting properties to these complexes. They melt at 127-8 and 116-7°C and, under a vacuum of 10 3 torr, sublime at 95 and 100°C, respectively ... 

Absorption peaks of hydroxamic acid and its metal salts in FTIR include 1650, 1550, 1465, 1332, 1120, and 1050 cm Absorption peaks of Fe salt precipitate of hydroxamic acid include 1518 and 1583 cm at pH 3.0. Absorption peaks of Fe salt precipitate of hydroxamic acid include 1500 and 1700 cm at pH 9.0. 

Hydroxylamine hydrochloride (34.8 g, 500 mmol) is dissolved with rapid stirring in 185 mL of hot methanol. Potassium hydroxide (42.0 g, 750 mmol) is dissolved in 115 mL of room-temperature methanol. After cooling both solutions to ambient temperature the potassium hydroxide solution is added with stirring to the hydroxylamine hydrochloride (an exothermic process ). The resulting solution and precipitated potassium chloride are cooled to — 20°C in a methanol ice bath before vacuum filtration. The clear colorless supernatant hydroxylamine KOH solution is immediately used in the preparation of the hydroxamic acid ligands. 

A number of types of compound can be considered as hydroxylamine derivatives. Hydroxamic acids have the general formula RC(OH)NOH and can be used to precipitate or extract a range of metal ions, including Zr, Th, Fe and Cr. Cupferron (ammonium iV-nitroso-Af-phenylhydroxylamine) and iV-substi-tuted phenylhydroxylamines such as iV-Benzoyl-IV-plienylliydroxylamine behave similarly to the hydroxamic acids, and are used for similar purposes. 

A colorless liquid, bp = 199-201 °C, bums with a yellow, sooty flame. The sodium fusion test proved negative for the presence of halogens, nitrogen, and sulfur. The compound was not soluble in water, 5% aqueous sodium hydroxide, or 5% hydrochloric acid. However, it dissolved in sulfuric acid with evolution of heat. It did not give a precipitate with 2,4-dinitrophenylhydrazine solution, and it did not decolorize bromine-methylene chloride solution. The unknown liquid did give a positive hydroxamate test and was found to have a saponification equivalent of 136. Identify the unknown liquid. 

Fatty acids and soaps dominate the nonsulflde flotation. These collectors also tend to be nonse-lective because almost all minerals can be floated. The use of appropriate activators or depressants alleviates the problem to some extent. The lack of selectivity is often related to the tendency of fatty acids to form a precipitated phase with dissolved multivalent ions. The more tolerant ether carboxylic acids have been tested in some cases. Amines are used invariably for silicate minerals. Other collectors such as sulfates, sulfonates, phosphonic acids, hydroxamates, and some amphoteric surfactants have gained little importance. 

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