Hydroxamic acids minerals

Acid Hydrolysis. With hot concentrated mineral acids, primary nitroparaffins yield a fatty acid and a hydroxylamine salt. If anhydrous acid and lower temperatures are used, the intermediate hydroxamic acid can be recovered. 

A-Acetoxy-A-butoxybenzamides (101) react in aqueous acetonitrile by an autocat-alytic process. In the presence of added mineral acid, they undergo acid-catalysed AaiI solvolysis forming A-aroyl-A-butoxynitrenium ions (102), which are trapped by water. The hydroxamic acid product (103) reacted under the conditions to give a range of products that included, n-butanol, butanal, benzoic acids, benzohydroxamic acids and butyl benzoates (Scheme 18)92.93,95, ns, i56 ... 

Hydroxamic acids are in general colorless, somewhat low-melting solids. However, most of them can be crystallized and the potassium salt of benzhydroxamic acid forms beautiful plates. In terms of stability to acid, the hydroxamic acid bond is intermediate between that of amides and esters. By use of carefully controlled conditions it is possible to split the hydroxamic bond in the presence of the peptide linkage. In the absence of iron, hydrolysis is effected cleanly with hot mineral acid in base extensive degradation occurs even without a contaminating metal ion. Once it has been liberated from the hydroxamic acid linkage the hydroxylamino moiety should always be maintained at a pH below the pKa ( 5). 

Three papers from Ghosh s group deal with the hydrolysis of benzohydroxamic acids in acidic and alkaline conditions. A pre-equihbrium protonation followed by a slow A-2 type nucleophilic attack by water is seen as the mechanism of the acid-catalysed hydrolysis of j -chlorophenylbenzohydroxamic acid (107 R = / -ClCgEU) by mineral acids (HCl, HCIO4) in 20% aqueous dioxane. An A-2 mechanism was also supported for the reaction of (107 R = Me) imder comparable conditions. The alkaline hydrolysis imder micellar conditions of (107 R = Ph) and a series of para-substituted derivatives has been investigated in the presence of cationic and anionic micelles in 5% dioxane-water medium at 55 °C. Cationic surfactants exerted a catalytic effect and anionic surfactants were inhibitory. The rate-surfactant profiles were analysed in terms of the pseudophase and Piszkiewicz models. The detection of N2O in the products of the oxidation of hydroxamic acids suggests the intermediacy of nitroxyl, HNO, in the process. Scheme 9 may represent the pathway followed. 

The original procedure for the Nef reaction involved the aqueous sulfuric acid hydrolysis of the salts (170) obtained by the treatment of primary and secondary nitroalkanes with sodium hydroxide (equation 30). In contrast, if a neutral primary nitro derivative is treated in hot concentrated mineral acid, the corresponding carboxylic acid (172) is formed via the hydroxamic acid (171 equation 31). This reaction is known as the Meyer reaction and was first described in 1873. Protonation of salts of nitroalkanes occurs preferentially at the oxygen atom to give the aci form (173 equation 32). 

One chemical test that is useful for textile wet processes may be the spot test. By using hydroxamic acid, waxes and fatty oils can be distinguished from their mineral counterparts." In a small crucible, one drop of a saturated ethanol solution of hydroxamic acid is mixed with one drop of an ethanol solution of the sample and one drop of an ethanol solution of KOH. The mixture is heated to bubbling (evaporation) and then allowed to cool and is acidified with HCl. A drop of FeCl, is added to the acidified sample. A violet colour confirms the existence of waxes and fatty oils. Carboxylates may also give a positive result. If the saponification number of waxes needs to be known, ASTM D1387 can be used. ASTM D1386 can be used to determine the acid number of waxes. ... 

Extraction with triphenylarsine oxide in CHCI3 followed by the reaction with Arsenazo III (after stripping of the analytes with 4 M HCl) makes a basis of the determination of Zr and Hf (and Ti) in minerals and alloys [1], Sequential liquid-liquid extraction and spectrophotometric determination of zirconium(IV) with calixarene hydroxamic acid and thiocyanate has been described [2]. Colorimetric determination of Zr and Hf with Xylenol Orange and a liquid-liquid extraction of thenoyltrifluoroacetone complexes using H2O-IBMK has been studied [3]. 

For this reason, we consider it hardly possible to cite all of the publications. Let us focus only on the following examples. Hydroxamic acids have already been for a long time subject of the classical analytical chemistry. In [71], the possibility of using these compounds in flotation of rare-earth minerals is shown. It has been concluded that on a mineral surface cerium chelates are formed. Besides, chemisorption is accompanied by a physical multilayer adsorption of hydroxamic acid derivatives formed by reaction with cations in the water phase. A number of chelate-forming compounds including hydroxamic acids has been tested in flotation of niobium ores [72]. The best results are obtained when using alkyl phosphonic acids. Chemisorption mechanism and the structure of the surface compounds are established by spectroscopic methods. 

The so-called chelating collectors, such as hydroxamic acids, continue to be studied by flotation specialists. The flotation selectivity of minerals partly soluble in the flotation pulp has been studied, at bench scale, in [159]. It has been shown that optimum results are achieved, when the mineral to be floated is the most soluble in the system and the chelate formed with the cation on the surface is most stable. 

In the presence of strong mineral acids the uronic acids give specific colours with phenolic compounds such as naphthoresorcin, and a colorimetric method for the determination of uronic acids utilizing carbazole and sulphuric acid has been developed. A similar method which depends on the colour produced with benzidene in glacial acetic acid has also been devised . Alternatively the acids can be converted into the hydroxamic acids which give intensely coloured compounds with ferric salts. The intensity of colour can be measured and the method is sufficiently accurate to be used on the semi-micro scale . Care should be observed in the interpretation of the results as other acids such as acetic acid derived from acetyl residues, interfere. 

The Ta/Nb flotation was accomplished using collector RS702. This collector is composed of amine acetate, phosphoric acid esters and hydroxamate. Collector RS702 is a powerful collector, capable of floating a variety of niobium minerals that are contained in the flotation feed. Metallurgical results obtained from a continuous locked-cycle test are shown in Table 23.14. 

Watteau F. and Berthelin J. (1994) Microbial dissolution of iron and aluminum from soil minerals efficiency and specificity of hydroxamate siderophores compared to aliphatic acids. Euro. J. Soil Biol. 30(1), 1-9. 

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. 

Complete hydrolysis of h3 uronic acid with mineral adds produces D-ghicosamine, acetic add, and carbon dioxide, the last named indicating the presence of a uronic acid. The latter compound was identified as d-g ucuronic acid by oxidation with nitric add, which led to the formation of D-glucaricacid. D-Glucuronic add was subsequently isolated after enzymic degradation. The carboxyl group of the uronic moiety is free, as shown by salt formation, titration, and the positive hydroxamic test after ester formation. 

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