Molybdic acid, molybdates complexes

Polarimetric analysis of sorbitol and mannitol in the presence of each other and of sugars is possible because of their enhanced optical rotation when molybdate complexes are formed and the higher rotation of the mannitol molybdate complex under conditions of low acidity (194). The concentration of a pure solution of sorbitol may be determined by means of the refractometer (195). Mass spectra of trimethylsilyl ethers of sugar alcohols provide unambiguous identification of tetritols, pentitols, and hexitols and permit determination of molecular weight (196). 

Co-extraction of Mo and Cu is potentially a problem with certain feed solutions,14 and again selectivities are very dependent on the nature of modifiers present in formulated reagents.142 The Mo species extracted have not been fully characterized, but may include a neutral dioxo complex, [Mo02L2], which can be assumed to have an N2022 donor set similar to that in the Cu11 complex, and molybdate complexes solvated by neutral phenolic oxime ligands such as [M0O4112 LI l].143 Formation of solvated forms of molybdic acid is supported by evidence that extraction is favorable at very low pH values and that the complexes are readily stripped by aqueous ammonia to produce ammonium molybdate,144... 

Peroxide titanate complexes, 25 98 Peroxide value, 20 827 in soap making, 22 736 Peroxidic compounds, 25 42 Peroxoborates, names, CAS numbers, and IUPAC names of, 18 398t Peroxocarbonates, 28 401 Peroxo compounds, 28 392-393, 397 Peroxodisulfate ion, 28 408 Peroxodisulfates, 28 392, 408-410 Peroxodisulfate salts, 28 418 uses for, 28 408-409 Peroxodisulfuric acid, 28 407 408 Peroxohydrate(s), 24 40 28 411—415 of melamine, 28 415 stabilization of, 28 413 Peroxo molybdate complexes, 2 7 22 Peroxomonophosphate ion, 28 403 Peroxomonophosphoric acid, 28 403 Peroxomonosulfates, 28 406 407... 

Figure 1. Characteristic EPR signals of Fe(II)Fe(III) sites in semimethemerythrinj (a), semimethemerythrinQ (b), reduced uteroferrin (c), reduced uteroferrin-molybdate complex (d), reduced bovine spleen purple acid phosphatase (e), reduced component A of methane monooxygenase (f). (Reproduced with permission from ref. 26. Copyright 1987 Elsevier.)...

Hexacyanoferrates were immobilized on Au covered with SAM of 3,3 -thiodipropionic acid [86]. It has been found from voltammetric studies that the surface coverage of hexacyanoferrate is close to one monolayer and such an electrode exhibits very good surface redox behavior. Cheng et al. [87] have described the formation of an extremely thin multilayer film of polybasic lanthanide heteropolytungstate-molybdate complex and cationic polymer of quaternary poly(4-vinylpyridine), partially complexed with osmium bis(2,2 -bipyridine) on a gold electrode precoated with a cysteamine SAM. Consequently, adsorption of inorganic species might also be related to the properties of SAMs. This problem will be discussed in detail in a separate section later. 

The silicic acid concentrations were analyzed at different times by withdrawing 1 ml. from the solution after a high speed centrifugation of the suspended particulates. The colorimetric determination of oligomeric silicic acid by means of the blue ammonium molybdate complex, as described by Stegemann and Fitzek (16), was used for the quantitative measurements. 

The absolute configuration of the side chain of isoharringtonine has been deduced (174) to be 2R,35(299) by comparing the CD spectra of its molybdate complexes with those of piscidic acid (300) of known absolute configuration. 

Molybdate diluting solution. Dissolve 0.5 g of Na2C03 and 0.5 g of Na2B407 in 100 ml of 0.39 M nitric acid. Add 100 ml of molybdate complexing solution and dilute to 500 ml with 0.126 M HN03. This solution can be used until a scale of hydrated molybdenum oxide develops on the container walls (several days to a week). Then a fresh solution should be prepared. The scale can be removed with ammonium hydroxide solution. 

The ability of zinc ions to block copper absorption, possibly by formation of- intestinal metallothionein that strongly binds copper, has led to its use in pharmacological doses in the management of Wilson s disease/ Similarly molybdate ion can form insoluble copper-molybdate complexes in the intestine that limit copper absorption. The detrimental effects of organic phosphate (phytic acid) in limiting zinc absorption are aggravated by excess dietary calcium, probably by formation of a highly insoluble Ca-Zn-phytate complex. The subject of these and other interactions has been reviewed, ... 

Combi cassette. The ColorLock Gold assay kit is based on malachite green-molybdate colorimetric assay, and the yellow reagent turns green in the presence of phosphate. The stabilizer stabilizes acid-labile substrates and the molybdate complex to maintain signal stability. 

Standard methods for phosphates, polyphosphates, and organic phosphates in environmental samples are predominantly nonchromatographic methods, which are based upon the molybdenum blue method. Within this colorimetric method ammonium molybdate and antimony potassium tartrate react under acidic conditions with dilute solution of phosphorous to form an antimony-phospho-molybdate complex which is then reduced to an intensely blue-colored complex by ascorbic acid. U.S. EPA Methods 365.1 to 365.4 are based upon this chemistry. 

Isobutylmalic acid (18) and (— )-2-benzylmalic acid (19), the constituent acids of cornucervine and phalaenopsine La, respectively, have now been shown to have the / -configuration. This was established by a partial asymmetric synthesis of the enantiomers of these acids and comparison of the c.d. spectra of their molybdate complexes with that of the molybdate complex of (-f )-citramalic acid (20) of known S-configuration. 

In acidic pH range, the sugar-molybdate complex decomposes as follows ... 

Glycosylmanganese pentacarbonyl complexes have been characterized on the basis of H-, and Mn-NMR spectral data, and ten tungstate and seven molybdate complexes of D-gulonic acid in aqueous solutions have been identified by multinuclear NMR studies ( H, O, Mo,... 

The cooled water sample is decomposed using hydrofluoric acid/per chloric acid, thereby depolymerizing the entire silicic acid and converting it into a form capable of reaction with ammonium molybdate (W. Fresenius and W. Schneider). After adding boric acid to complex the hydrofluoric acid,... 

The greatest advantage of using ascorbic acid as the reductant is that the blue phospho-molybdic complex formed is stable for hours, and that the colour intensity is not influenced by variations in salinity. However, the influence of some other ions occiurring in natural waters must be considered ... 

In these polyhetero acids the complexed molybdic acid has an enhanced oxidizing power toward many inorganic and organic compounds, which are oxidized slightly, if at all, by free molybdic acid and normal molybdates. For example, iodides are oxidized but slightly by molybdates in acid solution, even on warming, whereas phosphomolybdic acid liberates appreciable amounts of iodine, even in the cold. 

Procedure. About 0.1 - 2.0 grams is digested with the least possible volume of concentrated sodium hydroxide in a small crucible and then acidified with a drop of phosphoric acid. Soluble complex phosphotungstic and phospho-molybdic acids are formed. A few crystals of potassium xanthate are then added. A dark violet to red color forms, according to the molybdenum content. The color fades on standing. 

The same method has been applied with little modification for the determination of silicates in water extract of black liquor and pulp by reducing the molybdate complex with ferrous sulfate in a slightly acidic media [3]. 

Based on the results of studies with isotopically substituted D-fructoses, and following the stereochemical rules of molybdate complexes, the mechanism of the molybdic acid catalyzed mutual interconversion of 2-ketoses and 2-C-(hydroxymethyl)aldoses (referred to as the primary process) [54,55] is shown in Scheme 11. 

The study of the decondensation kinetics of the silicates is not easy. The NMR of Na reveals that when a solid sodium silicate is put into solution, the first step is the integral rehydration of the sodium that passes into the aqueous solvent. Afterward, there is progressive decondensation of the silicic polymers or oligomers. The decondensation reactions take place in the washing liquor, which is a dilute aqueous medium. The reactions evolve very rapidly, and the kinetics are difficult to measure by NMR. That is why other techniques, like the silico-molybdic complex, are used [16]. With this method, the quantity of silicic monomers in a solution resulting from the decondensation of the larger silicic species can be measured. The monomers formed react with the molybdic acid in controlled conditions to give a yellow complex that can be easily titrated by spectrophotometry. 

Instead of weighing the precipitate, various methods (both volumetric and colorimetric) have been described for determination of the excess precipitant in the filtrate and for the colorimetric determination of the molybdate or molybdate complex in the dissolved precipitate. These include a method due to Stevenson in which the precipitated phospho-molybdate is dissolved in sulphuric acid and the extinction of the solution measured at 520 m/i. 

The absolute configuration of norcaperatic acid (20) was determined as 2S,3S by CD measurements on the natural acid and optically active synthetic compounds as their molybdate complexes (2S). 

The synthesis, structures and function of caibohydiate-metal coordination conqmunds has beoi reviewed. Conqilexes of some hepurfiiranose derivatives containing primary-secondary 1,3-diol moieties with molybdenum tetraacetate have been studied and their CD spectra have allowed assignment of die configurations (rf the secondary alcohol centres. Aldoses of the arabino- and xylo- series have been shown to form tetradentate acyclic complexes with molybdare ions in aqueous acidic media, and the structure and conformation of molybdare conqil ces with S-deoxy-L-arabinose and S-deoxy-L-ribose have been studied. Molybdate complexes of D-allose, D-altrose, D-gulose and D-idose have been studied by NMR methods. ... 

The effect of various interfering ions on the molybdate complex must also be considered. Only a very small amount of nitrate can be tolerated, and the permissible chloride concentration depends upon the amount of HCl removed during preparation of the reducing solution (Andersson [1962a]). Molybdate complexes with sulphuric acid when the latter is present in large amounts, and under these conditions, decomposition of the silicomolybdate must occur to a certain extent. Since the heteromolybdates of arsenic and phosphorus are less stable than the corresponding silicomolybdates, interference by these elements can, to some extent, be eliminated by use of polybasic organic acids such as oxalic and tartatic, which form complexes with molybdate. Interference by phosphate, however, cannot be eliminated completely. 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

The tris (dithiolene) complexes of Mo can be formed by reaction of the corresponding dithiol and molybdate in acid solution. The intense green... 

When the Claus reaction is carried out in aqueous solution, the chemistry is complex and involves polythionic acid intermediates (105,211). A modification of the Claus process (by Shell) uses hydrogen or a mixture of hydrogen and carbon monoxide to reduce sulfur dioxide, carbonyl sulfide, carbon disulfide, and sulfur mixtures that occur in Claus process off-gases to hydrogen sulfide over a cobalt molybdate catalyst at ca 300°C (230). 

Phosphate. Phosphoms occurs in water primarily as a result of natural weathering, municipal sewage, and agricultural mnoff The most common form in water is the phosphate ion. A sample containing phosphate can react with ammonium molybdate to form molybdophosphoric acid (H2P(Mo202q)4). This compound is reduced with stannous chloride in sulfuric acid to form a colored molybdenum-blue complex, which can be measured colorimetrically. SiUca and arsenic are the chief interferences. 

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