Molybdophosphates reduced

Procedure has been proposed for the P(V) and As(V) determination based on the selective extraction of ionic associate of Crystal Violet with reduced molybdophosphate with mixture of inert (toluene) and active (methyl isobutyl ketone) solvents. Extraction of reagent is negligible. After concentration determination lower than 10 mol/1 of P(V) and As(V) is possible. 

It is shown that both Sb(III) and Bi(III) can speed reduction of 12-molybdophosphate (12-MPC) to the corresponding heteropoly blue (12-MPB) by ascorbic acid (AA). It is found that mixed polyoxometalates can be formed in solution which reduce considerably more rapidly than 12-MPC. Complete formation of mixed POM is observed only if significant excess of Me(III) ions is used in the reaction. POM responsible for blue color was synthesized by selective extraction. Chemical analysis of tetrabutyl-ammonium salt is in accordance with formula of (TBAl PMeflllfMo O j (Me = Sb, Bi). IR spectmm of mixed POM is identical to 12-MPC. 

Instead of being determined volumetrically, however, the ammonium or quinoline molybdophosphates are usually reduced to another molybdenum complex, molybdenum blue (heteropoly blue), which is then analysed spectrophotometrically (see Section II.B.2.C). 

The heteropoly molybdophosphates are much more reducible than the corresponding tungstates, but the latter exhibit one-electron transfer steps at high pH whereas the molybdophosphates did not (12). Otherwise, the electronic structures and behavior of the two are very similar (13), and perhaps the F-C reagent operates well, partly because one-electron transfers are possible, yet the reagent is a good oxidant. 

One common way to determine phosphorus in urine is to treat the sample, after removing the protein, with molybdenum(VI) and then reduce the resulting 12-molybdophosphate complex with ascorbic acid to give an intense blue-colored species called molybdenum blue. The absorbance... 

Caesium is separated from small amounts of rubidium and potassium as the sparingly soluble caesium tungstosilicate. The precipitate is dissolved, the tungstosilicic acid is reduced to silicotungsten blue, and the absorbance is measured at 640 nm [88], Caesium has been also determined indirectly as phosphomolybdenum blue (absorbance measured at 805 nm) after the precipitation of, and isolation of caesium molybdophosphate [89]. Caesium was also determined indirectly by precipitation of C 3Bi2l9 with subsequent determination of Bi by the iodide method [90]. 

Many methods for sulphide and H2S are based on the reducing properties of S(-II). Hydrogen sulphide reduces molybdate in acid medium to molybdenum blue, and the molybdophosphate to phosphomolybdenum blue [52]. Iron(III) reduced by H2S in the presence of 1,10-phenanthroline gives the orange Fe(phen)3 complex [2,53], Hydrogen sulphide may be determined after conversion into thiocyanate by the reaction with Fe(III) [54]. Sulphide has been determined also by a colour redox reaction with nitroprusside [55-57], In another sensitive reaction the sulphide ions decompose the Ag complex with Cadion 2B and Triton X-100 (e = 2.5-10 ) [58], In another indirect method sulphide releases the chloranilate ion from the Hg(Il) chloranilate [59]. Sulphide has also been determined by a method based on its reaction with bromate, followed by bromination of 2 ,7 -dichlorofluorescein by the bromine released [60]. 

The first examples of polyoxoanions are considered to have been described by Berzelius in 1826 (yellow ammonium 12-molybdophosphate and -arsenate, and their reduced blue derivatives), but it was not until the last third of the nineteenth century that detailed descriptive chemistry of many polymolybdates and polytungstates began to be reported. 

The ammonium molybdophosphate is extracted with a benzene/isobutyl alcohol mixture and reduced in the organic phase with acid tin (II) chloride solution to intensely blue-coloured phosphorus molybdenum blue ... 

Phosphate is another inorganic species commonly encountered in biological systems that can be assayed spectrophotometrically. It reacts with ammonium molybdate to form 12-molybdophosphate heteropolyacid [PMoi204o], which is reduced by ascorbic acid to a blue product (2n,ax = 820nm). 

In addition to catalyzed reactions, kinetic methods of analysis also can employ uncatalyzed reactions. As an example, phosphate can be determined by measuring the rate of its reaction with molybdate to form a heteropoly species, 12-molybdophosphate. More sensitivity can be achieved by reducing the 12-molyb-... 

On the other hand, a fourth type of catal3dic system studied over the last few years is the heteropolyacids and their salts. Composition, structure (including Keggin, Dawson, Anderson, etc.), nature, and number of cationic species can tailor both redox and acid characteristics. In addition, partially reduced heteropolyacids have also been employed as in the case of Keggin molybdophosphate catalysts (Fig. 24.2d) reduced with pyridine, reported by Li et al. ... 

SP (Vis) Two-electron reduced heteropolyblue is formed very fast at pH 3.75-4.75 in the reaction between Dawson-type molybdophosphate HPA and AA 1.0 60 No data Pharmaceuticals, fruit juices 2011 269... 

The four-step reduction of 12-molybdophosphoric acid by stannous chloride has been reported, one mole of Sn being involved in each case. It is suggested that the molybdophosphate anion can accept up to eight electrons without decomposition and that in this ion eight of the twelve molybdenum atoms originally in the +6 oxidation state have been reduced to the +5 state. 

Commercially available. Used in anal, of transition metals, as iron fertiliser, electron beam sensitiser, fuel additive. Used as a 0.1% soln. in dioxan as reducing agent for molybdophosphate in photometric detn. of P as a primary standard for redox titrations in MeCN. Orange cryst. (EtOH aq.). Sol. EtOH, C H, insol. H2O. Mp 120-123°, Mp 172.5-173°. Bp 249°. Sublimes above 100°, steam-volatile. Exists in ordered and disordered phases. Undergoes aromatic-type subn. reacns. 

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