Molybdenum blue oxides

Sonication of a solution containing metal precursors can also generate precipitation. For instance, the sonication of a solution of molybdenum hexacarbonyl (Mo(CO)g)) leads to the precipitation of a molybdenum oxide under air (40 2) and of molybdenum carbide under argon atmosphere (41). In the presence of a silica support, sonication of Mo(CO)g solution in decalin leads to molybdenum carbide (Mo2C)-silica material under argon atmosphere and to molybdenum blue oxide (M02O5.2H2O)-silica under... 

The reduction of molybdate salts in acidic solutions leads to the formation of the molybdenum blues (9). Reductants include dithionite, staimous ion, hydrazine, and ascorbate. The molybdenum blues are mixed-valence compounds where the blue color presumably arises from the intervalence Mo(V) — Mo(VI) electronic transition. These can be viewed as intermediate members of the class of mixed oxy hydroxides the end members of which are Mo(VI)02 and Mo(V)0(OH)2 [27845-91-6]. MoO and Mo(VI) solutions have been used as effective detectors of reductants because formation of the blue color can be monitored spectrophotometrically. The nonprotonic oxides of average oxidation state between V and VI are the molybdenum bronzes, known for their metallic luster and used in the formulation of bronze paints (see Paint). 

Molybdenum blue method. When arsenic, as arsenate, is treated with ammonium molybdate solution and the resulting heteropolymolybdoarsenate (arseno-molybdate) is reduced with hydrazinium sulphate or with tin(II) chloride, a blue soluble complex molybdenum blue is formed. The constitution is uncertain, but it is evident that the molybdenum is present in a lower oxidation state. The stable blue colour has a maximum absorption at about 840 nm and shows no appreciable change in 24 hours. Various techniques for carrying out the determination are available, but only one can be given here. Phosphate reacts in the same manner as arsenate (and with about the same sensitivity) and must be absent. 

The following procedure has been recommended by the Analytical Methods Committee of the Society for Analytical Chemistry for the determination of small amounts of arsenic in organic matter.20 Organic matter is destroyed by wet oxidation, and the arsenic, after extraction with diethylammonium diethyldithiocarbamate in chloroform, is converted into the arsenomolybdate complex the latter is reduced by means of hydrazinium sulphate to a molybdenum blue complex and determined spectrophotometrically at 840 nm and referred to a calibration graph in the usual manner. 

Apparent indicator constant 264, 267 Apparent stability constant 59 Aqua regia 111 Arc alternating current, 764 direct current, 763, 771 sensitivities of elements, (T), 766 Aromatic hydrocarbons analysis of binary mixtures, 715 Arsenates, D. of (ti) 357 Arsenic, D. of as silver arsenate, (ti) 357 as trisulphide, (g) 448 by iodine, (am) 634, (ti) 397 by molybdenum blue method, (s) 681 by potassium bromate, (ti) 406 by potassium iodate, (ti) 401 in presence of antimony, (s) 724 Arsenic(III) oxide as primary standard, 261... 

Molybdenum, tris(phenylenedithio)-structure, 1,63 Molybdenum alkoxides physical properties, 2,346 synthesis, 2,339 Molybdenum blue liquid-liquid extraction, 1,548 Molybdenum cofactor, 6,657 Molybdenum complexes acrylonitrile, 2,263 alkoxides, 3,1307 alkoxy carbonyl reactions, 2,355 alkyl, 3,1307 alkyl alkoxy reactions, 2,358 alkyl peroxides oxidation catalyses, 6,342 allyl, 3,1306... 

Johnson and Pilson [229] have described a spectrophotometric molybdenum blue method for the determination of phosphate, arsenate, and arsenite in estuary water and sea water. A reducing reagent is used to lower the oxidation state of any arsenic present to +3, which eliminates any absorbance caused by molybdoarsenate, since arsenite will not form the molybdenum complex. This results in an absorbance value for phosphate only. 

A sulfuric acid solution of the oxide (25-75% solution) can be reduced with tin, copper, zinc, and other reducing agents forming a blue solution of molybdenum blue which are hydrous oxides of non-stoichiometric compositions (see Molybdenum Blue). Reduction with atomic hydrogen under carefully controlled conditions yields colloidal dispersion of compounds that have probable compositions Mo204(OH)2 and Mo40io(OH)2. Reduction with lithium aluminum hydride yields a red compound of probable composition MosOtIOEOs. Molybdenum(Vl) oxide suspension in water also can be reduced to molybdenum blue by hydriodic acid, hydrazine, sulfur dioxide, and other reductants. 

For a number of years, phenolic substances were dosed by colorimetric techniques, based on redox reactions usually known as Folin Ciocalteau methods, even if a number of adjustments were developed to fit different matrix characteristics. The Folin Cioalteau reagent is a mixture of phosphomolybdic and phosphotingstic acids, with molybdenum in the 6+ oxidation state and, when the reaction takes place, it is reduced to form a complex called molybdenum blue and tungsten blue. In this complex, the mean oxidation state is between 5 and 6 and the formed complex is blue so it can be read spectrophotometrically at 750 nm. 

The spot-test technique of the reaction utilizes the conversion of the silicic and fluosilicic acids by means of ammonium molybdate into silicomolybdic acid H4[SiMo12O40]. The latter, unlike free molybdic acid, oxidizes benzidine in acetic acid solution to a blue dyestuff and molybdenum blue is simultaneously produced. (DANGER THE REAGENT IS CARCINOGENIC.)... 

Ammonium molybdate-benzidine test (DANGER THE REAGENT IS CARCINOGENIC.) Silicates react with molybdates in acid solution to form the complex silicomolybdic acid H4[SiMo12O40]. The ammonium salt, unlike the analogous phosphoric acid and arsenic acid compounds, is soluble in water and acids to give a yellow solution. The test depends upon the reaction between silicomolybdic acid and benzidine in acetic acid solution whereby molybdenum blue and a blue quinonoid oxidation compound of benzidine are produced. 

CARCINOGENIC.) In this test use is made of the fact that benzidine, which is unaffected by normal molybdates and by free molybdic acid, is oxidized in acetic acid solution by phosphomolybdic acid or by its insoluble ammonium salt (see reaction 4 above). This reaction is extremely sensitive two coloured products are formed, viz. the blue reduction product of molybdenum compounds ( molybdenum blue ) and the blue oxidation product of benzidine ( benzidine blue ). Moreover, solutions of phosphates which are too dilute to show a visible precipitate with the ammonium molybdate reagent will react with the molybdate reagent and benzidine to give a blue colouration. 

Some variants of these techniques have been described by Melville/ Benington, and Bartlett. " The technique described by Melville involves the ability of II atoms and alkyl free radicals to reduce the blue oxide coat on a polished molybdenum surface. By photometrically studying the change in optical color of the surface it was shown possible to make calculations of the relative concentrations of radicals diffusing through a vapor stream to the metal oxide surface. The mathematical calculations are involved, and the difficulties already described for mirror techniques occur here too. 

Total wine polyphenols are oxidised by the Folin-Ciocalteu reagent - composed of a mixture of phosphotungstic and phosphomolybdic acids which are reduced by the oxidation of the phenols, forming a mixture of blue oxides of tungsten and molybdenum. The blue coloration has an absorption maximum at approximately 750 nm, the intensity of which is proportional to the level of phenolic compounds present in the wine. The sequential analyser method is a direct automation of the manual method and results are expressed as a unit-less index. 

Molybdenum Hexafluoride, MoFg, the only fluoride known vith certainty to exist, is best prepared by the action of fluorine on the finely divided metal at 60° to 70° C., the product being collected in a vessel cooled by a mixture of solid carbon dioxide and alcohol. It forms white crystals which melt at 17° C., the boLling-poiiit of the liquid being 35° C. It is decomposed by water, yielding the blue oxide (see p. 131), but does not react with chlorine, sul2ihur dioxide, or dry air it is absorbed by alkali or ammonium hydroxides, and fomis double salts vith alkali fluorides. It also reacts with ammonia, vith 2>roduction of a brown powder. 

The pentachloride is a little unstable in air when heated to about 1380° C. or less it leaves a residue of molybdenum when heated in hydrogen at 250° C. it is reduced to amorphous molybdenum trichloride. Its aqueous solution is unstable in air, especially on warming, when hydrogen chloride is more rapidly evolved and the blue oxide (p. 131) remains. Decomposition of its solution in hydrochloric acid also readily takes place. In alcohol and ether it dissolves to a green solution in sulphuric acid its solution is bluish green and in nitric acid colourless alkalies dissolve it with production of the hydrated dioxide and a molybdate. ... 

Oxides of molybdenum corresponding to the formulae M02O3, MoOj, and M0O3 are known to exist that represented by the last formula, an add-forming oxide, has been studied in greatest detail. The intermediate blue oxide of molybdenum, obtained by the reduction of the trioxide, is well known, but its composition cannot be considered to be satisfactorily settled the formula MojOg is usually ascribed to it. 

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