Tungstic acids

Little work has been carried out on thiazole N-oxides. These products are unstable and breakdown by autoxidation to give thiazolium-A -oxide sulfates and other decomposition products (264). They are prepared by direct oxidation with hydrogen peroxide, or by tungstic acid (264, 265) or peracetic acid (265-267). 

Direct fluoridation of pure tungsten in a flow system at atmospheric pressure at 350—400°C is the most convenient procedure (4). Tungsten hexafluoride is extremely unstable in the presence of moisture and hydroly2es completely to tungstic acid [7783-03-1] ... 

Tungsten oxytetrafluofide [13520-79-17, WOF, mp 110°C, bp 187.5°C, forms colorless plates. It is prepared by the action of an oxygen—fluorine mixture on the metal at elevated temperatures (7). The compound is extremely hygroscopic and decomposes to tungstic acid in the presence of water. 

Tungsten oxytetrachlofide [13520-78-0], WOCl, mp 211°C, bp 221°(Z, is a red crystalline soHd. It is soluble in carbon disulfide and ben2ene and is decomposed to tungstic acid by water. It may be prepared by refluxing sulfurous oxychloride, SOCI2, on tungsten trioxide (12) and purified after evaporation by sublimation. 

Ammonium tungstate [11140-77-5] (NH 2 0cannot be obtained from an aqueous solution because it decomposes when such a solution is concentrated. It is prepared by the addition of hydrated tungstic acid to Hquid ammonia. 

Polytungsta.tes, An important and characteristic feature of the tungstate ion is its abiUty to form condensed complex ions of isopolytungstates in acid solution (38). As the acidity increases, the molecular weight of the isopolyanions increases until tungstic acid precipitates. However, the extensive investigations on these systems have been hampered by lack of weU-defined soHd derivatives. 

The tungstic acid was used as supplied by the Eastman Kodak Company. 

Oxidation of trimethylene sulfide catalyzed by tungstic acid is preferred to the uncatalyzed reaction Yields are better and the reaction time... 

Ammonium tungstate (VI) [11120-25-5] M 283.9, pK] 2.20, pK2 3.70 (for tungstic acid, H2WO4). Crystd from warm water by adding EtOH and cooling. 

The isolation of tungsten is effected by the formation of tungstic acid (hydrous WO3), but the chemical route chosen depends on the ore being used. After pulverization and concentration of the ore ... 

Tungstic acid is then roasted to WO3 which is reduced to the metal by heating with hydrogen at 850°C. Half of the tungsten produced is used as the carbide, WC, which is extremely hard and wear-resistant and so ideal as a tool-tip. Other... 

Determination of tungsten as the trioxide (tannic acid-phenazone method) Discussion. Tungstic acid is incompletely precipitated from solutions of tungstates by tannic acid. If, however, phenazone (2,3-dimethyl-l-phenyl-5-pyrazolone) is added to the cold solution after treatment with excess of tannic acid, precipitation is quantitative. This process effects a separation from aluminium, and also from iron, chromium, manganese, zinc, cobalt, and nickel if a double precipitation is used. 

Electrodeposition of polycrystalline mngsten disulfide (WS2) thin films on TO/glass, from an aqueous solution of tungstic acid and Na2S03 (pH 7.0-9.5), at different current densities ranging from 20 to 60 mA cm , and temperatures 40, 60, and 80 °C, has been reported [155]. Both the 2H and 3R phases of WS2 were found... 

The series of deviation from a strictly octahedral crystal field follows the sequence ammonium tungstate > tungstic acid > WO3 [14]. The s->d transition becomes allowed as distortion of the octahedral environment increases. Viewed as a fingerprint technique. Figure 6 shows that the bulk of W present in both WZ (calcined) and PtWZ(acac, reduced) behaves as WO3, as also shown by our XRD data [10], sugesting that only a small extent of W reduction is expected to have taken place during catalyst conditioning prior to reaction. 

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