Tungstic acid preparation

Richardson, E. (1959) Some studies of tungstic acid prepared by ion exchange. 

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). 

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. 

Lou and Zeng spotted the work of Park et al. and sought to improve on it by developing an aqueous synthetic route. In this method, water and sodium sulfate are added to freshly prepared tungstic acid and autoclaved at up to 200°C for up to 24 h (assuming saturated steam conditions, this corresponds to pressures of up to 15.5 bars). 

Tungstic acid is used in preparing tungsten metal and many tungsten compounds. Also, it is a mordant for textiles. 

Yellow amorphous powder density 5.59 g/cm decomposes at 100°C insoluble in water and most acids soluble in hydrofluoric acid, caustic alkalies and ammonia solution. Freshly prepared tungstic acid containing a molecule of water of crystaUization is moderately soluble in water. 

Tungstic acid is obtained as an intermediate in the recovery of tungsten from its minerals, scheebte and wolframite (See Tungsten). Also, the tungstic acid may be prepared by heating sodium tungstate with sulfuric acid or hydrochloric acid ... 

In 1783 the brothers collaborated in a research on tungsten and wolfram, and found that both these ores contained the tungstic acid that Scheele had reported. The first metallic tungsten was prepared not from... 

Dr. Fages and Dr. Moles both pointed out that, in isolating the new metal, the de Elhuyar brothers did much more than merely confirm the hypothesis of Torbem Bergman. Instead of analyzing tungstic acid intentionally prepared to test this hypothesis, as has so often been stated, they analyzed wolfram without any preconceived ideas. Dr. Fages stated that, after the de Elhuyar brothers had discovered the acid in wolframite ... 

Preparation of Normal Ammonium Tungstate. Weigh 0.5 g of tungstic acid in a test tube, put the latter into a cooling mixture (solid carbon dioxide with acetone), and pour in 1-2 ml of liquid ammonia. Stir the contents of the test tube with a cooled glass rod and let the ammonia evaporate. Examine the precipitated crystals under a microscope. What is the composition of the product ... 

Preparation of Sodium Paratungstate, a. Pour 20 ml of a 50% sodium hydroxide solution into a 100-ml porcelain beaker provided with a mechanical mixer, put the beaker on a water bath, and introduce the calculated amount of a freshly precipitated wet suspension of tungstic acid in small portions while vigorously stirring. At the end of the reaction, the pH of the solution should be 6-6.5. Filter the solution, evaporate it a little, and let it stand for 24 hours. Separate the formed crystals by filtration and dry them in the air. 

Sulfunes. A recent preparation of thietane 1,1-dioxide1 emphasizes the advantage of tungstic acid catalysis2 in the hydrogen peroxide oxidation of sulfides to sulfones an induction period is eliminated and the yield improved. 

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