Blue oxide

Reduction to Metal Powder. The metal powder is obtained from APT by stepwise reduction with carbon or hydrogen. The intermediate products are the yeUow oxide, WO blue oxide, (see Tungsten compounds) and brown oxide, WO2. Because carbon introduces impurities,... 

For the production of lamp-filament wire, aluminum, potassium, and siHcon dopants are added to the blue oxide. Some dopants are trapped in the tungsten particles upon reduction. Excess dopants are then removed by washing the powder in hydroflouric acid. Eor welding electrodes and some other appHcations, thorium nitrate is added to the blue oxide. After reduction, the thorium is present as a finely dispersed thorium oxide. 

Tungsten pentachlofide [13470-13-8], WCl, mp 243°C, bp 275.6°C, is a black, crystalline, deHquescent soHd. It is only slightly soluble in carbon disulfide and decomposes in water to the blue oxide, 200 2. Magnetic properties suggest that tungsten pentachlofide may contain trinuclear clusters in the soHd state, but this stmcture has not been defined. Tungsten pentachlofide may be prepared by the reduction of the hexachloride with red phosphoms (9). 

Tungsten dioxide [12036-22-5] WO2, is a brown powder formed by the reduction of WO3 with hydrogen at 575—600°C. Generally, this oxide is obtained as an intermediate in the hydrogen reduction of the trioxide to the metal. On reduction, first a blue oxide, then a brown oxide (WO2), is formed. The composition of the blue oxide was in doubt for a long time. However, it has since been resolved that W2Q03g and W are formed as intermediates, which may also be prepared by the reaction of tungsten with WO3. 

Fig. 8.6 Absorption spectra of slightly autoxidized dinoflagellate luciferin in 50% ethanol (A), and the blue oxidation product in methanol (B). From Dunlap et al., 1981, with permission from the Federation of the European Biochemical Societies.

The luciferin produces a blue oxidation product during its purification process. In the DEAE chromatography of luciferin, this blue compound is eluted before the fractions of luciferin. The fractions of the blue compound were combined and purified by HPLC on a column of Hamilton PRP-1 (7 x 300 mm) using methanol-water (8 2) containing 0.1% ammonium acetate. The purified blue compound showed absorption peaks at 234, 254, 315, 370, 410, 590 (shoulder) and 633 nm. High-resolution FAB mass spectrometry of this compound indicated a molecular formula of C l C Nai m/z 609.2672 (M - Na + 2H)+, and mlz 631.2524 (M + H)+]. These data, together with the HNMR spectral data, indicated the structure of the blue compound to be 8. 

Fig. 8.8 The chemical structures of dinoflagellate luciferin (5), the product of luminescence reaction catalyzed by luciferase (6), air-oxidation product formed at — 20°C (7), and the blue oxidation product (8). Note structural resemblance between these compounds and chlorophylls.

The catalysis by Mo(VI) of the oxidation of N2H5 to N2 by methylene blue depends on the steps given above, Mo(VI) being regenerated by methylene blue oxidation of the Mo(V) dimer . The latter reaction was studied independently and... 

Photosensitized oxidation offurans.3 The endoperoxide (2) formed in photosensitized (methylene blue) oxidation of 3-substituted or 3,4-disubstituted furans in acetone at -40° rearranges at 20° to 4-hydroxy-2-butenolides in 30-97% yield. Example ... 

In addition to the tungsten(II) bonde mentioned above, the element forms at least two other borides, W2B and WB2 it forms a similar series of phosphides, W2P, WP, and WP2 as well as W02 (brown oxide), W4On (blue oxide), and WO3 (yellow oxide), and two sulfides, WS2 and WS3. The tungsleu(IV) oxide and sulfide are representative uf the simple Lelravalent compounds, which also include a tetrabromide, WBr4, and tetraiodide, WI4. Like lire drhalides, these tetiahalides undergo hydrolysis quite readily. 

Ammonium paratungstate is recovered from the strip solution by evaporative crystallization, dried and calcined to produce blue oxide 208... 

Sabatier and Maihle have stndied the catalytic action of various metallic oxides upon the vapours of certain organic compounds. They find that alcohols are oxidised to aldehydes by manganous oxide and that they are dehydrated by alumina, thoria or the blue oxide of tungsten, with the formation of olefines and ethers. Those changes are explained in the case of thoria by the following equations ... 

Tungstic oxide at 350° is reduced to a blue oxide which has a dehydrating effect and ethylene results as well as aldehyde and acetic acid. 

The sensitivity can be increased by treating the resultant precipitate with an acetic acid solution of benzidine whereupon the manganese dioxide oxidizes the benzidine to a blue oxidation product. (DANGER THE REAGENT IS CARCINOGENIC). 

Benzidine acetate test (DANGER THE REAGENT IS CARCINOGENIC) A neutral or weakly acetic acid solution of a peroxodisulphate converts benzidine into a blue oxidation product. Perborates, percarbonates, and hydrogen peroxide do not react. Chromates, hexacyanoferrate(III) ions, permanganates, and hypohalites react similarly to peroxodisulphates. 

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. 

The dark blue oxide V02 is obtained by mild reduction of V205, a classic method being by fusion with oxalic acid it is amphoteric, being about equally readily soluble in both noncomplexing acids, to give the blue ion [V0(H20)5]2+, and in base. It has a distorted rutile structure one bond (the V=0) is much shorter than the others in the V06 unit (note that the Ti—O distances in Ti02 are essentially equal). 

Mixed oxide-hydroxide materials, called blue oxides, are obtained by reduction of acidified solutions of molybdates or tungstates (or suspensions of M03) with Sn11, S02, and so on. Because they are noncrystalline, the structures are not known and the cause of the color is uncertain, but speculation abounds.1... 

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