Molybdic acid anhydride

Synonyms molybdenum trioxide molybdic acid anhydride molybdic anhydride molybdic oxide... 

Molybdenum Trioxide (Molybdenum Anhydride, Molybdic Oxide, Molybdic Acid Anhydride). M0O3, mw 143.95, white powd, mp 795°, bp 1155°, d 4.696g/cc at 26/4°. SI sol in w, sol in acids, alk sulfates and amm hydroxide. Prepn is by first boiling coned nitric acid with NH4... 

Molybdic acid anhydride Molybdic anhydride Molybdic oxide Molybdic trioxide Natural molybdite NSC 216191. Source of Mo reagent for analytical chemistry agriculture manufacture of metallic molybdenum corrosion inhibitor ceramic glazes enamels pigments catalyst. Yellow-blue powder mp = 795° bp = 1155° 4.696 soluble in H2O (0.49 g/l), insoluble in organic solvents LDso (rat orl) = 2689 mg/kg, AAA Molybdenum Atomergic Chemetals Cerac Climax Molybdenum Co. 

Synonyms Molybdenum anhydride Molybdic acid anhydride Molybdic acid anhydrous Molybdic acid hydride Molybdic oxide Molybdic trioxide... 

Molybdic acid anhydride Molybdic acid anhydrous. See Molybdenum trioxide Molybdic acid, calcium salt (1 1). See Calcium molybdate... 

Recently, a direct synthesis of substituted isoindolinediimines starting from substituted derivatives of phthalic anhydride was reported. The respective derivative of phthalic anhydride was treated with urea and ammonium nitrate in the presence of molybdic acid to give the respective isoindolinediimine.123... 

Modification of the metal itself, by alloying for corrosion resistance, or substitution of a more corrosion-resistant metal, is often worth the increased capital cost. Titanium has excellent corrosion resistance, even when not alloyed, because of its tough natural oxide film, but it is presently rather expensive for routine use (e.g., in chemical process equipment), unless the increased capital cost is a secondary consideration. Iron is almost twice as dense as titanium, which may influence the choice of metal on structural grounds, but it can be alloyed with 11% or more chromium for corrosion resistance (stainless steels, Section 16.8) or, for resistance to acid attack, with an element such as silicon or molybdenum that will give a film of an acidic oxide (SiC>2 and M0O3, the anhydrides of silicic and molybdic acids) on the metal surface. Silicon, however, tends to make steel brittle. Nevertheless, the proprietary alloys Duriron (14.5% Si, 0.95% C) and Durichlor (14.5% Si, 3% Mo) are very serviceable for chemical engineering operations involving acids. Molybdenum also confers special acid and chloride resistant properties on type 316 stainless steel. Metals that rely on oxide films for corrosion resistance should, of course, be used only in Eh conditions under which passivity can be maintained. 

Deeper oxidation products like furan and, particularly, maleic acid anhydride, can be produced by catalysts that have a stronger oxidative power than the above type-(a) catalysts, but, at the same time, have retained the capacity to transfer oxygen selectively to the organic molecule (a capacity which is absent in the type-(b) catalysts). Besides, a more acidic character of the catalyst surface is probably required to produce an acidic product like maleic anhydride effectively. The most interesting catalysts of this group are V2Os-based catalysts and certain molybdates and Mo03-based catalysts. 

Molybdenum trioxide is a white solid at room temperature but becomes yellow when hot and melts at 795°C to a deep yellow liquid. It is the anhydride of molybdic acid, but it does not form hydrates directly, although these are known (see later). One of its two polymorphs, the stable a-form, has a rare type of layer structure in which each molybdenum atom is surrounded by a distorted octahedron of oxygen atoms. 

A pathway into this area arose in a study of the catalytic activity of molybdated zirconia (M03/Zr02) for the benzoylation of toluene with benzoic anhydride [72]. The catalysts were prepared by addition of different amounts of molybdic acid (H2M0O4) to zirconia gel and calcination at various temperatures. The activities are shown as a funchon of calcination temperature of the catalysts in Figure 17.8 [218]. The figure shows that the effect of modifying the proportion of Mo in the... 

Chlormolybdic" Acids.—The compound MoOCl2(OH)2, molybdenum hydroxychloride or dichlormolybdic add, is readily obtained by passing hydrogen chloride over any heated oxygenated compound of molybdenum. Fine white unstable needles are obtained, the aqueous solution of which deposits on evaporation amorphous molybdic anhydride. The substance is also soluble in ether, with which it forms a crystalline compound. An alternative method of preparation of dichlormolybdic acid consists in cooling a solution of molybdic acid saturated with hydrochloric acid. ... 

Forsmi describes a crystalline compound of composition H MogO, which he regards as an anhydride of the fundamental hexabasic molybdic acid HgMogOia (see p. 187). 

Molybdenum oxide catalysts are prepared by heating the ammonium molybdate or by depositing molybdic acid on inert supports. The oxide prepared from the ammonium salt is somewhat dark colored due to a certaiu amount of reduction caused by the hot ammonia. However, the degree of activity of this material as a catalyst is apparently independent of the method of preparation, degree of oxidation, or supporting material. Yields of only about SO to 60 per cent of theoretical as phthalic anhydride are obtainable with this catalyst. Molybdenum oxides have the added... 

Synthesis of phthalocyanine-2,9,16,23-tetracarboxylic acid cobalt(II) complex 48 (R = -COOH M = Co(II)) 0.26 g (2 mmol) water-free cobalt chloride, 1.54 g (8 mmol) 1,2,4-benzenetricarboxylic acid anhydride, 4.8 g (80 mmol) urea and around 20 mg ammonium molybdate are intensively mixed and heated under inert gas in a 100-mL glass vessel at 270 °C for 1 h. The blue-colored reaction mixture was pulverized, stirred in 400 mL 6 M aqueous HCl, filtered, intensively washed with 6 M HCl and then water and acetone. The product was treated in a Soxhlet apparatus with acetone and dried. The phthalocyanine tetracarboxylic acid amide obtained was saponified to the tetracarboxylic acid as follows. 1 g of the tetracarboxylic acid amide was heated in a mixture of 6 g KCl and 15 mL 2 M aqueous KOH at 90 °C until the ammonia evolution became weak. The filtered product was dissolved in a fairly small amount of 2 M NaOH and after filtration from byproducts separated with 2 M HCl and isolated by centrifugation. Purification was achieved by dissolving in 0.05 M NaOH, separation with 2 M HCl and centrifugation until the filtrate is free of chloride ions. Yield from 1 g tetracarboxylic acid amide 0.56 g (38%). IR (KBr) 1698, 1373, 1326, 1150, 1091, 743 cm . 

Oxidation. Maleic and fumaric acids are oxidized in aqueous solution by ozone [10028-15-6] (qv) (85). Products of the reaction include glyoxyhc acid [298-12-4], oxalic acid [144-62-7], and formic acid [64-18-6], Catalytic oxidation of aqueous maleic acid occurs with hydrogen peroxide [7722-84-1] in the presence of sodium tungstate(VI) [13472-45-2] (86) and sodium molybdate(VI) [7631-95-0] (87). Both catalyst systems avoid formation of tartaric acid [133-37-9] and produce i j -epoxysuccinic acid [16533-72-5] at pH values above 5. The reaction of maleic anhydride and hydrogen peroxide in an inert solvent (methylene chloride [75-09-2]) gives permaleic acid [4565-24-6], HOOC—CH=CH—CO H (88) which is useful in Baeyer-ViUiger reactions. Both maleate and fumarate [142-42-7] are hydroxylated to tartaric acid using an osmium tetroxide [20816-12-0]/io 2LX.e [15454-31 -6] catalyst system (89). 

Molybdic and Tungstic Anhydrides. Place several ammonium molybdate crystals onto the lid of a crucible and first heat them carefully, and then roast them strongly. What occurs Perform a similar experiment with ammonium tungstate or tungstic acid. Write the equations of the reactions. At what temperature do molybdic and tungstic anhydrides sublime ... 

Preparation of Potassium Hexachloromolybdate(III). Perform the experiment in a fume cupboard ) Dissolve 50 g of molybdic anhydride in 250 ml of concentrated hydrochloric acid. Spill the molyb-denum(Vl) oxide into the beaker in small portions as it dissolves during 6 hours. If the solution is turbid, filter it through a glass filter (prepare the solution beforehand). 

Phosphoric Acid. —Dissolve 10 gm. of molybdic anhydride in 25 cc. of water and 15 cc. of ammonia water (sp. gr. 0.91). The solution, mixed with 150 cc. of nitric acid, and allowed to stand for two hours at a temperature of about 40° C., must not contain a yellow precipitate. 

Nitric Acid. — Shake 1 gm. of molybdic anhydride with 10 cc. of water, and add a small crystal of sodium chloride, followed by one drop of a 1 1000 solution of indigo the blue color of the solution must not disappear on adding 10 cc. of concentrated sulphuric acid. 

Quantitative Determination. — The content of molybdic anhydride may be approximately determined by gently igniting about 1 gm. of the salt until the ammoniacal odor has disappeared, and then weighing the residue of inolybdic anhydride it should amount to about 81 per cent. The accurate determination is carried out in the manner described under Acid Molybdic Anhydride, on page 19. 

Heterogeneous oxidative processes operate at high temperatures (250-450 6C) and are useful for the synthesis of acrolein and acrylic acid from propylene over bismuth molybdate catalysts, the synthesis of maleic and phthalic anhydrides from the oxidation of benzene (or C4 compounds) and naphthalene (or o-xylene) respectively over vanadium oxide,101 arid the synthesis of ethylene oxide from ethylene over silver catalysts.102... 

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