Of molybdic acid

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... 

Co-extraction of Mo and Cu is potentially a problem with certain feed solutions,14 and again selectivities are very dependent on the nature of modifiers present in formulated reagents.142 The Mo species extracted have not been fully characterized, but may include a neutral dioxo complex, [Mo02L2], which can be assumed to have an N2022 donor set similar to that in the Cu11 complex, and molybdate complexes solvated by neutral phenolic oxime ligands such as [M0O4112 LI l].143 Formation of solvated forms of molybdic acid is supported by evidence that extraction is favorable at very low pH values and that the complexes are readily stripped by aqueous ammonia to produce ammonium molybdate,144... 

Normal isopoly- and peroxymolydates of ammonium and several metals are known. The normal or orthomolybdates may be considered as salts of molybdic acid having formulas H2Mo04 xH20 or M20 Mo03 xH20. They are either of monoclinic or scheelite type crystal structure and obtained as hydrated salts. 

Justus Christian Heinrich Heyer, in the account of his own researches on molybdenite, stated in 1787 that he had been unable to find from the literature how Hjelm had prepared the metal (75). Heyer repeated Scheele s synthesis of molybdenite by heating a mixture of molybdic acid and flowers of sulfur in a glass retort (75). In 1790, after both Scheele and Bergman had died, Hjelm wrote ... 

According to the reported results we assume that the interaction of molybdic acid with the surface acid groups occurs on the basis of an acid-base interaction accompanied by water elimination which leads to a structure such as... 

The preparation of silicomolybdic acid is based on a hydrolytic reaction similar to that used in the preparation of silicotungstic acid. (See synthesis 48.) Only a few modifications are necessary to avoid the precipitation or reduction of molybdic acid. 

One example will be given to show the influence of molybdic acid addition to fuller s earth, which was modified with minor amounts of MgO, ZnO, and Cr203. The experiments were made at 600 atm. pressure with bituminous-coal middle oil as feed. Figure 20 shows the splitting activ-... 

Fig. 20. Splitting rate with fuller s earth catalyst containing different amounts of molybdic acid. (Bituminous coal middle oil hydrogenated at 600 atm. pressure.)...

The ammonium salts of 12-heteropolymolybdate anions (usually insoluble in water) dissolve in solutions of H2O2. The oxidized silicon complex is less soluble than the phosphorus one, and the two anions may be separated by using this difference. The structures and formulas of the oxidized products are unknown. A peroxy heteropolymolybdate of composition (NH4)H2[PMo409(02)2] was isolated as a pale yellow solid from a solution of molybdic acid in 30% H2O2, addition of H3P04, and precipitation at pH 3-4 by 2-aminopyridine12 s ... 

The salts are strong reducing agents. If a solution of iron (III) chloride in hydrochloric acid is added to a solution of either of the salts, the molybdenum is oxidized, as is evidenced by a reversal of the color changes observed during the electrolytic reduction of molybdic acid. 

Procedure Dissolve 5 grams of M0O3 in 12 cc. of 6N NaOH. Barely neutralize with 6 N HNO3, using litmus as indicator. The neutral point must not be overstepped if a precipitate of molybdic acid is to be avoided. Dissolve 3.8 grams of anhydrous calcium chloride in 9 cc. of water and stir this into the sodium molybdate solution. Collect the precipitate, wash it with cold water, and dry it on the steam table (80-100°) over night. 

Molybdenum Oxides. Molybdenum oxide catalysts are prepared by the addition of hydrochloric acid to an ammoniacal solution of molybdic acid or ammonium molybdate. By heating to 400-500°C the molybdate is decomposed to the oxide.216 M0O3 is reduced to Mo02 in a stream of hydrogen at 300-400°C. 

Molybdenum forms compounds with oxidation numbers +2, +3, +4, +5, and + 6. Of these molybdates are the most important (with oxidation number +6). Molybdates are the salts of molybdic acid, H2Mo04. This acid tends to polymerize with the splitting off of molecules of water. Thus, the commercial... 

Dilute hydrochloric acid white or yellow precipitate of molybdic acid, H2Mo04, from concentrated solutions, soluble in excess mineral acid. 

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... 

Other Methods.—Electrolysis of a solution of molybdic acid in hydrochloric acid, using a mercury cathode, yields an amalgam, from which an active form of molybdenum is obtained on distillation. ... 

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. ... 

Molybdenum trioxide is an acidic oxide which dissolves in water yielding a solution of molybdic acids, and combines with basic oxides yielding molybdates. 

The solubility curve of the dihydrate cuts that of the monohydrate at 32° C. On heating, two distinct varieties of molybdic acid monohydrate are fonned on concentrating the solution of the dihydrate at 40° to 50° C., a-molyhdic acid monoJuidrate is formed as asbestos-like white needles, retaining their water of crystallisation much more readily than p-molybdic acid monohydrate, which is obtained as small white needles, soluble in water, but not regenerating the dihydrate, by heating the dihydrate to 70° C. White a-molybdic acid is readily obtained by treating methyl molybdate with water. The solubility in water of the monohydrate is as follows ... 

It is considered that the transformation of the various hydrates of molybdic acid into one another involves the formation of intermediate polymerides. 

A number of complexes of molybdic acid, particularly those -ith acetylacetone (Mo02[CH(COMe)2]2), with salicylaldehyde, and with organic acids, have been described, and a number of measurements made of rotatory power. ... 

Colloidal Molybdic Acid.—When solutions of sodium molybdate (1 molecule) and hydrochloric acid (4 molecules) are warmed together, or when a solution of molybdic acid dihydrate is evaporated over sulphuric acid under diminished pressure at 20° C., colloidal molybdic acid is formed. From the solution of the hydrosol so obtained, molybdic acid is precipitated by electrolytes. Graham considered that, by dialysis of a solution of sodium molybdate in hydrochloric acid, he obtained colloidal molybdic acid. ... 

A series of tetrabasic polymolybdates, containing up to seven molybdic groups, arise by the decomposition of the tridecamolybdates, and compounds containing more than thirteen molybdic groups are not known. The condensation of molybdic acid thus reaches its limit by the formation of tridecamolybdic acid. 

Calcium Trimolybdate, CaMogOxo-bHjO, is prepared by boding an aqueous suspension of calcium carbonate with excess of molybdic acid, and allowing the filtrate to evaporate. Silky needle-shaped crystals separate which dissolve readily in hot water. 

Molybdenum Sulphates.— Reduction of a solution of molybdic acid in sulphuric acid by means of hydrogen sulphide is stated to yield the compound M0O3.M0O0.2SO3 as a black substance, soluble in water to an unstable brown solution reduction with alcohol is said to yield soluble blue crystals of the sulphate 7MoO3.2MoO3.7SO3.aq. 

Other methods are similarly based on the reduction of molybdic acid for example, by means of zinc, magnesium, or sulphur dioxide, the resulting solution then being titrated with standard potassium per-... 

A white crystalline powder, prepared by hydrothermal treatment at 200°C of a mixture of molybdic acid, H2M0O4, and methylammonium ma) chloride, CH3NH3CI, taken in a 1 2 molar ratio and acidified with hydrochloric acid, HCl, to pH = 3.5, resulted in a complex powder diffraction pattern shown in Figure 6.29. It was indexed in the monoclinic crystal system as was discussed in section 5.12.2. The space group C2/c (or its acentric subgroup Cc) was established from the analysis of the systematic absences, and the unit cell dimensions were refined using 120 resolved reflections below 20 = 60° a = 23.0648(6) A, b = 5.5134(2) A, c = 19.5609(5) A, p = 122.931(1)°, and the sample displacement 8 = -0.098(3) mm for a 250 mm goniometer radius. The unit cell volume is 2087.8 A. ... 

Analytical System. The manifold schematic is illustrated in Fig. 2. An unmeasured aliquot is transferred to the sample cups. Samples are aspirated at a rate of 60 specimens/hour and added to an air-segmented stream of molybdic acid reagent followed by mixing. The stannous chloride reagent is then added to the reaction mixture. After mixing and a 3-4-minute time delay, the absorbance is measured at 660 mp., using a tubular flow cell with a 15-mm light path. 

Tin(II) chloride or oxalate, Fe(U) (Mohr s salt), ascorbic acid, sodium sulphite, and other reagents have been used as reductants [27,28]. To prevent partial reduction of molybdic acid, molybdosilicic acid is reduced in sufficiently acidic medium. Molybdosilicic acid is produced in a slightly acidic medium but, once formed, it does not decompose if the acidity is strongly increased (up to 1.5 M H2SO4). The most suitable acidity for the reduction depends on the reducing agent used. The various forms of molybdosilicic acid (a, P) and the various reductants yield products which differ in absorption spectra, absorption maxima, and stability [27]. 

Mnlybdic Acid, 85%, Consists largely of an ammonium molybdate. Contains 84-86% MoO,. It is the most widely used form of "molybdic acid . 

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