Acids molybdenum

In this process, catalysts, such as boric acid, molybdenum oxide, zirconium, and titanium tetrachloride or ammonium molybdate, are used to accelerate the reaction. The synthesis is either carried out in a solvent (aUphatic hydrocarbon, trichlorobenzene, quinoline, pyridine, glycols, or alcohols) at approximately 200°C or without a solvent at 300°C (51,52). 

Acids Molybdenum exhibits good resistance to hydrochloric, hydrofluoric, phosphoric and sulphuric acids (see Figs. 5.2, 5.3 and 5.4). In static tests in these acids at Ohio State University it was found that the corrosion rate for relatively long test periods (670 h) was about ten times that experienced in 47 h tests. 

In a method described by Kiriyama and Kuroda [500], molybdenum is sorbed strongly on Amberlite CG 400 (Cl form) at pH 3 from seawater containing ascorbic acid, and is easily eluted with 6 M nitric acid. Molybdenum in the effluent can be determined spectrophotometrically with potassium thiocyanate and stannous chloride. The combined method allows selective and sensitive determination of traces of molybdenum in seawater. The precision of the method is 2% at a molybdenum level of 10 xg/l. To evaluate the feasibility of this method, Kiriyama and Kuroda [500] spiked a known amount of molybdenum and analysed it by this procedure. The recoveries for 4 to 8 xg molybdenum added to 500 or 1000 ml samples were between 90 and 100%. 

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. 

The arsine analogues of this series, [MoX2(diars)2] (X = Cl, Br, I) have been obtained by the anaerobic reaction of acid molybdenum(III) halide solutions with diars in water and/or alcohol. They are paramagnetic (p.es 2.8-2.9BM), with a possible d-d UV band at 11000 cm-1 in [MoCl2(diars)2].74... 

In the case of solid or liquid solutions it is frequently observed that one component of the solution is present at a greater concentration in the surface region than in the bulk of the solution. Thus, for an ethanol-water system, die surface region will contain an excess of ethanol. The concentration of water will be higher at the surface than in the bulk, if the solute is sulfuric acid. Molybdenum oxide dissolved in glass will concentrate at the surface of the glass. The concentrating of solute molecules at a surface is called adsorption. 

Syntheses of MPc from phthalodinitrile or phthalic anhydride in the presence of urea are the two most important laboratory and industrial methods. They were also used originally by Linstead et al. [8,9], This procedure allows the production of many phthalocyanine compounds [35-37], Catalysts such as boric acid, molybdenum oxide, zirconium and titanium tetrachloride, or ammonium molybdate are used to accelerate the reaction and improve the yield [36,37], Ammonium molybdate is especially effective. Reaction is carried out either in a solvent or by heating the solid components. When metal chlorides and phthalodinitrile are used as starting materials, the reaction products are partially chlorinated (e.g.,7). 

In general molybdenum disulphide is chemically very inert. It is resistant to attack by most acids, except aqua regia and hot concentrated sulphuric, nitric and possibly hydrochloric acids. Whereas most metals form salts when attacked by acids, molybdenum has no such tendency, and the product of acid attack is normally molybdenum trioxide. The same appears to be true of the disulphide, and the limited attack by acids can be considered more as a form of oxidation. There is considerable variation in the resistance of different samples to acid attack, and the reactions involved may therefore be primarily those of contaminants rather than of the molybdenum disulphide itself. 

Kocovsky, P., Ahmed, G., SrogI, J., Maikov, A. V., Steele, J. New Lewis-Acidic Molybdenum(ll) and Tungsten(ll) Catalysts for Intramolecular Carbonyl Ene and Prins Reactions. Reversal of the Stereoselectivity of Cyclization of Citronellal. J. Org. Chem. 1999, 64, 2765-2775. 

Ammonium oxymolybdenum complexes with amines These complexes are prepared by the acid/base reaction of an acidic molybdenum source such as molybdenum trioxide, molybdic acid, ammonium molybdate [41] and ammonium thiomolybdates with oil-soluble amines [42], The preferred aminic compounds are lubricant additives known as dispersants, examples being succinimides and Mannich-type bases, as in Reactions (4.42) and (4.43) [41] ... 

The preparation typically involves a condensation reaction of acidic molybdenum sources such as molybdenum trioxide, molybdic acid and ammonium molybdate with dialkylammonium dialkyldithiocarbamate salts formed in situ by reaction of carbon disulphide and dialkylamine [45]. The extent of sulphurisation of the molybdenum core can be increased by the introduction of sulphurising agents such as sodiumhydrosulphide [46]. Patent literature reports that the greatest antioxidant effect of molybdenum dialkyldithiocarbamates is seen when combined with aminic and phenolic antioxidants [47]. 

Epoxidation m-Chloroperbenzoic acid. Molybdenum hexacarbonyl. Peracetic acid. Sodium perborate. 

Reduction of MO3 (M = Mo, W) by H2 yields M0O2 and WO2 which adopt rutile structures Figure 5.21), distorted (as in Nb02) by pairing of metal centres in M0O2, Mo—Mo distances are 251 and 311pm. The oxides do not dissolve in non-oxidizing acids. Molybdenum(IV) sulfide (equation 22.28) has a layer structure and is used as a lubricant (see Box 22.5). 

Various other catalysts such as sulfuric acid, molybdenum oxide, etc., also have been investigated for the isomerization of alkanes. The isomerization in the presence of the oxide catalysts proceeds usually at high temperatures and in the presence of hydrogen. These catalysts have no significant importance. Sulfuric acid is not a general isomerization catalyst it was successfully used in only a few isolated cases such as in the isomerization of 2-methylpentane to 3-methylpentane. 

Boric acid Molybdenum pentachloride Potassium fluoborate Trimethyl borate brazing flux, gaseous Tri methyl borate bread improver mfg. 

Hexacarbonylmolybdenum was synthesized in low yields by L. Mond by the reaction of pyrophoric molybdenum with carbon monoxide. Presently, it is prepared by carbonylation of M0CI5, molybdic acid, molybdenum sulfide, and other molybdenum compounds. The following reducing agents may be employed Mg, Al, Na, Zn, Fe, Grignard reagents, aluminum organometallic compounds, etc. Sometimes such syntheses involve dry methods whereby no solvent is used. However, most commonly. 

Reactions.—Desulphurization of thiirans to alkenes remains an important strategy for the preparation of hindered alkenes, e.g. (14), and is the most typical thiiran reaction. Phosphines and phosphites are the reagents that are most often used. Lithium reagents desulphurize rra s-2,3-diphenylthiiran to ( )-stilbene, while the ds-isomer is converted into a 1 1 mixture of (Z)-stilbene and the two isomers of tr-mercaptostilbene. 2-Phenylthiiran is desulphurized by cf-metallated isocyanides. Thermal extrusions of sulphur include the conversion of (15) into (16), amongst others. Desulphurizations using zinc and acetic acid, molybdenum or palladium complexes, and the oxaziridine (17) have been reported. 

A yellow precipitate of thallium phosphomolybdate is formed by the interaction of thallous salts and phosphomolybdic acid. When this precipitate is treated with concentrated hydrobromic acid, molybdenum blue and thal-lium bromide are formed. 

For the best conversion of lactic acid into AA, Katryniok et al. (2010) used silica-supported heteropolyacids (HPAs) as catalysts at 275°C in a fixed-bed gas phase reactor. More improvement of lactic acid (91%) conversion was observed when using the highly acidic silicotungstic acid. The proposed mechanism for conversion was decarbonylation/dehydration. However, by using less acidic molybdenum-based HPAs, propanoic acid was the dominant product, pointing to a more pronoxmced decarboxylation pathway producing H2 (and CO2). The resulting H2 can be used in situ to reduce lactic acid to propanoic acid (Katryniok et al., 2010). 

Fused salt solutions may be found in which the solubility of these oxides is appreciable at high temperatures and from which crystals grow as the solution is cooled. Some of the fluxes which have been used for growth of the oxides of concern here are (a) potassium nitrate-sodium nitrate, (b) lead fluoride-bismuth oxide, (c) lead oxide-bismuth oxide, and (d) lithium hydroxide-boric acid-molybdenum oxide. Temperatures frequently are in the range of 1300°C. 

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