Molybdates reactions

Schieffer, G. W., Preliminary examination of a new post-column photolysis-molybdate reaction detection system for the determination of organophos-phorus compounds by high performance liquid chromatography, Instr. Sci. Technol., 23, 255, 1995. 

The Bilik molybdate reaction has been used to prepare labelled carbohydrates. Thus D-[U- C]glucose from acid hydrolysis of the 0(-[U- Cjglucan of the alga Chlorella sp grown in 2 converted to D-[U- Cjmannose. D-[U- OErythrose,-threose,... 

Thilo. Wieker, and Stade (68a) standardized the molybdate reaction with silicate species and calculated the characteristic reaction rate constants ... 

A solution of SiO2 Naj0 ratio of 2 1 was shown to depolymerize with increasing dilution. Thus in a solution 1.0 M in SiOz, the molybdate reaction curve was very similar to that of cyclic tetramer. However, upon dilution to 0.1 M it acted like dimer and at 0.01 M had hydrolyzed to monomer. 

In 5 min, 40% of the silica had polymerized to dimer. By chromatography it was shown that after I hr, perhaps 40% of the monomer and dimer had polymerized to form cyclotetrasilicic acid as well as some he.xameric silicic acid and higher polymeric acid. After 4 hr, about 50% of the polymers up to tetramer were converted to cyclopolysilicic acids with an average molybdate reaction rate constant of 0.103 min. ... 

Sol Age (days) Molybdate Reaction Constant, H.w(min" ) Mol. Wt. Reported Corresponding Degree of Polymerization, n Observed Calculated X (from n)... 

From the molybdate reaction constant. However, molecular weight was much higher. 

As Stated earlier the most probable mechanism for Ni and Mo codeposition is the one reported by Podlaha and Landolt [117-120] after X-ray fluorescence analysis of the electrodeposited alloy. Their investigations were performed under controlled mass transport conditions (rotating cylinder electrode). The model assumes that the Ni electrodeposition occurs on the surface not covered by the molybdate ions as a reaction intermediate, by direct reduction of nickel species (all of them being complex of Ni " cations with the citrate anions), independently on the molybdate reaction which can occur only in the presence of nickel species [117-120], The model of the Mo-Ni alloy electrodeposition is described by the following reduction reactions ... 

The simplest method to avoid the interference of molybdates is to form the complex molybdenum oxahc acid Ha[MoOs(C204)]. The molybdate concentration is so reduced that neither the diphenylcarbazide, nor any other sensitive molybdate reaction takes place. The oxalic acid (1 drop of saturated solution) must be added to the test solution before the addition of diphenylcarbazide. Otherwise, the molybdic acid is partly reduced by reaction with diphenylcarbazide, forming molybdenum blue which is stable toward oxalic acid. This procedure will reveal 0.5 y CrOs in the presence of 20 mg MoOa. 

Patents claiming specific catalysts and processes for thek use in each of the two reactions have been assigned to Japan Catalytic (45,47—49), Sohio (50), Toyo Soda (51), Rohm and Haas (52), Sumitomo (53), BASF (54), Mitsubishi Petrochemical (56,57), Celanese (55), and others. The catalysts used for these reactions remain based on bismuth molybdate for the first stage and molybdenum vanadium oxides for the second stage, but improvements in minor component composition and catalyst preparation have resulted in yields that can reach the 85—90% range and lifetimes of several years under optimum conditions. Since plants operate under more productive conditions than those optimum for yield and life, the economically most attractive yields and productive lifetimes maybe somewhat lower. 

Molybdenum trioxide is a condensed-phase flame retardant (26). Its decomposition products ate nonvolatile and tend to increase chat yields. Two parts of molybdic oxide added to flexible poly(vinyl chloride) that contains 30 parts of plasticizer have been shown to increase the chat yield from 9.9 to 23.5%. Ninety percent of the molybdenum was recovered from the chat after the sample was burned. A reaction between the flame retardant and the chlorine to form M0O2 012 H20, a nonvolatile compound, was assumed. This compound was assumed to promote chat formation (26,27). 

The total phosphoms content of the sample is determined by method AOCS Ja 5-55. Analysis of phosphoUpid in lecithin concentrates (AOCS Ja 7-86) is performed by fractionation with two-dimensional thin-layer chromatography (tic) followed by acid digestion and reaction with molybdate to measure total phosphorous for each fraction at 310 nm. It is a semiquantitative method for PC, PE, PI, PA, LPC, and LPE. Method AOCS Ja 7b-91 is for the direct deterrnination of single phosphoHpids PE, PA, PI, PC in lecithin by high performance Hquid chromatography (hplc). The method is appHcable to oil-containing lecithins, deoiled lecithins, lecithin fractions, but not appHcable to lyso-PC and lyso-PE. 

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). 

Technical molybdic oxide can be reduced by reaction of ferrosiUcon in a thermite-type reaction. The resulting product contains about 60% molybdenum and 40% iron. Foundries generally use ferromolybdenum for adding molybdenum to cast iron and steel, and steel mills may prefer ferromolybdenum to technical molybdic oxide for some types of steels. 

The tris (dithiolene) complexes of Mo can be formed by reaction of the corresponding dithiol and molybdate in acid solution. The intense green... 

The dinuclear ion Mo2(S2) g (F - prepared from the reaction of molybdate and polysulfide solution (13) is a usehil starting material for the preparation of dinuclear sulfur complexes. These disulfide ligands are reactive toward replacement or reduction to give complexes containing the Mo2S " 4 core (Fig. 3f). 

Oxidation Catalysis. The multiple oxidation states available in molybdenum oxide species make these exceUent catalysts in oxidation reactions. The oxidation of methanol (qv) to formaldehyde (qv) is generally carried out commercially on mixed ferric molybdate—molybdenum trioxide catalysts. The oxidation of propylene (qv) to acrolein (77) and the ammoxidation of propylene to acrylonitrile (qv) (78) are each carried out over bismuth—molybdenum oxide catalyst systems. The latter (Sohio) process produces in excess of 3.6 x 10 t/yr of acrylonitrile, which finds use in the production of fibers (qv), elastomers (qv), and water-soluble polymers. 

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). 

Hydrogen sulfide has been produced in commercial quantities by the direct combination of the elements. The reaction of hydrogen and sulfur vapor proceeds at ca 500°C in the presence of a catalyst, eg, bauxite, an aluminosihcate, or cobalt molybdate. This process yields hydrogen sulfide that is of good purity and is suitable for preparation of sodium sulfide and sodium hydrosulfide (see Sodium compounds). Most hydrogen sulfide used commercially is either a by-product or is obtained from sour natural gas. 

When the Claus reaction is carried out in aqueous solution, the chemistry is complex and involves polythionic acid intermediates (105,211). A modification of the Claus process (by Shell) uses hydrogen or a mixture of hydrogen and carbon monoxide to reduce sulfur dioxide, carbonyl sulfide, carbon disulfide, and sulfur mixtures that occur in Claus process off-gases to hydrogen sulfide over a cobalt molybdate catalyst at ca 300°C (230). 

Reduction of sulfur dioxide by methane is the basis of an Allied process for converting by-product sulfur dioxide to sulfur (232). The reaction is carried out in the gas phase over a catalyst. Reduction of sulfur dioxide to sulfur by carbon in the form of coal has been developed as the Resox process (233). The reduction, which is conducted at 550—800°C, appears to be promoted by the simultaneous reaction of the coal with steam. The reduction of sulfur dioxide by carbon monoxide tends to give carbonyl sulfide [463-58-1] rather than sulfur over cobalt molybdate, but special catalysts, eg, lanthanum titanate, have the abiUty to direct the reaction toward producing sulfur (234). 

Catalysts. In industrial practice the composition of catalysts are usuaUy very complex. Tellurium is used in catalysts as a promoter or stmctural component (84). The catalysts are used to promote such diverse reactions as oxidation, ammoxidation, hydrogenation, dehydrogenation, halogenation, dehalogenation, and phenol condensation (85—87). Tellurium is added as a passivation promoter to nickel, iron, and vanadium catalysts. A cerium teUurium molybdate catalyst has successfliUy been used in a commercial operation for the ammoxidation of propylene to acrylonitrile (88). 

---