Vanadium complexes sulfates

C° total concentration of pyrosulfate and sulfate anions Cv concentration of biatomic vanadium complexes C3l concentration of S03 in the melt phase Cp specific heat (kcal/kg °C)... 

For the vanadophore region, the sulfate concentration has been estimated to be of the order of 1.3 M and pH 2.349 With no evidence for a stable complex within the vanadocyte, Figure 14 depicts an interesting mechanism proposed for vanadium and sulfate accumulation.350 Anionic vanadium(V) (as HVO ") and sulfate ions enter the cell. Provided that within the vanadophore there is a strong reducing agent, vanadium can be reduced to vanadium(IV) and vanadium(III), cationic at the low pH in the vanadophore. If the vanadophore membrane is permeable to anions but not cations, the reduced vanadium remains trapped. 

Comparison of V(IV,V) hydroxamic acid complexes showed the V(V) complex induced a stronger insulin-enhancing effect than the V(IV) complex, and both complexes were better than either of the salts, vanadyl sulfate or sodium vanadate, in relieving the symptoms of mice with STZ-induced diabetes. The distribution of vanadium in tissues was the same irrespective of the complex administered however, the tissue distribution of vanadium when the salts were administered was different from that seen after vanadium complex administration [146], These results suggest that the difference in the antidiabetic activity of the hydroxaminic acid V complexes is related to the different oxidation state, although there was no difference in the final tissue distribution of these complexes. 

Ioffe and Sherman (149) studied the kinetics of naphthalene oxidation to phthalic anhydride on a more complex vanadium-potassium-sulfate catalyst over a wide range of conversions and temperatures. The naphthalene oxidation was found to be independent of naphthalene concentration. This reaction is first order with respect to oxygen concentration and is inhibited with reaction products. 

The first supported molten salt catalyst systems date from 1914, where BASF filed a patent on a silica-supported V20s-alkali pyrosul te sulfur dioxide oxidation catalyst [48], which even today - as a slightly modified catalyst system - is still the preferred catalyst for sulfuric acid production [49]. However, it took many years to realize in the 1940s [50,51], that the catalyst system actually was a molten salt SLP-type system which is best described by a mixture of vanadium alkah sulfate/hydrogensulfate/pyrosulfate complexes at reaction conditions in the temperature range 400-600 °C with the vanadium complexes playing a key role in the catalytic reaction [49]. 

The 1,2-addition of a cyanide ion to a carbonyl compound to form a cyanohydrin is a fundamental carbon-carbon bond-forming reaction in organic chemistry, and has frequently been at the forefront of advances in chemical transformations. In 2000, Belokon and North developed a catalytic system based on a vanadium-salen complex (Scheme 9.1). The synthesis of vanadium(iv) complex 1 was accomplished by refluxing a mixture of the corresponding Schiff base with vanadium(iv) sulfate and pyridine in ethanol under an argon atmosphere. A very low catalyst loading of 0.1 mol% was employed to convert aromatic and aliphatic aldehydes to cyanohydrin silyl ethers 3 with enantioselectivities of 68-95% after 24 h. Further investigations... 

One possible way to achieve a uniform surface is by coating the solid support material with a thin liquid film, thereby defining the material properties by the liquid s properties. Such supported liquid phase (SLP) materials date back a 100 years ago till 1914, when BASF introduced a silica-supported V205-alkah/pyrosulfate SO2 oxidation catalyst for sulfuric acid production (see Figure 1.1) [3]. This catalyst, which is stiU the standard system for sulfuric acid production today, can be described as a supported molten salt, as it consists of a mixture of vanadium alkali sulfate/hydrogensulfate/pyrosulfate complexes that are present under reaction conditions (400-600 °C) [4],... 

V2O5 Oxides. - Supported V2O5 oxides are extremely important industrial catalysts for environmental pollution control, and are used in catalytic scrubbers for SO2 oxidation and NO reduction. During the operation of the catalyst (usually at 400-600 °C) in the SO2 oxidation reactions, pyrosulfate melts are formed in the pores of the catalysts, and V2O5 can dissolve in these melts forming vanadium oxo-sulfate complexes ... 

Vanadium Sulfates. Sulfate solutions derived from sulfuric acid leaching of vanadium ores are industrially important in the recovery of vanadium from its raw materials. Vanadium in quadrivalent form may be solvent-extracted from leach solutions as the oxycation complex (VO) ". Alternatively, the vanadium can be oxidized to the pentavalent form and solvent-extracted as an oxyanion, eg, (V O ) . Pentavalent vanadium does not form simple sulfate salts. 

The ascidians or tunicates (sea squirts) accumulate vanadium from seawater (about 5x 10-8 mol dm-3) to a level of about 1 mol dm-3 and store it in a dilute solution of sulfuric acid (pH<2) in blood cells called vanadocytes. The tunicates thus concentrate vanadium several million-fold. 079 NMR, ESR and EXAFS determinations on whole vanadocyte cells of Ascidia ceratodes and Ascidia nigra indicate that the vanadium is present mainly as aquated V111 probably complexed with sulfate. Some vanadyl ion (5-10%) is also present.1080 1081... 

Unlike V(II), both the V(III) and V(IV) oxidation states are stable in water. However, neither the V(III) nor the V(IV) oxidation states are easily maintained in the presence of oxygen if the pH is neutral or above, although, under acidic conditions, both these states are rather easily maintained. Somewhat surprisingly, the V(IV) species is more readily oxidized by 02 than is the V(III) species. In aqueous acidic solution, the vanadium(III) ion exists as a hexaqua octahedral complex that can deprotonate to form the 2+ and 1+ species, dependent on pH. Additionally, di, tri and tetra polymeric forms are known. Structures have been proposed and their formation constants determined [10], The occurrence of the various polymeric forms in the presence of sulfate has also been described and is particularly relevant to concentration of vanadium by bioaccumulators [10],... 

Complexes of the first two ligands are prepared by reaction of vanadyl sulfate with the ligand, preformed in situ in aqueous ethanol (38). Isolated as the vanadium(IV) complexes, they can be oxidized in aerobic methanol and reisolated as the methoxymethanol vanadium(V) derivatives (39). Alternatively, the reduced complexes can be dissolved in DMF and allowed to oxidize aerobically before use. Their reactivity parallels that of (HPS)VO(OEt)(EtOH). They have reaction rates for catalyzing bromide oxidation comparable to (HPS)VO(OH) (Table I). Interestingly, the rates of these reactions are quite sensitive to the amount of water. The increase from 0.5% to 1.0% added water causes a 10-20% decrease in rate. 

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