Reduction Of Vanadium Research Articles

Reactivity of α-Benzoin Oxime with Vanadium: Synthesis and Characterization of Vanadium Coordination Compounds and Polyoxovanadate Adducts

The reactivity of an ethanolic solution of α-benzoin oxime with an aqueous solution of vanadium in the V, IV or III oxidation states was investigated for different values of pH (2–4.5) and different values of the ligand/metal ratio. Under these experimental conditions, the reaction of α-benzoin oxime (H2L1) with vanadium(V) leads to the formation of various compounds: (1) A dimeric coordination complex of the formula [V2O4(H2L1)2(L2)2].3H2O in which L2 is C6H5(C˭O)(C˭NO′)C6H5, the deprotonated oxidized form of α-benzoin oxime. (2) An orange-yellow decavanadate adduct of the formula Na5[HV10O28(H2L1)2(HL2)2].6H2O. (3) A green mixed-valence decavanadate adduct of the formula Na6[H5V10O28(HL2)6]·10H2O. In all these compounds, ligand-metal redox reactions take place at room temperature which progressively lead to a reduction of vanadium(V) to vanadium(IV). Only one dimeric vanadium(IV) coordination compound of the formula [V2O4(HL2)4].0.5H2O was isolated. The reaction of a-benzoin oxime with vanadium(EI) leads to a dimeric coordination complex of vanadium(IV) of the formula [V2O4(H2O)2(L4)4] in which α-benzoin oxime was transformed to dibenzil (L4) after hydrolysis and oxidation. Under inert atmospher (nitrogen), α-benzoin oxime does not form any complex with vanadium(III). It was hydrolysed to benzoin (HL3), vanadium(III) being the catalyst of the reaction.

Specific S-nitrosothiol (thionitrite) quantification as solution nitrite after vanadium(III) reduction and ozone-chemiluminescent detection

Increasing evidence suggests that S-nitrosothiols (thionitrites) might represent naturally occurring nitric oxide surrogates and function as intermediates in nitrogen monoxide metabolism. A facile, sensitive, and selective micromethod has been developed and validated for quantification of S-nitrosothiols as their mercury-displaceable nitrogen monoxide content. In this method, brief (5-min), room-temperature pretreatment of S-nitrosothiol with a molar excess of aqueous mercuric chloride was used to liberate into solution, quantitatively, the nitrogen monoxide moiety, which rapidly and quantitatively converted to its stable solution end-product, nitrite. Solution nitrite was reduced back to nitric oxide with vanadium(III), and the nitric oxide was detected by gas-phase chemiluminescence after reaction with ozone in a commercial nitric oxide analyzer. A linear relationship was observed between S-nitrosothiol-bound nitrogen monoxide and ozone-chemiluminescent detector response over a wide range (16.3–3500 pmol) of nitric oxide, as generated by reaction of vanadium(III) with either nitrite standard or mercury-treated S-nitrosothiol. Assay response was quantitatively identical for equivalent amounts of nitrite and S-nitrosothiol-bound nitrogen monoxide. The method displayed 96% selectivity for nitrite vs. nitrate and negligible (<2%) interference by nitrosated compounds bearing nitrogen monoxide moieties bound to either nitrogen or carbon. The lower limits of quantitative sensitivity and qualitative detection were below 50 and 20 pmol S-nitrosothiol–bound nitrogen monoxide-equivalents, respectively. The intraday and interday coefficients of variation did not exceed 8%. This technique has been applied to quantify structurally diverse natural and synthetic S-nitrosothiols with quantitative recovery from complex biological samples such as culture media and plasma at levels of nitrogen monoxide-equivalents undetectable by the popular Saville colorimetric method.

Glucose-6-Phosphate Dehydrogenase in the Pentose Phosphate Pathway Is Localized in Vanadocytes of the Vanadium-Rich Ascidian,Ascidia sydneiensis samea

Ascidians are sessile marine animals known to accumulate high levels of vanadium selectively in vanadium-containing blood cells (vanadocytes). Almost all the vanadium accumulated in the vacuoles of vanadocytes is reduced to the +3 oxidation state via the +4 oxidation state, although vanadium is dissolved in the +5 oxidation state in sea water. Some of the reducing agents that participate in the reduction have been proposed. By chemical study, vanadium in the +5 oxidation state was reported to be reduced to the +4 oxidation state in the presence of NADPH. The present study revealed the existence of glucose-6-phosphodehydrogenase (G6PDH), the first enzyme to produce NADPH in the pentose phosphate pathway, in vanadocytes of a vanadium-rich ascidian. The results suggested that G6PDH conjugates the reduction of vanadium from the +5 through to the +4 oxidation state in vanadocytes of ascidians.

6-Phosphogluconate dehydrogenase is a 45-kDa antigen recognized by S4D5, a monoclonal antibody specific to vanadocytes in the vanadium-rich ascidian Ascidia sydneiensis samea.

We previously prepared a monoclonal antibody, S4D5, specific to vanadocytes, vanadium-containing blood cells, in the vanadium-rich ascidian Ascidia sydneiensis samea. Here, we demonstrate that a 45-kDa antigen recognized by S4D5 is 6-phosphogluconate dehydrogenase (6-PGDH), an enzyme of the pentose phosphate pathway, based on cDNA isolation of RNA samples from blood cells of the ascidian. Western blot analysis confirmed an abundance of 6-PGDH protein in the vanadocytes and localization of 6-PGDH in the soluble extract of the blood cells. Soluble protein exhibited a correspondingly high level of 6-PGDH enzymatic activity. Ascidians are known to selectively accumulate high levels of vanadium in vanadocytes, and the highest recorded concentration of accumulated vanadium is 350 mM, which is 10(7) times the concentration in sea water. Almost all vanadium ions are reduced to the +3 oxidation state via the +4 oxidation state in vanadocytes, indicating that reducing agents must participate in the accumulation. On the other hand, vanadium ions in the +5 oxidation state are reduced to the +4 oxidation state by the presence of NADPH in vitro. Together, these observations suggest that NADPH produced in the pentose phosphate pathway may conjugate the reduction of vanadium from the +5 oxidation state through the +4 oxidation state in vanadocytes of ascidians.

Organometallic vanadium-based heterogeneous catalysts for ethylene polymerization. Study of the deactivation process

Slurry polymerizations of ethylene over vanadium catalysts (based on VCl4 and VOCl3) and their MgCl2(THF)2-supported equivalents were studied. Unsupported vanadium catalysts were found to be unstable while the vanadium active sites deposited on the MgCl2(THF)2 complex are stable. A sharply outlined correlation was found between the concentration of vanadium(III) and catalyst productivity. The high activity and stability of the vanadium catalyst when supported on the magnesium complex is attributed to the increase of resistance to reduction of active vanadium(III) to inactive vanadium(II) by an organoaluminium co-catalyst.

Organometallic vanadium‐based heterogeneous catalysts for ethylene polymerization. Study of the deactivation process

Slurry polymerizations of ethylene over vanadium catalysts (based on VCl4 and VOCl3) and their MgCl2(THF)2-supported equivalents were studied. Unsupported vanadium catalysts were found to be unstable while the vanadium active sites deposited on the MgCl2(THF)2 complex are stable. A sharply outlined correlation was found between the concentration of vanadium(III) and catalyst productivity. The high activity and stability of the vanadium catalyst when supported on the magnesium complex is attributed to the increase of resistance to reduction of active vanadium(III) to inactive vanadium(II) by an organoaluminium co-catalyst.

Effects of preparation parameters on oxygen stoichiometry in Bi4V2O11−δ

The effects of various preparation parameters on vanadium reduction in Bi4V2O11–δhave been investigated using EPR, 51V MAS solid state NMR and UV diffuse-reflectance spectroscopies and also SQUID magnetometry and powder neutron diffraction. The results confirm that a greater amount of vanadium reduction is observed in rapidly quenched samples and that significant oxidation occurs when samples are slow cooled. Evidence for spin–spin dipolar coupling is seen in the EPR patterns while uncoupled V4+ spins contribute to weak paramagnetic behaviour. Band gaps of around 2 eV from the UV data suggest there may be a significant electronic component to low temperature conductivities. The 51V NMR data are not inconsistent with the presence of mainly distorted octahedral and tetrahedral coordinations for vanadium.

Specific S-nitrosothiol quantification as solution nitrite after vanadium(III) reduction and ozone chemiluminescent detection

Specific S-nitrosothiol quantification as solution nitrite after vanadium(III) reduction and ozone chemiluminescent detection

Ammoxidation of propane over modified V [sbnd]Sb [sbnd]Al-oxides — The role of acidity and redox properties of the catalysts

Vanadium-antimony-oxides are known to be active and selective catalysts for the ammoxidation of propane to acrylonitrile. The performance of these catalysts can be enhanced by doping with different metal ions. However, the catalytic function of these promoters is still unknown. In the present work the influence of promoters (W, Mg, Nb, Te, Ga, Pb, Sm) on the surface acidic and bulk redox properties and on the catalytic performance of VSb 5O x/Al 2O 3 catalysts was investigated. The freshly prepared catalysts exhibited only small differences in their acidic and redox properties, while dramatic changes occurred under reaction conditions in the first hours-on-stream. The selectivity to acrylonitrile of the modified catalysts in the final state (after 5 h on-stream) increased in the following order of dopants: Sm, Pb < Ga < unpromoted < Nb, Te < Mg < W. In the same order the surface Lewis-acidity increased, while basicity decreased. The catalysts exhibiting higher selectivity to acrylonitrile also showed a higher degree of reduction of vanadium. In the W modified catalyst only the redox pair V IV/V III could be detected. It is concluded that in the Me promoted catalysts which showed better performance than the unpromoted catalyst (Me W, Mg, Nb and Te) the role of the promoters is to catalyze the formation of the active and selective form of the vanadium, most probably a V IVSbO 4 phase, or to stabilize this phase under reaction conditions.

Reduction of vanadium(IV) to vanadium(III) by cysteine methyl ester in water in the presence of amino polycarboxylates

The reduction behavior of vanadium(IV) by several thiolate compounds in water was investigated in the presence of amino polycarboxylates. Vanadium(IV) can be reduced by cysteine methyl ester in the presence of edta or cydta to yield [VIII(edta or cydta)(H2O)]−, respectively.

Reduction of Vanadium(IV) to Vanadium(III) by Cysteine Methyl Ester in Water in the Presence of Amino Polycarboxylates

Abstract The reduction behavior of vanadium(IV) by several thiolate compounds in water was investigated in the presence of amino polycarboxylates. Vanadium(IV) can be reduced by cysteine methyl ester in the presence of edta or cydta to yield [VIII(edta or cydta)(H2O)]−, respectively.

ChemInform Abstract: New Chemistry of Vanadium(II)

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Simultaneous flow injection determination of iron(III) and vanadium(V) and of iron(III) and chromium(VI) based on redox reactions

A flow injection analysis (FIA) method is presented for the simultaneous determinations of iron(III)-vanadium(V) and of iron(III)-chromium(VI) using a single spectrophotometric detector. In the presence of 1,10-phenanthroline (phen), iron(III) is easily reduced by vanadium(IV) to iron(II), followed by the formation of a red iron(II)-phen complex ( λ max = 510 nm), which shows a positive FIA peak at 510 nm corresponding to the concentration of iron(III). On the other hand, in the presence of diphosphate the reductions of vanadium(V) and/or chromium(VI) with iron(II) occur easily because the presence of diphosphate causes an increase in the reducing power of iron(II). In this case iron(II) is consumed during the reaction and a negative FIA peak at 510 nm corresponding to the concentration of vanadium(V) and/or chromium(VI) is obtained. The proposed method makes it possible to obtain both positive (for iron(III)) and negative (for vanadium(V) or chromium(VI)) FIA peaks with a single injection.

Vanadium(V) reduction in Thiobacillus thiooxidans cultures on elemental sulfur

We describe the reduction of vanadium (V) to vanadium (IV) in cultures of Thiobacillus thiooxidans on elemental sulfur, for initial vanadium (V) concentrations up to 5 mM. The vanadium (V) is reduced by intermediate compounds generated by bacterial oxidation of elemental sulfur. The limit of initial vanadium (V) allowing bacterial action seems to be related to the inhibition caused by such vanadium species, rather than connected to the vanadium (IV) species, which did not show inhibitory effects up to concentrations of about 0.1 M. This reduction mechanism of vanadium (V) is potentially applicable in the recovery of vanadium from spent solid catalysts, by a low-cost methodology.

Electrochemical Properties and ESR Characterization of Mixed Valence alpha-[XMo(3)(-)(x)()V(x)()W(9)O(40)](n)()(-) Heteropolyanions with X = P(V) and Si(IV), x = 1, 2, or 3.

Electrochemical behavior of the alpha-[SiMo(3)(-)(x)()V(x)()W(9)O(40)]((4+)(x)()())(-) and alpha-[PMo(3)(-)(x)()V(x)()W(9)O(40)]((3+)(x)()())(-) anions with x = 1, 2, or 3 were studied. Electrochemical reduction of each compounds was consistent with its Mo/V ratio, reduction of vanadium and molybdenum atoms occurring in the +0.6 to -0.6 V potential range. The one-electron-reduced species were prepared by electrolysis and then characterized by ESR spectroscopy. The g and A values for V(4+)ions appeared to depend on the nature of the surrounding atoms (Mo(VI), W(VI), and V(V)). In solution at 330 K, the ESR spectrum of the protonated alpha-H[SiMoV(IV)VW(9)O(40)](6)(-) anion displayed 29 superhyperfine lines which were related to the partial localization of the electron on one vanadium nucleus. The ESR spectra at room temperature for the divanadium-substituted anions showed a strong anisotropy of the A tensor which would be related to the electron transfer along a preferential axis. An isolated V(4+) signal was not observed, even at 12 K, indicating that the electron is never firmly trapped on one single vanadium atom.

Electrochemical intercalation of lithium into vanadium pentaoxide: an in situ X-ray absorption study

An X-ray absorption study at the vanadium K edge has been performed on the LixV2O5(x= 0–0.78) system. For this, an electrochemical cell has been designed in order to allow in situ measurements. The spectra were recorded every 0.03 Li (mol V2O5)–1 using the same sample left in the X-ray beam. The study of the XANES spectra shows that the vanadium environment becomes more symmetrical as the intercalation progresses. Furthermore, the Natoli rule applied to these spectra reveals a mean lengthening of the vanadium–oxygen bond of 0.05 A. This result is confirmed by the EXAFS study. This EXAFS study also reveals a shortening of the vanadium–vanadium bond of 0.08 A. The results are interpreted as being due to the partial reduction of vanadium(V) to vanadium(IV), and its move from its initial position in a square pyramid towards the basal oxygen plane of the pyramid.

Speciation in Vanadium Bioinorganic Systems. 2. An NMR, ESR, and Potentiometric Study of the Aqueous H(+)-Vanadate-Maltol System.

A systematic study of the physiologically interesting vanadium-maltol (V-MaH) system has been performed in 0.150 M Na(Cl) at 25 degrees C, using NMR, ESR, and potentiometric techniques. Complexation occurs within a wide pH range, from around 1 up to 10.5. However, a pH-, concentration-, and time-dependent spontaneous reduction of vanadium(V) to vanadium(IV) occurs. From ESR spectra the conditions for this reduction are evaluated and discussed. From potentiometric (glass electrode) and quantitative (51)V NMR measurements, the full speciation in the H(+)-H(2)VO(4)(-)-MaH system was determined in the pH range 5-10.5. Data were evaluated with the computer program LAKE, which is able to treat combined emf and NMR data. The pK(a) value for MaH was determined to be 8.437 +/- 0.005. In the ternary system, three complexes are formed: VMa(2)(-), VMa(-), and VMa(2)(-), having log beta(0,1,2) = 7.02 +/- 0.03, log beta(0,1,1) = 2.66 +/- 0.05, and log beta(-)(1,1,1) = -7.37 +/- 0.21. The errors given are 3sigma. The VMa(2)(-) complex appears as the main species in a pH range from 4.5 to 8.5, whereas both mononuclear monoligand species are minor. Equilibrium conditions are illustrated in distribution diagrams, and the structures of the complexes formed are proposed.

Linear non‐conjugated dienes from biomass as termonomers in EPDM synthesis, 2. Comparison with 5‐ethylidene‐2‐norbornene termonomer

AbstractA comparative study of 5‐ethylidene‐2‐norbornene (ENB) or 5,7‐dimethylocta‐1,6‐diene (5,7‐DMO) as diene termonomer in ethylene‐propylene‐diene (EPDM) terpolymer synthesis is presented. The reactivities of the cyclic and linear non‐conjugated dienes are first compared in homopolymerization in the presence of two conventional Ziegler‐Natta catalytic systems: TiCl3, 1/3AlCl3, 14MgCl2 associated to AlEt3, and VOCl3 (or VCl4) associated to AlEt2Cl. ENB polymerization yields a branched poly(ENB) in agreement with a predominant cationic reaction, whereas polymerization of 5,7‐DMO proceeds exclusively by a Ziegler‐Natta mechanism. In terpolymerization, ENB is much more reactive than 5,7‐DMO and is incorporated more easily in the terpolymer. However, the high sensitivity of ENB toward acidic species also results in cationic side reactions and therefore limits the utilization of ENB to a low concentration range. We have shown that the productivity of vanadium catalysts, which are mainly used in industrial EPDM synthesis, is drastically reduced in the presence of ENB an 5,7‐DMO, due to the rapid reduction of vanadium involving the diene.

Relative reducing abilities in vitro of some hydroxy-containing compounds, including monosaccharides, towards vanadium(V) and molybdenum(VI)

The reduction of vanadium(V) and molybdenum(VI) has been carried out in aqueous HCl by various hydroxy-containing compounds such as hexoses ( d-glucose, d-fructose, and d-galactose), pentoses ( d-ribose and d-xylose), glycols [ethylene glycol, di(ethylene glycol), tri(ethylene glycol), tetra(ethylene glycol), and poly(ethylene glycol)], and mono-, di-, and tri-ethanolamines. The relative reducing abilities of these compounds are compared with those of l-ascorbic acid and l-cysteine. The trend is similar to that reported earlier for chromium(VI) reduction. Based on this study it is concluded that hydroxy-containing compounds play important roles in complexation and reduction of metal ions.

Characterization of Carbonaceous Deposits by Temperature-Programmed Oxidation

The selective oxidation of o-xylene to phthalic anhydride (PA) has been studied on a series of ternary V-Ti-Si oxides. Fresh and used catalysts, containing one monolayer of V2O5 on TiO2-SiO2 supports with 0.5, 1, 2 and 3 monolayers of TiO2 on SiO2, were characterised by Raman spectroscopy, X-ray diffraction (XRD) and temperature-programmed reduction (TPR). The characteristics and catalytic behaviour of these catalysts were compared with those of catalysts containing one monolayer of V2O5 supported on SiO2 and on TiO2. In the ternary V-Ti-Si catalysts, the presence of V2O5 and TiO2 (anatase) was detected, TiO2 (rutile) being also found in those with two and three monolayers of TiO2. The formation of TiO2 (rutile) due to exposure to reaction conditions was not observed. A moderate rearrangement of surface vanadium oxide species into crystalline V2O5 is observed. In addition, the formation of V2O4 was detected by XRD in the used catalyst containing one monolayer of V2O5 on the support with one monolayer of TiO2 on silica. The TPR of used and fresh samples showed that the reduction of vanadium occurs during reaction, such reduction being partially reversible after reoxidation in air flow at high temperature. This partial reduction may favour the aggregation of dispersed vanadia species into crystalline V2O5.The catalytic behaviour of ternary systems in the selective oxidation of o-xylene depends strongly on the characteristics of the support. An increase in the content of TiO2 leads to a decrease in the temperature required to achieve total conversion. The use of SiO2 as support causes formation of large amounts of undesirable C8 products, whereas the presence of TiO2 deposited on SiO2 leads generally to the formation of lower amounts of such products. The formation of both CO2 and tar is strongly favoured on the support composed of two monolayers of TiO2 on SiO2.