18252-79-4Relevant articles and documents
Study of the mechanism of the vanadium 4+/5+ redox reaction in acidic solutions
Gattrell,Park,MacDougall,Apte,McCarthy,Wu
, p. A123-A130 (2004)
The mechanism of the vanadium VO2+/VO2+ redox couple has been examined in acidic aqueous solutions. A detailed understanding of this chemistry is of interest for improving and optimizing the performance of vanadium redox-flow batteries, a promising electrochemical electricity storage technology. The vanadium 4+/5+ redox reactions were studied at a rotating disk graphite electrode and polarization curves were obtained in sulfuric acid and perchloric acid, with varying pH and vanadium concentrations. The results were compared to model predictions for different mechanisms. The data were consistent with a model with a multistep chemical-electrochemical-chemical mechanism at low overpotentials, which changes to a multistep electrochemical-chemical-chemical mechanism at higher anodic or cathodic overpotentials. Unusually high Tafel slopes (350-450 mV/decade) were observed for the reduction of VO2+ at higher overpotentials. While this could not be directly explained by the model, insights gained through the use of the model can provide the basis for some suggestions.
A study of the chemistry of the polyvanadates using salt cryoscopy
Naumann,Hallada
, p. 70 - 77 (1964)
Glauber's salt cryoscopy and pH measurements have been made on sodium vanadate solutions in the pH range 2.5 to 7. Vanadium was found to exist in neutral solutions as a tetramer of VO3-. At lower pH values, confirmation was found for the equilibria V10O28-6 ?H+ HV10O28-5 ?H+ H2V10O28-6 ?H+ VO2+ No evidence was found for a hexavanadate in the pH range studied. The formation of a heteropolyanion between vanadium and phosphorus was indicated. The heteropolyanion forms from H2V10O28-4, but not from the other anionic polyvanadates.
Oxidation by aqueous fluoroxysulfate: Catalysis by silver(I)
Thompson, Richard C.,Appelman, Evan H.
, p. 2114 - 2118 (1981)
The oxidations of the ions Cr3+, Co2+, and VO2+ by the fluoroxysulfate ion, SO4F-, in aqueous solution are catalyzed by Ag+. The rate-determining step for all three catalyzed reactions is the bimolecular oxidation of Ag+ by SO4F-, which has a rate constant of (1.3 ± 0.2) × 103 M-1 s-1 at 17°C. Activation parameters for this reaction are ΔH≠ = 6.1 ± 0.5 kcal/mol and ΔS = -23 ± 2 cal/(mol deg). In the absence of Ag+, Co2+ and VO2+ react very slowly with SO4F-, while Cr3+ does not react at all. Despite its high thermodynamic oxidizing power, the fluoroxysulfate ion acts as a very selective oxidant.
Oxidation of p-chlorotoluene and cyclohexene catalysed by polymer-anchored oxovanadium(iv) and copper(ii) complexes of amino acid derived tridentate ligands
Maurya, Mannar R.,Kumar, Maneesh,Kumar, Amit,Pessoa, Joao Costa
, p. 4220 - 4232 (2009/02/03)
3-Formylsalicylic acid (Hfsal), covalently bound to chloromethylated polystyrene (PS) and cross-linked with 5% divinylbenzene reacts with d,l-alanine and l-isoleucine to give the Schiff-base tridentate ligands PS-H 2fsal-d,l-Ala and PS-H2fsal-l-Ile, respectively. These anchored ligands upon reaction with VOSO4 and Cu(CH 3COO)2?H2O form the complexes PS-[VO(fsal-d,l-Ala)(H2O)], PS-[Cu(fsal-d,l-Ala)(H2O)], PS-[VO(fsal-l-Ile)(H2O)] and PS-[Cu(fsal-l-Ile)(H2O)]. The structures of these immobilized complexes have been established on the basis of scanning electron micrographs, spectroscopic (infrared, electronic and EPR), thermogravimetric and elemental analysis studies. The oxidation of p-chlorotoluene and cyclohexene has been investigated using these complexes as the catalysts in the presence of H2O2 as the oxidant. Reaction conditions have been optimised by considering the concentration of the oxidant, the amount of catalyst used and the temperature of the reaction mixture. Under the optimised conditions, p-chlorotoluene gave a maximum of 14% conversion using PS-[VO(fsal-d,l-Ala)(H2O)] as the catalyst, with the main products having a selectivity order of: p-chlorobenzaldehyde >> p-chlorobenzylalcohol > p-chlorobenzoic acid > 2-methyl-5-chlorophenol > 3-methyl-6-chlorophenol. The oxidation of cyclohexene with PS-[VO(fsal-d,l-Ala)(H2O)] proceeds with 79% conversion, which is followed by PS-[VO(fsal-l-Ile)(H2O)] with 77% conversion, and the oxidation of cyclohexene by Cu-based catalysts occurs with considerably lower conversions (29-32%). The selectivity of the products follows the order: 2-cyclohexene-1-ol > cyclohexene oxide > cyclohexane-1,2-diol > 2-cyclohexene-1-one. Recycling studies indicate that these catalysts can be reused at least three times without any significant loss in their catalytic potential. However, EPR studies indicate that while the polymer supported V(iv)O-complexes do not change after being used, the EPR spectra of the Cu-complexes show significant changes. The corresponding non-polymer bound complexes [VO(fsal-d,l-Ala)(H2O)], [Cu(fsal-d,l-Ala)(H 2O)], [VO(fsal-l-Ile)(H2O)] and [Cu(fsal-l-Ile)(H 2O)] have also been prepared in order to compare their spectral properties and catalytic activities. The non-polymer bound complexes exhibit lower conversion, along with lower turn-over frequency as compared to their polymer-bound analogues. Several EPR, 51V NMR and UV-vis studies have been undertaken to detect the intermediate species, and outlines for the mechanisms of the catalytic reactions are proposed.
Oxidation of peroxovanadium(V), VO3+, in acidic aqueous solution
Thompson, Richard C.
, p. 584 - 588 (2008/10/08)
The Cl2-VO3+ reaction proceeds by oxidation of trace amounts of H2O2 in equilibrium with VO3+. Preliminary results for the HOCl-VO3+ reaction are presented. The oxidation of VO3+ by S2O82- is catalyzed by Ag+, with the formation of the radical cation VO32+· via oxidation of VO3+ by Ag2+. The rate law for the SO4F--VO3+ reaction is -d(SO4F-)/dt = k9(SO4F-)(VO3+); again, formation of the intermediate VO32+· is indicated. In agreement with previous results, the decomposition of VO32+· involves an internal redox reaction to produce VO2+ and O2. The various pathways for the oxidation of VO3+ are summarized. A direct two-electron oxidation has not been observed, presumably because the formation of a peroxo complex with the oxidant prior to electron transfer is unfavorable when the peroxide moiety is complexed to vanadium(V).
