Vanadyl vanadates

Gamma sodium vanadyl vanadate (y5Na20 V204 V205), which has a melting point (MP) of approximately 1070 °F (577 °C)... 

Intermediate Oxides.—Oxides which are intermediate between liypovanadic oxide, V02, and vanadium pentoxide, V205, are known. By the partial reduction of vanadium pentoxide, or by the partial oxidation of one of the lower oxides, there have been prepared a number of oxides which are best considered as being formed by the combination of the acidic vanadium pentoxide with a lower basic oxide in varying molecular proportions. These oxides react yvith alkalis, and yield a series of salts called vanadyl vanadates, intermediate in composition between the vanadites and the vanadates. 

Damage is generally associated with the combined presence of vanadium (arising as a porphyrin in the fuel), sodium (derived from sodium chloride), sulfur (from the fuel), and oxygen. During combustion, vanadic oxides and sodium sulfate may condense as low melting vanadyl vanadates, which permit the rapid dissolution of surface oxides and metal alkali. The processes occur very rapidly. Oxide dissolution can appear to be synonymous with metallic loss (Johnson et al. 1975). 

R458 S. Ramos, J. J. G. Moura and M. Aureliano, Recent Advances into Vanadyl, Vanadate and Decavanadate Interactions with Actin , Metallo-mics, [online computer file], 2012, 4, 16. 

Minor uses of vanadium chemicals are preparation of vanadium metal from refined pentoxide or vanadium tetrachloride Hquid-phase organic oxidation reactions, eg, production of aniline black dyes for textile use and printing inks color modifiers in mercury-vapor lamps vanadyl fatty acids as driers in paints and varnish and ammonium or sodium vanadates as corrosion inhibitors in flue-gas scmbbers. 

Vanadyl trichloride (VOCI3) [7727-18-6] M 173.3, m-79.5°, b 124.5-125.5°/744mm, 127.16°/760mm, d 1.854, d 1.811. Should be lemon yellow in colour. If red it may contain VCI4 and CI2. Fractionally distil and then redistil over metallic Na but be careful to leave some residue because the residue can become EXPLOSIVE in the presence of the metal USE A SAFETY SHIELD and avoid contact with moisture. It readily hydrolyses to vanadic acid and HCl. Store in a tightly closed container or in sealed ampoules under N2. [Inorg Synth 1 106 1939, 4 80 1953.]... 

Vanadium in the feed poisons the FCC catalyst when it is deposited on the catalyst as coke by vanadyl porphydrine in the feed. During regeneration, this coke is burned off and vanadium is oxidized to a oxidation state. The vanadium oxide (V O ) reacts with water vapor in the regenerator to vanadic acid, HjVO. Vanadic acid is mobile and it destroys zeolite crystal through acid-catalyzed hydrolysis. Vanadic acid formation is related to the steam and oxygen concentration in the regenerator. 

Insulin binding to the extracellular side of cell membranes initiates the insulin cascade , a series of phosphorylation/dephosphorylation steps. A postulated mechanism for vanadium is substitution of vanadate for phosphate in the transition state structure of protein tyrosine phosphatases (PTP).267,268 In normal physiological conditions, the attainable oxidation states of vanadium are V111, Viv and Vv. Relevant species in solution are vanadate, (a mixture of HV042-/ H2VOO and vanadyl V02+. Vanadyl is not a strong inhibitor of PTPs, suggesting other potential mechanisms for insulin mimesis for this cation. 

The rate law for a redox reaction predicts the rate at which a species is transformed by a specific reaction mechanism, or combination of mechanisms, from one oxidation state to another. For example, Wehrli and Stumm (1988, 1989) studied the oxidation of vanadyl (Viv) to vanadate (Vv) by reaction with dissolved O2. 

To trace a reaction path incorporating redox kinetics, we first set a model in redox disequilibrium by disabling one or more redox couples, then specify the reaction in question and the rate law by which it proceeds. To model the progress of Reaction 17.1, for example, we would disable the redox couple between vanadyl and vanadate species. In a model of the oxidation of Fe++ by manganite (MnOOH), we would likely disable the couples for both iron and manganese. 

It was discovered nearly 20 years ago that V(V) as vanadate and V(IV) as vanadyl can mimic some of the effects of insulin (stimulate glucose uptake and oxidation and glycogen synthesis) (512, 513). Vanadate is an effective insulin mimetic in the diabetic rat (514), but has proved to be too toxic for human use. Vanadyl, as VOS04, is also unsuitable because high doses are needed on account of its poor oral absorption. Vanadium complexes with organic ligands have proved to be less toxic and can have improved aqueous solubility and lipophil-icity. 

It was reported in 1980 that vanadate showed insulin activity (415) at about the same time it was demonstrated that vanadate is reduced to vanadium(IV) in vivo (416,417). Subsequently it was found that orally administered vanadate restored blood glucose levels and cardiac function to normal in rats (418). Vanadyl sulfate, less toxic than vanadate, also lowers blood sugar levels and ameliorates cardiac... 

Bisconti L, Pepi M, Mangani S, Baldi F. 1997. Reduction of vanadate to vanadyl by a strain of Saccharomyces cerevisiae. Biometals 10 239-46. 

Vanadium occurs in soils predominantly as the +5 vanadate species (VO(OH)3°, V02(0H)2 and V03(0H) ) and under reducing conditions as the +4 vanadyl cation (VO +). Less commonly V + may also form and substitute for Fe in minerals. Interchange between these oxidation states with redox conditions greatly alters the solubility of V in soils. 

Analysis of structure-activity relationships shows that various species characterized by different reactivities exist on the surface of vanadium oxide-based catalysts.339 The redox cycle between V5+ and V4+ is generally accepted to play a key role in the reaction mechanism, although opposite relationships between activity and selectivity, and reducibility were established. More recent studies with zirconia-supported vanadium oxide catalysts showed that vanadium is present in the form of isolated vanadyl species or oligomeric vanadates depending on the loading.345,346 The maximum catalytic activity was observed for catalysts with vanadia content of 3-5 mol% for which highly dispersed polyvanadate species are dominant. 

B. Wet Processes.—These vary considerably in detail according to the nature and amount of constituents other than vanadium in the ore. An outline of the operations involved in the case of patronite is as follows The ore is roasted with common salt or sodium carbonate and then extracted either (a) with water to give an alkaline solution of sodium vanadate and soluble vanadates of other metals, any lead, zinc, copper, etc., being left in the residue or (b) with sulphuric acid to produce a solution of vanadyl sulphate. Acid extraction is usually employed when the vanadium content of the material is low. The alkaline extract from (a) is treated with excess of sodium carbonate in order to precipitate calcium and aluminium, after removal of which,... 

Vanadium Oxymonobromide, VOBr, is prepared by the decomposition of vanadyl dibromide, VOBr2, in vacuo at 360° C. It forms violet, octahedral crystals, density 4-000 at 18° C. On being heated in vacuo at 480° C. it yields vanadium tribromide and vanadous oxide, V203. It is almost insoluble in water and the usual organic solvents.7... 

Vanadium Oxytribromide, VOBr3, is produced when pure, dry bromine is passed over vanadous oxide, V2Os, heated to redness. Yellowish-white vapours are evolved which condense to a deep red, hygroscopic liquid, density 2-9673 at 0° C. It decomposes slowly at ordinary temperatures into vanadyl dibromide and bromine, but distils without decomposition at 130° to 136° C. under 100 mm. pressure. It is much less stable than vanadyl dibromide, VOBra.a... 

Vanadium pentoxide dissolves in acids, both organic and inorganic, to form vanadyl or unstable vanadic salts,7 and in alkalis to produce ortho-, pyro-, meta-, and poly-vanadates. The physico-chemical changes involved when vanadium pentoxide is heated with various basic oxides in the powder state have been investigated by Tammann.8 On being digested with liquid ammonia slow absorption of ammonia takes place the composition of the product has not been definitely established.9 The oxide also dissolves in alcohols to produce esters,10 and combines with methylamine and ethylamine to form compounds of the type 2(R.NHB).V205, where R represents the alkyl radical.11... 

Iron Vanadate is, metallurgically, the most important vanadate. Precipitation of a solution of a vanadate with ferrous sulphate gives rise to a precipitate of indefinite composition, ortlio-, pyro-, meta-, and perhaps a poly-vanadate being present, as well as ferric or ferrous oxide. Reduction of the vanadate to a vanadyl salt may also ensue. The precipitate is usually colloidal and carries down with it some sodium vanadate. The dried powder may be either green, yellow, brown, or red the more nearly the precipitate approximates to a red colour the lower is its vanadium content. An iron vanadate has also been prepared by electrolysis of a solution of sodium vanadate between iron poles.1... 

Acid Vanadous Sulphates and double vanadous sulphates.—Electrolytic reduction of solutions of vanadyl sulphate, V0S04, has given two green, crystalline, acid vanadous sulphates, according to the amount of sulphuric acid also added ... 

Double Salts of Vanadyl Sulphite.—By the action of sulphur dioxide on vanadates in the presence of varying molecular proportions of alkali sulphites, two series of alkali vanadyl sulphites have been obtained. 

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