Vanadium/ions/salts

Rapid reaction between gases and ions requires that the vanadium ion salt be molten (Folkmann et al., 1991 Hatem et al., 2002). Melting at moderate temperatures (-650 K) is obtained by combining high melting point ... 

Consider some vanadium ions in aqueous solution. Pale violet solutions of vanadium(ii) salts contain the [V(H20)6] ion. The vanadium(ii) center is only weakly polarizing, and the hexaaqua ion is the dominant solution species. Aqueous vanadium(ii) solutions are observed to be unstable with respect to reduction of water by the metal center. In contrast, vanadium(ni) is more highly polarizing and an equilibrium between the hexaaqua and pentaaquahydroxy ion is set up. The of 2.9 means that the [V(OH2)6] ion (Eq. 9.17) only exists in strongly acidic solution or in stabilizing crystal lattices. 

Stein et al. and Janauer et al. have synthesized layered mesostructured materials of (C,9H42N)6(H2W,204o) and [Ci2H25N(CH3)3]6(H2Wi2O40), respectively [2,8]. These materials are of great interest because their walls are made of cluster anions, in contrast to the amorphous walls of the other materials. The tungsten, vanadium, niobium, and molybdenum oxide precursors reacting with cationic surfactants, often form similar cluster ion salts with lamellar structures [2]. 

Because vanadium ions exist in four different oxidation states (as V2+, V3+, V02+ and V02+) in aqueous solution, redox couples can be formed by all vanadium ions. The emf of a vanadium redox battery is 1.4 V and the electrode kinetics are higher than those of the Fe-Cr battery. Also, the energy density of the battery can be increased due to the high solubility of vanadium salts.257 In the battery, vanadium sulfate solution is used,... 

The role of vanadium (IV) in the glasses and the crystals is not clear. However, from the fact that vanadyl ions, VO + are most stable in crystals and solutions of vanadium(IV) salts, the vanadium(IV) in the vanadate-phosphates may also be present as vanadyl ions and may play the role of a cation in a manner similar to sodium ions. 

Most of the catalysts employed in the chemical technologies are heterogeneous. The chemical reaction takes place on surfaces, and the reactants are introduced as gases or liquids. Homogeneous catalysts, which are frequently metalloorganic molecules or clusters of molecules, also find wide and important applications in the chemical technologies [24]. Some of the important homogeneously catalyzed processes are listed in Table 7.44. Carbonylation, which involves the addition of CO and H2 to a C olefin to produce a + 1 acid, aldehyde, or alcohol, uses rhodium and cobalt complexes. Cobalt, copper, and palladium ions are used for the oxidation of ethylene to acetaldehyde and to acetic acid. Cobalt(II) acetate is used mostly for alkane oxidation to acids, especially butane. The air oxidation of cyclohexane to cyclohexanone and cyclohexanol is also carried out mostly with cobalt salts. Further oxidation to adipic acid uses copper(II) and vanadium(V) salts as catalysts. The... 

The antidiabetic potential of the transition metal vanadium has been known for over 100 years [1], and the last 25 years has marked a period of intense research interest in the development of vanadium salts and complexes as a new treatment for diabetes mellitus. The first report of the strong inhibitory effects of sodium metavanadate (NaVOs) to phosphatases [2,3] was followed by subsequent experiments demonstrating insulin-like effects on isolated adipocytes [4] by vanadyl ion (VO ). Proof of in-vivo activity after oral administration of a vanadium(V) salt in diabetic rats [5] spurred a flurry of interest in vanadium(V), later followed by sus-... 

Where molybdenum (Mo02(acac)2) or vanadium (V2O5) salts were used as catalysts with O2 (Scheme 11.9), a metal-nitrogen interaction (in 25) vras proposed to facilitated simple elimination to give the iminium ion 26, to which nucleophilic addition occurred to give the product 277 The rationale for this mechanism is that the Af-oxides (which can be isolated) do not lead to CDC products under standard reaction conditions. The stoichiometric oxidant (O2) was thought to re-generate the catalyst, rather than oxidize the amine to the iminium ion, but no evidence for this was provided. When VO(acac)2 was used with BuOOH as the oxidant, the AAoxides could not be observed in the reaction but when they were separately made, they did not lead to the CDC reaction product coupled with the inhibition of the reaction in the presence of BHT, the conclusion was that the iminium ion formation... 

Overall, a decrease in the solution conductivity is observed with an increase in the vanadium salt concentration. When comparing between solutions with different sulphuric acid concentrations, the difference in conductivity decreases as the vanadium (III) salt concentration is increased. The initial conductivity values ([V2(S04)3] = 0 M) reflect the difference in the concentration of the hydronium ions in the solutions hence, higher conductivity... 

The chemistry of vanadium compounds is related to the oxidation state of the vanadium. Thus, V20 is acidic and weaMy basic, VO2 is basic and weaMy acidic, and V2O2 and VO are basic. Vanadium in an aqueous solution of vanadate salt occurs as the anion, eg, (VO ) or (V O ) , but in strongly acid solution, the cation (V02) prevails. Vanadium(IV) forms both oxyanions ((V O ) and oxycations (VCompounds of vanadium(III) and (II) in solution contain the hydrated ions [V(H20)g] and [V(H20)g], respectively. 

Other ions which are reduced in the reductor to a definite lower oxidation state are those of titanium to Ti3+, chromium to Cr2+, molybdenum to Mo3+, niobium to Nb3+, and vanadium to V2 +. Uranium is reduced to a mixture of U3 + and U4+, but by bubbling a stream of air through the solution in the filter flask for a few minutes, the dirty dark-green colour changes to the bright apple-green colour characteristic of pure uranium(I V) salts. Tungsten is reduced, but not to any definite lower oxidation state. 

Salt effects. The rate of reaction of vanadium(V) with iodide ions is independent of ionic strength.28 The rate law is v = fc[V(V)][I ][H+]2. What is the charge on the predominant V(V) species in these solutions ... 

The ability of metal ions to form complexes with formazans is utilized to determine these ions either directly (for low valent reducing ions) or indirectly in the presence of a reducing agent. Among others, molybdenum(VI) and vanadium(V) have been determined using this method.442,443 Indirect methods have been reported for the analyses of substances that do not reduce tetrazolium salts. Examples include arsenic in nickel ores436 and traces of selenium.437 A method for the extraction and analysis of a number of metal ternary ion association complexes has been described.444 - 448... 

The question about the competition between the homolytic and heterolytic catalytic decompositions of ROOH is strongly associated with the products of this decomposition. This can be exemplified by cyclohexyl hydroperoxide, whose decomposition affords cyclo-hexanol and cyclohexanone [5,6]. When decomposition is catalyzed by cobalt salts, cyclohex-anol prevails among the products ([alcohol] [ketone] > 1) because only homolysis of ROOH occurs under the action of the cobalt ions to form RO and R02 the first of them are mainly transformed into alcohol (in the reactions with RH and Co2+), and the second radicals are transformed into alcohol and ketone (ratio 1 1) due to the disproportionation (see Chapter 2). Heterolytic decomposition predominates in catalysis by chromium stearate (see above), and ketone prevails among the decomposition products (ratio [ketone] [alcohol] = 6 in the catalytic oxidation of cyclohexane at 393 K [81]). These ions, which can exist in more than two different oxidation states (chromium, vanadium, molybdenum), are prone to the heterolytic decomposition of ROOH, and this seems to be mutually related. 

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