Vanadium monoxide

Vanadium forms numerous oxides, the most important of which are vanadium monoxide, vanadium sesquioxide, vanadium dioxide and vanadium pentoxide. In the earlier examples (e.g., oxides of chromium and of niobium) the enthalpy values for the aluminothermic reduction of each of the oxides was given for the purpose of illustration. Normally, the consideration can be restricted to only those oxides which are readily obtained and which can be handled freely without any special or cumbersome precautions. In the case of vanadium for example, it is sufficient to consider the reduction of the sesquioxide (V203) and the pentoxide (V2Os). The pertinent reactions are ... 

In the case of vanadium, the suboxide, vanadium monoxide, would be more volatile than carbon monoxide except at very high carbon concentrations in the metal. The removal of the residual oxygen from this metal by carbon deoxidation is, therefore, difficult. In the case of niobium and tantalum, the partial pressure of carbon monoxide is higher than that of niobium monoxide or tantalum monoxide, even when the residual carbon concentration in the metal is as low as 200 ppm. It may therefore be expected that practically all the oxygen would be removed by evaporation of carbon monoxide without any metal loss from niobium and tantalum metals containing both oxygen and carbon. 

A phase diagram has been proposed for the V-VO system from m.p., d.t.a., X-ray, and other studies. In this system V9O4, V2O, and V4O have been identified at 510. 1185. and 1665°C. respectively, and the m.p, of VO was determined as 1790 The cubic vanadium monoxide phase has been shown to exhibit two closely related phase sections. VO — 091 os— 1.25-... 

An interesting group of non-stoichiometric oxides are the transition-metal monoxides (MO, where M = metal) for example, titanium monoxide (TiO) and vanadium monoxide (VO). These have a wide range of non-stoichiometric... 

Oxides Vanadium monoxide VO, gray solid vanadium trioxide V2O3, black solid vanadium dioxide VO2, dark blue solid vanadium pentoxide V2O5, orange to red solid. The last is the most important oxide formed by the ignition in an of vanadium sulfide, 01 othei oxide, 01 vanadium used as a catalyzer, e.g., the reaction SO2 gas plus oxygen of air to form sulfur tnoxide. and the oxidation of naphthalene by air to form phthalie anhydride. 

T. J. Groshens, 1. Molecular Vapor Synthesis The Use of Titanium Monoxide and Vanadium Monoxide. 2. Oxidative Insertion Reactions of First Row Early Transition Metal Atoms, Ph. D. Thesis, Kansas State University, 1988. 

It was already shown that spectroscopic states of vanadium monoxide are numerous and difficult to interpret in terms of one-electron based theories. At the same time, due to the existence of broad and very careful experimental evidence, they are a good subject for theoretical studies even if they do not strictly keep within the established bounds but push forward the understanding of physical phenomena. 

Aristov, N., Thermochemistry and mechanism of reactions of vanadium and vanadium monoxide ions, Ph.D. Thesis, University of California, Berkeley,... 

Weinstein, J.D., deCarvalho, R., Amar, K., Boca, A., Odom, B.C., Friedrich, B., and Doyle, J.M., Spectroscopy of buffer-gas cooled vanadium monoxide in a magnetic trapping field, J. Chem. Phys., 109(7), 2656-2661, 1998. 

The formula for vanadinite analogous to the other formulas is Pb5(V04)3CI. On reinvestigating the compounds of vanadium Roscoe found that this latter formula is indeed the correct one, and that Berzelius had accepted VO, vanadium monoxide, as the elementary substance. The atomic mass of vanadium now accepted is 50.942. 

Aristov, N. and Armentrout, P. B. (1986) Colhsion-induced dissociation of vanadium monoxide ion. J. Phys. Chem., 90, 5135. 

P. S. Bell and M. H. Lewis, Nonstoichiometric vacancy order in vanadium monoxide, Phys. Stat. Sol. 7, 431 (1971). 

Butane-Based Fixed-Bed Process Technology. Maleic anhydride is produced by reaction of butane with oxygen using the vanadium phosphoms oxide heterogeneous catalyst discussed earlier. The butane oxidation reaction to produce maleic anhydride is very exothermic. The main reaction by-products are carbon monoxide and carbon dioxide. Stoichiometries and heats of reaction for the three principal reactions are as follows ... 

During interaction of hydrogen or carbon monoxide photoexcitation centres of Si02 surface containing ions of five valance vanadium one observes a surface-adjacent photodissociation of hydrogen and photooxidation of carbon dioxide through the following scheme [93, 96]... 

The carbothermic reduction processes outlined so far apply to relatively unstable oxides of those metals which do not react with the carbon used as the reductant to form stable carbides. There are several metal oxides which are intermediate in stability. These oxides are less stable than carbon monoxide at temperatures above 1000 °C, but the metals form stable carbides. Examples are metals such as vanadium, chromium, niobium, and tantalum. Carbothermic reduction becomes complicated in such cases and was not preferred as a method of metal production earlier. However, the scenario changed when vacuum began to be used along with high temperatures for metal reduction. Carbothermic reduction under pyrovacuum conditions (high temperature and vacuum) emerged as a very useful commercial process for the production of the refractory metals, as for example, niobium and tantalum, and to a very limited extent, of vanadium. 

The process of oxygen removal from the metal-oxygen solid solution via the formation of carbon monoxide is known as carbon deoxidation. The terms [0]M and [C]M denote the oxygen and the carbon dissolved in the metal to be refined, for example, vanadium. The extent to which carbon deoxidation can occur in a metal under given conditions of temperature and pressure can be estimated by using the following relationship ... 

V metals, vanadium has the least tendency to deoxidize by carbon monoxide evolution. This means that, at a given temperature and a given value of Pco, the residual carbon and/or oxygen contents in vanadium will be compared more to niobium and tantalum. In other words, the removal of carbon and/or oxygen from vanadium will occur to a much lesser extent than in the cases of niobium or tantalum. The effect of carbon deoxidation can be quite complicated if there is a significant loss of the metal by vaporization. The requirement of a low vapor pressure is also better satisfied by niobium and tantalum than by vanadium. 

In the refining of the Group V metals (which are more accurately represented as metal-carbon-oxygen alloys), carbon deoxidation is not the only method by which oxygen is removed, because sacrificial deoxidation also occurs simultaneously. The relative extents to which each of these two deoxidation modes contributes to the overall removal of oxygen can be assessed by calculating the ratio of the vapor pressures of carbon monoxide and the metal monoxide over the M-C-0 alloy. The value of this ratio for vanadium at 2000 K is given by the expression... 

Insertions of isocyanide into niobium-carbon bonds follow a path similar to that with vanadium, resulting in the formation of the 7]2-iminoacyl complexes, which can then be involved in further chemistry.175 176 The reaction of acetone with cyclopentadienyl complex 110 under a carbon monoxide atmosphere gives the if -acetone compound 111. Complex 111 subsequently undergoes either stepwise insertion of two isocyanides via 112 or double insertion of the isocyanide to give complex 113 (Scheme 48).177... 

Figure 2.8 The surface reaction between adsorbed carbon monoxide and hydrogen to methane over rhodium catalysts occurs at lower temperatures in the presence of a vanadium oxide promoter, which is known to enhance the rate of CO dissociation (from Koerts el al. 113]). 

Caution. Tetrahydrofuran (THF) is extremely flammable and hygroscopic and forms explosive peroxides only anhydrous peroxide-free solvent should be used. Lithium wire is a hazardous substance and must be handled under strictly anaerobic conditions. Further, since it slowly reacts with dinitrogen at room temperature, lithium metal is best handled under an atmosphere of dry, oxygen-free argon. Vanadium trichloride is air-sensitive and should be transferred under an inert atmosphere. Carbon monoxide is a toxic and flammable gas and must be handled in a well-ventilated fume hood. 

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