Of vanadium compounds

The adopted values for TWAs for airborne vanadium, including oxide and metal dusts of vanadium, is 0.5 mg/m the values for fumes of vanadium compounds is 0.05 mg/m. These limits are for normal 8-h workday and 40-h work-week exposures. The short-term exposure limit (STEL) is 1.5 mg/m for dusts (25). A description of health ha2ards, including symptoms, first aid, and organ involvement, personal protection, and respirator use has beenpubhshed (26). 

Vanadium, a typical transition element, displays weU-cliaractetized valence states of 2—5 in solid compounds and in solutions. Valence states of —1 and 0 may occur in solid compounds, eg, the carbonyl and certain complexes. In oxidation state 5, vanadium is diamagnetic and forms colorless, pale yeUow, or red compounds. In lower oxidation states, the presence of one or more 3d electrons, usually unpaired, results in paramagnetic and colored compounds. All compounds of vanadium having unpaired electrons are colored, but because the absorption spectra may be complex, a specific color does not necessarily correspond to a particular oxidation state. As an illustration, vanadium(IV) oxy salts are generally blue, whereas vanadium(IV) chloride is deep red. Differences over the valence range of 2—5 are shown in Table 2. The stmcture of vanadium compounds has been discussed (6,7). 

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. 

Conversion of fused pentoxide to alloy additives is by far the largest use of vanadium compounds. Air-dried pentoxide, ammonium vanadate, and some fused pentoxide, representing ca 10% of primary vanadium production, are used as such, purified, or converted to other forms for catalytic, chemical, ceramic, or specialty appHcations. The dominant single use of vanadium chemicals is in catalysts (see Catalysis). Much less is consumed in ceramics and electronic gear, which are the other significant uses (see Batteries). Many of the numerous uses reported in the Hterature are speculative, proposed. 

Action of catalytic amounts of vanadium compounds on oxaziridine (52) yields caprolactam almost quantitatively. Reductive opening of the oxaziridine ring and /3-scission yield radical (118), which recyclizes with elimination of the metal ion to form the lactam (63) (77JPR274). 

Examples of Vanadium Compounds Tested as Insulin Mimetic Agents. 

Since the discovery of hexacarbonylvanadium(O) and hexacarbonylvanadate( 1-) by Calderazzo and co-workers in 1959 and 1960, these substances have been key precursors to a variety of vanadium compounds, including inorganic noncarbonyl species, organovanadium complexes," and other vanadium carbonyls. Neutral V(CO)6 is of special interest in that it is the only isolable 17-electron homoleptic metal carbonyl and exhibits fascinating chemical properties that are often reminiscent of iodine and classic pseudohalogens. ... 

The element was recognized in 1831, when N. G. Sefstrom was able to isolate and characterize the oxide the name vanadium was derived from Vanadis, a goddess in Scandinavian mythology. The beautiful colours of vanadium compounds had been observed as early as 1801, by A. M. del Rio in his experiments with a new element he called erythronium because of the red colour after treatment with acid.1... 

Preparation of Vanadium.—There is no demand for pure vanadium, and the isolation of the metal is therefore not an industrial process. Even on the small scale the operation is attended with considerable difficulty, owing to the very high temperature necessary for the reduction of vanadium compounds and the tendency for reoxidation to take place. The following methods have given products of variable purity —... 

Physiological Action.—Vanadium compounds are poisonous when taken internally.1 The usual symptoms are paralysis, convulsions, lowering of the body temperature, and feeble pulse. The fatal dose in the case of a rabbit is between 0-00918 and 0-01466 gram. Workmen exposed to fumes of vanadium compounds, especially those engaged on ore-reduction plants, are said to be susceptible to vanadium poisoning, but this has been denied.2 Vanadium compounds have been shown... 

The general characteristics of vanadium compounds are outlined in Chapter I. 

The table on the next page summarises the various types of vanadium compounds known. 

Electrolytic reduction of pentavalent and tetravalent vanadium salts has frequently been employed for the preparation of vanadium compounds of lower valency.4 Bleecker5 has also prepared vanadium pentoxide and several vanadates electrolytically. 

The several oxides of vanadium have already been referred to in the section describing the general properties of vanadium compounds (see p. 80). They are set out in the table on p. 38. The thermal changes involved in their formation are discussed collectively on p. 32. 

Most of the toxic effects of vanadium compounds result from local irritation of the eyes and upper respiratory tract rather than systemic toxicity. The only clearly documented effect of exposure to vanadium dust is upper respiratory tract irritation characterized by rhinitis, wheezing, nasal hemorrhage, conjunctivitis, cough, sore throat, and chest pain. Case studies have described die onset of asthma after heavy exposure to vanadium compounds, blit clinical studies to date have not detected an increased prevalence of asthma in workers exposed to vanadium. 

The low-temperature polymerization of propylene has been performed with various types of vanadium compounds instead of V(acac)3. The results are summarized in Table 1. Vanadium compounds such as VC14, VOCl3, VO(acac)2 and VOCl2(acac) afford syndiotactic polypropylenes with rather broad MWDs, close to the most probable distribution (Mw/lVln = 2.0). At present, V(acac)3 is the sole vanadium compound being effective for the living polymerization of propylene. 

The effect of temperature on the association of vanadium compounds in asphaltenes was investigated by Tynan and Yen (1969). Using electron spin resonance (ESR), they observed both anisotropic and isotropic hyperfine structures of vanadium, interpreted as bound or associated and free vanadium, from asphaltenes precipitated for a Venezuelan petroleum and reintroduced to various solvents. Higher temperatures and more polar solvents resulted in a transition from bound to free vanadium, as shown in Fig. 12. At 282°C, only 1% of the anisotropic spectrum was observed. An activation energy of 14.3 kcal/mole was observed for the transition. 

Information relating to the diffusion of metal-bearing compounds in catalytic materials at reaction conditions has been obtained indirectly through classic diffusion and reaction theory. Shah and Paraskos (1975) calculated effective diffusitivities of 7 x 10-8 and 3 x 10-8 cm2/sec for V and Ni compounds in reduced Kuwait crude at 760°F. These low values may be indicative of a small-pore HDS catalyst. In contrast, Sato et al. (1971) report that the effective diffusivity of vanadium compounds was one-tenth that of the nickel compounds on the basis of metal deposition profiles in aged catalysts. This large difference may be influenced by relative adsorption strengths not explicitly considered in their analysis. 

Yang, X., K. Wang, J. Lu, and D.C. Crans. 2003. Membrane transport of vanadium compounds and the interaction with the erythrocyte membrane. Coord. Chem. Rev. 237 103-111. 

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