Vanadium(V) oxide

Reduction to lower oxides Upon heating a mixture of vanadium(V) oxide and vanadium(III) oxide, comproportionation occurs to give vanadium(IV) oxide, as a deep-blue solid: :V2O5 + V2O3 → 4 VO2 The reduction can also be effected by oxalic acid, carbon monoxide, and sulfur dioxide. Further reduction using hydrogen or excess CO can lead to complex mixtures of oxides such as V4O7 and V5O9 before black V2O3 is reached. Acid-base reactions V2O5 is an amphoteric oxide, and unlike most transition metal oxides, it is slightly water soluble, giving a pale yellow, acidic solution. Thus V2O5 reacts with strong non-reducing acids to form solutions containing the pale yellow salts containing dioxovanadium(V) centers: :V2O5 + 2 HNO3 → 2 VO2(NO3) + H2O It also reacts with strong alkali to form polyoxovanadates, which have a complex structure that depends on pH. If excess aqueous sodium hydroxide is used, the product is a colourless salt, sodium orthovanadate, Na3VO4. If acid is slowly added to a solution of Na3VO4, the colour gradually deepens through orange to red before brown hydrated V2O5 precipitates around pH 2. These solutions contain mainly the ions and between pH 9 and pH 13, but below pH 9 more exotic species such as and (decavanadate) predominate. Upon treatment with thionyl chloride, it converts to the volatile liquid vanadium oxychloride, VOCl3: :V2O5 + 3 SOCl2 → 2 VOCl3 + 3 SO2 Other redox reactions Hydrochloric acid and hydrobromic acid are oxidised to the corresponding halogen, e.g., :V2O5 + 6 HCl + 7 H2O → 2 [VO(H2O)5]2+ + 4 Cl− + Cl2 Vanadates or vanadyl compounds in acid solution are reduced by zinc amalgam through the colourful pathway: The ions are all hydrated to varying degrees. ==Preparation==

Technical grade V2O5 is produced as a black powder used for the production of vanadium metal and ferrovanadium. :2 NH4VO3 → V2O5 + 2 NH3 + H2O ==Uses==

Ferrovanadium production In terms of quantity, the dominant use for vanadium(V) oxide is in the production of ferrovanadium (see above). The oxide is heated with scrap iron and ferrosilicon, with lime added to form a calcium silicate slag. Aluminium may also be used, producing the iron-vanadium alloy along with alumina as a byproduct. Sulfuric acid production Vanadium(V) oxide is used as the oxygen-transfer catalyst in the contact process, the only process now used for the industrial production of sulfuric acid. The catalyst phase is a molten salt formed from vanadium(V) oxide and added alkali metal sulfates acting as co-catalysts. In this melt, the reactive complex [(VO)2O(SO4)4]4−, which is regarded as the actual catalytic species, is formed. Oxygen and sulfur dioxide coordinate to this complex and react to form sulfur trioxide without a change in the oxidation state of vanadium. Maleic anhydride is produced by the V2O5-catalysed oxidation of butane with air: :C4H10 + 4 O2 → C2H2(CO)2O + 8 H2O Maleic anhydride is used for the production of polyester resins and alkyd resins. Phthalic anhydride is produced similarly by V2O5-catalysed oxidation of ortho-xylene or naphthalene at 350–400 °C. The equation for the vanadium oxide-catalysed oxidation of o-xylene to phthalic anhydride: :C6H4(CH3)2 + 3 O2 → C6H4(CO)2O + 3 H2O The equation for the vanadium oxide-catalysed oxidation of naphthalene to phthalic anhydride: :C10H8 + O2 → C6H4(CO)2O + 2 CO2 + 2 H2O Phthalic anhydride is a precursor to plasticisers, used for conferring pliability to polymers. A variety of other industrial compounds are produced similarly, including adipic acid, acrylic acid, oxalic acid, and anthraquinone. Vanadium oxide is also used as a cathode in lithium-ion batteries. Vanadium pentoxide is often used as a component in glazes where it produces a wide range of colours from greens and yellows to blues and grays. ==Biological activity==

Vanadium(V) oxide exhibits very modest acute toxicity to humans, with an of about 470 mg/kg. The greater hazard is with inhalation of the dust, where the LD50 ranges from 4–11 mg/kg for a 14-day exposure. Vanadate (), formed by hydrolysis of V2O5 at high pH, appears to inhibit enzymes that process phosphate (). However the mode of action remains elusive. ==References==