Vanadium, powder solution

To 325-mesh vanadium powder (3.87 g, 76.0 mmol) in a 250-mL round-bottomed flask equipped with a reflux condenser is added p-toluenesulfonic acid monohydrate (43.3 g, 228 mmol) and water (20 mL). The mixture is heated to reflux for 16 h. A deep purple solution is obtained, and some metal powder is still present. The mixture is filtered while hot through Celite and the purple filtrate concentrated to 10 ml. by vacuum distillation. The solution is cooled to room temperature, and large pale purple needles are deposited. The crystals are collected by filtration and dried overnight under vacuum at room temperature. Additional crops can be obtained from the filtrate by concentrating it to 5 mL by vacuum distillation, and then cooling the resulting solution to room temperature. Yield 23.0 g (45.1%). 

The vanadium pentoxide catalyst Is prepared as follows Suspend 5 g. of pure ammonium vanadate in 50 ml. of water and add slowly 7 5 ml. of pure concentrated hydrochloric acid. Allow the reddish-brown, semi-colloidal precipitate to settle (preferably overnight), decant the supernatant solution, and wash the precipitate several times by decantation. Finally, suspend the precipitate in 76 ml. of water and allow it to stand for 3 days. This treatment renders the precipitate granular and easy to 6lter. Filter the precipitate with suction, wash it several times with cold 5 p>er cent, sodium chloride solution to remove hydrochloric acid. Dry the product at 120° for 12 hours, grind it in a mortar to a fine powder, and heat again at 120° for 12 hours. The yield of catalyst is about 3 - 5 g. 

For solvent extraction of a tetravalent vanadium oxyvanadium cation, the leach solution is acidified to ca pH 1.6—2.0 by addition of sulfuric acid, and the redox potential is adjusted to —250 mV by heating and reaction with iron powder. Vanadium is extracted from the blue solution in ca six countercurrent mixer—settler stages by a kerosene solution of 5—6 wt % di-2-ethyIhexyl phosphoric acid (EHPA) and 3 wt % tributyl phosphate (TBP). The organic solvent is stripped by a 15 wt % sulfuric acid solution. The rich strip Hquor containing ca 50—65 g V20 /L is oxidized batchwise initially at pH 0.3 by addition of sodium chlorate then it is heated to 70°C and agitated during the addition of NH to raise the pH to 0.6. Vanadium pentoxide of 98—99% grade precipitates, is removed by filtration, and then is fused and flaked. 

For vanadium solvent extraction, Hon powder can be added to reduce pentavalent vanadium to quadrivalent and trivalent Hon to divalent at a redox potential of —150 mV. The pH is adjusted to 2 by addition of NH, and an oxyvanadium cation is extracted in four countercurrent stages of mixer—settlers by a diesel oil solution of EHPA. Vanadium is stripped from the organic solvent with a 15 wt % sulfuric acid solution in four countercurrent stages. Addition of NH, steam, and sodium chlorate to the strip Hquor results in the precipitation of vanadium oxides, which are filtered, dried, fused, and flaked (22). Vanadium can also be extracted from oxidized uranium raffinate by solvent extraction with a tertiary amine, and ammonium metavanadate is produced from the soda-ash strip Hquor. Fused and flaked pentoxide is made from the ammonium metavanadate (23). 

Solutions to similar problems of achieving catalytic turnover [22] in McMurry couplings [23], Nozaki—Hiyama reactions [24], and pinacol couplings [25] have been reported by Fiirstner and by Hirao. The key step in these reactions is the in situ silylation of titanium and vanadium oxo species with Me3SiCl and reduction of the metal halides by suitable metal powders, e. g. zinc and manganese dust, as shown in Scheme 12.13. 

The BASF route started from hydroquinone, which was converted to 2,5-dihydroterephthalic acid by a Kolbe-Schmitt reaction. One mole of this acid was treated with two moles of an arylamine, both components being in the form of a suspension in aqueous methanol. This was added to a small amount of a solution of vanadium(III) chloride and sodium chlorate. Gentle heating gave a 95% yield of 2,5-bis(arylamino)benzo-l,4-quinone-3,6-dicarboxylic acid. Ring closure to the trans-quinacridonequinone took place in the presence of concentrated sulphuric acid at 60-80 °C. This was then reduced to the required crude pigment by zinc or aluminium powder in caustic soda under pressure,in an aluminium chloride/urea melt or by the use of a sulphuric acid/polyphosphoric acid mixture. 

Research related to the use of vanadium phosphates or V2O5 as oxidants of gases such as CO and SO2 in commercial processes shows that solid vanadyl sulfate can serve as a gas-permeable solid-phase electrolyte [102]. Two reversible redox features are observable at slow scan rates (20-150 mV s ) by CV in a gas-tight two-electrode cell packed with powdered VOSO4 3H2O between a 10-mm carbon disk and a 3-mm glassy carbon electrode. The V(IV/V) couple was observed at 0.55 V versus C, and the V(IV/III) couple was observed at —0.97 V. Unlike in aqueous solution where vanadyl sulfate is reduced to [V(H20)6] ", the V=0 bond in the solid remains intact. The oxidation of CO(g) can be observed when it is introduced into this cell. 

Vanadyl Dibromide, VOBr2, is obtained by passing bromine vapour or, preferably, a mixture of sulphur bromide, SaBra, and bromine over a mixture of vanadium pentoxide and sulphur at a red heat the product is heated in vacuo at 240° C., whereupon the vanadyl dibromide is obtained as a yellow powder.8 An alternative method of preparation consists in heating vanadium oxytribromide, VOBr3, to 180° C.9 Vanadyl dibromide is no doubt present in the blue solution which results when hypovanadic oxide, VOa, is dissolved in hydrobromic acid. 

V0.V205 is produced as a dark blue, crystalline powder when either vanadium pentoxide or ammonium metavanadate is heated with excess of powdered arsenic, or when ammonium metavanadate is reduced with sulphur dioxide at a red heat. It dissolves in nitric acid to a blue solution.8... 

Barium Pyrovanadate, BaaVaO is precipitated on addition of barium chloride to a solution of sodium pyrovanadate or of other vanadates in the presence of ammonia.3 It has more recently been prepared by the action of barium peroxide on vanadium pentoxide.4 It is a white, amorphous powder which melts above 868° C.5... 

Thallium Pyrovanadate, T14V20 is precipitated as a light yellow powder by the addition of thallium sulphate to a cold, saturated solution of sodium orthovanadate. It also results on fusing a mixture of vanadium pentoxide and thallium carbonate.14 It melts at 454°15 or 416° C.,16 and is soluble in about 5000 parts of water at 14° C. 

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... 

Vanadium Subnitride, VgN, is described as a black powder which is not attacked by hydrochloric acid or caustic potash solution. It is soluble in concentrated nitric and sulphuric acids, and evolves ammonia on being heated with solid caustic potash. 

Since the approximate charge on vanadium is +1 in the M.O. approximation, a value of the spin orbital coupling constant = 135 cm.-1 is taken for V+.30 The calculation then gives g = 1.983, gll — 1.940, with (g) — 1.969. This is in excellent agreement with the accurately known (g) = 1.962 value for aqueous solutions of VO2, 25-27 The measurements on powdered samples of the vanadyl sulfates also give (g) values in reasonable agreement with this calculation. 

---