Phosphoric acid, vanadium complex

Phosphoric acids form many auto- and hetero-complexes, in which respect they are similar to the acids of vanadium and its congeners, as well as those of silicon. Three degrees of hydration, known as ortho-, pyro- and meta-, are also found, with certain differences, with other members of Group V. 

The diphenylcarbazide method is almost specific for chromium(Vl). Interferences result only from Fe, V, Mo, Cu, and Hg(II) present at much higher concentrations than the chromium. Iron(lll) can be masked by phosphoric acid or EDTA. Iron(III) can also be separated as Fe(OH>3, after chromium has been oxidized to Cr(VI), or by extraction. Vanadium can be separated from Cr(VI) by extraction as its oxinate at pH -4. Molybdenum is masked with oxalic acid, and Hg(II) is converted into the chloride complex. 

Extraction of the molybdenum complex with a-benzoinoxime (formula 31.1) into CHCI3, from 0.01-2 M HCl is a selective method for separating molybdenum [1 ]. Under the conditions employed in the extraction of the molybdenum a-benzoinoxime complex Mo, Mo02(C 4H 202N)2, only W, V, Cr, and Pd are also extracted. Tungsten and vanadium are not extracted in the presence of phosphoric acid and Fe(II). 

Twenty per cent TBF dissolved In kerosene was used as extractant. The partition coefficient, increases with Increased TBF concentration. Increases with increased pH, and decreases with increased sulfate concentration. Vanadium and Iron (ill) are appreciably extracted by TBP from thiocyanate solutions. Copper, titanium, cobalt are weakly extracted. Iron (ll), cadmium, molybdenum, magnesium and aluminum are essentially not extracted. Phosphate Ion may cause the precipitation of uranium or complex formation when present in large amounts. Okada, et al. report the extraction of uranium by TBP, mesityl oxide, and methyl ethyl ketone from phosphoric acid solutions having 20 times as much ammonium thiocyanate as uranium. 

In acidic solution, vanadium(V) exists as the univalent cation, V02. The hydrolytic behaviour of this ion is quite complex, forming a large number of monomeric and polymeric hydrolysis species. In this review, these species are related to reaction (2.5) (M = V02 ). Species with 1, 2, 4, 5 and 10 V02" molecules are believed to form, although other species have been reported. Once the univalent cation is hydrolysed as V020H(aq), or equivalently HjVOjfaq), the chemistry it displays is quite similar to that of the phosphate anion, in terms of its ability to form polymeric species and the strength of the various steps of dissociation of phosphoric acid. 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

Two studies have been made of the oxidation of hypophosphorous acid. In perchlorate media the rate law of the redox reaction is indicative of several vanadium(v)-phosphorous(i) complexes being kinetically... 

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