Double vanadates

Other double vanadates which have been prepared are ... 

Many of the naturally occurring ores of vanadium have also the composition of double vanadates (see table on p. 11). 

Acid Vanadous Sulphates and double vanadous sulphates.—Electrolytic reduction of solutions of vanadyl sulphate, V0S04, has given two green, crystalline, acid vanadous sulphates, according to the amount of sulphuric acid also added ... 

Carnotite is a double vanadate of potassium and uranium, of probable composition K2(U02)2(V04)2.8H30,2 but generally very impure with silica. It occurs as a yellow crystalline powder, or in loosely cohering masses, chiefl in Colorado and Utah, but also in South Australia and Portugal. The mineral has attained considerable importance in America as a source of uranium and radium. 

Bismuth Orthovanadate, BiV04, is a bright yellow compound obtained by the double decomposition of bismuth nitrate with an alkali vanadate.4... 

Pyrovanadates, R 4V207 or 2R a0.Va05.—The alkali pyrovana-dates are prepared by dissolving the equivalent quantity of vanadium pentoxide in solutions of alkalis, or by the spontaneous decomposition in solution of the alkali orthovanadates. Pyrovanadates of other metals are obtained by fusing vanadium pentoxide with the salts or hydroxides of the metals in molecular proportions, or, when they are sufficiently insoluble, by double decomposition between an alkali pyro-vanadate and a salt of the metal required. 

Double Salts of Vanadyl Sulphite.—By the action of sulphur dioxide on vanadates in the presence of varying molecular proportions of alkali sulphites, two series of alkali vanadyl sulphites have been obtained. 

Potassium Vanadicyanide, K3[V(CN)6], is prepared by the addition of excess of concentrated potassium cyanide solution to a concentrated solution of vanadous chloride, VC18 precipitation in the cold with alcohol gives rise to small rhombohedral plates. The solution is not very stable and rapidly becomes turbid, while addition of an acid produces the green colour which is characteristic of the V ion. The complex ion [V(CN)8]" appears, therefore, to be unstable, unlike the corresponding [Fe(CN)e] ", [Cr(CN)J ", and [Co(CN)e] " complex ions. The solution reacts with salts of heavy metals to yield variously coloured precipitates of double cyanides.7... 

Double Salts of Vanadous Thiocyanate.—When vanadous sulphate, V2(S04)3, in solution, is treated with barium thiocyanate, a green solution8 is obtained which is believed to contain vanadous thiocyanate, V(SCN)g, but attempts to isolate this compound have not met with success. Its double salts with the alkali thiocyanates have, however, been obtained in well-defined crystals when an alkali thiocyanate is substituted for the barium salt. The following are known —... 

Ulibarri, M. A., Labajos, F. M., Rives, V., Trujillano, R., Kagunya, W. and Jones, W. (1994). Comparative-study of the synthesis and properties of vanadate-exchanged layered double hydroxides. Inorg. Chem. 33, 2592. 

S. oneidensis cells pre-grown on fumarate exhibit a pronounced ability to use vanadate as an electron acceptor. Formate and, in particular, lactate are employed as electron sources. Under optimal conditions, ca 16 mM of vanadate is reduced per gram of bacteria per hour, with a biomass doubling time of 10( 1) the absolute yield being... 

Coumingine is a tertiary base, somewhat weaker than cassaine or cas-saidine. It is readily soluble in most organic solvents except hexane and ether. It does not give a color reaction with sulfuric acid, but with sulfo-vanadic acid it gives a pale green solution. It does not form an acetyl derivative, but a monoxime (m.p. 165°) can be obtained. A readily reducible double bond is in conjugation with the carboxyl, and dihydrocou-mingine melts at 95-96° ([ ] —8° (ethanol)) and forms a crystalline hydrochloride (m.p. 160-162°). 

Camotite is a potassium uranyl vanadate, K2O.2UO3.V2O5.11H2O. Since the uranium is in the fully oxidized condition, leaching can usually be carried out without an oxidant, at a particle size of about 100 mesh. The vanadium dissolves on leaching, to sodium vanadate, and the uranium forms a soluble double carbonate. The reaction may be represented approximately as ... 

The first step in the base-catalyzed condensation is the proton abstraction of active methylene groups with base catalysts, followed by attack of the anion on a carbonyl moiety. Elimination of water then produces the CMD double bond. Numerous heterogeneous catalysts have been reported to promote these condensations, including the rehydrated hydrotalcites described above for the Aldol reactions (41,51), vanadate apatite (52), and amine-functionalized silica (53). The merits of using these heterogeneous catalysts are the ease of product isolation and catalyst reusability, which is associated with elimination of the necessity to neutralize homogeneous bases such as NaOH and NaOMe. 

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