Vanadates, synthesis

Rearrangement of dehydrolinalool (4) using vanadate catalysts produces citral (5), an intermediate for Vitamin A synthesis as well as an important flavor and fragrance material (37). Isomerization of the dehydrolinalyl acetate (6) in the presence of copper salts in acetic acid followed by saponification of the acetate also gives citral (38,39). Further improvement in the catalyst system has greatly improved the yield to 85—90% (40,41). 

The charge densities and compositions of many known solids with VxOy layers were screened for possible charge density matches with M(pyz)x (M = Fe, Co, Ni, Cu, Zn) layers [35, 52], as an aid in the synthesis of new heterometallic multilayered vanadates. Close matches were found with M(pyz)x (M = Fe, Co, Ni) coordination polymers, ranging from 0.022/A -0.053/A, and which might suitably form in the presence of the flexible types of V2O5 layers. For example, Co(pyz) layers of chains in Co(pyz)(V03)2 [53] have a charge density of... 

Vniios A process for catalytically pyrolyzing hydrocarbons to low molecular weight alkenes, similar to catalytic cracking but more efficient. The catalyst is either potassium vanadate on corundum or indium oxide on pumice. Developed by the All-Union Research Institute for Organic Synthesis, Moscow. 

It was discovered nearly 20 years ago that V(V) as vanadate and V(IV) as vanadyl can mimic some of the effects of insulin (stimulate glucose uptake and oxidation and glycogen synthesis) (512, 513). Vanadate is an effective insulin mimetic in the diabetic rat (514), but has proved to be too toxic for human use. Vanadyl, as VOS04, is also unsuitable because high doses are needed on account of its poor oral absorption. Vanadium complexes with organic ligands have proved to be less toxic and can have improved aqueous solubility and lipophil-icity. 

Fotiev, A. Slobodin, B. V. Hodos, M. Y. Vanadates, their Synthesis, Composition and Properties, Nauka Moscow (in Russian), 1988. 

Fotiev, A. A. Ivakin, A. A. Vanadates of Divalent Metals and their Synthesis. Sverdlovsk (in Russian), 1970. 

Although a variety of synthesis, compositions and reactor parameters were studied, the P-V-0 catalysts in the temperature series were synthesized in the up flow HTAD reactor using a 0.12 M solution of anunonium vanadate in water which contained the required amount of 85% phosphoric acid to result in a 1.2/1.0 P/V atom ratio. This atom ratio is normally preferred for the most selective oxidation of butane to maleic anhydride. Table I shows that the P/V atom ratios obtained for the analyzed, finished (green colored) catalysts were approximately the same as the feed composition when a series of preparations were studied between 350 C and 800°C. This was typical for all of the catalysts synthesized under a variety of conditions. 

The synthesis of the title compositions has been selected as representative of compounds that can readily be prepared by the flux-reaction technique. In this technique, a halide melt serves both as a flux and as a constituent component of the basic reaction. The procedure has been described in the literature1 and has served for the preparation of a variety of ternary oxides, usually in the form of small, well-defined, single crystals. The halide phosphates and vanadates of strontium represent the apatite and spodiosite structures, both interesting compositions from a biochemical and solid-state point of view. 

VO(OR)3 — the alkoxides of vanadyl (V) or otherwise the esters of vanad-ic acid — belong to the most easily available derivatives and can be easily purified by distillation under low vacuum. The synthesis of these derivatives — from ethoxide to t-amyloxide—via alcoholysis of V2Os was first described at the beginning ofthe twentieth century by Prandtl and Hess [1313,743], The same work contained the first description ofthe hydrolysis of VO(OR)3, which laid basis for the numerous studies of the processes of formation of sols and gels of vanadic acid. The studies of the low-valent derivatives of vanadium that are very sensitive to oxidation were started in the 1960s by the works of Bradley on V(OR)4 and V(OR)3 [226]. The preparation, structure, and magnetic properties of vanadium(II) alkoxides were investigated only quite recently. 

Qi, Y.-F., Li, Y.-G., Wang, E. et al. (2007) Hydrothermal synthesis and structures of organic-inorganic hybrid solids based on arsenic-vanadate building blocks. Journal of Coordination Chemistry, 60(13), 1403-18. 

A similiar approach was performed by van de Velde (1999), using incorporation of vanadate into an acid phosphatase (phytase) to create a semi-synthetic peroxidase similar to the heme-dependent chloroperoxidase. The latter is a useful enzyme for the asymmetric epoxidation of olefins, but less stable due to oxidation of the porphyrin ring and difficult to express outside the native fungal host. The authors exploited the structural similarity of active sites from vanadate-dependent halo-peroxidases and acid phosphatases and have shown the useful application as an enantioselective catalyst for the synthesis of chiral sulfoxides (van de Velde, 1999). 

Alkyl hydroperoxides, including ethyl hydroperoxide, cuminyl hydroperoxide, and tert-butyl hydroperoxide, are not used by V-BrPO to catalyze bromination reactions [29], These alkyl hydroperoxides have the thermodynamic driving force to oxidize bromide however, they are kinetically slow. Several examples of vanadium(V) alkyl peroxide complexes have been well characterized [63], including [V(v)0(OOR)(oxo-2-oxidophenyl) salicylidenaminato] (R = i-Bu, CMe2Ph), which has been used in the selective oxidation of olefins to epoxides. The synthesis of these compounds seems to require elevated temperatures, and their oxidation under catalytic conditions has not been reported. We have found that alkyl hydroperoxides do not coordinate to vanadate in aqueous solution at neutral pH, conditions under which dihydrogen peroxide readily coordinates to vanadate and vanadium( V) complexes (de la Rosa and Butler, unpublished observations). Thus, the lack of bromoperoxidase reactivity with the alkyl hydroperoxides may arise from slow binding of the alkyl hydroperoxides to V-BrPO. 

Zhang, B., S. Zhang, and K. Wang. 1996. Synthesis, characterization and crystal structure of cyclic vanadate complexes with monosaccharide derivatives having a free adjacent diol system. J. Chem. Soc., Dalton Tram. 3257-3263. 

Rath, S.P., K.K. Rajak, S. Mondal, and A. Chakravorty. 1998. Synthesis and structure of vanadate esters of glycerol and propane-1,3-diol. J. Chem. Soc., Dalton Trans. 2097-2101. 

Sergienko, V.S., V.K. Borzunov, and A.B. Illyukhin. 1995. Synthesis and crystal and molecular structure of dioxobis(pyridine-2-carboxylato)vanadate(V) ammonium dihydrate, NH4[V02(pic)2] 2H20 A rare exception to the self-consistency rule. Russ. J. Coord. Chem. 21 107. 

Djordjevic, C., M. Lee, and E. Sinn. 1989. Oxoperoxo(citrato)vanadates(V) Synthesis, spectra, and structure of a hydroxyl oxygen bridged dimer, K2rV0(02)(C6H607)] 2H20. Inorg. Chem. 28 719-723. 

Sharma, S., M. Panthoefer, M. Jansen, and A. Ramanan. 2005. Ion exchange synthesis of silver vanadates from organically templated layered vanadates. Mat. Chem. and Physics. 91 257-260. 

Sharma, S., A. Ramanan, and M. Jansen. 2004. Hydrothermal synthesis of new organically intercalated layered vanadates. Solid State Ionics. 170 93-98. 

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. 

It has been reported that vanadate(V) enhances the stimulatory effects of insulin on DNA synthesis in cultured mammary gland cells of mice103 . Vanadate(V) in the absence of insulin has little effect. Insulin and vanadate(V) act as comitogens. The reported experiments do not preclude the possibility that vanadyl(IV) is the form of vanadium responsible for these effects. Vanadate(V) has also been reported to be an epidermal growth factor stimulating DNA synthesis104. ... 

Lowered levels of cholesterol, triglycerides, and phospholipid biosynthesis due to vanadium were discovered several years ago (see Refs. 3,4, and 14). It has recently been found that vanadate(V) at concentrations of 1 mM inhibits mevalonate synthesis, the rate limiting step in cholesterol biosynthesis159. In this instance the active form of the metal may be vanadyl(IV). 

Sodium and potassium vanadates. The authors [68] investigated mechanochemical synthesis of sodium and potassium decavanadates starting from V Oj and conesponding carbonates or metavanadates. They have shown that varying the initial ratio of components and the time of mechanical activation of the mixtures, the synthesis of different vanadates, including decavanadates, occurs, characterized by high rate of reactions. 

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