Vanadium compounds synthesis

This chapter summarizes results obtained during the past 5 years, on the design, preparation and study of titanium and vanadium compounds as candidate precursors to TiC, TiN, VC, and VN. The study of the precursor molecules was conducted through several steps. After their synthesis, thermoanalytical studies (TG-DTA), coupled to simultaneous mass spectroscopic (MS) analysis of the decomposition gases, were carried out to determine their suitability as precursors. CVD experiments were then conducted and were followed by characterization of the deposits by scanning electron microscopy (SEM) energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electron microprobe analysis with wavelength dispersion spectroscopy (EPMA-WDS). 

The mechanism of vanadium interaction with growth and differentiation pathways has been extensively studied [70], In tissue culture systems, vanadium has been shown to inhibit growth and, in some cases, modify DNA synthesis to block the G2-to-M transition. Cells blocked at M phase are susceptible to apoptosis, which can be stimulated by vanadium compounds. Vanadium compounds have also been shown to have mitotic effects stimulating growth, cell proliferation, or cell transformation. In some cases, vanadium compounds were able to promote cellular differentiation. Clearly, the addition of vanadium compounds would not have all of these... 

New approaches to the synthesis of SVO cathode material have been reported. In 1995, Takeuchi and Thiebolt patented a new preparation for SVO cathodes prepared via addition of elemental silver to vanadium compounds present in an anhydrous mixture. Oxygen-deficient SVO compounds were found, as well as compounds designed to provide a desired shape in the electrical discharge curve of the cell [59], Following this work in 1996, Takeuchi and Thiebolt patented several methods for the preparation of amorphous SVO prepared by chemical addition reaction at temperatures high enough to melt the mixture, coupled with rapid cooling... 

This section describes the organovanadium compounds containing jj -cyclopentadienyl (Cp) or substituted (Cp ) ligands, which are classified into half-sandwich (see Halfsandwich Complexes), sandwich (see Sandwich Compound), bent sandwich (see Bent Metallocenes), and pseudo-triple decker derivatives. Cyclopentadienyl vanadium compounds are nsed for the synthesis of varions vanadium compounds as mentioned above. Generally, the oxidation state of the cyclopentadienyl vanadium complexes is Irom — 1 to -1-5. 

In the case of low-valent vanadium compounds, metathesis or hydrovanadation is used for the synthesis of organovanadium compounds. Treatment of vanadocene with halomethane results in the formation of the methyl-substituted halo-vanadocene (95) (Scheme 53). The dianion species (96) is similarly used for this purpose (Scheme 54). ... 

Isomerization of alkenes is catalyzed by bis(j7 -allyl)(jj -cyclopentadienyl)vanadium(IV). Cyclohexene nndergoes catalytic stereoselective aerobic oxidation with CpV(CO)4. Reductive coupling (see Reductive Coupling) of aldehydes and aldimines is catalyzed by a Cp-substituted vanadium compound in the presence of a chlorosilane and zinc or aluminum. Vanadocene or bis( ] -cyclopentadienyl)dimethylvanadium(IV) catalyzes the synthesis of 1,2-diphenyldisilane and 1,2,3-triphenyltrisilane from phenylsilane. ... 

In 1972 Bayer and Kneifel isolated (98) a pale blue compound from A. muscaria containing vanadium, which they named amavadine. They proposed (98,99) that it consisted of a complex of AT-hydroxyimino-a,a -dipropionic acid with in a 2 1 ratio. From a comparison of the EPR spectra of segments of frozen mushrooms with those of vanadyl complexes of various amino acids, it was concluded (100,101) that this proposal was not very likely. However, Krauss et al. (102) synthesized amavadine and compared its EPR properties with the complex extracted from the mushroom and concluded that it was the same. Others were unable to reproduce the synthesis (103), although models analogous to amavadine were reported. The synthesis of the ligand N-hydroxy-a,a -iminodipropionic acid, and related compounds was, however, later confirmed (104-106). The stereochemistry and total synthesis of the vanadium compound of A. muscaria has now been elucidated (107). 

In addition to the bulk industrial applications of vanadium oxides in preparation of maleic anhydride from n-butate, vanadium compounds have for some time been useful catalysts in organic synthesis. The number of contributions in this area has increased tremendously aided by key contributions from several synthetic groups (Hirao, Modena, Furia, Conte, Pedersen,... 

Of phenolic oxidations using vanadium compounds, intramolecular oxidative phenolcoupling reactions are quite attractive from the viewpoint of natural products synthesis. A number of benzylisoquinoline alkaloids, lignans and neolignans are well known to be produced, in a key step, by oxidative radical coupling of open phenolic precursors. 

Vanadium has numerous industrial uses such as the processing of steel, chemical production, polymer synthesis, ceramics and electronics production (Nriagu, 1997). As a catalyst, V is used in the contact process for the production of sulfuric acid and a variety of organic reagents. Vanadium compounds are also used as mordants in dyeing and printing of cotton and silk (Nriagu, 1997). Because of the multiplicity of sources, the concentrations of vanadium in municipal wastewaters vary widely, from <1.0 to over 3000/rg/l (Blackmore et al, 1996 Adriano, 2001). 

H. Kneifel and E. Bayer, Stereochemistry and total synthesis of amavadin, the naturally occuring vanadium compound of kmanltd mu6CaKla, J.Am.Chem.Soc. 108 (1986) 3075-3077. 

Kneifel, H., and E. Bayer Stereochemistry and Total Synthesis of Amavadin, the Naturally Occurring Vanadium Compound of Amanita muscaria. J. Amer. Chem. Soc. 108, 3075 (1986). 

Vanadium-based catalytic systems for EP(D)M synthesis are comprised of a vanadium compound ( catalyst precursor ), a chlorinated aluminum alkyl ( cocatalyst ), and a chlorinated ester ( promoter ). Typical components of a vanadium-based catalytic system are the following ... 

Titanium-based TiC /AlRs (R = Me, Et, i-Bu) catalysts produce PI with high trans contents (>85%). However, the most active and stereoselective systems for the synthesis of trans-, A-polyisoprene are those based on vanadium compounds. Vanadium halides and mixtures of vanadium and titanium halides, in combination with aluminum alkyls, give high trans-1,4-polyisoprene ( 90%).i ... 

Parallel to the use of FeCU, the promoting effect of vanadium compounds (especially VOCI3 and VOCI2) has been developed. An early patent reports the synthesis of diethyl 2,4-toluendiearbamate in 76 % yield by carbonylation with a catalytic system composed of PdCb, VOCls and pyridine (molar ratios DNT/Pd = 133, V/Pd = 17.3, and VyN = 6.15) at 160 °C and 35 bar CO for 100 min... 

Oxides and oxohalides of transition metals (vanadium, chromium, molybdeniim, tungsten) stabilized by ir-aromatic ligands such as the unique cyclopentadienyl ligand have been observed from time to time for more than 20 years. Thus, the Munich laboratory of E.O. Fischer reported on the synthesis of the vanadium compounds (ti -C5H5)V0X2 (X = Cl, Br) in 1958 [18], before Cousins and Green [19] synthesized related... 

The second type of solution polymerization concept uses mixtures of supercritical ethylene and molten PE as the medium for ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization in supercritical ethylene at high pressure (see Olefin POLYMERS,LOW DENSITY polyethylene) were converted for the catalytic synthesis of LLDPE. Both stirred and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C can also be used for this purpose. Residence times in these reactors are short, from 1 to 5 minutes. Three types of catalysts are used in these processes. The first type includes pseudo-homogeneous Ziegler catalysts. In this case, all catalyst components are introduced into a reactor as hquids or solutions but form soHd catalysts when combined in the reactor. Examples of such catalysts include titanium tetrachloride as well as its mixtures with vanadium oxytrichloride and a trialkyl aluminum compound (53,54). The second type of catalysts are soHd Ziegler catalysts (55). Both of these catalysts produce compositionaHy nonuniform LLDPE resins. Exxon Chemical Company uses a third type of catalysts, metallocene catalysts, in a similar solution process to produce uniformly branched ethylene copolymers with 1-butene and 1-hexene called Exact resins (56). 

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