Vanadium catalysis

The asymmetric oxidation of sulphides to chiral sulphoxides with t-butyl hydroperoxide is catalysed very effectively by a titanium complex, produced in situ from a titanium alkoxide and a chiral binaphthol, with enantioselectivities up to 96%342. The Sharpless oxidation of aryl cinnamyl selenides 217 gave a chiral 1-phenyl-2-propen-l-ol (218) via an asymmetric [2,3] sigmatropic shift (Scheme 4)343. For other titanium-catalysed epoxidations, see Section V.D.l on vanadium catalysis. 

Vanadium catalysis mostly by cationic diene coupling metallocene by end group copolymerization can be controlled (information available from manufacturers)... 

Table II. t-Bu02H + Nucleophiles Alone and with Vanadium Catalysis...

The atroposelective construction of the 6,6 -biaryl linkage was recognized as the key step in the synthesis of viriditoxin. Although many atroposelective couplings of complex molecules have been completed and have been the subject of many reviews,most of these approaches relied on either proximal stereogenic centers or covalently linked chiral auxiliaries. Our objective was to explore the influence of distal chiral centers on the catalytic oxidative dimerization of naphthopyran-2-ones using vanadium catalysis (Scheme 7). Assembly of naphthopyran-2-ones has been well studied and recently reviewed." The Staunton-Weinreb annulation or the Michael-Dieckmann condensation is ideally suited for the rapid... 

The copolymers of ethylene and propylene (OCVP) are obtained by coordination catalysis using a derivative of vanadium and a derivative of an aluminum alkyl. Molar compositions of ethylene and propylene are usually on the order 45 and 55%. 

Other compounds which may be found in crude oil are metals such as vanadium, nickel, copper, zinc and iron, but these are usually of little consequence. Vanadium, if present, is often distilled from the feed stock of catalytic cracking processes, since it may spoil catalysis. The treatment of emulsion sludges by bio-treatment may lead to the concentration of metals and radioactive material, causing subsequent disposal problems. 

Conversion of fused pentoxide to alloy additives is by far the largest use of vanadium compounds. Air-dried pentoxide, ammonium vanadate, and some fused pentoxide, representing ca 10% of primary vanadium production, are used as such, purified, or converted to other forms for catalytic, chemical, ceramic, or specialty appHcations. The dominant single use of vanadium chemicals is in catalysts (see Catalysis). Much less is consumed in ceramics and electronic gear, which are the other significant uses (see Batteries). Many of the numerous uses reported in the Hterature are speculative, proposed. 

When heated in the presence of a carboxyHc acid, cinnamyl alcohol is converted to the corresponding ester. Oxidation to cinnamaldehyde is readily accompHshed under Oppenauer conditions with furfural as a hydrogen acceptor in the presence of aluminum isopropoxide (44). Cinnamic acid is produced directly with strong oxidants such as chromic acid and nickel peroxide. The use of t-butyl hydroperoxide with vanadium pentoxide catalysis offers a selective method for epoxidation of the olefinic double bond of cinnamyl alcohol (45). 

The most popular SCR catalyst formulations are those that were developed in Japan in the late 1970s comprised of base metal oxides such as vanadium pentoxide [1314-62-1J, V20, supported on titanium dioxide [13463-67-7] Ti02 (1). As for low temperature catalysts, NO conversion rises with increasing temperatures to a plateau and then falls as ammonia oxidation begins to dominate the SCR reaction. However, peak conversion occurs in the temperature range between 300 and 450°C, and the fah-off in NO conversion is more gradual than for low temperature catalysis (44). 

Attenlion should be drawn to ihe use of tin oxide systems as heterogeneous catalysts. The oldest and mosi extensively patented systems are the mixed lin-vanadium oxide catalysis for the oxidation of aromatic compounds such as benzene, toluene, xylenes and naphthalene in the. synthesis of organic acids and acid anhydride.s. More recenily mixed lin-aniimony oxides have been applied lo the selective oxidaiion and ammoxidaiion of propylene to acrolein, acrylic acid and acrylonilrile. 

The newer process uses a solid catalyst for reaction (19). Either finely divided platinum or vanadium pentoxide, V205, is effective. Because catalysis occurs where the gas contacts the surface of the catalyst, this process is called the contact process. 

Togni A., Pastor S. D. Cooperativity of Chirality in Homogeneous Catalysis The Gold(I)-Catalyzed Aldol Reaction and the Vanadium(IV)-Catalyzed Hetero-Diels-Alder Cycloaddition Chirality 1991 3 331-340... 

The presence of V V on the surface before catalysis is unessential for catalytic activity. We cannot however rule out an SCR redox mechanism involving VV-V V. ESR and IR results show that the oxidation state of surface vanadium at the reaction temperature is controlled mainly by the composition of the reactant mixture. 

Shiny silvery metal that is relatively soft in its pure form. Forms a highly resistant oxide coat. Used mainly in alloys, for example, in construction steel. Tiny amounts, in combination with other elements such as chromium, makes steel rustproof and improves its mechanical properties. Highly suited for tools and all types of machine parts. Also applied in airplane turbines. Chemically speaking, the element is of interest for catalysis (for example, removal of nitric oxides from waste gases). Vanadium forms countless beautiful, colored compounds (see Name). Essential for some organisms. Thus, natural oil, which was formed from marine life forms, contains substantial unwanted traces of vanadium that need to be removed. 

In the bulk form, vanadium oxides display different oxidation states and V—O coordination spheres and exhibit a broad variety of electronic, magnetic, and structural properties [96, 97], which make these materials attractive for many industrial applications. Prominent examples range from the area of catalysis, where V-oxides are used as components of important industrial catalysts for oxidation reactions [98] and environment pollution control [99], to optoelectronics, for the construction of light-induced electrical switching devices [100] and smart thermo-chromic windows. In view of the importance of vanadium oxides in different technological applications, the fabrication of this material in nanostructured form is a particularly attractive goal. 

The question about the competition between the homolytic and heterolytic catalytic decompositions of ROOH is strongly associated with the products of this decomposition. This can be exemplified by cyclohexyl hydroperoxide, whose decomposition affords cyclo-hexanol and cyclohexanone [5,6]. When decomposition is catalyzed by cobalt salts, cyclohex-anol prevails among the products ([alcohol] [ketone] > 1) because only homolysis of ROOH occurs under the action of the cobalt ions to form RO and R02 the first of them are mainly transformed into alcohol (in the reactions with RH and Co2+), and the second radicals are transformed into alcohol and ketone (ratio 1 1) due to the disproportionation (see Chapter 2). Heterolytic decomposition predominates in catalysis by chromium stearate (see above), and ketone prevails among the decomposition products (ratio [ketone] [alcohol] = 6 in the catalytic oxidation of cyclohexane at 393 K [81]). These ions, which can exist in more than two different oxidation states (chromium, vanadium, molybdenum), are prone to the heterolytic decomposition of ROOH, and this seems to be mutually related. 

The reaction of olefin epoxidation by peracids was discovered by Prilezhaev [235]. The first observation concerning catalytic olefin epoxidation was made in 1950 by Hawkins [236]. He discovered oxide formation from cyclohexene and 1-octane during the decomposition of cumyl hydroperoxide in the medium of these hydrocarbons in the presence of vanadium pentaoxide. From 1963 to 1965, the Halcon Co. developed and patented the process of preparation of propylene oxide and styrene from propylene and ethylbenzene in which the key stage is the catalytic epoxidation of propylene by ethylbenzene hydroperoxide [237,238]. In 1965, Indictor and Brill [239] published studies on the epoxidation of several olefins by 1,1-dimethylethyl hydroperoxide catalyzed by acetylacetonates of several metals. They observed the high yield of oxide (close to 100% with respect to hydroperoxide) for catalysis by molybdenum, vanadium, and chromium acetylacetonates. The low yield of oxide (15-28%) was observed in the case of catalysis by manganese, cobalt, iron, and copper acetylacetonates. The further studies showed that molybdenum, vanadium, and... 

Another interesting asymmetric epoxidation technique using metal catalysis involves the vanadium complexes of A-hydroxy-[2.2]paracyclophane-4-carboxylic amides (e.g., 19), which serve as catalysts for the epoxidation of allylic alcohols with f-butyl hydroperoxide as... 

The chapters for niobium and tantalum in COMC (1982) and COMC (1995) provide an in-depth discussion concerning complexes of these metals as well as their applications to catalysis.172 173 Alkylcyclopentadienyl complexes of niobium and tantalum have also been reviewed.1 Similarly to vanadium (Section 10.09.4.1.2), the... 

In furnaces using residual oils, heterogeneous catalysis is a possible route for the conversion of S02 to S03. Sulfur dioxide and molecular oxygen will react catalytically on steel surfaces and vanadium pentoxide (deposited from vanadium compounds in the fuel). Catalytic reactions may also occur at lower temperatures where the equilibrium represented by reaction (8.94) favors the formation of S03. 

Al-Shamma, E., Naman, S.A. 1989. Kinetie study for thermal production of hydrogen from H S by heterogeneous catalysis of vanadium sulfide in a flow system. Int J Hydrogen Energy 14 173-179. 

Although much of the V NMR has been performed on model systems or catalytic materials containing vanadium, 29 >30 compounds such as V2O5 or VOPO4 are used in both the catalysis and lithium battery fields, and many of the results can be used to help elucidate the structures of vanadium-containing cathode materials. V NMR spectra are sensitive to changes in the vanadium coordination number and distortions of the vanadium local environments from regular tetrahedra or octahedra. >33 5>V isotropic chemical shifts of between —400 and —800 ppm are seen for vanadium oxides, and unfortunately, unlike... 

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