Oxygen, reaction with vanadium

DR. JAKES ESPENSON (Iowa State University) Murmann s data [Murmann, R. K. Inorg. Chim. Acta 1977, 25 L43] on the exchange of the oxo oxygen of vanadium(IV) would certainly suggest that it would be possible to prove whether or not the oxygen was really transferred from perchlorate during its reaction with vanadium(II). Has that experiment actually been done ... 

Butane-Based Fixed-Bed Process Technology. Maleic anhydride is produced by reaction of butane with oxygen using the vanadium phosphoms oxide heterogeneous catalyst discussed earlier. The butane oxidation reaction to produce maleic anhydride is very exothermic. The main reaction by-products are carbon monoxide and carbon dioxide. Stoichiometries and heats of reaction for the three principal reactions are as follows ... 

Vanadium Carbide. Vanadium pentoxide [1314-62-17, V2O5, or vanadium trioxide [1314-34-7] VO3, are the most satisfactory oxides for the preparation of VC. Vanadium pentoxide is best prepared by igniting chemically pure ammonium vanadate [7803-55-6] NH VO, in the presence of moist oxygen to avoid reaction with nitrogen V2O3 is obtained by reduction of V2O3 with hydrogen (see Vanadium compounds). 

Sulfur dioxide combines with oxygen on heating and in the presence of a catalyst. This reaction proceeds at temperatures between 400 to 700°C with vanadium pentoxide catalyst to make sulfuric acid ... 

Table 17) with two substituents in position C3 the oxygen transfer by the chiral hydroperoxides occurred from the same enantioface of the double bond, while epoxidation of the (ii)-phenyl-substituted substrates 142c,g,i resulted in the formation of the opposite epoxide enantiomer in excess. In 2000 Hamann and coworkers reported a new saturated protected carbohydrate hydroperoxide 69b , which showed high asymmetric induction in the vanadium-catalyzed epoxidation reaction of 3-methyl-2-buten-l-ol. The ee of 90% obtained was a milestone in the field of stereoselective oxygen transfer with optically active hydroperoxides. Unfortunately, the tertiary allylic alcohol 2-methyl-3-buten-2-ol was epoxidized with low enantioselectivity (ee 18%) with the same catalytic system . 

In addition, the infrared examination of the mechanism of propane and oxygen interaction with the sample (Fig. 6) indicates the different mechanism of interaction of the intermediate propylene as compared to other supported vanadium catalysts such as V-Ti02 (10). In particular, the formation of a 7t-bonded complex stabilized by a nearlying silanol with weak basic character due to the inductive effect of vicinal vanadium is shown. This indicates the relative inertness of the V sites in the silicalite towards 0-insertion or allylic H-abstraction on the adsorbed propylene. It is evident that the reduced reactivity of V sites in these reactions limits the consecutive reactions of intermediate propylene, thus enhancing the selectivity in the formation of this product. 

The MR rate law relies on the assumption that the SCR reaction is governed by a redox mechanism and therefore predicts a kinetic dependence on oxygen. It has been derived assuming that (i) two types of sites for NH3 adsorption (acidic non-reducible sites) and for NO + NH3 activation/reaction (redox sites, associated with vanadium), respectively, prevail on the catalyst surface (ii) NH3 blocks the redox sites (iii) reoxidation of the redox sites is rate controlling. 

Vanadyl and nickel reactivity differences resulting from the chemistry of the oxygen ligand on vanadium were discussed in Section IV,A,l,c. Enhanced V reactivity could also arise from molecular size constraints. Beuther and co-workers (Beuther and Schmid, 1963 Larson and Beuther, 1966) speculate that nickel concentrates in the interior of asphaltene micelles while vanadium concentrates on the exterior. Thus a combination of stronger adsorption due to the oxygen ligand and inhibition of Ni reaction, coupled with the exposed position at the periphery of the asphaltene, may all contribute to the enhanced vanadium reactivity relative to nickel. 

Vanadium oxytrichloride is a lemon-yellow liquid. Its boiling point is 124.5°C. at 736 mm. and 127.16°C. at 760 mm. It remains liquid at —77°. The vapor pressure at —77° is 4.1 mm. at 0°, 21 mm. and at 85°C., 270 mm. Its density in grams per milliliter is 1.854 at 0° and 1.811 at 32°C. At ordinary temperatures, it neither dissolves nor reacts with carbon, hydrogen, nitrogen, oxygen, silicon, tellurium, or metals except the alkali metals and antimony. The reactions with the alkali metals are explosive at characteristic temperatures, varying from 30°C. for cesium to 180°C. for sodium (lithium not determined). Small... 

In 1983, Mimoun and co-workers reported that benzene can be oxidized to phenol stoichiometrically with hydrogen peroxide in 56% yield, using peroxo-vana-dium complex 1 (Eq. 2) [20]. Oxidation of toluene gave a mixture of ortho-, meta-and para-cresols with only traces of benzaldehyde. The catalytic version of the reaction was described by Shul pin[21] and Conte [22]. In both cases, conversion of benzene was low (0.3-2%) and catalyst turned over 200 and 25 times, respectively. The reaction is thought to proceed through a radical chain mechanism with an electrophilic oxygen-centered and vanadium-bound radical species [23]. 

Not many catalyzed processes involving free radicals are known with these metals. Some vanadium-catalyzed pinacol coupling reactions were developed (reviews [129, 171], [172, 173] and cited ref, [174]). Niobium and tantalum complexes were applied in pinacol coupling reactions [130]. Vanadium(IV) [175-179] and vanadium(V) ([129], reviews [180-186]) complexes are known to catalyze asymmetric oxidative dimerizations of phenols and naphthols in moderate to excellent ees applying oxygen as the terminal oxidant. Biaryls are accessible by intramolecular coupling of sodium tetraarylborates, catalyzed by EtOVOCl2 in the presence of air [187]. 

Sulphur trioxide S03 is obtained industrially as a route to sulphuric acid, by oxidising S02 with oxygen using a vanadium oxide catalyst. It can exist as a monomeric planar molecule but readily gives cyclic S309 trimers and linear polymers with corner-sharing S04 units. The highly exothermic reaction with... 

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