Oxidation vanadium-catalyzed

Son S, Toste FD (2010) Non-oxidative vanadium-catalyzed C-O hond cleavage appUcation to degradation of lignin model cmnpounds. Angew Chem Int Ed 49 3791... 

The mechanism by which the enantioselective oxidation occurs is generally similar to that for the vanadium-catalyzed oxidations. The allylic alcohol serves to coordinate the substrate to titanium. The tartrate esters are also coordinated at titanium, creating a chiral environment. The active catalyst is believed to be a dimeric species, and the mechanism involves rapid exchange of the allylic alcohol and /-butylhydroperoxide at the titanium ion. 

Gibbs A process for oxidizing naphthalene to phthalic anhydride, using air as the oxidant and catalyzed by vanadium pentoxide. Invented in 1917 by H. D. Gibbs and C. Conover. 

SCHEME 142. Vanadium-catalyzed oxidation of aromatic compounds using H2O2... 

Vanadium-catalyzed hydrocarbon oxidation with peroxides can be carried out also by supporting the catalyst with the appropriate ligand on polymers " , on sUica " or encapsulating it in zeolites ". Similar activity has been obtained with vanadium-containing... 

BUTYLPHENYL)METHYLENE]IMINE] AS A LIGAND FOR VANADIUM-CATALYZED ASYMMETRIC OXIDATION OF SULHDES. 293... 

BENZYL-4,6-O-ISOPROPYLIDENE-a-D-GLUCOPYRANOSIDE, 2-DEOXY-2-[[(2-HYDROXY-3,5-di-lerl-BUTYLPHENYL)METHYLENE]IMINE] AS A LIGAND FOR VANADIUM-CATALYZED ASYMMETRIC OXIDATION OF SULFIDES... 

SCHEME 146. Vanadium-catalyzed oxidation of cyclohexane with H202... 

The Rh-catalyzed reaction is more efficient than the vanadium-catalyzed process or stoichiometric oxidation with Cr03, but fails for benzene and naphthalene. 

From these results it seems that the epoxy alcohol, IX, does not arise via an intramolecular vanadium-catalyzed rearrangement of cyclohexenyl hydroperoxide, V. An alternative pathway is an intermolecular epoxida-tion reaction between the allylic hydroperoxide, V, and the allylic alcohol which is formed during the oxidation (Reaction 17). We found that IX was produced from reaction of V with VII in the presence of [C5H5V-... 

Oxides Vanadium monoxide VO, gray solid vanadium trioxide V2O3, black solid vanadium dioxide VO2, dark blue solid vanadium pentoxide V2O5, orange to red solid. The last is the most important oxide formed by the ignition in an of vanadium sulfide, 01 othei oxide, 01 vanadium used as a catalyzer, e.g., the reaction SO2 gas plus oxygen of air to form sulfur tnoxide. and the oxidation of naphthalene by air to form phthalie anhydride. 

Metalloenzymes contain a bound metal ion as part of their structure. This ion can either partidpate directly in the catalysis, or stabilize the active conformation of the enzyme. In Lewis acid catalysis (typically with zinc, vanadium, and magnesium), the M"+ ion is used instead of H+. Many oxidoreductases use metal centers such as V, Mo, Co, and Fe in much the same way as homogeneous catalysis uses ligand-metal complexes. Figure 5.7 shows a simplified mechanism for the halide oxidation readion catalyzed by vanadium chloroperoxidase. The vanadium atom ads as a Lewis add, activating the bound peroxide [30]. 

Rothenberg, G. and Clark, J.H. (2000) Vanadium-catalyzed oxidative bromination using dilute mineral acids and hydrogen peroxide an option for recycling waste acid streams. Org. Proce-ss Res. Dev., 4, 270. 

For the vanadium-catalyzed reaction, the involvement of radical species has been suggested [4], as shown in Scheme 4. The oxovanadium(V) species could abstract an H atom from CH4 to form the methyl radical CH3, which could react with CO to give the acetyl radical CH3CO. Oxidation of CH3CO to CH3CO+ by V(V)=0 would give acetic acid. 

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]. 

The molybdenum- and vanadium-catalyzed oxidation of sulfides to sulfoxides has also been described.417 477-480 In the presence of excess hydroperoxide, further oxidation to the sulfone occurs,477,480 e.g.,... 

It has recently been reported495 that the complex CsH5V(CO)4 (CSHS = cy-clopentadienyl) is an efficient catalyst for the stereoselective oxidation of cyclohexene to ris-l,2-epoxycyclohexane-3-ol in good yield (65% at 10% conversion). This high stereoselectivity is reminiscent of the highly selective vanadium-catalyzed epoxidations of allylic alcohols with alkyl hydroperoxides discussed earlier. The mechanism of reaction,... 

Scant attention has been paid to vanadium-catalyzed oxidation of alcohols, despite its ability to act according to the oxometal mechanism. Punniyamurthy recently reported that indeed vanadium turns out to be a remarkably simple and selective catalyst with a wide substrate scope, which requires few additives [212], albeit, the activities are still rather low. 

Among the first reports was the investigation of an iron-catalyzed oxidation system in 1997. ESI-MS was used to characterize the intermediate [Fe "-TPA(OOH)]2 in the stereospecific hydroxylation of alkanes by hydrogen peroxide (TPA, tris(2-pyridyl-methyl)amine) [35]. It is unique among oxidation reactions studied by ESI-MS in that all other reports address manganese- or vanadium-catalyzed systems. 

The few vanadium-based studies present in the literature are summarized briefly here and, as with the manganese systems, they focus on the identification of key Intermediates in vanadium-catalyzed oxidations. These cases readily Illustrate the importance of considering both the positive and negative ion modes of ESl-MS when probing reaction mixtures. 

In 2001, negative ion ESl-MS studies suggested that monoper-oxovanadium species are responsible for the vanadium-catalyzed oxidation of Isopropyl alcohol to acetone [30]. Fragmentation studies conducted In the gas phase showed loss of acetone from the species [0V(02)(0 Pr)2] (Fig. 2A, m/z 217), confirming that the reaction occurs within the Inner sphere of the metal. In a follow-up study, positive Ion ESl-MS lead to the observation of the intermediate [VO(OH2)(OH)(OBr)] " (Fig. 2B, m/z 197/199), which was implicated as a potential Intermediate in the vanadium-catalyzed oxidation of bromide by hydrogen peroxide [32]. 

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