Oxidation vanadium-catalyzed oxidations

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. 

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

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

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. 

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.,... 

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. 

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]. 

The coupling reaction of epoxide 69 with the anion derived from the allyl sulfide 57, a system derived from geraniol, was accomplished in a 99% yield by employing 4 equivalents of the anion (Scheme 13). Protection of the alcohol as the MOM ether (95%), followed by debenzylation and removal of the phenylthio group under Birch conditions (76%) gave diene 70. Vanadium catalyzed oxidation and spontaneous cyclization of 70 imder acidic conditions afforded a diastereomeric mixture of tetraols 71 and 72 in 61% and 14% yields, respectively. 

This vanadium-catalyzed oxidation is an example of a ligand accelerated catalysis [46]. As revealed by V-NMR-studies various vanadium species are formed... 

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... 

Finally, the relative rates of the vanadium catalyzed oxidation of some nucleophilic substrates by r-BuOOH in ethanol at 25 °C were found to be ( -Bu)2S(100) > PhS(n-Bu)(58)>(n-Bu)2SO(17)> cyclohexene (0.2). These data suggest strongly that electropositive oxygen is being transferred from the metal-activated hydroperoxide to the substrate. Thus, a polar mechanism can be advanced. A radical mechanism is ruled out by the observation of reproducible kinetics, the simple rate law, the failure of radical traps to influence rate, and by the absence of products expected to arise from radical intermediates. 

Balcells D, Maseras F, Ujaque G (2(X)5) Computational rationalization of the depoidence of the enantioselectivity on the nature of the catalyst in the vanadium-catalyzed oxidation of sulfides by hydrogen peroxide. J Am Chem Soc 127 3624-3634... 

Amberg M, Donges M, Stapf G, Harmng J. Formation of 3-acyloxy-y-butyrolactones from 4-pentenob in vanadium-catalyzed oxidations. Tetrahedron. 2014 70 5321-5331. 

Radesovich, A.T, Chan, V.S., Shih, H.-W, and Toste, F,D, (2008) Synthesis of (-)-octalactin A by a strategic vanadium-catalyzed oxidative kinetic resolution. Angeiv. Chem. Int. Ed., 120, 3815-3818,... 

Vanadium in the feed poisons the FCC catalyst when it is deposited on the catalyst as coke by vanadyl porphydrine in the feed. During regeneration, this coke is burned off and vanadium is oxidized to a oxidation state. The vanadium oxide (V O ) reacts with water vapor in the regenerator to vanadic acid, HjVO. Vanadic acid is mobile and it destroys zeolite crystal through acid-catalyzed hydrolysis. Vanadic acid formation is related to the steam and oxygen concentration in the regenerator. 

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. 

The selective oxidation of ra-butane to give maleic anhydride (MA) catalyzed by vanadium phosphorus oxides is an important commercial process (99). MA is subsequently used in catalytic processes to make tetrahydrofurans and agricultural chemicals. The active phase in the selective butane oxidation catalyst is identified as vanadyl pyrophosphate, (V0)2P207, referred to as VPO. The three-dimensional structure of orthorhombic VPO, consisting of vanadyl octahedra and phosphate tetrahedra, is shown in Fig. 17, with a= 1.6594 nm, b = 0.776 nm, and c = 0.958 nm (100), with (010) as the active plane (99). Conventional crystallographic notations of round brackets (), and triangular point brackets (), are used to denote a crystal plane and crystallographic directions in the VPO structure, respectively. The latter refers to symmetrically equivalent directions present in a crystal. 

The selective oxidation of saturated hydrocarbons is a reaction of high industrial importance. Besides a variety of other oxidants, hydrogen peroxide as a very clean oxidant has also been used for these purposes . As an example, in 1989 Moiseev and coworkers reported on the vanadium(V)-catalyzed oxidation of cyclohexane with hydrogen peroxide (Scheme 146) . When the reaction was carried out in acetic acid cyclohexanol and cyclohexanone were formed, bnt conversions were very poor and did not exceed 13%. Employing CF3COOH as solvent, complete conversions could be obtained within 5 min-ntes. Here, cyclohexyl trifluoroacetate was the main product (85% of the products formed) resulting from the reaction of cyclohexanol (the primary product of the oxidation) with CF3COOH. 

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... 

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