Vanadium complexes solvent effects

The drawback of this reaction is that trifluoroacetic acid for the solvent and excess K2S2O8 for the oxidant are required. Although a bimetallic system based on Pd and Cu was initially used as the catalyst, it was determined that the reaction can proceed using only the copper catalyst. A radical mechanism is proposed. Vanadium complexes such as VO(acac)2 also effectively catalyze acetic acid formation from methane and CO (57). The yield reached 93% based on methane. 

The catalysts are usually prepared in hydrocarbon solvents, essentially in the absence of air or moisture and are mixtures of ill-defined composition. In many instances dark-coloured precipitates are formed of variable stoichiometry containing complexes of the organo-metal compound with the transition metal in a lower valence state. Natta [5] showed that pure lower valence transition metal compounds, such as titanium or vanadium trichloride, when treated with organo-metal compounds were effective catalysts, and were particularly suitable for the preparation of crystalline high melting point polyolefins. The close identity of these two classes of catalyst has led to their description as... 

Spectrophotometry also provides rapid, cost-effective measurement of total uranium concentrations, at levels down to tens of pgl . In this method, a chelating agent is added to the digested solution to form colored uranium complexes. The most common chelator is 2-(5-bromo-2-pyridylazo)-5-diethylamino-phenol (bromo-PADAP), which may require removal of chromium, vanadium, or phosphate interferences by solvent extraction, prior to analysis. 

The most practical method that is used in the industrial synthesis of esomeprazole involves titanium-catalyzed oxidation with an alkyl hydroperoxide, and a dialkyltartrate as chiral ligand, in an organic solvent such as dichloromethane. A variety of oxidoreductases are known to catalyze the enantioselective oxidation of prochiral sulfides, usually as whole-cell biotransformations in aqueous media, but no simple metal complexes have been shown to be effective in water and the development of practical systems employing aqueous hydrogen peroxide as the primary oxidant is still an important challenge. In this context it is worth mentioning the enantioselective sulfoxidation of prochiral sulfoxides catalyzed by the semisynthetic peroxidase, vanadium-phytase, in an aqueous medium. 

Biomimetic Cu(II) and Fe(II) complexes with bis- and tris-pyridyl amino and imino thioether ligands and vacant (or potentially so) coordination positions (Fig. y are active as catalyst precursors for the solvent- and halogen-free MW-assisted oxidation of 1-phenylethanol by TBHP, in the presence of pyridazine or other N-based additives. Maximum TOF of 5220 h (corresponding to 87% yield) was achieved just after 5 min of reaction time under the low power MW irradiation. The same authors reported" the catalytic activity of related copper, iron, and vanadium systems with mixed-N,S pyridine thioether hgands. The Cu and Fe complexes proved to be useful catalysts in various MW-assisted alcohol oxidations with TBHP, at 80 °C. Thus, 5-containing ligands can also be used to create effective catalyst precursors. 

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