Stoichiometric oxidation with cobalt

Calciothermic reduction of samarium oxide, in the presence of cobalt powder, yields samarium-cobalt alloys in the powder form. The process is popularly known as reduction diffusion. Samarium oxide, mixed with cobalt powder and calcium hydride powder or calcium particles, is heated at 1200 °C under 1 atm hydrogen pressure to produce the alloys. Cobalt oxide sometimes partly replaces the cobalt metal in the charge for alloy preparation. This presents no difficulty because calcium can easily reduce cobalt oxide. A pelletized mixture of oxides of samarium and cobalt, cobalt and calcium, with the components taken in stoichiometric quantities, is heated at 1100-1200 °C in vacuum for 2 to 3 h. This process is called coreduction. In reduction diffusion as well as in coreduction, the metals samarium and/or cobalt form by reduction rather quickly but they need time to form the alloy by diffusion, which warrants holding the charge at the reaction temperature for 4 to 5 h. The yield of alloy in these processes ranges from 97 to 99%. Reduction diffusion is the method by which most of the 500 to 600 t of the magnetic samarium-cobalt alloy (SmCOs) are produced every year. 

Lead(IV)277 and silver(III)301 trifluoroacetates in TFA also oxidize alkanes at room temperature to give alkyl trifluoroacetates [see also Section III.D.3 for reactions of alkanes with Pd(II) trifluoroacetate]. The stoichiometric oxidation of cyclohexane to a mixture of cyclohexanol, cyclohexanone, and adipic acid by cobalt(III) perchlorate in aqueous acetonitrile has also been reported.240... 

Stoichiometric Oxidation of Lignin Model Compounds with Cobalt till) Acetate. In a typical procedure, a solution of DMMP (6.8 mg, 0.018 mmol) and cobalt (III) acetate (84.3%, 10.5 mg, 0.037 mmol) in 18 mL of glacial acetic acid was heated to reflux in 20 min with stirring. One hour later, the color turned from greenish black to pink. The solution was cooled to room temperature and veratrole (10.2 mg, 0.074 mmol) was added as an internal standard for HPLC analysis. A 67% selectivity to DMB at 99% conversion of DMMP was obtained. For reactions where cobalt(III) acetate still remained, an aqueous solution of ferrous sulfate was added dropwise until the color of the solution turned from green to pink then veratrole was added as internal standard. 

This chapter describes our initial investigations of cobalt complexes bound to colloidal polymers for the autoxidations (in which dioxygen is the stoichiometric oxidant) of tetralin, 2,6-di-r rr-butylphenol, and 1-decanethiol. The reactions of these water-insoluble organic compounds proceed faster in the colloids that they do with the same cobalt complexes as catalysts in aqueous solution. Autoxidations have been chosen because of their potential for low cost use for the decontamination of water and for chemical manufacturing processes. 

In this method, a metal oxide or hydroxide is slurried in an organic solvent, neodecanoic acid is slowly added, and the mixture is refluxed to remove the water. Salts that are basic can be prepared by using less than stoichiometric amounts of acid. This method has been used in the preparation of metal salts of silver (80) and vanadium (81). The third method of preparation is similar to the fusion process, the difference is the use of finely divided metal as the starting material instead of the metal oxide or hydroxide. This method has been appHed to the preparation of cobalt neodecanoate (82). Salts of tin (83) and antimony (84) have been prepared by the fusion method, starting with lower carboxyHc acids, then replacing these acids with neodecanoic acid. 

For more selective hydrogenations, supported 5—10 wt % palladium on activated carbon is preferred for reductions in which ring hydrogenation is not wanted. Mild conditions, a neutral solvent, and a stoichiometric amount of hydrogen are used to avoid ring hydrogenation. There are also appHcations for 35—40 wt % cobalt on kieselguhr, copper chromite (nonpromoted or promoted with barium), 5—10 wt % platinum on activated carbon, platinum (IV) oxide (Adams catalyst), and rhenium heptasulfide. Alcohol yields can sometimes be increased by the use of nonpolar (nonacidic) solvents and small amounts of bases, such as tertiary amines, which act as catalyst inhibitors. 

Schiff base-cobalt-nitro complexes are too mild as oxidants to react as such with alkenes. However, the addition of Lewis acids (e.g. BF3 Et20, LiPF6) to these complexes activates the nitro ligand and produces a variety of both stoichiometric and catalytic oxidations. Stoichiometric transformations involve the oxidation of sulfides to sulfoxides and 1,3-cyclohexadiene to benzene.467 Alcohols such as benzyl alcohol and cycloheptanol are catalytically transformed into the corresponding carbonyl compounds.467,474... 

Oxygen-transfer reactions have been shown to occur from cobalt(III)-nitro complexes to alkenes coordinated to palladium.472 Thus ethylene and propene have been oxidized stoichiometrically in quantitative yields to acetaldehyde and acetone respectively, with the concomitant reduction of the nitro- to the nitrosyl-cobalt analog. A catalytic transformation with turnover numbers of 4-12 can be achieved at 70 °C in diglyme. The mechanism shown in Scheme 11 has been suggested. 

Cobalt-coated pigment particles (1.6-4 wt.% Co) consist of a core of Y-F6203 or non-stoichiometric iron oxide phase, and a 1-2 nm coating of cobalt ferrite with a... 

Vitamin B12 is known for its ability to catalyze molecular rearrangements. A variety of cobalt chelates are logical models for vitamin B12, and their stoichiometric and catalytic activities in a variety of reactions,403 particularly olefin isomerizations, were studied intensively.404-411 Noncatalytic isomerization reactions based upon the synthesis of alkylcobalt chelates as model intermediates were favored. A variety of catalytic oxidations of substrates such as hydroquinone, azo compounds, phosphines, and olefins were also investigated.412-415 Copolymerization of a-methylstyrene and other monomers with oxygen in the presence of CoTPP led to alternating polyperoxides.416 418 Cobaloximes were found to catalyze... 

Cobalt complexes have been used to catalyze the carbonylation of chloroarenes to the corresponding carboxylic acids and their esters (Sect. 3.3). Some complexes of cobalt in the oxidation state -1 activate the Ar-Cl bond via an SRN1-type mechanism [2] involving single electron transfer from the metal to chloro-arene, followed by elimination of Cl . The simplest Co(-I) carbonyl species, [Co(CO)4] , is not electron-rich enough to react with haloarenes. However, its reactivity has been shown to enhance tremendously in the presence of Caubere s complex bases, mixtures of NaH and NaOAlk [23,66,67]. For instance, the stoichiometric carbonylation of chlorobenzene has been performed with the... 

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