Kinetics and mechanism of the oxidation of bis(acetylacetonato)-cobalt(II) by cumene hydroperoxide in the presence of pyridine

Zimin, Yu. S.; Talzi, E. P.; Nekipelov, V. M.; Chinakov, V. D.; Zamaraev, K. I.

doi:10.1007/bf02067972

Cited by 11 publications

(5 citation statements)

References 7 publications

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“…Gas chromatographic analysis indicates that free N-donor ligand (L) is always present in reaction mixtures at the end of oxidation. Whether L or the t BuOO • group is lost first is not clear at this time; however, Talzi and co-workers suggest that the t BuOO • unit is lost first …”

Section: Resultsmentioning

confidence: 97%

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Syntheses and Stuctures of Alkyl Peroxo Adducts of β-Diketonate Cobalt(III) Complexes and Their Role in Oxidation of Hydrocarbons and Olefin Epoxidation

et al. 1999

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To assess the oxidizing capacity of [Co( -diketonate) 2 (L)OOR] complexes, four such species, namely, [Co-(acac) 2 (L)(OO t Bu)] (acacH ) acetylacetone; L ) pyridine (py) (1), 4-methylpyridine (4-Mepy) (2), 1-methylimidazole (1-MeIm) (3)) and [Co(dbm) 2 (py)(OO t Bu)] (4, dbmH ) dibenzoylmethane), have been synthesized and the structures of 1, 3, and 4 have been determined by X-ray crystallography. Complex 1 crystallizes in the triclinic space group P1 h with a ) 9.149(2) Å, b ) 9.741(2) Å, c ) 13.067 (2) Å, R ) 84.22 (2)°, ) 77.89(2)°, γ ) 67.83(2)°, V ) 1054.1(4) Å 3 , and Z ) 2. Complex 3 crystallizes in the monoclinic space group P2 1 /n with a ) 11.341(2) Å, b ) 10.485(2) Å, c ) 18.863(2) Å, R ) 90°, ) 106.230(15)°, γ ) 90°, V ) 2153.6(8) Å 3 , and Z ) 4. Complex 4‚1.5C 6 H 6 crystallizes in the monoclinic space group P2 1 /c with a ) 14.907(5) Å, b ) 18.701-(5) Å, c ) 15.207(4) Å, R ) 90°, ) 103.52 (2)°, γ ) 90°, V ) 4122(2) Å 3 , and Z ) 4. The geometry around the Co(III) center in all four complexes is distorted octahedral, and the two -diketonate ligands are cis to each other. The Co-O and O-O bond distances in the Co-OO t Bu moiety fall in the narrow ranges of 1.860(3)-1.879 (2) and 1.451(3)-1.466(3) Å, respectively. Although stable in the solid state, these complexes decompose in benzene or halocarbon solutions to afford t BuOO • and t BuO • radicals. When alkanes like cyclohexane are present in the reaction mixture, these radicals initiate oxidation of the C-H bond. The oxidizing capacity follows the order 1 > 2 > 3 > 4. Decomposition of the complexes in the presence of cyclohexene and an aldehyde results in selective epoxidation in high yield.

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Section: Resultsmentioning

confidence: 97%

“…Talzi and co-workers have studied the decomposition of [Co(acac) 2 (py)(OOCMe 2 Ph)] in CDCl 3 by EPR spectroscopy …”

Section: Resultsmentioning

confidence: 99%

Syntheses and Stuctures of Alkyl Peroxo Adducts of β-Diketonate Cobalt(III) Complexes and Their Role in Oxidation of Hydrocarbons and Olefin Epoxidation

et al. 1999

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“…which leads to the same net eqn (9). It is still disputed which steps, between eqn ( 7) and (8) or between eqn ( 10) and ( 11), are rate determining, 151,152 as well as which of the various cobalt species is most dominant in solution. A recent study by Hermans and co-workers comprising both computational and kinetic studies of the autoxidation of cyclohexane by means of UV-Vis spectroscopy suggested that the dominant species is Co II .…”

Section: Reactantsmentioning

confidence: 99%

Catalytic oxygen activation versus autoxidation for industrial applications: a physicochemical approach

Liu

Ryabenkova

Conte

2015

Phys. Chem. Chem. Phys.

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The activation and use of oxygen for the oxidation and functionalization of organic substrates is among the most important reactions in a chemist's toolbox. Nevertheless, despite the vast literature on catalytic oxidation, the phenomenon of autoxidation, an ever-present background reaction that occurs in virtually every oxidation process, is often neglected. In contrast, autoxidation can affect the selectivity to a desired product, to those dictated by pure freeradical chain pathways, thus affecting the activity of any catalyst used to carry out a reaction.This critical review compares catalytic oxidation routes by transition metals versus autoxidation, particularly focusing on the industrial context, where highly selective and "green" processes are needed. Furthermore, the application of useful tests to discriminate between different oxygen activation routes, especially in the area of hydrocarbon oxidation, with the aim of an enhanced catalyst design, is described and discussed. In fact, one of the major targets of selective oxidation is the use of molecular oxygen as ultimate oxidant, combined with the development of catalysts capable to perform the catalytic cycle in a real energy and cost effective manner on a large scale. To achieve this goal, insights from metallo-proteins that could find application in some areas of industrial catalysis are presented, as well as considering the physicochemical principles that are at the fundament of oxidation and autoxidation processes.3

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“…According to this two‐step mechanism, the Co II ion is first oxidized by ROOH to a Co III OH intermediate, which can be regenerated back to the starting Co II ion upon reaction with a second ROOH molecule. At the moment, there is disagreement over which step [i.e., reaction (1) or (2)] is the rate‐determining step, and hence which cobalt species (i.e., Co II or Co III OH) is the dominant in solution 15. 16 Little information is available on the precise rate or temperature dependence of the reactions.…”

Section: Introductionmentioning

confidence: 99%

“…At the moment, there is disagreement over which step [i.e., reaction (1) or (2)] is the rate-determining step, and hence which cobalt species (i.e., Co II or Co III ÀOH) is the dominant in solution. [15,16] Little information is available on the precise rate or temperature dependence of the reactions. There is even controversy about the active species, that is, the monomeric or m-oxo/m-hydroxo-bridged species.…”

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confidence: 99%

Mechanism of the Catalytic Deperoxidation of tert‐Butylhydroperoxide with Cobalt(II) Acetylacetonate

Turrà

Neuenschwander

Baiker

et al. 2010

Chemistry A European J

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The Co(II)/Co(III)-induced decomposition of hydroperoxides is an important reaction in many industrial processes and is referred to as deperoxidation. In the first step of the so-called Haber-Weiss cycle, alkoxyl radicals and Co(III)-OH species are generated upon the reaction of the Co(II) ion with ROOH. The catalytic cycle is closed upon the regeneration of the Co(II) ion through the reaction of the Co(III)-OH species with a second ROOH molecule, thus producing one equivalent of the peroxyl radicals. Herein, the deperoxidation of tert-butylhydroperoxide by dissolved cobalt(II) acetylacetonate is studied by using UV/Vis spectroscopy in situ with a noninteracting solvent, namely, cyclohexane. Kinetic information extracted from experiments, together with quantum-chemical calculations, led to new mechanistic hypotheses. Even under anaerobic conditions, the Haber-Weiss cycle initiates a radical-chain destruction of ROOH propagated by both alkoxyl and peroxyl radicals. This chain mechanism rationalizes the high deperoxidation rates, which are directly proportional to the cobalt concentration up to approximately 75 μM at 333 K. However, at higher cobalt concentrations, a remarkable decrease of the rate is observed. The hypothesis put forward herein is that this remarkable autoinhibition effect could be explained by the hitherto overlooked chain termination of two Co(III)--OH species. The direct competition between the first-order Haber-Weiss initiation and the second-order termination can indeed explain this peculiar kinetic behavior of this homogeneous deperoxidation system.

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Kinetics and mechanism of the oxidation of bis(acetylacetonato)-cobalt(II) by cumene hydroperoxide in the presence of pyridine

Cited by 11 publications

References 7 publications

Syntheses and Stuctures of Alkyl Peroxo Adducts of β-Diketonate Cobalt(III) Complexes and Their Role in Oxidation of Hydrocarbons and Olefin Epoxidation

Syntheses and Stuctures of Alkyl Peroxo Adducts of β-Diketonate Cobalt(III) Complexes and Their Role in Oxidation of Hydrocarbons and Olefin Epoxidation

Catalytic oxygen activation versus autoxidation for industrial applications: a physicochemical approach

Mechanism of the Catalytic Deperoxidation of tert‐Butylhydroperoxide with Cobalt(II) Acetylacetonate

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