Formation and oxidation of alkyl radicals by cobalt(III) complexes

Lande, Sheldon S.; Kochi, Jay K.

doi:10.1021/ja01021a023

Cited by 79 publications

(42 citation statements)

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“…(2) and (3)] [5] (e À cb is a photogenerated electron in the conduction band). Such phenomena have also been observed in the thermal oxidative decarboxylation of these acids by high-valence metal ions, such as Co III , [7] Pb IV , [8] and Mn III , [9] although the main decarboxylation products were alkenes rather than alkanes since no reductive species [like the electrons shown in Eq. (3)] were involved.…”

Section: Introductionmentioning

confidence: 76%

An Unexplored O₂‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO₂ Photocatalysis: An Isotopic Probe Study

Wen

Chen

et al. 2010

Chemistry A European J

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The aerobic decarboxylation of saturated carboxylic acids (from C(2) to C(5)) in water by TiO(2) photocatalysis was systematically investigated in this work. It was found that the split of C(1)-C(2) bond of the acids to release CO(2) proceeds sequentially (that is, a C(5) acid sequentially forms C(4) products, then C(3) and so forth). As a model reaction, the decarboxylation of propionic acid to produce acetic acid was tracked by using isotopic-labeled H(2)(18)O. As much as ≈42% of oxygen atoms of the produced acetic acids were from dioxygen ((16)O(2)). Through diffuse reflectance FTIR measurements (DRIFTS), we confirmed that an intermediate pyruvic acid was generated prior to the cut-off of the initial carboxyl group; this intermediate was evidenced by the appearance of an absorption peak at 1772 cm(-1) (attributed to C=O stretch of α-keto group of pyruvic acid) and the shift of this peak to 1726 cm(-1) when H(2)(16)O was replaced by H(2)(18)O. Consequently, pyruvic acid was chosen as another model molecule to observe how its decarboxylation occurs in H(2)(16)O under an atmosphere of (18)O(2). With the α-keto oxygen of pyruvic acid preserved in the carboxyl group of acetic acid, ≈24% new oxygen atoms of the produced acetic acid were from molecular oxygen at near 100% conversion of pyruvic acid. The other ≈76% oxygen atoms were provided by H(2)O through hole/OH radical oxidation. In the presence of conduction band electrons, O(2) can independently accomplish such C(1)-C(2) bond cleavage of pyruvic acid to generate acetic acid with ≈100% selectivity, as confirmed by an electrochemical experiment carried out in the dark. More importantly, the ratio of O(2) participation in decarboxylation increased along with the increase of pyruvic acid conversion, indicating the differences between non-substituted acids and α-keto acids. This also suggests that the O(2)-dependent decarboxylation competes with hole/OH-radical-promoted decarboxylation and depends on TiO(2) surface defects at which Ti(4c) sites are available for the simultaneous coordination of substrates and O(2).

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Section: Introductionmentioning

confidence: 76%

An Unexplored O₂‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO₂ Photocatalysis: An Isotopic Probe Study

Wen

Chen

et al. 2010

Chemistry A European J

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“…For the metalcatalysed pathway, Mn(III,IV) and Co(III) are known to be present in autoxidation [1] and it is well-established that they can decarboxylate aromatic acids. [20,21] The decarbonylation mechanism is important in aliphatic aldehydes but not aromatic ones. [22] To confirm this we aerobically oxidised heptaldehyde and p-tolualdehyde with a Co/Mn/Br catalyst in acetic acid at 95 8C and atmospheric pressure.…”

Section: Full Papersmentioning

confidence: 99%

Is it Possible to Achieve Highly Selective Oxidations in Supercritical Water? Aerobic Oxidation of Methylaromatic Compounds

et al. 2004

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Abstract:We have demonstrated that different methylaromatic compounds [1,4-dimethylbenzene (p-xylene), 1,3-dimethylbenzene (m-xylene), 1,2-dimethylbenzene (o-xylene), 1,3,5-trimethylbenzene (mesitylene) and 1,2,4-trimethylbenzene (pseudocumene)] can be aerobically oxidized in supercritical water (scH 2 O) using manganese(II) bromide as catalyst to give corresponding carboxylic acids in the continuous mode over a sustained period of time in good yield. No partially oxidized intermediates (i.e., toluic acid and benzaldehydes) were detected for the dimethylbenzenes and mesitylene reactions. By fine tuning pressure and temperature, scH 2 O becomes a solvent with physical properties suitable for single-phase oxidation since both organic substrate and oxygen are soluble in scH 2 O. There is a strong structural similarity of metal/bromide coordination compounds in the active oxidation solvents (acetic acid and scH 2 O) which does not exist in the much less active H 2 O at lower temperatures. This may account for the successful catalysis of the reactions reported herein. Aromatic acids produced by the loss of one methyl group occurred in all of these reactions, i.e., 3 ± 6% benzoic acid formed during the oxidation of the dimethylbenzenes. Part of this loss is thought to be due to thermal decarboxylation. The thermal decarboxylation process is monitored via Raman spectroscopy.

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“…The mechanism given below is similar to the formation of benzylic bromide from Co(III)/bromide mixtures for which there is kinetic evidence. [20,22,23] One still needs to explain why this behavior is peculiar to DMtoluene oxidation and not to 4-methoxytoluene or toluene autoxidation. Perhaps the steric hindrance of the metamethoxy group in the coordination sphere allows the methyl radical unusually good access to the DMbenzoic acid.…”

Section: ð6þmentioning

confidence: 99%

The Unusual Characteristics of the Aerobic Oxidation of 3,4‐Dimethoxytoluene with Metal/Bromide Catalysts

Partenheimer

2004

Adv Synth Catal

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DMtoluene (3,4-dimethoxytoluene; DM ¼ 3,4-dimethoxy), a model compound for lignin oxidation, can be autoxidized in acetic acid using a Co/Mn/ Br catalyst to its benzaldehyde in 51 mol % yield, and to its acid in 85 -92 mol % yield. This synthesis is unusual because a number of unprecedented phenomena occur. 1) The rate of molecular oxygen reacting with the substrate is bi-phasic, i.e., two maximum in the rate of reaction are observed. 2) In the first phase, all of the 3,4-dimethoxytoluene is converted to intermediates, but very little to the carboxylic acid. 3) During the second maximum of activity, virtually all the intermediates are converted to the carboxylic acid with 95 -100% mass accountability. 4) The rate of carbon monoxide and carbon dioxide formation is considerably higher during the second phase during which 5) 9 -12% of methyl 3,4-dimethoxybenzoate (the methyl ester of the benzoic acid) is formed. Mechanisms are suggested for these unusual phenomena.

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Formation and oxidation of alkyl radicals by cobalt(III) complexes

Cited by 79 publications

References 1 publication

An Unexplored O₂‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO₂ Photocatalysis: An Isotopic Probe Study

An Unexplored O₂‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO₂ Photocatalysis: An Isotopic Probe Study

Is it Possible to Achieve Highly Selective Oxidations in Supercritical Water? Aerobic Oxidation of Methylaromatic Compounds

The Unusual Characteristics of the Aerobic Oxidation of 3,4‐Dimethoxytoluene with Metal/Bromide Catalysts

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Formation and oxidation of alkyl radicals by cobalt(III) complexes

Cited by 79 publications

References 1 publication

An Unexplored O2‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO2 Photocatalysis: An Isotopic Probe Study

An Unexplored O2‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO2 Photocatalysis: An Isotopic Probe Study

Is it Possible to Achieve Highly Selective Oxidations in Supercritical Water? Aerobic Oxidation of Methylaromatic Compounds

The Unusual Characteristics of the Aerobic Oxidation of 3,4‐Dimethoxytoluene with Metal/Bromide Catalysts

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An Unexplored O₂‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO₂ Photocatalysis: An Isotopic Probe Study

An Unexplored O₂‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO₂ Photocatalysis: An Isotopic Probe Study