Phenolic Hydrogen Transfer by Molecular Oxygen and Hydroperoxyl Radicals. Insights into the Mechanism of the Anthraquinone Process

Korth, Hans‐Gert

doi:10.1021/acs.joc.9b03286

Cited by 28 publications

(32 citation statements)

References 61 publications

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“…To arrive at H 2 O 2 from O 2 , two H obviously need to be attached to the latter, and the role of anthrahydroquinone (reduced anthraquinone) consists of providing them by two direct HATs. A number of hydroxyl-containing organic molecules were recently investigated for their HAT ability, 16 but reduced EPI was not among them. In the DFT calculations (including implicit water as solvent) presented above, we studied the interaction between molecular oxygen and EPI-2H as well as between the intermediates resulting after the first HAT.…”

Section: Discussionmentioning

confidence: 99%

“… 15 One can legitimately wonder why such a complex procedure was necessary and what is actually the role of anthraquinone. As discussed in a recent and very thorough theoretical study, 16 an enol or a phenol is among rare molecules that can ensure efficient hydrogen atom transfer (HAT) from the hydroxy group to molecular oxygen. Note that the formation of oxygen adduct intermediates has been considered and discarded in both refs ( 14 ) and ( 16 ).…”

Section: Introductionmentioning

confidence: 99%

“…As discussed in a recent and very thorough theoretical study, 16 an enol or a phenol is among rare molecules that can ensure efficient hydrogen atom transfer (HAT) from the hydroxy group to molecular oxygen. Note that the formation of oxygen adduct intermediates has been considered and discarded in both refs ( 14 ) and ( 16 ). Indeed, the total spin conservation requirement imposes severe constraints on the mechanisms of reactions of triplet dioxygen with singlet molecules in particular (see ref ( 17 ) for a discussion).…”

Section: Introductionmentioning

confidence: 99%

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Density Functional Theory Mechanistic Study on H₂O₂ Production Using an Organic Semiconductor Epindolidione

et al. 2020

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Organic semiconductors have recently emerged as promising catalytic materials for oxygen reduction to hydrogen peroxide, H 2 O 2 , a chemical of great importance in industry as well as biology. While examples of organic semiconductor-mediated photocatalytic and electrocatalytic processes for H 2 O 2 production become more numerous and improve in performance, fundamental understanding of the reaction mechanisms at play have been explored far less. The aim of the present work is to computationally test hypotheses of how selective oxygen reduction to H 2 O 2 generally occurs on carbonyl dyes and pigments. As an example material, we consider epindolidione (EPI), an industrial pigment with demonstrated semiconductor properties, which photocatalytic activity in oxygen reduction reaction (ORR) and thereby producing hydrogen peroxide (H 2 O 2 ) in low pH environment has been recently experimentally demonstrated. In this work, the ability of the reduced form of EPI, viz. EPI-2H (which was formed after a photoinduced 2e − /2H + process), to reduce molecular triplet oxygen to peroxide and the possible mechanism of this reaction are computationally investigated using density functional theory. In the main reaction pathway, the reduction of O 2 to H 2 O 2 reaction occurs via abstraction of one of the hydrogen atoms of EPI-2H by triplet dioxygen to produce an intermediate complex consisting of the radicals of hydrogen peroxide (HOO • ) and EPI-H • at the initial stage. HOO • thus released can abstract another hydrogen atom from EPI-H • to produce H 2 O 2 and regenerates EPI; otherwise, it can enter another pathway to abstract hydrogen from a neighboring EPI-2H to form EPI-H • and H 2 O 2 . EPI, after reduction, thus plays in ORR the role of hydrogen atom transfer (HAT) agent via its OH group, similar to anthraquinone in the industrial process, while HAT from its amino hydrogen is found unfavorable.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Density Functional Theory Mechanistic Study on H₂O₂ Production Using an Organic Semiconductor Epindolidione

et al. 2020

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“…In this work a crucial step is missing where the hydroperoxyl (OOH • ) radical transitions across the partially dehydrogenated AHQ molecule to perform the second hydrogen abstraction. Given that the overall AQ process is still being determined 30,31 , the goal of this investigation is to calculate the transition of the OOH • across the AHQ molecule in an effort to examine one of many possibilities so that an accurate representation of this process can be determined. It was found that this transition has a deep potential well in the singlet state that probably acts as the rate-determining step as the OOH • transitions across the AHQ molecule.…”

Section: Introductionmentioning

confidence: 99%

Reduction of O2 to H2O2 using Small Polycyclic Molecules

Lopez¹,

Groves

2021

Preprint

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Hydrogen peroxide is an environmentally friendly oxidizing agent that is important in several industries. It is currently produced industrially via the anthrahydroquinone (AHQ) process where O2 reacts with a functionalised version of anthrahydroquinone to produce H2O2 and anthraquinone. In the previously published DFT pathway for this process the transition of the OOH? radical across the partially dehydrogenated AHQ catalyst was not explored. In this paper, we will use DFT to explore this step and show that there is a deep potential energy minimum that inhibits the OOH<sup>.</sup> from being fully reduced. We then examine other similar sized polycyclic molecules with two OH-groups on the same side that could serve as alternative catalysts without this issue. In this analysis, we identify Phenanthraquinone as a possible alternative and present the pathway for this candidate to produce H2O2 as well as its regeneration with H2.

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“…For example, they are used as stoichiometric reagents (often in combination with strong acids) in a number of (Scholl‐type) aryl‐aryl coupling reactions, and as redox catalysts for example, for the oxidation of amines and alcohols . The anthraquinone process for hydrogen peroxide production is a large‐scale industrial application of quinones . They are also applied in some steps of the synthesis of pharmaceuticals and drugs .…”

Section: Introductionmentioning

confidence: 99%

1,2,4,5‐Tetrakis(tetramethylguanidino)‐3,6‐diethynyl‐benzenes: Fluorescent Probes, Redox‐Active Ligands and Strong Organic Electron Donors

Wagner

Kreis

Popp

et al. 2020

Chemistry A European J

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In this work, the change of reactivity induced by the introduction of two para ‐ethynyl substituents (CCSi( i Pr) 3 or CCH) to the organic electron‐donor 1,2,4,5‐tetrakis(tetramethylguanidino)‐benzene is evaluated. The redox‐properties and redox‐state dependent fluorescence are evaluated, and dinuclear Cu I and Cu II complexes synthesized. The Lewis‐acidic B(C 6 F 5 ) 3 substitutes the proton of the ethynyl −CCH groups to give new anionic −CCB(C 6 F 5 ) 3 − substituents, leading eventually to a novel dianionic strong electron donor in its diprotonated form. Its two‐electron oxidation with dioxygen in the presence of a copper catalyst yields the first redox‐active guanidine that is neutral (instead of cationic) in its oxidized form.

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Phenolic Hydrogen Transfer by Molecular Oxygen and Hydroperoxyl Radicals. Insights into the Mechanism of the Anthraquinone Process

Cited by 28 publications

References 61 publications

Density Functional Theory Mechanistic Study on H₂O₂ Production Using an Organic Semiconductor Epindolidione

Density Functional Theory Mechanistic Study on H₂O₂ Production Using an Organic Semiconductor Epindolidione

Reduction of O2 to H2O2 using Small Polycyclic Molecules

1,2,4,5‐Tetrakis(tetramethylguanidino)‐3,6‐diethynyl‐benzenes: Fluorescent Probes, Redox‐Active Ligands and Strong Organic Electron Donors

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Phenolic Hydrogen Transfer by Molecular Oxygen and Hydroperoxyl Radicals. Insights into the Mechanism of the Anthraquinone Process

Cited by 28 publications

References 61 publications

Density Functional Theory Mechanistic Study on H2O2 Production Using an Organic Semiconductor Epindolidione

Density Functional Theory Mechanistic Study on H2O2 Production Using an Organic Semiconductor Epindolidione

Reduction of O2 to H2O2 using Small Polycyclic Molecules

1,2,4,5‐Tetrakis(tetramethylguanidino)‐3,6‐diethynyl‐benzenes: Fluorescent Probes, Redox‐Active Ligands and Strong Organic Electron Donors

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Density Functional Theory Mechanistic Study on H₂O₂ Production Using an Organic Semiconductor Epindolidione

Density Functional Theory Mechanistic Study on H₂O₂ Production Using an Organic Semiconductor Epindolidione