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Dinda S, Bhavana R, Behera S, Mondal B. Metal-free electrocatalytic upcycling of polyethylene terephthalate plastic to C 2 products. Chem Commun (Camb) 2024; 60:7777-7780. [PMID: 38976316 DOI: 10.1039/d4cc01609b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/09/2024]
Abstract
Polyethylene terephthalate (PET) is one of the most used polymers, but the non-degradable and persistent nature of PET waste in the environment is a global menace. Hence upcycling PET waste becomes indispensable. Herein, we introduce the first metal-free electrochemical-upcycling of PET into value-added chemicals and H2 fuel using an organo-electrocatalyst (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO). Electrolysis at pH 10 produces glycolate and oxalate exclusively while at pH 14, over-oxidation and subsequent C-C bond cleavage produce formate and carbonate as well. Tuning the rate and product selectivity via pH regulation with mechanistic insight displays a sustainable route to implement waste PET recycling.
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Affiliation(s)
- Soumitra Dinda
- Department of Chemistry, IIT Gandhinagar, Palaj, Gandhinagar-382355, Gujarat, India.
| | - R Bhavana
- Department of Chemistry, IIT Gandhinagar, Palaj, Gandhinagar-382355, Gujarat, India.
| | - Snehanjali Behera
- Department of Chemistry, IIT Gandhinagar, Palaj, Gandhinagar-382355, Gujarat, India.
| | - Biswajit Mondal
- Department of Chemistry, IIT Gandhinagar, Palaj, Gandhinagar-382355, Gujarat, India.
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2
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Sun J, Wang B, Nie Z, Jia X, Li C, Li M, Zhao Y, Zhang X, Wang B, Xiao J. Selective Oxidation of Alcohol to Valuable Aldehydes Using Water as a Promoter in a Photoelectrochemical Cell. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:13265-13275. [PMID: 38857070 DOI: 10.1021/acs.langmuir.4c01453] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2024]
Abstract
Artificial photoelectrochemistry (PEC) has emerged as a promising and efficient technology for the sustainable conversion of solar energy into chemicals. In this study, we present a refined PEC process that enables the highly selective and stable production of piperonal and other valuable aldehydes through the oxidation of the corresponding alcohols. By employing Fe2O3 or TiO2 as the photoanode material and 2,2,6,6-tetramethylpiperidinooxy (TEMPO) as a redox mediator in an H2O/acetonitrile solution, we achieve 100% selectivity and a >95% Faradaic efficiency for piperonal production from piperonyl alcohol (PA) oxidation. Remarkably, we reveal the enhancing effect on the PA oxidation reactivity of appropriate-amount water in the solvent as it plays a crucial role in inhibiting the photoelectron-hole recombination efficiency and facilitating charge transfer. Mechanistic analysis suggests that TEMPO-mediated PA oxidation involves the formation of •O2- radicals by the reduction of oxygen on the cathode, resulting in water as the sole byproduct. Furthermore, our PEC oxidation system exhibits applications on the 100%-selective production of various conjugated aldehydes, including 4-anisaldehyde, cuminaldehyde, and the vitamin B6 derivative. By implementing a TiO2//Fe2O3 dual-photoanode system, we achieve an enhanced piperonal production rate of 31.2 μmol h-1 cm-2 at 1.0 V vs Ag/Ag+ and demonstrate its stability over a 102 h cyclic test, ensuring near-quantitative yield. This research illuminates the potential of the PEC strategy as a generally applicable method for the efficient production of high-value aldehydes.
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Affiliation(s)
- Jialin Sun
- College of Chemical and Biological Engineering, Shandong University of Science and Technology, Qingdao 266590, China
| | - Binbin Wang
- College of Chemical and Biological Engineering, Shandong University of Science and Technology, Qingdao 266590, China
| | - Zunyan Nie
- College of Chemical and Biological Engineering, Shandong University of Science and Technology, Qingdao 266590, China
| | - Xin Jia
- College of Chemical and Biological Engineering, Shandong University of Science and Technology, Qingdao 266590, China
| | - Chunxiao Li
- College of Chemical and Biological Engineering, Shandong University of Science and Technology, Qingdao 266590, China
| | - Mingjun Li
- College of Chemical and Biological Engineering, Shandong University of Science and Technology, Qingdao 266590, China
| | - Yingchun Zhao
- State Key Laboratory Base for Eco-Chemical Engineering, College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266061, China
| | - Xuekai Zhang
- College of Chemical and Biological Engineering, Shandong University of Science and Technology, Qingdao 266590, China
| | - Bo Wang
- College of Chemical and Biological Engineering, Shandong University of Science and Technology, Qingdao 266590, China
| | - Jingran Xiao
- College of Chemical and Biological Engineering, Shandong University of Science and Technology, Qingdao 266590, China
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She Y, Chen X, Wang M, Liu A, Wang X, Gao D, Hu K, Hu M. Heterogeneous solvent-metal-free aerobic oxidation of alcohol under ambient conditions catalyzed by TEMPO-functionalized porous poly(ionic liquid)s. RSC Adv 2024; 14:20199-20209. [PMID: 38919279 PMCID: PMC11196979 DOI: 10.1039/d4ra02241f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2024] [Accepted: 05/11/2024] [Indexed: 06/27/2024] Open
Abstract
Heterogeneous solvent-metal-free aerobic oxidation of alcohols under ambient conditions is interesting but remains a significant challenge. Herein, a series of porous TEMPO-functionalized poly(ionic liquid)s (TEMPO-PILs) featuring a pure polycationic framework were successfully developed through the free radical polymerization of the ionic liquid 3-(2-chloroacetic acid-2,2,6,6-tetramethyl-1-oxo-4-piperidyl)-1-vinylimidazolium chloride and bis-vinylimidazolium bromide salt. Characterizations revealed that the obtained TEMPO-PILs possessed a high TEMPO density, abundant bromide ions, and a tunable porous structure, which enabled them to serve as solvent-free heterogeneous organocatalysts for the metal-free aerobic oxidation of benzyl alcohol under ambient conditions, exhibiting high catalytic activity and stable recyclability. A high yield of 99% coupled with a turnover frequency (TOF) of 13.3 h-1 was obtainable, which is higher than most of the reported TEMPO-based heterogeneous catalysts, even superior to homogeneous TEMPO-functionalized ionic liquids. Furthermore, a broad range of alcohols were effectively converted into their corresponding ketones and aldehydes. A possible reaction mechanism is proposed for understanding the catalytic oxidation behavior, indicative of the synergistic effect of TEMPO moieties and bromide ions.
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Affiliation(s)
- Yaping She
- School of Energy Materials and Chemical Engineering, Hefei University Hefei 230601 China +86-551-62158395
| | - Xinyu Chen
- School of Energy Materials and Chemical Engineering, Hefei University Hefei 230601 China +86-551-62158395
| | - Mengya Wang
- School of Energy Materials and Chemical Engineering, Hefei University Hefei 230601 China +86-551-62158395
| | - Anqiu Liu
- School of Energy Materials and Chemical Engineering, Hefei University Hefei 230601 China +86-551-62158395
| | - Xiaochen Wang
- School of Energy Materials and Chemical Engineering, Hefei University Hefei 230601 China +86-551-62158395
| | - Daming Gao
- School of Energy Materials and Chemical Engineering, Hefei University Hefei 230601 China +86-551-62158395
| | - Kunhong Hu
- School of Energy Materials and Chemical Engineering, Hefei University Hefei 230601 China +86-551-62158395
| | - Miao Hu
- School of Energy Materials and Chemical Engineering, Hefei University Hefei 230601 China +86-551-62158395
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Yeo J, Kim K, Kwak SJ, Kim MS, Yang JH, Lee WB, Kim Y, Chae J, Chang J. Probing Local pH Change during Electrode Oxidation of TEMPO Derivative: Implication of Redox-Induced Acidity Alternation by Imidazolium-Linker Functional Groups. Anal Chem 2024; 96:5537-5545. [PMID: 38545995 DOI: 10.1021/acs.analchem.3c05796] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/10/2024]
Abstract
The chemical degradation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-based aqueous energy storage and catalytic systems is pH sensitive. Herein, we voltammetrically monitor the local pH (pHlocal) at a Pt ultramicroelectrode (UME) upon electro-oxidation of imidazolium-linker functionalized TEMPO and show that its decrease is associated with the greater acidity of the cationic (oxidized) rather than radical (reduced) form of TEMPO. The protons that drive the decrease in pH arise from hydrolysis of the conjugated imidazolium-linker functional group of 4-[2-(N-methylimidazolium)acetoxy]-2,2,6,6-tetramethylpiperidine-1-oxyl chloride (MIMAcO-T), which was studied in comparison with 4-hydroxyl-TEMPO (4-OH-T). Voltammetric hysteresis is observed during the electrode oxidation of 4-OH-T and MIMAcO-T at a Pt UME in an unbuffered aqueous solution. The hysteresis arises from the pH-dependent formation and dissolution of Pt oxides, which interact with pHlocal in the vicinity of the UME. We find that electrogenerated MIMAcO-T+ significantly influences pHlocal, whereas 4-OH-T+ does not. Finite element analysis reveals that the thermodynamic and kinetic acid-base properties of MIMAcO-T+ are much more favorable than those of its reduced counterpart. Imidazolium-linker functionalized TEMPO molecules comprising different linking groups were also investigated. Reduced TEMPO molecules with carbonyl linkers behave as weak acids, whereas those with alkyl ether linkers do not. However, oxidized TEMPO+ molecules with alkyl ether linkers exhibit more facile acid-base kinetics than those with carbonyl ones. Density functional theory calculations confirm that OH- adduct formation on the imidazolium-linker functional group of TEMPO is responsible for the difference in the acid-base properties of the reduced and oxidized forms.
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Affiliation(s)
| | - Kyungmi Kim
- Sungshin Women's University, Seoul 01133, Republic of Korea
- Korea Institute of Science and Technology Europe, Campus E7 1, 66123 Saarbrücken, Germany
| | - Seung Jae Kwak
- School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University, Seoul 08826, Republic of Korea
| | - Mi Song Kim
- Sungshin Women's University, Seoul 01133, Republic of Korea
| | - Jung Hoon Yang
- Korea Institute of Energy Research (KIER), Daejeon 34129, Republic of Korea
| | - Won Bo Lee
- School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University, Seoul 08826, Republic of Korea
| | - YongJoo Kim
- Department of Materials Science and Engineering, Kookmin University, Seoul 02707, Republic of Korea
- Department of Materials Science and Engineering, Korea University, Seoul 02841, Republic of Korea
| | - Junghyun Chae
- Sungshin Women's University, Seoul 01133, Republic of Korea
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Abstract
Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R1R2N-O•. The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R1 and R2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R1R2N═O+) or reduced to anions (R1R2N-O-), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C-O bonds, allowing for the thermal generation of C radicals through reversible C-O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.
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Affiliation(s)
- Dirk Leifert
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
| | - Armido Studer
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
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Goloviznina K, Salanne M. Electrochemical Properties and Local Structure of the TEMPO/TEMPO + Redox Pair in Ionic Liquids. J Phys Chem B 2023; 127:742-756. [PMID: 36651119 DOI: 10.1021/acs.jpcb.2c07238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Redox-active organic species play an important role in catalysis, energy storage, and biotechnology. One of the representatives is the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical, used as a mediator in organic synthesis and considered a safe alternative to heavy metals. In order to develop a TEMPO-based system with well-controlled electrochemical and catalytic properties, a reaction medium should be carefully chosen. Being highly conductive, stable, and low flammability fluids, ionic liquids (ILs) seem to be promising solvents with easily adjustable physical and solvation properties. In this work, we give an insight into the local structure of ILs around TEMPO and its oxidized form, TEMPO+, underlining striking differences in the solvation of these two species. The analysis is coupled with a study of thermodynamics and kinetics of oxidation in the frame of Marcus theory. Our systematic investigation includes imidazolium, pyrrolydinium, and phosphonium families combined with anions of different size, polarity, and flexibility, opting to provide a clear and comprehensive picture of the impact of the nature of IL ions on the behavior of radical/cation redox pairs. The obtained results will help to explain experimentally observed effects and to rationalize the design of TEMPO/IL systems.
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Affiliation(s)
- Kateryna Goloviznina
- Sorbonne Université, CNRS, Physicochimie des Électrolytes et Nanosystèmes Interfaciaux, F-75005Paris, France.,Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039Amiens Cedex, France
| | - Mathieu Salanne
- Sorbonne Université, CNRS, Physicochimie des Électrolytes et Nanosystèmes Interfaciaux, F-75005Paris, France.,Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039Amiens Cedex, France.,Institut Universitaire de France (IUF), 75231Paris, France
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Chandra P. A Review on the Consequence of 3D-Orienation of Cu/TEMPO/Imidazole Sequence on Selective Alcohol Oxidation. J Mol Struct 2022. [DOI: 10.1016/j.molstruc.2022.134249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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