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Shah R, Poon JF, Haidasz EA, Pratt DA. Temperature-Dependent Effects of Alkyl Substitution on Diarylamine Antioxidant Reactivity. J Org Chem 2021; 86:6538-6550. [PMID: 33900079 DOI: 10.1021/acs.joc.1c00365] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Alkylated diphenylamines are among the most efficacious radical-trapping antioxidants (RTAs) for applications at elevated temperatures since they are able to trap multiple radical equivalents due to catalytic cycles involving persistent diphenylnitroxide and diphenylaminyl radical intermediates. We have previously shown that some heterocyclic diarylamine RTAs possess markedly greater efficacy than typical alkylated diphenylamines, and herein, report on our efforts to identify optimal alkyl substitution of the scaffold, which we had found to be the ideal compromise between reactivity and stability. Interestingly, the structure-activity relationships differ dramatically with temperature: para-alkyl substitution slightly increased reactivity and stoichiometry at 37 and 100 °C due to more favorable (stereo)electronic effects and corresponding diarylaminyl/diarylnitroxide formation, while ortho-alkyl substitution slightly decreased both reactivity and stoichiometry. No such trends were evident at 160 °C; instead, the compounds were segregated into two groups based on the presence/absence of benzylic C-H bonds. Electron spin resonance spectroscopy indicates that increased efficacy was associated with lesser diarylnitroxide formation, and deuterium-labeling suggests that this is due to abstraction of the benzylic H atom, precluding nitroxide formation. Computations predict that this reaction path is competitive with established fates of the diarylaminyl radical, thereby minimizing the formation of off-cycle products and leading to significant gains in high-temperature RTA efficacy.
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Affiliation(s)
- Ron Shah
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
| | - Jia-Fei Poon
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
| | - Evan A Haidasz
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
| | - Derek A Pratt
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
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Raycroft MAR, Chauvin JPR, Galliher MS, Romero KJ, Stephenson CRJ, Pratt DA. Quinone methide dimers lacking labile hydrogen atoms are surprisingly excellent radical-trapping antioxidants. Chem Sci 2020; 11:5676-5689. [PMID: 32832049 PMCID: PMC7422964 DOI: 10.1039/d0sc02020f] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Accepted: 05/06/2020] [Indexed: 11/21/2022] Open
Abstract
Quinone method dimers, (bio)synthetic intermediates en route to many naturally products derived from resveratrol, are potent radical-trapping antioxidants, besting the phenols from which they are derived and to which they can be converted.
Hydrogen atom transfer (HAT) is the mechanism by which the vast majority of radical-trapping antioxidants (RTAs), such as hindered phenols, inhibit autoxidation. As such, at least one weak O–H bond is the key structural feature which underlies the reactivity of phenolic RTAs. We recently observed that quinone methide dimers (QMDs) synthesized from hindered phenols are significantly more reactive RTAs than the phenols themselves despite lacking O–H bonds. Herein we describe our efforts to elucidate the mechanism by which they inhibit autoxidation. Four possible reaction paths were considered: (1) HAT from the C–H bonds on the carbon atoms which link the quinone methide moieties; (2) tautomerization or hydration of the quinone methide(s) in situ followed by HAT from the resultant phenolic O–H; (3) direct addition of peroxyl radicals to the quinone methide(s), and (4) homolysis of the weak central C–C bond in the QMD followed by combination of the resultant persistent phenoxyl radicals with peroxyl radicals. The insensitivity of the reactivity of the QMDs to substituent effects, solvent effects and a lack of kinetic isotope effects rule out the HAT reactions (mechanisms 1 and 2). Simple (monomeric) quinone methides, to which peroxyl radicals add, were found to be ca. 100-fold less reactive than the QMDs, ruling out mechanism 3. These facts, combined with the poor RTA activity we observe for a QMD with a stronger central C–C bond, support mechanism 4. The lack of solvent effects on the RTA activity of QMDs suggests that they may find application as additives to materials which contain H-bonding accepting moieties that can dramatically suppress the reactivity of conventional RTAs, such as phenols. This reactivity does not extend to biological membranes owing to the increased microviscosity of the phospholipid bilayer, which suppresses QMD dissociation in favour of recombination. Interestingly, the simple QMs were found to be very good RTAs in phospholipid bilayers – besting even the most potent form of vitamin E.
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Affiliation(s)
- Mark A R Raycroft
- Department of Chemistry and Biomolecular Sciences , University of Ottawa , Ottawa , ON K1N 6N5 , Canada .
| | - Jean-Philippe R Chauvin
- Department of Chemistry and Biomolecular Sciences , University of Ottawa , Ottawa , ON K1N 6N5 , Canada .
| | - Matthew S Galliher
- Department of Chemistry , University of Michigan , Ann Arbor , MI 48109 , USA .
| | - Kevin J Romero
- Department of Chemistry , University of Michigan , Ann Arbor , MI 48109 , USA .
| | | | - Derek A Pratt
- Department of Chemistry and Biomolecular Sciences , University of Ottawa , Ottawa , ON K1N 6N5 , Canada .
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Chauvin JPR, Griesser M, Pratt DA. The antioxidant activity of polysulfides: it's radical! Chem Sci 2019; 10:4999-5010. [PMID: 31183049 PMCID: PMC6524666 DOI: 10.1039/c9sc00276f] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2019] [Accepted: 02/22/2019] [Indexed: 01/25/2023] Open
Abstract
Sulfurized olefins (polysulfides) containing four (or more) sulfur atoms react efficiently with peroxyl radicals by homolytic substitution, accounting for their primary antioxidant activity.
Olefin sulfurization, wherein alkenes and sulfur are heated together at high temperatures, produces branched polysulfides. Due to their anti-wear properties, they are indispensible additives to lubricants, but are also added to other petroleum-derived products as oxidation inhibitors. Polysulfides also figure prominently in the chemistry and biology of garlic and other plants of the Allium species. We previously reported that trisulfides, upon oxidation to their corresponding 1-oxides, are surprisingly effective radical-trapping antioxidants (RTAs) at ambient temperatures. Herein, we show that the homolytic substitution mechanism responsible also operates for tetrasulfides, but not trisulfides, disulfides or sulfides. Moreover, we show that this reactivity persists at elevated temperature (160 °C), enabling tetrasulfides to not only eclipse their 1-oxides as RTAs, but also hindered phenols and alkylated diphenylamines – the most common industrial antioxidant additives. The reactivity is unique to higher polysulfides (n ≥ 4), since homolytic substitution upon them at S2 yields stabilized perthiyl radicals. The persistence of perthiyl radicals also underlies the greater reactivity of polysulfides at elevated temperatures relative to their 1-oxides, since homolytic S–S bond cleavage is reversible in the former, but not in the latter. These results suggest that olefin sulfurization processes optimized for tetrasulfide production will afford materials that impart significantly better oxidation stability to hydrocarbon-based products to which polysulfides are added. Moreover, it suggests that RTA activity may contribute to the biological activity of plant-derived polysulfides.
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Affiliation(s)
- Jean-Philippe R Chauvin
- Department of Chemistry and Biomolecular Sciences , University of Ottawa , Ottawa , Ontario , Canada K1N 6N5 .
| | - Markus Griesser
- Department of Chemistry and Biomolecular Sciences , University of Ottawa , Ottawa , Ontario , Canada K1N 6N5 .
| | - Derek A Pratt
- Department of Chemistry and Biomolecular Sciences , University of Ottawa , Ottawa , Ontario , Canada K1N 6N5 .
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Clatworthy EB, Picone-Murray JL, Yuen AKL, Maschmeyer RT, Masters AF, Maschmeyer T. Investigating homogeneous Co/Br−/H2O2 catalysed oxidation of lignin model compounds in acetic acid. Catal Sci Technol 2019. [DOI: 10.1039/c8cy01902a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The catalytic oxidation of lignin model compounds by Co/Br−/H2O2 is investigated; substituting Br− for N-hydroxyphthalimide improved substrate conversion and product yield.
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Shah R, Pratt DA. Determination of Key Hydrocarbon Autoxidation Products by Fluorescence. J Org Chem 2016; 81:6649-56. [DOI: 10.1021/acs.joc.6b01032] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Ron Shah
- Department of Chemistry and
Biomolecular Sciences University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
| | - Derek A. Pratt
- Department of Chemistry and
Biomolecular Sciences University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
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Shah R, Haidasz EA, Valgimigli L, Pratt DA. Unprecedented Inhibition of Hydrocarbon Autoxidation by Diarylamine Radical-Trapping Antioxidants. J Am Chem Soc 2015; 137:2440-3. [DOI: 10.1021/ja5124144] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- Ron Shah
- Department
of Chemistry, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
| | - Evan A. Haidasz
- Department
of Chemistry, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
| | - Luca Valgimigli
- Department
of Chemistry “G. Ciamician”, University of Bologna, Bologna I-40126, Italy
| | - Derek A. Pratt
- Department
of Chemistry, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
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Haidasz EA, Shah R, Pratt DA. The Catalytic Mechanism of Diarylamine Radical-Trapping Antioxidants. J Am Chem Soc 2014; 136:16643-50. [DOI: 10.1021/ja509391u] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Evan A. Haidasz
- Department of Chemistry, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
| | - Ron Shah
- Department of Chemistry, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
| | - Derek A. Pratt
- Department of Chemistry, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
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Hanthorn JJ, Haidasz E, Gebhardt P, Pratt DA. A versatile fluorescence approach to kinetic studies of hydrocarbon autoxidations and their inhibition by radical-trapping antioxidants. Chem Commun (Camb) 2012; 48:10141-3. [DOI: 10.1039/c2cc35214a] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Han S, Qiu C, Cheng X, Ma S, Ren T. Study of the Reasons for Discoloration of Hydrotreated Naphthenic Lube Base Oil under Ultraviolet Radiation. Ind Eng Chem Res 2004. [DOI: 10.1021/ie049550m] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Sheng Han
- School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China, Research and Development Center of PetroChina Lubricating Oil Company, Lanzhou 730060, People's Republic of China, and Research and Development Center of PetroChina Lubricating Oil Company, Kelemayi 934003, People's Republic of China
| | - Chao Qiu
- School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China, Research and Development Center of PetroChina Lubricating Oil Company, Lanzhou 730060, People's Republic of China, and Research and Development Center of PetroChina Lubricating Oil Company, Kelemayi 934003, People's Republic of China
| | - Xingguo Cheng
- School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China, Research and Development Center of PetroChina Lubricating Oil Company, Lanzhou 730060, People's Republic of China, and Research and Development Center of PetroChina Lubricating Oil Company, Kelemayi 934003, People's Republic of China
| | - Shujie Ma
- School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China, Research and Development Center of PetroChina Lubricating Oil Company, Lanzhou 730060, People's Republic of China, and Research and Development Center of PetroChina Lubricating Oil Company, Kelemayi 934003, People's Republic of China
| | - Tianhui Ren
- School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China, Research and Development Center of PetroChina Lubricating Oil Company, Lanzhou 730060, People's Republic of China, and Research and Development Center of PetroChina Lubricating Oil Company, Kelemayi 934003, People's Republic of China
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Liquid-phase autoxidation of organic compounds at elevated temperatures. Absolute rate constant for intermolecular hydrogen abstraction in hexadecane autoxidation at 120-190°C. INT J CHEM KINET 2004. [DOI: 10.1002/kin.550260608] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Precipitation of Manganese in the p-Xylene Oxidation with Oxygen-Enriched Gas in Liquid Phase. B KOREAN CHEM SOC 2002. [DOI: 10.5012/bkcs.2002.23.3.369] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Affiliation(s)
- Alexander E. Shilov
- N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Russia
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Kamiya Y, Hama T, Kijima I. Formation of 2,6-Naphthalenedicarboxylic Acid by the Co–Mn–Br-Catalyzed Autoxidation of 2,6-Diethylnaphthalene in Acetic Acid. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 1995. [DOI: 10.1246/bcsj.68.204] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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