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Price NJ, Nakamura A, Castagnoli N, Tanko JM. Why Does Monoamine Oxidase (MAO) Catalyze the Oxidation of Some Tetrahydropyridines? Chembiochem 2024:e202400126. [PMID: 38602445 DOI: 10.1002/cbic.202400126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2024] [Revised: 03/18/2024] [Indexed: 04/12/2024]
Abstract
Results pertaining to the mechanism of the oxidation of the tertiary amine 1-methyl-4-(1-methyl-1-H-pyrrol-2-yl)-1,2,3,6-tetrahydropyridine (MMTP, a close analog of the Parkinsonism inducing compound MPTP) by 3-methyllumiflavin (3MLF), a chemical model for the FAD cofactor of monoamine oxidase, are reported. MMTP and related compounds are among the few tertiary amines that are monoamine oxidase B (MAO-B) substrates. The MMTP/3MLF reaction is catalytic in the presence of O2 and the results under anaerobic conditions strongly suggest the involvement of radical intermediates, consistent with a single electron transfer mechanism. These observations support a new hypothesis to explain the MAO-catalyzed oxidations of amines. In general, electron transfer is thermodynamically unfavorable, and as a result, most 1° and 2° amines react via one of the currently accepted polar pathways. Steric constraints prevent 3° amines from reacting via a polar pathway. Those select 3° amines that are MAO substrates possess certain structural features (e. g., a C-H bond that is α- both to nitrogen and a C=C) that dramatically lower the pKa of the corresponding radical cation. Consequently, the thermodynamically unfavorable electron transfer equilibrium is driven towards products by an extremely favorable deprotonation step in the context of Le Chatelier's principle.
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Affiliation(s)
- Nathan J Price
- Department of Chemistry, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Akiko Nakamura
- Department of Chemistry, Colorado State University, Fort Collins, CO, 80523, USA
| | - Neal Castagnoli
- Department of Chemistry, Virginia Tech, Blacksburg, VA, 24061, USA
| | - James M Tanko
- Department of Chemistry, Virginia Tech, Blacksburg, VA, 24061, USA
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2
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Paradzinsky M, Troya D, Tanko JM. Insight into Hydrogen Abstractions by Nitrate Radical: Structural, Solvent Effects, and Evidence for a Polar Transition State. J Phys Chem A 2021; 125:5471-5480. [PMID: 34157229 DOI: 10.1021/acs.jpca.1c01726] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The role of a polarized transition state and solvent effects on nitrate radical reactions was examined with a previously under-reported class of substrates, ethers, for their atmospheric implications. Absolute rate constants for hydrogen abstraction from a series of alcohols, ethers, and alkanes by nitrate radical have been measured in acetonitrile, water, and mixtures of these two solvents. Across all of these classes of compounds, using a modified form of the Evans-Polanyi relationship, it is demonstrated that the observed structure/reactivity trends can be reconciled by considering the number of abstractable hydrogens, strength of the C-H bond, and ionization potential (IP) of the substrate. Hydrogen abstractions by nitrate radical occur with low selectivity and are characterized by an early transition state (α ≈ 0.3). The dependence of the rate constant on IP suggests a polar transition state with some degree (<10%) of charge transfer. These conclusions stand for reactions conducted in solution (CH3CN and H2O) as well as gas-phase values. Because of this polar transition state, the rate constants increase going from the gas phase to a polar solvent, and the magnitude of the increase is consistent with Kirkwood theory.
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Affiliation(s)
- Mark Paradzinsky
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States
| | - Diego Troya
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States
| | - James M Tanko
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States
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3
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Spencer JN, Grimm ML, Tanko JM. Interplay between Structure and Mechanism in Reductive Dissociative Electron Transfers to α,β -Epoxyketones. Chempluschem 2020; 85:2387-2396. [PMID: 33140919 DOI: 10.1002/cplu.202000305] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 07/31/2020] [Indexed: 11/08/2022]
Abstract
The electrochemical reduction of several α,β -epoxyketones was studied using cyclic (linear sweep) voltammetry, convolution voltammetry, and homogeneous redox catalysis. The results were reconciled to pertinent theories of electron transfer. α,β -Epoxyketones undergo dissociative electron-transfer reactions with C-O bond cleavage, via both stepwise and concerted mechanisms, depending on their structure. For aliphatic ketones, the preferred mechanism of reduction is consistent with the "sticky" concerted model for dissociative electron transfer. Bond cleavage occurs simultaneously with electron transfer, and there is a residual, electrostatic interaction in the ring-opened (distonic) radical anion. In contrast, for aromatic ketones, because the ring-closed radical anions are resonance-stabilized and exist at energy minima, a stepwise mechanism operates (electron transfer and bond cleavage occur in discrete steps). The rate constants for ring opening are on the order of 108 s-1 , and not significantly affected by substituents on the 3-membered ring (consistent with C-O bond cleavage). These results and conclusions were fully supported and augmented by molecular orbital calculations.
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Affiliation(s)
- Jared N Spencer
- Department of Natural Sciences, Montreat College, Montreat, NC 28757, USA
| | - Michelle L Grimm
- Department of Chemistry, Virginia Tech, Blacksburg, VA 24060, USA
| | - James M Tanko
- Department of Chemistry, Virginia Tech, Blacksburg, VA 24060, USA
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4
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Grimm ML, Suleman NK, Hancock AN, Spencer JN, Dudding T, Rowshanpour R, Castagnoli N, Tanko JM. Stereoelectronic and Resonance Effects on the Rate of Ring Opening of N-Cyclopropyl-Based Single Electron Transfer Probes. J Am Chem Soc 2020; 142:2640-2652. [PMID: 31913031 DOI: 10.1021/jacs.9b12617] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
N-Cyclopropyl-N-methylaniline (5) is a poor probe for single electron transfer (SET) because the corresponding radical cation undergoes cyclopropane ring opening with a rate constant of only 4.1 × 104 s-1, too slow to compete with other processes such as radical cation deprotonation. The sluggish rate of ring opening can be attributed to either (i) a resonance effect in which the spin and charge of the radical cation in the ring-closed form is delocalized into the phenyl ring, and/or (ii) the lowest energy conformation of the SET product (5•+) does not meet the stereoelectronic requirements for cyclopropane ring opening. To resolve this issue, a new series of N-cyclopropylanilines were designed to lock the cyclopropyl group into the required bisected conformation for ring opening. The results reveal that the rate constant for ring opening of radical cations derived from 1'-methyl-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-quinoline] (6) and 6'-chloro-1'-methyl-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-quinoline] (7) are 3.5 × 102 s-1 and 4.1 × 102 s-1, effectively ruling out the stereoelectronic argument. In contrast, the radical cation derived from 4-chloro-N-methyl-N-(2-phenylcyclopropyl)aniline (8) undergoes cyclopropane ring opening with a rate constant of 1.7 × 108 s-1, demonstrating that loss of the resonance energy associated with the ring-closed form of these N-cyclopropylanilines can be amply compensated by incorporation of a radical-stabilizing phenyl substituent on the cyclopropyl group. Product studies were performed, including a unique application of EC-ESI/MS (Electrochemistry/ElectroSpray Ionization Mass Spectrometry) in the presence of 18O2 and H218O to elucidate the mechanism of ring opening of 7•+ and trapping of the resulting distonic radical cation.
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Affiliation(s)
- Michelle L Grimm
- Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24060 , United States
| | - N Kamrudin Suleman
- Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24060 , United States
| | - Amber N Hancock
- Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24060 , United States
| | - Jared N Spencer
- Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24060 , United States
| | - Travis Dudding
- Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24060 , United States
| | - Rozhin Rowshanpour
- Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24060 , United States
| | - Neal Castagnoli
- Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24060 , United States
| | - James M Tanko
- Department of Chemistry , Virginia Tech , Blacksburg , Virginia 24060 , United States
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5
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Nakamura A, Latif MA, Deck PA, Castagnoli N, Tanko JM. Frontispiece: Evidence for a Proton‐Coupled Electron Transfer Mechanism in a Biomimetic System for Monoamine Oxidase B Catalysis. Chemistry 2020. [DOI: 10.1002/chem.202080463] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Akiko Nakamura
- Department of Chemistry Virginia Tech Blacksburg VA 24060 USA
| | | | - Paul A. Deck
- Department of Chemistry Virginia Tech Blacksburg VA 24060 USA
| | - Neal Castagnoli
- Department of Chemistry Virginia Tech Blacksburg VA 24060 USA
| | - James M. Tanko
- Department of Chemistry Virginia Tech Blacksburg VA 24060 USA
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6
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Nakamura A, Latif MA, Deck PA, Castagnoli N, Tanko JM. Evidence for a Proton-Coupled Electron Transfer Mechanism in a Biomimetic System for Monoamine Oxidase B Catalysis. Chemistry 2020; 26:823-829. [PMID: 31658386 DOI: 10.1002/chem.201904634] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Indexed: 11/11/2022]
Abstract
Mechanistic studies with 5-ethyl-3-methyllumiflavinium (Fl+ ) perchlorate, a biomimetic model for flavoenzyme monoamine oxidase B (MAO-B) catalysis, and the tertiary, allyl amine 1-methyl-4-(1-methyl-1 H-pyrrol-2-yl)-1,2,3,6-tetrahydropyridine (MMTP) reveal that proton-coupled electron transfer (PCET) may be an important pathway for MAO catalysis. The first step involves a single-electron transfer (SET) leading to the free radicals Fl. and MMTP. , the latter produced by deprotonation of the initially formed and highly acidic MMTP.+ . Molecular oxygen (O2 ) is found to play a hitherto unrecognized role in the early steps of the oxidation. MMTP and several structurally similar tertiary amines are the only tertiary amines oxidized by MAO, and their structural/electronic properties provide the key to understanding this behavior. A general hypothesis about the role of SET in MAO catalysis, and the recognition that PCET occurs with appropriately substituted substrates is presented.
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Affiliation(s)
- Akiko Nakamura
- Department of Chemistry, Virginia Tech, Blacksburg, VA, 24060, USA
| | | | - Paul A Deck
- Department of Chemistry, Virginia Tech, Blacksburg, VA, 24060, USA
| | - Neal Castagnoli
- Department of Chemistry, Virginia Tech, Blacksburg, VA, 24060, USA
| | - James M Tanko
- Department of Chemistry, Virginia Tech, Blacksburg, VA, 24060, USA
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7
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Abdel Latif MK, Spencer JN, Paradzinsky M, Tanko JM. Does Metal Ion Complexation Make Radical Clocks Run Fast? An Experimental Perspective. J Phys Chem A 2017; 121:9682-9686. [PMID: 29016138 DOI: 10.1021/acs.jpca.7b07575] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The rate constant for the β-scission of the cumyloxyl radical (kβ) was measured in the presence of various added electrolytes in acetonitrile and DMSO solvent. The results show that in CH3CN, kβ increases in the presence of added electrolyte, roughly paralleling the size of the cation: Li+ > Mg2+ ≈ Na+ > nBu4N+ > no added electrolyte. As suggested by Bietti et al. earlier, this effect is attributable to stabilizing ion-dipole interactions in the transition state of the developing carbonyl group, a conclusion further amplified by MO calculations (gas phase) reported herein. Compared to the gas phase predictions, however, this effect is seriously attenuated in solution because complexation of the cation to the electrophilic alkoxyl radical (relative to the solvent, CH3CN) is very weak. Because the interaction of Li+ and Na+ is much stronger with DMSO than with CH3CN, addition of these ions has no effect on the rate of β-scission.
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Affiliation(s)
- Marwa K Abdel Latif
- Department of Chemistry, Virginia Polytechnic Institute And State University , Blacksburg, Virginia 24061, United States
| | - Jared N Spencer
- Department of Chemistry, Virginia Polytechnic Institute And State University , Blacksburg, Virginia 24061, United States
| | - Mark Paradzinsky
- Department of Chemistry, Virginia Polytechnic Institute And State University , Blacksburg, Virginia 24061, United States
| | - James M Tanko
- Department of Chemistry, Virginia Polytechnic Institute And State University , Blacksburg, Virginia 24061, United States
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8
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Thompson-Witrick KA, Rouseff RL, Cadawallader KR, Duncan SE, Eigel WN, Tanko JM, O'Keefe SF. Comparison of Two Extraction Techniques, Solid-Phase Microextraction Versus Continuous Liquid-Liquid Extraction/Solvent-Assisted Flavor Evaporation, for the Analysis of Flavor Compounds in Gueuze Lambic Beer. J Food Sci 2015; 80:C571-6. [DOI: 10.1111/1750-3841.12795] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2014] [Accepted: 12/21/2014] [Indexed: 11/30/2022]
Affiliation(s)
| | - Russell L. Rouseff
- Citrus Research & Education Center; Univ. of Florida; 700 Experiment Station Rd. Lake Alfred FL 33880 U.S.A
| | - Keith R. Cadawallader
- Dept. of Food Science and Human Nutrition; Univ. of Illinois; 1302 West Pennsylvania Ave. Urbana IL 61801 U.S.A
| | - Susan E. Duncan
- Dept. of Food Science and Technology; Virginia Tech, Blacksburg; VA 24061 U.S.A
| | - William N. Eigel
- Dept. of Food Science and Technology; Virginia Tech, Blacksburg; VA 24061 U.S.A
| | - James M. Tanko
- Dept. of Chemistry; Virginia Tech; Blacksburg VA 24061 U.S.A
| | - Sean F. O'Keefe
- Dept. of Food Science and Technology; Virginia Tech, Blacksburg; VA 24061 U.S.A
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9
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Patil S, Chen L, Tanko JM. Effect of Lewis acids and low temperature initiators on the allyl transfer reaction involving phthalimido-N-oxyl radical. Tetrahedron Lett 2014. [DOI: 10.1016/j.tetlet.2014.10.129] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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10
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Patil S, Chen L, Tanko JM. C-H Bond Functionalization with the Formation of a C-C Bond: A Free Radical Condensation Reaction Based on the Phthalimido-N-oxyl Radical. European J Org Chem 2013. [DOI: 10.1002/ejoc.201301530] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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11
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Sarnoski PJ, Johnson JV, Reed KA, Tanko JM, O’Keefe SF. Separation and characterisation of proanthocyanidins in Virginia type peanut skins by LC–MSn. Food Chem 2012. [DOI: 10.1016/j.foodchem.2011.09.081] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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12
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Holland KW, Balota M, Eigel WN, Mallikarjunan P, Tanko JM, Zhou K, O'Keefe SF. ORAChromatography and total phenolics content of peanut root extracts. J Food Sci 2011; 76:C380-4. [PMID: 21535803 DOI: 10.1111/j.1750-3841.2011.02069.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A large number of compounds have been reported in peanut plants. Many of these compounds are phytoalexins, which are produced by plants experiencing environmental stress and often exhibit antioxidant activity. It is difficult to determine which of the many compounds has the greatest impact on total antioxidant capacity in a mixture. The objectives of this research were to examine the oxygen-radical absorbing capacity (ORAC) value and total phenolic contents of peanut root extracts and peanut root extract fractions collected via HPLC. Peanut roots were extracted from four different cultivars (Brantley, NC-12, Phillips, and Wilson) with 70% aqueous ethanol with ultrasonic assistance. Each cultivar was sampled in duplicate. The extracts were fractionated into 18 3-min fractions by HPLC using a C-18 column. Fractions and crude extracts were freeze dried. ORAC values and total phenolic content were then determined for all fractions and crude extracts. Fractions had a significant effect on the μM TE/mg gallic acid equivalents (GAE). ORAC values ranged from -46.89 μM TE to 185 μM TE in HPLC fractions. ORAChromatography can be used to focus on antioxidants in complex samples.
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Affiliation(s)
- Kevin W Holland
- Department of Food Science & Technology, Virginia Tech, Blacksburg, VA 24061, USA.
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13
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Jo CH, Dietrich AM, Tanko JM. Simultaneous degradation of disinfection byproducts and earthy-musty odorants by the UV/H2O2 advanced oxidation process. Water Res 2011; 45:2507-2516. [PMID: 21392812 DOI: 10.1016/j.watres.2011.02.006] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2010] [Revised: 02/03/2011] [Accepted: 02/04/2011] [Indexed: 05/30/2023]
Abstract
Advanced treatment technologies that control multiple contaminants are beneficial to drinking water treatment. This research applied UV/H(2)O(2) for the simultaneous degradation of geosmin, 2-methylisoborneol, four trihalomethanes and six haloacetic acids. Experiments were conducted in de-ionized water at 24 ± 1.0 °C with ng/L amounts of odorants and μg/L amounts of disinfection byproducts. UV was applied with and without 6 mg/L H(2)O(2.) The results demonstrated that brominated trihalomethanes and brominated haloacetic acids were degraded to a greater extent than geosmin and 2-methylisoborneol. Tribromomethane and dibromochloromethane were degraded by 99% and 80% respectively at the UV dose of 1200 mJ/cm(2) with 6 mg/L H(2)O(2), whereas 90% of the geosmin and 60% of the 2-methylisoborneol were removed. Tribromoacetic acid and dibromoacetic acid were degraded by 99% and 80% respectively under the same conditions. Concentrations of trichloromethane and chlorinated haloacetic acids were not substantially reduced under these conditions and were not effectively removed at doses designed to remove geosmin and 2-methylisoborneol. Brominated compounds were degraded primarily by direct photolysis and cleavage of the C-Br bond with pseudo first order rate constants ranging from 10(-3) to 10(-2) s(-1). Geosmin and 2-methylisoborneol were primarily degraded by reaction with hydroxyl radical with direct photolysis as a minor factor. Perchlorinated disinfection byproducts were degraded by reaction with hydroxyl radicals. These results indicate that the UV/H(2)O(2) can be applied to effectively control both odorants and brominated disinfection byproducts.
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Affiliation(s)
- Chang Hyun Jo
- Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, VA 24061, USA
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14
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Grimm ML, Allen WJ, Finn M, Castagnoli N, Tanko JM. Reaction of benzophenone triplet with aliphatic amines. What a potent neurotoxin can tell us about the reaction mechanism. Bioorg Med Chem 2011; 19:1458-63. [DOI: 10.1016/j.bmc.2011.01.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2010] [Revised: 12/28/2010] [Accepted: 01/01/2011] [Indexed: 10/18/2022]
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15
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Affiliation(s)
- Susan Mitroka
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
| | - Stephanie Zimmeck
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
| | - Diego Troya
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
| | - James M. Tanko
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
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16
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Struss JA, Sadeghipour M, Tanko JM. Radical additions to allyl bromides. A synthetically useful, ‘Tin-Free’ method for carbon–carbon bond formation. Tetrahedron Lett 2009. [DOI: 10.1016/j.tetlet.2009.02.154] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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17
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Abstract
Results pertaining to the electrochemical reduction of 1,2-diacetylcyclopropane (5), 1-acetyl-2-phenylcyclopropane (6), 1-acetyl-2-benzoylcyclopropane (7), and 1,2-dibenzoylcyclopropane (8) are reported. While 6*- exists as a discrete species, the barrier to ring opening is very small (<1 kcal/mol) and the rate constant for ring opening is >10(7) s(-1). For 7 and 8, the additional resonance stabilization afforded by the benzoyl moieties results in significantly lower rate constants for ring opening, on the order of 10(5)-10(6) s(-1). Electron transfer to 8 serves to initiate an unexpected vinylcyclopropane --> cyclopentene type rearrangement, which occurs via a radical ion chain mechanism. The results for reduction of 5 are less clear-cut: The experimental results suggest that the reduction is unexceptional, with a symmetry coefficient alpha </= 0.5, and reorganization energy consistent with a simple electron-transfer process (one electron reduction, followed by ring opening). In contrast, molecular orbital calculations suggest that 5*- has no apparent lifetime and that reduction of 5 may occur by a concerted dissociative electron transfer (DET) mechanism (i.e., electron transfer and ring opening occur simultaneously). These seemingly contradictory results can be reconciled if the increase in the internal reorganization energy associated with the onset of concerted DET is offset by a lowering of the solvent reorganization energy associated with electron transfer to a more highly delocalized LUMO.
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Affiliation(s)
- J M Tanko
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA.
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18
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Li X, Grimm ML, Igarashi K, Castagnoli N, Tanko JM. The first calibration of an aminiumyl radical ion clock: why N-cyclopropylanilines may be poor mechanistic probes for single electron transfer. Chem Commun (Camb) 2007:2648-50. [PMID: 17579767 DOI: 10.1039/b702157g] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Using direct and indirect electrochemical methods, the rate constant for ring opening of the radical cation generated from N-cyclopropyl-N-methylaniline was found to be 4.1 x 10(4) s(-1).
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Affiliation(s)
- Xiangzhong Li
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
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19
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Tanko JM, Gillmore JG, Friedline R, Chahma M. Cyclopropylcarbinyl → Homoallyl-Type Ring Opening of Ketyl Radical Anions. Structure/Reactivity Relationships and the Contribution of Solvent/Counterion Reorganization to the Intrinsic Barrier. J Org Chem 2005; 70:4170-3. [PMID: 15876112 DOI: 10.1021/jo047917r] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
[reaction: see text] Following a protocol developed by Mathivanan, Johnston, and Wayner (J. Phys. Chem. 1995, 99, 8190-8195), the radical anions of several cyclopropyl- and oxiranyl-containing carbonyl compounds were generated in an effort to measure the rate constants for their ring opening (k(o)) by laser flash photolysis. The results of these experiments are compared to those obtained from earlier electrochemical studies, and the combined data set is used to rationalize the kinetics of radical anion ring opening in a general context by using Saveant's theory pertaining to stepwise dissociative electron transfer (Acc. Chem. Res. 1993, 26, 455-461). Compared to cyclopropylcarbinyl --> homoallyl rearrangements of neutral free radicals, at comparable driving force, the radical anion ring openings are slightly slower. The small difference in rate is attributed to the contribution of an additional, approximately 2 kcal/mol, solvent reorganization component for the radical anion rearrangements. The solvent reorganization energy for ring opening of these radical anions is believed to be small because the negative charge does not move appreciably in the progression reactant --> transition state --> product.
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Affiliation(s)
- J M Tanko
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA.
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20
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Chahma M, Li X, Phillips JP, Schwartz P, Brammer LE, Wang Y, Tanko JM. Activation/Driving Force Relationships for Cyclopropylcarbinyl → Homoallyl-Type Rearrangements of Radical Anions. J Phys Chem A 2005; 109:3372-82. [PMID: 16833672 DOI: 10.1021/jp050193i] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
By using direct and indirect electrochemical methods, rate constants (ko) for cyclopropane ring opening of radical anions derived from the one-electron reduction of trans-1-benzoyl-2-phenylcyclopropane, trans-1-benzoyl-2-vinylcyclopropane, 2-methylenecyclopropyl phenyl ketone, spiro[anthracene-9,1'-cyclopropan-10-one], 3-cyclopropylcyclohex-2-en-1-one, and 3-(1-methylcyclopropyl)cyclohex-2-en-1-one were determined. Qualitatively, rate constants for ring opening of these (and other cyclopropyl- and cyclobutyl-containing radical anions) can be rationalized on the basis of the thermodynamic stability of the radical anion, the ability of substituents on the cyclopropyl group to stabilize the radical portion of the distonic radical anion, and the stability of the enolate portion of the distonic radical anion. On the basis of this notion, a thermochemical cycle for estimating deltaG(o) for ring opening was presented. For simple cyclopropyl-containing ketyl anions, a reasonable correlation between log(ko) and deltaG(o) was found, and stepwise dissociative electron transfer theory was applied to rationalize the results. Activation energies calculated with density functional theory (UB3LYP/6-31+G*) correlate reasonably well with measured log(ko). The derived log(ko) and deltaG(o) and log(ko) vs E(a) plots provide the basis for a "calibration curve" to predict rate constants for ring opening of radical anions derived from carbonyl compounds, in general.
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Affiliation(s)
- M'hamed Chahma
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA
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Finn M, Friedline R, Suleman NK, Wohl CJ, Tanko JM. Chemistry of the t-butoxyl radical: evidence that most hydrogen abstractions from carbon are entropy-controlled. J Am Chem Soc 2004; 126:7578-84. [PMID: 15198605 DOI: 10.1021/ja0493493] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Absolute rate constants and Arrhenius parameters for hydrogen abstractions (from carbon) by the t-butoxyl radical ((t) BuO.) are reported for several hydrocarbons and tertiary amines in solution. Combined with data already in the literature, an analysis of all the available data reveals that most hydrogen abstractions (from carbon) by (t) BuO. are entropy controlled (i.e., TdeltaS > deltaH, in solution at room temperature). For substrates with C-H bond dissociation energies (BDEs) > 92 kcal/mol, the activation energy for hydrogen abstraction decreases with decreasing BDE in accord with the Evans-Polanyi equation, with alpha approximately 0.3. For substrates with C-H BDEs in the range from 79 to 92 kcal/mol, the activation energy does not vary significantly with C-H BDE. The implications of these results in the context of the use of (t) BuO. as a chemical model for reactive oxygen-centered radicals is discussed.
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Affiliation(s)
- Meghan Finn
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA
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Tanko JM, Skell PS, Seshadri S. Absolute rate constants for bromine abstraction from N-bromoimides and Br2 by alkyl radicals. J Am Chem Soc 2002. [DOI: 10.1021/ja00218a035] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Tanko JM, Drumright RE, Suleman NK, Brammer LE. Radical Ion Probes. 3. The Importance of Resonance vs. Strain Energy in the Design of SET Probes Based upon the Cyclopropylcarbinyl-to-Homoallyl Radical Rearrangement. J Am Chem Soc 2002. [DOI: 10.1021/ja00084a020] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Khanna R, Armstrong B, Cui H, Tanko JM. Inverted regioselectivities in the reactions of chlorine atoms with heteroarylmethanes. J Am Chem Soc 2002. [DOI: 10.1021/ja00041a015] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Tanko JM, Drumright RE. Radical ion probes. 2. Evidence for the reversible ring opening of arylcyclopropylketyl anions. Implications for mechanistic studies. J Am Chem Soc 2002. [DOI: 10.1021/ja00031a045] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Tanko JM, Suleman NK. Solvent Pressure Effects in Free Radical Reactions. 2. Reconciliation of the Gas and Condensed Phase Chlorination of Cyclopropane. J Am Chem Soc 2002. [DOI: 10.1021/ja00091a020] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Tanko JM, Mas RH, Suleman NK. Stereoelectronic effects on chemoselectivity in the free radical bromination of arylcyclopropanes. J Am Chem Soc 2002. [DOI: 10.1021/ja00170a021] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Skell PS, Luning U, McBain DS, Tanko JM. Ground- and excited-state succinimidyl radicals in chain reactions: a reexamination. J Am Chem Soc 2002. [DOI: 10.1021/ja00261a020] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Tanko JM, Suleman NK, Hulvey GA, Park A, Powers JE. Solvent pressure effects in free-radical reactions. A selectivity inversion in free-radical brominations induced by solvent. J Am Chem Soc 2002. [DOI: 10.1021/ja00064a013] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Tanko JM, Kamrudin N, Blackert JF. Kinetic vs. thermodynamic factors in .alpha.-hydrogen atom abstractions from alkylaromatics. 2. Reactivities of .alpha.-alkylnaphthalenes and several conformationally locked alkylaromatics toward bromine atom. J Org Chem 2002. [DOI: 10.1021/jo00022a034] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Stevenson JP, Jackson WF, Tanko JM. Cyclopropylcarbinyl-type ring openings. Reconciling the chemistry of neutral radicals and radical anions. J Am Chem Soc 2002; 124:4271-81. [PMID: 11960456 DOI: 10.1021/ja0041831] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Cyclopropylcarbinyl --> homoallyl and related rearrangements of radical ions (a) are frequently used as mechanistic "probes" to detect the occurrence of single electron transfer in chemical and biochemical processes, (b) provide the basis for mechanism-based drug design, and (c) are important tools in organic synthesis. Unfortunately, these rearrangements are poorly understood, especially with respect to the effect of substrate structure on reactivity. Frequently, researchers assume that the same factors which govern the reactivity of neutral free radicals also pertain to radical ions. The results reported herein demonstrate that in some cases structure-reactivity trends in radical ion rearrangements are very different from neutral radicals. For radical ions, delocalizations of both charge and spin are important factors governing their reactivity.
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Affiliation(s)
- J Paige Stevenson
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA
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Affiliation(s)
- J M Tanko
- Department of Chemistry, Virginia Polytechnic Institute and State University Blacksburg, Virginia 24061-0212, USA
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Tanko JM, Pacut R. Enhanced cage effects in supercritical fluid solvents. the behavior of diffusive and geminate caged-pairs in supercritical carbon dioxide. J Am Chem Soc 2001; 123:5703-9. [PMID: 11403602 DOI: 10.1021/ja002800f] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The behavior of geminate and diffusive radical caged-pairs arising from the photolysis of dicumyl ketone in conventional and supercritical carbon dioxide (SC--CO(2)) solvents has been examined. The results suggest that locally enhanced solvent density about a solute (solvent/solute clustering) can lead to an enhanced cage effect near the critical pressure in supercritical fluid solvents. This enhanced cage effect is similar in magnitude for both diffusive and geminate caged-pairs.
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Affiliation(s)
- J M Tanko
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0212, USA
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Dandekar SA, Greenwood SN, Greenwood TD, Mabic S, Merola JS, Tanko JM, Wolfe JF. Synthesis of Succinimido[3,4-b]indane and 1,2,3,4,5,6-Hexahydro-1,5-methano-3-benzazocine-2,4-dione by Sequential Alkylation and Intramolecular Arylation of Enolates Derived from N,N,N'N'-Tetramethylbutanediamides and N,N,N'N'-Tetramethylpentanediamides. J Org Chem 1999; 64:1543-1553. [PMID: 11674217 DOI: 10.1021/jo982000b] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
The tricyclic title compounds, 4 and 5, were synthesized by initial alkylation of the lithium monoenolates of N,N,N',N'-tetramethylbutanediamide (6) and N,N,N',N'-tetramethylpentanediamide (19) with 2-iodobenzyl chloride in liquid NH(3) at -60 degrees C to afford 2-(2-iodobenzyl)-N,N,N',N'-tetramethylbutanediamide (9) and 2-(2-iodobenzyl)-N,N,N',N'-tetramethylpentanediamide (20) in yields of 88 and 87%, respectively. Treatment of 9 with KNH(2) in liquid NH(3) resulted in formation and intramolecular arylation of the less-substituted alpha-enolate to produce trans-1,2-bis(N,N-dimethylcarboxamido)indane (10a) in 60% yield. Selective hydrolysis of 10a with aqueous Na(2)O(2) gave trans-1-(N,N-dimethylcarboxamido)indane-2-carboxylic acid (17), which was then converted to bridged succinimide 4 by transformation to trans-1-(N,N-dimethylcarboxamido)indane-2-carboxamide (10c) followed by cyclization of this mixed primary/tertiary amide by means of NaH in refluxing THF. Treatment of 20 with KNH(2) in liquid NH(3) led to intramolecular arylation and accompanying ammonolysis to afford trans-1-(N,N-dimethylcarboxamido)-1,2,3,4-tetrahydronaphthalene-3-carboxamide (21b). Conversion of 21b to 5 was similarly effected by means of NaH. Experiments designed to test the mechanistic aspects of the intramolecular arylations provided evidence for competing aryne and SET pathways.
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Affiliation(s)
- Sushama A. Dandekar
- Department of Chemistry and the Harvey W. Peters Research Center for the Study of Parkinson's Disease and Disorders of the Central Nervous System, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0212
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Tanko JM, Brammer LE. Radical Ion Probes. 7. Behavior of a “Hypersensitive” Probe for Single Electron Transfer in Reactions Not Involving Electron Transfer. J Org Chem 1997. [DOI: 10.1021/jo970584w] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- James M. Tanko
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0212
| | - Larry E. Brammer
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0212
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Tanko JM, Blackert JF. Absolute rate constants for abstraction of chlorine from three chlorinating agents by alkyl radicals. ACTA ACUST UNITED AC 1996. [DOI: 10.1039/p29960001775] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Abstract
Free-radical side-chain brominations of alkylaromatics in supercritical carbon dioxide (SC-CO(2)) are reported. Direct bromination of toluene and ethylbenzene form the corresponding benzyl bromides in high yield. The observed selectivity in SC-CO(2) is similar to that observed in conventional organic solvents. Also, SC-CO(2) is an effective alternative to carbon tetrachloride for use in the classical Ziegler bromination with N-bromosuccinimide. Reaction yields are high, side products are minimized, and bromine-atom selectivities are observed. Thus, SC-CO(2) must be useful as a viable, environmentally benign substitute for many of the solvents typically used for free-radical reactions.
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Tanko JM, Brammer LE. Utilization of 1,1-dimethyl-4,6-di-tert-butylspiro[2,5]octa-3,6-dien-5-one as a ‘hypersensitive’ probe for single electron transfer to carbonyl compounds. ACTA ACUST UNITED AC 1994. [DOI: 10.1039/c39940001165] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Tanko JM, Suleman NK, Blackert JF. Kinetic vs. thermodynamic factors in .alpha.-hydrogen atom abstractions from alkylaromatics. 2. Reactivities of .alpha.-alkylnaphthalenes and several conformationally locked alkylaromatics toward bromine atom. [Erratum to document cited in CA115(19):207432f]. J Org Chem 1992. [DOI: 10.1021/jo00030a052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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