Reduction pathways of 2,4,6-trinitrotoluene : an electrochemical and theoretical study
The reduction pathways of trinitrotoluene are studied using electrochemical and computational methods. The electrochemical reduction of three nitro groups in 2,4,6-trinitrotoluene (TNT) is characterized by three major reduction peaks in cyclic voltammograms at the peak potentials of −0.310, −0.463,...
| Main Authors: | , , |
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| Other Authors: | |
| Format: | Journal Article |
| Language: | English |
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2013
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| Online Access: | https://hdl.handle.net/10356/99220 http://hdl.handle.net/10220/17251 |
| _version_ | 1811679230918918144 |
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| author | Chua, Chun Kiang Pumera, Martin Rulíšek, Lubomír |
| author2 | School of Physical and Mathematical Sciences |
| author_facet | School of Physical and Mathematical Sciences Chua, Chun Kiang Pumera, Martin Rulíšek, Lubomír |
| author_sort | Chua, Chun Kiang |
| collection | NTU |
| description | The reduction pathways of trinitrotoluene are studied using electrochemical and computational methods. The electrochemical reduction of three nitro groups in 2,4,6-trinitrotoluene (TNT) is characterized by three major reduction peaks in cyclic voltammograms at the peak potentials of −0.310, −0.463, and −0.629 V vs a normal hydrogen electrode (NHE). The second and third peaks coincide with the two peaks observed for the 2-amino-4,6-dinitrotoluene (at the potentials of −0.475 and −0.627 V vs NHE), whereas the two peaks in the 4-amino-2,6-dinitrotoluene voltammograms appear at −0.537 and −0.623 V and deviate more significantly from the corresponding two peaks in 2,4,6-trinitrotoluene. It suggests that the first NO2 group reduced in the overall process is the one in ortho position with respect to the CH3 group. Analogously, the 2,6-diamino-4-nitrotoluene exhibits a reduction peak at −0.629 V, almost identical to the third and second reduction peaks of 2,4,6-trinitrotoluene and 2-amino-4,6-dinitrotoluene, respectively. Since the other isomer, 2,4-diamino-6-nitrotoluene, exhibits a reduction peak at −0.712 V, we conclude that the second reduction occurs also in the ortho position with respect to the methyl group. Most of these observations are corroborated by quantum chemical calculations, which yielded reduction potentials in a good agreement with the experimental values (in relative scale). Thus, studying in detail all of the possible protonation and redox states in the reduction of the first nitro group and the key steps in the reduction of the second and third nitro groups, we have obtained a comprehensive and detailed picture of the mechanism of the full 18e–/18H+ reduction of TNT. Last but not least, the calculations have shown that the thermodynamic stabilities of (isomeric) neutral radical species (X +e–+ H+)—presumably the regioselectivity-determining steps in the 6e–/6H+ reductions of the individual NO2 groups—are within 2 kJ·mol–1 (i.e., comparable to RT). Therefore, the course of the reduction can be governed by the effect of the surroundings, such as the enzymatic environment, and a different regioselectivity can be observed under biological conditions. |
| first_indexed | 2024-10-01T03:05:52Z |
| format | Journal Article |
| id | ntu-10356/99220 |
| institution | Nanyang Technological University |
| language | English |
| last_indexed | 2024-10-01T03:05:52Z |
| publishDate | 2013 |
| record_format | dspace |
| spelling | ntu-10356/992202020-03-07T12:31:29Z Reduction pathways of 2,4,6-trinitrotoluene : an electrochemical and theoretical study Chua, Chun Kiang Pumera, Martin Rulíšek, Lubomír School of Physical and Mathematical Sciences The reduction pathways of trinitrotoluene are studied using electrochemical and computational methods. The electrochemical reduction of three nitro groups in 2,4,6-trinitrotoluene (TNT) is characterized by three major reduction peaks in cyclic voltammograms at the peak potentials of −0.310, −0.463, and −0.629 V vs a normal hydrogen electrode (NHE). The second and third peaks coincide with the two peaks observed for the 2-amino-4,6-dinitrotoluene (at the potentials of −0.475 and −0.627 V vs NHE), whereas the two peaks in the 4-amino-2,6-dinitrotoluene voltammograms appear at −0.537 and −0.623 V and deviate more significantly from the corresponding two peaks in 2,4,6-trinitrotoluene. It suggests that the first NO2 group reduced in the overall process is the one in ortho position with respect to the CH3 group. Analogously, the 2,6-diamino-4-nitrotoluene exhibits a reduction peak at −0.629 V, almost identical to the third and second reduction peaks of 2,4,6-trinitrotoluene and 2-amino-4,6-dinitrotoluene, respectively. Since the other isomer, 2,4-diamino-6-nitrotoluene, exhibits a reduction peak at −0.712 V, we conclude that the second reduction occurs also in the ortho position with respect to the methyl group. Most of these observations are corroborated by quantum chemical calculations, which yielded reduction potentials in a good agreement with the experimental values (in relative scale). Thus, studying in detail all of the possible protonation and redox states in the reduction of the first nitro group and the key steps in the reduction of the second and third nitro groups, we have obtained a comprehensive and detailed picture of the mechanism of the full 18e–/18H+ reduction of TNT. Last but not least, the calculations have shown that the thermodynamic stabilities of (isomeric) neutral radical species (X +e–+ H+)—presumably the regioselectivity-determining steps in the 6e–/6H+ reductions of the individual NO2 groups—are within 2 kJ·mol–1 (i.e., comparable to RT). Therefore, the course of the reduction can be governed by the effect of the surroundings, such as the enzymatic environment, and a different regioselectivity can be observed under biological conditions. 2013-11-05T04:47:35Z 2019-12-06T20:04:47Z 2013-11-05T04:47:35Z 2019-12-06T20:04:47Z 2012 2012 Journal Article Chua, C. K., Pumera, M., & Rulíšek, L. (2012). Reduction Pathways of 2,4,6-Trinitrotoluene: An Electrochemical and Theoretical Study. The Journal of Physical Chemistry C, 116(6), 4243-4251. https://hdl.handle.net/10356/99220 http://hdl.handle.net/10220/17251 10.1021/jp209631x en The journal of physical chemistry C |
| spellingShingle | Chua, Chun Kiang Pumera, Martin Rulíšek, Lubomír Reduction pathways of 2,4,6-trinitrotoluene : an electrochemical and theoretical study |
| title | Reduction pathways of 2,4,6-trinitrotoluene : an electrochemical and theoretical study |
| title_full | Reduction pathways of 2,4,6-trinitrotoluene : an electrochemical and theoretical study |
| title_fullStr | Reduction pathways of 2,4,6-trinitrotoluene : an electrochemical and theoretical study |
| title_full_unstemmed | Reduction pathways of 2,4,6-trinitrotoluene : an electrochemical and theoretical study |
| title_short | Reduction pathways of 2,4,6-trinitrotoluene : an electrochemical and theoretical study |
| title_sort | reduction pathways of 2 4 6 trinitrotoluene an electrochemical and theoretical study |
| url | https://hdl.handle.net/10356/99220 http://hdl.handle.net/10220/17251 |
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