Reduction Pathways of 2,4,6-Trinitrotoluene: An Electrochemical and Theoretical Study
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- 作者：Chun Kiang Chua ; Martin Pumera ; Lubom铆r Rul铆拧ek
- 刊名：The Journal of Physical Chemistry C
- 出版年：2012
- 出版时间：February 16, 2012
- 年：2012
- 卷：116
- 期：6
- 页码：4243-4251
- 全文大小：391K
- 年卷期：v.116,no.6(February 16, 2012)
- ISSN：1932-7455
文摘
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 鈭?.310, 鈭?.463, and 鈭?.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 鈭?.475 and 鈭?.627 V vs NHE), whereas the two peaks in the 4-amino-2,6-dinitrotoluene voltammograms appear at 鈭?.537 and 鈭?.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 鈭?.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 鈭?.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鈥?/sup>/18H+ reduction of TNT. Last but not least, the calculations have shown that the thermodynamic stabilities of (isomeric) neutral radical species (X +e鈥?/b>+ H+)鈥攑resumably the regioselectivity-determining steps in the 6e鈥?/sup>/6H+ reductions of the individual NO2 groups鈥攁re within 2 kJ路mol鈥? (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.