Electrochemical Reduction of 2,4-Dinitrotoluene in Room Temperature Ionic Liquids: A Mechanistic Investigation*
Junqiao Lee A , Catherine E. Hay A and Debbie S. Silvester A BA Curtin Institute for Functional Molecules and Interfaces, and School of Molecular and Life Sciences, Curtin University, GPO Box U1987, Perth, WA 6845, Australia.
B Corresponding author. Email: d.silvester-dean@curtin.edu.au
Australian Journal of Chemistry 71(10) 818-825 https://doi.org/10.1071/CH18315
Submitted: 3 July 2018 Accepted: 9 August 2018 Published: 12 September 2018
Abstract
The reduction mechanism of 2,4-dinitrotoluene (DNT) has been studied in eight room temperature ionic liquids (RTILs) using cyclic voltammetry (CV), square wave voltammetry (SWV), chronoamperometry, and digital simulation. Two distinctive peaks are observed in the voltammetry, corresponding to the stepwise reduction of the two nitro groups on the aromatic ring. Diffusion coefficients (D) and electron counts (n) were calculated from chronoamperometric transients, revealing an electron count of one in most RTILs, and a linear relationship between D and the inverse of viscosity. Focusing on the first reduction only, the peak appears to be chemically reversible at low concentrations. However, as the concentration increases, the current of the reverse peak diminishes, suggesting that one or more chemical steps occur after the electrochemical step. The results from digital simulation of the CVs in one of the RTILs reveal that the most likely mechanism involves a deprotonation of the methyl group of a parent DNT molecule by the electrogenerated radical anion and/or a dimerisation of two electrogenerated radical anions. Elucidation of the reduction mechanism of DNT (and other explosives) is vital if electrochemical techniques are to be employed to detect these types of compounds in the field.
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