Spectroelectrochemistry of Non-Aromatic Explosives in Acetonitrile and the Influence of Superoxide

Abstract

The spectroelectrochemistry of non-aromatic explosive compounds, namely two nitramines (RDX and HMX), a nitrate ester (PETN), and a plastic explosive composite (Semtex 1A) in acetonitrile (AN) is reported. The redox behavior of these compounds is studied using cyclic voltammetry while monitoring changes in UV absorbance to identify transient intermediates and product species. In search of a low-cost solution-phase detection technique for explosives, we compare the spectroelectrochemistry of these compounds in the presence and absence of naturally dissolved oxygen (2 mM in AN), where the superoxide radical is co-electrogenerated during analyte reduction. Free superoxide yields a prominent UV signal in this medium (λmax = 250 nm) that the explosives’ nitro or methylene groups attenuate stoichiometrically. Overlapping UV spectra of multiple species are deconvoluted using a new strategy, spectral regional baselining, for time- and potential-resolved spectroelectrochemical (SEC) analysis. SEC data for nitrite (NO2 -), nitrate (NO3 -), and nitromethane (CH3NO2) were also collected to support proposed reaction mechanisms for the transformation of explosives that include superoxide adducts and dimerized azoxy reduced intermediates. The findings expand the understanding of high-explosive solution-phase chemistry and offer a route to novel signal transduction for (electro-)chemical sensors for energetic materials.Figure 1. Spectroelectrochemistry of PETN in aerated acetonitrile with regions denoted for differential baseline analysis. (a) 3-D projected cyclic voltammogram (black) with UV absorbance from relevant wavelength (red, unscaled) as a function of time and potential; (b) full spectra (time domain) during cyclic voltammogram. Figure 1