Predicting Reduction Rates of Energetic Nitroaromatic Compounds Using Calculated One-Electron Reduction Potentials

Abstract

The evaluation of new energetic nitroaromatic compounds (NACs) for use in green munitions formulations requires models that can predict their environmental fate. Previously invoked linear free energy relationships (LFER) relating the log of the rate constant for this reaction (log(k)) and one-electron reduction potentials for the NAC (E1NAC) normalized to 0.059 V have been re-evaluated and compared to a new analysis using a (nonlinear) free-energy relationship (FER) based on the Marcus theory of outer-sphere electron transfer. For most reductants, the results are inconsistent with simple rate limitation by an initial, outer-sphere electron transfer, suggesting that the linear correlation between log(k) and E1NAC is best regarded as an empirical model. This correlation was used to calibrate a new quantitative structure-activity relationship (QSAR) using previously reported values of log(k) for nonenergetic NAC reduction by Fe(II) porphyrin and newly reported values of E1NAC determined using density functional theory at the M06-2X/6-311++G(2d,2p) level with the COSMO solvation model. The QSAR was then validated for energetic NACs using newly measured kinetic data for 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT), and 2,4-dinitroanisole (DNAN). The data show close agreement with the QSAR, supporting its applicability to other energetic NACs.

Batch soil adsorption and column transport studies of 2,4-dinitroanisole (DNAN) in soils

“…Based on one-electron standard reduction potentials DNAN has lower tendency for nitro to amino group reductions than TNT (Salter-Blanc et al, 2015). The mass-loss rate for DNAN was slower than the ones previously observed for TNT in one of the studied soils.…”

Metal‐Free and Heterogeneous Photocatalytic Reduction of 4‐Nitroaniline by a Poly(Ethylene Glycol)‐Supported Eosin Dye under Visible‐Light Exposure

“…[27] This suggests an electron transfer reaction from EY* (560 nm) to 4-NA and the formation of 4-NA radical anion species (NH 2 À PhÀ NO 2 * À ) ( Figure 7D). According to the negative free energy change~G = À 0.546 V calculated from the Rehm-Weller equation, [65] it could be concluded that the photoinduced electron transfer reaction between EY* and 4-NA is favored in water/ACN considering the values of E ox (EY) = + 0.78 eV, [40] E Red (4-NA) = À 0.564 V, [66] eosin triplet state energy ET (EY) = 1.89 eV, and negligible electrostatic interaction energy for the initially formed ion pair in polar solvents. The experimental value of bimolecular quenching rate constant between EY* and 4-NA (k (EY*/4-NA)) was evaluated at 4.8 × 10 8 M À 1 s À 1 .…”

In silico environmental chemical science: properties and processes from statistical and computational modelling

“…This level of accuracy is not satisfactory for some purposes (e.g., direct calculation of absolute values of specic rate constants for contaminant degradation 78 ), but it may be satisfactory for triaging among possible chemical reaction pathways or for descriptor data in QSAR development. 79,80 In addition, the overall accuracy of DFT calculations can be improved by using methods that make use of empirical additivity rules for molecular properties, where various properties of larger molecules can be thought of as being made up of additive contributions of atoms, bonds, or collections of atoms and bonds (i.e., functional groups) of the molecule. 81,82 These approaches have proven to be effective for small organic molecules, [83][84][85][86][87][88][89][90] and recently they have been used in advanced computational algorithms that can be used to simulate extremely large molecules, even including complex proteins and DNA chains.…”