Unimolecular Decomposition Reactions of Picric Acid and Its Methylated Derivatives─A DFT Study

Abstract

To handle energetic materials safely, it is important to have knowledge about their sensitivity. Density functional theory (DFT) has proven a valuable tool in the study of energetic materials, and in the current work, DFT is employed to study the thermal unimolecular decomposition of 2,4,6-trinitrophenol (picric acid, PA), 3-methyl-2,4,6-trinitrophenol (methyl picric acid, mPA), and 3,5-dimethyl-2,4,6-trinitrophenol (dimethyl picric acid, dmPA). These compounds have similar molecular structures, but according to the literature, mPA is far less sensitive to impact than the other two compounds. Three pathways believed important for the initiation reactions are investigated at 0 and 298.15 K. We compare the computed energetics of the reaction pathways with the objective of rationalizing the unexpected sensitivity behavior. Our results reveal a few if any significant differences in the energetics of the three molecules, and thus do not reflect the sensitivity deviations observed in experiments. These findings point toward the potential importance of crystal structure, crystal morphology, bimolecular reactions, or combinations thereof on the impact sensitivity of nitroaromatics.

Understanding Explosive Sensitivity with Effective Trigger Linkage Kinetics

“…This picture is supported by the systematic study by Zhang of bond dissociation energies in nitromethane as a function of molecular distortion . In addition, recent gas-phase DFT studies of a set of derivatives of picric acid by Wiik et al highlighted the potential shortcomings of using simple bond dissociation energies to infer explosive sensitivities and reaction mechanisms …”

“…For instance, Jensen et al and Wiik et al computed−NO 2 bond dissociation energies using gasphase DFT for a set of explosive molecules to estimate trigger linkage strengths. 23,76 However, based on our work, their focus on −NO 2 loss is likely to be an oversimplification of the first reactions in many explosives because reactions can often start at non-energetic moieties. A properly thermostated MD simulation samples the full potential energy surface of the reactant molecule and will find all possible decomposition pathways with the correct probabilities (which are based on their rates via eq 3) without requiring any prior physical intuition or guidance from the user.…”

“…75 In addition, recent gasphase DFT studies of a set of derivatives of picric acid by Wiik et al highlighted the potential shortcomings of using simple bond dissociation energies to infer explosive sensitivities and reaction mechanisms. 76 The Arrhenius plots presented in Figures 2 and 3 provide a considerable amount of insight into the relative stabilities and sensitivities of the set of explosives. For instance, those molecules that lie toward the right of the plot, which include the sensitive explosives ETN, tetryl, and PETN and its derivatives, react at lower temperatures than those that lie toward the left, which include the relatively insensitive explosives 2,4,6-TNT, DATB, TATB, and NQ.…”

Efficient photocatalytic degradation of o-nitrophenol using ZrO2 -RGO nanocomposite : Hydrothermal approach

“…Phenolic compounds are regarded as priority pollutants and listed as hazardous pollutants by the environmental protection agencies of India [3]. The release of the ortho-nitrophenols into the environment without treatment or partial treatment poses a severe threat to living beings in the ecological system [4]. Even though several methods are available for treating these compounds, like the Fenton process, membrane ltration, electrochemical methods, biodegradation etc., they have high associated costs and require more skills for implementation [5][6].…”

Complete and selective nitration of tyrosine residue in peptides caused by ultraviolet matrix-assisted laser desorption/ionization

“…Nitroaromatic compounds have provided unique aspects regarding the reactivities of nitro group (NO 2 ) such as intramolecular hydrogen transfer, isomerization and C-NO 2 bond homolysis caused by thermal and light stimuli [1,2]. A nitroaromatic biological compound, 3-nitrotyrosine (3-NT) in peptides and proteins, is of interest in connection with oxidative post-transnational modifications, signal transduction, pathogens of specific diseases, and a biomarker [3,4].…”