Comprehensive investigations of kinetics of alkaline hydrolysis of TNT (2,4,6-trinitrotoluene), DNT (2,4-dinitrotoluene), and DNAN (2,4-dinitroanisole)

Experimental and Computational Study of Pyrogenic Carbonaceous Matter Facilitated Hydrolysis of 2,4-Dinitroanisole (DNAN)

This study investigated the reaction pathway of 2,4-dinitroanisole (DNAN) on the pyrogenic carbonaceous matter (PCM) to assess the scope and mechanism of PCM-facilitated surface hydrolysis. DNAN degradation was observed at pH 11.5 and 25 °C with a model PCM, graphite, whereas no significant decay occurred without graphite. Experiments were performed at pH 11.5 due to the lack of DNAN decay at pH below 11.0, which was consistent with previous studies. Graphite exhibited a 1.78-fold enhancement toward DNAN decay at 65 °C and pH 11.5 relative to homogeneous solution by lowering the activation energy for DNAN hydrolysis by 54.3 ± 3.9%. This is supported by our results from the computational modeling using Car-Parrinello simulations by ab initio molecular dynamics/molecular mechanics (AIMD/MM) and DFT free energy simulations, which suggest that PCM effectively lowered the reaction barriers by approximately 8 kcal mol-1 compared to a homogeneous solution. Quaternary ammonium (QA)-modified activated carbon performed the best among several PCMs by reducing DNAN half-life from 185 to 2.5 days at pH 11.5 and 25 °C while maintaining its reactivity over 10 consecutive additions of DNAN. We propose that PCM can affect the thermodynamics and kinetics of hydrolysis reactions by confining the reaction species near PCM surfaces, thus making them less accessible to solvent molecules and creating an environment with a weaker dielectric constant that favors nucleophilic substitution reactions. Nitrite formation during DNAN decay confirmed a denitration pathway, whereas demethylation, the preferred pathway in homogeneous solution, produces 2,4-dinitrophenol (DNP). Denitration catalyzed by PCM is advantageous to demethylation because nitrite is less toxic than DNAN and DNP. These findings provide critical insights for reactive adsorbent design that has broad implications for catalyst design and pollutant abatement.

Heuristic-Based Alkaline Hydrolysis Mechanism of Nitrate Ester (Nitrocellulose Monomer) and Nitroamine (Hexogen) Compounds: Electrostatic Attraction Effect of the Nitro Group

The alkaline hydrolysis reaction of energetic materials is important and complex. With improved performance, AMK_Mountain was used to systematically study the alkaline hydrolysis of the nitrocellulose monomer and hexogen. The reaction pathways showed that the nitrocellulose monomer produces the nitrate anion and nitrite anion differently, while hexogen only produces the nitrite anion. Electronic structure results at the M06-2X/6-311G(d,p)/PCM(Pauling) level showed that the nitrocellulose monomer and hexogen have a similar pathway in their main energy-releasing process (nitrite anion production): with electrostatic attraction effects after proton transfer, the nitrite anion dissociates from the original structure with a low barrier. Moreover, during the alkaline hydrolysis of the nitrocellulose monomer, the metastable intermediates after proton transfer may be directly generated following transition states that, structurally, tend to produce nitrite anions "proximal" to the proton transfer site and produce nitrate anions "distal" to the proton transfer site. Electronic structure analysis showed that representative metastable intermediates revealed that the charge transfer caused by electrostatic attraction may be the direct cause of these reactions.

Surface-catalyzed hydrolysis by pyrogenic carbonaceous matter and model polymers: An experimental and computational study on functional group and pore characteristics

We employed a polymer network to understand what properties of pyrogenic carbonaceous matter (PCM; e.g., activated carbon) confer its reactivity, which we hereinafter referred to as PCM-like polymers (PLP). This approach allows us to delineate the role of functional groups and micropore characteristics using 2,4,6-trinitrotoluene (TNT) as a model contaminant. Six PLP were synthesized via cross-coupling chemistry with specific functionality (-OH, -NH2, -N(CH3)2, or -N ( CH 3 ) 3 + ) and pore characteristics (mesopore, micropore). Results suggest that PCM functionality catalyzed the reaction by: (1) serving as a weak base (-OH, -NH2) to attack TNT, or (2) accumulating OH- near PCM surfaces (-N ( CH 3 ) 3 + ). Additionally, TNT hydrolysis rates, pH and co-ion effects, and products were monitored. Microporous PLP accelerated TNT decay compared to its mesoporous counterpart, as further supported by molecular dynamics modeling results. We also demonstrated that quaternary ammonium-modified activated carbon enhanced TNT hydrolysis. These findings have broad implications for pollutant abatement and catalyst design.

Density functional theory explorations of parathion and paraoxon hydrolysis as a function of the underlying alkaline environment

Parathion, a once commonly used pesticide known for its potential toxicity, can follow several degradation mechanisms in the environment. Given the species stability and persistence, parathion can be washed into waterways from rain, and therefore an atomistic perspective of the hydrolysis of parathion, and its byproduct paraoxon, is required in order to understand its fate in the environment. Experimental studies have determined that pH plays an important role in the calculated hydrolysis rate constants of parathion degradation. In this work, the degradation of parathion into either paraoxon or 4-nitrophenol, and the degradation of paraoxon to 4-nitrophenol are explored through density functional theory using the M06-2X functional. How the level of basicity affects the reaction mechanism is explored through two different hydroxide/water environments. Our calculations support the anticipated mechanisms determined by previous experimental work that the formation of 4-nitrophenol is the predominant pathway in hydrolysis of parathion.

Computational Predictions of the Hydrolysis of 2,4,6-Trinitrotoluene (TNT) and 2,4-Dinitroanisole (DNAN)

Hydrolysis is a common transformation reaction that can affect the environmental fate of many organic compounds. In this study, three proposed mechanisms of alkaline hydrolysis of 2,4,6-trinitrotoluene (TNT) and 2,4-dinitroaniline (DNAN) were investigated with plane-wave density functional theory (DFT) combined with ab initio and classical molecular dynamics (AIMD/MM) free energy simulations, Gaussian basis set DFT calculations, and correlated molecular orbital theory calculations. Most of the computations in this study were carried out using the Arrows web-based tools. For each mechanism, Meisenheimer complex formation, nucleophilic aromatic substitution, and proton abstraction reaction energies and activation barriers were calculated for the reaction at each relevant site. For TNT, it was found that the most kinetically favorable first hydrolysis steps involve Meisenheimer complex formation by attachment of OH^- at the C1 and C3 arene carbons and proton abstraction from the methyl group. The nucleophilic aromatic substitution reactions at the C2 and C4 arene carbons were found to be thermodynamically favorable. However, the calculated activation barriers were slightly lower than in previous studies, but still found to be ΔG^‡ ≈ 18 kcal/mol using PBE0 AIMD/MM free energy simulations, suggesting that the reactions are not kinetically significant. For DNAN, the barriers of nucleophilic aromatic substitution were even greater (ΔG^‡ > 29 kcal/mol PBE0 AIMD/MM). The most favorable hydrolysis reaction for DNAN was found to be a two-step process in which the hydroxyl first attacks the C1 carbon to form a Meisenheimer complex at the C1 arene carbon C1-(OCH₃)OH^-, and subsequently, the methoxy anion (-OCH₃) at the C1 arene carbon dissociates and the proton shuttles from the C1-OH to the dissociated methoxy group, resulting in methanol and an aryloxy anion.

Decomposition of 2,4,6-trinitrotoluene (TNT) and 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO) by Fe13O13 nanoparticle: density functional theory study

To obtain more insight into the mechanisms of the decomposition of energetic compounds, we performed a computational study of the interaction of Fe₁₃O₁₃ nanoparticles with two energetic molecules such as 2,4,6-trinitrotoluene (TNT) and 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO). The density functional theory using M06-2X, B3LYP, and BLYP density functionals was applied. We found that the reactivity of these molecules strongly depends on the place of adsorption (so-called top and bottom planes of Fe₁₃O₁₃). Namely, only the interaction with the bottom plane results in the thermodynamic characteristics of the decomposition that provide a medium reaction rate for the studied processes. Several pathways for such decomposition were found. One of them is the inter-complex oxygen transfer of nitro-group oxygen to Fe₁₃O₁₃. This pathway results in the formation of adsorbed nitroso compounds. The second pathway describes a more complex decomposition that includes the transfer of the nitro-group oxygen accompanied by the hydrogen transfer. In all cases, the interaction of energetic molecules with Fe₁₃O₁₃ nanoparticles takes place along with a barrier-less electron transfer from Fe₁₃O₁₃ to TNT or NTO species.

Degradation of Dissolved RDX, NQ, and DNAN by Cathodic Processes in an Electrochemical Flow-Through Reactor

Both legacy munitions compounds (e.g., RDX) and new insensitive high explosives (e.g. DNAN, NQ) are being manufactured and utilized concurrently, and there exists a need for wastewater treatment systems that are able to degrade both classes of explosives. Electrochemical systems offer treatment possibilities using inexpensive materials and no chemical additions. Electrochemically induced removal of RDX, NQ, and DNAN were separately studied within an electrochemical plug flow reactor hosting a stainless steel (SS) cathode and downstream Ti/MMO anode. Varying wire mesh cathodes and operating conditions were evaluated in an effort to identify the optimal cathode material, to determine the relative contributions of cathodically-induced removal processes, to shorten time to steady-state removal conditions, and to find practical ranges of operating conditions. Applied current allowed the cathode to support munitions removal mainly by direct reduction at the cathode surface, and the secondary reactions of cathodically-induced alkaline hydrolysis and catalytic hydrogenation by adsorbed H on Ni-containing cathode surfaces might contribute to some munitions degradation. The optimal cathode material was identified as SS grade 316, possibly due to its superior Ni content and lack of corrosion protection coating. Higher current, longer cathode length, and smaller mesh pore sizes resulted in slightly greater removal extents and shorter acclimation times to steady state removal conditions, but there are practical upper limits to these properties. Higher Ni content within SS improved RDX and NQ removal but does not affect DNAN removal. Prolonged use of SS grade 316 showed no debilitating changes in electrical performance or chemical content.

Automated reaction mechanisms and kinetics based transition state search process AMK-gau_xtb and its application to the substitution reaction of the nitroso group in 2,4,6-trinitrotoluene by hydroxide anion in the aqueous phase

The automated reaction mechanisms and kinetics (AutoMeKin) program evolved from a transition state search using chemical dynamics simulations (TSSCDS). It combines a series of empirical, semi-empirical and ab initio calculation methods to provide a two-step transition state search process from low-level calculation to high-level calculation. However, in this process, with the lack of solution keywords, low-level calculation has the problem of low accuracy or high computational cost. To address this problem, the gau_xtb interface that combines the high efficiency of xTB and the comprehensiveness of Gaussian09 was incorporated into the AutoMeKin2020 in this work and after adding some keywords, the AMK-gau_xtb software was obtained. Meanwhile, to adapt to the interface, the MD sampling results used Quadratic Synchronous Transit 3 (QST3) for the low-level transition state search. As an application, the reaction in which the nitroso group is replaced by hydroxide anion during the alkaline hydrolysis of 2,4,6-trinitrotoluene (TNT) in the water phase was studied with AMK-gau_xtb. The results of Intrinsic Reaction Coordinate (IRC) calculations revealed that the reactions on the front side and back side are different, with higher energy barriers obtained for the reactions on the front side. In addition, the hydrogen atom of the hydroxide anion has a slightly higher energy barrier for motion toward the inside of the benzene ring than for motion out of the benzene ring. Examination of the transition state structures of the low-level and high-level results showed that all reactions involve the stretching and restoration of the benzene ring. This process will lead to the incorrect identification of several transition states by the gau_xtb-based low-level calculation, while high-level calculation eliminates these incorrect results. The results of this research showed that AMK-gau_xtb has high efficiency and high fault tolerance, and has potential for use in large-scale system transition state searches.

Position-specific isotope effects during alkaline hydrolysis of 2,4-dinitroanisole resolved by compound-specific isotope analysis, 13C NMR, and density-functional theory

Compound-specific isotope analysis (CSIA), position-specific isotope analysis (PSIA), and computational modeling (e.g., quantum mechanical models; reactive-transport models) are increasingly being used to monitor and predict biotic and abiotic transformations of organic contaminants in the field. However, identifying the isotope effect(s) associated with a specific transformation remains challenging in many cases. Here, we describe and interpret the position-specific isotope effects of C and N associated with a S_N2Ar reaction mechanism by a combination of CSIA and PSIA using quantitative ¹³C nuclear magnetic resonance spectrometry, and density-functional theory, using 2,4-dinitroanisole (DNAN) as a model compound. The position-specific ¹³C enrichment factor of O-C₁ bond at the methoxy group attachment site (ε_C1) was found to be approximately -41‰, a diagnostic value for transformation of DNAN to its reaction products 2,4-dinitrophenol and methanol. Theoretical kinetic isotope effects calculated for DNAN isotopologues agreed well with the position-specific isotope effects measured by CSIA and PSIA. This combination of measurements and theoretical predictions demonstrates a useful tool for evaluating degradation efficiencies and/or mechanisms of organic contaminants and may promote new and improved applications of isotope analysis in laboratory and field investigations.

Selecting the best electron donor and operational temperature for the rapid biotransformation of the insensitive munitions compound 2,4-dinitroanisole (DNAN) by anaerobic sludge

2,4-Dinitroanisole (DNAN) is a toxic compound increasingly used by the military that can be released into the environment on the soil of training fields and in the wastewater of manufacturing plants. DNAN's nitro groups are anaerobically reduced to amino groups by microorganisms when electron donors are available. Using anaerobic sludge as the inoculum, we tested different electron donors for DNAN bioreduction at 20 and 30 °C: acetate, ethanol, pyruvate, hydrogen, and hydrogen + pyruvate. Biotic controls without external electron donors and abiotic controls with heat-killed sludge were also assayed. No DNAN conversion was observed in the abiotic controls. In all biotic treatments, DNAN was reduced to 2-methoxy-5-nitroaniline (MENA), which was further reduced to 2,4-diaminoanisole (DAAN). Ethanol or acetate did not increase DNAN reduction rate compared to the endogenous control. The electron donors that caused the fastest DNAN reductions were (rates at 30 °C): H₂ and pyruvate combined (311.28 ± 10.02 μM·d^-1·gSSV^-1), followed by H₂ only (207.19 ± 5.95 μM·d^-1·gSSV^-1), and pyruvate only (36.35 ± 2.95 μM·d^-1·gSSV^-1). Raising the temperature to 30 °C improved DNAN reduction rates when pyruvate, H₂, or H₂ + pyruvate were used as electrons donors. Our results can be applied to optimize the anaerobic treatment of DNAN-containing wastewater.

One-Step Instantaneous Detection of Multiple Military and Improvised Explosives Facilitated by Colorimetric Reagent Design

Although colorimetric detection based on reagents has been widely used in the fields of practical trace analysis, its versatility for detecting multitargets remains the most challenging problem. As a proof of concept, a general colorimetric reagent based on potassium isopropanol (C₃H₇KO) and dimethyl sulfoxide for one-step instantaneous detection and discrimination of typical military and improvised explosives was designed. Vivid colors from none to purple red, blue green, yellow green, and green were shown, respectively, when detecting 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), elemental sulfur (S), and potassium permanganate (KMnO₄). The unique design including the specific nucleophilic addition reaction and the base-catalyzed oxidation-induced electron transfer ensures perfect selectivity even upon facing more than 20 interferents. It is further experimentally demonstrated that the confinement effect introduced by Tween-20 plays an essential role in enhancing the color signal on the surface and thus boosts the detection performance even with a mass as low as 1.45 ng. The applicability of this versatile colorimetric reagent was further verified by integrating the reagent onto paper strips for the in-field identification of TNT, DNT, S, and KMnO₄ with the help of a portable smartphone-based microscope apparatus, and a practical detection mass of 10.3 ng could be realized. We expect the present colorimetric reagent design strategy would pave a way for one-step instantaneous visual detection toward trace multianalytes.

A Density Functional Theory Study toward Ring-Opening Reaction Mechanisms of 2,4,6-Trinitrotoluene's Meisenheimer Complex for the Biodegradation of Old Yellow Enzyme Flavoprotein Reductase

The subsequent degradation pathway of the dihydride-Meisenheimer complex (2H^--TNT), which is the metabolite of 2,4,6-trinitrotoluene (TNT) by old yellow enzyme flavoprotein reductases of yeast and bacteria, was investigated computationally at the SMD/TPSSH/6-311+G(d,p) level of theory. Combining the experimentally detected products, a series of protonation, addition, substitution (dearomatization), and ring-opening reaction processes from 2H^--TNT to alkanes were proposed. By analyzing reaction free energies, we determined that the protonation is more advantageous thermodynamically than the dimerization reaction. In the ring-opening reaction of naphthenic products, the water molecule-mediated proton transfer mechanism plays a key role. The corresponding activation energy barrier is 37.7 kcal·mol^-1, which implies the difficulty of this reaction. Based on our calculations, we gave an optimum pathway for TNT mineralization. Our conclusions agree qualitatively with available experimental results. The details on transition states, intermediates, and free energy surfaces for all proposed reactions are given and make up for a lack of experimental knowledge.

Alkaline hydrolysis pathway of 2,4-dinitroanisole verified by 18O tracer experiment

The environmental fate of insensitive munitions compounds, such as 2,4-dinitroanisole (DNAN), has drawn increasing attention because of their growing use in military activities. One of the main attenuation mechanisms of DNAN degradation in aqueous environments is alkaline hydrolysis. We investigated the pathway for alkaline hydrolysis of DNAN at pH 12 by a combined approach of experiment and theory. An experiment using ¹⁸O-labeled water was performed to verify the reaction pathway. Calculated free energies for two putative reaction pathways by density-functional theory optimized at the SMD(Pauling)/M06-2X/6-311++G(2d,2p) level including explicit solvation of DNAN by 10 H₂O molecules and one OH^- ion gave a prediction in agreement with the experimental result. The verified reaction pathway for alkaline hydrolysis of DNAN is a S_N2Ar nucleophilic aromatic substitution with a methoxy leaving group (OCH₃) at the C1 site.

Role of Singlet Oxygen in the Degradation of Selected Insensitive Munitions Compounds: A Comprehensive, Quantum Chemical Investigation

DNAN (2,4-dinitroanisole), NTO (3-nitro-1,2,4-triazol-5-one), and NQ (nitroguanidine) are important energetic materials used in military applications. They may find their way to the environment during manufacturing, transportation, storage, training, and disposal. A detailed investigation of possible mechanisms for reactions of the nitrocompounds with singlet oxygen, one of the potential methods for their degradation, was performed by computational study using the PCM(Pauling)/M06-2X/6-311++G(d,p) approach. Obtained results suggest that reactivity of the investigated munitions compounds toward singlet oxygen follows the order: DNAN > NTO(anion) > NQ ≫ NTO. DNAN is involved in [4 + 2]-addition with oxygen, and further formation of diepoxide or epoxyketone through diradical intermediates have been predicted. The NTO may undergo intramolecular rearrangement with formation of peroxide compound or nitrite radical elimination, and NQ may be transformed into urea.

Reaction yield model of nitrocellulose alkaline hydrolysis

Military nitrocellulose waste is flammable and explosive, and thus requires safe disposal and resource utilization. The alkaline hydrolysis process is a potential treatment method for nitrocellulose waste. In this study, a reaction yield model of nitrocellulose alkaline hydrolysis reaction was studied. For this purpose, a theoretical reaction yield model of nitrocellulose alkaline hydrolysis was developed based on Fick's law and scanning electron microscopy analysis. Additionally, the reaction yield model was experimentally validated. The results revealed a linear relationship between the nitrocellulose alkaline hydrolysis rate of x_NC and the reaction time of t, which is given by t/t_f = x_NC. The limiting step of the alkaline hydrolysis of nitrocellulose is the rate of diffusion of OH^- through the large pore channels. Accordingly, the reaction rate of the nitrocellulose alkaline hydrolysis can be increased by increasing the KOH concentration, reaction temperature, and reducing the size of the nitrocellulose granules. Thus, this model provides theoretical and technical support for the safe disposal and resource utilization of nitrocellulose waste.

Computational Investigation on Electronic Structures and Properties of 4,6-Bis(nitroimino)-1,3,5-triazinan-2-one: An Insensitive Munition Compound

In order to minimize unintentional detonation, munitions researchers have focused on the development of chemical compounds that are insensitive to external stimuli while maintaining their effectiveness. Although these compounds, known as high-performance insensitive munition compounds, are promising in terms of potency and stability, their environmental impacts have either not been fully understood or are yet to be investigated. In the present research, we have performed a quantum chemical investigation on electronic structures and properties of an insensitive munition compound 4,6-bis(nitroimino)-1,3,5-triazinan-2-one (DNAM). The density functional theory using the B3LYP and M06-2X functionals and MP2 methodology were used for geometry optimization of various tautomeric forms of DNAM. The effect of bulk water solution was evaluated using the conductor-like polarizable continuum model and the density-based solvation model. Ionization potentials, electron affinities, redox properties, and p K_a values were also computed and compared with the available experimental data. These physical and chemical properties of DNAM have been discussed with regard to the varying tautomeric forms in which DNAM can exist.

A theoretical insight into the reaction mechanisms of a 2,4,6-trinitrotoluene nitroso metabolite with thiols for toxic effects

2,4,6-Trinitrotoluene (TNT) is a class C carcinogen as rated by the Environmental Protection Agency. One of the toxicity mechanisms of TNT is the covalent binding of its metabolites to critical proteins. However, knowledge about their molecular reaction mechanisms is scarce. Herein, we have provided density functional theory (DFT) simulation evidences for the reaction mechanisms of the nitroso metabolite of TNT with the sulfhydryl group of model thiols for the first time. The results show that the solvent-mediated proton-transfer mechanism plays a significant role in the entire process. For the formation of semimercaptal, the mechanism is slightly different from the previous one where the thiolate anion attacks the nitroso group. The rearrangement of semimercaptal needs to be triggered by an acid or hydrated ion (H₃O⁺), which is consistent with the previous assumption. The other pathway, the conversion of semimercaptal to hydroxylamine, has to overcome a higher barrier, although it does not need the participation of an acid or a hydrated ion. In addition, the details on transition states, intermediates and free energy surfaces for three reactions are given, which make up for the lack of experimental knowledge. These conclusions can help to deeply understand the toxic effects of TNT and other nitroaromatic explosives.

Mineral identity, natural organic matter, and repeated contaminant exposures do not affect the carbon and nitrogen isotope fractionation of 2,4-dinitroanisole during abiotic reduction

The recent development of insensitive munitions, such as 2,4-dinitroanisole (DNAN), as components of military explosives has generated concern for potential subsurface contamination and created a need to fully characterize their transformation processes. Compound specific isotope analysis (CSIA) has proven to be a useful means of assessing transformation pathways according to characteristic stable isotope fractionation patterns. The C and N isotope fractionation of DNAN associated with abiotic and enzymatic hydrolysis was recently assessed. The extent to which DNAN isotope fractionation will be affected by other potentially competing transformation pathways known for nitroaromatic compounds (e.g., reduction) and if previous knowledge can be extrapolated to other environmental matrices remains to be understood. Here, we investigated the C and N isotope fractionation and reaction rate constants of DNAN during abiotic reduction mediated by mineral-associated Fe(ii) species as a function of mineral type, natural organic matter presence, and repeated exposures to DNAN. Though rate constants varied, N and C apparent kinetic isotope effects (AKIEs) remained consistent across all experiments (averaged values of 15N-AKIE = 1.0317 ± 0.0064 and 13C-AKIE = 1.0008 ± 0.0005) and revealed significant 15N- and minimal 13C-enrichment in agreement with previous work on nitroaromatic compounds. Moreover, the observed fractionation was clearly distinct from trends for abiotic and enzymatic hydrolysis. This study provides a strengthened basis for the use of CSIA as a robust tool for monitoring DNAN degradation in complex environmental matrices as a component of future remediation efforts.

Surface-promoted hydrolysis of 2,4,6-trinitrotoluene and 2,4-dinitroanisole on pyrogenic carbonaceous matter

This study investigates the fate of sorbed nitroaromatics on the surface of pyrogenic carbonaceous matter (PCM) to assess the feasibility of a PCM-promoted hydrolysis. The degradation of two nitroaromatic compounds, 2,4,6-trinitrotoluene (TNT) and 2,4-dinitroanisole, was observed at pH 7 in the presence of graphite powder, a model PCM. By contrast, no decay occurred without graphite. Using TNT as a model compound, our results suggest that TNT decay demonstrated a strong pH dependence, with no reaction at pH 3-5 but rapid degradation at pH 6-10. Moreover, by fitting TNT decay at different pH conditions along with its sorption kinetics to the Langmuir Kinetic Model, our results suggest that the base-catalyzed hydrolysis was important. The activation energy for TNT decay was obtained by measuring reaction rates at different temperatures with or without graphite and no significant difference was observed. However, the addition of tetramethylammonium cation was able to promote TNT decay possibly due to its ability to attract more OH^- from the aqueous solution, leading to an increase in the sorbed OH^- concentrations. Nitrite and a Meisenheimer complex were identified as degradation products for TNT. Other PCM, such as biochar, also demonstrated a comparable ability in promoting TNT decay at pH 7. Furthermore, a rapid degradation of TNT at pH 7 was observed when biochar was used as a soil amendment (4% by weight). Our results suggest that PCM can facilitate TNT and 2,4-dinitroanisole decay via a surface-promoted hydrolysis at neutral pH conditions, suggesting a promising alternative for in situ soil remediation.

In silico kinetics of alkaline hydrolysis of 1,3,5-trinitro-1,3,5-triazinane (RDX): M06-2X investigation

Alkaline hydrolysis of RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), as one of the most promising methods for nitrocompound remediation, was investigated computationally at the PCM(Pauling)/M06-2X/6-311++G(d,p) level of theory. Computational simulation shows that RDX hydrolysis is a highly exothermic multistep process involving initial deprotonation and nitrite elimination, cycle cleavage, further transformation of cycle-opened intermediates to end products caused by a series of C-N bond ruptures, hydroxide attachments, and proton transfers. Computationally predicted products of RDX hydrolysis such as nitrite, nitrous oxide, formaldehyde, formate, and ammonia correspond to experimentally observed ones. Accounting of specific hydration of hydroxide is critical to create an accurate kinetic model for alkaline hydrolysis. Simulated kinetics of the hydrolysis are in good agreement with available experimental data. A period of one month is necessary for 99% RDX decomposition at pH 10. Computations predict significant increases of the reaction rate of hydrolysis at pH 11, pH 12, and pH 13.

Photo-degradation of 2,4-dinitroanisole (DNAN): An emerging munitions compound

The US military is developing insensitive munitions (IM) that are less sensitive to shock and high temperatures to minimize unintentional detonations. DNAN (2,4-dinitroanisole) is one of the main ingredients of these IM formulations. During live-fire training, chunks of IM formulations are scattered by partial detonations and, once on the soil, they weather and dissolve. DNAN changes color when exposed to sunlight suggesting that it photodegrades into other compounds. We investigated the photo-degradation of DNAN both as a pure solid and as part of solid IM formulations, IMX101, IMX104 and PAX21. The concentrations of degradation products found were small, <1%, relative to DNAN concentrations. We saw transient peaks in the chromatograms indicating intermediate, unstable products but we consistently found methoxy nitrophenols and methoxy nitroanilines. We also found one unknown in most of the samples and other unknowns less frequently.

In Silico Alkaline Hydrolysis of Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine: Density Functional Theory Investigation

HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), an energetic material used in military applications, may be released to the environment during manufacturing, transportation, storage, training, and disposal. A detailed investigation of a possible mechanism of alkaline hydrolysis, as one of the most promising methods for HMX remediation, was performed by computational study at PCM(Pauling)/M06-2X/6-311++G(d,p) level. Obtained results suggest that HMX hydrolysis at pH 10 represents a highly exothermic multistep process involving initial deprotonation and nitrite elimination, hydroxide attachment accompanied by cycle cleavage, and further decomposition of cycle-opened intermediate to the products caused by a series of C-N bond ruptures, hydroxide attachments, and proton transfers. Computationally predicted products of HMX hydrolysis such as nitrite, 4-nitro-2,4-diazabutanal, formaldehyde, nitrous oxide, formate, and ammonia correspond to experimentally observed species. Based on computed reaction pathways for HMX decomposition by alkaline hydrolysis, the kinetics of the entire process was modeled. Very low efficiency of this reaction at pH 10 was observed. Computations predict significant increases (orders of magnitude) of the hydrolysis rate for hydrolysis reactions undertaken at pH 11, 12, and 13.

Alkaline hydrolysis of hexahydro-1,3,5-trinitro-1,3,5-triazine: M06-2X investigation

Alkaline hydrolysis mechanism of possible environmental contaminant RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) was investigated computationally at the PCM(Pauling)/M06-2X/6-311++G(d,p) level of theory. Results obtained show that the initial deprotonation of RDX by hydroxide leads to nitrite elimination and formation of a denitrated cyclohexene intermediate. Further nucleophilic attack by hydroxide onto cyclic CN double bond results in ring opening. It was shown that the presence of hydroxide is crucial for this stage of the reaction. The dominant decomposition pathway leading to a ring-opened intermediate was found to be formation of 4-nitro-2,4-diazabutanal. Hydrolytic transformation of its byproduct (methylene nitramine) leads to end products such as formaldehyde and nitrous oxide. Computational results are in a good agreement with experimental data on hydrolysis of RDX, suggesting that 4-nitro-2,4-diazabutanal, nitrite, formaldehyde, and nitrous oxide are main products for early stages of RDX decomposition under alkaline conditions.