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

Abstract

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 2,4dinitroaniline (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−(OCH 3 )OH − , and subsequently, the methoxy anion (−OCH 3 ) 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.

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

“…Previous modeling efforts identified two hydrolysis pathways of DNAN, both involving nucleophilic aromatic substitution by OH – (Figure ). In the first reaction pathway, an attack of OH – at the C1 position of DNAN produces a methoxide leaving group and DNP, which have been reported by many studies of DNAN hydrolysis in solution. ,,,− This is problematic because DNP is more toxic than DNAN . In the second pathway, DNAN undergoes direct substitution (Sub@2 or Sub@4) by the attack of OH – and releases nitrite .…”

“…Our previous work suggests that solvent properties are critical in influencing reaction dynamics in solution, particularly in specialized environments like nano-pores. 100 For instance, solvents with a lower dielectric constant can significantly impact the thermodynamics and kinetics of hydrolysis reactions. As the dielectric constant lowers in solvents, the reaction energy decreases due to less hydration energy.…”

Degradation of Chloroform by Zerovalent Iron: Effects of Mechanochemical Sulfidation and Nitridation on the Kinetics and Mechanism

“…The Arrows API provides a web-based graphical user interface to NWChem, , with an integrated database for managing chemical structure information and properties from past and new calculations and options for visualization of reaction pathways and mechanisms. A detailed overview of Arrows capabilities is provided in Bylaska et al, and recent examples of Arrows applications for the characterization of contaminant degradation reaction networks are available for 2,4-dinitroanisole (DNAN) and 1,2,3-trichloropropane (TCP) . In this study, Arrows was used to calculate the aqueous free energies for the species summarized in Table S14 and reactions in Table S15 using density functional theory (DFT) and the more accurate WFT-based (wave function theory) method CCSD­(T) (Table S16), coupled cluster single-double (triple), with solvation energies estimated by COSMO (Conductor-like Screening Model of Klamt and Schürmann).…”

Development and Application of Hybrid AIMD/cDFT Simulations for Atomic-to-Mesoscale Chemistry

“…Meanwhile, embedded calculations (e.g., continuum solvation models 78,79 ) tend to favor the calculation of transition states, and dynamical simulations (e.g., AIMD/MM free energy 80 ) simulations tend to favor the calculation of reaction pathways. Our hybrid AIMD/cDFT method can be used for calculating both transition states and reaction pathways.…”