The studied transition states of proton hopping transfer and bimolecular substitution are the main energy release processes of TNT to 2,4,6-trinitrobenzoic acid catalyzed by THICA.

Abstract

As an organic molecule catalyst, N,N′,N″-trihydroxyisocyanuric acid can selectively catalyze the oxidation of the methyl group of waste 2,4,6-trinitrotoluene to generate 2,4,6-trinitrobenzoic acid. This reaction can avoid environmental pollution by inorganic heavy metal catalysts. In this study, four reaction stages of this catalytic reaction were designed and validated computationally at the M06-2X-D3ZERO/6-311G(d,p) level using the acetic acid solvent model. These validations include transition state searches, intrinsic reaction coordinate calculations, reactant and product optimizations, and frequency calculations. The final reaction network of 23 transition states shows that after N,N′,N″-trihydroxyisocyanuric acid activation and common reaction, the network bifurcates into two stages: alcohol to carboxylic acid and aldehyde to carboxylic acid. Although the former stage releases about 155 kcal/mol of Gibbs free energy, less than the 177 kcal/mol from the latter stage, the overall reaction equation shows that the pathway including former stage does not consume the catalytically active substance IM_T2, which saves the energy required for reactivation and is thus more favorable. Furthermore, the key transition states in the reaction network include bimolecular substitution reactions and proton-hopping transfer reactions. Analyses of their interaction region indicators and intrinsic reaction coordinate results demonstrate strong selectivity. Additionally, the energy barriers and heat releases of the latter are twice and 1.3 times greater than those of the former, respectively. In summary, this study elucidated two competitive reaction pathways and identified the more energetically favorable and selective pathway, and it provides useful insights for further optimization of industrial utilization of 2,4,6-trinitrotoluene.