Role of Hydroxyl Radical in the Degradation of ATO: DFT Study.

Large-scale implementation of NTO (5-nitro-1,2,4-triazol-3-one), an energetic material used in military applications, causes its discharge to the environment. Reduction of NTO with bacterial nitroreductase or iron-containing minerals results in the formation of ATO (5-amino-1,2,4-triazol-3-one), which is an important intermediate in the process of NTO degradation in the environment. ATO may be dissolved in surface water and groundwater due to its good water solubility. Many organic pollutants in surface water can be decomposed under the action of the hydroxyl radical, an important reactive oxygen species produced under sunlight irradiation. A detailed investigation of possible mechanisms for ATO decomposition in water induced by the hydroxyl radical as one of the pathways for ATO environmental degradation was performed by computational study at the PCM(Pauling)/M06-2/6-311++G(d,p) level. Decomposition of ATO was found to be a multistep process that can begin with a hydrogen atom abstraction from ATO. Formed intermediates undergo further H atom abstraction, hydroxyl radical attachment to carbon atoms, and rupture of C-N bonds, leading to low-weight inorganic species such as nitrogen gas, ammonia, nitric acid, and carbon(IV) oxide. The calculated activation energy and exergonicity of the studied reactions support the contribution of hydroxyl radical to ATO degradation in the environment.