Transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by permanganate

The chemical oxidant permanganate (MnO₄^-) has been shown to effectively transform hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) at both the laboratory and field scales. We treated RDX with MnO₄ ^- with the objective of quantifying the effects of pH and temperature on destruction kinetics and determining reaction rates. A nitrogen mass balance and the distribution of reaction products were used to provide insight into reaction mechanisms. Kinetic experiments (at pH ∼ 7, 25 °C) verified that RDX-MnO₄^- reaction was first-order with respect to MnO₄^- and initial RDX concentration (second-order rate: 4.2 × 10^-5 M^-1 s^-1). Batch experiments showed that choice of quenching agents (MnSO₄, MnCO₃, and H₂O₂) influenced sample pH and product distribution. When MnCO₃ was used as a quenching agent, the pH of the RDX-MnO ₄^- solution was relatively unchanged and N₂O and NO₃^- constituted 94% of the N-containing products after 80% of the RDX was transformed. On the basis of the preponderance of N₂O produced under neutral pH (molar ratio N₂O/NO ₃ ∼ 5:1), no strong pH effect on RDX-MnO₄^- reaction rates, a lower activation energy than the hydrolysis pathway, and previous literature on MnO₄^- oxidation of amines, we propose that RDX-MnO₄^- reaction involves direct oxidation of the methylene group (hydride abstraction), followed by hydrolysis of the resulting imides, and decarboxylation of the resulting carboxylic acids to form N₂O, CO₂, and H₂O.