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−MnO4 − 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/NO3 ∼ 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.