Theoretical predictions of chemical degradation reaction mechanisms of RDX and other cyclic nitramines derived from their molecular structures

Abstract

Analysis of environmental degradation pathways of contaminants is aided by predictions of likely reaction mechanisms and intermediate products derived from computational models of molecular structure. Quantum mechanical methods and force-field molecular mechanics were used to characterize cyclic nitramines. Likely degradation mechanisms for hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) include hydroxylation utilizing addition of hydroxide ions to initiate proton abstraction via 2nd order rate elimination (E₂) or via nucleophilic substitution of nitro groups, reductive chemical and biochemical degradation, and free radical oxidation. Due to structural similarities, it is predicted that, under homologous circumstances, certain RDX environmental degradation pathways should also be effective for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and similar cyclic nitramines. Computational models provided a theoretical framework whereby likely transformation mechanisms and transformation products of cyclic nitramines were predicted and used to elucidate in situ degradation pathways.

Keywords:

• Cyclic nitramines
• Sites of reactivity
• Semiempirical computational chemistry
• Classical force field
• Environmental degradation

Acknowledgements

The tests described and the resulting data presented herein, unless otherwise noted, were conducted under the US Army Environmental Quality Technology Program. The research was conducted at the US Army Engineer Research and Development Center (ERDC), Environmental Laboratory, Vicksburg, MS. We appreciate the encouragement of Dr John Cullinane, ERDC Technical Director for Environmental Engineering. We also wish to thank Dr Peter Politzer of the University of New Orleans for sharing his insights, and Dr Tommy Myers, Roy Wade, and Dr Altaf Wani of ERDC for their helpful suggestions during manuscript review. Permission was granted by the Chief of Engineers to publish this information.