Thermal Decomposition of Energetic Materials. 4. Deuterium Isotope Effects and Isotopic Scrambling (H/D, (13)C/(18)O, (14)N/(15)N) in Condensed-Phase Decomposition of 1,3,5-Trinitrohexahydro-s-triazine

Article abstract of DOI:10.1021/j100201a037

The inter- vs intramolecular origin of the products formed in the thermal decomposition of 1,3,5-trinitrohexahydro-s-triazine (RDX) has been traced by isotopic crossover experiments using mixtures of differently labeled analogues of RDX.The isotopic analogues of RDX used in the experiments include (2)H, (13)C, (15)N, and (18)O.The fraction of isotopic scrambling and the extent of the deuterium kinetic isotope effect (DKIE) are reported for all the different decomposition products.Isotopic scrambling is not observed for the N-N bond in N2O and only in small amounts (7percent) in the C-H bonds in CH2O, consistent with a mechanism of their formation through methylene nitramine precursors.A product, oxy-s-triazine (OST, C3H3N3O) does not undergo isotopic scrambling in H/D, (14)N/(15)N, or (13)C/(18)O experiments, and its rate of formation exhibits a DKIE of 1.5.These results are consistent with the formation of OST via unimolecular decomposition of RDX.Another product, 1-nitroso-3,5-dinitrohexahydro-s-triazine (ONDNTA, C3H6N6O5) is found to be formed with complete scrambling of the N-NO bond, suggesting an N-N bond cleavage and a radical recombination process in its formation.One of the hydrogen containing products, H2O, exhibits a DKIE of 1.5 +/- 0.1.In contrast, CH2O and ONDNTA have DKIEs f 1.5 +/- 0.1 and 1.05 +/- 0.2, respectively, indicating that hydrogen transfer is not involved in the rate-limiting step of the reaction pathway leading to the formation of these products.