5755-27-1

The thermal decomposition of a number of nitramines was studied in dilute solution and in the melt.The nitramines included acyclic mononitramines , cyclic mononitramines , cyclic dinitramines , and 1,3,5-trinitro-1,3,5-triazocyclohexane (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), hexanitrohexaazaisowurtzitane (HNIW), and 1,3,3-trinitroazetidine (TNAZ).For the acyclic and cyclic mono- and dinitramines, the corresponding nitrosamines were the only or major condensed-phase product.Kinetics and activation parameters were determined for the thermolysis of dilute solutions (0.01-1.0 wtpercent) over the range 200-300 deg C.The thermolyses were found to be first-order with the rate constants unaffected by the use of deuterated solvent.As the nitramines became more complex than dimethylnitramine (DMN), the rate of decomposition increased and the product distribution became more complex.As the length of the aliphatic chain increased (DMN DEN DPN), the rate of thermolysis increased, yet nitrosamine remained the only observed condensed-phase product.When a secondary carbon was attached to the N-nitramine (DIPN) rather than the primary (DPN), the rate of decomposition increased and a new condensed-phase product was observed.Among the cyclic nitramines, the rate of decomposition increased as the number of NNO2 groups increased (NPIP pDNP; NPyr DNI; mDMP RDX).The position of the nitramine groups affected the decomposition: meta NNO2 groups (mDNP) decomposed faster than para (pDNP).Ring strain decreased stability: mDNP DNI; HMX RDX.In complex nitramines, the increase in decomposition rate, the appearance of new products, and the change in the relative importance of nitrosamine and of N2 and N2O are attributed to new decomposition routes available to them.However, since complex nitramines (e.g.RDX) maintain first-order kinetics and since most have activation energies in the range of 40-50 kcal/mol, it is belived that the triggering mechanism remains N-NO2 homolysis.Intramolecular hydrogen transfer is also considered an important mode of nitramine decomposition.

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.

Through the use of simultaneous thermogravimetry modulated beam mass spectrometry (STMBMS) measurements, time-of-flight (TOF) velocity-spectra analysis, and (2)H, (13)C, (15)N and (18)O labeled analogues of 1,3,5-trinitrohexahydro-s-triazine (RDX), the thermal decomposition products of RDX have been identified as H2O, HCN, CO, CH2O, NO, N2O, NH2CHO, NO2, HONO, (CH3)NHCHO, oxy-s-triazine (OST), and 1-nitroso-3,5-dinitrohexahydro-s-triazine (ONDNTA) and all of their gas formation rates have been measured as a function of time.From these results the primary reaction pathways that control the decomposition of RDX in both the solid and liquid phases have been discovered.Four primary reaction pathways control the decomposition of RDX in the liquid phase between 200 and 215 deg C.Two pathways are first-order reactions solely in RDX.One produces predominantly OST, NO, and H2O and accounts for approximately 30percent of the decomposed RDX, and the other produces predominantly N2O and CH2O with smaller amounts of NO2, CO, and NH2CHO and accounts for 10percent of the decomposed RDX.The third pathway consists of formation of ONDNTA by reaction between NO and RDX, followed by the decomposition of ONDNTA to predominantly CH2O and N2O.The fourth reaction pathway consists of decomposition of RDX through reaction with a catalyst that is formed from the decomposition products of previously decomposed RDX.The third and fourth reaction channels each account for approximately 30percent of the decomposed RDX.Experiments with solid-phase RDX have shown that its decomposition rate is very much slower than that of liquid-phase RDX.ONDNTA is the only product that appears to be formed during the early stages of decomposition of RDX in the solid phase.As the solid-phase decomposition progresses, N2O and lesser amounts of CH2O start to evolve and their rates of evolution increase until products associated with the liquid-phase RDX decomposition appear and the rates of gas formation of all products rapidly increase.This behavior strongly suggests the decomposition of solid RDX occurs through formation of ONDNTA within the lattice, the subsequent decomposition of it within the lattice to N2O and CH2O, followed by the dispersion of CH2O in the RDX, leading to its eventual liquefaction and the onset of the liquid-phase decomposition reactions.