Thermal decomposition of nitramines: dimethylnitramine, diisopropylnitramine, and N-nitropiperidine

Abstract

2505the results of section 11.3. dN0 ,In eq A l , No, NI and Po, PI are the ground-and excited-state populations of the normal and photoisomer species, respectively, and N No + N1 + Po + PI. B = uP/uN, with u p and UN as the absorption cross section coefficients of the P and N species. a = IpN, which is the rate of light absorption, where I, is the excitation fluence. w is the rate of sample renewal within the irradiated volume by circulation of the solution. k and k'are the rate constants of the Po -No and No -Po processes, and T N and rp are the lifetimes of excited states for the normal and photoisomeric species. @"p and @ p~ are the quantum yields of N 1 -Po and PI -No isomerization processes.Under steady-state irradiation conditions and low absorption, the following expression can be obtained:where excited-state populations are taken negligibly small because the pump intensity, 11, is small compared to the saturation intensity for the excited-state populations, I = hv/u which are in the MW/cm2 region and the depopulation of N, and PI by circulation (Kinetics and activation parameters of the solution thermolysis of nitramines dimethylnitramine, diisopropylnitramine, and N-nitropiperidine were determined over the temperature range 200-300 OC. Each formed the corresponding nitrosamine as the only, or major, condensed-phase product. For dimethylnitramine the products were completely characterized. The observations of a large positive activation volume in the thermolysis of dimethylnitramine and of the slowing of the decomposition reaction with increased solvent viscosity both suggest that the rate-determining step is homolysis, the N-NO2 bond being the most obvious point for this. Nitrosamines could be produced by this route; however, when doubly ISN-labeled dimethylnitramine was heated with unlabeled dimethylnitramine, little scrambling of the label in the reactant was observed. Label scrambling was observed in the nitrosamine but could have resulted from subsequent N-NO homolysis. Scrpmbling of the label in the product gases and the observation of a kinetic isotope effect when perdeuterated dimethylnitramine was decomposed were explained in terms of a second decomposition route involving transfer of hydrogen from the a carbon to one of the NO2 oxygens.

Mechanisms of Nitramine Thermolysis

“…The only condensed phase product was dimethylnitrosamine, formed in over 80% yield. 2 The nitrosamine was assumed to arise from N-NO 2 homolysis. Examining the condensedphase species remaining from the thermolysis of mixed However, in contrast to their findings, we also observed a limited amount of label scrambling in the reactant nitramine.…”

“…13 Isothermal decompositions of the nitramines were conducted in sealed glass tubes as previously discussed. 2 Typically, samples were benzene,isooctane, or acetone solutions containing 0.1-1.0 wt% nitramine (N-nitropiperidine was10wt% in benzene). Thermolyses were performed isothermally in the temperature range 200 o C to 300 o C, with the bath temperature maintained within 1 o C of the desired temperature.…”

“…Gaseous products were separated and quantitatively identified using a Varian 3600 gas chromatograph equipped with a thermal conductivity detector (GC-TCD). 2 The GC was configured with a PORAPAK-Q column in series across the TCD detector with a molecular sieve (MS13X) column. Identification and quantification of the gases was achieved by comparing the retention times and areas to calibration curves of known gases.…”

“…2 To avoid complications resulting from multiphase decomposition and autocatalysis, 3,4 we studied the thermolysis in dilute solution. Two different 15 N-labeling studies were performed.…”

“…Only partial scrambling of the 15 N-label was observed in the reactant, DMN. 2 Kinetic studies of DMN, diisopropylnitramine (DIPN), and N-nitropiperidine (NPIP) showed that as the viscosity of the solvent increased, the rate of decomposition decreased. This solvent cage effect and the observations of a large positive activation volume (V * = +30) for DMN suggested that the ratedetermining step was homolysis, the N-NO 2 bond being the most obvious point.…”