Leanna M. G. Minier

Mass spectra of 2,4-dinitroimidazole and its isotopomers using simultaneous thermogravimetric modulated beam mass spectrometry

The EI mass spectrum of 2,4-dinitroimidazole (2,4-DNI) was studied at 20 and 70 eV ionizing energy using simultaneous thermogravimetric modulated beam mass spectrometry. Product ion formulas and their origin from within the 2,4-DNI molecule were identified from the evaluation of perdeuterated and various 15 N-labeled 2,4-DNI mass spectra. The molecular ion (M +. ; m/z 158) is present in all the spectra and the NO + ion (m/z 30) is the major primary product ion. The base peak is formed by the M .+ ion at 20 eV and by the NO + ion at 70 eV. Other primary product ions are NO 2 + (m/z 46), CH 2 N + (m/z 28) and CHN 2 O 2 + (m/z 73). Fragmentation pathways are postulated based on the identity and relative abundance of the product ions, and on the change in relative abundance of the ions as a function of ionizing energy. Comparisons of the 70 eV mass spectra of 2,4-DNI, 4,5-dinitroimidazole (4,5-DNI) and 1,4-dinitroimidazole (1,4-DNI) show that the fragment product ions have the same m/z values in the three spectra but differ in their relative abundance and in the ion that forms the base peak. The base peak for 2,4-DNI and 4,5-DNI is formed by the ion at m/z 30 (NO + ) and for 1,4-DNI, the ion at m/z 46 (NO 2 + ). This difference is probably due to the nitramine functionality of 1,4-DNI

Solid-phase thermal decomposition of 2,4-dinitroimidazole (2,4-DNI)

The solid-phase thermal decomposition of the insensitive energetic nitroaromatic heterocycle 2,4-dinitroimidazole (2,4-DNI: mp 265--274C) is studied utilizing simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) between 200 and 247C. The pyrolysis products have been identified using perdeuterated and {sup 15}N-labeled isotopomers. The products consist of low molecular-weight gases and a thermally stable solid residue. The major gaseous products are NO, CO{sub 2}, CO, N{sub 2}, HNCO and H{sub 2}O. Minor gaseous products are HCN, C{sub 2}N{sub 2}, NO{sub 2}, C{sub 3}H{sub 4}N{sub 2}, C{sub 3}H{sub 3}N{sub 3}O and NH{sub 3}. The elemental formula of the residue is C{sub 2}HN{sub 2}O and FTIR analysis suggests that it is polyurea- and polycarbamate-like in nature. Rates of formation of the gaseous products and their respective quantities have been determined for a typical isothermal decomposition experiment at 235C. The temporal behaviors of the gas formation rates indicate that the overall decomposition is characterized by a sequence of four events; (1) an early decomposition period induced by impurities and water, (2) an induction period where C0{sub 2} and NO are the primary products formed at relatively constant rates, (3) an autoacceleratory period that peaks when the sample is depleted and (4) a final period in which the residue decomposes. Arrhenius parameters for the induction period are E{sub a} = 46.9 {plus_minus} 0.7 kcal/mol and Log(A) = 16.3 {plus_minus} 0.3. Decomposition pathways that are consistent with the data are presented.

Coupling experimental data and a prototype model to probe the physical and chemical processes of 2,4-dinitroimidazole solid-phase thermal decomposition

The time-dependent, solid-phase thermal decomposition behavior of 2,4-dinitroimidazole (2,4-DNI) has been measured utilizing simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) methods. The decomposition products consist of gaseous and non-volatile polymeric products. The temporal behavior of the gas formation rates of the identified products indicate that the overall thermal decomposition process is complex. In isothermal experiments with 2,4-DNI in the solid phase, four distinguishing features are observed: (1) elevated rates of gas formation are observed during the early stages of the decomposition, which appear to be correlated to the presence of exogenous water in the sample; (2) this is followed by a period of relatively constant rates of gas formation; (3) next, the rates of gas formation accelerate, characteristic of an autocatalytic reaction; (4) finally, the 2,4-DNI is depleted and gaseous decomposition products continue to evolve at a decreasing rate. A physicochemical and mathematical model of the decomposition of 2,4-DNI has been developed and applied to the experimental results. The first generation of this model is described in this paper. Differences between the first generation of the model and the experimental data collected under different conditions suggest refinements for the next generation of the model.