Thermal stability of a eutectic mixture of bis(2,2-dinitropropyl) acetal and formal: Part A. Degradation mechanisms in air and under nitrogen atmosphere

Abstract

We investigated the chemical and thermal stability of a eutectic mixture of bis(2,2-dinitropropyl)acetal (BDNPA) and bis(2,2-dinitropropyl)formal (BDNPF) (referred to as NP) in various environments at temperatures below 70 °C. Changes in the chemical composition of aged samples were characterized using TGA, FTIR, GPC, ESI-MS, and 1 H NMR spectroscopies over a period of two years. The results show that the initial signs of NP degradation can be detected as early as 12 months at 70 °C in air. The initial step in the degradation is the elimination of HONO molecules, followed by the formation of nitroso-alcohol isomers. While the temperature plays a key role in determining the degradation kinetics of the initial stages, the absence or presence of oxygen determines the types and rates of formations of various isomers and intermediates during the thermal decomposition processes. In addition, oxygen accelerates the decomposition of the isomers and intermediates, whereas nitrogen has a stabilizing effect. BDNPA shows higher reactivity than BDNPF regardless of the aging conditions, which is attributed to the presence of an extra methyl group in its structure.

Thermal stability of a eutectic mixture of bis(2,2-dinitropropyl) acetal and formal: Part B. Degradation mechanisms under water and high humidity environments

“…The spectra of both Air and N2 samples are dominated by a strong BDNPF feature (between 3050 and 2800 cm -1 ), suggesting that the degradation more preferentially affect the BDNPA than BDNPF molecules. [1] On the other hand, this preferential trend is not clearly observed in the hydrate sample. Instead, the fine features between 3000 and 2920 cm -1 suggest the formation of new -CH group in the hydrate sample, which indicates that the degradation mechanism of NP in the water environment is different from that occurring under the dry environments.…”

“…These intermediates are produced from the HONO elimination from BDNPA/F. [1] Interestingly, these three samples give different spectral features between 3010 and 2800 cm -1 . The spectra of both Air and N2 samples are dominated by a strong BDNPF feature (between 3050 and 2800 cm -1 ), suggesting that the degradation more preferentially affect the BDNPA than BDNPF molecules.…”

“…In contrast, since the intensities of peaks at m/z= ~230 and ~303, associated with the transstate compounds found in BDNPA, in the hydrated sample are slightly smaller than those in the N2 sample, we conclude that the presence of water accelerates the conversion of the BDNPA into the nitroso alcohol isomer. [1] In the m/z <150 range, the hydrated sample yields peaks found in both the N2 and Air samples as well. The intensities of the peaks at m/z = 30, 41-42, 55-57, 65-68, 93, 118 and 134 are clearly higher than those observed in the N2 sample, but lower than in the Air sample, as shown in Figure 7(b).…”

“…We suspect that after the samples being aged for 6 months, some BDNPA/F start to change into BNPeA/F though the HONO elimination. [1] When HONO molecules decompose, water will be produced. At the early stage, the water molecules are isolated and dispersed in the hydrated samples without much H-bonding interaction, which may be responsible for the free-OH peaks.…”

“…In Part A of this series, we investigated the mechanism and dynamics of chemical degradation of NP in air and under nitrogen atmosphere. [1] In addition to air and nitrogen, plastic-bonded explosive (PBX) materials, such as PBX 9501, are often exposed to other types of environments, such as humidity. In the PBX 9501 formula, two binders are used.…”