Dinitrogen Release from Arylpentazole: A Picosecond Time-Resolved Infrared, Spectroelectrochemical, and DFT Computational Study

Abstract

p-(Dimethylamino)phenyl pentazole, DMAP-N5 (DMAP = Me2N-C6H4), was characterized by picosecond transient infrared spectroscopy and infrared spectroelectrochemistry. Femtosecond laser excitation at 310 or 330 nm produces the DMAP-N5 (S1) excited state, part of which returns to the ground state (τ = 82 ± 4 ps), while DMAP-N and DMAP-N3 (S0) are generated as double and single N2-loss photoproducts with η ≈ 0.14. The lifetime of DMAP-N5 (S1) is temperature and solvent dependent. [DMAP-N3](+) is produced from DMAP-N5 in a quasireversible, one-electron oxidation process (E1/2 = +0.67 V). Control experiments with DMAP-N3 support the findings. DFT B3LYP/6-311G** calculations were used to identify DMAP-N5 (S1), DMAP-N3(+), and DMAP-N in the infrared spectra. Both DMAP-N5 (S1) and [DMAP-N5](+) have a weakened N5 ring structure.

Detection of Cyclo‐N5− in THF Solution

“…However, the origin of the radical anion in the experiments reporting the gas‐phase production of cyclo‐N 5 − was unclear. Attempts to reduce aryl pentazoles electrochemically or with alkali metals in solution did not lead to the detection of cyclo‐N 5 − . The proposed weakening of the C−N bond in the RA was supported by a recent theoretical study, in which it was shown that the phenylpentazole radical anion (PPRA) is stable and observable at low temperatures in polar solvents.…”

Theoretical studies on the stability of phenylpentazole and its substituted derivatives of –OH, –OCH3, –OC2H5and –N(CH3)2

“…This conclusion is consistent with the experimental results. 25,27,[34][35][36] E a,2 s of derivatives are generally larger than that of A. Although the increases in E a,2 caused by introduction of electron donating groups are not signicant, these groups generally do improve the stability of the pentazole.…”

“…According to experimental investigations, [25][26][27][34][35][36]60 A and its derivatives easily decompose into N 2 and azido compounds. This suggests that breaking of the N-N bonds of the N 5 ring may take place.…”

“…[25][26][27] In recent years, several photochemistry experimental investigations reveal that the N 5 rings of arylpentazole derivatives such as p-(dimethylamino)phenyl pentazole (DMAP) and p-oxidophenylpentazole easily decompose into N 2 and the corresponding phenyl azides. [34][35][36] Hence, the low stability of the N 5 ring should be the crucial factor in preventing the development of the pentazole derivatives.…”

Symmetrical cyclo-N5− hydrogen bonds: stabilization mechanism of four non-metallic cyclo-pentazolate energetic salts

“…1,2 Its high-energy release and environmentally friendly products are the main reasons for many years of pursuit. 3–10 However, cyclo -N 5 − obtained from the experimentally synthesized scheme is extremely short-lived, unstable under common conditions, and extremely susceptible to decomposition into N 2 and N 3 − . 11–13 Therefore, stability has always been one of the important topics in the study of cyclo -N 5 − -containing HEDMs.…”