An experimental (flash vacuum pyrolysis) and theoretical study of the tautomerism of pyrazolinones at high temperatures

Yranzo, Gloria I.; Moyano, Elizabeth L.; Rozas, Isabel; Dardonville, Christophe; Elguero, José

doi:10.1039/a807669c

Cited by 17 publications

(23 citation statements)

References 26 publications

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“…The energy barrier of this channel is 65.2 kcal/mol, which shows the lowest energy barrier (LEB) among all the pathways, and the barrier calculated at the level of the G3X method is 68.6 kcal/mol . Therefore, PA might decay through N 2 extrusion, consistent with previous studies. ,,, We found two different paths to form CHCH: one is the formation of CHCH and CHNNH with an energy barrier of 106.2 kcal/mol (Path II) and the other is the formation of CHCH and CH 2 NN with an energy barrier of 89.4 kcal/mol (Path III). The barrier for the path of CHCH formation is regarded as 105.54 kcal/mol by the G3B3 method .…”

Section: Resultssupporting

confidence: 87%

“…This channel is difficult to take place due to the high barrier, similar to the channel of CHCH formation. According to the above analysis, the most likely decomposition path for PA is Path I to generate N2, which is consistent with the experimental studies. ,,, …”

Section: Resultssupporting

confidence: 85%

“…Previous studies mainly focused on the physicochemical properties of pyrazoles and imidazoles. − N 2 extrusion is suggested to be the favorable channel of pyrazoles through the flash vacuum pyrolysis experiment , and the first principles study . The possible pathways in the thermal decomposition of pyrazole and its nitro derivatives were presumed based on the thermogravimetric–differential thermal analysis (TG–DTA) results .…”

Section: Introductionmentioning

confidence: 99%

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Comparative Quantum Chemistry Study on the Unimolecular Decomposition Channels of Pyrazole and Imidazole Energetic Materials

et al. 2021

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The difference in the initial decomposition step of pyrazoles and imidazoles was explored using the M062X method for optimization and G4-MP2 and approximated CCSD(T) methods for energies. Laplacian bond order analysis was used to study the effect of the nitro group on the bond strength and predict the bond dissociation energy (BDE) of the ring. Thermochemistry results show that the most possible decay channel of 1H-pyrazole and 3-nitropyrazole is the N 2 elimination, while the preferred initial step of 1H-imidazole is the CHN elimination. However, the nitro−nitrite isomerization dominates the decomposition of other nitro derivatives of 1H-pyrazole and 1H-imidazole. As for the formation of HO and HONO, the high energy barrier makes it difficult to take place. Based on the analysis of the lowest energy barrier and the BDE of NO 2 loss, it can be concluded that imidazoles are more stable than pyrazoles. This work contributes to revealing the difference in the initial step of energetic isomers and the understanding of the decomposition mechanism of energetic azoles.

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Section: Resultssupporting

confidence: 87%

Section: Resultssupporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

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Comparative Quantum Chemistry Study on the Unimolecular Decomposition Channels of Pyrazole and Imidazole Energetic Materials

et al. 2021

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“…The channel of N 2 formation is also not a thermodynamically preferential pathway due to the high energy of TS3 (111.9 kcal/mol). From previous studies, the possible initial decomposition reaction of pyrazole is the formation of N 2 and vinylcarbene, − and the energy barrier is 68.6 kcal/mol, which is about half that of OA1. This channel is also important for triazoles , and tetrazoles, and the energy barriers are lower than that of pyrazole.…”

Section: Resultsmentioning

confidence: 95%

Initial Steps and Thermochemistry of Unimolecular Decomposition of Oxadiazole Energetic Materials: Quantum Chemistry Modeling

et al. 2021

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In order to resolve the existing discrepancies in the mechanism and key intermediates of oxadiazole thermolysis, the initial decomposition pathways of oxadiazoles have been studied comprehensively using the M062X method for optimization and CBS-QB3 and DLPNO-CCSD(T) methods for energies. The transformation from the furoxan ring to nitro group was suggested as a potential decay channel of furoxan compounds. Results of thermochemistry calculations showed that the preferred decomposition reaction of oxadiazoles is the ring-opening through the cleavage of the O−C or O−N bond. The introduction of the nitro group has little effect on the preferential path of oxadiazole thermal decomposition, but a great impact on the energy barrier. The lowest energy barrier and bond dissociation energy of NO 2 loss of azoles were comprehensively studied based on the quantum chemistry calculations. The initial decay steps of 3,4-dinitrofurazanfuroxan and benzotrifuroxan were also studied to give insights into the mechanism of primary stages of thermal decomposition of oxadiazoles.

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“…The most reliable results are those of Refs. 31, 32 and 37, which we have averaged in the last column of Table 2 47. 48…”

Section: Introductionmentioning

confidence: 99%

Computational Study of Proton Transfer in Tautomers of 3‐ and 5‐Hydroxypyrazole Assisted by Water

et al. 2015

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The tautomerism of 3- and 5-hydroxypyrazole is studied at the B3LYP, CCSD and G3B3 computational levels, including the gas phase, PCM-water effects, and proton transfer assisted by water molecules. To understand the propensity of tautomerization, hydrogen-bond acidity and basicity of neutral species is approached by means of correlations between donor/acceptor ability and H-bond interaction energies. Tautomerism processes are highly dependent on the solvent environment, and a significant reduction of the transition barriers upon solvation is seen. In addition, the inclusion of a single water molecule to assist proton transfer decreases the barriers between tautomers. Although the second water molecule further reduces those barriers, its effect is less appreciable than the first one. Neutral species present more stable minima than anionic and cationic species, but relatively similar transition barriers to anionic tautomers.

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An experimental (flash vacuum pyrolysis) and theoretical study of the tautomerism of pyrazolinones at high temperatures

Cited by 17 publications

References 26 publications

Comparative Quantum Chemistry Study on the Unimolecular Decomposition Channels of Pyrazole and Imidazole Energetic Materials

Comparative Quantum Chemistry Study on the Unimolecular Decomposition Channels of Pyrazole and Imidazole Energetic Materials

Initial Steps and Thermochemistry of Unimolecular Decomposition of Oxadiazole Energetic Materials: Quantum Chemistry Modeling

Computational Study of Proton Transfer in Tautomers of 3‐ and 5‐Hydroxypyrazole Assisted by Water

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