TY - JOUR

T1 - Thermochemistry, Tautomerism, and Thermal Stability of 5,7-Dinitrobenzotriazoles

AU - Melnikov, Igor N

AU - Kiselev, Vitaly G

AU - Dalinger, Igor L

AU - Starosotnikov, Alexey M

AU - Muravyev, Nikita V

AU - Pivkina, Alla N

N1 - Funding: N.V.M. and A.N.P. acknowledge the support of the experimental part of this work by the Russian Science Foundation (project 23-43-00090). V.G.K. acknowledges the Supercomputer Center of Novosibirsk State University and the Russian Science Foundation for financial support of the computational part of this work (project 22-13-00077).

PY - 2023/3/10

Y1 - 2023/3/10

N2 - Nitro derivatives of benzotriazoles are safe energetic materials with remarkable thermal stability. In the present study, we report on the kinetics and mechanism of thermal decomposition for 5,7-dinitrobenzotriazole (DBT) and 4-amino-5,7-dinitrobenzotriazole (ADBT). The pressure differential scanning calorimetry was employed to study the decomposition kinetics of DBT experimentally because the measurements under atmospheric pressure are disturbed by competing evaporation. The thermolysis of DBT in the melt is described by a kinetic scheme with two global reactions. The first stage is a strong autocatalytic process that includes the first-order reaction (Ea1I = 173.9 ± 0.9 kJ mol-1, log(A1I/s-1) = 12.82 ± 0.09) and the catalytic reaction of the second order with Ea2I = 136.5 ± 0.8 kJ mol-1, log(A2I/s-1) = 11.04 ± 0.07. The experimental study was complemented by predictive quantum chemical calculations (DLPNO-CCSD(T)). The calculations reveal that the 1H tautomer is the most energetically preferable form for both DBT and ADBT. Theory suggests the same decomposition mechanisms for DBT and ADBT, with the most favorable channels being nitro-nitrite isomerization and C-NO2 bond cleavage. The former channel has lower activation barriers (267 and 276 kJ mol-1 for DBT and ADBT, respectively) and dominates at lower temperatures. At the same time, due to the higher preexponential factor, the radical bond cleavage, with reaction enthalpies of 298 and 320 kJ mol-1, dominates in the experimental temperature range for both DBT and ADBT. In line with the theoretical predictions of C-NO2 bond energies, ADBT is more thermally stable than DBT. We also determined a reliable and mutually consistent set of thermochemical values for DBT and ADBT by combining the theoretically calculated (W1-F12 multilevel procedure) gas-phase enthalpies of formation and experimentally measured sublimation enthalpies.

AB - Nitro derivatives of benzotriazoles are safe energetic materials with remarkable thermal stability. In the present study, we report on the kinetics and mechanism of thermal decomposition for 5,7-dinitrobenzotriazole (DBT) and 4-amino-5,7-dinitrobenzotriazole (ADBT). The pressure differential scanning calorimetry was employed to study the decomposition kinetics of DBT experimentally because the measurements under atmospheric pressure are disturbed by competing evaporation. The thermolysis of DBT in the melt is described by a kinetic scheme with two global reactions. The first stage is a strong autocatalytic process that includes the first-order reaction (Ea1I = 173.9 ± 0.9 kJ mol-1, log(A1I/s-1) = 12.82 ± 0.09) and the catalytic reaction of the second order with Ea2I = 136.5 ± 0.8 kJ mol-1, log(A2I/s-1) = 11.04 ± 0.07. The experimental study was complemented by predictive quantum chemical calculations (DLPNO-CCSD(T)). The calculations reveal that the 1H tautomer is the most energetically preferable form for both DBT and ADBT. Theory suggests the same decomposition mechanisms for DBT and ADBT, with the most favorable channels being nitro-nitrite isomerization and C-NO2 bond cleavage. The former channel has lower activation barriers (267 and 276 kJ mol-1 for DBT and ADBT, respectively) and dominates at lower temperatures. At the same time, due to the higher preexponential factor, the radical bond cleavage, with reaction enthalpies of 298 and 320 kJ mol-1, dominates in the experimental temperature range for both DBT and ADBT. In line with the theoretical predictions of C-NO2 bond energies, ADBT is more thermally stable than DBT. We also determined a reliable and mutually consistent set of thermochemical values for DBT and ADBT by combining the theoretically calculated (W1-F12 multilevel procedure) gas-phase enthalpies of formation and experimentally measured sublimation enthalpies.

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85151108915&origin=inward&txGid=748a27aaad9d5efe4d60e04d2ed83c2a

UR - https://www.mendeley.com/catalogue/596ac046-116b-3ffb-9092-d6f7d2a2769e/

U2 - 10.3390/ijms24065330

DO - 10.3390/ijms24065330

M3 - Article

C2 - 36982405

VL - 24

JO - International Journal of Molecular Sciences

JF - International Journal of Molecular Sciences

SN - 1661-6596

IS - 6

M1 - 5330

ER -