materials Article Benzimidazole Derivatives as Energetic Materials: A Theoretical Study Jonas Sarlauskas 1 , Jelena Tamuliene 2 , Svajone Bekesiene 3,4, * and Alexander Kravcov 4, *   Citation: Sarlauskas, J.; Tamuliene, J.; Bekesiene, S.; Kravcov, A. Benzimidazole Derivatives as Energetic Materials: A Theoretical Study. Materials 2021, 14, 4112. https://doi.org/10.3390/ma14154112 Academic Editor: Tomasz Sadowski Received: 18 May 2021 Accepted: 20 July 2021 Published: 23 July 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Life Sciences Centre, Department of Xenobiotic Biochemistry, Institute of Biochemistry, Vilnius University, Sauletekio av. 7, 01513 Vilnius, Lithuania; jonas.sarlauskas@bchi.vu.lt 2 Physics Faculty, Institute of Theoretical Physics and Astronomy, Vilnius University, Sauletekio av. 3, 01513 Vilnius, Lithuania; jelena.tamuliene@tfai.vu.lt 3 Research Group on Logistics and Defence Technology Management, General Jonas Zemaitis Military Academy of Lithuania, Silo 5a, 10322 Vilnius, Lithuania 4 Department of Construction Technology, Faculty of Civil Engineering, Czech Technical University in Prague, Thákurova 7/2077, Prague 6—Dejvice, 16629 Prague, Czech Republic * Correspondence: svajone.bekesiene@lka.lt (S.B.); kravtale@fsv.cvut.cz (A.K.); Tel.: +370-686-48-000 (S.B.) Abstract: The explosive properties and stability of benzimidazole compounds are studied to deter- mine the influence of substituents and their position. The results obtained reveal the conjugation of substituents as one of the crucial factors for the thermal stability of these compounds. We also found that two -CH 3 substituents increase the thermal stability of the parent compound, while nitro groups decrease it. Moreover, the study clearly exhibits that the combination of an -NO 2 substituent with -CH 3 does not change the stability of the benzimidazole. On the other hand, nitro groups increase the chemical stability and explosive properties of the compounds under investigation, but their sensitivity could not fully satisfy the requirements of their safety and increase their toxicity. The main results of the study indicate that high thermal and chemical stability, low toxicity and sensitivity, and good explosive properties could be achieved by the precise combination of nitro, -CH 3 , and triazole ring substituents. These findings are very important for the design of new, effective, and non-sensitive explosives. Keywords: benzimidazole nitro compounds; explosives; detonation pressure; detonation velocity; sensitivity; toxicity; substituents 1. Introduction The synthesis of energetic materials with high density, detonation velocity, pressure, thermal and chemical stability has been a research focus in the past decade. Low costs and high yields in synthesis, low toxicity, high chemical and thermal stability, etc., are the main criteria that new energetic materials (explosives) should fulfill. These criteria are skeleton-molecule dependent and they are crucial in considering which substituents improve the explosive properties of materials and how they affect thermal stability. For example, the connection of two imidazole rings obtaining 2,2 ′ -bisimidazoles follow the trend of generating larger energetic molecules, and the thermal stability of nitrobenzene is increased due to the introduction of amino groups ([1] and refs. cited herein). A decrease in the sensitivity of the product relative to the unsubstituted starting material is obtained due to the introduction of amino groups into the nitroaromatic molecules [2,3]. An increase in the number of methyl substituents enhances the thermal stability and reactivity of methylammonium perchlorates [4]. Moreover, when hydrogens at the 3- and 5-positions on the picric acid ring are substituted with two amino groups, the resulting compound—ammonium diamino picrate, i.e., picric acid substituted with amino groups— show enhanced thermal stability and shock insensitivity, marking it out as a powerful secondary explosive with improved practical characteristics [5]. The conjugation (three Materials 2021, 14, 4112. https://doi.org/10.3390/ma14154112 https://www.mdpi.com/journal/materials