Computational Simulation Screening Of Energetic Materials For Tetrazole Derivatives

Ideal energetic materials should firstly possess high energy high loading density and low impact sensitivity for their practical applications. Traditional energetic materials are difficult to make tradeoffs between energy and sensitivity. In order to meet their future requirements, screening new energetic materials with desirable properties is urgent, while it is a challenging work. Multiple nitrogen heterocyclic compounds have attracted worldwide attentions over the last century for their high nitrogen content, positive enthalpy of formation and a conjugated and stable system which azole ring forms. Especially for tetrazole, its nitrogen contends is the highest among the present existing stable five-membered heterocyclic. There are two sites in the ring of tetrazole that can be replaced. Some substituted compounds with energetic groups, like nitro and amino, would largely improve its performance.Based on the aforementioned background, this article focuses on tetrazole. We choose 14 derivatives of tetrazole as our research subject and calculate some of their energetic properties, such as the gas-phase formation enthalpies、loading density and sensitivity、detonation velocity and explosive pressure. The approach of atomization reaction is applied to evaluate the gas-phase formation enthalpies (△fH) for the designed 14 derivatives using four different methods with different accuracy. These four methods all get the same trend of AfH, that is to say, no matter the substitutions of nitro occurs on C or N, all result in higher gas-phase formation enthalpies AfH no matter which method is used. Meanwhile we design these 14 isodesmic reactions and recalculate their gas-phase formation enthalpies, we also obtain the same trend with atomization reaction which further indicates the accuracy of the results.Then we use Politzer and his coworkers developed QSPR (Quantitative Structure Property Relationship) model to predict the density and sensitivity of the 14 compounds. The model correlated the unbalanced distribution of molecular electrostatic potential with loading density and impact sensitivity. The trivial deviations for some reference compounds between experimental values and calculated values based on the QSPR model indicate the reliance of this model; the result showed that the compounds whose nitro substituted on C and the compounds whose hydrogen atoms on C and N site are both replaced by nitro and amino groups possess high loading density. As for the prediction of sensitivity, Politzer’QSPR model divides energetic compounds to two kinds of relationship according to the correlation, one is for N-NO2 compounds and another is for nitro aromatic compounds. These two models both get similar result between experimental and calculated values. Except for 2-amino-5-nitrotetrazole which is synthesized recently and its calculated sensitivity level have huge deviations with experimental value. We think that it may lack of azoles compounds in the Politzer’ straining set for the construction of the QSPR model of sensitivity. Moreover the experimental impact sensitivity value itself also is somewhat unfaithful and repeatable.According to these calculations, we drew the conclusion that the compounds which are both replaced on C and N possess ideal formation enthalpies and density. Finally we chose four derivatives and some traditional compounds, design their corresponding explosion reaction and get some parameters for the calculation of explosive velocity and pressure. Our calculated explosive velocity and pressure values are coincide with experimental values for commercial explosives which all indicate these four derivatives all possess the same or better performance than traditional compounds.Upon on the above-mentioned analysis about their explosive properties and structure, we choose 1-amino-5-nitrotetrazole (ANTz) as our research subject. The whole molecule form a conjugated system and all its atoms are in a same plane. The H of NH2 and the O of NO2 form an intramolecular hydrogen bond, which further increase its stability. Then we analyzed ANTz’s thermal decomposition. Considering that there is a hydrogen bond in ANTz, three main possible routes are under our consideration:a. directly ring-opening; b. ring-opening after hydrogen transfer; c. hydrogen transfer after ring-opening, and finally we get four main corresponding reaction routes. From these reaction routes we draw the conclusion that, the comparative data demonstrates that ANTz prefers to decompose by direct ring-opening (Route 1) from a view of reaction kinetics. And the preferable products are HNO2, CN3H and N2. The decomposition can release huge energy of 34.91kcal/mol from view of thermodynamic.Besides QSPR model, we also predict the packing way of ANTz based on molecular mechanics to estimate crystal density. The intramolecular force field parameters are originated from QM Hessian matrix. Intermolecular interaction mainly considered about electrostatic interaction, which is calculated using classical ESP charge, and dispersive interaction, which is modeled by 12-6 Lennard-Jones potential from the default of Dreiding force field. We use Polymorph Prediction coupled with the re-edited force field parameters and default Dreiding force field potential function to look for all the possible packing forms with low binding energies. From the 9 lowest energy crystal packing arrangements, we realize that ANTz tend to pack in π-π conjugated form and its crystal density reaches up to 1.75g/cm3.In conclusion, we use computational simulation method to calculate a series of energetic properties of tetrazole and its derivatives and screen out 1-amino-5-nitrotetrazole which possesses excellent performance as our research subject. We analyzed its structure and thermal decomposition reaction mechanism and its packing arrangements based on molecular mechanics force field. The remaining work is to realize its actual production and detect and verify whether this compound really possesses ideal performance. Computational simulation indeed provides some reference and guidance.