Theoretical Investigation into the Solvent Effect on the Thermal Decomposition of RDX in Tetrahydrofuran, Acetone, Toluene and Benzene

In order to clarify the solvent effect on the thermal decomposition of explosive, the N–NO2 trigger-bond strengths and ring strains of RDX (cyclotrimethylenetrinitramine) in its H-bonded complexes with solvent molecules (i.e., tetrahydrofuran, acetone, toluene and benzene), and the activation energies of the intermolecular hydrogen exchanges between the solvent molecules and C3H8O2N4 or CH4O2N2, as the model molecule of RDX, were investigated by the BHandHLYP, B3LYP, MP2(full) and M06-2X methods with the 6-311++G(2df,2p) basis set, accompanied by a comparison with the calculations by the integral equation formalism polarized continuum model. The solvent effects ignore the ring strain while strengthen the N–NO2 bond, leading to a decreased sensitivity, as is opposite to the experimental results. However, the activation energies are in the order of C3H8O2N4/CH4O2N2∙∙∙acetone < C3H8O2N4/CH4O2N2∙∙∙THF < C3H8O2N4/CH4O2N2∙∙∙toluene < C3H8O2N4/CH4O2N2∙∙∙benzene < C3H8O2N4/CH4O2N2, suggesting that the order of the critical explosion temperatures should be RDX∙∙∙acetone < RDX∙∙∙THF < RDX∙∙∙toluene < RDX∙∙∙benzene < RDX, as is roughly consistent with the experimental results. Therefore, the intermolecular hydrogen exchange with the HONO elimination is the essence of the solvent effect on the thermal decomposition of RDX. The solvent effect is confirmed by reduced density gradient, atoms in molecules and surface electrostatic potentials.