Quantum-chemical studies on thermodynamic feasibility of 1-methyl-2,4,5-trinitroimidazole processes.

1-Methyl-2,4,5-trinitro imidazole (MTNI) is a well-known melt cast explosive possessing good thermal stability and impact insensitivity. MTNI has been synthesized from multi-step nitration followed by methylation of imidazole exhibiting low yield. It is desirable to screen the process thermodynamically for evaluating feasibility of the process. In the present investigations, B3LYP method in combination with 3-21G** basis set has been chosen to evaluate the enthalpy of formation for reaction species by designing reasonable isodesmic reactions. Thermodynamic feasibility of the processes has been worked out assuming free energies of reactions as derived from standard enthalpy and entropy of the reaction species. All possible synthesis routes for the target molecule, MTNI has been conceptualized from different precursors/intermediates viz. imidazole, 2-nitroimidazole, 4-nitroimidazole, 1-methyl imidazole and 2,4,5-triiodoimidazole. Various nitrating agents have been employed and their effect studied for deciding the feasibility of the reaction. It has been found that reaction entropy and enthalpy are favorable on usage of NO2BF4 as nitrating agent. The charge on nitro group (-QNO2) has been used for better understanding of the reactivity of substrates/intermediates. Overall, the study helped in screening several possible routes for MTNI synthesis and identified the thermodynamically feasible process by using NO2BF4 as nitrating agent.