Density functional theory study of the reactions of 2-azido-N,N-dimethylethanamine with nitric acid and nitrogen dioxide

The reactions of azido-N,N-dimethylethanamine (DMAZ) with pure nitric acid (HNO₃) and nitrogen dioxide (NO₂) were investigated by using the B3LYP density functional theory, for their importance in understanding the ignition mechanism of the DMAZ/HNO₃ system. Results identify two important low-temperature reaction pathways that are both exothermically and kinetically favored for triggering the DMAZ/HNO₃ ignition. The first is the proton transfer reaction from HNO₃ to the amine nitrogen of DMAZ in the liquid phase. The azido nitrogen atoms of DMAZ are substantially less reactive to receive proton than the amino nitrogen. In addition, the azido group of DMAZ is found to play a role of suppressing the proton transfer to the amine nitrogen and hence reduce the reactivity of DMAZ. The second type of reactions responsible for the DMAZ/HNO₃ ignition is the gas-phase reactions between DMAZ and NO₂. The slightly higher energy barriers for these reactions is another factor influencing the long ignition delay of DMAZ/HNO₃ compared with that of TMEDA/HNO₃. The significantly large heat release of the reactions of DMAZ with NO₂, especially of those leading to the N₂ formation at low temperatures, substantiates the recent interest in DMAZ as an alternative hypergolic propellant. These results agree with previous experimental observations on the ignition delay of DMAZ with nitric acid.