Theoretical Investigation of the Reactivity of Sodium Dicyanamide with Nitric Acid

There is a need to replace current hydrazine fuels with safer propellants, and dicyanamide (DCA(-))-based systems have emerged as promising alternatives because they autoignite when mixed with some oxidizers. Previous studies of the hypergolic reaction mechanism have focused on the reaction between DCA(-) and the oxidizer HNO3; here, we compare the calculated pathway of DCA(-) + HNO3 with the reaction coordinate of the ion pair sodium dicyanamide with nitric acid, Na[DCA] + HNO3. Enthalpies and free energies are calculated in the gas phase and in solution using a quantum mechanical continuum solvation model, SMD-GIL. The barriers to the Na[DCA] + HNO3 reaction are dramatically lowered relative to those of the reaction with the bare anion, and an exothermic exit channel to produce NaNO3 and the reactive intermediate HDCA appears. These results suggest that Na[DCA] may accelerate the ignition reaction.