A mechanism for the radical reactions of hydroxylamine nitrate (HAN) in the aqueous phase was identified and investigated. Optimized structures for the reactants, products and transition states were obtained at the ωB97X-D/6-311 ++G(d,p)/SCRF=(solvent=water) level of theory and the total electron energies of such structures were calculated at the CBS-QB3 level of theory. The H· abstraction reactions, NH2OH + OH·, NH2OH + NO2·, NH2O· (or HNOH·) + OH·, NH2O· (or HNOH·) + NO2·, HNO + OH·, HNO + NO2·, and other reactions including decomposition of HONO and HNO were investigated. HAN ([NH2OH][HNO3]) has a high reactivity and ignitability compared to ammonium nitrate ([NH3][HNO3]). H· abstraction from NH2OH has a considerably lower barrier than is the one from NH3. The difference in reactivity of NH3 and NH2OH is the source of the difference in thermal stability of ammonium nitrate and HAN. The initial reaction that triggers this mechanism has the highest energy barrier (205.0 kJ mol-1) of all the reactions investigated in this work. Thus, we conclude that the homolytic cleavage of HNO3 is the rate-determining step for the decomposition of aqueous HAN solution.
hydroxylamine nitrate, aqueous phase reaction, reaction mechanism, density functional theory