Quantum Chemical Study On Thermal Decomposition Mechanisms Of Several Hydroxylamine Hydrochloride Compounds

Hydroxylamine(HA)and its salts are important chemicals in industry.Since Hydroxylamine is instable at room temperature,it usually exists as the corresponding salts.Hydroxylamine hydrochloride(HH)and hydroxylaminenitrate(HAN)have been confirmed to decompose autocatalytically.It is important to understand thermal decomposition characteristics of HA salts to enhance security of hydroxylamine and its hydrochloride salts during production,usage and storage.Thermal decomposition mechanisms of protonated HA(exists widely in HA salts),N-methyl hydrochloride(NMHH),N-Ethylhydroxylamine Hydrochloride(NEHH)and N-isopropylhydroxylamine hydrochloride(NiPHH)were calculated based on quantum chemical calculations.Ab initio MP2 method was used to study the thermal decomposition mechanism of protonated hydroxylamine(HA)to understand thermal decomposition characteristics of HA salts.The geometrical structures,of all the related reactants,transition states,intermediates,complexes,and products were optimized at the MP2/aug-cc-pVDZ level and their energies were calculated at the MP2/aug-cc-pVDZ and MP2/6-311++g(2df,2pd)level.A new decomposition pathway was found.The main product NH can combine with the protonated HA to form a complex and decrease the effective energy barriers of subsequent decomposition reactions,so catalyze the decompositions.The results indicate that the decomposition of the protonated HA has an autocatalytic characteristic.Theoretical research based on Density Functional Theory(DFT)was performed for NMHH,NEHH and NiPHH to investigate its thermal decomposition characteristics.Calculation results show all substances can be decomposed in two ways,N-O bond break and C-O bond break.And the energy barrier of similar path for protonated first-step product is much lower than that of direct decomposition.Moreover,in terms of NMHH result,the formation and decomposition of protonated NMHA will be more likely to occur as the reaction continues.The results indicate an autocatalysis characteristic during NMHH decomposion.The autocatalytic decomposition of HH and NMHH was confirmed by thermal differential scanning calorimetry(DSC)and adiabatic accelerated calorimetry(ARC)tests,which were in agreement with the theoretical results.