The Synthesis Mechanism And Kinetics Of Energetic Plasticizers TMETN And DIANP

Energetic plasticizer has become one of the most important components of rocket propellants,in view that it can not only effectively improve the energy,speed and range of propellants,but also significantly develop the machinability and mechanical properties of propellants.Until now,many kinds of energetic plasticizers have been found,such as plasticizers of nitrate esters(-ONO2),nitro-group(-NO2),nitramine(-NNO2),azide(-N3),and two kinds of energetic groups.Recently,two novel energetic plasticizers of trimethylolethane trinitrate(TMETN)and 1,5-diazido-3-nitrazapentane(DIANP)have attracted much attention in view of the excellent physical and chemical properties.However,the synthesis mechanism and kinetics of TMETN and DIANP have been seldom investigated so far.The absence of a detailed synthesis mechanism hinders their further study and application to a large extent.Therefore,the synthesis mechanism and kinetics of TMETN and DIANP are systematically investigated by quantum chemical calculation method in the present work.The main results are summaried as follows:(1)The nitration mechanism of trimethylolethane(TME)in the preparation of TMETN in the nitric-sulfuric acid system was studied in the gas and solvent phase by M06-2X/6-311+G(d,p)//M06-2X/6-311G(d)method.The conventional transition state theory(TST)method with Eckart tunneling correction was used to calculate the rate constants of all elementary reactions.It is found that the coexistance HSO4-can induce the O-nitration of TME and NO2+,and promote the formation of TMETN.The introduced order of-NO2 may be not significant in the nitration of TME.The solvent effect can significantly impact on the active free enegies and the geometries of relative intermediates and transition states in the nitration of TME.The activation energy is very small and the rate constant is very large in the elementary reactions of the HSO4--induced nitration of TME,indicating that the nitration of TME is a very esasy and rapid reaction process.In view that the nitration of TME is a strong exothermic process,the generated heat in the actual nitration must be removed in time in order to avoid the danger of local overheating.(2)The synthesis?mechanism of DIANP in nitric-sulfuric acid system was systematically investigated by M06-2X/6-311+G(d,p)//M06-2X/6-311G(d)method.The synthesis of DIANP involved in two processes of the nitration of diethanolamine(DEA)and the azotized reaction of N-nitro-dihydroxyethylamie dinitrate(DINA).It is found that the HSO4-can induce/catalyze the nitration of DEA and NO2+ in nitric-sulfuric acid system,and promote the formation of DIANP.It is also found that the solvent effect can significantly impact on the active free enegies and the geometries of relative intermediates and transition states in the nitration of DEA.The attacked order of NO2+is found to be not significant in the nitration of DEA.The results of the activation energy and the rate constant indicate that the nitration of DEA is a very esasy and rapid reaction process.Therefore,the generated heat in the actual nitration of DEA must be removed in time in order to avoid the danger of local overheating,ensuring the safe and efficient experimental process.The synthesis process of DIANP by DINA is a mechanism of SN2,in which the addition of the nucleophile(N3-)and the elimination of leaving group(NO3-)take place simultaneously from the different sides.The active free energies of the azotized reaction of DINA in the gas and solvent phase are 22.22 and 26.59 kcal-mol-1.Moreover,the structural changes of transition states are slight between the gas and solvent phase.These results indicate that the impact of the solvent effect on the azotized reaction of DINA is lower than the nitration of DEA.In the experimental temperatue(353 K)of the azotized reaction of DINA,the rate constant of the rate-determing in the the azotized reaction is merely 4.16×10-4S-1,indicating that the azotized reaction of DIN is a slow reaction process,and controlled by the kinetics.The azotized reaction of DINA can be considered a non-homogeneous reaction of SN2,the actual reaction should be fully stirred,so that the system is sufficiently dispersed to ensure that the azotized reaction can effectively occur in the synthesis of DIANP.