Study On The Mechanism Of Nitrifying Methenamine Using In-situ Infrared Technology

Hexogen(RDX)is one of the largest elementary explosives currently used in weaponry and has the advantages of high power,high detonation speed,and good safety.The direct nitration of methenamine(HA)with nitric acid is the main method of the synthetic of RDX in China.Due to the limitations of previous separation detection and instrumental analysis techniques,the study of the reaction mechanism of this process has not been well resolved,so limit their process improvement.The development of in-situ infrared detection technology and chemometrics provide a new way to further study the reaction mechanism.Therefore,the in-situ infrared detection technology is used to study the reaction mechanism of the preparation of RDX by direct nitration of methenamine in this paper,which has important theoretical and practical value for improving the production process of RDX.Infrared spectroscopy technology was used to obtain the infrared spectrum data of salt formation and nitration of methenamine.The change law of the important groups was revealed in the reaction process.The results showed that the reaction from HA to HAMN was very fast.The reaction from HAMN to HADN was relatively slow.When the concentration of nitric acid reached 5.97 mol/L,HADN was formed.The reaction of nitroxide to prepare RDX could be completed within 8.8 seconds after the completion of feeding.The B3LYP/6-31G* was used to optimize the structure of the intermediate products or by-products in the reaction process and the vibrational spectra were calculated.The corrected theoretical spectra were in good agreement with the experimental spectra.The three-dimensional infrared spectrum data of the process of preparation of RDX using HA,HAMN,and HADN as raw materials measured by an in-situ infrared analyzer was subjected to noise reduction,principal component analysis,and evolving factor analysis to determine the number of components of the reaction system.The initial concentration matrix was obtained,and finally the multivariate curve resolution-alternating least square regression was used to iterate to obtain the corresponding concentration change curve and infrared spectrum of the separated pure components.The structure of the reactants,products and 55 possible intermediates of each reaction were optimized and their theoretical spectra were obtained by calculating the vibration frequency.Through comparison and identification,the four main intermediate products of the three reactions were obtained respectively.The nitration mechanisms of HA,HAMN and HADN as raw materials were inferred respectively.The research results are of great significance for the in-depth understanding of the reaction mechanism of the preparation of RDX by nitration of urotropine and optimization of the reaction process.