Study On Syntheses And Performances Of 1,1-Diamino-2,2-Dinitroethylene

As the most important killing measure and active working medium in the weaponsystem, the explosive has been widely considered as a basic industry and a hot topic forthe national defense industry as well as the whole national economy. As for the processof the study of the explosives, which underwent from the widely used TNT (2,4,6-trini-trotoluene),then HMX (cyclotetramethylene tetranitramine) and later TATB(triamino-trinitrobenzene), the focus of the study has been shifted from the high energy to highsafety. Thus, it makes the study of a new generation of insensitive high explosive(IHE) with a fairly good compromise between the "high energy" and "high safety" acommon target for experts all over the world. In this way, a new type ofmonoplasmaticIHE based on new design and synthesis would be a basic solution to the contradictionbetween the "high energy" and "high safety".And just for the above considerations, a new explosive named as 1,1-diamino-2,2-dinitroethylene (FOX-7) was developed. In accordance with the simulation andprediction, such kind of explosive is characterized in stable molecular structure andexcellent all-over properties, making it a favorite option for the development of the newgeneration IHE formulation.And just because of it wide prospect for application, suchkind of explosive has been a common focus all over the world.In this paper, the synthetic route and reaction mechanism, structural characteristics,crystal phase transformation, thermal decomposition mechanism and dynamics, and theall-over properties of FOX-7 are presented relatively symmetrically. Based on theinvestigation, the characteristics and mechanism of the thermal decomposition of FOX-7are discussed in detail, providing a solid technical and theoretical ground for the application of such a new type IHE.As for the synthetic route and reaction mechanism, 2-methylpyrimidine-4, 6-dionewas used as raw material for the FOX-7 synthesis by means of nitration and hydrolyticreaction. As a new route for the FOX-7 synthesis with a high yield, such kind ofsynthesis can provide a maximum yield up to 84.5ï¼…. And the characterization of theproduct is made with elemental analysis, infrared analysis, nuclear magnetic analysisand mass spectrometry. In accordanee with the nitrifying mechanics, the nitrificationreaction of 2-methylpyrimidine-4, 6-dione was studied thoroughly for the first time,based on which, a relatively reasonable synthetic reaction mechanism was presented toprovide a reference for the further investigation of the similar synthetic reactions.Based on the discussion of various effective factors upon the synthesis, the study of thelaboratory-level synthetic amplification proces.s was made to provide a stable processfor 100g-level synthesis with a yield of over 80ï¼…and a fairly good purity, presenting asolid foundation for the further investigation of the FOX-7 properties and formulation.As for the crystal structural characteristics and phase transformation, FOX-7 singlecrystal for the structural analysis was developed for the first time in China. And thecrystal structure was analyzed with single crystal X-ray diffraction characterization,providing a guiding principle of the efficient characteristic method for the similarexplosives and the relationship between the explosives and their properties. As for theFOX-7 phase transformation, which is controversial internationally, the on-linetemperature-changing X-ray diffraction was used in combination with DSCmeasurement. It is well indicated that before the FOX-7 decomposition, there're twophase transforming process and three crystallographic forms before the decompositionof FOX-7. In this paper, the crystallizing law, appearance, crystal size and the thermalproperties of the FOX-7 crystal was investigated relatively systematically under varioustechnical conditions of solvents and recrystalization, providing a substantial support andexperimental data for the further investigations concerning with the FOX-7 crystalproperties and formulation.As for the thermal decomposition mechanism, with a combination of the experi-mental study and the quantum chemistry, the prediction of the thermal decompositionmechanism of FOX-7 was made, as well as the computations of the major dynamic parameters of the main functional groups during the thermal decomposition process.During the experimental study, the in-situ FTIR spectroscopy, together with the pyrolyticcrocking GC/MS, was used for the first time to study the thermal decomposition processof FOX-7. The prediction indicated that, during the thermal decomposition, thenitro-nitrite rearrangement occurs at the first before the N-O bond cracks to produce NO,and then various small molecules are produced. With the combination of the ab initiomolecular dynamic simulation and molecular orbit theory, the route of the FOX-7thermal decomposition was predicted successfully. The computational results indicatedthat, under a high temperature (＞1000K), C-NO₂ bond cracking is the major initialdecomposition channel compared with a higher reactive ratio of nitro-nitrite rearrange-ment at lower temperature (＜500K). In this way, the arguments on the major initiativedecomposition route are settled. Based on the changes.of the condensed phase FOX-7decomposition obtained with in-situ FTIR spectroscopy, a reasonable explanation waspresented to settle the existing arguments on the first exothermal peak in the DSCspectrum. Namely, due to the heating, hydrogen bonds in and between FOX-7 themolecules crack, resulting in the combination of H₂O molecular with twoamido-hydrogen and one nitryl oxygen in the neighboring FOX-7 molecules,companied with C-C double bond condensation reaction, which provides a reference forthe explanation of the decomposition exothermal peak of the similar explosives.As for the thermal decomposition dynamics, such experimental measures as DSC,accelerating rate calorimeter and Blush pressure method was used to study the thermaldecomposition of FOX-7 under various conditions. The thermal decomposition dynamicparameters respectively under isothermal, heterothermal and insulate condition wereobtained-to provide a ground for the further application and the life-span prediction forFOX-7.The last part of this paper is dealing with the initial study of the all-over propertiesof FOX-7, providing such basic data as thermal sensitivity, impacting sensitivity,frictional sensitivity, detonation performance and compatibility with other materials.According to the results, as an explosive with excellent thermal stability, FOX-7 canprovide an energy yield about 85ï¼…of that provided by HMX (cyclotetramethylene), andalmost the same safety performance with that of RDX(hexahydro-1, 3, 5-trinitro-1, 3, 5- triazine), which can' be considered as a further evidence to identify FOX-7 as an IHE, aswell as data support for its further application as IHE.