Theoretical Investigation On The Reaction Mechanism Of Coupling Synthesis Or Thermal Decomposition Of Carbon–carbon Skeleton Organic Small Molecule Compounds

Quantum chemistry can be used to explain chemical phenomena and predict chemical reactions.Due to the characteristics of instantaneous reaction,complexity and changeability of intermediates and diversity of products,the pyrolysis of high-energy density compounds and coupled reactions under liquid phase limit the accurate observation and interpretation of the reaction process by experimental means.Therefore,it is necessary to clarify the underlying mechanism by theoretical chemical calculation.In this paper,the cross coupling reaction of ferric catalytic alcohol in liquid phase and the pyrolysis reaction mechanism of high energy density compounds in gas phase are studied systematically by using the method of quantum chemistry calculation.1)We used density functional theory to study the alkylation reactions of benzyl alcohol and 1–phenylethano catalyzed by ferrous acetylacetonate.The reaction consists of three successive stages:(1)the oxidation of alcohols into aldehydes or ketones,followed by the capture of hydrogen anions by the iron center of the catalyst;(2)hydroxyaldehyde condensation reaction forms chalcone;(3)hydrogen captured by the catalyst is fed back to the C=C or C=O unsaturated bonds of chalcone to produce dihydrochalcone or 1,3–diphenyl–1–propanol.Selectivity of the product can be achieved simply by adjusting the amount of the solvent(p-xylene)and the yield is greater than 90%.We suggest that water,the only by-product of the reaction,may be the root cause of the product selectivity.Eight transition states of catalyst hydrogenation and four transition states of catalyst dehydrogenation were studied.We found two types of Fe…H…C transition states: two hydrogen atoms of alcohol anion point to the same oxygen atom of the catalyst ligand(type I);The benzene ring of alcohol anion is almost parallel to the catalyst ligand plane(type II).It is the key to determing the selectivity of the products whether to hydrogenate continuously the intermediate dihydrochalcone.The calculation shows that the presence of water has little effect on the hydrogen barrier of the catalyst and the reduction energy barrier of the C=C bond in chalcone.However,the presence of water significantly increased the energy barrier for the hydrogenation reduction of dihydrochalcone,and the hydrogenation dominant reaction pathways were interchanged(type I and II).We conducted molecular orbital and charge analysis of dihydrogen chalcone hydrogenation reduction.According to modifying the ferrous acetylacetonate,two catalysts for the formation of dihydrochalcone was designed.2)We studied the mechanism of spontaneous combustion between 1–chloro–1,1–dinitro–2–(N–chloroamidino)ethane and monomethylhydrazine,and determined six main reaction channels.Two key factors at atomic level were determined:(1)the 2CDNCE·MMH complex formed in the initial stage of the reaction would release a large amount of heat(23.4 kcal/mol),and the initial heat accumulation and temperature rise of the system were achieved;(2)the initial reaction is the sp3 hybrid carbon in CDNCE attacked by monomethylhydrazine’s central nitrogen nucleophilic attack,which is also the speed limit step of the decomposition path.The activation energy barrier of the initial reaction was 27.4 kcal/mol,lower than the energy required for CDNCE decomposition.At the same time,the calculated reaction rate indicated that the rate of CDNCE decomposition to generate NO2 at room temperature was 4 orders of magnitude lower than that of the nucleophilic reaction rate.3)The optimized geometry,natural population analysis charges and electronic density,the HOMO–LUMO gap,electronic affinity,electrostatic potential on the surface of molecules,reduced density gradient and the decomposition mechanism of CDNCE were calculated.Two lowest energy full decomposition paths were presented: The path of nitro-nitrite rearrangement;Concerted decomposition of CDNCE to HONO.Interestingly,we found two kinds of carbon-carbon bond synergistic rupture as the initial reaction at the activation energy of only about 60 kcal/mol.In addition,physical and chemical properties such as density,the standard molar enthalpy of three phases,the detonation velocity and detonation pressure of CDNCE had been predicted.