Direct C-N Coupling Of Benzene Derivatives And Molecular Nitrogen Based On Nonthermal Plasma Combined With Mass Spectrometry Technique

Nitrogen fixation（NF）is an extremely important chemical process.Industirally,NF is dominately realized with ammonia synthesis through Haber-Bosch（H-B）process,which is associated with high energy consumption and high carbon emission.A considerable part of the synthetic ammonia is then used as a nitrogen-containing intermediate to be upgraded into nitrogen-containing organic compounds.Arylamines such as aniline and diphenylamine are an important class of nitrogen-containing chemicals and intermediate raw materials.In indurstry,arylaimes are is mainly manufactured based on the multi-step route operated at high temperature and high pressure.The nitrogen source used ultimately depends on the Haber-Bosch process to synthesize ammonia,and the entire industrial chain involved has the problems of high energy consumption,pollution emissions and high device costs.Therefore,it is of great theoretical and practical significance to develop a C-N coupling method using nitrogen as the nitrogen source to synthesize nitrogen-containing organic compounds such as arylamines.By taking advantages of non-thermal plasmas such as simple devices,mild reaction conditions and flexible and controllable parameters,we successfully realized the coupling reaction of benzene derivatives with nitrogen gas based on non-thermal plasma.The reaction mechanism has been explored,and main research results in this work are highlighted as follows:（1）Atmospheric pressure chemical ionization-mass spectrometry（APCI-MS）based on corona discharge ionization principle was designed,and the formation process of nitrogen-containing intermediates was observed based on that.Real-time detection of nitrogen-containing intermediates was identified of an arry of carefully selected benzene derivatives using a customized APCI-MS sample online device,and it was successfully proved that benzene derivatives and dinitrogen can be effectively coupled under atmospheric pressure discharge conditions.A mechanism is proposed for aryl cations to capture ground state molecule N₂ to generate Ar N₂⁺.The isomerization of molecular ions was found,and the effects of steric hindrance and other factors affecting the formation of nitrogen-containing intermediates were revealed,which provides a kinetic basis for further research on organic nitrogen fixation.（2）On the basis kinetics understanding of plasma gaseous reactions,the synthesis of arylamines was for the first time successfully achieved directly from benzene and dinitrogen by using plasmas.To avoid the problem of product decomposition in non-thermal plasma gas-phase reaction,non-thermal plasma-liquid interactions were used for organic nitrogen fixation.Several arylamine products were verified by ultra-performance liquid chromatography-high-resolution mass spectrometry（UPLC-HRMS）,and the discharge conditions were optimized.Further with dielectric material packing and screening of promoters,the plasma discharge characteristics are tuned to increase the concentration of nitrogen active species,which resulted in an amination yield as high as 44.9%.By means of electrical analysis and spectroscopic measurements,the generation channels of effective nitrogen-active species and their interaction mechanism with benzene were revealed.Two reaction channels involving the metastable excited state of nitrogen molecules and molecualr nitrogen cations were initially proposed.The plasma-based amination reaction developed in this thesis can be rapidly completed at room temperature and pressure,with the advantages of simple devices,instant on and off modes,easy integration with intermittent clean power.Compared with the traditional multi-step arylamine synthesis method,it is a potential green electrical route for arylamine synthesis.With further research in the future,it will help to achieve the carbon peak and carbon neutral development goals proposed in China.