Study On The Preparation Of Nitro-aromatic Compounds From The Liquid-phase Catalytic Nitration Of Aromatic With NO₂

Nitration of aromatics is an industrially important reaction for the formation of many aromatic nitro compounds,which are versatile building blocks for the manufacture of various industrial products such as pharmaceuticals,dyes,explosives,pesticides,plastic,etc.Traditionally,industrial-scale production of aromatic nitro compounds still relies on the classic nitration reaction with the mixed-acids containing nitric and sulfuric acids.Despite of the high efficiency,the mixed-acid process is not eco-friendly,as it produces large amount of acid waste.Therefore researchers are devoted to developing a economical and environmentally friendly production route of aromatic nitro compounds.In this paper,the production of aromatic nitro compounds from the nitration of nitrogen dioxide has many advantages such as efficient atom economy,simple technological process and without waste acids,which is an promising nitration method.In this paper,the catalytic performance of different transition metal salts as catalysts in liquid-phase nitration of benzene with NO₂ to nitrobenzene was investigated.The results showed that the transition metal salts exhibited different catalytic activity in nitration reaction.FeCl₃,ZrCl4,Fe?NO3?3,Bi?NO3?3,Zr?NO3?4 with higher electronegativity of metal cations in metal salts showed better catalytic activity.The catalytic performance of metal salts containing crystalline water is higher than that of anhydrous metal salt.In addition,the effects of different reaction conditions on the nitration of benzene catalyzed by FeCl₃ were investigated.The optimal reaction conditions were obtained: that is,a molar ratio of benzene to NO₂ of 1:5,a reaction temperature of 100 ?,the amount of the catalyst of 0.06 g,and a reaction time of 4 h.At this reaction condition,the conversion of benzene and selectivity of nitrobenzene are both 99%.On the basis of previous studies,the immobilized catalysts were prepared,the catalytic activity of the immobilized catalysts for nitration of benzene with NO₂ was compared,and the reaction conditions were optimized.Compared with anhydrous FeCl₃,the FeCl₃-SiO₂ catalysts showed good stability in the liquid phase nitration of benzene.Finally,the immobilized catalyst was characterized by BET,XRD,TG-DTG,NH₃-TPD,FT-IR,UV-vis DRS,Raman spectra and SEM.The nitration of different aromatic substrates was compared,and it was concluded that the degree of difficulty of nitration reaction was obtained: that is,benzene>toluene>benzene>chlorobenzene>nitrobenzene.In the next chapter,we have focused on the nitration of toluene with NO₂ catalyzed by different molecular sieve catalysts.The results showed that the shape selectivity of HZSM-5 zeolite in toluene nitration was better than others.When the molar ratio of toluene to NO₂ is 10:1,the reaction temperature is 45 ?,the reaction time is 0.5 h,the conversion of toluene is 16.4% and the selectivity of p-nitrotoluene is 57.6%.The catalysts and the used catalysts were characterized by XRD,BET,NH₃-TPD and FT-IR.The results show that the surface acidity of the used catalyst decreased,resulting in the decreased conversion of toluene during the reaction rate,and the selectivity is basically unchanged.XRD and BET also proved that the structure and pore size of the catalyst before and after the reaction had no significant change.