Non-Noble Metal(Hydro) Oxides Catalyzed Oxidation Synthesis Of Aromatic Nitrogenous Compounds

The aromatic nitrogenous compounds such as imines,azoxybenzene,azobenzene and nitrobenzene are important fine chemicals and medical intermediates.Among them,imines can be prepared by catalytic oxidation coupling of alcoholamine,azoxybenzene,azobenzene and nitrobenzene can be synthesized by selective catalytic oxidation of aniline as raw materials.First of all,in view of the reported problems of poor oxygen activation ability and low catalytic efficiency of metal oxides catalyzing alcohol-amine oxidation coupling into imines,this paper constructs a system of amorphous Fe₂O₃modified cerium and manganese oxide.By utilizing the low redox potential of Fe³⁺/Fe²⁺in amorphous Fe₂O₃,the transfer cycle of[O]in cerium oxide and manganese oxide is effectively promoted.The catalytic oxidation capacity was improved,and the high efficiency green catalyzed the oxidation coupling of benzyl alcohol and aniline into imines was realized.In the above research process,we found that iron zirconium composite oxide showed a certain aniline oxidation activity.After detailed screening of the catalyst,we found that Zr（OH）₄ can be used as a stable catalyst.With H₂O₂ or O₂as oxidant,azoxybenzene,symmetrical/asymmetric azobenzene or nitrobenzene compounds can be obtained with high selectivity by simple solvent regulation,which solves the problems of using additives and difficult reaction selective control in the existing aniline oxidation system.On this basis,we also developed a physical mixed catalytic system with Zr（OH）₄ and CuO,which further improved the selective regulatory performance.The main contents are as follows:1.A novel amorphous Fe₂O₃ modified CeO₂ catalytic system was established by simple coprecipitate method for the synthesis of imines by oxidation cross-coupling of benzyl alcohol and aniline.The target catalyst Fe8Ce2-100 showed high catalytic activity for atomic economic synthesis of imines.The characterization results and a series of mechanism experiments show that the enhanced catalytic activity of Fe8Ce2-100 is attributable to the synergistic effect between CeO₂ and amorphous Fe₂O₃.Amorphous Fe₂O₃ acts as an engine and greatly improves the[O]transfer cycle of Ce⁴⁺/Ce³⁺in CeO₂.The redox properties and acidity-alkalinity of the catalyst were enhanced.2.Amorphous Fe₂O₃ modified Mn₃O₄ catalyst was constructed for oxidation cross-coupling of benzyl alcohol and aniline to form imines.The characterization results and a series of mechanism experiments showed that the good catalytic activity was attributed to the acceleration of the oxygen transfer cycle of Mn³⁺/Mn²⁺in Mn₃O₄ by amorphous Fe₂O₃.Thus,the catalytic activity of the target catalyst Fe5Mn5-100 is higher than that of all reported non-precious metals and precious metals.In addition,the catalyst also achieves the synthesis of various imines derivatives in an amplified solvent-free system.3.Zr（OH）₄ can be used as a heterogeneous catalyst for aniline oxidation.It is the first time to selectively oxidize anilines to synthesize azoxybenzene,symmetric/asymmetric azobenzene compounds and nitrobenzene compounds without any additives,just by changing the solvent.It is also the first time to report the simultaneous activation of H₂O₂ or O₂ by a single catalyst for the selective oxidation of aniline.The mechanism experiments and DFT calculations revealed that the bridging hydroxyl site（b-OH）of Zr（OH）₄ is the active site in the H₂O₂ system,which plays a major role in the activation of H₂O₂,while the terminal hydroxyl site（t-OH）of Zr（OH）₄is the main active site in the O₂ system,which plays a major role in the activation of O₂.4.The heterogeneous Zr（OH）₄+CuO physical mixed catalyst system was constructed to achieve the selectivity regulation of azoxybenzene and nitrobenzene in aniline oxidation reaction.Selectivity is only adjusted by adding heterogeneous CuO without any additives or toxic solvents.The experimental and characterization results show that Zr（OH）₄+CuO has a suitable two-component weak chemical interaction,while retaining the function of Zr（OH）₄ to initiate aniline conversion and CuO to regulate selectivity,so it has a high conversion and selectivity.The experimental results show that the reaction mechanism may follow a new Ph-NOH intermediate mechanism.The Ph-NOH intermediate can be converted to azoxybenzene on Zr（OH）₄ catalyst,and the Ph-NOH intermediate can be converted to nitrobenzene on CuO catalyst.