Study On Selective Oxidation Of Organic Amines Catalyzed By Biomass Hydrothermal Carbon

Selective oxidation of organic amines to synthesize oximes or imines is a very important reaction in the chemical industry,which plays a pivotal role in the production of drugs,pesticides and polymer materials.At present,the traditional synthetic routes have the disadvantages of high cost of metal catalysts,the harsh reaction conditions,the low utilization of oxygen atoms,and environment unfriendly.Therefore,it is of great theoretical significance and application prospect to research and develop an economical and efficient catalytic system composed of metal-free catalyst and green oxidant.Biomass hydrothermal carbon has obvious advantages such as wide source of raw materials,low production cost,and large-scale promotion.As a new green catalytic material in recent years,it has attracted the attention of scholars.However,it has rarely been reported that it is used in the reaction of organic amines to oxime or coupled to form imines.This paper mainly studied the application of biomass hydrothermal carbon material as catalyst from the following two aspects:?1?Using glucose as raw material and acrylic acid as comonomer,porous carbon spheres?HTC?with rich carboxyl and hydroxyl groups on the surface were prepared by low temperature hydrothermal and high temperature roasting.The microstructures,physical and chemical properties of HTC were studied by FT-IR,Raman,XRD,SEM,XPS,nitrogen adsorption and desorption and other characterization techniques.Using cyclohexylamine as the model substrate,the catalytic performance of HTC-catalyzed oxidation of cyclohexylamine for the synthesis of cyclohexanone oxime was investigated.The results show that the catalytic activity of HTC and the selectivity of cyclohexanone oxime were significantly higher than the commercial activated carbons tested and the C₃N₄.It was also found that the addition of acrylic acid during the preparation of HTC can improve its catalytic activity and the selectivity to cyclohexanone oxime.When the mass fraction of acrylic acid is 10%of the mixed solution,the prepared catalyst has the highest catalytic activity.The conversion of cyclohexylamine is 42.0%,and the selectivity of cyclohexanone oxime is 95.5%.In addition,the stability test of HTC catalyst and the experiment results of different amines show that the catalyst has good stability and reaction universality.Combined with spectroscopic characterization and analysis of catalytic reaction data of small molecule models,ketone groups on the surface of HTC induce the activation of O-O bonds in H₂O₂ molecules,thereby promoting the selective oxidation of N-H bonds.At the same time,the carboxyl and hydroxyl groups on the surface adsorb and activate the organic amine molecules,which promote the whole oxidation reaction synergistically.?2?The biomass hydrothermal carbon material with surface oxygen functionalization were prepared from various crop wastes?wood powder,bamboo powder,reed and straw?by low-temperature hydrothermal method,and applied to catalyze the oxidative coupling reaction of benzylamine.It was found that maple-based hydrothermal carbon was the best catalyst in this reaction system.The results showed that 99.6%of benzylamine conversion and 92%of imine selectivity were achieved when oxygen was used as oxidant and toluene was used as solvent for 4 h reaction at 100?.This catalytic result was the same as all the fossil-based catalysts reported so far.This catalyst can be reused at least 7times,and its catalytic activity is almost same.It is stable and has a wide range of substrate universality.In combination with FT-IR,XRD,TEM,XPS,nitrogen desorption and other characterization techniques,it was found that carboxyl group,phenolic hydroxyl group or quinone on the surface of biomass hydrothermal carbon were the main active centers of catalysts through small molecule model catalyst experiment and quantum chemical theory calculation of iso-structure-activity relationship research,and the possible reaction mechanism was proposed.