Diatomite Supported Nickel Catalysts For Selective Regulation Of Aldehyde Reductive Amination And Nitrile Reduction

Aromatic amines are important organic nitrogen-containing intermediates,such as primary amines,secondary imines and secondary amines,which are widely used in the synthesis of fine chemicals,medicine and pesticides.A variety of aromatic amines,including primary amines,secondary imines and secondary amines,can be obtained from cheap and readily available aromatic aldehydes or aromatic nitriles by reductive amination and selective reduction,respectively.This method has attracted much attention due to its economical,efficient,high atomic utilization rate and environmental protection characteristics.Up to now,a variety of efficient homogeneous or heterogeneous catalysts have been applied to these two reaction systems,but often only one single product can be generated,and it is difficult to achieve selective regulation of multiple products by changing the reaction conditions.For this purpose,we designed and prepared a nickel catalyst with uniform macroporous structure supported by commercial diatomite with Ni⁰ and Ni²⁺coexisting.After determining the optimal ratio of Ni⁰ and Ni²⁺,we achieved the controlled selective reduction amination of benzaldehyde and selective reduction of benzonitrile by adjusting the reaction conditions,and obtained the corresponding primary amine,secondary imine and secondary amine with high yields.At the same time,we also studied the catalytic mechanism by combining the characterization methods of physical and chemical parameters and mechanism experiments.The main contents are as follows:1.Reduced amination can transform carbonyl compounds into nitrogenous compounds with high added value,such as primary amine,secondary imine and secondary amine,which is of great significance in organic synthesis industry.Ni/diatomite-400 has a high activity for the reductive amination of benzaldehyde,and can selectively generate benzylamine,N-benzylidenebenzylamine and dibenzylamine under different reaction conditions.The characterization results show that Ni⁰ and Ni²⁺coexist in the catalyst,and the proportion of Ni⁰ gradually increases with the increase of reduction temperature.The proportion of Ni^0/2+in the optimal catalyst is 56:44.The synergistic effect of Ni⁰/Ni²⁺is the key to successfully control the selectivity.Based on the characterization and mechanism experiments,the reaction mechanism of aldehyde reduction amination was proposed.In addition,Ni/diatomite-400 also has good substrate applicability,stability and heterogeneity.2.Hydrogenation of nitrile to benzylamine is the most widely studied path with the highest atomic utilization rate among all the preparation methods of amines.We used Ni/diatomite-500 for the hydrogenation of benzonitrile.By screening the reaction conditions such as solvent and ammonia dosage,it was found that different solvent systems had great influence on the product distribution.Benzylamine could be highly selectively generated in ethanol solvent,while dibenzylamine was mainly generated in cyclohexane system.Combining various characterization results and mechanism experiments,it is confirmed that benzylamine was generated by reduction-coupling-redecomposition steps,and the reason why different protic solvent systems can affect the selectivity is analyzed.Moreover,Ni/diatomite-500 has good catalytic ability for nitrile derivatives replaced by a variety of groups,and the recyclability and stability of catalysts were explored through repeated experiments and characterization of recovery catalysts.