Study On The Selective Synthesis Of Formamide And Methylamine Using Carbon Dioxide As A Carbon Sourc

With the implementation of the“carbon peaking and carbon neutral”strategies,how to effectively reduce the concentration of carbon dioxide（CO₂）in the atmosphere has become an urgent challenge for researchers worldwide.From the viewpoint of the carbon cycle economy and green chemistry,the conversion of CO₂into high value-added products（such as formamide or methylamine）would be of greater research interest,as formamide or methylamine are key intermediates for the synthesis of,for example,drugs,pesticides,or natural products.Moreover,the preparation of formamide or methylamine by N-formylation or N-methylation of CO₂and amine,respectively,would be a greener and more attractive method than the conventional synthesis of formamide or methylamine.Due to the high stability of the CO₂molecule,hydrosilane,hydroborane,or hydrogen（H₂）are currently mainly used as reducing agents to activate the CO₂molecule in this process.Although considerable progress has been made in these processes,there are still a number of pressing issues or challenges that need to be addressed.For example,the currently developed reaction systems suffer from low atomic economy,high costs,complexity,or environmental problems.Therefore,there is an urgent need to develop a simple,economical,and efficient green reaction system for the selective preparation of formamide and methylamine from CO₂and amine by reductive functionalisation,which is also the key scientific question to be addressed in this thesis.The selective preparation of formamide or methylamine by catalytic-free CO₂with amine reduction functionalisation has been a challenge.Inspired by the strong reducing properties of hydroborane and its ability to react with CO₂to formic acid borohydrides or methyl borohydrides,which are key intermediates in the synthesis of formamide or methylamine,respectively.This paper begins with the development of an efficient and catalyst-free method for amine selective N-formylation and N-methylation reactions using borane triethylamine[BH₃N（C₂H₅）₃]as the reducing agent and CO₂as the C1 source.The system is suitable for a wide range of substrates such as aromatic secondary amines,aliphatic secondary amines,heterocyclic amines,and primary amines.By simply regulating the reaction conditions,it is possible to obtain the desired formamide and methylamine in excellent yields.Optimum yields of up to 99%for methylamide and methylamine are comparable to the figures obtained with various catalysts.Furthermore,mechanistic studies have shown that CO₂is activated by insertion into the B–H bond of BH₃N（C₂H₅）₃and that formamide can be considered as an intermediate in the formation of N-methylation.Through investigation,sodium borohydride（Na BH₄）was found to be a cheaper,more atomically economical,and safer reducing agent than BH₃N（C₂H₅）₃.Subsequently,an amine selective N-formylation and N-methylation reaction using CO₂as a sustainable C1 source in the catalyst-free is described.The selective synthesis of formamide and methylamine was achieved by simple adjustment of the reaction solvent and temperature using Na BH₄as a sustainable reducing agent.In addition,mechanistic studies have shown that formamide is not an intermediate for the synthesis of methylamine in this method.Notably,this work has developed a simple,economical,and efficient green reaction system for the selective preparation of formamide and methylamine from CO₂and amine by reductive functionalisation.The cheapness,cleanliness and high atomic economy of hydrogen（H₂）compared to hydrosilane or hydroborane make it a more desirable reductant for CO₂N-formylation.The key to this process is the precise activation of inert CO₂and H₂molecules at the same time,which has been a challenging topic in the field of catalysis.Inspired by the interaction between precious and non-precious metal atoms and the green,fast,and economical characteristics of mechanochemical methods,this paper finally describes an efficient method for the preparation of bimetallic mesoporous catalysts Pd_xCu_1-x/Al₂O₃-y by mechanochemical methods.The resulting Pd_0.25Cu_0.75/Al₂O₃catalysts showed good catalytic activity and selectivity for the N-formylation reactions of various aliphatic amines with CO₂and H₂.The Pd_0.25Cu_0.75/Al₂O₃-0.1 not only has the lowest Pd loading（0.20 wt%）but also achieves a higher turnover number（TON=527）compared to the reported heterogeneous catalysts for N-formylation.Further mechanistic studies have shown that carbamate and formate are key intermediates in this N-formylation reaction over a Pd_0.25Cu_0.75/Al₂O₃catalyst.This mechanochemical strategy provides an opportunity for the green and economic preparation of heterogeneous metal catalysts.