The Research Of Photocatalytic C-H Bond Direct Trifluoromethylation Of Arenes And Heteroarenes By Semiconductor Under Visible-light Irradiation

Trifluoromethylation reaction as an efficient strategy that can introduce fluorine atoms into organic molecular has attracted much attention in the synthesis of novel pharmaceuticals,agrochemicals and materials.In recent years,though a lot of trifluoromethylation methods have been published,the problems of complexity of reaction system,environmental harmful,high cost have limited the practical application.In order to resolve these problems,we introduced the semiconductor photocatalyst into the trifluoromethylation reaction based on the oxidation mechanism of photo-generated holes and expected to establish a green,mild and cost economic reaction system.The main contents and conclusions of this dissertation are disclosed as follows:(1)GO as a carbon material can initiate the trifluromethylation of aromatic compounds under visible-light irradiation,the reaction efficiency has direct relationship with light.The oxygen-containing groups on the GO surface have tremendous influence on the reaction,once these oxygen-containing groups were damaged,the GO lost its reactivity;(2)The trifluoromethylation of arenes and heteroarenes can be successfully accomplished under irradiation of visible-light by using traditional semiconductors as photocatalyst(such as CdS,C3N4),CF3SO2Na as trifluoromethylation reagent;Though the contrast of different semiconductors we found not all semiconductors which have more positive valence band position than the oxidization potential of CF3SO,Na could catalyze this reaction,the position of semiconductor conduction band must be more negative than the reduction potential of oxygen;Though the optimization of reaction conditions we found CH3CN as solvent,air as reaction atmosphere has the best experimental result,the efficiency of the reaction has close relationship with the intensity and wave length of light;By the study of reaction dynamics we found the break of C-H bond is not the rate-determining step.In the continuous experiments,the photocatalyst could keep same reaction reactivity;In additional,this method has also satisfied tolerance of different functional groups;(3)Through the investigation of mechanism we found photo-generated holes could oxidize CF3SO2Na to trifluoromethyl radical(·CF3),·CF3 has innate electrophilicity and would attack electron-rich arenes and heteroaenes to form an intermediate specie,after further oxidized and lost a proton,the final product obtained;On the other hand,the photo-generated electrons were trapped by oxygen,and super oxygen radical anions further participated in the later reaction.(4)Based on the mechanism we proposed a project which would make best use of semiconductor photocatalyst to realize the one-pot synthesis of trifluoromethylated anilines from nitro-aromatic compounds.The innovations of this dissertation include:using CF3SO2Na as trifluoromethyl reagent and GO or traditional semiconductors like CdS,C3N4 as photocatalyst successfully realized the C-H bond direct trifluoromethylation of arenes and heteroarenes under irradiation of visible-light;One-pot synthesis of trifluoromethylated anilines from nitro-aromatic compounds was proposed based on the reaction mechanism.In conclusion,this method not only enriches the methodology of trifluoromethylation but also extents the application of semiconductor photocatalyst in the field of organic synthesis.