Merging Visible Light Photocatalysis Of Dye-sensitized TiO₂ With TEMPO To Construct Selective Oxidation Systems

The use of photocatalysis to achieve selective oxidation under mild conditions attracts much attention recently.In particular,it is quite challenging to carry out the selective oxidation of organic compounds with atmosphere O2 at room temperature.The visible light photocatalytic selective oxidation of amines and sulfides received much interest.Herein,with TEMPO as a redox mediator,we select TiO2 as the visible-light-induced reaction platform with atmosphere O2 as the terminal oxidant to construct selective oxidation systems successfully.We adopted the strategy of dye-sensitized TiO2 in which the photocatalytic processes can be incorporated with the redox catalytic cycles of TEMPO,realizing the efficient selective oxidation of amines and sulfides at room temperature.In this dissertation,the major progresses are as follows:(1)We coupled the photocatalytic processes with the redox catalytic cycles of TEMPO,alizarin red S(ARS)-sensitized TiO2 as photocatalyst,and TEMPO as a redox mediator,a series of primary amines and secondary amines could be highly selectively transformed into the corresponding imines using atmosphere O2 as the terminal oxidant under blue LED(460 nm)irradiation.In detail,we have used the conduction band electron of TiO2 to activate O2 and subsequent oxidation.Dye molecules absorb visible light and electron transfer to the conduction band of TiO2,forming dye free radical cations.The catalytic redox cycle of TEMPO?TEMPO+ pushes forward charge transfer from dye*+to amines,TEMPO is a two-electron oxidant which can oxidize amines to imines.Next,the electron travels through the conduction band electron(ecb-)of TiO2 to react with O2.thereby forming OiO2 O2-interact with TEMPOH to form TEMPO.This shows that everyone plays a role in the cooperative photocatalytic system,namely:TiO2 can activate O2,organic dye captures visible light,TEMPO can regulate the conversion and selectivity of the reaction.(2)We synthesized anatase TiO2 under very mild conditions.Then,based on this synthesized TiO2.ARS-sensitized TiO2 photocatalytic system was constructed with TEMPO as a redox mediator and atmosphere O2 as the terminal oxidant.Improved selectivity for sulfoxide was achieved when the conversion of sulfide is very high.It was realized that when the conversion of sulfide is greater than 90%and the selectivity of sulfoxide is greater than 90%at the same time under 460 nm blue LED irradiation.Importantly,we conducted the reaction at very high substrate concentrations(0.3 mol/L).Specifically.thioanisole and its derivatives can be transformed to the corresponding sulfoxides with higher conversion for sulfides and excellent selectivity for sulfoxides.