Design,Preparation And Application Of Cathode Materials In Asymmetric Electroreduction Of Aromatic Ketones

With the social advancement and economic development,the living standards of human beings have been continuously improved.Therefore,the theme of life has become the most intense topic in today's society.With the development of science and technology,human beings pay more and more attention to life.As one of the means that can directly affect the quality of life,the market demand of chiral drugs is also increasing year by year.Sales of chiral drugs accounted for the top of the total drug categories.The types and quantities of chiral drugs that can be directly extracted from nature are limited.Therefore,the development of chiral drugs through the study of chiral synthesis methods has become the main way of new drug development.Optically active aromatic alcohols obtained by asymmetric reduction of prochiral aromatic ketones in chiral drug synthesis are effective structural units for chiral drug synthesis.So the asymmetric reduction of aromatic ketones is also the focus in the field of asymmetric synthesis in recent years.Asymmetric synthesis reactions catalyzed by transition metals in homogeneous systems have always been common and effective methods in chiral synthesis,but homogeneous catalysts in such reaction systems are usually expensive and difficult to be separated in the post-reaction process,which will cause the waste of resources and environmental pollution.As another mainstream catalytic method,heterogeneous catalysis can effectively solve the problem of catalyst separation and recycling,but it cannot avoid high temperature and high pressure reaction conditions.Taking heterogeneous asymmetric hydrogenation as an example,the hydrogen source used in the reaction is usually high pressure hydrogen.So the reaction process is not very safe and the operation is relatively difficult.The emerging electrochemical method to catalyze asymmetric chiral synthesis can effectively avoid relatively harsh reaction conditions and achieve chiral catalysis under normal temperature and pressure conditions.The cathode material is the key to the asymmetric reduction of aromatic ketones by electrochemical methods.Therefore,the design and preparation of efficient cathode materials is the most important thing to achieve efficient catalytic asymmetric reduction of aromatic ketones.Based on the above problems,this thesis mainly explores through the following five parts.?1?Asymmetric electroreduction of 2,2,2-trifluoroacetophenone catalyzed by copper-platinum bimetalPt@Cu NPs were obtained by loading Pt nanoparticles with small particle size on the surface of Cu nanoparticles by metal replacement.And Pt@Cu NPs were applied to the asymmetric electroreduction of aromatic ketones which was induced by cinchonidine.Due to the uniform dispersion of the small Pt particles on the bimetal surface,the concentration of the adsorbed cinconidine was considerable.Therefore,it was more favorable for the substrate to generate optical activity product on the surface of bimetallic electrode.In the asymmetric electroreduction reaction of the model molecule2,2,2-trifluoroacetophenone,the product yield and ee value could reach 25%and 59%respectively when Pt@Cu NPs were used as the cathode,which were obvious better than those obtained on Pt and Cu.The bimetallic material had stable catalytic performance,and the yield and optical activity of the product did not changed significantly after continuous repeated electrolysis for 6 times.It could be a nice material with low cost and high efficiency in asymmetric electroreduction of aromatic ketones.?2?Asymmetric electroreduction of 2,2,2-trifluoroacetophenone catalyzed by copper-platinum alloyThe application of noble metal Pt catalysts in asymmetric reduction reactions has been widely reported.The catalytic performance of Pt-based alloys is significantly enhanced compared to single metals.The catalytic performance of Cu is good and the price of Cu is relatively lower.Therefore,CuPt alloy can improve the catalytic efficiency of the catalyst while reducing the Pt content.CuPt alloy had highly effective catalytic effect on asymmetric reduction of various aromatic ketone compounds induced by CD.Among them,the model substrate 2,2,2-trifluoroacetophenone had the reduction yield and ee values up to 83%and 44%respectively.Compared with the Cu-Pt bimetal catalytic system,the results were significantly improved.Moreover,the alloy electrode had strong stability,and the asymmetric electroreduction reaction of the catalytic model substrate could still obtain a level equivalent to that of the first electrolysis after repeated use 6 times.?3?Asymmetric electroreduction of 2,2,2-trifluoroacetophenone catalyzed by L-cysteine-modified platinum-based alloySince the asymmetric intermolecular aldol reaction catalyzed by L-proline had been reported,more and more scientists had begun to study the application of chiral amino acids in asymmetric synthesis reactions.L-cysteine was widely used in chiral catalytic reactions as a cheap and naturally available chiral inducer.The characteristic sulfhydryl groups in L-cysteine can interact with metals to form strong metal sulfur bonds,which provides the possibility for the formation of chiral electrodes by grafting chiral amino acids on metal surfaces.Since the chiral amino acid was grafted directly on the alloy surface,no additional chiral inducer was needed in the asymmetric electroreduction reaction of aromatic ketones catalyzed by L-cysteine-CuPt.It avoided the waste and environmental pollution caused by the difficult separation of the inducer during the electrolytic post-treatment process in the Cu-Pt bimetal and CuPt alloy catalytic system.The yield and ee value of the product could reach 73%and 43%when L-cysteine-CuPt-5 was used as the cathode to catalyze asymmetric electroreduction of the substrate.And it avoided the low activity product optical obtained when the same amount of L-cysteine was directly added to the electrolyte.L-cysteine could be firmly grafted on the alloy surface even after repeated reuse of the material,so its induction effect did not decrease with the increase of the number of electrolysis.?4?L-lysine-MWCNTs applied in asymmetric electroreduction of 2,2,2-trifluoroacetophenoneMulti-walled carbon nanotubes were treated with mixed acid of concentrated sulfuric acid and concentrated nitric acid,stirred under reflux in SOCl₂,and finally reacted with L-lysine to obtain L-lysine-MWCNTs.The same method could also be used to prepare different chiral amino-modified multi-wall carbon nanotube composites such as L-arginine-MWCNTs and D-arginine-MWCNTs.This kind of chiral amino acid modified multi-wall carbon nanotube material was different from amino acid modified metal materials,and its main constituent element was earth abundant carbon.It avoided the use of resource-limited metals used in L-cysteine-CuPt alloy catalytic systems.And it was more in line with the theme of green chemistry.In addition,L-lysine-MWCNTs played a considerable role in the asymmetric electroreduction reaction of aromatic ketones.Taking model substrates as an example,the product yield and ee value up to64%and 30%under the optimization of electrolytic conditions.This material not only had an effect on the asymmetric electroreduction reaction of a variety of aromatic ketones,but also had a strong stability in the electrochemical system.Even after repeated use,phase separation of chiral amino acids grafted on the surface of multi-walled carbon nanotubes would not occur.?5?D-PHE-MWCNTs applied in asymmetric electroreduction of 2,2,2-trifluoroacetophenoneD-PHE-MWCNTs were prepared by modifying D-phenylalanine on the surface of carbon nanotubes with only one reaction step?diazotization reaction?.The preparation method of the chiral amino acid-modified multi-wall carbon nanotube material was simple.The low yield of the material intermediate that might exist in the multi-step functional modification method was avoided.Deionized water was used as a solvent to make the material preparation process cleaner.In addition,this method shortened the material preparation time and simplified the experimental steps.D-PHE-MWCNTs had a good application effect in asymmetric electroreduction of aromatic ketones.Taking the 2,2,2-trifluoroacetophenone as a model substrate,the product yield and ee value could reach 65%and 40%,respectively.The chiral inducer was firmly grafted on the surface of carbon nanotubes during the electrochemical process,so that the material could maintain the comparable effect to the first electrolysis after 6 cycles of use.