Mechanism Investigation Of Aerobic Baeyer-Villiger Reaction And Aerobic Oxidation Of Methylaromatic Compounds And Their Applications

The aerobic oxidation of the carbon-hydrogen compound to obtain daily products in industry is the technology that mimics the process of living-substance production in biology through respiration.However,there are two main difficulties needed to be overcomed for chemists currently:(1)For some inert substance,finding an efficient method to activate the oxidation.(2)Improving of the selectivity of desire products in the aerobic oxidation of carbon-hydrogen bond.Thus,my doctoral work was focused on these two problems in oxidation.In the first part,enhancing the activity of aerobic oxidation is the core project to be discussed.Baeyer-Villiger oxidation is discovered by Aldolf von Baeyer and Victor Villiger in 1899.Industrially,peroxy acids were primarily used as the oxidant for the transformation of cyclic ketones to lactones.Due to the explosive property of peroxy acid,it is an imminient problem for scientist to develop molecular oxygen as the alternative oxidant.Thus,how to develop new methods to activate oxygen in oxidizing ketones becomes the key topic in the Baeyer-Villiger oxidation.In the Chapters 2 and 3,an investigation in the development of new methods to achieve Baeyer-Villiger oxidation with oxygen as the oxidant was discussed.In Chapter 2,the one-pot cooxidation of toluene and cyclic ketones to benzaldehyde,benzoic acid and lactones was developed.The benzoic peroxyacid in situ generated from the aerobic oxidation of toluene was active reagent oxidizing the ketones to lactones,which overcomes the inert property of oxygen for Baeyer-Villiger oxidation.We found Fe(NO3)3/NHPI as the suitable catalyst of the cooxidation with 1,2-dichloroethane as the solvent.Toluene was successfully conveted with the generation of 38%benzaldehyde and 49%benzoic acid,and the selectivities of lactones were among 32-92%.Subsequetly,18O2 labeling experiment,control experiments and intermediate analysis suggested that both NO3-and O2 were the active species for toluene oxidation.The process analysis of the oxidation indicated that benzoic peroxyacid in situ generated from the oxidation of toluene is responsible for oxidation of cyclic oxidation.In addition,to develop a simple Baeyer-Villiger oxidation with oxygen as the primary oxidant,a sacrifice-free approach to lactone/esters from ketones using molecular oxygen as the oxidant was discussed in chapter 3.Cerium ammonium nitrate and N-hydroxyphthalimide were optimized as the most efficient catalysts,and they also showed a good tolerance to cyclic and aromatic ketones.In a mechanism investigation,control experiments,byproduct analysis,and isotope analysis of 2H demonstrated that the oxidation is initiated from the deprivation of the a-hydrogen of ketone,and the '80 labeling experiment suggested that NO3-oxidized the carbonyl species to lactone/ester with the assistance of Ce4+,and it was then regenerated by molecular oxygen.The recyle of(NH4)2Ce?(NO3)6 and(NH4)2Ce?(NO3)5 during the reaction and the structure of ceric complex were also reflected in the EPR and XRD spectra.SEM spetra and experimental results suggested the reactivity of(NH4)2,Ce?(NO3)6 was highly dependented on the size of catalyst.In chapter 4,selective oxidation of methylaromatic compounds to aromatic aldehydes is discussed.The mechanism for aerobic oxidation of methylaromatic compounds via Co(CH3COO)2-Mn(CH3COO)2-KBr was further studied.The experimental results suggested that the intermediates(aromatic alcohols)are unexpectedly inert to be directly oxidized in Co-Mn-Br system.In addition,it is found that both aromatic and aliphatic alcohols could inhibit the oxidation of the substrates and other intermediates(aromatic esters,aromatic aldehydes).It was indicated by UV-Vis spectra that the variation of valence from Co(?)to Co(?)would be interrupted in the presence of a given amount of alcohol.The intermediates analyzed by LC-MS and control experiments showed that aromatic alcohols preferred to esterify acetic acid rather than being directly oxidized described in the previous mechanism,and the aromatic acetates were subsequently oxidized to corresponding aldehydes.According to the new mechanism,a strategy of high selectively synthesizing aromatic alcohols and aldehydes from corresponding methylaromatic compounds was designed.In summary,new reaction-system design and mechanism analysis were investigated to solve the problems of inertness and selectivity in the oxidation of aromatic methyl compound and Baeyer-Villiger oxidation.The development of new methods and new catalysts facilliate the further development of the Baeyer-Villiger reaction and aromatic methyl compounds oxidation.