Controlled Synthesis Of Molybdenum-based Organic Frameworks And Catalytic Selective Oxidation Of Thioethers

As important intermediate molecules in organic synthesis,sulfoxides and sulfones are widely used in fine chemicals,medicines,and pesticides.Due to the increasing demand of sulfoxide and sulfone compounds in recent years,it is particularly important to develop a green,economical and efficient thioether oxidation method.As a green oxidant in nature,oxygen is rarely used in the oxidation of sulfides because it is difficult to activate.Metal molybdenum has shown good catalytic activity in the oxidation of thioethers with hydrogen peroxide,but it has not been reported so far in the oxidation with oxygen.Metal-organic framework materials are porous materials composed of organic ligands and inorganic metal ion,which can make metals highly dispersed,thereby improving the catalytic activity of metals.Therefore,in consideration of the shortcomings of previous studies,we designed and synthesized the single metal organic framework material Mo-MOF and the double metal organic framework material Sn Mo-BTC to catalyze the selective oxidation reaction of diphenyl sulfide with oxygen.Without other additives,the higher conversion of diphenyl sulfide and the selectivity of the product diphenyl sulfoxide were obtained.The research content of this paper is mainly divided into two aspects:1.Using molybdic acid as the metal source and terephthalic acid as the ligand,a series of monometallic Mo-MOF materials were synthesized by static solvothermal method,which were characterized by XRD,SEM,EDX,TEM,IR and pyridine-IR,BET,XPS,NH₃-TPD,Solvent-CA.The oxidation reaction of thioethers were carried out with oxygen as the oxygen source and diphenyl sulfide as the reaction substrate without other additives.The effects of the kinds of metals and ligands,synthesis methods,the composition of mixed solvents,the ratio of mixed solvents,crystallization temperatures and crystallization times on the catalytic activity of Mo-MOF were explored.Then the effects of reaction temperatures,reaction times,amount of catalyst,oxygen pressures,and reaction solvents on the selective oxidation of diphenyl sulfide were investigated.The experimental results showed that the conversion of diphenyl sulfide reached as high as 100%and the selectivity of diphenyl sulfoxide reached86.4%when Mo-MOF-180°C-20h（water:ethanol=3:7）was used as the catalyst.The reaction was carried out at 90°C only for 0.75h under the oxygen pressure of 1.0 MPa.A series of Mo-MOF materials were synthesized by using ammonium molybdate as the molybdenum source,and a series of Mo-ZIF materials were synthesized by using molybdic acid as the molybdenum source which were characterized.The effects of crystallization temperatures and crystallization times on the catalytic activity of Mo-MOF and Mo-ZIF were investigated respectively,and then the effects of reaction temperatures,reaction times and amount of catalyst on the selective oxidation of diphenyl sulfide were investigated.2.On the basis of the above single metal Mo-MOF catalyst materials,a series of bimetallic Sn Mo-BTC materials were synthesized by static solvothermal method with the introduction of metal tin and trimesic acid as a ligand,which were characterized by XRD,SEM,EDX,TEM,IR and pyridine-IR,BET,XPS,NH₃-TPD,Solvent-CA.The oxidation reaction of thioethers were carried out with oxygen as the oxygen source and diphenyl sulfide as the reaction substrate without other additives.The effects of molybdenum sources,the composition of bimetals and the ratio of metals,the kinds of ligands,synthesis methods,the ratio of mixed solvents,crystallization temperatures and crystallization times on the catalytic activity of Sn Mo-BTC were explored.Then the effects of reaction temperatures,reaction times,amount of catalyst,oxygen pressures,and reaction solvents on the selective oxidation of diphenyl sulfide were investigated.The experimental results show that under the conditions of oxygen pressure of 1.0 MPa and reaction at 80°C for 2h,when Sn_0.1Mo₁-BTC-150°C-20h（water:ethanol=3:7）was used as the catalyst,the conversion rate of diphenyl sulfide reaches100%,and the selectivity of diphenyl sulfoxide reaches 91.8%.Under the same other conditions,the conversion of difurfuryl sulfide could reach 100%after 4 h of reaction,and the selectivity of difurfuryl sulfone could reach 98.1%.