| Selective Oxidation of Organic Compounds for synthesis of oxygenated chemicals is a very important type of conversion reaction in organic synthesis.The development of a green oxidation technique based on hydrogen peroxide,especially molecular oxygen as an oxidant,to achieve such conversion reactions under mild reaction conditions is particularly important.In this dissertation,the vanadium-substituted heteropolyacids with Keggin type(K-type)structure and its quaternary ammonium salts or vanadium(Ⅴ)and vanadium(Ⅳ)compounds were used as catalysts to photocatalytic oxygen and HCl selective oxidation of cyclohexane to KA Oil or reaction with cyclohexene to halogenated alcohols;The boro-fluoro-hybridized C3N4 promotes the oxidation of cyclohexane by hydrogen peroxide catalyzed by 8-hydroxyquinoline iron complexes.The following valuable research results have been obtained:The following valuable research results have been obtained:1.vanadium-substituted K-type 12-phosphorus tungsten/molybdenum(W/Mo)heteropoly acid and its quaternary ammonium salt(X-PM12-nVn(X=H,TBA,CTMA,M=W,Mo))catalyst were synthesized,and used ICP,FT-IR,UV-Vis,XRD,CV and other methods performed a series of characterization tests on the catalyst.Studies on the X-PM12-nVn as catalysts under room temperature and oxygen atmosphere,in acetonitrile medium with hydrochloric acid,using visible light to catalyze the oxidation of cyclohexane to cyclohexanone and cyclohexanol(KA oil).Experimental investigated that the coordination atoms W.and Mo,the number of heteroatoms Ⅴ,the cation Ⅹ,and the additive water to the regulation of photocatalytic reaction.The results showed that 12-phosphorus tungsten or molybdic acid(H-PW12 or H-Mo12)and HPW11V are inactive for this photoxidation reaction regardless of with or without hydrochloric acid in MeCN;While without hydrochloric acid participating in the reaction,other vanadium-substituted X-PM12-nVn have less than 3.6%cyclohexane conversion and 51-58.3%cyclohexanone selectivity;The addition of proper amount of hydrochloric acid not only can significantly increase the photocatalytic reaction efficiency,but also the main product obtained is KA oil,but there is a small amount of by-product chlorocyclohexane.However,other chlorine-containing organic compounds or chlorine-containing inorganic salts or inorganic acids did not have this promoting effect,indicating that only hydrochloric acid had a special promoting effect on the photocatalytic reaction;The photocatalytic activity of X-PM12-nVn increases with the number of substituted V atoms,and the activity of molybdenum series is slightly higher than that of tungsten series,and the activity of quaternary ammonium salt is slightly higher than that of acid;The addition of appropriate amount of water not only has promoting effect on the reaction,but also can significantly inhibit the chlorinated side reactions,thereby significantly increasing the selectivity of cyclohexanone;However,a slight excess of water can significantly reduce the catalytic activity,but the excess water has a weaker inhibitory effect on the catalytic activity of the quaternary ammonium salt system than that of the acid system;The catalytic reaction of TBA-PMo9V3 can achieve 32.2%conversion of cyclohexane,and KA oil selectivity can reach more than 95%.2.Based on the results of the X-PM12-nVn photocatalytic system,this article used a variety of characterization methods to conduct a detailed characterization of the catalytic system.The results indicate that the Vv-Ob/c-M and V=Ot(M=VⅤ,MoⅥ or WⅥ)sites in X-PM12-nVn capture HCl by protonation to form photoactive species(PA,POM-(VⅤOHM)+Cl-),solvent acetonitrile may also participate in the formation of this PA species through weak coordination.The PA species has a characteristic absorption band of 475 nm in the visible region of the UV-Vis spectrum,and has-550 ppm chemical shift signal in the 51V-NMR spectrum,and has a higher vanadium oxidation potential in the CV plot.Along with the increase of V atom substitution,the formation of PA species increased significantly.Because of the substitution effect of water on the coordination of HCl,the formation of PA species will gradually decrease with the increase of the amount of added water,which is consistent related to the inhibition of photocatalytic reaction by water.However,the inhibitory effect of water on the formation of PA species was significantly stronger than its inhibitory effect on the photocatalytic oxidation activity,indicating that the generation of PA species is probably not the current rate-control step of photocatalytic oxidation.According to monitoring the generation rate of PA species by UV-Vis spectroscopy,it was found that due to the hydrophobicity of the quaternary ammonium salt catalyst,its PA species formation is significantly less hindered by water than acidic series catalysts.The isotopic tracer method of heavy oxygen water H218O(97%)combined with MS analysis confirmed that the product contains 18O-labeled cyclohexanol(about 8.2%),especially cyclohexanone(about 33.3%),indicating that is likely to generate hypochlorous acid by water react with the chlorine atoms in the photoreaction,which is involved in the formation of oxidation products.Based on these findings,combined with free radical trapping experiments and EPR characterization results,we proposed a free radical mechanism for the generation of Cl radicals in visible light-excited POM-(VvOHM)+Cl-)species and the Cl radicals to initiate photo-oxidation reactions.3.Based on the characteristics of X-PM12-nVn-MeCN-HCl-H2O system photo-catalytic oxidation reaction process will generate HClO,this article developed a phospho-molybdenum vanadium heteropoly acid,and vanadium(Ⅴ)or vanadium(Ⅵ)compound were uesed as catalyst to photocatalytic oxidation of HCl to react with cyclohexene to synthesis of chlorohydrins.The results show that these selected vanadium-containing catalysts have good activity for this type of reaction,in which vanadyl acetylacetonate(Ⅳ)have 33.71%of cyclohexene conversion product,the selectivity of chlorohydrin is 72.92%.Taking water as the main variable condition and V2O5 as the representative,the influence of water quantity on the selectivity of chlorohydrin was discussed.The halohydrin(haloketone)selectivity can be increased to 87.41%by adjusting the amount of water.By adjusting the O2 concentration in the reaction,we found that the catalytic efficiency of V2O5 and vanadium(Ⅳ)oxides was significantly reduced,while the polyacids,due to their cage effect,increased the contact between the reactants and the effective collisions between the molecules and were relatively less affected.The Uv-vis spectroscopy and CV characterization were used to investigate the formation steps and rates of reactive intermediates for different catalysts.Meanwhile,above founds combined with the catalytic results,a photo-catalytic oxidation of HCl with cyclohexene to produce a halohydrin was proposed.4.Studied on the 5,7-dichloro-8-hydroxyquinoline iron(FeⅢQc3)were used as catalytic to catalyze hydrogen peroxide oxidization cyclohexane at room temperature.The FeⅢQc3 catalytic oxidation of cyclohexane conversion rate of 8.05%,but addition of a small amount of C3N4BF to this catalyst system can significantly increase the conversion of cyclohexane to 23.19%and cyclohexanone selectivity to 31.11%and 68.89%,respectively.The additive itself does not have any catalytic activity for this reaction.The effect of additives on the catalytic reaction was studied through condition experiments to find the optimal catalytic reaction conditions.Uv-vis spectrum and EPR characterization confirmed the presence of phenoxy radicals in the solution after the reaction.Uv-vis spectroscopy analysis compared the concentration of phenoxy-free radicals in the reaction solution with and without additives,and found higher concentration of the former.The FeⅢQc3 was immobilized on C3N4BF,and its TGA characterization showed that its decomposition temperature had a certain increase,indicating that it interacted with C3N4BF.Theoretical chemical calculations further confirm the existence of π-π weak interaction between C3N4 or C3N4BF and FeⅢQc3,which leads to distortion of the octahedral symmetry structure of FeⅢQc3.Moreover,C3N4BF has stronger interaction force and greater induced distortion effect than C3N4.The interaction force of C3N4BF and catalyst is about 16.28 kj·mol-1,and the Fe-0 coordination bond been lengthen 1.84%,and the bond level is weakened by 13.4%.Therefore,we infer that FeⅢQc3 due to C3N4BF strong induction of"distortion" effect,making it part of the Fe-0 bond is weakened,resulting in it more easily react with H2O2 generate hydroxyl radicals and initiate cyclohexane oxidation. |
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