Direct Catalytic Synthesis Of Aromatic Phenols(Amines) From Aromatics And Hydroxylamine

Generally, a multi-stage reaction system is needed to produce a product from startingmaterial in chemical manufacturing process. However, these processes have severaldisadvantages such as multi-step procedures, more devices needed for reaction and separation,low production efficiency, high energy consumption and waste discharge. Evenmore, there alsoexist unsafe intermediate products such as inflammable or explosive compounds, toxic andharmful substances. To aovid producing and using the unsafe intermediate products, directsynthesis process is a better way to solve these problems. Aromatic amines and phenols arevaluable intermediate for organic synthesis. Traditional ways for producing these compoundsinvolve multi-step processes, suffering from the drawbacks like low atomic utilization,producing more side products, unsafe process and environmental pollution, etc. Based on theidea of high efficiency, clean and safety chemical process, a direct process for the production ofphenols （aromatic amines） was investigated in this study, including catalyst design andpreparation, new catalytic reaction, regulation of product distribution and the application of ionicliquid.New supported catalyst design and preparation for direct catalytic synthesis oftoluidines from toluene and hydroxylamine: Comparson with traditional synthetic routes,unsafe process including nitration of toluene and hydrogenation of nitro-toluene, were removedfrom this process. Then a series of vanadium （NaVO₃、NH₃VO₃） and molybdenum salts(Na₂MoO₄、（NH₄）₆Mo₇O₂₄) were used as catalysts and tried for amination of toluene. The resultsshowed that different catalysts need different reaction media to show higher activity. A suitablesolvent is HOAc-H₂O acid media （v/v=2:1） for vanadium catalysts, and that, for molybdenumcatalysts, is H₂SO₄-HOAc solution （v/v=4:11）. Moreover, the highest yield of toluidines above80%was obtained on the molybdenum catalysts. Based on the research on the activity ofhomogeneous vanadium-based catalyst, supported vanadium catalysts were prepared, and the effect of carrier and promoter on the catalyst activity was investigated in the reaction of tolueneamination. It was found that carriers with weak acidity have a beneficial effect on the catalystactivity. Furthermore, adding Cu species to vanadium catalysts shows a peculiar behavior,maintaining a high activity toward toluene amination. An optimum Cu/V ratio appears at lowdopant loading （V/Cu=16/1）. Subsequently, new supported vanadium catalysts CuO-V₂O₅/Al₂O₃were prepared prepared, and characterized by various techniques such as XRF, BET, XPS andXRD. The optimized reaction conditions investigated were HOAc:H₂O （v/v）2:1, conducted at85°C for4h. More than60%total yield of toluidines was obtained under the optimizedconditions. Catalyst characterizations revealed that V₂O₅phase was in a highly dispersed state onthe catalyst. Copper was present mainly in the+2valence, and the addition of copper improvedthe formation of V5+species, thus enhancing the activity of the catalyst. This may be due tophysical or chemical change in the environment of the vanadium species by the introduction ofCu species.A new approach for direct catalytic synthesis of phenols: Currently there are severalapproaches, involving direct oxidation of aromatics employing N₂O, O₂, and H₂O₂as oxidant.However, the present route was more safe for direct synthesis of phenols. In this work, a newapproach was proposed for direct catalytic synthesis of phenols from aromatics andhydroxylamine. Initially, the reaction between toluene and hydroxylamine catalyzed by（NH₄）₆Mo₇O₂₄·4H₂O was selected as a model reaction for optimizing the reaction conditions.The results showed that the incorporation of water into HOAc-H₂SO₄acidic media wouldimporved the selectivity for cresol. Thus the reaction was conducted in variousH₂O–HOAc–H₂SO₄solvents containing different amount of water. The best result is obtained fora H₂O/HOAc/H₂SO₄volumeratio of4:10:1. The optimized reaction conditions investigated wereNH₂OH/toluene （molar ratio）1:1, conducted at80°C for4h. And high toluene conversion andcresol selectivity were obtained, corresponding to36.3%and61.3%respectively. Moreover, avariety of aromatics including benzene, ethylbenzene and xylene, were examined. And thesearomatics could be hydroxylated with hydroxylamine to give the corresponding phenols. Theconversion of benzene, ethylbenzene and xylene were51%,13%and17%respectively, and theselectivity for the corresponding phenols were all above45%,74%and70%.A new environmental friendly reaction medium of ILs-HOAc-H₂O media: The aim ofthis study was to explore the possiblity of using ILs as a media to replace sulfuric acid in thereaction of direct synthesi of phenol, cresol and2,5-xylenol. And Several SO₃H-functionalizedILs was prepared. Then an eco-friendly and reusable catalytic system, i.e., combination of thenew reaction media with Mo catalyst （called ILs-Mo catalytic system）, was designed for aromatics hydroxylation. It was found that [HSO₃-bmim][CF3SO₃]-HOAc-H₂O solution with aweight ratio of6:8:8was a better reaction media for the hydroxylation using（NH₄）₆Mo₇O₂₄·4H₂O as catalyst. And all the aromatics including benzene, ethylbenzene andxylene could be hydroxylated with hydroxylamine to give the corresponding phenols.Furthermore, high selectivity （nearly100%） of2,5-xylenol was achieved in this catalytic system.All the organic compounds could be entirely extracted by ether, and the residue including ILsand Mo catalyst can be used again. Recycling experiments suggested that the catalytic systemwas stable enough to be recycled for the hydroxylation.