Studies On The Catalytic Oxidative Dehydrogenation Of4-acetamidocyclohexanol To4-acetamidocyclohexanone In Liquid Phase

As an important pharmaceutical intermediate,4-acetylaminocyclohexanone is mainly used for the synthesis of thiazole ring compounds, such as Pramiprexole, used for the treatment of Parkinson’s disease. The oxidation of4-acetylaminocyclohexanol is a main way for the synthesis of4-acetylaminocyclohexanone. At present,4-acetylaminocyclohexanol is used as raw material under the action of Jones reagent dehydrogenation, but due to the reaction process will produce large amounts of chromium slag, which does not conform to the requirements of environmental protection. As a result, it is with highly significant to look for environment-friendly catalyst. Therefore, the relevant research has both important theoretical significance and application value.In this paper we have investigated the preparation of different kinds of W-based catalyst and their catalytic activities in the liquid phase oxidation of trans-4-acetylaminocyclohexanol. The catalysts were characterized by various spectral and physicochemical techniques. The effects of reaction conditions and reaction mechanisms were further discussed.The main contents and results were as follows:1. Tungsten acid salt catalysts were prepared by precipitation. Supported catalysts with different loadings were prepared via supported on some carriers by impregnation. Supported catalysts with different loadings and different tungsten source were prepared by sol-gel method. Their physicochemical properties were characterized by XRD, BET and Raman. The results showed that:①Supported catalysts were prepared by precipitation. With the increase of the content of WO3in the catalyst, the intensity of WO3diffraction peaks were gradually increased. Diffraction peak of reused catalyst was consistent with that of fresh catalyst, which showed that catalyst used for reaction still maintained the structure of WO3. But the diffraction peak intensity was decreased obviously. ②Specific surface area of supported catalysts prepared by impregnation were smaller than supported catalysts prepared by sol-gel method. However the catalyst surface areas were decreased with the increasing of loading amounts for the two different catalyst preparation methods.③In the XRD and Raman spectra of catalysts prepared by impregnation method and sol-gel method, there were no characteristic peaks as the content of WO3is low. As the loading percent of WO3reached to10%, the corresponding characteristic peak showed, and peak strength increased with the increase of loading.2. With trans-4-acetylaminocyclohexanol as reactant,30%H2O2as oxidant, tungsten acid salts material as catalyst,4-acetylaminocyclohexanone was produced in the liquid phase oxidation. The catalytic activity of different catalysts and the effects of reaction conditions were further investigated. The results are as follows:①The conversion of raw material was varied with different catalysts. Ammonium tungstate had the best catalytic activity among different kinds of tungsten acid salts for the oxidation reaction. When Ammonium tungstate was used as catalyst, conversion can reach more than90%, the target product selectivity of was100%.②Both the amount of catalyst and the reaction temperature were critical to the reaction activity. Too little of catalyst or too low reaction temperature would cause underutilization of oxidizability of30%H2O2.Increasing the amount of the catalyst and reaction temperature would be conducive to increase utilization of30%H2O23. With trans-4-acetylaminocyclohexanol as reactant,30%H2O2as oxidant, supported catalysts as catalyst,4-acetylaminocyclohexanone was got in the liquid phase oxidation. The catalytic activity of different catalysts and the effects of reaction conditions were further investigated. The results are as follows:①Some oxides were chose as carrier. The catalyst with SiO2as the carrier for this reaction had better catalytic activity. At the same time, the rate of decomposition of hydrogen peroxide for SiO2was slow, which was also helpful for better oxidation of reactant.②For the catalyst with SiO2as the carrier, the reaction activity increased as the increasing of the loading percent of WO3on SiO2till to25wt%. With25wt%WO3/ SiO2as catalyst, catalytic activities were investigated under various reaction conditions. The amount of catalyst, reaction temperature and reaction time all affected the yield to4-acetylaminocyclohexanone.③According to the result of the reuse of catalyst, the conversion decreased sharply after repeated three times but the selectivity was still100%. The performance of the catalyst in the repeated use remains to be further improved.4. In order to avoid the loss of the activity component of catalyst during the reaction, some ways were tried to make the activity component W fixed into the structure of catalyst. However, the expected result was not obtained during the preliminary experiments. Further research work in the preparation, characterization and mechanism should be done in the further.