The Synthesis Of 2,3,5-trimethyl-1,4-hydroquinone From 1,2,4-trimethylbenzene

As an important raw material of synthetic vitamin E,2,3,5-trimethyl hydroquinone is obtained by the reduction of 2,3,5-trimethyl benzenequinone,which can be directly oxidized from 1,2,4-trimethyl benzene according to literatures in recent years.In this paper,2,3,5-trimethyl benzenequinone was synthesized by one-step catalytic oxidation of 1,2,4-trimethylbenzene.The main contents and results were as follows:A variety of single component and multi-component catalysts were used in 1,2,4-trimethyl benzene-acetic acid-hydrogen peroxide system.Reactant conversion and product yield were measured by external standard method for gas chromatography.Industrial packing ?-Al₂O₃ and agent ?-Al₂O₃ were selected as two preferable catalysts.In experiments of industrial packing ?-Al₂O₃,influence of amount of catalyst and oxidant,reaction temperature and time on reaction were studied,1,2,4-trimethyl benzene conversion of 20.0%,2,3,5-trimethyl benzenequinone yield of 13.0%,selectivity of 64.9% were attained under the optimized conditions.Data analysis of XRD,SEM,FTIR,BJH showed that the crystalline state of ?-Al₂O₃ is the main factor affecting its catalytic effect.In addition,the study of aluminum phthalocyanine-?-Al₂O₃ composite catalyst indicated acetic acid will corrode surface of industrial packing ?-Al₂O₃.Several methods were utilized to modify preferred catalyst ?-Al₂O₃,wherein coupling agent KH-560 performed as the best modifier.Single factor experiments of coupling agent amount,hydrolysis time,adsorption time and temperature were carried out to clarify their impact on reaction.The results optimized were: 1,2,4-Trimethyl benzene conversion of 14.3%,2,3,5-trimethyl benzenequinone yield of 13.3%,selectivity of 72.4%.Analysis test of the modified ?-Al₂O₃ demonstrated that coupling agent KH-560 can enhance catalytic behavior of ?-Al₂O₃ through strengthening its surface hydroxyl effect and reducing its pore diameter,instead of changing the morphology.?-Al₂O₃ was successfully prepared by sol-gel method and citric acid method.Further evidences that ?-Al₂O₃ possessing better crystalline state and crystal form has better catalytic effect were given.CuO-?-Al₂O₃ catalyst was prepared by means of precipitation.Experimental results showed that ?-Al₂O₃ in catalyst CuO-?-Al₂O₃ can be effectively dispersed by CuO.