Studies On The Synthesis Of Tetralone Derivatives By Friedel-Crafts Reactions Under Fixed-bed Catalytic Condition

As important chemical products and intermediates, tetralone derivatives have been widely applied in pharmaceuticals, pesticides, dyes and other fields. Friedel-Crafts reaction is one of the most important and widely used synthetic methods for the preparation of aromatic ketones due to its advantages of simplicity and high selectivity. The traditional catalysts used in Friedel-Crafts reaction were Lewis acids (such as AICl3,FeCl3,TiCl4,BF3) or Bronsted acids (such as HF,H2SO4,HCl). However, there were some disadvantages for these catalysts, such as complexity in the technical process, large amount of usage, large amount of wastes and un-recoverability for the used catalysts. In order to solve these problems, it is with highly significant to replace liquid acid catalysts with environment-friendly solid acid catalysts. Up to now, most of the studies are concerning with intermittent liquid-solid phase reaction system. If the reaction could proceed over the fixed bed reactor continuously, the production efficiency would be increased for the continuous run. Therefore, the relevant research has both important theoretical significance and application value.In this paper we have investigated the intramolecular acylation of 4-phenylbutyric acid and the reaction of p-xylene with y-butyrolactone over fixed bed reactor with solid acid catalysts, especially zeolite and heteropoly acids. The catalysts were characterized by various spectral and physicochemical techniques. The effects of reaction conditions and reaction mechanisms catalyzed by solid acids were further discussed.The main contents and results were as follows:1. Different modified Beta zeolite and supported heteropoly acids were prepared. Different loading amount of silicotungstic acid catalysts were prepared via supported on some carriers by impregnation. The Beta zeolite was modified by cation exchange, calcination, acid treatment and impregnation. Their physicochemical properties were characterized by XRF, XRD, NH3-TPD, SEM, BET and the probe reaction of cyclohexanol dehydration. The results showed that: ①The cation exchange modification had little effect on the crystal structure, Si/Al ratio of Beta zeolite, but showed obvious difference in the cyclohexanol dehydration reaction. The reaction activity of the modified Beta zeolite was significantly lower than that of H-Beta.②High calcination temperature increased the disordered structure of Beta zeolite, and then decreased its degree of crystallinity. The Beta zeolite which were calcinated at 500℃showed highest specific surface area, acidity, and the best catalytic activity in the cyclohexanol dehydration reaction.③The Si/Al ratio of Beta zeolite was increased by the acid treatment. Although the modified zeolite maintained its topology, the degree of crystallinity was declined because the intensity of diffraction peak decreased. The acidity of Beta zeolite was reduced to some extent after the treatment of acids, while its specific surface area had no great change. The diffraction peak intensity of Beta zeolite was decreased after supported by heteropoly acids.2.α-Tetralone was synthesized by intramolecular acylation of 4-phenylbutyric acids over a fixed bed reactor. The catalytic activity of different catalysts and the effects of reaction conditions over Beta zeolite were further investigated. The results are as follows:①Both the reaction temperature, the acidity and structure of catalysts were critical to the reaction activity. The decarboxylation byproduct of propylbenzene was formed as the reaction temperature or acidity was too high. The acidity of the catalyst or the reaction temperature should be adjusted to a suitable value to obtain the higher selectivity of the target product. The small pore size of zeolite would prevent reactant molecules enter into the pore, the coke formed in the reaction would cover the surface active sites and block the zeolite channels, which would make the conversion and the yield decreased. H-Beta zeolite exhibited high activity and stability in the reaction because of its suitable pore structure and medium acidity.②The calcination temperature had much impact on the catalytic activity while the Si/Al ratio of zeolite had little effect. The experimental results indicated that H-Beta zeolite which was calcined at 900℃exhibited high activity and stability in the 10 hour's continuous run for stability test.3. Under the fixed bed continuous flow conditions,5,8-dimethyl-l-tetralone was synthesized by the reaction of p-xylene and y-butyrolactone. The effects of reaction conditions and the catalytic activity of different catalysts were further discussed. The results showed that:①Compared with other solid acids, the supported heteropoly acids and H-Beta exhibited higher catalytic activity for the reaction, but the selectivity to the target product of 5,8-dimethyl-1-tetralone for the supported heteropoly acids is much lower than that for H-Beta.②Over the catalyst of H-Beta, the effects of different reaction conditions were investigated. Higher yield of target product were obtained at moderate reaction temperature (240～260℃) and calcination temperature (500℃). The H-Beta zeolite with medium Si/Al ratio exhibited higher catalytic activity and stability. The flow rate of nitrogen and input flow rate of liquid would affect the contact time of reactants and catalyst. The longer the contact time and the greater volume ratio of reactants, the higher the conversion, but the selectivity to the target product decreased.③The cation exchange modification had little effect on the catalytic activity. The selectivity was improved with H-Beta zeolite catalyst modified by copper acetate. Compared with other acid treatment catalysts, H-Beta zeolite modified by the treatment of 0.5mol/L phosphoric acid under heat exhibited higher catalytic activity and stability.④The deactivation of the catalysts is probably due to the formation of crotonic acid which was decomposed by y-butyrolactone. The presence of crotonic acid is likely to cause the surface of the catalysts coking or carbon deposition to make the catalysts deactivated. But the deactivated catalysts can be regenerated in the fixed-bed by calcination under the air or oxygen flow, and the regenerated catalysts had good repeatability.