Study On The Preparation And Catalytic Properties Of Dodetungstophosphoric Acid And Its Salts Catalysts

Heteropoly compounds as environmentally friendly, reusable and heterogeneous catalysts have widely been used for the acid-catalyzed reactions and oxidation reactions, due to their specific properties such as unique structure, hydrophobicity, strong acidity, "pseudoliquid phase", activated crystal lattice oxygen, etc.In this paper, the preparation and characteristics of heteropoly compounds and their application in acid-catalyzed reactions and oxidation reactions were reviewed. The physical and chemical properties of the dodetungstophosphoric acid and its salts were characteristized by IR, TG-DSC, XRD, ICP, TPD and Potentiometri titration. Their activities and selectivities were tested in the synthesis of important pharmaceutical intermediates and alcohol dehydration reaction, respectively.Dodetungstophosphoric acid and its salts catalysts were applied in synthesis of 2-acetlythiophene by Friedel-Crafts acetylation of thiophene with acetic anhydride for the first time. The results showed that the modified and unmodified, supported and unsupported dodetungstophosphoric acid and its salts exhibited different catalytic performance in acetylation of thiophene. Aluminum dodetungstophosphate prepared by dodetungstophosphoric acid and Al³⁺ had higher catalytic activity and selectivity in acetylation of thiophene. The thermal stability, acidic sites and acidic intensity of SiO₂-supported aluminum dodetungstophosphate catalysts increased compared with unsupported aluminum dodetungstophosphate. Under the optimized reaction conditions, the yield and selectivity of 2-acetylthiophene are 92.0% and 99.7%, respectively.The catalyst characterization results showed that the dodetungstophosphate catalysts modified with different transition metals and different metal atom number still kept the Keggin structure. The properties, e.g. surface area, acidity and acidic amounts were enhanced obviously. The dodetungstophosphate catalysts were used for the Biginelli reaction to synthesis 6-methyl-4-aryl-3,4-dihydropyrimidin-2(1H)-one for the first time. The experiment results showed that the dodetungstophosphate catalysts activated at 400℃exhibited the best catalytic activity and selectivity in the Biginelli reaction. Under the selected reaction conditions, the aim product yields were ranged in 67～94%. Further, the catalytic performance of Co_1.5PW₁₂O₄₀ catalyst was tested in the ternary condensation reaction with ethyl cyanoacetate, aldehyde and urea. The results showed that this reaction is different from all the reported reactions. The synthetic compounds are kinds of new pyrimidin-2(1H)-one.The surface reaction of ethanol dehydration on supported dodetungstophosphoric acid catalysts and the effect of active component loading on dehydration reaction of ethanol on the H₃PW₁₂O₄₀/C catalysts were studied by C₂H₅OH-TPSR and some other methods. The results showed that in the lower loading, the acidity amount of the catalyst is appropriate to H₃PW₁₂O₄₀loading, and the absorb amount of C₂H₅OH on the catalyst is appropriate to the acidity amount of the catalyst. Dehydration of C₂H₅OH on the H₃PW₁₂O₄₀/C catalysts is surface reaction. The removing H⁺ of ethoxyl absorbed on B-acid site produces ethylene, and the interaction between ethoxyl absorbed on B-acid site and free-C₂H₅OH produces diethyl ether.