Synthesis Of Temperature Sensitive P?DEA-co-DMAEMA?/Na₂WO₄ Hydrogel And Its Catalytic Behaviors Toward Oxidation Of Benzyl Alcohol

Sodium tungstate dihydrate?Na₂WO₄·2H₂O?is an important transition metal catalyst which is widely used in the oxidation of alcohols and olefins.But due to the separation of water-organic two-phase,Na₂WO₄ and substrate are only in contact with the two phases which leads to very low catalytic efficiency.Thermo-sensitive hydrogels are widely used in the field of catalysis due to their unique three-dimensional network structure and special phase transition behavior.The catalytic efficiency could be improved due to the enrichment of the catalyst and substrate by the shrink of the volume with the rise of environmental temperature.In this thesis,Na₂WO₄ was loaded by one pot and impregnation method respectively,and the structure and properties of hydrogels were studied.Besides,the green oxidation of benzyl alcohol was achieved by the use of hydrogen peroxide?H₂O₂?as oxidant,and thermo-sensitivity and interaction between polymers and Na₂WO₄ were explored with respect to catalytic performance.Main contents are as follows: 1.Temperature and pH sensitive poly?N,N-diethylacrylamide-co-dimethylaminoethyl methacrylate??P?DEA-co-DMAEMA??hydrogel was synthesized by one pot method.The structure and composition of the hydrogel were determined by FT-IR and SEM.The result of rheological test showed that there existed a physical cross-linking?hydrogen bonding and coordination?between Na₂WO₄ and polymers in addition to chemical cross-linking in composite hydrogel.The storage modulus of the composite hydrogel increased with the increasement of Na₂WO₄ content.When the content of Na₂WO₄ was 3%,the storage modulus of the hydrogel reached 2.26 kPa.The hydrogel also exhibited excellent temperature and pH sensitivity,and both of the sensitivities could be adjusted by varying the Na₂WO₄ content.2.P?DEA-co-DMAEMA?/Na₂WO₄ hydrogel which was prepared by one pot method was used as catalyst to catalyze the oxidation of benzyl alcohol with H₂O₂ as oxidant in aqueous phase.The composition and thermal stability of P?DEA-co-DMAEMA?/Na₂WO₄ hydrogel were determined by TEM and TG.The benzyl alcohol adsorption and desorption capacities of the hydrogel were studied.The effects of different catalysts,reaction temperature and catalyst dosage on the catalytic results were investigated.When the mass of D7:3W2 hydrogel was 1.0 g,n?H₂O₂?: n?benzyl alcohol?=1:1,and reacted at 80°C for 14 h,the conversion of benzyl alcohol was 23.1%,while the selectivity and yield of benzaldehyde reached 84.4% and 19.5%,respectively.However,Na₂WO₄ dropped from the polymer matrix due to the weak interaction between Na₂WO₄ and polymers.3.The P?DEA-co-DMAEMA?/Na₂WO₄ hydrogel catalyst was prepared by impregnation method using P?DEA-co-DMAEMA?hydrogel as supporter to adsorb Na₂WO₄ in the acidic environment.As a result,there existed electrostatic interaction between protonated amine groups in hydrogel and Na₂WO₄.The structure and dosage of catalyst were determined by FT-IR,SEM and TG.The catalytic performance of the oxidation of benzyl alcohol was also studied.When the mass of D7:3/W hydrogel was 0.05 g,n?H₂O₂?: n?benzyl alcohol?=1:1,and reacted at 80°C for 8 h,the conversion of benzyl alcohol was 30%,while the selectivity and yield of benzaldehyde reached 66% and 19.8%,respectively.Compared with the composite hydrogel prepared by one pot method,the interaction between Na₂WO₄ and polymers is enhanced,so it has relatively good recycling capability.The conversion of benzyl alcohol was 19.1% after three cycles of recycling.