Preparation Of Phase Transfer Catalytic System In Pickering And Its Application In Substitution Reaction

Phase transfer catalysis is an important basic reaction and has a wide range of applications in the synthesis of textile chemicals such as dyes and auxiliaries.However,the existing reaction system has the disadvantages of high equipment requirements?violent stirring?,difficulty in scale,and high reaction energy consumption,and the construction of a green and efficient phase transfer catalytic reaction system has become an urgent problem to be solved.Due to its high interface area,high stability,low surfactant dosage,etc.,the application of Pickering emulsion in the field of catalytic reaction has received more and more attention.In recent years,the environmental responsiveness of Pickering emulsion has been continuously explored,which provides a new idea for the efficient and green construction of heterogeneous reaction systems.Based on the goal of constructing static and high-efficiency phase transfer reaction system,the most commonly used SiO₂ particles of Pickering emulsion were used to prepare the conventional and temperature-responsive Pickering emulsion by physical modification of cationic surfactant and nonionic surfactant.By analyzing the factors affecting the stability of the emulsion,two Pickering emulsions were applied to the phase transfer catalysis Williamson etherification reaction and esterification reaction.The applicability of the reaction system and the factors affecting the catalytic activity were analyzed,which laid a foundation for the wide application of Pickering emulsion in phase transfer catalysis.The main research contents are as follows:?1?A conventional Pickering emulsion system was prepared by using a water-oil heterogeneous phase of a catalytic reaction and a cationic surfactant-modified SiO₂ particle as a stabilizer.The zeta potential of SiO₂ particles in the aqueous phase was characterized,and the factors affecting the stability of Pickering emulsion were analyzed.The results showed that the water and oil phases were emulsified at 11800 rpm for 2 min to prepare an O/W Pickering emulsion with an average particle size of 21?m.And there was no change in the particle size of the emulsion after standing for 3 months.Among them,7 mL of aqueous phase contains 2wt.%SiO₂,5%DTAB,6%TBAB,sodium p-cresol?0.14M?,and 7 mL oil phase?diisopropyl ketone?contains p-nitrobenzyl bromide?0.1M?).Compared with the traditional Pickering emulsion,the Pickering emulsion system prepared in this paper needs a higher concentration of solid particles and modifier to stabilize the emulsion because the aqueous phase contains a higher concentration of alkali and salt.And conventional PTC catalysts are not suitable for the modification of SiO₂ particles in the Pickering emulsion prepared herein.?2?Taking the Williamson etherification reaction as an example,the effects of the components in the conventional Pickering emulsion system on the catalytic activity,such as the type and concentration of the modifier,the type and concentration of the phase transfer catalyst,and the reaction substrate,were analyzed.The feasibility of the conventional Pickering emulsion system for esterification was discussed.The results show that the conventional Pickering emulsion system can be successfully applied to phase transfer catalysis Williamson etherification and esterification.And the conversion rate of the etherification reaction at 90?is over 90%,and the conversion rate of the esterification reaction is 96%.It was found that the phase transfer catalyst had a synergistic catalytic effect.When 6%of the phase transfer catalyst was added,the catalytic reaction rate and conversion rate increased rapidly,the conversion rate corresponding to 30minutes of reaction increased by 30%,and the final conversion rate increased to 96%.?3?Based on the temperature-responsive Pickering emulsion system constructed with SiO₂-nonionic surfactant,the applicability of the emulsion in the phase transfer catalysis reaction was analyzed.The effects of nonionic surfactants and phase transfer catalysts on the stability of emulsions were investigated.The factors affecting the temperature response of Pickering emulsions were analyzed.The results show that the temperature-responsive Pickering phase transfer catalyst system is prepared with a water-to-oil phase volume ratio of 7:7,of which 7 mL of aqueous phase contains 1 wt.%SiO₂,3%TBAB,3 mM AEO-7 and sodium acetate?2.85M?.And 7 mL of the oil phase?diisopropyl ketone?contained p-nitrobenzyl bromide?0.15 M?.The oil-water two phase was emulsified at 11800 rpm for 2 min to prepare an O/W type Pickering emulsion.The adsorption of TBAB and AEO-7 on the surface of SiO₂ particles is the key to the formation of stable Pickering emulsion.Stirring and temperature are the key to temperature-responsive Pickering emulsion demulsification.When the temperature is greater than the cloud point,the two phases can be completely separated,and as the temperature is further increased,the emulsion viscosity decreases and the demulsification time becomes shorter.The emulsion corresponding to AEO-7 can be completely demulsified in 10 minutes at 90°C.?4?The temperature-responsive Pickering emulsion was applied to the phase transfer catalyzed esterification reaction,and the effects of the type and concentration of the modifier and the reaction substrate on the catalytic activity were compared.The results show that the temperature-responsive Pickering phase transfer catalytic reaction system exhibits high catalytic activity,and the conversion rate of different kinds of raw materials can reach more than 94%.The modifier TBAB of SiO₂ particles also plays a catalytic role in the reaction system,and the reaction rate increases rapidly as the concentration of TBAB increases.When the amount of nonionic surfactant is increased,the diameter of the emulsion was decreased,and the interface between the two phases is increased,thereby causing a slight increase in the reactivity.