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Synthesis of Hydroxybenzoic Acid Esters by Ultrasound-Assisted Novel Dual-Site Phase-Transfer Catalyst in Tri-Phase System
This proposal is to investigate the application of dual-site phase-transfer catalyst tosynthesize hydroxybenzoates via ultrasound-assisted phase transfer catalysis with the third orthird-liquid phase in a batch reactor or continuous-flow reactor. The formation of thethird-liquid or third phase and the catalytic activity of dual-site phase-transfer catalyst underultrasonic irradiation, reaction mechanism, and kinetics will be explored. The purpose of thisproposal is to setup the green process of ultrasound-assisted dual-site phase-transfer catalysis,which behaves high product yield and is an environmentally benign technology without usinghalide-containing solvents.Phase transfer catalysts have been employed to enhance the reaction of immisciblereactants under mild conditions with high conversion and high product selectivity. If amolecule of catalyst contains dual sites, it can be used to increase the reaction rate more andmore. Thus it is valuable to change the traditional manufacturing method into a phase-transfercatalyzed esterification processes with third phase which is highly concentrated in a separatephase and can be easily separated and recovered from the reaction mixture. The ultrasoundtechnology has been proved to greatly enhance the rate of chemical reaction and product yield.Hence, this proposal is willing to explore the activity of dual-site phase transfer catalysts intri-phase system under ultrasonic irradiation. It is expected to develop the related theory ofphase transfer catalysis and interfacial catalysis.The benzoates are widely used as flavoring agents, perfumery, lacquers and solvent forcellulose derivatives, and as an additive in liquid crystal materials. p-Hydroxybenzoates areused in perfumery, sunscreeing agent, etc. In the past, the manufacturing processes forsubstituted benzoates were to conduct esterification reaction with the corresponding alcoholsin the presence of sulfuric acid, and having the disadvantages of severe reaction conditions,slow reaction rates, and low yields due to reversible reactions and hydrolysis side recations.Moreover, the materials of reactors should be specially considered due to the use of sulfuricacid. Those drawbacks can be overcome by applying phase-transfer catalyzed esterificationprocesses.This proposal is the extended work of the last project and is willing to be completedwithin two years. The goal and items done are as follows. For the first year, the formation ofthe third-liquid or the third phase by the novel dual-site phase-transfer catalyst will beexplored. Effects on the third phase formation investigated will include the aqueous reactant,inorganic salt, dual-site PTC and reaction conditions, etc. the reactivity of dual-site PTC withthe organic reactant and the distribution of the catalytic intermediate between the tri-phases,the interfacial reaction mechanism and kinetics of the overall reaction under ultrasoundirradiation. The kinetic model is also developed to describe the interfacial reactions intri-phase system. For the second year, a continuous flow reactor system with ultrasoundirradiation will be set-up and employed to investigate the catalytic activity of dual-sitephase-transfer catalyst, reaction mechanism, catalyst distribution, and the effect of ultrasound,etc. The system model for the continuous flow reactor in tri-phases will be developed. Theresearch results can be used as the basis for reactor design in the future.
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