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Reaction Control Phase Transfer Catalysis: Keggin Type Polyoxometalate Catalyzed Acetal Reaction

Posted on:2016-05-31Degree:MasterType:Thesis
Country:ChinaCandidate:C H MaFull Text:PDF
GTID:2431330464961105Subject:Physical chemistry
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In recent years,polyoxometalates due to acidity and oxidation,attach great importantance in the field of catalysis.Heteropolyacid salts of Keggin type are the most stable and most easily prepared catalysts of POMs.As acid catalysts,redox catalysts and bifunctional catalysts,POMs have been widely reported.In comparison to other types of catalysts,the advantages of POMs lie in high catalytic activity,recyclable reuse,little corrosion of equipment,no pollution and so on.Acetal reaction occupies a very important position in modern organic,and that not only can protect the aldehyde group,but also can be used as special solvent.The acetals are also the new high-grade fine spices and food additives.As spices,acetal has many advantages,such as soft and elegant aroma,strong ability of proliferation,and stable chemical properties.The conventional synthetic method is based on the liquid protic acid(such as phosphoric acid,sulfuric acid,hydrochloric acid,etc.)as catalyst.The disadvantage is that the catalyst can not be reused,has bad product selectivity,produces byproducts that lead to post-processing part of the production process quite troublesome,severe corrosion of the equipment,and environmental pollution.In view of the above:In order to obtain the catalytic system of good reactivity and high catalyst recovery(a reaction-controlled phase transfer catalytic system),in paper we firstly design and synthesize a series of Keggin-type POMs,and then apply them to catalyze acetal reactions.1.Preparation and characterization of Keggin-type POMsIn the chapter,we utilize phosphotungstic acid and nitrogenous organic compounds,quaternary ammonium salts as raw materials by a simple acid-base reaction,or take advantage of differences of the material in solubility synthesized[PyH]3PW12O40,[PhNH3]3PW12O40,[TEAH]3PW12O40,[Hmim]3PW12O40,TMB3W12O40,TBA3PW12O40 and TEA3PW12O40 7 kinds of catalysts in aqueous solution.And we use sodium tungstate dihydrate and cobalt acetate tetrahydrate as raw materials to synthesize catalysts K6CoW12O40,TBA6CoW12O40,TEA6CoW12O40,TMB6CoW12O40,[Hmim]6CoW12O40 and[PyH]6CoW12O40.The synthesized samples are measured and characterized by IR,UV-visible spectroscopy,elemental analysis,TG-DTA and 1H NMR,and the results show that the counter ions of the Keggin structure heteropoly acid(salt)was substituted by big organic cation remains basic structure of the parent acid(salt).2.Catalytic performance of Keggin-type POMs on acetal reactionsWe utilize PW12 and CoW12 two series of samples as catalysts to study their catalytic activity of acetal reaction.The benzaldehyde and 1,2-propanediol are used as reactant,and cyclohexane as water-carrying agent,n-dodecane as internal standard,using the internal standard method and gas chromatography to investigate the catalytic activity of these catalysts.It is found that with[PyH]3PW12O40,[PhNH3]3PW12O40,[TEAH]3PW12O40 and[Hmim]3PW12O40 as catalysts,the system forms reactant-product controlled-phase transfer catalytic system,and[PyH]3PW12O40 has the best activity.We have a detailed discussion about the phenomenon.The remaining several other catalysts are heterogeneous catalysts and the activity is poor.With[PyH]3PW12O40 as a catalyst,benzaldehyde and 1,2-propanediol acetal reaction as probes to study reaction conditions,under optimal conditions,the yield of benzaldehyde 1,2-propanediol acetal was nearly 99%,and the selectivity was 100%.The reuse of the catalyst is also investigated,and after cycle 10 times,the yield and selectivity of the reaction was nearly unchanged.Meanwhile IR proved Keggin structure of the catalyst did not change before and after reaction.The samples of high catalytic activity:[PyH]3PW12O40 and[PhNH3]3PW12O40 have been applied to different acetal reactions.Hexanal?benzaldehyde and ethylene glycol?1,2-propanediol are used as reactants.The results show that the yield of each acetal reactions is very good,and no other by-products.Four synthetic acetal products:(1)benzaldehyde 1,2-propanediol acetal,(2)benzaldehyde glycol acetal,(3)hexanal 1,2-propanediol acetal and(4)hexanal glycol acetal have been determined structure by gas chromatography,IR and 1H NMR It is proved that the synthesized products are desired ones.
Keywords/Search Tags:polyoxometalates, Keggin structure, catalytic synthesis, acetal reaction, reaction controlled-phase transfer
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