Study On Self-condensation Of Aromatic Aldehydes Catalyzed By Ionic Liquid Salts And Transition Metal Composite Catalysts

In self-condensation of aromatic aldehydes,one molecule of aromatic aldehyde provides an acyl anion under the action of catalyst and the other molecule is used as a carbonyl electrophile,which producing a bifunctional productα-hydroxy ketone.Because of its bifunctional structure,α-hydroxy ketone is an important intermediate in organic synthesis.Imidazole ionic liquid salts were selected as catalysts to study the self-condensation reaction of aromatic aldehydes.The reaction was carried out in tetrahydrofuran under 60℃.In this reaction system,using benzaldehyde as a substrate,imidazole ionic liquid salt 1-butyl-3-methyl-tetrafluoroborate imidazole salt as a catalyst,Cs₂CO₃ as a co-catalyst,after stirring 8 h,the conversion of benzaldehyde was98.2%,and the yield of 2-hydroxy-1,2-diphenylethanone was up to 90.3%.The most critical step in the self-condensation of benzaldehyde was that one molecule of benzaldehyde underwent polarity reversion under the catalysis of an ionic liquid salt,and the carbonyl carbon of benzaldehyde changed from electrophilic to nucleophilic.Another molecule of benzaldehyde acted as electrical reagents.Through substrate extension experiments,it could be found that this kind of imidazole-type ionic liquid salt also catalyzed the self-condensation reaction of a series of aromatic aldehydes.A new composite catalyst Sm₂O₃@g-C₃N₄ was prepared by using g-C₃N₄ as a carrier and transition metal oxide Sm₂O₃ as a load through a method of wet impregnation and calcination.XRD,FT-IR,SEM,TEM and other analytical testing methods were used to characterize the structure and morphology of the prepared catalyst.Composite catalysts with different Sm₂O₃ loadings were applied to the condensation reaction of aromatic aldehydes,the results showed that the 10 wt%loaded composite performed to be the optimal catalyst,the conversion of benzaldehyde was72.5%,and the yield of 2-hydroxy-1,2-diphenylethyl ketone was 61.7%.Sm₂O₃@g-C₃N₄ also had catalytic activity in the condensation reaction of aromatic aldehydes.