Synthesis Of Magnetic Nanocatalysts And Their Applications In One-pot Tandem Aerobic Oxidation/Knoevenagel Condensation

First,amino group functionalized MNPs(Fe3O4@PEI)was prepared by coating polyethyleneimine on nano-Fe3O4.The structure of MNPs was characterized by TEM,XRD,TG and FT-IR.The MNPs(Fe3O4@PEI)was applied to Knoevenagel condensation reaction.Initially,the effects of solvent,catalyst dosage and molar ratio of substrate on the reaction were investigated using benzaldehyde and malonitrile as model substrates,from which the optimal reaction conditions were obtained which are reaction temperature 25℃,benzaldehyde 1 mmol,catalyst 50 mg,molar ratio of benzaldehyde to malonitrile 1:1.1,ethyl acetate(1.5 ml)as solvent.Under the optimal conditions,the catalyst can efficiently catalyze various aldehydes including aromatic,heterocyclic and aliphatic aldehydes reacting with malonitrile or ethyl cyanoacetate to the corresponding condensation products,both the conversion of substrate and selectivity of the target product were higher than 99%in most cases.This catalyst was also active in the condensation reaction of acetophenone and malonitrile.The recyclability of the catalyst(Fe3O4@PEI)was investigated by using the reaction of benzaldehyde with malonitrile as model reaction.After each run,the catalyst can be easily recovered by simple magnetic separation and subjected to next run.The recycle test results showed that the conversion and selectivity of the reaction remained higher than 99%after the sixth recycle.Second,a multifunctional magnetic catalyst(Fe3O4@SiO2@PEI@Ru(OH)x)was prepared by loading Ru species on to polyethyleneimine coated nano-Fe3O4 protected by SiO2.The structure of the catalyst was characterized by means of XRD、TG、FT-IR、ICP and XPS.This catalyst was applied to one-pot tandem aerobic oxidation/Knoevenagel condensation of alcohols.The effects of temperature,oxygen pressure,amount of catalyst and reaction time on the aerobic oxidation were investigated using benzyl alcohol as model substrate,from which the optimal reaction conditions for the reaction were obtained,which are benzyl alcohol I mmol,O2 0.2 MPa,catalyst loading 100 mg(2.2 mol%),reaction temperature 110℃.Under the optimal conditions,the catalyst was applied to the oxidation of different substrates to screen the substrate tolerance of the catalyst.It was found that the catalyst showed excellent catalytic performance for aromatic primary alcohols,moderate activity for aromatic secondary alcohols,but very low activity for aliphatic primary alcohols.Subsequently,the catalyst was applied to one-pot tandem aerobic oxidation/Knoevenagel condensation of alcohols.It was found that most of the alcohols could be converted into their corresponding condensation products with malonitrile.It was also found that the catalytic activity of the catalyst in the one-pot tandem aerobic oxidation/Knoevenagel condensation of alcohols was obviously decreased in the recycle run.ICP and XPS analysis revealed that the deactivation of the catalyst was due to the oxidation of active Ru3+to inert Ru4+during the oxidation process.