Preparation And Application Of CuL_x-NH₂-SBA-15 As Catalyst For Selective Oxidation Of Alcohols

Aldehyde/ketone has been widely used in medicine and pesticide fields due to its excellent biological activity.In general,alcohols have been selective oxidized directly under the action of catalyst is an effective strategy for constructing such molecules.However,in the reaction,it is often difficult to control the selectivity of the site during the reaction,and there is a potential problem of excessive oxidation.Therefore,it is important to find more efficient ways to catalytical oxidation alcohols to corresponding carbonyl compounds in a highly selective manner.Schiff base metal complexes are widely used in selective catalytic oxidation of alcohols,but they are easy to form dimers or have poor dispersion during the reaction process,which effects the catalyst activity,and makes it difficult to separate and recover the catalyst.Therefore,researchers have tried to prepare heterogeneous catalysts with highly active Schiff base metal complexes by loading to solve the above problems.In this paper,three types of CuL_x-NH₂-SBA-15 were synthesized by simple and efficient synthesis pathway from cheap and readily available raw materials,and then characterized accordingly and the structure of their catalysts was determined.The specific characterization methods are as follows:¹HNMR,IR,TGA,XRD,SEM,N₂adsorption and desorption,BET and ICP-OES.1.L_py1 and L_py2 Schiff bases were obtained by the condensation of 2,3-diaminopyridine with salicylaldehyde and o-vanillin,respectively.Then L_py1 and L_py2reacted with Cu（CH₃COO）₂,respectively,to obtain the Schiff alkali Cu complex CuL_py1 and CuL_py2.Finally,CuL_py1-NH₂-SBA-15 and CuL_py2-NH₂-SBA-15 multiphase catalysts were prepared by loading Schiff alkali Cu complex on SBA-15.The catalytic performance of its application in the catalytic oxidation reaction of benzyl alcohol was explored,and the effects of oxidant,reaction solvent,reaction temperature,reaction time and additives on the catalytic performance were investigated respectively.The optimal reaction conditions were obtained with 3 mmol%catalyst CuL_py-NH₂-SBA-15,2 mmol benzyl alcohol,2 m L CH₃CN,8 mol%TEMPO,1 m L[Bmim][BF₄]and 60℃for 4 h.The yields of formaldehyde were 88.94%and 89.40%,respectively.After repeated use for 3 times,the catalytic activity did not decrease significantly.In addition,the catalytic oxidation effect of other alcohols in the system was also investigated.The experimental results show that the system has catalytic activity for most alcohols,especially for aromatic alcohols.2.Schiff base ligands L_OPD1,L_OPD2 and L_OPD3 were prepared by the synthesis of 4-bromo-1,2-phenylenediamine with o-vanillin,5-methylsalicylaldehyde and salicylaldehyde,respectively.Schiff base ligands L_OPD4,L_OPD5 were prepared by the synthesis of 4-tert-butyl-1,2-o-phenylenediamine,5-methylsalicylaldehyde and salicylaldehyde.The Schiff alkali Cu complexes CuL_OPD1,CuL_OPD2,CuL_OPD3,CuL_OPD4and CuL_OPD5 were obtained by reacting the prepared ligands with Cu（CH₃COO）₂,respectively.Finally,the Schiff alkali Cu complex was loaded on SBA-15 to prepare CuL_OPD1-NH₂-SBA-15,CuL_OPD2-NH₂-SBA-15,CuL_OPD3-NH₂-SBA-15,CuL_OPD4-NH₂-SBA-15 and CuL_OPD5-NH₂-SBA-15 polyphase catalyst.The catalytic performance of benzyl alcohol was investigated.The optimal reaction conditions were obtained:3 mmol%catalyst,2 mmol benzyl alcohol,1 m L DMF,8 mol%TEMPO and1 m L[Bmim][BF4]at 60℃for 3 h.The yields of benzaldehyde in this catalytic system were 87.33%,90.52%,92.33%,93.02%and 93.77%,respectively.After repeated use for 3 times,the catalytic activity of benzaldehyde did not decrease significantly.In addition,the catalytic oxidation effect of other alcohols in the system was also investigated.The experimental results show that the system has catalytic activity for most alcohols,especially for aromatic alcohols.3.The ligands L_nap1,L_nap2 and L_nap3 were prepared by the synthesis of 1,8-diaminaphthalene with o-vanillin,5-methylsalicylaldehyde and salicylaldehyde,respectively.Then,the obtained ligands reacted with Cu（CH₃COO）₂ to obtain Schiff alkali Cu complexes CuL_nap1,CuL_nap2 and CuL_nap3.Finally,the Schiff alkali Cu complex was loaded onto SBA-15 to prepare CuL_nap1-NH₂-SBA-15,CuL_nap2-NH₂-SBA-15 and CuL_nap3-NH₂-SBA-15 multiphase catalysts.The catalytic performance of benzyl alcohol was investigated.The optimal reaction conditions were obtained:3mmol%catalyst,2 mmol benzyl alcohol,1 m L DMF,8 mol%TEMPO and 1 m L[Bmim][BF₄]at 50℃for 3 h.The yields of benzaldehyde were 94.15%,94.77%and95.24%,respectively.The modified catalyst had good stability,and its catalytic performance did not decrease significantly after repeated use for 3 times.In addition,the catalytic oxidation effects of other alcohols in the system were also investigated.The experimental results show that the system has catalytic activity for most alcohols,especially for aromatic alcohols.