| As an efficient organic small molecule catalyst,4-dimethylaminopyridine(DMAP)can not only catalyze the homogeneous reaction,but also can be used for heterogeneous reactions.It has the advantages of less dosage,good solubility,mild reaction conditions and high catalytic efficiency.And it is especially used for acylation of compounds with large steric hindrance and low reaction activity.DMAP is widely used in the fields of fine chemicals and polyester materials.Because DMAP is not easy to separate from the product and it is difficult to reuse,which will cause many issues,such as high production cost,low product quality and environmental pollution.Therefore,load the DMAP on the appropriate carrier is a subject attracted much attention.This paper tried to find a safe and easy method for DMAP loading,this novel method was presented that DMAP is attached on carrier with the covalent binding through the N-alkylation of DMAP precursor and coupled silica.the optimization of load conditions and catalytic properties of immobilized DMAP were studied.Firstly,4-(methylamino)pyridine(MAP),the analogues of DMAP,were synthesized by a two-step method.As the intermediate of this reaction,N-(4-Pyridyl)pyridinium chloride hydrochloride was prepared with pyridine and sulfoxide chloride,and then,the intermediate react with N-methyl formamide to form MAP.The effect of material ratio,reaction temperature,reaction time and the dosage of extractant were investigated and analyzed through the orthogonal optimization experiment and single factor method.Finally the optimum synthetic procedure conditions were determined as follows:The ratio of N-methyl formamide and intermediate was 2.5:1,the reaction temperature was 160?,the reaction time is 4 h.The yield of MAP approached the highest which is 63%.Secondly,the immobilized catalyst was synthesized through the N-alkylation of MAP and coupled silica.firstly,the Mesoporous Silica Particles reacted with ?-Chloropropyl Triethoxysilane to synthetize the coupled silica based support(MSP-Cl),the coupling rate of MSP-Cl was 9.87%,it meant the active chlorine content on this surface was 0.968 mmol/g;secondly,the immobilized catalyst(MSP-DMAP)could be obtained by N-alkylation of MAPwith MSP-C1.And the immobilization conditions were optimized to obtain the optimal immobilized conditions:O-xylene was used as solvent,the mole quantities of MAP was 1.5 times of the active chlorine content on MSP-C1,and the mole quantities of K2CO3 and KI were 1.5 and 0.5 times of MAP,respectively,with the protection of N2,treaction temperature was 13 0?,stirring rate was 600rpm,reaction time was 12 h.And the immobilized capacity of MSP-DMAP could be reached 0.906 mmol/g,with the utilization rate of active chlorine on MSP-C1 reached 93.6%.Finally,the structure of the immobilized catalysts were characterized by TG-DTG,FT-IR and SEM.Thirdly,the performance of the immobilized catalyst(MSP-DMAP)was studied,and it could highly efficiently catalyze the acylation of hydroxyl compounds with large steric hindrance.And with the acetylation of menthol as an example,the influence of catalyst dosage,stirring rate and reaction temperature on heterogeneous catalytic reaction were explored,the optimal reaction conditions were obtained:The concentration of menthol and acetic anhydride is 0.4 mol/L and 0.8 mol/L,the quantities of MSP-DMAP is 60 g/L;reaction temperature is 50?,the stirring rate is 400 rpm and the reaction time is 8h,the conversion of menthol was 84.9%.It was found that the catalyst not only has the advantages of simple separation and recovery,but also has a stable catalytic activity,and it can be reused for 6 times without obvious attenuation in the acetylation reaction. |
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