Study On The Preparations Of Supported Heterogeneous Lewis Acid Catalysts And Lications In Organic Reactions

Lewis acids which are commonly used catalysts in the organic reactions show excellent catalytic activity in Friedel-Crafts alkylations and acylations, esterification, Knoevenagel condensations, Michael additions, Diels-Alder reaction, etc. As efficient homogeneous catalysts, they still have several inadequacies such as being corrosive, high toxicity, side reactions, use of large amount, leading to a large quantity of waste liquid after workup. Supported Lewis acid is a class of clean, environmentally friendly heterogeneous catalysts, supported Lewis acids as active as its homogeneous counterparts have several distinguishing characteristics:easy workup, recyclability, reusability, nontoxicity and good stability, etc.Polystyrene supported TiCl4(Ps-TiCl4) and polystyrene supported FeCl3(Ps-FeCl3) were prepared by coordinating Lewis acids with polystyrene. The catalysts were characterized by TGA, BET, SEM, IR, pyridine-adsorbed IR and titration analysis. Titration experiments determined the loadings of Ps-TiCl4and Ps-FeCl3were0.35and0.3mmol g-1respectively. Both catalysts had good catalytic activity for the tetrahydropyranylation of various alcohols and phenols, at the same time, detetrahydropyranylation of tetrahydropyranyl ethers preceded smoothly in the presence of the two catalysts in methnol. Mild reaction conditions, easy workup, less by-products, high yields are the advantages of the catalytic reactions. Two catalysts can be recovered and reused for five times with good activity.Polystyrene supported AICl3(Ps-AlCl3) was prepared by coordinating aluminum chloride with polystyrene. The catalyst was characterized by TGA, BET, IR, pyridine-adsorbed IR and titration analysis, the loading of Ps-AlCl3was0.45mmol g-1. Knoevenagel condensations of1,3-dicarbonyl compounds with aldehydes could be catalyzed by PS-AICl3under solvent-free conditions. This catalytic method was simple and efficient; the condensations were carried out smoothly with high yields (87-98%) at60℃for2-4h in the presence of the Ps-AlCl3catalyst. Ps-AlCl3could be applicable to the condensations of a series of aromatic aldehydes, and had good recyclability and could be reused five times without apparent loss of activity. Aza-Michael additions of various amines with conjugated alkenes bearing electron withdrawing group could be catalyzed by polystyrene-supported aluminum chloride (PS-AICl3) without the use of any solvents. The aliphatic adducts could be synthesized through additions of various aliphatic amines and conjugated alkenes for0.8-2h using6mol%Ps-AlCl3under room temperature with high yields (91-94%), however, the additions of aromatic amines proceded well only when using15mol%Ps-AlCl3for2.1-3h, under70℃. Using the different reactivities of two types of amines, chemoselective additions were achieved under room temperature, a mixture (1:1) of aromatic amines and aliphatic amines was treated with conjugated alkenes, aliphatic adducts were obtained exclusively; Regioselective additions of two different amino groups in one molecule also proceeded smoothly, the aliphatic adducts were the only products under room temperature. Ps-AlCl3had good recyclability and could be reused several times without apparent loss of activity.Three novel heterogeneous catalysts (AlCl3/chitin, AlCl3/chitosan, AICl3/acetylated chitin) were prepared. The catalysts were characterized by IR, ICP, BET, SEM and27Al solid state NMR. The loading of AlCl3/chitin which was higher than that of silica supported AICl3was2.54mmol/g. The catalysts demonstrated good catalytic activity in Friedel-Crafts alkylation of anisole with benzyl chloride and acylation of benzene with benzoyl chloride. The order of the three catalysts’activity was AlCl3/chitosan>AlCl3/chitin>AlCl3/acetylated chitin. According to the27Al solid state NMR spectra and the order of the three catalysts’activity, we concluded the peak at0ppm in the27Al solid state NMR spectra was attributed to physical adsorbed aluminum chloride not to six-coordinate Al species, and supported the viewpoint of Dube which said peak at85ppm was assigned to an aluminum chloride grafted on two silanol groups. The catalysts still remained active after reuse of four times.