| During the past decades, substitution of traditional homogeneous catalysts with heterogeneous ones for the production of fine chemicals has been one of the hot research areas in chemical industry. Compared with conventional chemical processes involved with homogeneous catalysts, heterogeneous patterns have several distinguish advantages, such as easy to separate the products from the reaction mixture, generally able to reuse the catalysts, greatly diminishing the waste outputs and thus remarkly decreasing the environmental impact, and so on.Aziridines are a class of important intermediates in organic synthesis. Due to their nitrogen-containing three-membered ring with high tension, these compounds facilitate to carry out the ring-opening and cycloaddition addition reactions. Among them, the acid-promoted(3+2) cycloaddition reaction of aziridines and isothiocyanates is more important, since the formed products, 2-iminesthiazolidines, have a wide applications. In this thesis, the cycloaddition reaction of aziridines and isothiocyanates by heterogeneous catalysis have been disscused. The contents are as follows:Part I: the(3+2) cycloaddition reaction of aziridines with isothiocyanates by the catalysis of metal-exchanged heteropolyacid salts have been studied. At first, a series of polyoxometalate salts(MPWs), including BiPW, Zn3(PW)2, Sn3(PW)2, FeHPW, Cu3(PW)2, InPW, ScPW, Cs2.5H0.5PW, AgH2 PW, were prepared by reaction of phosphotungstic acid(HPW) with a suitable amount of corresponding metal salts by wet ion-exchange method. Then the catalytic activity of these MPWs on the(3+2) cycloaddition reaction of aziridines and isothiocyanates was investigated. The experiment results revealed that the catalytic activities of MPWs were greatly effected by both the type of substituent group on the N-position of aziridines and the metal species of MPWs. ScPW showed the best catalytic ability on the reaction of N-alkyl substituted aziridines and 2-phenyl isothiocyanates, while FeHPW showed the best catalytic ability on the reaction of N-tosyl substituted aziridines and 2-phenyl isothiocyanates. Finally, two different kinds of N-substituted 2-iminesthiazolidines, N-alkyl and N-tosyl substituted 2-iminesthiazolidines, were respectively prepared under heterogeneous catalysis conditions by using ScPW and FeHPW as heterogeneous catalysis.Part II, the(3+2) cycloaddition reaction of aziridines with isothiocyanates by the catalysis of Sc(OTf)3 supported mesoporous SBA-15 silica(SBA-15/Sc(OTf)2) was studied. At first, SBA-15/Sc(OTf)2 was prepared via two exchange steps by using propylsulfonic-functionalized SBA-15 silica(SBA-15-PrSO3H) as support precursor. SBA-15-PrSO3 H was first carried out with sodium cation exchange with wet NaCl to form SBA-15-PrSO3 Na, which was followed by trifluoromethanesulfonic anion exchange with Sc(OTf)3 to form the SBA-15/Sc(OTf)2 catalyst. Then, with the reaction of 1-isopropyl-2-phenyl aziridine with 2-phenyl isothiocyanate as the model reaction, the catalytic activity of SBA-15/Sc(OTf)2 on this(3+2) cycloaddition reaction was studied. The experimental results revealed that in the presence of 5 mol% of SBA-15/Sc(OTf)2 and with DMF as solvent, the addition reaction of 1-isopropyl-2-phenyl aziridine and 2-phenyl isothiocyanates could be completed after reacted at 80 oC for 3h. The regioselectivity of the addition product reached at 96%. Furthermore, the catalyst SBA-15/Sc(OTf)2 can be reysed for 5 times without obvious loss of activity after simple treatment. Finally, with SBA-15/Sc(OTf)2 as heterogeneous acid catalyst, several N-alkyl substituted 2-iminesthiazolidines were prepared under heterogeneous catalysis conditions in good to excellent yield.In conclusion, two methods for the(3+2) cycloaddition reaction of aziridines and isothiocyanates to afford 2-iminesthiazolidine under heterogeneous conditions was provided. The catalysts showed good catalytic activity on this reaction. Noteworthy, SBA-15/Sc(OTf)2 can be reused for more than 5 times after simple treatment. |
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