凹凸棒土固载N-杂环卡宾催化安息香缩合反应

Attapulgite supported N-heterocyclic carbens for benzoin condensation reactions

将5种不同的N-杂环卡宾(NHCs)前体固载到凹凸棒土(ATP)表面,制备了5种固载NHCs催化剂。通过FTIR、元素分析、BET和TEM对其进行了表征。以苯甲醛的安息香缩合反应为模板,对反应条件进行了优化,并考察了底物的普适性。最后对催化剂的重复使用性进行了评价。结果表明,NHCs前体成功地固载到凹凸棒土表面,制备的固载NHCs催化剂能有效催化安息香缩合反应,其中,1-正丁基-3-(3-三甲氧基硅丙基)苯并咪唑氯化物(BTBCl)@ATP性能最优。当BTBCl@ATP中苯并咪唑盐用量为1%(以苯甲醛物质的量计,下同),Na OH用量40%,2m L甲醇,在氩气中110℃下反应4h,产物的收率可达90%。在优化条件下,BTBCl@ATP可催化多种芳香醛的安息香缩合反应,收率在61%~86%之间。BTBCl@ATP使用5次后,其催化活性没有明显下降。

Five N-heterocyclic carbens(NHCs)supported catalysts were prepared by grafting five different NHCs precursors onto the surface of attapulgite(ATP)and characterized by FTIR,elemental analysis,BET and TEM.Taking benzoin condensation reaction of benzaldehyde as template,the reaction conditions were optimized,and the universality of substrate was investigated.Finally,the reusability of the catalyst was evaluated.The results showed that the NHCs precursors were successfully supported on the surface of attapulgite,and the prepared NHCs catalysts could effectively catalyze benzoin condensation reaction,among which,1-n-butyl-3-(3-trimethoxysilpropyl)benzoimidazolium chloride(BTBCl)@ATP had the best performance.Under the conditions of the dosage of benzimidazole salt in BTBCl@ATP of 1%(based on the amount of substance of benzaldehyde,the same below),NaOH dosage of 40%,2 m L methanol as solvent,reaction temperature of 110℃and reaction time of 4 h in Ar atmosphere,the yield of product could reach 90%.Under the above-mentioned optimized conditions,BTBCl@ATP could catalyze the benzoin condensation reaction of various aromatic aldehydes with yields ranging from 61%to 86%.The catalytic activity of BTBCl@ATP had no obvious decrease after 5 times of use.