微波辐射下咪唑类离子液体催化安息香缩合反应研究

Benzoin condensation reaction catalyzed by imidazolium ionic liquids under microwave irradiation

探讨了微波辐射下四种咪唑类离子液体催化不同取代基芳香醛的安息香缩合反应,并对反应条件进行了优化。结果表明,[Bmim]Im是合成目标产物的良好催化剂,在微波辐射时间5min、反应温度55℃、催化剂用量x([Bmim]Im)=1%、溶剂THF15m L、芳香醛用量5mmol、50%氢氧化钠水溶液0.5m L时,最高产率可达到81%。该方法耗时短、环境友好。在考查的底物中,除高位阻和具有较强p-π共轭效应的2-氯苯甲醛和4-甲氧基苯甲醛没有检测到产物外,其他不同取代芳香醛均得到了相应产物。反应后离子液体可以回收循环使用至少4次。

Four types of imidazolium ionic liquids were synthesized and used to catalyze benzoin condensation reaction of aldehydes under microwave irradiation. The optimized conditions were as follows： aldehyde 5mmol,microwave irradiation reaction time 5 minute and reaction temperature 55℃,THF15 m L,50% Na OH aqueous solution 0. 5m L,the highest yield could reach 81% in the presence of x（ [Bmim]Im） = 1%. A wide range of substrates were investigated under the optimized conditions and gained the products except 2-chlorobenzaldehyde and 4-methoxybenzaldehyde due to the stereo-hindrance effect and p-π conjugative effect,respectively. This method had advantages of short reaction time and being environmentally benign. Moreover,the catalyst could be reused at least four times.