Brønsted酸性离子液体催化Fries重排合成对羟基苯乙酮的研究

Synthesis of p-hydroxyacetophenone through Fries rearrangement catalyzed by Brønsted acidic ionic liquid

采用一步法合成了[PPh_(3)][TfOH]_(2)、[TNOA][TfOH]_(2)、[TNOA][TfOH]和[PPh_(3)][TfOH]共4种离子液体。通过红外探针法对离子液体的酸性类型与酸性强弱进行了表征;同时对离子液体催化Fries重排选择性合成对羟基苯乙酮的收率进行了条件优化。结果表明,当选择[PPh_(3)][TfOH]_(2)作催化剂兼溶剂时,在反应温度为60℃、n(乙酸苯酯)∶n(离子液体)为1∶2、反应时间为6 h的条件下,选择性生成对羟基苯乙酮最高收率达到75%;催化剂可循环利用5次不失活。通过1HNMR监测反应前后催化剂结构变化,推导了其可能的反应机理。

Four kinds of ionic liquids(ILs),including[PPh_(3)][TfOH]_(2),[TNOA][TfOH]_(2),[TNOA][TfOH]and[PPh_(3)][TfOH],are synthesized via one-step method.The type and intensity of acidity of the ILs are characterized through FT-IR probe method.The catalytic performance of these Brønsted ILs is evaluated in selective synthesis of p-hydroxyacetophenone through Fries rearrangement process.It is shown that the yield of p-hydroxyacetophenone reaches 75%,the highest when[PPh_(3)][TfOH]_(2)is used as catalyst and solvent,the reaction temperature is at 60℃,n(PA):n(IL)=1:2,and the reaction time is 6 h.[PPh_(3)][TfOH]_(2)will not lose its activity after it has been recycled for 5 times.The changes of catalyst structure before and after the reaction are monitored by means of 1H NMR and the possible reaction mechanism is deduced.