分子筛催化邻氟甲苯区域选择性硝化反应的研究

The study on the regioselective nitration of o-fluorotoluene catalyzed by zeolite

采用不同类型的分子筛催化剂对邻氟甲苯硝化的区域选择性进行了研究,以高选择性、高收率合成2-氟-5-硝基甲苯。在乙酸酐存在下,以发烟硝酸为硝化剂,探讨了不同类型分子筛催化剂对邻氟甲苯硝化反应的影响,结果表明具有较强酸性的Hβ型分子筛具有较高的转化率和区域选择性。当Hβ型催化剂的用量为邻氟甲苯的25%,n（醋酸酐）：n（发烟硝酸）：n（邻氟甲苯）摩尔比为1.20∶1.05∶1.0,反应温度0~5℃,邻氟甲苯的滴加时间2 h时,邻氟甲苯转化率大于99.5%,2-氟-5-硝基甲苯选择性85%,经简单分离2-氟-5-硝基甲苯化合物的收率75%。催化剂经过5次循环使用转化率和选择性没有明显降低,表明该催化剂具有较高的稳定性。与传统工艺相比,该方法具有较高的区域选择性、方法简单、环境友好。

2 - Fluorotoluene has been nitrated regioselectively for synthesizing 2 - fluoro - 5 - nitrotoluene under mild conditions using different zeolite catalysts. Under acetic anhydride, the effects of the different zeolite catalysts on 2 - fluorotoluene nitration were obtained with fume nitric acid as nitrating agent. The results showed that H - be- ta zeolite had higher conversion and selectivity in all isomers due to higher acidity. As the 25% amount of H - beta catalyst for 2 - Fluorotoluene, 1.20： 1.05 ： 1.0 molar ratio of acetic anhydride： fume nitric acid： 2 - fluorotoluene were used, 2 - fluorotoluene at - 5℃C and 2 h aditione time showed 99.5 % convertion with 85 % selectivity for 2 - fluoro- 5 -nitrotolueneo By simple seperation, higher pure 2 -fluoro -5 -nitrotoluene was obtained in the yield of 75 %. A recycling study of catalyst H - beta for nitration of 2 - fluorotoluene showed no significant loss in conversion as well as selectivity even after 5 recycles indicating the high stability of the catalyst. Compared to the conventional process, 2 - fluorotoluene nitration over H - beta acid catalysts is a highly regioselective, environmentally friendly process with a simpler work up procedure.