磷钨酸催化下甲苯的区域选择性硝化

Regioselective Nitration of Toluene with Nitric Acid in the Presence of Phosphotungstic Acid Catalysts

为解决硝硫混酸对硝化甲苯过程中因甲苯的非选择性硝化产生的o-MNT和大量废酸对环境的危害,研究了磷钨酸对甲苯硝化反应的催化活性。通过气相色谱研究了催化剂用量、硝化反应时间、硝化反应温度及催化剂的重复使用等因素对甲苯硝酸硝化区域选择性的影响。结果表明,在醋酐存在的条件下,以CCl4为溶剂,以质量分数95%的硝酸为硝化剂,反应温度控制在50℃,反应进行90 min,0.8 g经300℃焙烧1.5 h后的磷钨酸催化剂,对甲苯表现出了强的区域选择性,甲苯硝化产物邻对位摩尔比达1.11,较硝硫混酸的1.67显著降低,产物得率达99.9%。该催化剂可循环使用5次,催化活性变化很小。

In order to solve the problem of producing large amounts of wastes and undesired o- nitrotoluene in synthesis of p-nitrotoluene with the mixed concentrated mineral acids, the catalytic activity of phosphotungstic acid for selective nitration of toluene was studied and the optimum conditions for preparing the catalyst were investigated. The results show that, when the nitration temperature is controlled at 50℃ ,and the reaction time is 90 min, nitration of toluene by using 95% nitric acid as nitrating agent in the presence of acetic anhydride and phosphotungstic acid catalyst calcinated at 300℃ for 1.5 h shows high regioselectivity, up to ortho-para isomer mol ratio of 1.11 in the product distribution,greatly below 1.67 when mixed acids are used, and give a yield of 99.9%. The catalyst can be reused up to five times with little decrease in activity.