固体铌酸催化下甲苯的硝化

Regioselective Nitration of Toluene in the Presence of Solid Niobic Acid Catalysts

在不同焙烧温度下制备了一系列固体铌酸催化剂。测定了固体铌酸催化剂的比表面积、表面酸强度及表面酸量。研究了催化剂焙烧温度、硝化反应时间、硝化反应温度、有无醋酐存在、硝酸浓度、催化剂的重复使用等因素对甲苯硝化反应影响。实验结果表明,当反应温度为40℃,反应时间为60 min时,以CCl4为溶剂,以质量分数为95%的硝酸为硝化剂,在醋酐存在条件下,以经300℃焙烧3 h后的铌酸作为催化剂,甲苯硝化产物中异构体的邻对比达1.26,较硝硫混酸的1.67显著降低,产物得率达99.3%。且该催化剂循环使用5次,催化活性基本不变,是一种极具应用前景的绿色硝化反应催化剂。

A series of niobic acids at different calcination temperatures was prepared. BET, acid amount and distribution of acidity of niobic acid catalysts were investigated . The effects of all kinds of factors, just like calcination temperature of niobic acid catalysts, nitration reaction time, nitration reaction temperature, recovered catalyst, acetic anhydride and concentration of nitric acid were studied by gas chromatography （GC）. The nitration of toluene was carried out in the presence of acetic anhydride with CCl4 as solvent, 95% nitric acid as nitrating reagent, and niobic acid calcinated at 300 ℃ for 3 h as catalyst for 60 min at 40℃. A yield of 99.3% of mononitoluene with an ortho-para-isomer ratio of 1.26 was obtained, which is greatly below 1.67 with sulfonitric acid as catalyst. The catalyst could be re-utilized up to five times with little decrease in activity. It is a clean nitrated reaction catalyst in vast prospects of application.