铌酸及其改性催化剂上甲苯的区域选择性硝化

研究了铌酸催化剂上甲苯硝化反应的区域选择性。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,经300℃焙烧3 h后的铌酸催化剂,对甲苯硝化表现出了强的区域选择性;催化剂用量为0.8 g,甲苯硝化产物邻对位摩尔比达1.20,较硝硫混酸的1.67显著降低,产物得率达99.7%。且该催化剂循环使用5次,催化活性变化很小。制备了4种改性铌酸催化剂,结果分析表明,改性铌酸催化剂对甲苯硝化均表现出了比铌酸催化剂强的区域选择性,分别以硫酸铈改性的固体铌酸、硫酸铈和磷酸改性的铌酸、硝酸改性的铌酸、硝酸和磷酸改性的铌酸为催化剂,甲苯硝化产物的邻对位摩尔比可分别达1.15,1.11,1.09,1.04。

Regioselective Nitration of Toluene in the Presence of Solid Niobic Acid and Its Modified Catalysts

Nitration of toluene at 40 ℃ for 60 min,using CCl4 as solvent and 95% nitric acid as nitrating reagent,in the presence of acetic anhydride,and over 0.8 g niobic acid catalyst calcinated at 300 ℃ for 3 h,gave high regioselective mononitoluene in 99.7% yield with ortho/para mole ratio 1.20,far below 1.67 by mixed nitric and sulfuric acid.The catalyst could be reused up to five times with little decrease in activity.It is a clean nitration catalyst with vast prospects.Four kinds of modified niobic acid catalysts were prepared,which exhibited higher regioselectivity in mononitration of toluene than the unmodified one.Nitration of toluene in the presence of niobic acid catalysts modified by cerium sulfate,cerium sulfate and phosphoric acid,nitric acid,and nitric acid and phosphoric acid gave mononitrotoluene with ortho/para mole ratio up to 1.15,1.11,1.09 and 1.04 respectively.