Regioselectivity Of Toluene In The Ionic Liquid Nitration Study

Green synthesis of nitro-aromatic compounds is an important trend in the development of nitration.A series of novel lower toxicity caprolactam-cation-based Bronsted acid ionic liquids [Caprolactam]X(X^-=PTSO^-,BSO,^- CF₃COO^-,BF₄^-,HSO₄^-,NO₃^-)and the admixtures of rare earth metal(Nd,Y,La,Yt)salt and ionic liquid were prepared and used as solvents and catalysts in the nitration of toluene and 1 equiv of 67%nitric acid.The structure and acidic scale of ionic liquids was characterized by ¹H NMR,FTIR and UV.The effects of reaction temperature,reaction time, catalysts and the amount of catalysts on product yield and para-selectivity for the nitration of toluene were investigated.Among of them,[Caprolactam]PTSO and the admixture of [Caprolactam]BSO(IL)and Yb(BSO)₃ displayed excellent activity.Nitrotoluene with the yield of 37.1%,ortho-para isomer ration 1.2 by using 20 mol%(to toluene)IL,and the yield of 46.5%,the ration of 1.1 by using 10 mol%(to toluene)admixture(molar ratio=1:1)were obtained under the optimal conditions(55℃,24h).The catalysts were recycled 4 times with a little decreasing yield and the same para-selectivity.Some reaction mechanism and related reaction conditions were discussed.