Green Toluene Nitration Reaction In Ionic Liquids

The practical purport of investigation nitration of aromatic compounds is to explore a methodology which could meet desirable environment and improve the para-selectivity. And clean nitration of aromatic compounds is an important trend for development of nitration.According to the mechanism of nitration reaction, a series of pyridinium cation-based ionic liquids were designed and synthesized as catalyst and solvent. The ionic liquids were characterized by ¹H NMR and IR. The acidity order of ionic liquids was determined with UV-visible spectroscopy and the acidity-catalytic relationship was discussed. Reaction conditions which effect on the technology of nitration of toluene in NO₂-air and 67% nitric acid catalyzed by ionic liquid were investigated, including reaction temperature, reaction time, and the amount of catalyst and nitrating agent and so on. The results indicated that SO₃H-functionalized ionic liquid show better catalytic activity. [SO₃H(CH₂)₄Py]HSO₄ which offer two protic acidic sites showed the best catalytic acidity. A yield of 77% and an ortho/para ratio of 1.27 for mono-nitrotoluene were gained with NO₂-air as nitric agent. A yield of 39.6% and an ortho/para ratio of 1.18 for mono-nitrotoluene were gained with 67% nitric acid as nitric agent. Ionic liquid could be conveniently separated with the products and reused for four times with good catalytic activity and para-selectivity. Both of the two methodologies are green process with regard to simplicity in operation and green aspects by avoiding toxic catalysts and solvents, and can be well developed in future.