Nitration of simple aromatics with NO2 under air atmosphere in the presence of novel Bronsted acidic ionic liquids

Aromatics nitrate with NO2/air catalyzed by novel Brnsted acidic ionic liquids (ILs) without any volatile chlorinated organic solvent under mild conditions. The ILs employed were caprolactam based, [Caprolactam]X (X-=pTSO(-), BSO-, BF4-, NO3-), which are of relatively lower cost and lower toxicity than traditional imidazolium-based ILs. The nitration reactions were carried out at -15 to -0 degrees C first, then at room temperature for a longer time with a little excessive NO2 (ca. 1.4 eqv.) for moderate yield (for toluene). The IL could be reused four times.