The Regioselectivity For Mononitrochlorobenzene Preparation Over Imidazolium Ionic Liquids

Three imidazolium ionic liquids, [Hmim]HSO4, [Hmim]NO3, [Hmim]CF3COO were prepared and used as solvents and catalysts for the formation of mononitrochlorobenzene based on the structure of chlorobenzene. The ionic liquids were characterized by 1HNMR and IR. And the acidity order of ionic liquids was determined with UV-visible spectroscopy and the catalytic activity related on the ionic liquids acidity was discussed. The results for chlorobenzene nitration indicated that [Hmim]HSO4 of two Br?nsted acid sites showed better catalytic activity. It found that the conversion of chlorobenzene and the yield of mononitrochlorobenzene can be up to 57.7% and 54.7%,respectively, in a ratio of para- and ortho-nitrochlorobenzenes of 3.26 when using 20% molar amount of ionic liquid as substrate and employing 2 : 1 of molar ratio of nitric acid to chlorobenzene at 60℃for 5 h. And a 94.8% of high nitration selectivity was achieved under the mild reaction conditions. Compared to traditional method with sulfuric-nitric acids, the regioselectivity of mononitrochlorobenzene was effectively improved by the use of ionic liquid-nitric acid system. Ionic liquid could be easily worked out by a biphasic medium separation and reused with good catalytic activity and regioselectivity.