Nitration of Dibenzofurant

Abstract

Products distributions in nitration of dibenzofuran (DBF) have been examined in detail under 35 reaction conditions. Each condition has been evaluated from the view point of the yield of nitrodibenzofuran.3-Nitrodibenzofuran was selectively prepared under the following nitration conditions (nitrating reagents, molar ratio to DBF, reaction temp., time, and the yield by GLC): 99% HNO₃ in AcOH, 12, RT-95°C, 1h, 79%; 99% HNO₃ in CF₃COOH, 1.2, 0°C, 1h, 89%; and 65% HNO₃ in 65% H₂SO₄, 50-400°C, 4h, 69%. On the other hand, 2-nitrodibenzofuran was obtained as a major product (47% yield) in the reaction of DBF with 1-cyano-1-methylethyl nitrate/AlCl₈ (1.2 equiv.) in nitromethane at 25°C for 1h. The isomer distribution in the nitration products of DBF has been determined. under the controlled reaction conditions, low conversion and no formation of dinitrodibenzofurans. The distribution order 3>2>1>4 was observed in nitration with HNO₈, while, 2>3>1>4 with alkyl nitrate/Lewis acid or NO₂BF₄. Comparing with isomer distributions for other electrophilic reactions of DBF, the positional reactivity has been discussed by the nature of transition state of the nitration.