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The reactivity of nitronium tetrafluoroborate in the nitration of deactivated di-and trifluoronitrobenzenes is enhanced in superacidic trifluoromethanesulfonic (triffic) acid compared with aprotic methylene chloride and sulfolane solutions. The enhanced reactivity is discussed in terms of better solubility and higher dissociation of the nitronium salts, as well as protosolvation of NO2 by superacids.The nitration of aromatic systems by nitronium salts in aprotic organic solvents has been extensively studied (1-8; for review see ref. a slurry of nitronium salt (1.38 mmol) in dry CH2CI2 (20 ml) was added the aromatic (1.2 mmol) diluted in CH2CI2 (5 ml) under a dry nitrogen atmosphere at room temperature. The heterogeneous mixture was sonicated for 30 min and an aliquot was withdrawn for GC analysis. The mixture was then refluxed for 2-3 hr. After cooling to room temperature, the reaction mixture was poured into ice/bicarbonate and extracted with CH2Cl2. The organic phase was separated and dried (MgSO4) prior to GC-MS analysis.Nitration in Sulfolane. In a typical experiment, the aromatic (6 mmol) was added to a stirred suspension of NO2BF4 (7.5 mmol) in sulfolane (5 ml) at room temperature under dry nitrogen. The reaction mixture was heated as required and then worked up and analyzed as described above.Nitration in TfOH. In a typical reaction NO'BF-(7.5 mmol) was charged into a dry reaction tube under nitrogen.TfOH (":3 ml) was added with cooling at' dry ice/acetone temperature. The temperature was allowed to rise during vigorous vortex mixing. At 35-40"C BF3 was evolved. Following BF3 evolution, the tube was cooled and the aromatic (6 mmol) was added. The solution was heated as required and worked up as above. RESULTS AND DISCUSSION Nitrations of 2,4-difluoronitrobenzene, 1; 2,3,4-trifluoronitrobenzene, 4; and 1,3,5-trifluorobenzene, 7, with NO2+BF4 in both CH2CI2 and sulfolane solutions were studied. Compound 1 was not nitrated at room temperature in CH2Cl2, but on refluxing for 2 hr a 30%6 yield of the dinitro product 2 was shown by GC-MS. In sulfolane, 1 was not 'nitrated after heating at 700C for 2 hr. Compound 4 was not nitrated after refluxing in CH2C02 or after heating in sulfolane at 700C for 2 hr. Compound 7 was mononitrated to 8 in 90%o yield on refluxing in CH2Cl2, but no further nitration occurred. In sulfolane the nitration of 7 to 8 was not observed. The low reactivity of deactivated aromatics with NO2BF4 in sulfolane solution was not unexpected (12). These results show that nitration of these aromatic systems in aprotic solvents is very limited.

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