1-Naphthalenamine, 5-nitro- → 1-Fluoro-5-nitronaphthalene

Sodium nitrite (660 mg, 9.57 mmol) was added portionwise to a suspension of 5-nitronaphthalen-1-amine (1.2 g, 6.38 mmol) in a 1:1 mixture of water/concentrated hydrochloric acid (10 mL) at −5° C. The mixture was stirred for 15 min at −5° C. and a 60% w/w hexafluoro phosphoric acid solution (6 mL) was added. The brown precipitate was filtered and washed with cold water and diethyl ether and then allowed to dry in vacuo. The resulting solid was suspended in toluene and heated to 110° C. for 2 h before the mixture was then allowed to cool to ambient temperature and the solvent removed in vacuo to afford the crude product. Purification by column chromatography over silica gel (100-200 mesh) using petroleum ether as eluent afforded 1-fluoro-5-nitro-naphthalene (450 mg, 37%) as a yellow solid.