GENERAL METHODS: Thiourea dioxide (20 mmol) was added in batches to a mixture of water (15 mL) and ethanol (5 mL) containing 4-fluoro-2-nitroaniline (5 mmol) and sodium hydroxide (20 mmol), and the temperature of the reaction was maintained at 70°C. The reaction was carried out by thin-layer chromatography (TLC). The progress of the reaction was monitored by thin layer chromatography (TLC) until the reaction was completed. Upon completion of the reaction, the mixture was cooled to room temperature and the pH was subsequently adjusted to 9-10 by addition of 10% sodium hydroxide solution. the precipitated solid was collected by filtration and washed with distilled water to afford the crude product of 5-fluoro-1H-benzo[D]imidazole. The crude product was purified by aqueous recrystallization to give a final white solid product. The physical properties and spectral data of compounds 2a-h are described below.
