Step a) 2-fluoro-4-methoxybenzaldehyde (15 g, 97.4 mmol) was added to a mixture of silver oxide (Ag2O, 13.5 g, 58.4 mmol), sodium hydroxide (NaOH, 19.5 g, 487 mmol), and water (200 mL) preheated to 55 °C. The reaction mixture was stirred at 55 °C for 1 h. Subsequently, it was filtered and the precipitated solid was washed with hot water (10 mL). The filtrate was slowly added to 5N hydrochloric acid (HCl) pre-cooled to 0°C under vigorous stirring. The precipitated solid was filtered, washed with water and dried to give 2-fluoro-4-methoxybenzoic acid as a white solid (13.6 g, 82% yield, melting point 194-196°C); mass spectrum (MS) showed m/e 169 (M-H)+.
