General procedure for the synthesis of 4-fluoro-N-isopropylaniline from 4-fluoroaniline: 22.2 g (0.2 mol) of 4-fluoroaniline and 17.6 mL (0.24 mol) of acetone were added to a 500 mL three-necked, round-bottomed flask, dissolved in 120 mL (2 mol) of glacial acetic acid, mechanically stirred, and cooled in an ice bath to about 10°C. The mixture was then purified to about 10°C with mechanical stirring. 9.4 g (0.25 mol) of sodium borohydride was added in batches while keeping the temperature below 20°C. After addition, the reaction mixture was stirred at 20°C for 30 minutes to 1 hour. Subsequently, the mixture was poured into 500 mL of ice water. The aqueous solution was made alkaline by dropwise addition of 120 mL of 50% aqueous sodium hydroxide (keeping the temperature below 25°C). The product was extracted with hexane (2 x 100 mL) and the organic phases were combined, washed with saturated sodium chloride solution and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure to give a clarified liquid. The product was purified by distillation and the fraction with a boiling point of 40 °C/0.5 mmHg was collected to give 21.8 g of clarified colorless liquid product in 71% yield.
