The general procedure for the synthesis of 4-iodo-1,3-dimethyl-1H-pyrazole from 1,3-dimethyl-1H-pyrazole was as follows: 1,3-dimethyl-1H-pyrazole (50 g, 520 mmol) was dissolved in 500 mL of water, followed by the sequential addition of iodine (66 g, 260 mmol) and 30% aqueous hydrogen peroxide solution (35.4 g, 312 mmol). The reaction mixture was stirred continuously at 20 °C for 20 hours. Upon completion of the reaction, 100 mL of saturated aqueous sodium sulfite solution was added to quench the reaction. The reaction mixture was extracted with ethyl acetate (2 x 300 mL) and the organic phases were combined. The organic phase was washed with 400 mL of saturated sodium chloride aqueous solution, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give the yellow oily product 4-iodo-1,3-dimethyl-1H-pyrazole. Yield: 100 g, 450 mmol, 87% yield.1H NMR (400 MHz, CDCl3) δ 7.32 (s, 1H), 3.85 (s, 3H), 2.24 (s, 3H).
