Dissolve 1.7g 3-methyl-5-bromopyrazole in 20ml 0.1M hydrochloric acid, put in 100mL three-necked flask, heated to 50; take about 1.5g potassium permanganate dissolved in 5mL water, use constant pressure funnel to add to the three-necked flask slowly; after the addition of material is completed, the reaction solution was stirred at 70 for 30min, and after that it was cooled down to room temperature, and pH of the solution was adjusted to acidic, 20mL EtOAc was added. EtOAc, extracted three times, the organic layer pH adjusted to alkaline, washed with water to obtain 5-bromo-1H-3-pyrazolecarboxylic acid, the yield was 85%.
