1H-Indazol-3-ol

118-92-3

7364-25-2

1) First, 250 g of o-aminobenzoic acid and 1665 g of water were added to a 15 L four-necked flask, mechanical stirring was initiated, and 361.25 mL of concentrated hydrochloric acid was added slowly. After the system was clarified, it was placed in an ice bath to lower the temperature to 2 °C. Maintaining the reaction temperature in the range of 0~5°C, NaNO2 solution prepared from 125.75g NaNO2 and 273.25g water was added drop by drop, and held for 30 min after addition. the reaction solution showed reddish brown color, and the temperature was lowered to -8°C. The temperature was reduced to -5°C. Subsequently, 627.25 g of solid Na2SO3 was added in batches, and the addition time was controlled to be completed within 16 min. At this time a large amount of foam was generated in the reaction system. The temperature was raised to 5 °C and stirring was continued for 4 hours. The reaction was continued by adding 555 mL of concentrated hydrochloric acid drop by drop, and the solution turned reddish brown again, controlling the temperature to no more than 15°C during the process. After 30 minutes of stirring, the system turned yellow and a solid precipitated. Slowly heat to 80°C and keep the total reaction time is 38 hours. 2) At the end of the reaction, stop heating and let the system cool naturally to room temperature. Add 1665mL of water and place in an ice bath. The temperature was controlled in the range of 0-14 °C. 750 mL of NaOH solution with a mass fraction of 30% was added to adjust the pH of the system to 5.5. The pH was re-determined after 15 min, and the stirring in the ice bath was continued for 1 h. Subsequently, the system was filtered and dried. The filter cake was washed with plenty of water until it was free of salt, and 216.43 g of light yellow powder BZ-01 was finally obtained with a purity of 96.54% and a yield of 88.52%.