1. Place a 3-necked, 2-L round-bottomed flask equipped with a mechanical stirrer, dosing funnel, and thermometer in an ice-water bath. Add concentrated sulfuric acid (150mL) to the flask.
2. 2-Amino-3-methylpyridine (50.0 g, 0.463 mol) was weighed in a 125 mL conical flask and preheated in a warm water bath until melted. The melted feedstock was slowly added to the reaction flask via a preheated Pasteur pipette while keeping the conical flask in a warm water bath to prevent the feedstock from solidifying. During the addition process, the reaction temperature rose to about 45°C and white smoke/mist was observed to be generated in the flask.
3. Concentrated sulfuric acid (100 mL) was added to the residual feedstock and the mixture was transferred to the reaction flask to form a milky white suspension.
4. premixed concentrated sulfuric acid (35 mL) and 70% nitric acid (35 mL) and cooled in an ice water bath and transferred to a charging funnel. After the internal temperature of the reaction mixture is cooled to 10-15°C (not less than 10°C), the premixed sulfuric acid/nitric acid solution is slowly added dropwise, and the rate of dropwise acceleration is controlled so that the reaction temperature is maintained at 20-25°C (dropwise time 5-10 minutes).
5. Upon completion of the dropwise addition, replace the ice water bath with a tap water bath and allow the reaction temperature to slowly rise to approximately 30°C and then cool to room temperature. This process requires monitoring of the reaction temperature to avoid overshooting.
6. After stirring the reaction mixture overnight, 70% nitric acid (35 mL) was slowly added dropwise through the addition funnel to the dark reddish-brown mixture, controlling the rate of the dropwise acceleration so that the temperature did not exceed 35 °C. The reaction flask was placed at room temperature. At this point, the reaction flask was placed in a water bath at room temperature.
7. Add water (500mL) to the reaction flask in batches. Approximately 150mL of water was first added slowly and dropwise to gradually increase the internal temperature to 50-60°C while increasing the stirring rate to prevent foaming. Brown gas escaped during the initial addition of water. After the gas escape stops and the temperature no longer rises, the remaining ~350mL of water is added quickly and the reaction solution changes from a dark grayish brown color to a clarified orange solution. A yellow precipitate may form when cooled to below 50°C. 8.
8. Remove the water bath, replace with a heating jacket, and replace the addition funnel with a condenser. Heat the reaction mixture (light orange or bright yellow solution) to 115-118°C and maintain for 1.75-2 hours. Additional gas escapes during heating at about 115°C.
9. Upon completion of the reaction, the reaction mixture is cooled to room temperature first in an ice-water bath and then further cooled to 0°C by direct addition of ice.
10. The solid formed was collected on a Brinell's funnel and washed sequentially with cold water and minimal amounts of cold ethanol and cold ether. Vacuum drying afforded 3-methyl-5-nitropyridin-2-ol (53.5 g, 75% yield) as a light yellow solid with a melting point of 228-229 °C. The product was dried over 1H NMR.
11. The structure of the product was confirmed by 1H NMR, 13C NMR, LRMS (ESI) and elemental analysis.
