Synthesis
General procedure for the synthesis of 2-hydroxy-4-methyl-5-nitropyridine from 2-amino-4-methyl-5-nitropyridine: 2-amino-4-methyl-5-nitropyridine (10 g, 23 mmol) was weighed and placed in a 250 ml round-bottomed flask, and 70 ml of concentrated sulphuric acid was added to dissolve it until the raw material was completely dissolved. The reaction flask was placed in a cold bath at a low temperature of -5 °C, and a pre-configured aqueous solution of sodium nitrite (NaNO2, 6.76 g) was slowly added dropwise through a constant pressure dropping funnel. A large number of bubbles were generated during the addition, and the rate of titration needed to be controlled to avoid a rapid increase in temperature and to ensure that the reaction temperature did not exceed 0 °C. The reaction was carried out at a constant pressure. A solid was gradually precipitated during the reaction. After dropwise addition, stirring was continued for 10 minutes, and the reaction solution turned orange and clarified. The reaction was continued at 0 °C and the progress of the reaction was monitored by thin layer chromatography (TLC).The reaction was stopped after 3 hours when the TLC showed that the reaction was complete. The reaction solution was slowly poured into a beaker containing about 300 mL of water and a large amount of yellow solid precipitated. After leaving to crystallize for 3 h at room temperature, the solid was collected by filtration and dried under infrared lamp to give 6.72 g of yellow solid product in 67.2% yield.
References
[1] Patent: CN105906621, 2016, A. Location in patent: Paragraph 0045
[2] Patent: EP2366691, 2011, A1. Location in patent: Page/Page column 13
[3] Journal of the Chemical Society, 1954, p. 2448,2455
[4] Journal of Organic Chemistry, 1955, vol. 20, p. 1729,1731
[5] Patent: WO2007/53394, 2007, A1. Location in patent: Page/Page column 12
