Synthesis
Step 2. Preparation of 2-chloro-5-methyl-4-nitropyridine-1-oxide: To a mixture of 165 mL of concentrated nitric acid and 209 mL of concentrated sulfuric acid, 56.4 g of 2-chloro-5-methylpyridine-1-oxide was slowly added. The reaction mixture was stirred at 100 °C for 2 h, subsequently cooled to room temperature and poured into ice water. The pH was adjusted to 2-3 with sodium carbonate solution. the resulting yellow solid was collected by filtration and washed with ice water. The filtrates were combined and extracted with hot chloroform. The organic phases were combined, dried over anhydrous sodium sulfate and concentrated under reduced pressure to give 59.1 g of 2-chloro-5-methyl-4-nitropyridine-1-oxide in 80% yield. Mass spectral data: M + H = 189.
References
[1] Patent: WO2007/23105, 2007, A1. Location in patent: Page/Page column 43
[2] Patent: US2005/203091, 2005, A1. Location in patent: Page/Page column 35; 44
[3] Heterocycles, 2009, vol. 78, # 11, p. 2811 - 2826
[4] Patent: US2016/362407, 2016, A1. Location in patent: Paragraph 0532-0533
[5] Patent: CN103193704, 2016, B. Location in patent: Paragraph 0025; 0030-0034
