Synthesis
The general procedure for the synthesis of 2,6-dichloropyridine-N-oxide from 2,6-dichloropyridine was as follows: 2.0 g of silica tungstate heteropolyacid catalyst was weighed, and 150 g of pulverized 2,6-dichloropyridine was added to 95 g of trifluoroacetic acid (TFA), which was stirred and heated up to 80°C to dissolve it slowly. Subsequently, 115 g of a 50% concentration hydrogen peroxide (H2O2) solution was slowly added dropwise for about 1 hour. After the dropwise addition, the reaction mixture was heated to reflux with continuous stirring and kept for 2 hours. Upon completion of the reaction, the catalyst was first filtered to remove the catalyst, then the reaction solution was cooled to room temperature and slowly poured into 300 mL of ice water and filtered to remove unreacted 2,6-dichloropyridine residue. The filtrate was dehydrated and extracted by adding an appropriate amount of trichloromethane (CHCl3) to dissolve the yellowish loose 2,6-dichloropyridine-N-oxide. The final product was analyzed by high performance liquid chromatography (HPLC) with 98.9% purity and 90.15% yield.
References
[1] Patent: CN103787964, 2016, B. Location in patent: Paragraph 0019-0020
[2] Patent: US2012/289497, 2012, A1. Location in patent: Page/Page column 51-52
[3] Patent: EP2524917, 2012, A1. Location in patent: Page/Page column 58
[4] Angewandte Chemie - International Edition, 2013, vol. 52, # 24, p. 6277 - 6282
[5] Angew. Chem., 2013, vol. 125, # 24, p. 6397 - 6402,6
