Uses
5-Chloro-2,3-difluoropyridine is a 2,3,5-trihalopyridine used in the preparation of the herbicides and pesticides such as chodinafop-propargyl.
Synthesis
General procedure for the synthesis of 2,3-difluoro-5-chloropyridine from 2,3,5-trichloropyridine: First, 400 g of cyclobutanesulfone and 400 g of dimethylsulfoxide were added to a 1000 mL flask, and dehydrated to a moisture content of less than 0.05% at 200 °C under 0.05 MPa (negative pressure). Subsequently, 96 g (1.66 mol) of potassium fluoride, 120 g (0.67 mol) of 2,3,5-trichloropyridine, 2 g of 18-crown ether, and 3 g of potassium carbonate were added to the reaction flask at 120 °C and heated to 200 °C for about 3 hours. After completion of the reaction, the product was collected to give 95 g (0.51 mol) of 2,3-difluoro-5-chloropyridine in 90% yield. The purity of the product was 96.8% as determined by gas chromatography.
References
[1] Patent: CN106008329, 2016, A. Location in patent: Paragraph 0008; 0009
[2] Synthetic Communications, 2004, vol. 34, # 23, p. 4301 - 4311
[3] Patent: US33478, 1990, E1
[4] Patent: US4565568, 1986, A
[5] Patent: US4678509, 1987, A
