Sodium Chlorite → 1-(2-chlorophenyl)-3-(trifluoromethyl)-1H-pyrazole-5-carboxylic acid

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A 2 L flask was charged with 37.31 g of 1-(2-chlorophenyl)-5-furan-2-yl-3-trifluoromethyl-1H-pyrazole (119 mmol), 470 mL of acetonitrile, then a solution of NaH2PO4 (71.49 g in 174 mL of water) was added. The resulting solution was cooled to 0-30C in an ice bath and a NaClO2 solution (80%, 107.84 g in 391 mL of water) was added portionwise. The resulting solution was allowed to warm to room temperature where it remained for 42 h. The reaction was then concentrated in vacuo to remove acetonitrile. The residue was washed into a separatory funnel with 525 mL of 2.0 M NaOH and CH2Cl2. The CH2Cl2 was separated and was washed twice with 2.0 M NaOH. The NaOH washings were combined, acidified with concentrated HCl, and were extracted with CH2Cl2. The CH2Cl2 was then concentrated in vacuo and the crude acid was precipitated from CH2Cl2 with hexanes. 2-(2-chlorophenyl)-5-trifluoromethyl-2H-pyrazole-3-carboxylic acid was recovered as a tan solid, yield: 20.1 g (58%); 1H NMR (400 MHz, DMSO-d6): δ 14.1 (s, 1H), 7.86-7.90 (m, 2H), 7.80 (dt, J=1.5, 7.5 Hz, 1H), 7.76 (s, 1H), 7.73 (dt, J=1.5, 7.5 Hz, 1H); MS (ES): 291 [M+H]+.

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