3-(Trifluoromethyl)-1H-pyrazol-4-ylmethanol (54.00 g, 0.325 mol) was used as a raw material and suspended in toluene (2 L). Manganese dioxide (113.00 g, 1.30 mol) and 4molecular sieve powder (54.00 g) were added to the suspension. The reaction mixture was stirred at reflux for 5.5 hours under nitrogen protection, assembled with a Dean-Stark splitter. Upon completion of the reaction, the reaction mixture was filtered while hot, the filter cake was collected and cooled to room temperature. The filter cake was washed with a 1:1 mixture of dichloromethane and methanol (3 x 500 mL). All the filtrates were combined and the solvent was removed by concentration under reduced pressure to afford the target product 3-(trifluoromethyl)pyrazole-4-carbaldehyde (54.00 g, 0.329 mol, 100% yield). The product was characterized by 1H NMR (400 MHz, DMSO-d6): δ 8.72 (s, 1H), 9.91 (s, 1H).
