Water → 5-Bromo-3-(trifluoromethyl)-4-isothiazolecarboxylic acid

Into a 100-mL round-bottom flask, was placed 5-bromo-3-(trifluoromethyl)-1,2-thiazole-4-carbonitrile (4.2 g, 16.34 mmol, 1.00 equiv), con. H2SO4 (10 mL). This was followed by the addition of a solution of NaNO2 (1.69 g, 24.49 mmol, 1.50 equiv) in water (5 mL) dropwise with stirring at 0° C. To this was added water (25 mL) dropwise with stirring at 0° C. The resulting solution was stirred for 2 days at 20° C. The resulting solution was allowed to react, with stirring, for an additional 5 h while the temperature was maintained at 50° C. in an oil bath. The reaction progress was monitored by LCMS. The resulting solution was extracted with 3×50 mL of ethyl acetate and the organic layers combined and dried over anhydrous sodium sulfate. The solids were filtered out. The resulting mixture was concentrated under vacuum. This resulted in 4.5 g of 5-bromo-3-(trifluoromethyl)-1,2-thiazole-4-carboxylic acid as yellow crude oil. Mass spectrum (ESI, m/z): Calcd. for C5HBrF3NO2S, 273.9 (M−H). found 273.9.