The general procedure for the synthesis of thiazole-4-carboxylic acid from 4-methylthiazole was as follows: 4-methylthiazole (19.8 g, 0.2 mol), 200 mL of water, and potassium permanganate (173.8 g, 1.1 mol) were added to a 500 mL three-necked flask, which was heated to 55 °C with stirring and kept for 22 hours. After completion of the reaction, the reaction mixture was cooled and filtered. The filter cake (mainly composed of manganese dioxide) was washed with hot water at 50°C. The filtrate was adjusted to pH 3 with dilute hydrochloric acid, precipitated as a solid and filtered. The filter cake was washed with a small amount of water and dried to give 18.1 g of thiazole-4-carboxylic acid in 70.2% yield, melting point 196-198 °C.
