The above residue was dissolved in ethanol (300 mL). Concentrated sulfuric acid (98%, 30 mL, 522 mmol, 2.76 eq.) was added slowly and dropwise with stirring while controlling the reaction temperature to not exceed 25°C. The reaction mixture was heated and refluxed and stirred for 7 hours, followed by continued stirring at room temperature overnight. Upon completion of the reaction, ethanol was removed by distillation under reduced pressure. The resulting suspension was diluted with ice water (200 mL) and the pH was adjusted to 5-6 with concentrated ammonia, keeping the temperature below 5 °C during the process. The solid product was collected by filtration, washed with water (10 mL x 3) and dried under vacuum to give the first crude product (10 g). The filtrate was extracted with ethyl acetate (200 mL×2), the organic phases were combined, washed with saturated brine, dried with anhydrous sodium sulfate and filtered. The filtrate was concentrated under reduced pressure, combined with the first batch of crude product, and finally recrystallized in isopropyl ether to obtain ethyl 1H-imidazole-2-carboxylate (18 g, yield 64.3%).
