4.0 g of aminourea hydrochloride, 9.67 mL of 2-chloro-1,1,1-trimethoxyethane and 40 mL of methanol were mixed in a reaction vial and the reaction was stirred at room temperature for 3 days. Subsequently, 3.5 mL of 2-chloro-1,1,1-trimethoxyethane was added to the reaction system to ensure complete reaction. Upon completion of the reaction, the reaction mixture was concentrated under reduced pressure to remove the solvent. The concentrated crude product was extracted by partitioning between ethyl acetate and 1N hydrochloric acid solution. The organic phase was separated and washed twice with 1N hydrochloric acid solution. All aqueous phase extracts were combined and then extracted five times with ethyl acetate. All organic phases were combined, dried over anhydrous sodium sulfate, filtered to remove the desiccant and the filtrate was concentrated under reduced pressure. The resulting solid was ground with ethyl acetate to give 5-chloromethyl-2,4-dihydro[1,2,4]triazol-3-one, and the product could be used in subsequent reactions without further purification. Yield: 2.97 g (62% yield). The product was characterized by 1H NMR (500 MHz, DMSO-d6): δ 4.49 (2H, s), 11.55 (1H, br.s), 11.70 (1H, br.s).
