Phosphorus pentachloride → 2-Ethoxyimino-2-(5-amino-1,2,4-thiadiazol-3-yl)acetyl chloride hydrochloride

To a solution of phosphorus pentachloride (54.6 g) in methylene chloride (500 ml) was added 2-ethoxyimino-2-(5-amino-1,2,4-thiadiazol-3-yl)-acetic acid (syn isomer) (54.0 g) under stirring and cooling at -20° C. The mixture was stirred for 30 minutes at -15° to -12° C. and for 2 hours at -5° C. To the mixture containing precipitates of an object compound was added diisopropyl ether (500 ml) at -5° C. and the mixture was stirred for 30 minutes at -5° to 10° C. The resulting precipitates were collected by filtration, washed with diisopropyl ether and dried to give 2-ethoxyimino-2-(5-amino-1,2,4-thiadiazol-3-yl)acetyl chloride hydrochloride (syn isomer) (60.17 g), mp. 125° to 127° C. (dec.).