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A 500 ml reactor equipped with mechanical stirrer, thermometer and condenser was loaded with 280 ml of acetonitrile, 71 g of 2-amino-4,5,6,7-tetrahydro-benzothiazole-6-carboxylic acid ethyl ester [(III), R1=ethyl] and 38.75 g of acetic anhydride. 38.03 g of triethylamine were dropwise added to the resulting suspension in about 10 minutes. The suspension was refluxed, obtaining complete dissolution at a temperature ranging from 70 to 75° C. After approx. 2 hours 30 minutes the solution was concentrated to dryness, and the residue was crystallized from 450 ml of isopropanol to obtain 74.5 g of 2-acetylamino-4,5,6,7-tetrahydro-benzothiazole-6-carboxylic acid ethyl ester.

1. customA 500 ml reactor equipped with mechanical stirrer
2. temperatureThe suspension was refluxed
3. customobtaining complete
4. dissolutiondissolution at a temperature
5. customranging from 70 to 75° C
6. concentrationAfter approx. 2 hours 30 minutes the solution was concentrated to dryness
7. customthe residue was crystallized from 450 ml of isopropanol