[CH3:1][C:2]1[CH2:3][N:4]([NH:9]C(=O)C)[C:5](=[O:8])[NH:6][N:7]=1.Cl.Cl.NN1CC(C)=NNC1=O>CO>[NH2:9][N:4]1[CH2:3][C:2]([CH3:1])=[N:7][NH:6][C:5]1=[O:8]A suspension is prepared of 6-methyl-4-acetylamino-4,5-dihydro-1,2,4-triazin-3-(2H)-one in methanol. The suspension is heated to 45° C. and becomes a clear colourless solution. At between 45° C. and 50° C. gaseous HCl (a) or aqueous HCl (b) is added to this solution over a 2 to 3 hour period. After about 30% of the gaseous HCl (a) or 50% of the aqueous HCl (b) has been added the reaction mixture is seeded with 4-amino-6-methyl-3-oxo-2,3,4,5-tetrahydro-1,2,4-triazine hydrochloride. Thereafter 4-amino-6-methyl-3-oxo-2,3,4,5-tetrahydro-1,2,4-triazine precipitates out continuously as the hydrochloride salt. After about 2 hours stirring, the maximum conversion is reached. The reaction mixture is brought to pH 5 by the addition of 50% NaOH solution, thereby forming free 4-amino-6-methyl-3-oxo-2,3,4,5-tetrahydro-1,2,4-triazine.
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