Hydrazine hydrate (1:1) → 4-Chloro-6-hydrazinylpyrimidine

11.8 ml (12.1 g, 241.6 mmol) hydrazine hydrate are added dropwise to a solution of 20.0 g (134.3 mmol) 4,6-dichloropyrimidine in ethanol at RT, while stirring. If clouding of the solution occurs during metering in of the hydrazine hydrate, further ethanol (approx. 400 ml) is added. The reaction solution is subsequently stirred at RT for 12 h. For working up, the solid which has precipitated out is filtered off, the residue on the filter is washed twice with 150 ml water each time and twice with 100 ml diethyl ether each time and the product is dried in vacuo. A further crystalline product fraction is obtained from the concentrated mother liquor.