1100 g of ammonium chloride and 2 L of 40% formaldehyde are placed in a reflux apparatus, after which slow heating is started. At 90°C, exothermic reaction kicks in and the mixture needs to be cooled down in an ice bath in order to keep the temperature below 104-106°C. The solution is refluxed at 104-106°C for 4h and then the water is boiled off until a white precipitate starts to form. The mixture is cooled down and the residue is discarded. The solution is then distilled at vacuum until the internal temperature rises over 160°C. The residue is then let to crystallize, combined with 500 mL of chloroform and filtered.
The exothermic reaction
The solution after reflux and filtration
Boiling the water off
The crude product crystallizing
Washing the crude product with chloroform
The pure product