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0 °C

Sodium dithionite (30 g.) was added in portions to an agitated suspension of 4-amino-2-benzyl-5-phenylazo-pyrimid-6-one (14 g.) in a mixture of ethanol (200 ml.) and 2N aqueous sodium hydroxide solution (200 ml.) maintained at a temperature near to the reflux temperature. The mixture was then heated under reflux for 20 minutes, treated with a further quantity of sodium dithionite (20 g.) and the mixture heated under reflux for a further 30 minutes. The mixture was then evaporated to dryness, the residue was dissolved in water (200 ml.), acidified to pH 6 by means of concentrated hydrochloric acid, cooled to 0° C, and filtered. The solid thus obtained was recrystallised from water to give 4,5-diamino-2-benzyl-pyrimid-6-one (4.4 g.), m.p. 243°-246° C.

1. temperaturemaintained at a temperature near to the reflux temperature
2. temperatureThe mixture was then heated
3. temperatureunder reflux for 20 minutes
4. temperaturethe mixture heated
5. temperatureunder reflux for a further 30 minutes
6. customThe mixture was then evaporated to dryness
7. dissolutionthe residue was dissolved in water (200 ml.)
8. filtrationfiltered
9. customThe solid thus obtained
10. customwas recrystallised from water