Patent ID: 6538135
Filing Date: 2003-03-25
Classification: C07D

Abstract:
A process for preparing 4-amino-5-chloro-1-phenyl-pyridazin-6-one comprisinga) reacting 4,5-dichloro-1-phenylpyridazin-6-one with aqueous ammonia in the presence of a catalyst which is soluble in the aqueous alkaline reaction medium but becomes essentially insoluble in the reaction medium when this is being acidified, b) removing the precipitated 4-amino-5-chloro-1-phenyl-pyridazin-6-one, c) acidifying the reaction medium, and d) isolating the precipitated catalyst, wherein the catalyst used is a carbocyclic phenolic compound or a salt thereof, whose aromatic ring system is substituted not only by the phenolic hydroxy group or groups but also by at least one further electron-withdrawing substituent without acidic hydrogen atoms, selected from SO2R1, NO2, COR1, CF3 or CN, where R1 is C1-C6-alkyl or phenyl which may be substituted by 1 or 2 hydroxy groups.