4,5-Di:chloro-2-phenyl-3(2H)-pyridazinone prepn. - from herbicidally inactive pyrazinone isomer by diazotisation of corresp. 4-amino-5-chloro cpd. and treatment with thionyl chloride

摘要

The prepn. of 4,5-dichloro-2-phenyl-3(2H)-pyridatinone of formula (I) comprises (a) diazotisation of 4-amino-5-chloro-2-phenyl-3-2H)pyridazinone (II) and, after isolation of the intermediate of formula (III) by dilution with water and filtration, (b) treating (III) with thionye chloride to give (I) which is isolated by dilution with water and then filtration. (I) is used in the prepn. of the herbicide 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone, an isomer of (II). However, an isomer mixt. of the herbicide and (II), which has no herbicidal effect, is obtd. This invention allows the conversion of the inactive isomer to the active isomer.