| 摘要 |
PROBLEM TO BE SOLVED: To profitably purify a pyridazin-3-one derivative having a herbicidal activity in a high purity and in a low color degree by removing impurities by the use of sulfuric acid. SOLUTION: This method for purifying a pyridazin-3-one derivative of the. formula (R1, R2 are each H or a 1-3C alkyl; X is H or halogen; Y is a halogen, nitro, cyano or the like) comprises removing impurities from a reaction mixture consisting mainly of the compound of the formula by the use of sulfuric acid. The sulfuric acid is preferably used as an extraction solvent for the impurities and as a recrystallization solvent, and a mixture solvent of sulfuric acid-water- alcohol is also preferably used as the recrystallization solvent. The sulfuric acid includes concentrated sulfuric acid and aqueous sulfuric acid solutions containing the sulfuric acid in concentrations of 1-98 wt.%, and is used in an amount of >=1 mole times that of the derivative of the formula. The purification is preferably carried out at a temperature within a range of about -20 to 100 deg.C.
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