3-Phenyl-4,5,6-trichloro-pyridazine derivs prepn - by reacting 3-phenyl-4,5-dihydro-6(1H)-pyridazones with chlorine in phosphorus oxychloride

摘要

3-Phenyl-4,5,6-trichloro-pyridazine derivs. of formula (I): (where R1 and R2 are H or halogen), e.g. 3-phenyl-4,5,6-trichloropyridazine or 3-(p-chlorophenyl)-4,5,6-trichloropyridazine, are prepd. by suspending 3-phenyl-4,5-dihydro-6(5H)-pyridazones of formula (II) in POCl3 and reacting with Cl2. (I) are useful as intermediates for herbicides. Single-stage process giving (I) in good yields and purity. Starting materials (II) are obtainable by cyclising 3-(opt. substd. benzoyl)-propionic acids with hydrazine. The conversion into (I) is effected by passing Cl2 gas through a suspension of (II) in POCl3. The initial reaction temp. is pref. held below 40 degrees C, being increased to up to 100 degrees C during the course of the reaction.