1-Fluoro-3,5-dimethyl-benzene → 2,4-Dichloro-1-fluoro-3,5-dimethylbenzene

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Reaction Steps

An alternative process for preparing the intermediate 2,4-dichloro-3-cyano-5-fluorobenzoyl chloride (European Patent Application 276 700), which can be converted into 3-cyano-2,4,5-trifluoro-benzoyl fluoride, starts with 5-fluoro-1,3-xylene: 5-fluoro-1,3-xylene is dichlorinated at the ring in the presence of a catalyst under ionic conditions to give 2,4-dichloro-5-fluoro-1,3-dimethylbenzene which is subsequently chlorinated in the side chains under radical conditions to give 2,4-dichloro-5-fluoro-3-dichloromethyl-1-trichloromethylbenzene. This is hydrolysed via the 2,4-dichloro-5-fluoro-3-dichloromethylbenzoic acid to give 2,4-dichloro-5-fluoro-3-formylbenzoic acid, which is subsequently converted into 2,4-dichloro-5-fluoro-3-N-hydroxyiminomethyl-benzoic acid. Treatment with thionyl chloride gives 2,4-dichloro-3-cyano-5-fluoro-benzoyl chloride which can then be converted into 3-cyano-2,4,5-trifluoro-benzoyl fluoride by chlorine-fluorine exchange.

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