4- Fluorobenzenediazonium tetrafluoroborate

First, pellets of the diazonium tetrafluoroborate are spread on a cylindrical nickel roll, internally heated with Dowtherm.202Iftheroll is heated 100 to 150°C above the decomposition temperature, the diazonium tetrafluoroborate is decomposed within 10 to 25 seconds. If the temperature is nearer to the decomposition point, decomposition requires around 30 minutes. The roll speed is adapted to the reaction time. The roll surface is regenerated by a doctor blade which scratches off the residues. In this way, 4-chloro-l,2-difluorobenzene was obtained in 36 % yield from 4-chloro-2-fluorobenzenediazonium tetrafluoroborate at 290-310 C within 10 to 25 seconds. 

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