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0 °C

To 520 cm3 of sulphuric acid, stirred and cooled to 0° C., 60 cm3 of fuming nitric acid are added in the course of 30 minutes. 100 g of 3,4-difluorobenzaldehyde are added in the course of 30 minutes at approximately 0° C. to the solution obtained. The temperature is allowed to rise to approximately 20° C. and the mixture is stirred for a further 3 hours at this temperature. After cooling to approximately 5° C., the reaction mixture is introduced in the course of 30 minutes with vigorous stirring into 1,200 g of crushed ice. The temperature is allowed to rise to approximately 20° C. and the mixture is extracted with twice 600 cm3 of toluene. The combined organic extracts are washed with 3 times 1,000 cm3 of water and concentrated under reduced pressure (20 kPa) to 50° C. 113 g of 3,4 -difluoro-6-nitrobenzaldehyde are obtained in the form of a brown oil, which is used in the subsequent syntheses without further treatment. A purified sample of 3,4-difluoro-6-nitrobenzaldehyde gives the following characteristics:

1. customobtained
2. customto rise to approximately 20° C.
3. temperatureAfter cooling to approximately 5° C.
4. additionthe reaction mixture is introduced in the course of 30 minutes
5. customto rise to approximately 20° C.
6. extractionthe mixture is extracted with twice 600 cm3 of toluene
7. washThe combined organic extracts are washed with 3 times 1,000 cm3 of water
8. concentrationconcentrated under reduced pressure (20 kPa) to 50° C