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The general procedure for the synthesis of 2,3-difluoro-5-nitrobenzonitrile from 2,3-difluorobenzonitrile was as follows: 2,3-difluorobenzonitrile (20.8 g, 149.82 mmol) was dissolved in sulfuric acid (100 mL) at 0 °C, followed by the addition of potassium nitrate (30.3 g, 299.59 mmol) in batches, and the addition process was controlled to be completed within 1 hour. The reaction mixture was continued to be stirred at 0°C for 2 hours. Upon completion of the reaction, the mixture was quenched by slowly pouring it into ice water (500 mL). The aqueous phase was extracted with ethyl acetate (300 mL x 3) and the organic phases were combined, washed with saturated brine and dried over anhydrous sodium sulfate. The organic solvent was removed by concentration under reduced pressure and the residue was purified by fast column chromatography with ethyl acetate/hexane (0 to 10% gradient) as eluent to give 2,3-difluoro-5-nitrobenzonitrile (3.6 g, 13% yield) as a brown solid.

[1] Patent: US2016/376283, 2016, A1. Location in patent: Paragraph 0271; 0272
[2] Patent: WO2010/114971, 2010, A1. Location in patent: Page/Page column 236-237