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The general procedure for the synthesis of 3-chloro-4-nitrobenzonitrile from 4-amino-3-chlorobenzonitrile is as follows: sodium borate tetrahydrate (32.5 g, 211.2 mmol) was suspended in 195 ml of acetic acid and heated until the temperature of the reaction mixture exceeded 50 °C. At this temperature, 2-chloro-4-cyanobenzenamine (5.93 g, 38.9 mmol) was added in batches over a period of 1 hour. After the addition was completed, the reaction mixture was placed in an oil bath at 62°C and continued to be heated with stirring for 2 hours. After completion of the reaction, it was cooled to room temperature and the reaction mixture was poured into 1 L of ice water. The aqueous layer was extracted with ether (3×), the organic layers were combined and washed with deionized water (2×) and dried with anhydrous magnesium sulfate. The desiccant was removed by filtration and the solvent was removed by evaporation under reduced pressure. The residue was separated by silica gel column chromatography using ether/petroleum ether (1:3) as eluent to give 5.27 g (74% yield) of the target product 3-chloro-4-nitrobenzonitrile.

[1] Patent: US2006/122189, 2006, A1. Location in patent: Page/Page column 22
[2] Chemical and Pharmaceutical Bulletin, 1992, vol. 40, # 9, p. 2399 - 2409
[3] Patent: US2003/69257, 2003, A1
[4] Patent: EP1247810, 2002, A1. Location in patent: Page 59