The general procedure for the synthesis of 5-chloro-2-hydroxybenzonitrile from 5-chlorosalicylaldehyde is as follows:
1. 5-Chloro-2-hydroxybenzaldehyde (300 g, 1.92 mol) was suspended in water (4.5 L) with hydroxylamine-O-sulfonic acid (260 g, 2.30 mol) at room temperature.
2. The reaction mixture was stirred at 60 °C for 7 hours.
3. Upon completion of the reaction, water (3 L) was added to the mixture, which was subsequently chilled with ice.
4. The precipitated crystals were collected by filtration and washed with 1.5 L of water.
5. The resulting crystals were re-suspended in 1.5 L of water, filtered and washed with water. 6.
6. Finally, the crystals were tray dried at 50 °C for 22 h to give 272 g of 5-chloro-2-hydroxybenzonitrile (white crystals, yield: 93%).
The structure of the product was confirmed by 1H-NMR (CDCl3): δ 6.94 (1H, d, J = 8.8 Hz), 7.42 (1H, dd, J = 8.8,2.9 Hz), 7.47 (1H, d, J = 2.9 Hz).
