General procedure for the synthesis of 2-hydroxynicotinaldehyde from 2-chloro-3-pyridinecarboxaldehyde: 2-chloro-3-pyridinecarboxaldehyde (0.283 g, 2.00 mmol) was suspended in 3 M aqueous hydrochloric acid solution (2 mL). Four drops of 3% hydrogen peroxide solution were added and the mixture was placed in a sealed vial and microwaved at 100 °C for 2 hours. After the reaction was completed, it was cooled to room temperature and the product began to crystallize. The suspension was neutralized by addition of solid potassium carbonate. The precipitate was separated by filtration and recrystallized with a minimum volume of ethanol to give 2-hydroxynicotinaldehyde (0.190 g, 77% yield). The melting point was 224-225 °C (literature value: 224 °C).1H NMR (300 MHz, DMSO-d6) δ 12.37 (broad peak, 1H), 10.05 (d, J = 0.7 Hz, 1H), 7.95 (ddd, J = 7.1, 2.3 Hz, 1H), 7.80 (ddd, J = 6.3, 2.3 Hz, 1H), 6.36 ( ddd, J = 7.1, 6.3, 0.7 Hz, 1H). 13C NMR (75 MHz, DMSO-d6) δ 189.0, 162.0, 143.4, 142.6, 124.2, 105.3.
