Hydrochloric Acid → 4-Azidobenzaldehyde

To a 500-mL round bottom flask with stirbar was added 4-amino-benzaldehyde (2.0 g, 0.0165 mol) and diluted hydrochloric acid (4 N, 150 mL). The mixture was cooled in ice-water bath to keep the temperature around 0° C. Sodium nitrite (2.28 g, 0.033 mol) solution in water (20 mL) was added to the above mixture at 0° C. and stirred for 0.5 h, and then sodium azide (2.15 g, 0.033 mol) solution in water (20 mL) was added to the above mixture dropwise to keep the temperature at 0° C. (a lot of foam were formed in this process). The reaction was warmed gradually to room temperature over 1 h, and then permitted to react at room temperature overnight. TLC showed that there was only one main product in the reaction mixture so the reaction was stopped. The crude product was extracted with EtOAc (50 mL×5) and the combined organic layers were dried with anhydrous MgSO4. After removing the solvent, a light yellow liquid was obtained as the pure final product (2.30 g, 95% yield). IR (neat): 3062, 2114, 1693, 1597, 1578, 1503, 1282, 1166, 1126, 852 cm−1. 1H NMR (400 MHz, CDCl3): δ 9.97 (s, 1H), 7.91 (dt, J=8.8, 2.0 Hz, 2H), 7.19 (dt, J=8.8, 2.0 Hz, 2H); 1H NMR (400 MHz, MeOD): δ 7.45 (dt, J=8.8, 2.0 Hz, 2H), 7.08 (dt, J=8.8, 2.0 Hz, 2H), 5.38 (s, 1H); 13C NMR (100 MHz, CDCl3): δ 190.7, 146.4, 133.2, 131.6, 119.5.