General procedure for the synthesis of 2-chloro-5-aminobenzothiazole from 2-chloro-5-nitrobenzo[d]thiazole:
1. In a reaction flask, 2-chloro-5-nitrobenzo[d]thiazole (2.18 g, 10.2 mmol) was dissolved in a solvent mixture of EtOH:acetic acid (91:9, 102 mL).
2. Iron powder (5.70 g, 102 mmol) was carefully added to the above solution and the reaction mixture was heated to reflux for 1.5 hours.
3. After completion of the reaction, the reaction mixture was filtered while hot to remove insoluble matter.
4. The filtrate was concentrated under reduced pressure to about one-third of the original volume.
5. The pH of the concentrate was adjusted to 8 with 10% aqueous NaOH. 6.
6. The mixture was extracted with ethyl acetate (150 mL) and the organic layer was separated.
7. The organic layer was washed with saturated saline, dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure.
8. The crude product was suspended in ethanol (4 mL), filtered, washed with a small amount of ethanol (0.5 mL) and dried to give 2-chloro-5-aminobenzothiazole (1.55 g) solid.
LC-MS: tR = 0.78 min; [M + H]+ = 185.03.
1H NMR (400 MHz, D6-DMSO) δ: 7.65 (d, J = 8.7 Hz, 1H), 7.06 (d, J = 1.9 Hz, 1H), 6.79 (dd, J1 = 2.0 Hz, J2 = 8.7 Hz, 1H), 5.43 (s, 2H).
