Synthesis
6-Hydroxybenzothiazole was synthesized using 2-cyano-6-methoxybenzothiazole as starting material after the following steps: first, the ethyl acetate extract was washed with 1 M NaOH solution (50 mL), followed by acidification of the aqueous phase with 3 M HCl and extraction with ethyl acetate. The extract was evaporated from the solvent at 60 °C to induce complete decarboxylation of the unstable acid 13b. Purification of the product by column chromatography (eluent ratio dichloromethane/acetone 95:5) afforded 6-hydroxybenzothiazole 14 as a colorless solid. Further purification by recrystallization from aqueous ethanol gave 0.7 g (4.6 mmol, 50% yield) of the target product. The melting point of the compound was 190-192 °C (literature value 24: 184-185 °C), and the Rf value for thin layer chromatography was 0.35 (unfolding agent ratio petroleum ether/ethyl acetate 6:4).1H NMR (CD3OD) data were as follows: δ = 8.98 (s, 1H, 2-H), 7.88 (d, J = 8.3 Hz, 1H, 4-H), 7.38 (d, J = 2.1 Hz, 1H, 7-H), 7.06 (dd, J = 8.3 and 2.1 Hz, 1H, 5-H) ppm. 13C NMR (CD3OD) data were as follows: δ = 164.8 (6-C), 155.9 (9-C), 152.1 (2-CH), 134.9 (8-C), 122.8 (4-CH), 115.9 (5 -CH), 106.1 (7-CH) ppm.
References
[1] Synthesis, 2001, # 12, p. 1780 - 1783
[2] Tetrahedron, 2013, vol. 69, # 29, p. 5893 - 5897
