Synthesis
Step 1: Synthesis of 3-amino-5-hydroxybenzoic acid hydrochloride
A mixture of 3,5-dihydroxybenzoic acid (250.0 g), ammonium chloride (213.0 g) and 28% ammonium hydroxide solution (750.0 mL) was placed in an autoclave and the reaction was stirred at 180 °C for 3 days. Upon completion of the reaction, the mixture was cooled to room temperature and subsequently concentrated under reduced pressure. The concentrated residue was dissolved in 6N hydrochloric acid solution (3.0 L) and the reaction mixture was heated at 100 °C for 24 hours. After that, the reaction mixture was cooled to 70°C~80°C, decolorized by adding activated carbon (30.0 g) and subsequently filtered through a diatomaceous earth pad. The filtrate was concentrated under reduced pressure and the resulting residue was washed twice with 6N hydrochloric acid solution and finally dried under reduced pressure to give 192.0 g of 3-amino-5-hydroxybenzoic acid hydrochloride (yield: 62.4%).
1H-NMR (d6-DMSO) δ 7.81 (s, 1H), 7.69 (s, 1H), 7.56 (s, 1H).
References
[1] Journal of the American Chemical Society, 2010, vol. 132, # 36, p. 12757 - 12765
[2] Patent: US2012/178765, 2012, A1. Location in patent: Page/Page column 11
[3] Synthetic Communications, 1999, vol. 29, # 8, p. 1379 - 1382
[4] Tetrahedron, 1983, vol. 39, # 24, p. 4189 - 4192
[5] Bioorganic and Medicinal Chemistry, 2006, vol. 14, # 7, p. 2242 - 2252
