(c) Methyl indole-6-carboxylate (11.0 g) was dissolved in a solvent mixture of tetrahydrofuran (150 ml), methanol (150 ml) and water (63 ml) and lithium hydroxide monohydrate (15.8 g) was added. The reaction mixture was stirred at 60 °C for 6 h. After completion of the reaction, the organic solvent was removed by concentration under reduced pressure. The residue was dissolved in water and acidified with 50% (v/v) hydrochloric acid to pH < 3. The precipitate precipitated was collected by filtration and dried to give indole-6-carboxylic acid (9.6 g, 95% yield) as a tan powder with a melting point of 253°C-254°C. The NMR hydrogen spectroscopic (80 MHz, CDCl3) data were as follows: δ 6.51 (m, 1H, H-3) 8.04 (m, 1H, H-7), 11.43 (br s, 1H, NH), 12.42 (br s, 1H, OH).