Sodium Hydroxide → 5-Nitroindole-2-carboxylic acid

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Reaction Steps

To a stirred solution of ethyl-5-nitroindole-2-carboxylate (8) (25.0 g, 106.8 mmol), in 500 mL of THF-methanol (1:1, v/v) at room temperature, was added a solution of NaOH (40 g, 1.0 mmol) in 300 mL of water. The resulting deep red-brown solution was stirred for 3 h, then quenched by acidification to pH 1 with dilute HCl. The precipitated product was collected by vacuum filtration, and the remaining dissolved product was extracted with THF/ethyl acetate (1:2, v/v, 2×400 mL). The precipitate was dissolved in THF and this solution was combined with the organic layers from the extractions, supra. Drying over magnesium sulfate, filtration, concentration in vacuo, and crystallization of the residue from THF/ethyl acetate/hexane afforded 21.1 g (96% yield) of 5-nitroindole-2-carboxylic acid (9). 1H NMR (DMSO), 11.50 (s, 1H), 7.20 (d, 1H, J=8.4 Hz), 6.85 (s, 1H), 6.70 (m, 2H).

Provenance & Evidence