Water → 7-Chloro-1H-indole-3-carboxylic acid

Participants

Reaction Conditions

Reaction Steps

A solution of 7-chloroindole (7.1 g, 47.0 mmol) in dimethylformamide (60 ml) was cooled to 5° C. under nitrogen and trifluoroacetic anhydride (7.6 ml, 54.0 mmol) was added over 10 mins, maintaining the temperature below 10° C. The mixture was stirred at 5-10° C. for 2 h, then poured into water (600 ml). The resulting suspension was stirred for 15 mins and the 7-chloro-3-[(trifluoromethyl)carbonyl]-1H-indole precipitate was filtered off, washing with water to neutrality. The damp solid was suspended in 4 M aqueous sodium hydroxide (500 ml) and heated to reflux with stirring for 1 h. The mixture was cooled and washed with diethyl ether (2×100 ml). The aqueous phase was then acidified to pH 1 using 5 M hydrochloric acid and the resulting fine precipitate filtered off, washed with water to neutrality and dried to afford 7-chloro-1H-indole-3-carboxylic acid as a pink solid (7.5 g, 38.0 mmol).

Provenance & Evidence