Hydrochloric Acid → 4-Hydroxyindole-3-carboxaldehyde

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Reaction Steps

Phosphorous oxychloride 7.35 ml was added dropwise to dry dimethylformamide 15 ml under cooling in ice-methanol bath and the mixture was stirred for 15 min. Then, a solution of the 4-hydroxyindole 5.0 g in dry dimethylformamide 10 ml was added dropwise to the mixture under cooling in ice and the mixture was stirred for 2 h at room temperature. Water was added under cooling in ice to the mixture, which was made alkaline with a 30% aqueous sodium hydroxide solution and was stirred for 15 min. Then, the mixture was acidified to pH 4 with 5N-HCl and the precipitate was collected by filtration, washed with water and dried to give the titled compound 4.99 g as crude crystalline materials. Yield 82%. Crude crystalline materials are recrystallized from methanol to give yellow crystals m.p. 190-193° C.

Provenance & Evidence