Hydrochloric Acid → 5,6-Dimethoxyindoline-2-carboxylic acid hydrochloride

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Reaction Steps

The starting material is prepared as follows: The suspension of 10.8 g of 5,6-dimethoxyindole-2-carboxylic acid in 150 ml of acetic anhydride is heated at the steam bath for 15 minutes and the mixture evaporated at 65°-70°. The residue is added to the mixture of 30 g of sodium bicarbonate and 200 ml of water and the mixture heated at the steam bath for 20 minutes. It is filtered, cooled and acidified with concentrated hydrochloric acid, filtered again and the residue suspended in 300 ml of methanol. The suspension is hydrogenated overnight in the presence of 1 g of platinum oxide at room temperature and atmospheric pressure. Removal of the catalyst and evaporation of the solvent yields the crude 1-acetyl-5,6-dimethoxyindoline-2-carboxylic acid. Hydrolysis in 90 ml of 2N hydrochloric acid under reflux overnight, washing with diethyl ether and evaporation of the aqueous solution yields the hygroscopic 5,6-dimethoxyindoline-2-carboxylic acid hydrochloride. It is esterified with ethanolic hydrogen chloride at room temperature for 3 hours to give the 5,6-dimethoxyindoline-2-carboxylic acid ethyl ester showing IR-bands at 3500 and 1740 cm-1.

Provenance & Evidence