Hydrochloric Acid → Alpha-amino-6-chloro-3-indoleacrylic acid methylester hydrochloride

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Reaction Steps

A 3-l. three-necked flask, equipped with a thermometer and a mechanical stirrer was charged with 316 g (1.4 moles) of stannous chloride dihydrate and a solution of 111 g (3 moles) of dry hydrogen chloride gas in 1 l. of methyl alcohol. The colorless solution was stirred and cooled to -30° in a dry ice-acetone bath. 112.3 g (0.40 moles) of alpha-nitro-6-chloro-3-indoleacrylic acid methylester was added in 4 equal portions over 1 hour, maintaining the temperature between -25° and -20°. After the addition was complete, the temperature was allowed to rise to -10° and stirring at this temperature was continued for 90 minutes. Then 500 ml. of ether was added to the yellow suspension, followed by addition of 500 ml of 12 N hydrochloric acid (concentrated), the temperature was kept below 5°. The mixture was then filtered through a Buchner funnel. The filter cake was washed with 1000 ml of methyl alcohol-9N aqueous hydrochloric acid 1:1, precooled to -20°, and 400 ml of ether. The tan product was dried at 40°/0.1 mmHg for 8 hours and then at 20°/0.1 mmHg to constant weight to yield 103.4 g (90%) of crude product, m.p. 191° (dec.).

Provenance & Evidence