Synthesis of 3-Indoleacetic acid

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Known in the art are the methods of synthesizing 3-indolylacetic acid from compounds containing the indole ring. For example, the products obtained by interacting 3-indolylmagnesium halide with chloroacetonitrile, N,N-diethylchloroacetamide or ethylene oxide can be converted into the heteroauxine by hydrolysis or oxidation. 3-indolylacetic acid can likewise be produced by the reaction of hydrocyanic acid or salts thereof with indole in the presence of formalin, followed by the hydrolysis of the nitrile obtained.

The process of the present invention is carried out by reacting indole, chloroacetic acid and an aqueous alkaline solution in an autoclave. The reaction mixture is heated to 250-290°C, preferably to 285-290° C, maintained for several hours under a pressure of 50 to 90 atm, cooled and filtered. The filtrate is acidified, and the crystals that precipitate are pressed, washed with ice water and dried.


Into a 0.5 lit. pressure vessel were charged 5.85 g.(0.05 mole) of indole, 14 g. (0.15 mole) of chloroacetic acid and 150 ml, of 17% aqueous solution of potassium hydroxide. The reactor was next charged with nitrogen to a pressure of 5 atm. and the reaction mixture was heated to 285-290°C. and maintained at this temperature for 15 hours, the pressure in the reactor being 85-90 atm. Then the reaction mixture was cooled, discharged from the pressure vessel and filtered. The filtrate, with external cooling, was acidified with concentrated hydrochloric acid, until it showed an acid reaction to Congo red, and maintained for 2-3 hours at a temperature of 8-10°C. The precipitated crystals of 3-indolylacetic acid were filtered off, washed on the filter with ice water until the washing water was acid-free, and dried. The product consisted of 4.52 g. of a white crystalline compound (mp 159-162°C.). The yield was 51% of the theoretical (on the basis of indole used).


[1] US Pat 3,320,281