A
3-l. stainless steel, rocking autoclave (Note
1) is charged with
270 g. (4.1 moles) of 85% potassium hydroxide and
351 g. (3.00 moles) of indole (Note
2), and then
360 g. (3.3 moles) of 70% aqueous glycolic acid is added gradually (Note
3). The autoclave is closed and rocked at 250° for about 18 hours (Note
4). The reaction mixture is cooled to below 50°, 500 ml. of water is added, and the autoclave is rocked at 100° for 30 minutes to dissolve the
potassium indole-3-acetate. The aqueous solution is cooled to 25° and removed from the autoclave, the autoclave is rinsed out well with water, and water is added until the total volume of solution is 3 l. The solution is extracted with
500 ml. of ether (Note
5). The aqueous phase is acidified at 20–30° with
12N hydrochloric acid and then is cooled to 10° (Note
6). The
indole-3-acetic acid that precipitates is collected on a
Büchner funnel, washed with copious amounts of cold water, and dried in air or a
vacuum desiccator out of direct light (Note
7); weight
455–490 g. (
87–93%); m.p.
163–165° (dec.).
The
indole-3-acetic acid, which is cream-colored, is of high purity. If further purification is desired, it may be done conveniently by recrystallization from water. One liter of water is used for
30 g. of acid, with
10 g. of decolorizing carbon added. Recovery is about
22 g. of a nearly colorless product, m.p.
164–166° (dec.).