Author Topic: indole-3-acetic acid synthesis  (Read 5161 times)

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indole-3-acetic acid synthesis
« on: June 24, 2002, 08:56:00 PM »
Here is a synthesis of Indoleacetic acid taken from Organic Syntheses website. The Hive's search engine didn't came up with any results so I assume this hasn't been posted yet.

A 3L stainless steel, rocking autoclave (Note 1) is charged with 270g (4.1 moles) of 85% potassium hydroxide and 351g (3.00 moles) of indole (Note 2), and then 360g (3.3 moles) of 70% aqueous glycolic acid is added gradually (Note 3). The autoclave is closed and rocked at 250° C for about 18 hours (Note 4). The reaction mixture is cooled to below 50° C, 500mL of water is added, and the autoclave is rocked at 100° C for 30 minutes to dissolve the potassium indole-3-acetate. The aqueous solution is cooled to 25° C and removed from the autoclave, the autoclave is rinsed out well with water, and water is added until the total volume of solution is 3L. The solution is extracted with 500mL of ether (Note 5). The aqueous phase is acidified at 20–30° C with 12N hydrochloric acid and then is cooled to 10° C (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 455–490g (87–93%); m.p. 163–165° C (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 30g of acid, with 10g of decolorizing carbon added. Recovery is about 22g of a nearly colorless product, m.p. 164–166° C (dec.).

1. A stirred autoclave is just as satisfactory. The scale is not critical, for the checkers got equally good results on one-third the scale; they used a 1L rocking autoclave.

2. Indole from the Union Carbide Olefins Company, Institute, West Virginia, is satisfactory.

3. If the reactants are added in this order, with the glycolic acid being introduced over a 5–10 minute period, there is no violent heating because the heat of neutralization is used to melt the indole. An equivalent amount of anhydrous glycolic acid may be used, but this offers no special advantage.

4. These limits are not critical, but they are probably optimum. Reaction times of 24–30 hours are not particularly detrimental, and high yields of product can be obtained within 12 hours. The temperature can range from 230° C to 270° C with but slight effect on the yield of product.

5. This extraction may be omitted. It does, however, remove traces of neutral material and consequently gives a product with greater color stability.

6. This operation is most conveniently conducted in a flask equipped with a stirrer.

7. The product dries slowly, and several days in air or 24 hours in a vacuum desiccator is usually required. Considerable coloration will result if this is done in direct light. Drying in a heated oven or removing the water as a benzene azeotrope is not satisfactory because of some decarboxylation to skatole. The product should be stored in a dark bottle away from direct sunlight.

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