Indol has long been known to occur in the animal organism as a product of intestinal digestion. It has also been produced artificially for some time, but it is only recently that its occurrence in the vegetable kingdom has been established: first by Hesse3) who found it in the oil obtained from jasmine flowers. Since then it has been found in neroli oil, also in the wood of the trunk of Celtis reticu/osa.1) By means of color reactions its presence has likewise been established in the flowers of Caladium species, Murraya exotica and Visnea Mocanera.
1) Seifensieder Ztg. 32 (1905), 112; Report of Schimmel & Co. April 1905, 117.
2) Report of Schimmel & Co. April 1905, 118.
3) Berl. Berichte 32 (1899), 2612.
Indol consists of shiny white laminae, which, however, soon assume a dark color under the influence of light and air. They melt at 52°, b. p. 253 to 254° (corr.). It is readily soluble in hot water and is volatile with water vapor. The common commercial article has an exceedingly disagreable, fecal odor. It is only when carefully purified that a product is obtained the odor of which is not decidedly disagreable and which when properly diluted reveals a floral odor.
Solutions of oxalic acid2) and of p-dimethylaminobenz-aldehyde3) are colored red by indol.
When an ethereal solution of indol is shaken with an aqueous alcoholic solution of sodium acid sulphite a hydrosulphonate results which crystallizes from methyl alcohol in white laminae with a silky lustre.4)
For the isolation of indol, the picrate, crystallizing in long, red, shiny needles, is best suited. For the identification and quantitative determination of indol, Hesse5) gives the following directions:
To the crude floral oil about 10 p. c. of picric acid are added. The mixture is heated to from 50 to 60° until the precipitate, first formed on the addition of the picric acid, is dissolved. To the cooled solution, from which an abundant precipitate of indol picrate has separated, a large excess of petroleum ether is added. The crystalline precipitate, consisting of indol picrate and the larger amount of uncombined picric acid, and which is colored more or less red in accordance with its indol picrate content, is removed by filtration and repeatedly washed with petroleum ether. The crystals thus purified are dissolved in ammonia or soda solution with the aid of gentle heat. Upon cooling the solution is shaken out with ether, and the ethereal residue distilled with water vapor. Thus the total indol of the floral oil is obtained in an almost pure state.
1) Herter, Journ. biol. Chem. 5 (1909), 489. According to Apotheker Ztg. 24 (1909), 885.
2) Borzi, Rendiconti della R. Accad. dei Lincei 13 (1904), 372; Verschaffelt, Rec. trav. bot. Neerland. 1 (1904). Comp. also Report of Schimmel & Co. October 1905, 123.
3) Weehuizen, Pharm. Weekblad 45 (1908), 1325; Steensma, Zeitschr. f. physiol. Chem. 47 (1906), 15; Gautier and Noyer, Compt. rend. Soc. biol. December 19th 1908; abstract in Bull. Soc. chim. IV. 5 (1909), 256. Comp. also Report of Schimmel & Co. April 1909, 140 and October 1909, 213.
4) Hesse, loc. cit. 2615. 5) Loc. cit. 2612.