Oleum Iridis. - Irisol. - Essence d' lris concrete. Beurre de Violettes.
Origin and Production. Of the genus Iris (Ger. Schwertlilie), belonging to the family Iridaceae, three species contain a fragrant volatile oil in their rhizomes, viz., Iris germanica, L., Iris pallida, Lam. and Iris florentina, L.
1) Berl. Berichte 17 (1884), 2228.
2) Chem. Ztg. 23 (1899), 854; Chem. Zentralbl. 1900, II. 576. For the older literature on crocus oil see: Dehne, Crell's Chem. Journ. 3 (1780), 11. - Aschoff, Berl. Jahrb. 1818, 51. - Henry, Journ. de Pharm. 7 (1821), 400. -B. Quadrat, Journ. f. prakt. Chem. 56 (1852), 68. - B. Weiss, ibidem 101 (1867), 65. - W. W. Stoddart, Pharmaceutical Journ. III. 7 (1876), 238.
For commercial purposes, the first two species1), are more particularly cultivated, principally in the province of Florence. The cultivation is carried on chiefly in the municipalities Greve, Dicomano, Pelago, Regello, Bagno a Ripoli, Pontassieve, Galluzzo, S. Casciano in Val di Pesa and Montespertoli. The very best root is cultivated in the villages S. Polo and Castellina belonging to the municipality of Greve. Cultivations to no mean extent have also developed in provinces bordering upon that of Florence, viz. in Arezzo, Castelfranco di Sopra and Lore Ciuffenna, all in the province of Arezzo; in Grosseto in the province of like name; in Faenza, province of Ravenna; and in Terni, province of Perugia. As to quality, the product of these provinces corresponds to that of Florence.
Iris is planted on hills or the slopes of hills, never in the valley, mostly in open, sunny spaces in the woods, or in narrow strips between vineyards, and rarely in extensive fields. It flourishes particularly in stony, very dry soil2). As a rule the root is harvested after three years. However, when prices are high, it is frequently cut after 2 years. The freshly cut rhizomes are first placed in water in order to facilitate the removal of the skin. They are then spread out on terraces and dried, a process requiring about a fortnight. When dry, the rhizomes are turned in a lathe to the so-called "orris root" (Ger. Veilchenwurzeln) which are given to children when teething. Rosaries are also made therefrom in large numbers. Orris powder is used in the making of sachets. The unsightly rhizomes, fragments and waste from peeling and cutting, enter commerce as crude material for the distillation of orris oil.
The principal places of export of Italian or Florentine orris root are Leghorn, Verona, and Trieste.
1) According to H. Blin (Parfum. moderne 3 , 13) the variety "Clio" of Iris pallida is principally cultivated.
*2) For a more detailed account on the cultivation see U. Somma, Staz. sperim. agrar. ital. 34 (1901), 417. - G. L. Mazuyer, Americ. Perfumer 6 (1911), 31. - Daily Consular and Trade Report June 1st 1911; Report of Schimmel & Co. October 1911, 65.
For the purpose of distillation the Florentine drug is used almost exclusively. Of inferior quality and but rarely used for distillation is the Veronese drug derived from Iris germanica. Still poorer is the Moroccan or Mogador orris root, which also is obtained from Iris germanica. It is darker in color and has but a faint odor. In order to impart a lighter color to the root, it is occasionally bleached with sulphurous acid, thus rendering it unfit for the distillation of the volatile oil.
Now and then Indian roots have1) entered the London market. Their inferior quality was probably due to improper methods of collecting and treatment. Hence they have so far been found unfit for purposes of distillation.
Upon steam distillation, orris root yields but 0,1 to 0,2 p.c. of volatile oil. The distillation is tedious and difficult because of the strong frothing, largely due to the high starch content of the root. In order to facilitate the distillation, the addition of sulphuric acid has been recommended, whereby the orris starch is partly converted into sugar. This process, however, has not come into general use since it impairs the odor of the oil.
Composition. The bulk of the oil of orris, about 85 p.c. thereof, consists of the completely odorless myristic acid-). The substance which imparts to it the violet-like odor is the irone, a ketone of the formula C13H20O3). In addition to these two substances the oil contains very small amounts of myristic acid methyl ester, and of oleic acid and its esters.
In order to obtain the irone from the orris oil, the myristic acid, according to Tiemann and Kruger3), is first removed by means of dilute potassium hydroxide. This solution is shaken out with ether and the ether extract distilled with water vapor.
In the residue there remains iregenin, iridic acid, and esters of myristic and oleic acid, whereas myristic acid methyl ester, oleic acid and one of its esters together with irone distil over.
1) Report of Schimmel & Co. October 1896, 55.
2) F. A. FIuckiger, Arch, der Pharm. 208 (1876), 481. Of the older references compare Vogel, Journ. de Pharm. III. 1 (1815), 483, Trommsdorff's Journ. der Pharm. 24, II. (1815), 64, Dumas, Journ. de Pharm. II. 21 (1835), 191 and Liebig's Annalen 15 (1835), 158.
3) Berl. Berichte 26 (1893), 2675.
During the second steam distillation of the first distillate the irone passes over first, and can thus be separated to a certain extent from the other constituents.
For the purpose of rectification the irone is converted into its phenylhydrazone by means of phenylhydrazine, and regenerated by means of sulphuric acid. In order to obtain an entirely pure irone, the crystalline irone oxime is prepared and this again decomposed with dilute acid.
According to Tiemann and Kruger, irone has the specific gravity of 0,939 at 20°; it boils at 144° (16 mm.); and in a 100 mm. tube it deviates the ray of polarized light about 40° to the right. In water it is wellnigh insoluble, but readily soluble in alcohol, ether, chloroform, benzene and ligroin. For its constitution, constants and derivatives see vol. I, p. 469.