Irone, C13H20O, has thus far been found only in orris oil, the German "Veilchenwurzelol" (from Iris florentina, I. pallida, I. germanica). Tiemann and Kriiger1) were the first tho isolate it from orris root and to recognize it as a cyclic ketone isomeric with ionone. They obtained it by extracting orris root with organic solvents and distilling the evaporated extract with steam. Since liquid orris oil is to be had in the market, irone can be obtained from it by fractional distillation. It collects in fraction 105 to 120° obtained under a pressure of 4 mm. It is purified through the oxime or phenylhydrazone from either of which it can be conveniently regenerated.
Irone is a colorless oil. Its peculiar odor,2) which reminds of certain species of violets, is brought out only in extreme dilution. For the carefully purified ketone, Tiemann and Kruger (loc. cit) report the following constants:
B. p. 144° (16 mm.); d20o 0,939; aD abt. +40°; nD20o1,50113.
For a preparation isolated from the sodium salt of the phenyl-hydrazine sulphonic acid derivative,3) Schimmel & Co. observed the following constants:
B. p. 111 to 112° (2mm.); d15o 0,9391; aD +33°31'; nD20ol,50173.
For the characterization of irone its p-bromphenylhydrazone is well suited. According to Schimmel & Co. it melts at 174 to 175V) It is crystallized from methyl alcohol. According to Chuit-) the thiosemicarbazone melts at 181°. The oxime, which melts at 121,5°, crystallizes with difficulty. The melting point of 70 to 80°, found for amorphous semicarbazone3) by Schimmel & Co., gives rise to the suspicion that this is a mixture of isomeric derivatives.
1) Berl. Berichte 26 (1893), 2675.
2) Tiemann's observation that irone possesses a pungent odor is not correct.
8) For the technique to be observed in the preparation of this compound compare the expert testimony given by v. Baeyer, Berlin 1899, p. 22.
When irone is acted upon by hydrogen iodide, dehydration and ring-formation take place and irene, C13H18, is formed, which hydrocarbon is isomeric with ionene.
It is only recently that Merling and Welde4) have succeeded in preparing irone synthetically. This synthesis is based on the formation of v4-cyc/ocitral which, upon condensation with acetone, yields irone. Isopropylideneacetoacetic ester is condensed with sodium acetoacetic ester to Isophorone carboxylic acid ester. From this d-chlorc/c/ogeranioldiene carbonic acid and v4-cyclo-geranic acid are obtained. According to a special method5) the latter is converted into v4-cyc/ocitral.