Artificially it is obtained by the oxidation of dihydrocarveol with chromic acid in glacial acetic acid solution,2) also by the reduction of carvone with zinc dust and alkali or glacial acetic acid.3) In the latter case some dihydrocarveol always results.
Dihydrocarvone combines readily with sodium acid sulphite2) and can be obtained in a pure state by means of this addition product.
It is a liquid, the odor of which resembles that of menthone as well as that of carvone. Wallach (loc. cit.) records the following properties:
B. p. 221 to 222°; d19o 0,928; nD19o1,47174. The optical rotation varies according to the material from which it is prepared: d-carvone yields laevogyrate dihydrocarvone, /-carvone yields dextrogyrate dihydrocarvone.
Schimmel & Co. (loc. cit.) record the following constants for a dihydrocarvone isolated from caraway oil:
B. p. 221° (735,5 mm.); d15o 0,9297; aD - 16° 18'; nD20o1,47107.
1) Report of Schimmel & Co. April 1905, 20.
2) Wallach, Liebig's Annalen 275 (1893), 115.
3) Wallach and Schrader, ibidem 279 (1894), 377.
The following characteristic derivatives may here be mentioned. According to Wallach1) the dibromide is readily obtained by the addition of bromine to a solution of dihydrocarvone in glacial acetic acid-hydrogen bromide. The active modifications of the dihydrobromide melt at 69 to 70°, the racemic mixture at 96 to 97°. The active oxime melts at 88 to 89°, the racemic mixture at 115 to 116°. The oximes deviate the plane of polarized light in the same direction as do the corresponding ketones.2) The melting point of the semicarbazone is given by Wallach3) as 189 to 191°. Harries and Roeder4) record 201 to 202° for a preparation washed with ether. In addition to the constants, the above-mentioned derivatives may be utilized for the characterization of dihydrocarvone.