The dextrogyrate modification of carvone, C10H14O, occurs to the extent of from 50 to 60 p. c. in caraway oil, also in dill oil in much the same amount. /-Carvone is not as common and has been found in kuromoji oil and in spearmint oil. Inactive carvone has been found only in gingergrass oil. In the oil from the Spanish dill herb, carvone has likewise been observed.

In order to obtain the ketone in the pure state from the oil, it can be converted into its crystalline hydrogen sulphide addition product, (C10H14O)2H2S. When a solution of 20 parts of the carvone fraction, 5 parts of alcohol and 1 part ammonia (d15o 0,96) is saturated with hydrogen sulphide, the addition product crystallizes out. Drained, and recrystallized from methyl alcohol it is decomposed by boiling with alcoholic potassa, and the regenerated carvone purified by distillation with steam. A slightly modified method of preparation is given by Wallach.1)

The same object is accomplished much more readily by isolating the carvone by means of normal sodium sulphite with which carvone combines to form a water-soluble compound. The oil is shaken with a sufficient amount of a concentrated aqueous sodium sulphite solution, the sodium hydroxide which is set free being neutralized from time to time. The reaction being completed, those oily compounds that have not united with the sulphite are shaken out repeatedly with ether and removed. The carvone is then set free with soda lye and distilled with steam. This method may also be utilized for the quantitative determination of carvone. (See the chapter in "The examination of volatile oils".)

1) Liebig's Annalen 305 (1899), 224.

Artificially, carvone and its derivatives have been obtained in a variety of ways. However, a detailed account of the relationship between carvone, pinene, limonene, pinol, and terpineol would lead too far.

Carvone is a colorless liquid possessing a decided odor of caraway. At a low temperature it congeals.1) In the laboratory of Schimmel & Co. the following properties have been determined:

For J-carvone prepared from caraway oil by means of the sulphite addition product:

B.p.230°(755mm.),91°(5to6mm.); d15o0,9645; aD-f-59°57'; nD20o1,49952.

For /-carvone prepared from spearmint oil by means of the sulphite addition product:

B.p.230to231° (763mm.); d15o0,9652; aD - 59°40'; nD20o 1,4988; soluble in 17 vols, of 50 p. c. alcohol and in 4 vols. of 60 p. c. alcohol.

Commercial preparations, own manufacture, varied as follows: d15o0,963 to 0,966; aD + 57°30' to 4- 60°; nD20o1,497 to 1,500; soluble in 16 to 20 vols. of 50 p. c. alcohol, in 4 vols. of 60 p. c. alcohol, and in 1,5 to 2 vols, of 70 p. c. alcohol.

Carvone is an unsaturated ketone which combines with hydrogen chloride to form a liquid compound,2) and with hydrogen bromide to one melting at 32°.3) If hydrogen bromide be split off from the latter, an isomeric ketone C10H14O, eucarvone results.4) The bromine substitution products obtained by the action of bromine on hydrobromcarvone, viz., the tribromide,

1) Wallach, Liebig's Annalen 252 (1889), 129, footnote.

2) Goldschmidt and Kisser, Berl. Berichte 20 (1887), 487, 2071. 3) Ibidem 2071; Baeyer, Berl. Berichte 27 (1894), 811.

4) Baeyer, Berl. Berichte 27 (1894), 811; Wallach, Liebig's Annalen 305 (1899), 234; 339 (1905), 94.

C10H14OHBrBr2, the tetrabromide, C10H14OBr4, and the penta-bromide, C10H13OBr5, have been examined by Wallach.1)

With acid sulphites, carvone yields salts of the carvone dihydrosulphonic acid. It also adds sulphurous acid. With hydroxylamine it yields a well crystallizable oxime,2) of which the optically active modifications melt at 72°.3) Union of equal parts of d- and /-carvoxime yields the inactive carvoxime which melts at 93V)

In the preparation of carvoxime, care should be exercised not to use too large an excess of hydroxylamine, otherwise an addition product of hydroxylamine to carvoxime, C10H14NOHNH2OH (m. p. 174 to 175°) may be formed.5) If the freshly prepared oxime does not congeal readily, it can at times be made to crystallize by driving it over with steam. Artificially the oximes of carvone are obtained by splitting off hydrogen chloride from the nitrosochlorides of limonene and dipentene.6) With phenyl-hydrazine, carvone yields a phenylhydrazone that melts at 109 to 110°,7) with semicarbazide d- and /-carvone yield the semicar-bazones. Whereas the d- and /-carvone semicarbazone melt at 162 to 163°,8) i-carvone semicarbazone melts at a lower temperature, viz., at 154 to 156°.9)

By allowing an excess of free hydroxylamine to act on hydro-bromcarvone and subsequently splitting off hydrogen bromide, Isocarvoxime melting at 142 to 143° results.10) Under the dehydrating influence of dilute acids, the latter yields carvoline.11)

1) Liebig's Annalen 286 (1895), 119.

2) Goldschmidt, Berl. Berichte 17 (1884), 1578; Harries, in Meyer-Jacobson, Lehrbuch der organischen Chemie, Leipzig (1902), Vol. II. part 1, p. 939.

3) Wallach, Liebig's Annalen 246 (1888), 226.

4) Wallach, ibidem 245 (1888), 268.

5) Wallach and Schrader, Liebig's Annalen 279 (1894), 368; Harries and Jablonski, Berl. Berichte 31 (1898), 1384; Harries, ibidem 1810.

6) Goldschmidt and Zurrer, Berl. Berichte 18 (1885), 2220; Wallach, Liebig's Annalen 245 (1888), 256, 268; 246 (1888), 226.

7) Baeyer, Berl. Berichte 27 (1894), 811; see also Goldschmidt, ibidem 17 (1884), 1578.

8) Baeyer, ibidem 27 (1894), 1923. 9) Baeyer, ibidem 28 (1895), 640.

10) Goldschmidt and Kisser, Berl. Berichte 20 (1887), 2073. 11) Goldschmidt, ibidem 26 (1893), 2086; Wallach, Liebig's Annalen 346 (1906), 266.

When reduced in alcoholic solution with sodium, carvone is not reduced to carveol, C10H16O, but takes up four hydrogen atoms at once with the formation of dihydrocarveol. (See p. 385). If in alcoholic-alkaline solution, carvone be reduced with zinc dust, two atoms of hydrogen are added, but the resulting compound is no alcohol but a ketone C10H16O, dihydrocarvone.1) As a by-product a bimolecular ketone, a-dicarvelone, m. p. 148 to 149°, results.-)

When carvone is shaken with 40 p. c. sulphuric acid a hydroxy dihydrocarvone3) results which melts at 41 to 42°. Potassium permanganate oxidizes carvone to hydroxyterpenylic acid, C8H12054) which melts at 190 to 192°. It is because of these oxidation products as well as because of those obtained by Tiemann and Semmler5) from dihydrocarveol and dihydrocarvone that these investigators adopted as the most probable expression for the constitution of carvone the formula given above, a formula previously suggested by Wagner.

When heated with sulphuric acid, phosphoric acid, phosphorus oxychloride, zinc chloride, or alkalies, carvone is converted into the isomeric benzene derivative, carvacrol, C6H3CH3[1]OH[2] •C3H7[4). A similar intermolecular rearrangement takes place when carvoxime is heated with alcoholic sulphuric acid or with a strong solution of alkali to 230 to 240°, whereby the oxime is changed to carvacrylamine.6) When carvoxime is added to concentrated sulphuric acid, it rearranges itself to p-amido thymol,7) m. p. 173 to 174°.

When carvone is heated with ammonium formate, dihydro-carvylamine is formed.8) The same base results when carvoxime is reduced in alcoholic solution with sodium.9)

1) Wallach and Schrader, Liebig's Annalen 279 (1894), 377.

2) Wallach and Schrader, ibidem 380; Wallach, ibidem 305 (1899), 223.

3) Rupe and Schlochoff, Berl. Berichte 38 (1905), 1719.

4) Best, Berl. Berichte 27 (1894), 1218; Wallach, ibidem 1495. 5) Berl. Berichte 28 (1895), 2148.

6) Wallach, Liebig's Annalen 275 (1793), 118; 279 (1894), 374.

7) Wallach, Liebig's Annalen 279 (1894), 369.

8) Leuckartand Bach, Berl. Berichte 20 (1887), 113; Wallach, Berl. Berichte 24 (1891), 3984.

9) Wallach, Liebig's Annalen 275 (1893), 119.

Carvone is characterized by its peculiar odor by means of which it can readily be recognized. If it is to be isolated from a volatile oil, its hydrogen sulphide addition product or the sodium acid sulphite addition product may be utilized for this purpose. (See above.) It should be noted, however, that the hydrogen sulphide addition product does not melt at 187°, as stated by Baeyer,1) but at 210 to 211°.2)