Thujone 172

Thujone, C10H16O, occurs in two physically isomeric forms, namely as lasvogyrate a-thujone and as dextrogyrate B-thujone (the tanacetone of Semmler). These two modifications are not optical antipodes. They can be clearly distinguished by means of their semicarbazones, and by treatment with alkali can be converted partly into each other.2) Thujone was discovered simultaneously by Wallach3) and Semmler:4) the Isevogyrate thujone by Wallach in thuja oil, the dextrogyrate thujone by Semmler in tansy oil. To the latter ketone Semmler applied the name tanacetone, whereas Wallach named this dextrogyrate modification B-thujone.

In addition to the oils already mentioned, a-thujone occurs in the leaf oil of Thuja plicata, in oil of sage, and in the oil of

1) Scientific and Industrial Bulletin of Roure-Bertrand Fils October 1909, 39; Report of Schimmel & Co. April 1910, 184.

2) Wallach, Liebig's Annalen 336 (1904), 249. 3) Liebig's Annalen 272 (1893), 99. 4) Berl. Berichte 25 (1892), 3343.

Artemisia Barrelieri; B-thujone in oil of sage, in the oil of Artemisia Barrelieri, and particularly in oil of wormwood. From oils rich in thujone, such as tansy oil and the oil of Artemisia Barrelieri, the ketone can readily be separated in the form of its bisulphite addition product, which, upon decomposition with soda, yields pure thujone. For the preparation of the acid sulphite addition product, ammonium bisulphite is used, some alcohol is added to the mixture, which is set aside for some time and is frequently shaken.

Thujone is a colorless liquid with a pleasant, refreshing odor. For the ketone regenerated from the bisulphite addition product or from the semicarbazone, Wallach found the following constants:1) d19o0,9175; nD 1,45109; d20o 0,916; nD 1,4507.

For a-thujone regenerated from the semicarbazone by means of dilute sulphuric acid, Wallach2) found:

B. p. 200 to 201°; d 0,912; aD - 5° 13'; nD22o1,4503.

When phthalic acid anhydride was used for the regeneration an optical rotation [a]D - 10,23° was observed. For B-thujone, obtained from the semicarbazone, [a]D + 76,16° was observed. When acted upon with alkali, a-thujone is very readily changed to B-thujone, a change that must not be overlooked in the attempt to identify a natural thujone.

Thujone is a saturated ketone, nevertheless it is readily acted upon by permanganate. Bromine produces substitution products.

As already pointed out thujone differs in its behavior from camphor and fenchone in the formation of an acid sulphite addition product. With hydroxylamine it yields an oxime3) which melts at 54 to 55° and which corresponds to B-thujone, whereas the oxime of a-thujone is liquid. When acted upon by phosphorus pentachloride, the crystalline oxime is changed to an isoxime4) melting at 90°, and, when heated with dilute alcoholic sulphuric acid, into carvacrylamine.1) With semicarbazide solution,2) a-thujone yields a semicarbazone that melts at 186 to 188°.3) There exists also an amorphous modification which melts at about 110°. From B-thujone a hexagonal semicarbazone, melting at 174 to 175°, can be derived which changes spontaneously into a stable rhombic form that melts at 170 to 172°.

1) Berl. Berichte 28 (1895), 1965.

2) Liebig's Annalen 336 (1904), 263.

3) Wallach, Liebig's Annalen 277 (1893), 159; Semmler, Berl. Berichte 25 (1892), 3344.

4) Wallach, Liebig's Annalen 286 (1895), 94; 336 (1904), 270.

Upon reduction thujone is changed to thujyl alcohol, C10H18O, the corresponding secondary alcohol,4) which has already been described on p. 397.

When oxidized with permanganate in the cold, thujone yields a saturated ketonic acid C10H16O3,5) the a-thujaketonic acid, which melts at 75 to 76°. When heated or distilled in vacuo, it is readily changed into the isomeric, unsaturated B-thujaketonic acid, which melts at 78 to 79°. When acted upon by hypo-bromite, the corresponding dicarboxylic acids C9H1404 result,6) of which the a-acid melts at 141,5°, the B-acid at 116 to 118°. Upon destructive distillation, both ketonic acids yield thujaketone,7) C9H160, the odor of which resembles that of methylheptenone. As "Abbau" product, both ketones also yield (s-(w-)dimethyl-lasvulinic acid, which melts at 32°.8)

If thujone is heated for a long time to 280° in sealed tubes, it is changed into an isomeric, unsaturated ketone C10H16O, the odor of which resembles that of carvone, and which has been named carvotanacetone.9) judging from the reduction in the angle of rotation, this change appears to take place even upon prolonged boiling. Another isomeric, unsaturated ketone, isothujone, results when thujone is moderately heated with dilute sulphuric acid.10)

1) Semmler, Berl. Berichte 25 (1892), 3352.

2) Wallach, Liebig's Annalen 286 (1895), 94; 336 (1904), 270.

3) This melting point applies to the perfectly pure compound only. Commonly 184,5 to 186° is found.

4) Semmler, Berl. Berichte 25 (1892), 3344.

5) Semmler, Ibidem 3347; Wallach, Liebig's Annalen 272 (1893), 111; Berl. Berichte 30 (1897), 423.

6) Semmler, Ibidem 3346.

7) Wallach, Liebig's Annalen 272 (1893), 116; 275 (1893), 164.

8) Tiemann and Semmler, Berl. Berichte 30 (1897), 429; 31 (1898), 2311.

9) Semmler, Berl. Berichte 27 (1889), 895.

10) Wallach, Liebig's Annalen 286 (1895), 101; 323 (1902), 334; Berl. Be-richte 28 (1895), 1959; 30 (1897), 26.

Upon reduction, Isothujone is converted into the saturated thuja-menthol. When boiled with a solution of ferric chloride, thujone is converted into carvacrol.

The structural formula given above was based by Semmler1) on the physical and chemical properties of thujone. Somewhat later it was accepted by Wallach.2)

The tribromide is best suited for the characterization of thujone. According to Wallach3) it is prepared by adding at once 5 ccm. of bromine to a solution of 5 g. of thujone in 30 ccm. petroleum ether contained in large beaker. After a few seconds a rather violent reaction sets in accompanied by the evolution of hydrogen bromide. Upon evaporation of the solvent, the tribromide separates gradually as a crystalline mass which is freed from adhering oil by washing it with cold alcohol, and which can be recrystallized from hot acetic ether. The melting point of the pure compound lies at 121 to 122°. When acted on with methyl-alcoholic or ethylalcoholic potassium hydroxide solution, the phenols C10H11Br(OH)OCH3) and C10H11Br(OH)(OC2H5 respectively result. The former melts at 156 to 157°, the latter at 144 to 145°.

For the identification of the a- and B-modifications of thujone the semicarbazones described above are made use of.