Commercial and scientific notes on essential oils. 23 



As regards the preparation of thymol, menthone and menthol from piperitone Ci Hi 6 O, 

 which, according to H. G. Smith and A. R. Penfold, is contained in the essential oils of 

 many kinds of eucalyptus and in the oil of Eucalyptus dives, in addition to phellandrene, 

 to the amount of 40 to 50 per cent., we have a long report by these authors 1 ). Since the 

 inactive racemic modification of piperitone, which is originally lasvorotatory, is formed 

 when the oil is heated at ordinary pressure, the natural laevorotatory piperitone is only 

 obtained when exparated by distillation at strongly-reduced pressure. Such a piperitone 

 purified with bisulphite possessed the constants: — b. p. 229 to 230° (not corrected, 

 usual pressure), 106 to 107° (10 mm.); d 20 o 0.9348; « D — 40.05°; n D20 o 1.4837; semi- 

 carbazone, m. p. 219 to 220°; oxime, m. p. 110 to 111°; oxamino oxime, m. p. 169 to 

 170°; mol. refr. 46.49 (calculated for Ci Hi 6 O 45.82; the difference in the values is 

 ascribed to the double bond) 2 ). The .oxidation of piperitone with potassium perman- 

 ganate yielded among other products isobutyric acid. Since further the ketone could 

 be oxidised to thymol and reduced to methone, the authors assume that piperitone is 

 constitutionally a zl 4 -menthenone-3 or a A l -menthenone-3 3 ). 



By the oxidation of piperitone with ferric chloride in glacial acetic acid Smith and 

 Penfold obtained 25 per cent, of thymol. By reducing the ketone by means of hydrogen 

 they obtained menthone in almost quantitative yield (b.p.208°; d 2 oo0.8978; [«] D — 0°15'; 

 n D20o 1.4529; oxime, m. p. 80°; semicarbazone m. p. 156°). By treatment with sodium 

 in aqueous-ethereal solution the menthone was further converted into inactive menthol 

 (m. p. 34°). The reduction of piperitone with sodium or sodium amalgam in alkaline 

 solution led to a bimolecular ketone C20H34O2 (m. p. 148 to 149°). The authors believe 

 that it will be possible to prepare from the abundant raw material both thymol in 

 better yields and active menthol so as to satisfy medicinal requirements, on a large scale. 



In the eucalyptus oils which contain piperitone R.T.Baker and H. G. Smith 4 ) found 

 an alcohol corresponding to this ketone, which they called piperitol. A larger quantity 

 of this piperitol they obtained from the oil of Eucalyptus radiata, Sieb. by removing 

 the ketone from the piperitone fraction of b. p. 100 to 103° (10 mm.) by shaking with 

 sodium bisulphite and further by fractionated distillation of the residue at a pressure 

 of 10 mm. The piperitol prepared in this way (b. p. 95 to 96° (10 mm.); d 20 o 0.9230; 

 « D — 34.1°; n D220 1.4760; mol. refr. 47.04; calculated for C 10 H 18 O/r 47.14) could be oxi- 

 dised, by means of potassium dichromate, to piperitone (di 5 o 0.9390; « D — 24.0°; 

 n D20 o 1.4832. It is noteworthy that piperitone has not conversely been converted so 

 far into piperitol by reduction. 



C. Kleber and W. v. Rechenberg 5 ) determined the cineole contents of eucalyptus oil 

 by determining the solidification temperature of the respective oils and by calculations 

 based upon their tables. In this determination, which is carried out in a double-walled 

 refrigerator, if possible provided with a vacuum jacket, attention should be paid to the 

 true solidification point, that is to say, the temperature at which crystalisation just 

 begins or stops. This is best done by repeatedly remelting the solidified oil and by 



: ) Baker and Smith, A Research on the Eitcalypts. 2 nd ed., 1920, p. 390. — 2 ) Cf. Berl. Berichte 41 (1908), 

 1812. — '■) The formation of /.sobutyric acid speaks for the 4-position of the double bond; according to Wallach 

 Zentrulhl. 1912, II, 923), however, ^ 4 -menthenone-3 is not oxidised to thymol by boiling with ferric 

 chloride in glacial acetic acid, contrary to J l -menthenone-3. Assuming the authors to be correct, piperitone 

 should then have the constitution of a ^-menthenone-S. We should say, however, that 1-piperitone is not 

 identical with the dextrorotatory ^-menthenone-S with we have found in Japanese oil of peppermint, although 

 many constants of the two substances approach one another closely (see Report Oct. 1910, 97). There are 

 possibly two modifications of the same substance. — *) Baker and Smith, A research on the eucalypts 

 regard to their essential oiis. 2 nd ed., p. 373. — 5 ) Journ. f prakt. Chem. N. F. 101 (1920), 171. 



