— n5 — 



atives of menthol, and he has found that they are all identic. They 

 have all the same boiling point (between 167° and 168 ) and the 

 same rotatory power [a] D -|- 1 13,28° to 116,74°; the specific gravity 

 is d^- 0,8122, and the index of refraction n D 20° 1 A5 2 4 2 - All the 

 menthenes produced yield the same nitrosochloride. On fractional 

 oxidation of all the hydrocarbons, only fractions of the same rotatory 

 power are obtained, which proves their uniform character. With hydrogen 

 bromide in solution of glacial acetic acid, the menthene from the 

 xanthogene compounds yields a tertiary bromide which is optically 

 almost inactive, p-4-bromomenthane, C 10 H 19 Br. To this belongs the 

 structure of a p-menthene (3). From the nitrosochloride nitrosomenthene 

 was obtained, from the latter menthenone, and from this by reduction 

 menthol, so that the cycle 1-menthol, xanthogenic acid ester, menthene, 

 nitrosochloride, nitrosomenthene, menthenone, 1-menthol is complete. 

 Tschugaeff next discusses the menthenes which are obtained 

 from 1-menthol by means of halogen derivatives or by abstraction of 

 water, and arrives at the conclusion that the menthene from halogen 

 compounds consists chiefly of menthene (3), which yields a solid nitroso- 

 chloride, and that the one obtained by splitting off water is a men- 

 thene (4?) which does not yield a solid nitrosochloride. 



Zelikow 1 ) has used organic acids such as oxalic acid, succinic acid, 

 tartaric acid, citric acid, phthalic acid, terephthalic acid and camphoric acid, 

 as water- abstracting agents for the production of menthene from menthol. 

 With the exception of tartaric acid, all the acids examined yielded 

 the looked-for menthene. The best results were obtained with cam- 

 phoric acid. The reaction takes place with formation of an acid ester, 

 and decomposition of the latter when the temperature is raised further. 

 In this process the presence of free acids plays an important part, as 

 in such case a larger quantity of menthene is produced than in their 

 absence. The dehydration was carried out by heating the mixture 

 of menthol and acid in a retort in an air-bath. For details of the 

 experiments with the various acids we must refer to the original work. 

 The intermediate products isolated for the purpose of clearing up the 

 reaction were, in addition to menthol, neutral and acid esters. The 

 former, however, can play no part in the production of menthene, as for 

 example neutral oxalic ester distils at 225° without decomposition, 

 whilst the dehydration already takes place at 120°. If a large excess 

 of free oxalic acid is present, menthene is no doubt formed during 

 the distillation, but only in small quantity. The acid oxalic acid ester 

 also, when distilled as such, yields no menthene, but it does yield 

 the theoretical quantity when free oxalic acid is added. 



*) Berl. Berichte 37 (1904), 1374. 



