180 



Most interesting are the observations of Pickard and Littlebury on 

 the occurrence of weomenthol in Japanese peppermint oil. At their request 

 we had placed at their disposal a Japanese peppermint oil which had been 

 freed from menthol as far as possible and which, after removal of the first 

 and the last runnings, had been warmed with an equal quantity of benzoyl 

 chloride. When the reaction was completed, and the hydrochloric acid 

 had been removed by shaking with soda solution, menthone and other 

 volatile substances were distilled off with steam. The residual esters, 

 when saponified, yielded a mixture of alcohols from which a fraction was 

 obtained possessing the following characters: b. p. 80 to 82° (4 mm.), 

 d 15 o 0,9032, a D — 8° 48' (menthol-content about 90°/o). 



The authors converted this menthol fraction into its acid phthalate, 

 which gave m. p. 140 to 143°, [ a ] D + 4,58°. The ester was recrystallised 

 28 times from 95°/o acetic acid, after which it melted between 141 and 144°, 

 the specific rotation being +57,16° (in chloroform). Mixed with d-neo- 

 menthyl phthalic ester, the ester melted between 142 and 144°. The alcohol 

 which was regenerated from the ester, when oxidised with Beckmann's 

 chromic acid mixture, yielded Z-menthone ([«] D — 28,33°). 



The odour of d- and Z-neomenthol differs altogether from that of 

 d- and Z-menthol. 



The following arrangement explains the reactions described by the 

 authors: — 



Thymol 



I 



I " 1 



Menthone Isomenthone 



(Semicarbazone m. p. 158°) (Semicarbazone m. p. 217°) 



I 



I 



Menthol m. p. 34° 

 (Phthalic ester m. p. 130°) 



I 

 iVeomenthol m. p. 51° 

 (Phthalic ester m. p. 177°) 



I 



I 



^-Menthol d-Menthol <i-iVeomenthol l-Neomen\ho\ 



(m.p.43°[a] D -49°) (m.p.43°;M D + 49°) 0>] D + 19,6°) ([«] D -19,6°) 



liquid liquid 



Z-Menthone 



^-Menthone 



