phellandrenes ; to these he gave the names normal-phellandrene and pseudo- 

 phellandrene. In recent determinations these isomers are usually referred to as 

 the a- and /3-forms of phellandrene. 



Wallach and Beschke [Ann. 336 (1904) 9] undertook an extensive 

 investigation with the phellandrenes, and the conclusion to which they arrive is 

 that laevo-phellandrene from Eucalyptus oil is /-a-phellandrene. 



It appears, however, that both the /-a-phellandrene and the l-ft- 

 phellandrene do occur in Eucalyptus oils, but where the line of demarcation 

 exists in the genus is not at present clear. It is probable that the /Morm is 

 present in greatest abundance in the oils of those species in which the cyclic 

 aromatic aldehydes occur, as for instance those of certain "Boxes," because 

 cymene is always a pronounced constituent in the oils of this group, whereas 

 in those of the "peppermint" group of Eucalypts, the principal phellandrene is 

 the a-form, and associated with piperitone. It would thus be interesting to 

 know from which Eucalypt the oil upon which Semmler worked was derived. 



Both the a- and /3-forms of phellandrene have been synthesised, the 

 normal or a-form by Harries and Johnson [Ber. 38 (1905) 1832] , and the pseudo 

 or /3-form by Kondakow and Schindelmeister [J. pr. Ch. II, 72 (1905) 193]. 



The normal or a-form was prepared from the ketone carvone. The 

 required menthenone was first made, and this when treated with phosphorus 

 pentachloride formed the required chlorophellandrene, which on reduction with 

 zinc dust in methyl alcohol was converted into a-phellandrene. 



The pseudo or /8-form was also obtained through carvone, the tertiary 

 carvomenthene being first prepared. This hydrocarbon reacted with bromine to 

 form the dibromide, and this substance, when treated with alcoholic potash, 

 formed the /3-phellandrene. 



The normal or a-phellandrene was also synthesised from Sabina ketone 

 by Wallach and Heyer [Ann. 359 (1908) 2652-2686]. 



The two forms of phellandrene are considered to have the following 

 structures : ru CH 2 



H 2 C 



CH 



CH 



C 3 H 7 

 a-phellandrene. 



C 3 H, 

 /3-phellandrene. 



Phellandrene readily yields a nitrosite C IO H l6 N,O 3 , and this reaction is 

 employed for the detection of this terpene in Eucalyptus oils ; it may be carried 

 out in the following manner : 5 c.c. of the oil to be tested are dissolved m 

 10 cc. of petroleum ether, and to the mixture is added half the volume of a 

 saturated aqueous solution of sodium nitrite; 5 c.c. of glacial acetic acid are 

 then added in order to liberate the nitrous acid. The amount of resulting 

 crystalline compound will serve to indicate whether much or little phellandrene 

 is present in the oil, this result being confirmed by the physical properties of the 

 particular sample. If desired the crystals may be recovered by filtration, washed 

 with water and alcohol, and then dissolved in chloroform and again precipitated 

 by the addition of alcohol. 



