The Cyclic (Aromatic) Aldehydes occurring in 



Eucalyptus Oils 



Cuminal C 10 H 12 O, Aromadendral C 10 H 14 O. Cryptal C 10 H 16 O, and Another. 



ONE or more members of this very interesting group of aromatic aldehydes occur 

 in the oils distilled from the members of the typical " Box " group (E. hemiphloia, 

 &c.) and chemically related " Malices " (E. polybractea, &c.), as well as from 

 other closely associated Eucalypts.* 



These aldehydes do not seem to occur in the oils of the earlier members 

 of the genus (the pinene yielding group), nor in those of the more recent species, 

 particularly those in which phellandrene is the more pronounced terpene. In 

 these latter species the characteristic constituent is the ketone piperitone. 



It thus appears that they are common to a large proportion of the oils of 

 Eucalyptus species occupying the middle portion in the evolutionary sequence of 

 the genus (groups IV and V), and they are so shown grouped together in the 

 evolutionary table elaborated in this work. 



It may also be stated as a general rule that cymene is present in either 

 larger or smaller amount in the oils of species containing these aldehydes, and we 

 have isolated this hydrocarbon from many of the oils of this class, and proved 

 its identity chemically. 



When the members of this aldehydic group are pronounced, at least two 

 and sometimes three or them occur together, particularly at certain periods of 

 the year ; at other times the cuminal is practically absent, and it is probably due 

 to this peculiarity that the conclusions of previous investigators have not been 

 altogether in agreement. The presence of cuminal in the oils of certain 

 Eucalypts was noticed many years ago. 



Some members of the " Box " group yield an oil in which the terpene 

 phellandrene can be detected at certain periods of the year, although absent at 

 other times (E. hemiphloia for instance), and this has often been observed with 

 species which are on the border line, as it were, of phellandrene production. One 

 peculiarity which has been noticed is that when phellandrene can be readily 

 detected in these oils, cuminal is present in greatest amount ; and it was fortunate 

 that in the work originally carried out on these alhehydes from the oil of 

 E. hemiphloia, for the first edition of this work, the material was distilled at the 

 time of the year when phellandrene could not be detected, and cuminal absent 

 or only present in very small amount, consequently the aldehyde regenerated 

 from the crystallised sulphite compound was at that time almost entirely 

 aromadendral. 



This diminution in the amount of cuminal, and the deficiency in 

 phellandrene, is probably responsible to a certain extent for the formation of the 

 dihydro- and tetrahydrocuminals, which can then be isolated from these oils. 



Wallach has shown [Ann. 340 (1905) 12] that the oxidation of 

 /3-phellandrene produces a glycol, which on treating with dilute sulphuric acid 

 gives dihydro- and tetrahydfocuminaldehydes. Molecular re-arrangement of a 

 somewhat similar character may perhaps take place naturally under climatic 

 conditions and the seasons' changes. 



In the first edition of this work, the optically active aldehydes peculiar to the oils of certain Eucalypts, were 



considered to be a single substance and named aromadendral. This name is retained m this edition to denote the 



pccurrence of one or more members of this group of aldehydes, 



