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Piperitone, the Peppermint Ketone of 

 Eucalyptus Oils. 



This unsaturated aromatic ketone is more generally distributed in the oils of 

 Eucalypts growing in the Eastern and South Eastern portion of the continent, 

 and in Tasmania, where the members of the whole group are known vernacularly 

 as " Peppermints." 



This peppermint odour was noticed by the first white settlers in 

 Australia in 1788, and oil was distilled by them at that time, from the leaves of 

 Eucalyptus piperita, a tree somewhat extensively distributed around Sydney, the 

 coastal ranges, and coastal districts of New South Wales and Victoria. It is thus 

 worthy of notice that both the vernacular name (" Peppermint ") and the 

 scientific name (Eucalyptus piperita) were given to this tree on account of the 

 presence of this peppermint constituent in the oil; in fact, chemical constituents 

 were often a guiding factor in the early naming of Eucalypts. 



On the mountain ranges in New South Wales and Victoria, as well as in 

 Tasmania, the members of the " Peppermint " group of Eucalypts form a large 

 proportion of the natural vegetation, and are distributed over hundreds of square 

 miles of country. 



It is now recognised that all the principal constituents found in Eucalyptus 

 oils increase in amount through a range of species until a maximum is reached 

 in one or mote of them. Piperitone follows this rule, and Eucalyptus dives, 

 a " Broad-leaved Peppermint," appears to be the species in which it reaches a 

 maximum content. This Eucalypt is one of the most plentiful of all the members 

 of the " Peppermint " group, and also gives a good yield of oil, averaging from 

 3 to 4 per cent, according to the time of year, the care taken in collecting, and on 

 the duration of the primary distillation, and if this be somewhat extended, say from 

 6 to 8 hours, the oil will often contain as much as from 40 to 50 per cent, of 

 piperitone. It is thus evident that this ketone could be produced in great 

 quantity, and at a cheap rate. The remainder of the oil of E. dives consists 

 largely of phellandrene, and is employed in the mining industry for flotation 

 work, as well as for other economic purposes. 



Piperitone is the only ketone found in Eucalyptus oils ; it was first 

 isolated by one of us, and the results of a preliminary chemical investigation 

 submitted to the Royal Society of New South Wales, in October, 1900. It was 

 named piperitone by us in the first edition of this work. 



Piperitone appears to occur only in the oils of species occupying the more 

 recent end of the genus, and is not found in the oil of any member of the groups 

 occupying the anterior position in the evolutionary sequence of the genus. 



Although piperitone is usually found occurring with phellandrene, yet. in 

 the case of E. apiculata, this terpene was not detected; and altogether the oil of 

 this species was of such a character as not to be readily placed in any of the well 

 defined groups. 



In the oils of most species piperitone is found associated with the 

 corresponding laevo-rotatory secondary alcohol piperitol, and we have isolated 

 this alcohol from the oil of E. radiata, where it occurs as a well-defined 

 constituent. 



Under natural conditions piperitone is laevo-rotatory, but readily forms 

 the racemic modification when heated above its boiling point, in the process of 

 separation by direct distillation of the original oil. This alteration appears to be 



