42 H. G. SMITH AND A. R. PENFOLD. 



flotation process, and it is already recognised as being the 

 best of all the essential oils for flotation work, and is also 

 in request for other economic purposes. 



For the manufacture of thymol, piperitone could easily 

 be supplied in ton lots if required, and as the molecular 

 transformation from piperitone to thymol is not at all com- 

 plex, and can be brought about in one operation, it should 

 not be a difficult matter to devise methods for the prepara- 

 tion of thymol from piperitone on the manufacturing scale, 

 and because of the great quantity available, probably more 

 cheaply than from any other source, not even excepting 

 Ajowan oil. 



The formation of menthone by the reduction of piperitone 

 is easily carried out if a catalyst be employed, and this 

 result naturally leads to the preparation of menthol on 

 further reduction. 



Piperitone. 



Piperitone under natural conditions is Isevo-rotatory, 

 as is also the corresponding alcohol piperitol, but the ketone 

 readily forms the racemic modification if heated to its 

 boiling point under certain conditions. The piperitone 

 described in the original paper was shown to be inactive, 

 for the reason that it had been separated by direct distilla- 

 tion from the crude oil under atmospheric pressure. If, 

 however, the ketone be separated under greatly reduced 

 pressure, this tendency to racemisation is overcome, and 

 the lsevo-rotatory form can thus be isolated. This alter- 

 ation appears to be brought about by the influence of the 

 acid split off from the esters at the temperature required 

 to distil the ketone, because pure piperitone when distilled 

 by itself alters its rotation but slightly, but if some geranyl- 

 acetate be first added, the diminution in rotation is con- 

 siderable. 



