352 CHEMICAL DISCOVERY AND INVENTION 



The perfume of the violet was the subject of research by 

 Tiemann and Kriiger so long ago as 1893. They found it im- 

 possible to obtain sufficient material for their work from the 

 flowers, but as this characteristic fragrance is possessed by the 

 dried root of iris (orris), the latter was used by these chemists a t s 

 the source of the fragrant oil on which their experiments were 

 made. To this substance when purified they gave the name 

 irone. It belongs to the class of compounds, called in chemical 

 language ketones, and its composition is expressed by the formula 

 C 13 H 20 0. 



Protracted study of this compound led to the synthetical 

 production of another substance to which the name ionone is 

 given. This has the same ultimate composition, namely C 13 H 20 0, 

 and closely similar properties, including especially the fragrant 

 odour of the violet. No time was lost in applying these facts to 

 the manufacture of artificial essence of violet. Ionone is made 

 from citral, an aldehyde existing in considerable proportion in 

 essences of lemon, and citron, and in lemon grass oil, to which 

 the characteristic lemon odour of these materials is due. 



Citral and acetone heated together in presence of an alkali 

 condense together to form a compound called pseudo-ionone, 

 which when boiled with dilute sulphuric acid yields a mixture of 

 two isomeric substances, a and /3 ionone. The relation of these 

 compounds to one another is shown in the following con- 

 stitutional formulae, from which it will be seen that the arrange- 

 ment of the atoms in each is essentially the same. 



CH, 



H 2 C 



H 2 C 



CH-CH : CH-CO-CH 3 H 2 C 



C-CH 3 



H 2 C 



C-CH : CH-CO-CH: 



C-CH 3 



