- 8 5 - 



of the latter as follows: "Aldehydes which are derived from cyclo- 

 geraniolene form, with acetone, combinations possessing an odour of 

 violets, insofar as the aldehyde group is adjacent either to the 

 methyl or to the gem-dim ethyl group, or to both at the same time, 

 and the intensity of the violet-odour increases in proportion to the 

 number of methyl-groups which are adjacent to the aldehyde-groups. 

 The condensation product of acetone loses its characteristics as an 

 odoriferous substance as soon as the aldehyde group is removed from 

 the proximity of the methyls (Aldehyde I)". Merling and Welde have 

 also discovered that isopropyl ethyl acetaldehyde, in which the atoms 

 were grouped as follows: 



CH q 



-C- 



CH 3 COH CH 3 



(a grouping which is also found in the cyclogeraniolene ring) , was 

 capable of being condensed with acetone to a body possessing an 

 odour which, although agreeable, no longer had the character of a 

 violet- scent. 



The synthesis of natural irone, called by the authors /?-irone 

 CH a CH 3 

 C 



HC 



CH.CH:CH.CO.CH 3 , 



HC 



CH 2 



and of its isomeride, a-irone 



CH 3 CH, 



\/ 

 C 



CH.CH, 



H 2 C 

 HC 



/\ C H.CH:CH.CO.CH 8 , 



CH-CH, 



CH 



starts from /^propylidene aceto-acetic ester, a yellowish oil, boiling 

 at 70 to 73 (2 to 3 mm.), or at 75 to 78 (6 mm.). This body 

 is obtained by Pauly's 1 ) process, slightly modified, which consists of 

 saturating a mixture of 1 part acetone and 2 parts aceto-acetic ester 

 with hydrogen chloride at — 5° With sodium aceto-acetic ester it 



*) Berl. Berichte 30 (1897), 482. 



