174 R. 8. HUGHESDON, H. G. SMITH AND J. READ. 
ancusa, to similar treatment (compare Trans. Chem. Soc., 
1921, 119, 1644; 1922, 121,582). A specimen of the dextro- 
gyrate piperitone, having «1 +47°46°, was thereby converted 
into a levo-gyrate isomenthone, having a; —57°40°, thus 
confirming the previous result. 
The work of Pope and Read (Trans. Chem. Soc., 1913, 
103, 1515) on partially racemic compounds of the non- 
electrolytic type suggested the possibility of the optically 
active isomenthones now described belonging to this type. 
In such an event these isomers would be represented by the 
symbols Dd,Dl and Ld,Ll respectively, and the catalytic 
hydrogenation of the optically active forms of piperitone 
would not be an asymmetric synthesis. Correspondingly, 
a second pair of partially racemic menthones can be 
imagined, in which carbon atom No. 4 fails to exert its 
potential activity; these would be represented by the 
symbols Dd,Ld and Dl,Ll respectively. All such isomers 
might perhaps be classified most simply as partially racemic 
isomenthones: 1-racemic in the first instance, and 4-racemic 
in the second. 
On the whole it appears unlikely that the catalytic 
hydrogenation of the optically active forms of piperitone 
should occur otherwise than as an asymmetric, or, at least, 
a partially asymmetric synthesis. Further investigations, 
including inversion experiments, are being undertaken in 
order to test this point and other closely associated ideas. 
In addition, attention is being devoted to the characteristics 
of the optically active and inactive menthols which it has 
been found possible to derive in various ways from piperit- 
one. It may be stated that preliminary work has resulted 
in the isolation of an inactive menthol, which in view of its 
melting point (89-—41°) is probably to be classified as an 
isomenthol, derived from isomenthone (compare Pickard — 
and Littlebury, loc. cit.). 
