393 



Analysis of the dimolecular ketone, purified from alcohol, gave the 

 following result : 



0-150 gram, gave 0-4298 gram. CO., and 0-1568 gram. H 2 O. 



C. = 78-20 and H. = 11-60 per cent. 

 C 20 H 34 O 2 contains C. = 78-36 and H. = 11-21. 



A molecular weight determination by the freezing method, using benzene 

 as solvent, gave 308 ; by the Landsberger boiling method, using acetone, it 

 was 306. 



The oxime formed with the dimolecular ketone was very insoluble in all 

 the usual neutral organic solvents, but was soluble in glacial acetic acid, separating 

 again on dilution. The dioxime was prepared by adding an excess of 

 hydroxylamine hydrochloride to 5 gram, of the dimolecular ketone in boiling 

 absolute alcohol, and adding slowly 5 gram, potassium hydrate in 10 c.c. water. 

 On boiling under a reflex for some time the compound separated, and was purified 

 by boiling in alcohol and in water. The dioxime was a white crystalline powder and 

 melted at 245 C. Almost a theoretical percentage of nitrogen for C 20 H 36 N,O, was 

 obtained both by Dumas' and Kjeldahl's methods. 



Piperitone and the dimolecular ketone have most probably the following 

 molecular structures : 



CH 3 



I 



CH 



CH 3 

 CH 



CH S 

 CO 



PREPARATION OF MENTHONE AND MENTHOL FROM PIPERITONE. 



When piperitone was reduced with purified hydrogen in the presence of a 

 nickel catalyst, at a temperature of about 180 C. for six hours, the double bond 

 was opened out, and, under the best conditions, menthone formed in almost 

 quantitative yield; continuation of the treatment did not, however, result in 

 the reduction of the carbonyl group even after two days. The menthone thus 

 prepared had all the properties of this ketone and gave its characteristic 

 chemical reactions and compounds. It also formed inactive menthol, melting at 

 34 C. when reduced by sodium in aqueous ether solution. 



' Piperitone could also be partly reduced to inactive menthol directly by 

 the action of sodium and aqueous ether, but the yield was poor, as large 

 quantities of the dimolecular ketone were formed at the same time. The 

 menthol was separated from the other substances by combining it with 

 phthalic anhydride in the usual way. As thus prepared it crystallised very well 

 and melted at 34 C. 



Pickard and Littlebury [Journ. Chem. Soc., 101 (1912) 109] have shown 

 that the inactive menthol melting at 34 C. can be split into Isevo-rotatory 

 menthol melting at 43 C. and dextro-rotatory menthol melting at the same 

 temperature. 



5006820 



