When piperitone was reduced with purified hydrogen in the presence of a nickel catalyst, at a temperature of about 1800 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 340 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 340 C.

Pickard and Littlebury [Journ. Chem. Soc, 101 (1912) 109] have shown that the inactive menthol melting at 340 C. can be split into lævo-rotatory menthol melting at 430 C. and dextro-rotatory menthol melting at the same temperature.