When the ketone is reduced by sodium-amalgam in alcoholic solution, large quantities of a dimolecular ketone are formed, the bulk of the reaction taking this direction. This substance crystallises well, melts at 149 to 150° C. and has the formula C20H34O2. This reaction is due to the conjugated double bond, and it is worthy of notice that Carvone, with a double bond at 6 and the carbonyl at 1, also forms a dimolecular ketone melting at 148-149° C.

The dimolecular ketone with piperitone, can, however, be separated into two bodies, melting at different temperatures. When dissolved in chloroform and fractionally precipitated with ether, and the process repeated several times, one set of crystals melted at 135-136°, and the other at 166-167° C. Both were optically inactive.

Analysis of the dimolecular ketone, purified from alcohol, gave the following result: -

0.150 gram. gave 0.4298 gram. CO2 and 0.1568 gram. H2O.

C. - 78.20 and H. = 11.60 per cent. C20H34O2 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 C20H36N2O2, was obtained both by Dumas' and Kjeldahl's methods.

Piperitone and the dimolecular ketone have most probably the following molecular structures: -