392 



These two fractions were repeatedly distilled at n millimetres until a 

 portion, boiling at to8° C. and containing 98 per cent, ketone, was obtained. 

 This had specific gravity at 15 C. = 0-9392 ; rotation a D — 50-02°, and refractive 



index at 20° — 1-4850. 



Another commercial sample of oil of E. dives was first distilled under 

 reduced pressure and the ketone fraction separated; the piperitone was then 

 prepared in the pure condition by the aid of sodium bisulphite. This had 

 specific gravity at 20 C. = 0-9348; rotation a D 40-05°; refractive index at 

 20° = 1-4837, and boiled at 106-107° under 10 millimetres pressure, and at 

 229-230° (uncorr. at 760 millimetres. 



There appears to be no uniformity in optical rotation with the several 

 samples of piperitone which have so far been separated, and it is thus evident 

 that the left rotation is only the predominant form. 



Analysis of piperitone showed the formula to be C IO H l0 O. 

 0-1064 gram, gave 0-3067 C0 2 and 0-1030 H„0. 



C. = 78-62, and H. = 10-75 per cent. 

 C IO H l6 requires C. = 78-94, and H. = 10-53 P er cent. 



The molecular refraction calculated for a C IO H l6 ketone with one double 

 bond, is 45-82 ; found 46-49. It has been shown by Auwers and Hessenland 

 [Ber. 41 (1908) 1812] that menthenones of this character, with a conjugated 

 double bond, require an addition of 0-83 to the aggregate, and if this addition be 

 made for piperitone the result is closely theoretical. 



The reaction with bromine in chloroform solution showed the molecule to 

 be unsaturated. The bromine was absorbed in quantity, but eventually gave off 

 hydrobromic acid. 



The bromide was a heavy mobile oil, and on analysis gave a return of 

 58-9 per cent, bromine. 



C IO H l6 Br„0 contains 51-2 per cent. Br., and C IO H I5 Br 3 0, 61-3 per cent. Br. 



With hydroxylamine, piperitone gave a normal oxime and an oxamino- 

 Qxime, the former melting at 110-111 C. and the latter at 169-170° C, the 

 oxamino-oxime readily decomposed Fehling's solution, and when boiled with 

 mercuric oxide in alcoholic solution, the mixture assumed a blue colour due to 

 the formation of a nitroso-compound from the NHOH group. 



The semicarbazone, prepared with piperitone which had been regenerated 

 from the bisulphite compound, melted at 219-220° C. If it had been prepared 

 with the ketone obtained directly by repeated distillation under reduced 

 pressure, two semicarbazones were formed, the least soluble of these melting at 

 175-176° C. and the more soluble at 182-183°. The latter was always tinted 

 yellow. The semicarbazones can thus be prepared in three modifications. 



REDUCTION OF PIPERITONE. 



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 C 20 H 34 0„. 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 carbonvl 

 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. 



