46 H. G. SMITH AND A. R. PENFOLD. 



finely crystallised substance, melts at 148-149° C, and 

 has the formula O20H34O2. Piperitone thus follows the rule 

 with substances having a conjugated double bond — Carvone 

 for instance, which also forms a bimolecular ketone on 

 reduction, melting at 148-149° C. 



The menthone was prepared from piperitone in almost 

 quantitative yield, and had the characteristic peppermint 

 odour of this substance. It was colourless ; boiled at 208° 

 O., had specific gravity at 20° = 0*8978; optical rotation 

 a D -0*15°, and refractive index at 20° = 1*4529. The oxime 

 melted at 80° C, the more soluble semicarbazone at 156° 0., 

 while the least soluble melted at 187- 188° O. Any unre- 

 duced piperitone can be removed from the menthone by the 

 action of neutral sodium sulphite. 



Preparation of Menthol. 



Piperitone was partly reduced to menthol directly, by 

 employing sodium in aqueous ethereal solution; a consider- 

 able quantity of the bimolecular ketone was, however, 

 formed at the same time. 



The reduction product from the piperitone was heated at 

 170 - 180° C. for two hours with an equal weight of phthalic 

 anhydride, the melt dissolved in sodium hydrate, a small 

 quantity of menthone removed by ether, and the phthalic 

 acid compound regenerated by means of dilute hydrochloric 

 acid. The phthalic acid ester was then decomposed by 

 boiling with alcoholic potash, and the menthol separated 

 and crystallised. The odour was excellent. 



The menthol thus obtained from the Isevo-rotatory 

 piperitone melted at 34° C, and was optically inactive, 

 thus following the general rule for synthetically prepared 

 substances. 



The preparation of menthol from piperitone by direct 

 reduction does not, however, appear to be technically 



