The Limonene Group of Terpenes. 
317 
position of the clipentene derivatives when compared with the optically 
inactive derivatives of pinene and camphene must be considered later. 
It is no doubt largely due to these peculiarities that our knowledge of 
the relations existing between the members of the limonene group was 
so long retarded. 
« 
Lcevogyrctte Limonene. 
Limonen — Wallach 2 1884. 
Citrene —- Yoshida 3 1885. 
Links-Limonen — Wallach 4 1888. 
Apparently Deville 1 (1849) has first described laevogyrate limonene, 
without, however, recognizing its peculiar relation to dextrogyrate limo¬ 
nene, then chiefly known as citrene. From elemioil Deville obtained a 
hydrocarbon which had the constant boiling point 174°, and to which he 
assigned the composition Ci 0 e . At 11° it had the specific gravity 0.849; 
coefficient of refraction 1.4719 at 14°C; specific rotatory power -90 s , 30; 
vapor density 4.84 (calculated 4.76). With hydrogen chloride he obtained 
a compound to which he assigned the formula C 10 H 8 H Cl, and of which 
he states: “La rotation de a camphre est nulle comme celle du cam- 
phre de citron, son isomere.” 
In 1884 Wallach demonstrated by means of the tetrabromide reaction 
the presence of limonene in the oil from pinns sylvestris without, how¬ 
ever, paying attention to its optical properties. In the following year 
Yoshida 3 isolated from camphor oil a fraction 172-173° of the com¬ 
position C 10 H 16 of which he writes (p. 787): “This hydrocarbon is 
probably chemically identical with citrene, the main constituent of the 
so-called essence of lemon. The point of difference from the lemon oil 
citrene is its lsevorotatory power, viz. [a]. = —68.3°, but this can be 
J 
looked upon as a physical difference between the two, such cases being 
common among the optically active terpenes.” Yoshida obtained from 
this fraction a “Dihydrochloride of Citrene,” C 10 H 16 2 H Cl (melting 
point 58-59° C.), but did not succeed in making the nitroso-chloride. By 
the addition of one molecule of bromine and splitting off hydrobromic 
acid he obtained cymol, which upon oxidation yielded 40 p. c. tereph- 
thalic acid. 
In 1888 Wallach 4 showed that laevogyrate limonene occurs in the oil 
from the leaves of pinns picaea. “ The lsevogyrate limonene has a con¬ 
stant boiling point of 175-176°, its spec, gravity was 0.846 5 at 20°, [u] D = 
— 105°. Tetrabromide and nitroso-chloride clearly demonstrate the op¬ 
posite character of the hydrocarbon with reference to its dextrogyrate 
congener. 
