The Limonene Group of Terpenes. 
323 
pared synthetically from the optically active modifications, have but a 
simple molecule has been shown by Wallach in connection with opti¬ 
cally inactive carvoxime. 43 On account of the peculiar position of the-, 
optically inactive members of derivatives from the limonene group he. 
has retained the designation “ dipentene ” in preference to 0-limonene^ 
for optically inactive limonene derivatives corresponding to those of 
optically inactive tartaric acid may yet be found. 
Properties. 
The hydrocarbons of the limonene group are colorless liquid terpenes 
of an agreeable lemon-like odor. 1 Two of the three are optically active, 
being opposite in character. The physical constants of the limonenes 
have been determined as follow's : 
Boiling point, 175—176°. 2 3 
Spec, gravity at 20° 0,816. 3 
[a] = 105° 3 resp. + 106.8° 2 
Coefficient of refraction n D 1.17459. 3 
Molelecular refraction ^ n , —15.23. 3 
(n 2 + 2)d 
Chemically the two modifications are identical. They add one mole¬ 
cule of hydrogen chloride without losing their optical activity. When 
every trace of moisture is avoided they will not add more. 4 In the 
presence of moisture, however, they add two molecules of hydrogen 
chloride and thereby become optically inactive, i. e., are converted into 
a dipentene derivative, dipentene dihydrochloride. The dibromine ad¬ 
dition products appear to be viscid liquids and are therefore not charac¬ 
teristic. When hydrobromic acid is split off cymol results. 13 The 
tetrabromides, however, are very characteristic. 5 Optically 6 as well as 
crystalographically 7 their character is opposite. The limonenes add also 
nitrosyl chloride, apparently but one molecule. However, two addition 
products of j qP result, an a — and a (5 — nitroso-chloride. With bases 
Like limonene the mon- 
NO 
Cl 
and 
NO 
O (NO) a . 
both yield the same a — and (5 — nitrolamines. 
hydrochloride is still capable of adding the groups 
In this case, however, but one hydrochlor-nitroso chloride or hydo- 
chlor-nitrosate resp. results. The molecule of hydrogenchloride can 
also be added after the addition of the NO Cl group, viz., by the nitrol¬ 
amines. Thus e. g. the u-nitrolanilid will yield an u-hydrochlor addition 
product, the /3-nitrol anilid a /?-hydrochlor addition product. Of these 
the u-base is identical with the one obtained from the hydrochlor-nitroso- 
chloride. 8 These peculiarities, which have thus far been observed in con¬ 
nection with limonene group only indicate a different behavior of the two 
double bonds toward regents. 
