The Limonene Group of Terpenes. 
321 
Hirzel 7 (1854) regards the rectified “ 01 Cinae ” to consist of a mixture 
of a hydrocarbon “Cinaeben” “C 10 H 8 ” with “Cinaeben campher,” 
“ C 10 H 9 O.” The latter when distilled with anhydrous phosphoric acid 
yields among other products “ Cinaeben.” 
Kraut’s 29 analysis of wormseed oil (1862) would lead him to the form¬ 
ula “ C 24 H 20 O 2 ,” However, his vapor-density determinations bring him 
to the conclusion that the oil is a mixture of a substance “C 20 H 18 O 2 ,” 
with little of a hydrocarbon “(probably of the formula C 20 H 16 ).” 
Kraut and Wahlforss 30 verify Volckel’s statement in so far as the oil 
when distilled with anhydrous phosphoric acid yields a hydrocarbon. 
Their analyses and vapor-density determinations, however, lead them to 
the formula “ C 10 H 16 .” “ This hydrocarbon is optically inactive .” 
Graebe 9 replaced (1872) phosphorus pentoxide by phosphorus penta 
sulphide. He obtained a hydrocarbon which he supposed to be “ cy- 
nen.” However it must have been cymol, since it yielded terephthalic 
acid upon oxidation. Graebe’s “cynen sulfosaeure, C 10 H 15 (S0 3 H)” 
when fused with caustic potassa did not yield a phenol of “ cynen” but 
of cymol, consequently it must have been a derivative of the latter. 
Faust and Homeyer 31 prepared “ Cynen” according to Graebe’s method 
and identified it as cymol by means of paratoluic acid and of cymol sul- 
phonate of barium. They believe that there can be no further doubt as 
to the identity between “ cynen ” and cymol. 
Hell and Stiircke 32 (1884) again use phosphorus pentoxide as dehydrat¬ 
ing agent and obtain the hydrocarbon C 10 H 16 . Fuming sulphuric acid 
blackens it and converts only a part of it into the sulphonic acid. The 
barium salt is stated to be identical with the barium cymol-sulphonate 
obtained by Kraut from caraway oil. Hell and Stiircke arrive at the 
conclusion that by the action of phosphorus pentoxide upon worm- 
seed oil “ cynen ” and not cymol results, but that the sulphuric acid by 
abstracting two hydrogen atoms oxidizes the former into the latter 34 . 
Hell and Ritter 35 (1884) have observed that when hydrogen chloride is 
passed into wormseed oil, this becomes heated and C 10 H 18 0. H Cl is not 
formed but water is split off and “ cynendihydrochlorid ” C 10 H 18 Cl 
(melting point 50-51°) results (dipentene dihydrochloride). From this 
“ cynen ” (dipentene) can be obtained by distillation wth caustic soda 
and rectification over metallic sodium. These reactions are to be ex¬ 
pressed by the following equations. 
1. C 10 H 18 O + H Cl = C 10 H 18 Cl (OH), [a chlorhydrin.] 
2. C 10 H 18 Cl (OH) + H Cl = C 10 H 18 Cl 2 + H 2 O. 
3. C 10 H 18 Cl 2 = C 10 H 16 + 2H Cl. 
About the same time with Hell, Wallach 36 began his investigations 
of the terpenes. In part they meet on the same ground, in part they 
supplement each other. However, where Hell feigned analogies to exist 
21—A. & L. 
