328 
Wisconsin Academy of Sciences , Arts and Letters. 
to make the latter fact apparent, but Wallach first called attention to it. 
Physical as well as chemical characteristics were first studied by him. 
Wallach’s monohydrochloride was, as I have shown, chiefly dipentene- 
monhydrochloride. 10 The optically active monhydrochlorides were first 
described by me. 11 
Properties. 
Since there is no criterion to ascertain the purity of the monhydro- 
chlorides the following data found for the three physical isomers will 
have to be accepted at present: 11 
+ Limonene-monhydrochloride. 
44 A colorless, mobile liquid of faint limonene odor. It boils at 97-98° 
under pressure of 11.-12 mm. Spec, gravity 0.973 at 17.8°; [u] D = -f- 39.5°.” 
—Limonene-monhi/drochloride. 
“This corresponds with the dextrogyrate compound in all but its 
optical properties. The rectified product boiled at 95-96° under a pres¬ 
sure of about 11-12 mm.; spec. grav. 0.982 at 16°; [or] = + 40.0°.” 
Dipentene-monhydroeliloride. 
It was prepared by mixing equal parts of the above dextrogyrate and 
lgevogyrate compounds. “The mixture was optically inactive; spec^ 
gravity 0.982 at 16.5°; boiling point 98° under pressure of 12 mm.” Wal¬ 
lach 12 ascertained the physical properties of a dipentene compound to 
be as follows; Boiling point 90° under pressure of 11 mm.; spec. grav. 
0.98; nc = 1.4789, molecular refraction 49,86, calculated for an unsatu¬ 
rated compound C 10 H 17 C1 50,28. 
Chemically the monhydrochloride behaves like an unsaturated com¬ 
pound. Under the conditions, however, which are most favorable to its 
formation it will not add a second molecule of hydrogen chloride. 11 But 
in the presence of moisture it adds another molecule and the limonene 
derivative is thereby converted into a dipentene derivative. It also adds 
H 13 
Br 
NO 
Cl 
14 
and 
NO 
O (NO a ). 
15 
Chlorine very likely also can be added, but 
this apparently substitutes at the same time. 16 Water is not added di¬ 
rectly. In the presence of water the chlorine is substituted by hydroxyl, 1& 
and the aqueous hydrochloric acid acts upon the terpineol to form ter- 
pin hydrate. 17 
The monhydrochlorides polymerize in a very peculiar manner. 18 Hy¬ 
drogen chloride is split off at the same time and partial inactivity results 
when the underlying hydrocarbon was optically active. 
