The Limonene Group of Terpenes. 
333 
Properties. 
In its properties the bromide resembles the chloride. Melting point 
64°. (Hell & Ritter 16 42°.) 
Methods of Formation. 
These are analogous to those of the chloride. In how far they have 
been carried out can be seen from the historical sketch. 
Preparation. 
Dipentene dihydrobromide can be prepared in few minutes when to a 
solution of limonene or dipentene an excess of a saturated solution of 
hydrobromic acid is added. The mixture must be left cold, and when 
poured into water the dihydrobromide is precipitated in pure condi¬ 
tion. 45 . 
Dipentene Dihydriodide. 
Zweifach jodwasserstolfsaures Terpilen — Oppenheim. 14 1862. 
Cynen-Dihydrojodid — Hell und Ritter. 16 1884. 
Dipenten-Dihydrojodid — Wallach. 17 1887. 
History. 
Wiggers 46 and also List 10 did not succeed in preparing a hydriodide- 
analogous to the hydrochloride. Oppenheim was the first to succeed. 
He obtained it by treating terpin hydrate with phosphorus iodide. The 
product, however, cannot have been pure as indicated by the melting point 
48°. Hell & Ritter 16 (1884) obtained the hydriodide analogous to the hydro¬ 
chloride and hydromide from cineol. Melting point 76-77°. At the 
same time and independently Wallach and Brass 47 obtained the same 
compound from the same material. Wallach also prepared it from 
terpin-hydrate 48 and terpineol 49 with the aid of hydriodic acid. 
/ 
Properties. 
In its properties the dihydriodide is analogous to the dihydrochloride 
and dihydrobromide, but it is less stable. However with its purity its 
stability increases. Prom petroleum ether it crystallizes in two phys¬ 
ically isomorphous modifications 60 : rhombic crystals melting at 77° and 
monosymmetric crystals melting at 78-79°. 
Methods of Formation: 
These are analogous to those above mentioned. In how far they have 
been carried out can readily be seen from the historical notes. 
