THE CHEMISTRY OF INDIARUBBER 501 



M. G. Bouchardat studied the action of the halogen acids 

 upon isoprene, and found that two classes of compounds could 

 be obtained by the addition of one, or two, molecules of the 

 halogen acid, e.g. (1) C 5 H S ■ HC1 and (2) C 6 H 8 ■ 2HCI, thus in- 

 dicating the presence of two unsaturated linkings or double 

 bonds in the C 3 H 8 molecule. Further proof of this was provided 

 by Prof. TildenMn 1882, who prepared the additive compound 

 C 5 H 8 Br 4 , isoprene tetrabromide. From a consideration of these 

 derivatives as well as of the fact that on oxidation isoprene 

 yields carbonic, formic and acetic acids, Tilden concluded that 

 isoprene was /3-methyl-crotonylene — 



CH 3 \ 



) C - CH = CHo, 

 CH 2 / 



and the subsequent researches of Gadziatzky, Mokiewsky, and 

 Ipatieff supported this view. The synthesis of isoprene in 1897 

 byEuler 2 from /3-methyl-pyrollidine settled beyond doubt the 

 constitution of isoprene, and proved the correctness of the above 

 formula. The question of how a compound possessing such a 

 formula can pass in one case into dipentene (Ci H 16 ), and in 

 another case into caoutchouc, will be considered at a later stage. 

 The low-boiling portion of the distillate obtained from rubber 

 constitutes only a very small fraction of the total. At the first 

 distillation, the thermometer shows a gradual rise with no very 

 distinctive stationary points. On redistillation, however, it is 

 found that after the low boiling portion, above referred to, has 

 passed over, the temperature rises rapidly to about i40°C, and 

 between 140 and 190° C. about one-third of the total distils over. 

 The major portion of this is found to boil between 170° and 180 C. 



Dipentene (Caoutchine, Di-isoprene, or Cinene), 

 C 10 H 16 , Boiling Point (171-5°), (175° — 176°), 180 — 181°) 



A. F. C. Himly, in the paper before mentioned (Gottingen^ 

 I ^35), separated a fraction which, after distillation and purification,, 

 had a boiling point i7i'5°C. This was a neutral oil with an 

 orange-like odour, and of sp. gr. '8423 at i6°C. It was a hydro- 

 carbon, and analysis and vapour density determination showed 

 it to have the formula C 10 H 16 . Himly gave to this liquid the name 

 "caoutchine." 



1 Chem. News, 1882, p. 120 (vol. xlvi.). 



2 Berichte, 30 (1897), p. 1989-91. 



