THE CHEMISTRY OF INDIARUBBER 503 



terpineol, C 10 H ls O, and later Wallach l showed that by spitting 

 off the elements of water from this alcohol, dipentene was readily 

 obtained. Wagner 2 first proposed the formula 



^/CH - CHA /CH 3 



CH 3 -Cf >CH - CC 



\CH, - CH, / ^CH, 



for dipentene as the result of an exhaustive consideration of its 

 properties and of its relationship to terpineol, pinene, and 

 sobrerol. 



The proof of the correctness of this formula was supplied by 

 Prof. W. H. Perkin, jun., 3 in 1904, who, by accomplishing its 

 complete synthesis from S-keto-hexahydrobenzoic acid, removed 

 all doubt as to its constitution. 



The question now arises, How does isoprene pass into a 

 compound having the above constitution ? Ipatieff 4 suggested 

 a probable transition by the condensation of two molecules of 

 isoprene in the following manner : 



CH :i CH 



i ' I 



c c 



CH, CH CH, CH 



2 molecules isoprene — > 1 molecule dipentene. 



CH„ CH, CH, CH 2 



\/ \y 



CH CH 



I I 



c c 



CH, CH 3 CH 2 CH S 



The relationship of dipentene to the rubber molecule will be 

 considered later. 



Other Hydrocarbons of the Formula C 10 H 10 



From the indiarubber distillation products there have been 

 also isolated several other hydrocarbons having the same 

 empirical formula as dipentene, viz. C, H 10 . On carefully re- 

 distilling the dipentene fraction — i.e. that portion boiling between 



1 Annalen, 1885 (230), p. 258. 



2 Ber. 27, p. 1636. 



3 Journ. Chem. Soc. 1904, p. 654. 



4 fourn. f. Prakt. Chem. 55 (1897). 



