ON THB PRESENT POSITION OF THE CHEMISTRY OF RUBBER. 245 



careful consideratioa of the relationship of terpineol to pinene, pinol, and 

 sobrerol, deduced the formula 



//CH - CH„ V yCH., 



CHj . C^ >nH - C^CH, 



\CH,-CH/ \0H 



as best representing terpineol, and represented the constitution of 

 dipentene as 



^CH — CH., V yCH^ 



CHj . C^ ' >CH . C^ 



\CH,,-CH/ ^CH; 



Ipatieff' suggested the probable formation of dipentene from isoprene 

 by the condensation of two molecules of the latter in the following 

 manner : — 



CH3 ^Hg 



I I 



CH,-^ \CH Ch/ '^'^CH 



CHov 

 "^CH 



CHy ^^2 \ / ^^2 



CH 

 ^\rrr CH./ \CH3 



CH.^ ^CH, 



The proof of the correctness of Wagner's formula for dipentene was 

 supplied by Professor W. H. Perkin, jun., 2 in 1904, by his synthesis of 

 terpineol and dipentene from B keto hexahydrobenzoic ester. 



This ester, after treatment with magnesium methyl iodide and sub- 

 sequent hydrolysis, yields 8 hydroxy hexahydro p-toluic acid, which on 

 the addition of fuming HBr passes into 8 brom-hexa-hydro-^^-toluic 

 acid, 



CH, Br 



\/ 



CO C 



CHj /\ CH, CH„ /'^ CH2 CH, f^\ CH, 



CH, 



\/ CH, CH, I J CH, CH, .} CH, 



CH . COO Et CH . COOH CH . COOH. 



Weak alkalies or pyridine eliminate HBr from this acid, yielding 

 A"* tetrahydro-^j-toluic acid. 



CH, 



I 

 G 



CH., /^ CH 



CH, V ^ 



CH, 

 CH . COOH 



The ester of this acid on subsequent treatment with magnesium- 



' JoKvn. f. Frakt. Chem., 55 (1897). 

 - Jourii. Chem. Soc, 1904, p. 654. 



