[boswell] the constitution OF RUBBER 33 



CH3 ÇH3 



^CH^-C = CH- CH2-CH2- C = CH-CH2-CH2 

 CH= C—CH^-CH^- CH= C- CH^-CH^ — CH 



Neiv Views Regarding the Constitution 



In 1917 work commenced on the constitution of rubber in the 

 School of Engineering Research of the University of Toronto. A 

 study of the literature led me to the conclusion that the dimethyl 

 cyclo octadiene constitution of Harries is unsatisfactory for the follow- 

 ing reasons: 



(1) The formation of two mois of isoprene from one mol of 

 dimethyl cyclo octadiene requires a severing of two single bonds in 

 a molecule containing two double bonds. Double bonds between 

 carbons are usually points of weakness in a molecule and consequently 

 rupture when it occurs usually takes place there rather than between 

 carbons formed by a single bond. This had been pointed out by 

 Pickles. 



(2) The formation of dipentene from dimethyl cyclo octadiene 

 entails a very extensive intermolecular change, the mechanism of 

 which is not clear unless the intermediate formation of molecules of 

 isoprene is assumed with subsequent polymerization to dipentene. 



Were dipentene and isoprene actually linked up as constituents 

 of the rubber molecule both of these objections would be removed. 



(3) With double bonds existing in the rubber molecule it should 

 be possible to add hydrogen directly and produce a saturated hydro- 

 carbon. The endeavours of Harries (20) and of Hinrichsen (21) and 

 Kempf to accomplish this failed. Likewise all attempts made in 

 this laboratory were unsuccessful. This would seem to indicate that 

 rubber contains no ethylene linkages at all. Belief in the unsaturated 

 character of rubber depends on the observations that rubber adds 

 on approximately four bromines and two hydrochloric acid mois for 

 each C10H16. However, as these are adm.ittedly very drastic actions, 

 almost certainly accompanied by deep seated depolymerization of the 

 rubber molecule, it is conceivable that the rubber mol itself contains 

 no double bonds whatever, and that these are only produced by the 

 breaking up of the complex rubber molecule by the act ion of bromine 



3— c 



