Section III, 1922 [27] Trans. R.S.C. 



The Constitution of Rubber 

 By Maitland C. Boswell 



Among the well-known carbon compounds, whose constitutions 

 still remain to be determined, is rubber. The literature is not wanting 

 in structural formulas, each of which represents satisfactorily one or 

 more of the chemical reactions of rubber. However none of these 

 is an adequate picture of all the facts which are now known regarding 

 rubber, and the general feeling among organic chemists to-day, even 

 among those who themselves have contributed most to our knowledge 

 of rubber, and advanced constitutional formulas to represent it, is 

 that the rubber molecule is much more complex than pictured by any 

 of the constitutional formulas yet devised. 



That rubber chemistry should be in this unsatisfactory condition, 

 notwithstanding that sixty-two years have elapsed since Williams in 

 1860 first investigated the products of the destructive distillation of 

 rubber, may occasion some surprise among those chemists who have 

 not had laboratory experience in the preparation of rubber derivatives. 

 However, it is not at all surprising to any one who has tried to isolate 

 any of the exceedingly fragile and sensitive compounds in the pure 

 state, from the unpromising looking sticky messes, which often result 

 from rubber reactions. None of these compounds is crystalline, and 

 the only method of isolation and purification available is successive 

 solution and precipitation, using as many dififerent solvents and pré- 

 cipitants as are applicable. This has been the chief difficulty. How- 

 ever, an equally important reason for the delay in arriving at a satis- 

 factory representation of the constitution lies, in my opinion, in the 

 unfortunate choice of reactions which have been used for constitution 

 determination. The reactions are altogether too drastic and carry 

 the process of depolymerization of the rubber molecule so far that the 

 final products bear, in most instances, no simple relationship to the 

 original rubber, and have led to the opinion that the rubber molecule 

 is much simpler than it really is. Such reactions as bromination, 

 action of ozone, and of hydrochloric acid gas on rubber, the removal 

 of chlorine from the product of the action of hydrochloric acid gas 

 by heating with pyridine under pressure and others are, though they 

 have given valuable information, too deep seated to enable final 

 inferences to be drawn regarding constitution. 



The object of this paper is very briefly to review the facts regard- 

 ing rubber, which have given rise to the formulas already suggested, 



