46 THE ROYAL SOCIETY OF CANADA 



Rubber consists of six isoprene molecules polymerized to form a 

 molecule C30H48 of the constitution shown in Fig. 1. Upon oxidation ' 

 with hydrogen peroxide this is oxidized first to C30H48O, probably of 

 the constitution shown in Fig. 2. This is the beginning of the insertion 

 of oxygen between the isoprene groups. This compound readily loses 

 its central CsHg group, which is, as we have seen, oxidized to CO2, 

 and a water soluble compound, and an oxygen enters the molecule in its 

 place, making the compound C25H40O2 represented by Fig. 3. This 

 compound C25H40O2 can also be made by the oxidation of rubber by 

 potassium permanganate. In this case the central isoprene is oxidized 

 off to CO2 and a water soluble compound, and C25H40O is formed, which 

 is represented in Fig. 4. This readily takes up oxygen and passes 

 into C25H40O2, represented in Fig. 3. Another product of the oxidation 

 of rubber by hydrogen peroxide has the composition of C15H24O. 

 This probably forms from the further oxidation of the C25H40O2 

 compound, whereby the split occurs along the line x — x, the two free 

 bonds uniting with an oxygen to produce C)5H240 of the constitution 

 in Fig. 5. It is probable that another oxidation product C20H32O2 is 

 also formed in this reaction, of the constitution represented in Fig. 6, 

 although this was not isolated. However, this compound was found 

 among the oxidation products of rubber by oxygen of the air. In this 

 oxidation of rubber by air the final product of the oxidation before the 

 molecule disintegrates is C25H40O9, represented by Fig. 7. Here the five 

 isoprene groups are separated from each other by oxygens. The mole- 

 cule is unable to take up more oxygen without rupture. 



The action of iodine and hydrogen peroxide on rubber gives two 

 compounds only one of which was purified and analysed. It has the 

 composition C25H40I Os- An important consideration in arriving at 

 its constitution is the fact that iodine alone acts with very great slow- 

 ness on rubber but that in the presence of oxygen it acts at once with 

 the entrance of a single iodine and eight oxygens for every C25H4o- 

 Since the final product of oxidation of rubber by free oxygen has the 

 composition C25H40O9, it seems highly probable that this single iodine 

 serves to link up the five isoprene groups in the C25H40 molecule 

 occupying then a central position in some such way as represented in 

 Fig. 8. This requires another oxygen in order to make up the required 

 eight oxygens. This is represented as united to the iodine by a single 

 bond. A second residue may possibly be united to this at the two 

 oxygens giving the molecular formula C.5oH8ol20i6. Only a molecular 

 weight determination can decide whether any combination of this 

 kind occurs. Iodine here acts with a valency of five, which is not 

 unusual for iodine as it is found with this valency in iodic acid and 

 iodine pentroxide. 



