Research on Modified Rubbers. Part IV. The Oxidation of Rubber with Aqueous Hydrogen Peroxide-Acetic Acid Mixtures

Mair and Todd (J. Chem. Soc., 1932,, 386), in extending the earlier work of Robertson and Mair (J. Soc. Chem. Ind., 46, 41T (1927)), studied the interaction of a chloroform solution of purified rubber with concentrated hydrogen peroxide (100 vols.) dissolved in glacial acetic acid; by this means they obtained a non-acidic substance of the empirical formula C50H92O16, which was unsaturated toward bromine and permanganate, and was considered to have all its oxygen present in the form of hydroxyl groups. Other workers have reported that when peracetic acid dissolved in glacial acetic acid is used in place of the hydrogen peroxide—acetic acid mixture, the products of reaction are acetylated derivatives of rubber (British Patent 369,716). These acetylated derivatives are stated to be obtainable either from solid rubber or from solutions of rubber, but no evidence as to their constitution has been advanced. Now the oxidative degradation of rubber is of considerable interest from two points of view: first, with regard to the light which it may throw on the size, structure, homogeneity, and normality of chemical behavior of the molecules of rubber; and, second, with regard to its efficacy as a means of transforming rubber into derivatives of similar or smaller molecular weight, capable of useful application in industry. The very careful work of Mair and Todd has gone far to show that hydrogen peroxide under the conditions of their experiments attacks the unsaturated centers of the rubber molecule and effects more or less complete hydroxylation of the carbon chain; at the same time it brings about a considerable degree of degradation of the molecule. The product of Mair and Todd, however, is produced under rather restricted conditions of reaction and the reagents employed are costly; consequently the extent to which the character of the product can be modified (i. e., by controlling the degree of degradation, hydroxylation, and acetylation) is left undetermined, and the possibility of producing useful materials at a reasonably low cost by modifying the conditions of reaction and the form of reactants is left unexplored. On the other hand, the employment of peracetic acid as an oxidizing agent, though offering a theoretically elegant way of effecting hydroxylation or acetoxylation at the unsaturated centers of the rubber molecule, is not without drawbacks: the preparation of the reagent is expensive and on a large scale dangerous; moreover, in spite of the fact that it is claimed to be employable either with solutions of rubber or with solid rubber, its reaction with rubber is so vigorous that the prospect of exercising any effective control over the extent of degradation or degree of hydroxylation (acetoxylation) is greatly diminished.