Showing papers in "Journal of The Chemical Society (resumed) in 1943"

144. The course of autoxidation reactions in polyisoprenes and allied compounds. Part VII. Rearrangement of double bonds during autoxidation

Abstract: In Part V of this series, it was reported that a typical drying-oil ester, methyl docosahexaenoate, showed a marked increase in its capacity to absorb ultraviolet light as the result of exposure to atmospheric oxygen in the illumination of the laboratory. The rapid peroxidation of the polyene system which set in during this exposure promoted a structural change apparently of a conjugative nature. The nature of this change is now examined. Two types of unconjugated unsaturation are, however, taken into consideration: (1) the methylene-interrupted unsaturation, ⋅C:C⋅C⋅C:C⋅C⋅C:C⋅, characteristic of numerous unconjugated drying-oil acids such as linoleic, linolenic, and various polyene fish-oil acids, and (2) the more widely spaced unsaturation found in rubber and in other unconjugated polyisoprene hydrocarbons. The structural changes that ensue on oxidation are of particular interest in relation to the free-radical mechanism of olefinic peroxidation already formulated by Farmer, Bloomfield, Sundrali...

39. The course of autoxidation reactions in polyisoprenes and allied compounds. Part VI. The peroxidation of rubber

Abstract: Peroxides have repeatedly been shown to appear during the slow oxidation (perishing) of rubber in air, and during both its milling in air and the passage of air or oxygen through its solutions: yet in none of the recorded experiments has the production of any very substantial proportion of peroxide been demonstrated. This arises largely because, under many conditions of autooxidation, no very considerable proportion of peroxide is present in the oxidation product at any stage, but in part because no convenient and reasonably accurate method of determining the peroxide content in so insoluble a substance as rubber has been available. It must inevitably happen in a long-chain molecule of polymer-homologous type containing on the average about 5,000 autoxidisable olefinic units that the progressive entrance of a heterogeneous element will yield a large variety of closely similar products if attack is fairly evenly distributed over the chain, but when, as in the case of oxygen, the heterogeneous elem...