Reaction of Ozone with Diene Rubbers

Ozone is known to react with virtually all organic materials, the rate of reaction being considerably faster with certain unsaturated compounds than with saturated materials. In the latter case it is probable that ozone attack is associated with an autoxidation initiation process. In addition, certain reactions of ozone with organic materials may provide a source of singlet oxygen. It is however in unsaturated materials that ozone has the greatest effect and it is with this aspect that this section is concerned. 

Although the full significance of the reactions of ozone with diene rubbers was not to be appreciated until the mid-1940s its importance was recognized in part, by the early years of this century, with the ozonolysis techniques developed by Harries (see Chapters 1 and 2). Subsequently the reactions between olefins and ozone were studied by various workers and much of the experimental data obtained can be accounted for by a series of mechanisms proposed by Criegee (1951, 1954, 1955). The essential proposals are summarized below. 

In the Criegee proposals the initial product is stipulated to have a 1,2,3-trioxolane structure (I) which is also known as a molozonide structure. This undergoes a concerted decomposition to give a zwit-terion (II) and a carbonyl compound (III). The decomposition products (II) and (III) in most cases recombine to give the normal ozonide (IV). Other possible reactions include dimerization of the zwitterion to yield a diperoxide (V) or a higher peroxide (VI) whilst in the presence of methanol as a reactive solvent a methoxy-hydroperoxide (VII) may be produced. 

Amongst the evidence that the Criegee proposals can account for at least some ozone-olefin reactions may be cited the following  

NMR evidence that the initial adduct has a trioxolane structure (I) although in some cases it appears that the initial product has the so-called r-structure (VIII) 

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