Decomposition of lauroyl, decanoyl, and octanoyl peroxides in solution

Abstract

The thermal decomposition from 50 to 250° of lauroyl, decanoyl, and octanoyl peroxides in solution in a high molecular weight hydrocarbon was studied. These peroxides are convenient sources of C-11, C-9, and C-7 straight-chain aliphatic free radicals, whose reactions may be considered as models for the higher molecular weight radicals formed during thermal cracking of polyolefins.The ratio of disproportionation to combination for these radicals is about 0.2, which is very similar to the values obtained for lower alkyl radicals in the gas phase. This ratio appears to be relatively independent of temperature. Intramolecular chain transfer, which results in the isomerization of the radical, occurs at the higher temperatures, and the process has an apparent activation energy of about 2 kcal per mole.The product distribution indicates that at reaction temperatures up to 250° a statistically random distribution of alkyl radicals is never achieved in solution. Since the radicals are formed in pairs, they tend to react with each other rather than with radicals formed from other peroxide molecules. This is demonstrated by the near absence of cross-combination products when two different peroxides are decomposed in the same solution simultaneously at 70°. At 250°, some cross-product is formed but less than one-fifth of the amount expected if the radicals were uniformly distributed in the solution. The activation energy for the formation of cross-product is of the same order as that for diffusion. The significance of these results in terms of the classical picture of "cage reactions" is discussed.